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diff --git a/doc/gawk.info b/doc/gawk.info index 037522e9..075d4947 100644 --- a/doc/gawk.info +++ b/doc/gawk.info @@ -1,35 +1,40 @@ -This is gawk.info, produced by makeinfo version 4.0 from ./gawk.texi. +This is gawk.info, produced by makeinfo version 4.0 from gawk.texi. -INFO-DIR-SECTION Programming Languages +INFO-DIR-SECTION GNU Packages START-INFO-DIR-ENTRY -* Gawk: (gawk). A Text Scanning and Processing Language. +* Gawk: (gawk). A text scanning and processing language. +END-INFO-DIR-ENTRY +INFO-DIR-SECTION Individual utilities +START-INFO-DIR-ENTRY +* awk: (gawk)Invoking gawk. Text scanning and processing. END-INFO-DIR-ENTRY This file documents `awk', a program that you can use to select particular records in a file and perform operations upon them. - This is Edition 1.0.6 of `Effective AWK Programming', for the -3.0.6 version of the GNU implementation of AWK. + This is Edition 3 of `GAWK: Effective AWK Programming: A User's +Guide for GNU Awk', for the 3.1.0 version of the GNU implementation of +AWK. - Copyright (C) 1989, 1991, 1992, 1993, 1996-2000 Free Software + Copyright (C) 1989, 1991, 1992, 1993, 1996-2001 Free Software Foundation, Inc. - Permission is granted to make and distribute verbatim copies of this -manual provided the copyright notice and this permission notice are -preserved on all copies. + Permission is granted to copy, distribute and/or modify this document +under the terms of the GNU Free Documentation License, Version 1.1 or +any later version published by the Free Software Foundation; with the +Invariant Sections being "GNU General Public License", the Front-Cover +texts being (a) (see below), and with the Back-Cover Texts being (b) +(see below). A copy of the license is included in the section entitled +"GNU Free Documentation License". - Permission is granted to copy and distribute modified versions of -this manual under the conditions for verbatim copying, provided that -the entire resulting derived work is distributed under the terms of a -permission notice identical to this one. + a. "A GNU Manual" - Permission is granted to copy and distribute translations of this -manual into another language, under the above conditions for modified -versions, except that this permission notice may be stated in a -translation approved by the Foundation. + b. "You have freedom to copy and modify this GNU Manual, like GNU + software. Copies published by the Free Software Foundation raise + funds for GNU development." -File: gawk.info, Node: Top, Next: Preface, Prev: (dir), Up: (dir) +File: gawk.info, Node: Top, Next: Foreword, Prev: (dir), Up: (dir) General Introduction ******************** @@ -37,313 +42,386 @@ General Introduction This file documents `awk', a program that you can use to select particular records in a file and perform operations upon them. - This is Edition 1.0.6 of `Effective AWK Programming', -for the 3.0.6 version of the GNU implementation -of AWK. + This is Edition 3 of `GAWK: Effective AWK Programming: A User's +Guide for GNU Awk', for the 3.1.0 version of the GNU implementation of +AWK. * Menu: -* Preface:: What this Info file is about; brief - history and acknowledgements. -* What Is Awk:: What is the `awk' language; using this - Info file. -* Getting Started:: A basic introduction to using `awk'. How - to run an `awk' program. Command line - syntax. -* One-liners:: Short, sample `awk' programs. -* Regexp:: All about matching things using regular - expressions. -* Reading Files:: How to read files and manipulate fields. -* Printing:: How to print using `awk'. Describes the - `print' and `printf' statements. - Also describes redirection of output. -* Expressions:: Expressions are the basic building blocks of - statements. -* Patterns and Actions:: Overviews of patterns and actions. -* Statements:: The various control statements are described - in detail. -* Built-in Variables:: Built-in Variables -* Arrays:: The description and use of arrays. Also - includes array-oriented control statements. -* Built-in:: The built-in functions are summarized here. -* User-defined:: User-defined functions are described in - detail. -* Invoking Gawk:: How to run `gawk'. -* Library Functions:: A Library of `awk' Functions. -* Sample Programs:: Many `awk' programs with complete - explanations. -* Language History:: The evolution of the `awk' language. -* Gawk Summary:: `gawk' Options and Language Summary. -* Installation:: Installing `gawk' under various operating - systems. -* Notes:: Something about the implementation of - `gawk'. -* Glossary:: An explanation of some unfamiliar terms. -* Copying:: Your right to copy and distribute `gawk'. -* Index:: Concept and Variable Index. - -* History:: The history of `gawk' and `awk'. -* Manual History:: Brief history of the GNU project and this - Info file. -* Acknowledgements:: Acknowledgements. -* This Manual:: Using this Info file. Includes sample - input files that you can use. -* Conventions:: Typographical Conventions. -* Sample Data Files:: Sample data files for use in the `awk' - programs illustrated in this Info file. -* Names:: What name to use to find `awk'. -* Running gawk:: How to run `gawk' programs; includes - command line syntax. -* One-shot:: Running a short throw-away `awk' program. -* Read Terminal:: Using no input files (input from terminal - instead). -* Long:: Putting permanent `awk' programs in - files. -* Executable Scripts:: Making self-contained `awk' programs. -* Comments:: Adding documentation to `gawk' programs. -* Very Simple:: A very simple example. -* Two Rules:: A less simple one-line example with two rules. -* More Complex:: A more complex example. -* Statements/Lines:: Subdividing or combining statements into - lines. -* Other Features:: Other Features of `awk'. -* When:: When to use `gawk' and when to use other - things. -* Regexp Usage:: How to Use Regular Expressions. -* Escape Sequences:: How to write non-printing characters. -* Regexp Operators:: Regular Expression Operators. -* GNU Regexp Operators:: Operators specific to GNU software. -* Case-sensitivity:: How to do case-insensitive matching. -* Leftmost Longest:: How much text matches. -* Computed Regexps:: Using Dynamic Regexps. -* Records:: Controlling how data is split into records. -* Fields:: An introduction to fields. -* Non-Constant Fields:: Non-constant Field Numbers. -* Changing Fields:: Changing the Contents of a Field. -* Field Separators:: The field separator and how to change it. -* Basic Field Splitting:: How fields are split with single characters or - simple strings. -* Regexp Field Splitting:: Using regexps as the field separator. -* Single Character Fields:: Making each character a separate field. -* Command Line Field Separator:: Setting `FS' from the command line. -* Field Splitting Summary:: Some final points and a summary table. -* Constant Size:: Reading constant width data. -* Multiple Line:: Reading multi-line records. -* Getline:: Reading files under explicit program control - using the `getline' function. -* Getline Intro:: Introduction to the `getline' function. -* Plain Getline:: Using `getline' with no arguments. -* Getline/Variable:: Using `getline' into a variable. -* Getline/File:: Using `getline' from a file. -* Getline/Variable/File:: Using `getline' into a variable from a - file. -* Getline/Pipe:: Using `getline' from a pipe. -* Getline/Variable/Pipe:: Using `getline' into a variable from a - pipe. -* Getline Summary:: Summary Of `getline' Variants. -* Print:: The `print' statement. -* Print Examples:: Simple examples of `print' statements. -* Output Separators:: The output separators and how to change them. -* OFMT:: Controlling Numeric Output With `print'. -* Printf:: The `printf' statement. -* Basic Printf:: Syntax of the `printf' statement. -* Control Letters:: Format-control letters. -* Format Modifiers:: Format-specification modifiers. -* Printf Examples:: Several examples. -* Redirection:: How to redirect output to multiple files and - pipes. -* Special Files:: File name interpretation in `gawk'. - `gawk' allows access to inherited file - descriptors. -* Close Files And Pipes:: Closing Input and Output Files and Pipes. -* Constants:: String, numeric, and regexp constants. -* Scalar Constants:: Numeric and string constants. -* Regexp Constants:: Regular Expression constants. -* Using Constant Regexps:: When and how to use a regexp constant. -* Variables:: Variables give names to values for later use. -* Using Variables:: Using variables in your programs. -* Assignment Options:: Setting variables on the command line and a - summary of command line syntax. This is an - advanced method of input. -* Conversion:: The conversion of strings to numbers and vice - versa. -* Arithmetic Ops:: Arithmetic operations (`+', `-', - etc.) -* Concatenation:: Concatenating strings. -* Assignment Ops:: Changing the value of a variable or a field. -* Increment Ops:: Incrementing the numeric value of a variable. -* Truth Values:: What is ``true'' and what is ``false''. -* Typing and Comparison:: How variables acquire types, and how this - affects comparison of numbers and strings with - `<', etc. -* Boolean Ops:: Combining comparison expressions using boolean - operators `||' (``or''), `&&' - (``and'') and `!' (``not''). -* Conditional Exp:: Conditional expressions select between two - subexpressions under control of a third - subexpression. -* Function Calls:: A function call is an expression. -* Precedence:: How various operators nest. -* Pattern Overview:: What goes into a pattern. -* Kinds of Patterns:: A list of all kinds of patterns. -* Regexp Patterns:: Using regexps as patterns. -* Expression Patterns:: Any expression can be used as a pattern. -* Ranges:: Pairs of patterns specify record ranges. -* BEGIN/END:: Specifying initialization and cleanup rules. -* Using BEGIN/END:: How and why to use BEGIN/END rules. -* I/O And BEGIN/END:: I/O issues in BEGIN/END rules. -* Empty:: The empty pattern, which matches every record. -* Action Overview:: What goes into an action. -* If Statement:: Conditionally execute some `awk' - statements. -* While Statement:: Loop until some condition is satisfied. -* Do Statement:: Do specified action while looping until some - condition is satisfied. -* For Statement:: Another looping statement, that provides - initialization and increment clauses. -* Break Statement:: Immediately exit the innermost enclosing loop. -* Continue Statement:: Skip to the end of the innermost enclosing - loop. -* Next Statement:: Stop processing the current input record. -* Nextfile Statement:: Stop processing the current file. -* Exit Statement:: Stop execution of `awk'. -* User-modified:: Built-in variables that you change to control - `awk'. -* Auto-set:: Built-in variables where `awk' gives you - information. -* ARGC and ARGV:: Ways to use `ARGC' and `ARGV'. -* Array Intro:: Introduction to Arrays -* Reference to Elements:: How to examine one element of an array. -* Assigning Elements:: How to change an element of an array. -* Array Example:: Basic Example of an Array -* Scanning an Array:: A variation of the `for' statement. It - loops through the indices of an array's - existing elements. -* Delete:: The `delete' statement removes an element - from an array. -* Numeric Array Subscripts:: How to use numbers as subscripts in - `awk'. -* Uninitialized Subscripts:: Using Uninitialized variables as subscripts. -* Multi-dimensional:: Emulating multi-dimensional arrays in - `awk'. -* Multi-scanning:: Scanning multi-dimensional arrays. -* Calling Built-in:: How to call built-in functions. -* Numeric Functions:: Functions that work with numbers, including - `int', `sin' and `rand'. -* String Functions:: Functions for string manipulation, such as - `split', `match', and - `sprintf'. -* I/O Functions:: Functions for files and shell commands. -* Time Functions:: Functions for dealing with time stamps. -* Definition Syntax:: How to write definitions and what they mean. -* Function Example:: An example function definition and what it - does. -* Function Caveats:: Things to watch out for. -* Return Statement:: Specifying the value a function returns. -* Options:: Command line options and their meanings. -* Other Arguments:: Input file names and variable assignments. -* AWKPATH Variable:: Searching directories for `awk' programs. -* Obsolete:: Obsolete Options and/or features. -* Undocumented:: Undocumented Options and Features. -* Known Bugs:: Known Bugs in `gawk'. -* Portability Notes:: What to do if you don't have `gawk'. -* Nextfile Function:: Two implementations of a `nextfile' - function. -* Assert Function:: A function for assertions in `awk' - programs. -* Round Function:: A function for rounding if `sprintf' does - not do it correctly. -* Ordinal Functions:: Functions for using characters as numbers and - vice versa. -* Join Function:: A function to join an array into a string. -* Mktime Function:: A function to turn a date into a timestamp. -* Gettimeofday Function:: A function to get formatted times. -* Filetrans Function:: A function for handling data file transitions. -* Getopt Function:: A function for processing command line - arguments. -* Passwd Functions:: Functions for getting user information. -* Group Functions:: Functions for getting group information. -* Library Names:: How to best name private global variables in - library functions. -* Clones:: Clones of common utilities. -* Cut Program:: The `cut' utility. -* Egrep Program:: The `egrep' utility. -* Id Program:: The `id' utility. -* Split Program:: The `split' utility. -* Tee Program:: The `tee' utility. -* Uniq Program:: The `uniq' utility. -* Wc Program:: The `wc' utility. -* Miscellaneous Programs:: Some interesting `awk' programs. -* Dupword Program:: Finding duplicated words in a document. -* Alarm Program:: An alarm clock. -* Translate Program:: A program similar to the `tr' utility. -* Labels Program:: Printing mailing labels. -* Word Sorting:: A program to produce a word usage count. -* History Sorting:: Eliminating duplicate entries from a history - file. -* Extract Program:: Pulling out programs from Texinfo source - files. -* Simple Sed:: A Simple Stream Editor. -* Igawk Program:: A wrapper for `awk' that includes files. -* V7/SVR3.1:: The major changes between V7 and System V - Release 3.1. -* SVR4:: Minor changes between System V Releases 3.1 - and 4. -* POSIX:: New features from the POSIX standard. -* BTL:: New features from the Bell Laboratories - version of `awk'. -* POSIX/GNU:: The extensions in `gawk' not in POSIX - `awk'. -* Command Line Summary:: Recapitulation of the command line. -* Language Summary:: A terse review of the language. -* Variables/Fields:: Variables, fields, and arrays. -* Fields Summary:: Input field splitting. -* Built-in Summary:: `awk''s built-in variables. -* Arrays Summary:: Using arrays. -* Data Type Summary:: Values in `awk' are numbers or strings. -* Rules Summary:: Patterns and Actions, and their component - parts. -* Pattern Summary:: Quick overview of patterns. -* Regexp Summary:: Quick overview of regular expressions. -* Actions Summary:: Quick overview of actions. -* Operator Summary:: `awk' operators. -* Control Flow Summary:: The control statements. -* I/O Summary:: The I/O statements. -* Printf Summary:: A summary of `printf'. -* Special File Summary:: Special file names interpreted internally. -* Built-in Functions Summary:: Built-in numeric and string functions. -* Time Functions Summary:: Built-in time functions. -* String Constants Summary:: Escape sequences in strings. -* Functions Summary:: Defining and calling functions. -* Historical Features:: Some undocumented but supported ``features''. -* Gawk Distribution:: What is in the `gawk' distribution. -* Getting:: How to get the distribution. -* Extracting:: How to extract the distribution. -* Distribution contents:: What is in the distribution. -* Unix Installation:: Installing `gawk' under various versions - of Unix. -* Quick Installation:: Compiling `gawk' under Unix. -* Configuration Philosophy:: How it's all supposed to work. -* VMS Installation:: Installing `gawk' on VMS. -* VMS Compilation:: How to compile `gawk' under VMS. -* VMS Installation Details:: How to install `gawk' under VMS. -* VMS Running:: How to run `gawk' under VMS. -* VMS POSIX:: Alternate instructions for VMS POSIX. -* PC Installation:: Installing and Compiling `gawk' on MS-DOS - and OS/2 -* Atari Installation:: Installing `gawk' on the Atari ST. -* Atari Compiling:: Compiling `gawk' on Atari -* Atari Using:: Running `gawk' on Atari -* Amiga Installation:: Installing `gawk' on an Amiga. -* Bugs:: Reporting Problems and Bugs. -* Other Versions:: Other freely available `awk' - implementations. -* Compatibility Mode:: How to disable certain `gawk' extensions. -* Additions:: Making Additions To `gawk'. -* Adding Code:: Adding code to the main body of `gawk'. -* New Ports:: Porting `gawk' to a new operating system. -* Future Extensions:: New features that may be implemented one day. -* Improvements:: Suggestions for improvements by volunteers. +* Foreword:: Some nice words about this + Info file. +* Preface:: What this Info file is about; brief + history and acknowledgments. +* Getting Started:: A basic introduction to using + `awk'. How to run an `awk' + program. Command-line syntax. +* Regexp:: All about matching things using regular + expressions. +* Reading Files:: How to read files and manipulate fields. +* Printing:: How to print using `awk'. Describes + the `print' and `printf' + statements. Also describes redirection of + output. +* Expressions:: Expressions are the basic building blocks + of statements. +* Patterns and Actions:: Overviews of patterns and actions. +* Arrays:: The description and use of arrays. Also + includes array-oriented control statements. +* Functions:: Built-in and user-defined functions. +* Internationalization:: Getting `gawk' to speak your + language. +* Advanced Features:: Stuff for advanced users, specific to + `gawk'. +* Invoking Gawk:: How to run `gawk'. +* Library Functions:: A Library of `awk' Functions. +* Sample Programs:: Many `awk' programs with complete + explanations. +* Language History:: The evolution of the `awk' + language. +* Installation:: Installing `gawk' under various + operating systems. +* Notes:: Notes about `gawk' extensions and + possible future work. +* Basic Concepts:: A very quick intoduction to programming + concepts. +* Glossary:: An explanation of some unfamiliar terms. +* Copying:: Your right to copy and distribute + `gawk'. +* GNU Free Documentation License:: The license for this Info file. +* Index:: Concept and Variable Index. + +* History:: The history of `gawk' and + `awk'. +* Names:: What name to use to find `awk'. +* This Manual:: Using this Info file. Includes + sample input files that you can use. +* Conventions:: Typographical Conventions. +* Manual History:: Brief history of the GNU project and this + Info file. +* How To Contribute:: Helping to save the world. +* Acknowledgments:: Acknowledgments. +* Running gawk:: How to run `gawk' programs; + includes command-line syntax. +* One-shot:: Running a short throw-away `awk' + program. +* Read Terminal:: Using no input files (input from terminal + instead). +* Long:: Putting permanent `awk' programs in + files. +* Executable Scripts:: Making self-contained `awk' + programs. +* Comments:: Adding documentation to `gawk' + programs. +* Quoting:: More discussion of shell quoting issues. +* Sample Data Files:: Sample data files for use in the + `awk' programs illustrated in this + Info file. +* Very Simple:: A very simple example. +* Two Rules:: A less simple one-line example using two + rules. +* More Complex:: A more complex example. +* Statements/Lines:: Subdividing or combining statements into + lines. +* Other Features:: Other Features of `awk'. +* When:: When to use `gawk' and when to use + other things. +* Regexp Usage:: How to Use Regular Expressions. +* Escape Sequences:: How to write non-printing characters. +* Regexp Operators:: Regular Expression Operators. +* Character Lists:: What can go between `[...]'. +* GNU Regexp Operators:: Operators specific to GNU software. +* Case-sensitivity:: How to do case-insensitive matching. +* Leftmost Longest:: How much text matches. +* Computed Regexps:: Using Dynamic Regexps. +* Records:: Controlling how data is split into records. +* Fields:: An introduction to fields. +* Non-Constant Fields:: Non-constant Field Numbers. +* Changing Fields:: Changing the Contents of a Field. +* Field Separators:: The field separator and how to change it. +* Regexp Field Splitting:: Using regexps as the field separator. +* Single Character Fields:: Making each character a separate field. +* Command Line Field Separator:: Setting `FS' from the command-line. +* Field Splitting Summary:: Some final points and a summary table. +* Constant Size:: Reading constant width data. +* Multiple Line:: Reading multi-line records. +* Getline:: Reading files under explicit program + control using the `getline' function. +* Plain Getline:: Using `getline' with no arguments. +* Getline/Variable:: Using `getline' into a variable. +* Getline/File:: Using `getline' from a file. +* Getline/Variable/File:: Using `getline' into a variable from a + file. +* Getline/Pipe:: Using `getline' from a pipe. +* Getline/Variable/Pipe:: Using `getline' into a variable from a + pipe. +* Getline/Coprocess:: Using `getline' from a coprocess. +* Getline/Variable/Coprocess:: Using `getline' into a variable from a + coprocess. +* Getline Notes:: Important things to know about + `getline'. +* Getline Summary:: Summary of `getline' Variants. +* Print:: The `print' statement. +* Print Examples:: Simple examples of `print' statements. +* Output Separators:: The output separators and how to change + them. +* OFMT:: Controlling Numeric Output With + `print'. +* Printf:: The `printf' statement. +* Basic Printf:: Syntax of the `printf' statement. +* Control Letters:: Format-control letters. +* Format Modifiers:: Format-specification modifiers. +* Printf Examples:: Several examples. +* Redirection:: How to redirect output to multiple files + and pipes. +* Special Files:: File name interpretation in `gawk'. + `gawk' allows access to inherited + file descriptors. +* Special FD:: Special files for I/O. +* Special Process:: Special files for process information. +* Special Network:: Special files for network communications. +* Special Caveats:: Things to watch out for. +* Close Files And Pipes:: Closing Input and Output Files and Pipes. +* Constants:: String, numeric and regexp constants. +* Scalar Constants:: Numeric and string constants. +* Non-decimal-numbers:: What are octal and hex numbers. +* Regexp Constants:: Regular Expression constants. +* Using Constant Regexps:: When and how to use a regexp constant. +* Variables:: Variables give names to values for later + use. +* Using Variables:: Using variables in your programs. +* Assignment Options:: Setting variables on the command-line and a + summary of command-line syntax. This is an + advanced method of input. +* Conversion:: The conversion of strings to numbers and + vice versa. +* Arithmetic Ops:: Arithmetic operations (`+', `-', + etc.) +* Concatenation:: Concatenating strings. +* Assignment Ops:: Changing the value of a variable or a + field. +* Increment Ops:: Incrementing the numeric value of a + variable. +* Truth Values:: What is ``true'' and what is ``false''. +* Typing and Comparison:: How variables acquire types and how this + affects comparison of numbers and strings + with `<', etc. +* Boolean Ops:: Combining comparison expressions using + boolean operators `||' (``or''), + `&&' (``and'') and `!' (``not''). +* Conditional Exp:: Conditional expressions select between two + subexpressions under control of a third + subexpression. +* Function Calls:: A function call is an expression. +* Precedence:: How various operators nest. +* Pattern Overview:: What goes into a pattern. +* Regexp Patterns:: Using regexps as patterns. +* Expression Patterns:: Any expression can be used as a pattern. +* Ranges:: Pairs of patterns specify record ranges. +* BEGIN/END:: Specifying initialization and cleanup + rules. +* Using BEGIN/END:: How and why to use BEGIN/END rules. +* I/O And BEGIN/END:: I/O issues in BEGIN/END rules. +* Empty:: The empty pattern, which matches every + record. +* Using Shell Variables:: How to use shell variables with + `awk'. +* Action Overview:: What goes into an action. +* Statements:: Describes the various control statements in + detail. +* If Statement:: Conditionally execute some `awk' + statements. +* While Statement:: Loop until some condition is satisfied. +* Do Statement:: Do specified action while looping until + some condition is satisfied. +* For Statement:: Another looping statement, that provides + initialization and increment clauses. +* Break Statement:: Immediately exit the innermost enclosing + loop. +* Continue Statement:: Skip to the end of the innermost enclosing + loop. +* Next Statement:: Stop processing the current input record. +* Nextfile Statement:: Stop processing the current file. +* Exit Statement:: Stop execution of `awk'. +* Built-in Variables:: Summarizes the built-in variables. +* User-modified:: Built-in variables that you change to + control `awk'. +* Auto-set:: Built-in variables where `awk' + gives you information. +* ARGC and ARGV:: Ways to use `ARGC' and `ARGV'. +* Array Intro:: Introduction to Arrays +* Reference to Elements:: How to examine one element of an array. +* Assigning Elements:: How to change an element of an array. +* Array Example:: Basic Example of an Array +* Scanning an Array:: A variation of the `for' statement. It + loops through the indices of an array's + existing elements. +* Delete:: The `delete' statement removes an + element from an array. +* Numeric Array Subscripts:: How to use numbers as subscripts in + `awk'. +* Uninitialized Subscripts:: Using Uninitialized variables as + subscripts. +* Multi-dimensional:: Emulating multidimensional arrays in + `awk'. +* Multi-scanning:: Scanning multidimensional arrays. +* Array Sorting:: Sorting array values and indices. +* Built-in:: Summarizes the built-in functions. +* Calling Built-in:: How to call built-in functions. +* Numeric Functions:: Functions that work with numbers, including + `int', `sin' and `rand'. +* String Functions:: Functions for string manipulation, such as + `split', `match' and + `sprintf'. +* Gory Details:: More than you want to know about `\' + and `&' with `sub', `gsub', + and `gensub'. +* I/O Functions:: Functions for files and shell commands. +* Time Functions:: Functions for dealing with timestamps. +* Bitwise Functions:: Functions for bitwise operations. +* I18N Functions:: Functions for string translation. +* User-defined:: Describes User-defined functions in detail. +* Definition Syntax:: How to write definitions and what they + mean. +* Function Example:: An example function definition and what it + does. +* Function Caveats:: Things to watch out for. +* Return Statement:: Specifying the value a function returns. +* Dynamic Typing:: How variable types can change at runtime. +* I18N and L10N:: Internationalization and Localization. +* Explaining gettext:: How GNU `gettext' works. +* Programmer i18n:: Features for the programmer. +* Translator i18n:: Features for the translator. +* String Extraction:: Extracting marked strings. +* Printf Ordering:: Rearranging `printf' arguments. +* I18N Portability:: `awk'-level portability issues. +* I18N Example:: A simple i18n example. +* Gawk I18N:: `gawk' is also internationalized. +* Non-decimal Data:: Allowing non-decimal input data. +* Two-way I/O:: Two-way communications with another + process. +* TCP/IP Networking:: Using `gawk' for network + programming. +* Portal Files:: Using `gawk' with BSD portals. +* Profiling:: Profiling your `awk' programs. +* Command Line:: How to run `awk'. +* Options:: Command-line options and their meanings. +* Other Arguments:: Input file names and variable assignments. +* AWKPATH Variable:: Searching directories for `awk' + programs. +* Obsolete:: Obsolete Options and/or features. +* Undocumented:: Undocumented Options and Features. +* Known Bugs:: Known Bugs in `gawk'. +* Library Names:: How to best name private global variables + in library functions. +* General Functions:: Functions that are of general use. +* Nextfile Function:: Two implementations of a `nextfile' + function. +* Assert Function:: A function for assertions in `awk' + programs. +* Round Function:: A function for rounding if `sprintf' + does not do it correctly. +* Cliff Random Function:: The Cliff Random Number Generator. +* Ordinal Functions:: Functions for using characters as numbers + and vice versa. +* Join Function:: A function to join an array into a string. +* Gettimeofday Function:: A function to get formatted times. +* Data File Management:: Functions for managing command-line data + files. +* Filetrans Function:: A function for handling data file + transitions. +* Rewind Function:: A function for rereading the current file. +* File Checking:: Checking that data files are readable. +* Ignoring Assigns:: Treating assignments as file names. +* Getopt Function:: A function for processing command-line + arguments. +* Passwd Functions:: Functions for getting user information. +* Group Functions:: Functions for getting group information. +* Running Examples:: How to run these examples. +* Clones:: Clones of common utilities. +* Cut Program:: The `cut' utility. +* Egrep Program:: The `egrep' utility. +* Id Program:: The `id' utility. +* Split Program:: The `split' utility. +* Tee Program:: The `tee' utility. +* Uniq Program:: The `uniq' utility. +* Wc Program:: The `wc' utility. +* Miscellaneous Programs:: Some interesting `awk' programs. +* Dupword Program:: Finding duplicated words in a document. +* Alarm Program:: An alarm clock. +* Translate Program:: A program similar to the `tr' + utility. +* Labels Program:: Printing mailing labels. +* Word Sorting:: A program to produce a word usage count. +* History Sorting:: Eliminating duplicate entries from a + history file. +* Extract Program:: Pulling out programs from Texinfo source + files. +* Simple Sed:: A Simple Stream Editor. +* Igawk Program:: A wrapper for `awk' that includes + files. +* V7/SVR3.1:: The major changes between V7 and System V + Release 3.1. +* SVR4:: Minor changes between System V Releases 3.1 + and 4. +* POSIX:: New features from the POSIX standard. +* BTL:: New features from the Bell Laboratories + version of `awk'. +* POSIX/GNU:: The extensions in `gawk' not in + POSIX `awk'. +* Contributors:: The major contributors to `gawk'. +* Gawk Distribution:: What is in the `gawk' distribution. +* Getting:: How to get the distribution. +* Extracting:: How to extract the distribution. +* Distribution contents:: What is in the distribution. +* Unix Installation:: Installing `gawk' under various + versions of Unix. +* Quick Installation:: Compiling `gawk' under Unix. +* Additional Configuration Options:: Other compile-time options. +* Configuration Philosophy:: How it's all supposed to work. +* Non-Unix Installation:: Installation on Other Operating Systems. +* Amiga Installation:: Installing `gawk' on an Amiga. +* BeOS Installation:: Installing `gawk' on BeOS. +* PC Installation:: Installing and Compiling `gawk' on + MS-DOS and OS/2. +* PC Binary Installation:: Installing a prepared distribution. +* PC Compiling:: Compiling `gawk' for MS-DOS, Win32, + and OS/2. +* PC Using:: Running `gawk' on MS-DOS, Win32 and + OS/2. +* VMS Installation:: Installing `gawk' on VMS. +* VMS Compilation:: How to compile `gawk' under VMS. +* VMS Installation Details:: How to install `gawk' under VMS. +* VMS Running:: How to run `gawk' under VMS. +* VMS POSIX:: Alternate instructions for VMS POSIX. +* Unsupported:: Systems whose ports are no longer + supported. +* Atari Installation:: Installing `gawk' on the Atari ST. +* Atari Compiling:: Compiling `gawk' on Atari. +* Atari Using:: Running `gawk' on Atari. +* Tandem Installation:: Installing `gawk' on a Tandem. +* Bugs:: Reporting Problems and Bugs. +* Other Versions:: Other freely available `awk' + implementations. +* Compatibility Mode:: How to disable certain `gawk' + extensions. +* Additions:: Making Additions To `gawk'. +* Adding Code:: Adding code to the main body of + `gawk'. +* New Ports:: Porting `gawk' to a new operating + system. +* Dynamic Extensions:: Adding new built-in functions to + `gawk'. +* Internals:: A brief look at some `gawk' + internals. +* Sample Library:: A example of new functions. +* Internal File Description:: What the new functions will do. +* Internal File Ops:: The code for internal file operations. +* Using Internal File Ops:: How to use an external extension. +* Future Extensions:: New features that may be implemented one + day. +* Basic High Level:: The high level view. +* Basic Data Typing:: A very quick intro to data types. +* Floating Point Issues:: Stuff to know about floating-point numbers. To Miriam, for making me complete. @@ -360,331 +438,383 @@ of AWK. To Malka, for the new beginning. -File: gawk.info, Node: Preface, Next: What Is Awk, Prev: Top, Up: Top +File: gawk.info, Node: Foreword, Next: Preface, Prev: Top, Up: Top + +Foreword +******** + + Arnold Robbins and I are good friends. We were introduced 11 years +ago by circumstances--and our favorite programming language, AWK. The +circumstances started a couple of years earlier. I was working at a new +job and noticed an unplugged Unix computer sitting in the corner. No +one knew how to use it, and neither did I. However, a couple of days +later it was running, and I was `root' and the one-and-only user. That +day, I began the transition from statistician to Unix programmer. + + On one of many trips to the library or bookstore in search of books +on Unix, I found the gray AWK book, a.k.a. Aho, Kernighan and +Weinberger, `The AWK Programming Language', Addison-Wesley, 1988. +AWK's simple programming paradigm--find a pattern in the input and then +perform an action--often reduced complex or tedious data manipulations +to few lines of code. I was excited to try my hand at programming in +AWK. + + Alas, the `awk' on my computer was a limited version of the +language described in the AWK book. I discovered that my computer had +"old `awk'" and the AWK book described "new `awk'." I learned that +this was typical; the old version refused to step aside or relinquish +its name. If a system had a new `awk', it was invariably called +`nawk', and few systems had it. The best way to get a new `awk' was to +`ftp' the source code for `gawk' from `prep.ai.mit.edu'. `gawk' was a +version of new `awk' written by David Trueman and Arnold, and available +under the GNU General Public License. + + (Incidentally, it's no longer difficult to find a new `awk'. `gawk' +ships with Linux, and you can download binaries or source code for +almost any system; my wife uses `gawk' on her VMS box.) + + My Unix system started out unplugged from the wall; it certainly was +not plugged into a network. So, oblivious to the existence of `gawk' +and the Unix community in general, and desiring a new `awk', I wrote my +own, called `mawk'. Before I was finished I knew about `gawk', but it +was too late to stop, so I eventually posted to a `comp.sources' +newsgroup. + + A few days after my posting, I got a friendly email from Arnold +introducing himself. He suggested we share design and algorithms and +attached a draft of the POSIX standard so that I could update `mawk' to +support language extensions added after publication of the AWK book. + + Frankly, if our roles had been reversed, I would not have been so +open and we probably would have never met. I'm glad we did meet. He +is an AWK expert's AWK expert and a genuinely nice person. Arnold +contributes significant amounts of his expertise and time to the Free +Software Foundation. + + This book is the `gawk' reference manual, but at its core it is a +book about AWK programming that will appeal to a wide audience. It is +a definitive reference to the AWK language as defined by the 1987 Bell +Labs release and codified in the 1992 POSIX Utilities standard. + + On the other hand, the novice AWK programmer can study a wealth of +practical programs that emphasize the power of AWK's basic idioms: data +driven control-flow, pattern matching with regular expressions, and +associative arrays. Those looking for something new can try out +`gawk''s interface to network protocols via special `/inet' files. + + The programs in this book make clear that an AWK program is +typically much smaller and faster to develop than a counterpart written +in C. Consequently, there is often a payoff to prototype an algorithm +or design in AWK to get it running quickly and expose problems early. +Often, the interpreted performance is adequate and the AWK prototype +becomes the product. + + The new `pgawk' (profiling `gawk'), produces program execution +counts. I recently experimented with an algorithm that for n lines of +input, exhibited ~ C n^2 performance, while theory predicted ~ C n log n +behavior. A few minutes poring over the `awkprof.out' profile +pinpointed the problem to a single line of code. `pgawk' is a welcome +addition to my programmer's toolbox. + + Arnold has distilled over a decade of experience writing and using +AWK programs, and developing `gawk', into this book. If you use AWK or +want to learn how, then read this book. + + Michael Brennan + Author of `mawk' + + +File: gawk.info, Node: Preface, Next: Getting Started, Prev: Foreword, Up: Top Preface ******* + Several kinds of tasks occur repeatedly when working with text files. +You might want to extract certain lines and discard the rest. Or you +may need to make changes wherever certain patterns appear, but leave +the rest of the file alone. Writing single-use programs for these +tasks in languages such as C, C++ or Pascal is time-consuming and +inconvenient. Such jobs are often easier with `awk'. The `awk' +utility interprets a special-purpose programming language that makes it +easy to handle simple data-reformatting jobs. + + The GNU implementation of `awk' is called `gawk'; it is fully +compatible with the System V Release 4 version of `awk'. `gawk' is +also compatible with the POSIX specification of the `awk' language. +This means that all properly written `awk' programs should work with +`gawk'. Thus, we usually don't distinguish between `gawk' and other +`awk' implementations. + + Using `awk' allows you to: + + * Manage small, personal databases + + * Generate reports + + * Validate data + + * Produce indexes and perform other document preparation tasks + + * Experiment with algorithms that you can adapt later to other + computer languages. + + In addition, `gawk' provides facilities that make it easy to: + + * Extract bits and pieces of data for processing + + * Sort data + + * Perform simple network communications. + This Info file teaches you about the `awk' language and how you can use it effectively. You should already be familiar with basic system -commands, such as `cat' and `ls',(1) and basic shell facilities, such -as Input/Output (I/O) redirection and pipes. +commands, such as `cat' and `ls',(1) as well as basic shell facilities, +such as Input/Output (I/O) redirection and pipes. Implementations of the `awk' language are available for many different computing environments. This Info file, while describing the -`awk' language in general, also describes a particular implementation -of `awk' called `gawk' (which stands for "GNU Awk"). `gawk' runs on a +`awk' language in general, also describes the particular implementation +of `awk' called `gawk' (which stands for "GNU awk"). `gawk' runs on a broad range of Unix systems, ranging from 80386 PC-based computers, up -through large scale systems, such as Crays. `gawk' has also been ported -to MS-DOS and OS/2 PC's, Atari and Amiga micro-computers, and VMS. +through large-scale systems, such as Crays. `gawk' has also been ported +to Mac OS X, MS-DOS, Microsoft Windows (all versions) and OS/2 PC's, +Atari and Amiga micro-computers, BeOS, Tandem D20, and VMS. * Menu: -* History:: The history of `gawk' and `awk'. +* History:: The history of `gawk' and + `awk'. +* Names:: What name to use to find `awk'. +* This Manual:: Using this Info file. Includes sample + input files that you can use. +* Conventions:: Typographical Conventions. * Manual History:: Brief history of the GNU project and this Info file. -* Acknowledgements:: Acknowledgements. +* How To Contribute:: Helping to save the world. +* Acknowledgments:: Acknowledgments. ---------- Footnotes ---------- - (1) These commands are available on POSIX compliant systems, as well + (1) These commands are available on POSIX-compliant systems, as well as on traditional Unix based systems. If you are using some other operating system, you still need to be familiar with the ideas of I/O redirection and pipes. -File: gawk.info, Node: History, Next: Manual History, Prev: Preface, Up: Preface +File: gawk.info, Node: History, Next: Names, Prev: Preface, Up: Preface History of `awk' and `gawk' =========================== - The name `awk' comes from the initials of its designers: Alfred V. -Aho, Peter J. Weinberger, and Brian W. Kernighan. The original version -of `awk' was written in 1977 at AT&T Bell Laboratories. In 1985 a new -version made the programming language more powerful, introducing -user-defined functions, multiple input streams, and computed regular -expressions. This new version became generally available with Unix -System V Release 3.1. The version in System V Release 4 added some new -features and also cleaned up the behavior in some of the "dark corners" -of the language. The specification for `awk' in the POSIX Command -Language and Utilities standard further clarified the language based on -feedback from both the `gawk' designers, and the original Bell Labs -`awk' designers. - - The GNU implementation, `gawk', was written in 1986 by Paul Rubin -and Jay Fenlason, with advice from Richard Stallman. John Woods -contributed parts of the code as well. In 1988 and 1989, David -Trueman, with help from Arnold Robbins, thoroughly reworked `gawk' for -compatibility with the newer `awk'. Current development focuses on bug -fixes, performance improvements, standards compliance, and -occasionally, new features. + Recipe For A Programming Language - -File: gawk.info, Node: Manual History, Next: Acknowledgements, Prev: History, Up: Preface + 1 part `egrep' 1 part `snobol' + 2 parts `ed' 3 parts C -The GNU Project and This Book -============================= + Blend all parts well using `lex' and `yacc'. Document minimally + and release. - The Free Software Foundation (FSF) is a non-profit organization -dedicated to the production and distribution of freely distributable -software. It was founded by Richard M. Stallman, the author of the -original Emacs editor. GNU Emacs is the most widely used version of -Emacs today. + After eight years, add another part `egrep' and two more parts C. + Document very well and release. - The GNU project is an on-going effort on the part of the Free -Software Foundation to create a complete, freely distributable, POSIX -compliant computing environment. (GNU stands for "GNU's not Unix".) -The FSF uses the "GNU General Public License" (or GPL) to ensure that -source code for their software is always available to the end user. A -copy of the GPL is included for your reference (*note GNU GENERAL -PUBLIC LICENSE: Copying.). The GPL applies to the C language source -code for `gawk'. - - A shell, an editor (Emacs), highly portable optimizing C, C++, and -Objective-C compilers, a symbolic debugger, and dozens of large and -small utilities (such as `gawk'), have all been completed and are -freely available. As of this writing (early 1997), the GNU operating -system kernel (the HURD), has been released, but is still in an early -stage of development. - - Until the GNU operating system is more fully developed, you should -consider using Linux, a freely distributable, Unix-like operating -system for 80386, DEC Alpha, Sun SPARC and other systems. There are -many books on Linux. One freely available one is `Linux Installation -and Getting Started', by Matt Welsh. Many Linux distributions are -available, often in computer stores or bundled on CD-ROM with books -about Linux. (There are three other freely available, Unix-like -operating systems for 80386 and other systems, NetBSD, FreeBSD,and -OpenBSD. All are based on the 4.4-Lite Berkeley Software Distribution, -and they use recent versions of `gawk' for their versions of `awk'.) - - This Info file itself has gone through several previous, preliminary -editions. I started working on a preliminary draft of `The GAWK -Manual', by Diane Close, Paul Rubin, and Richard Stallman in the fall -of 1988. It was around 90 pages long, and barely described the -original, "old" version of `awk'. After substantial revision, the first -version of the `The GAWK Manual' to be released was Edition 0.11 Beta in -October of 1989. The manual then underwent more substantial revision -for Edition 0.13 of December 1991. David Trueman, Pat Rankin, and -Michal Jaegermann contributed sections of the manual for Edition 0.13. -That edition was published by the FSF as a bound book early in 1992. -Since then there have been several minor revisions, notably Edition -0.14 of November 1992 that was published by the FSF in January of 1993, -and Edition 0.16 of August 1993. - - Edition 1.0 of `Effective AWK Programming' represents a significant -re-working of `The GAWK Manual', with much additional material. The -FSF and I agree that I am now the primary author. I also felt that it -needed a more descriptive title. - - `Effective AWK Programming' will undoubtedly continue to evolve. An -electronic version comes with the `gawk' distribution from the FSF. If -you find an error in this Info file, please report it! *Note Reporting -Problems and Bugs: Bugs, for information on submitting problem reports -electronically, or write to me in care of the FSF. - - -File: gawk.info, Node: Acknowledgements, Prev: Manual History, Up: Preface - -Acknowledgements -================ - - I would like to acknowledge Richard M. Stallman, for his vision of a -better world, and for his courage in founding the FSF and starting the -GNU project. + The name `awk' comes from the initials of its designers: Alfred V. +Aho, Peter J. Weinberger and Brian W. Kernighan. The original version +of `awk' was written in 1977 at AT&T Bell Laboratories. In 1985, a new +version made the programming language more powerful, introducing +user-defined functions, multiple input streams, and computed regular +expressions. This new version became widely available with Unix System +V Release 3.1 (SVR3.1). The version in SVR4 added some new features +and cleaned up the behavior in some of the "dark corners" of the +language. The specification for `awk' in the POSIX Command Language +and Utilities standard further clarified the language. Both the `gawk' +designers and the original Bell Laboratories `awk' designers provided +feedback for the POSIX specification. + + Paul Rubin wrote the GNU implementation, `gawk', in 1986. Jay +Fenlason completed it, with advice from Richard Stallman. John Woods +contributed parts of the code as well. In 1988 and 1989, David +Trueman, with help from me, thoroughly reworked `gawk' for compatibility +with the newer `awk'. Circa 1995, I became the primary maintainer. +Current development focuses on bug fixes, performance improvements, +standards compliance, and occasionally, new features. - The initial draft of `The GAWK Manual' had the following -acknowledgements: + In May of 1997, Ju"rgen Kahrs felt the need for network access from +`awk', and with a little help from me, set about adding features to do +this for `gawk'. At that time, he also wrote the bulk of `TCP/IP +Internetworking with `gawk'' (a separate document, available as part of +the `gawk' distribution). His code finally became part of the main +`gawk' distribution with `gawk' version 3.1. - Many people need to be thanked for their assistance in producing - this manual. Jay Fenlason contributed many ideas and sample - programs. Richard Mlynarik and Robert Chassell gave helpful - comments on drafts of this manual. The paper `A Supplemental - Document for `awk'' by John W. Pierce of the Chemistry Department - at UC San Diego, pinpointed several issues relevant both to `awk' - implementation and to this manual, that would otherwise have - escaped us. + *Note Major Contributors to `gawk': Contributors, for a complete +list of those who made important contributions to `gawk'. - The following people provided many helpful comments on Edition 0.13 -of `The GAWK Manual': Rick Adams, Michael Brennan, Rich Burridge, Diane -Close, Christopher ("Topher") Eliot, Michael Lijewski, Pat Rankin, -Miriam Robbins, and Michal Jaegermann. + +File: gawk.info, Node: Names, Next: This Manual, Prev: History, Up: Preface - The following people provided many helpful comments for Edition 1.0 -of `Effective AWK Programming': Karl Berry, Michael Brennan, Darrel -Hankerson, Michal Jaegermann, Michael Lijewski, and Miriam Robbins. -Pat Rankin, Michal Jaegermann, Darrel Hankerson and Scott Deifik -updated their respective sections for Edition 1.0. +A Rose by Any Other Name +======================== - Robert J. Chassell provided much valuable advice on the use of -Texinfo. He also deserves special thanks for convincing me _not_ to -title this Info file `How To Gawk Politely'. Karl Berry helped -significantly with the TeX part of Texinfo. + The `awk' language has evolved over the years. Full details are +provided in *Note The Evolution of the `awk' Language: Language History. +The language described in this Info file is often referred to as "new +`awk'" (`nawk'). - David Trueman deserves special credit; he has done a yeoman job of -evolving `gawk' so that it performs well, and without bugs. Although -he is no longer involved with `gawk', working with him on this project -was a significant pleasure. - - Scott Deifik, Darrel Hankerson, Kai Uwe Rommel, Pat Rankin, and -Michal Jaegermann (in no particular order) are long time members of the -`gawk' "crack portability team." Without their hard work and help, -`gawk' would not be nearly the fine program it is today. It has been -and continues to be a pleasure working with this team of fine people. - - Jeffrey Friedl provided invaluable help in tracking down a number of -last minute problems with regular expressions in `gawk' 3.0. - - David and I would like to thank Brian Kernighan of Bell Labs for -invaluable assistance during the testing and debugging of `gawk', and -for help in clarifying numerous points about the language. We could -not have done nearly as good a job on either `gawk' or its -documentation without his help. + Because of this, many systems have multiple versions of `awk'. Some +systems have an `awk' utility that implements the original version of +the `awk' language and a `nawk' utility for the new version. Others +have an `oawk' for the "old `awk'" language and plain `awk' for the new +one. Still others only have one version, which is usually the new +one.(1) - I would like to thank Marshall and Elaine Hartholz of Seattle, and -Dr. Bert and Rita Schreiber of Detroit for large amounts of quiet -vacation time in their homes, which allowed me to make significant -progress on this Info file and on `gawk' itself. Phil Hughes of SSC -contributed in a very important way by loaning me his laptop Linux -system, not once, but twice, allowing me to do a lot of work while away -from home. - - Finally, I must thank my wonderful wife, Miriam, for her patience -through the many versions of this project, for her proof-reading, and -for sharing me with the computer. I would like to thank my parents for -their love, and for the grace with which they raised and educated me. -I also must acknowledge my gratitude to G-d, for the many opportunities -He has sent my way, as well as for the gifts He has given me with which -to take advantage of those opportunities. + All in all, this makes it difficult for you to know which version of +`awk' you should run when writing your programs. The best advice I can +give here is to check your local documentation. Look for `awk', `oawk', +and `nawk', as well as for `gawk'. It is likely that you already have +some version of new `awk' on your system, which is what you should use +when running your programs. (Of course, if you're reading this Info +file, chances are good that you have `gawk'!) + Throughout this Info file, whenever we refer to a language feature +that should be available in any complete implementation of POSIX `awk', +we simply use the term `awk'. When referring to a feature that is +specific to the GNU implementation, we use the term `gawk'. + ---------- Footnotes ---------- -Arnold Robbins -Atlanta, Georgia -February, 1997 + (1) Often, these systems use `gawk' for their `awk' implementation! -File: gawk.info, Node: What Is Awk, Next: Getting Started, Prev: Preface, Up: Top - -Introduction -************ - - If you are like many computer users, you would frequently like to -make changes in various text files wherever certain patterns appear, or -extract data from parts of certain lines while discarding the rest. To -write a program to do this in a language such as C or Pascal is a -time-consuming inconvenience that may take many lines of code. The job -may be easier with `awk'. +File: gawk.info, Node: This Manual, Next: Conventions, Prev: Names, Up: Preface - The `awk' utility interprets a special-purpose programming language -that makes it possible to handle simple data-reformatting jobs with -just a few lines of code. +Using This Book +=============== - The GNU implementation of `awk' is called `gawk'; it is fully upward -compatible with the System V Release 4 version of `awk'. `gawk' is -also upward compatible with the POSIX specification of the `awk' -language. This means that all properly written `awk' programs should -work with `gawk'. Thus, we usually don't distinguish between `gawk' -and other `awk' implementations. + Documentation is like sex: when it is good, it is very, very good; + and when it is bad, it is better than nothing. + Dick Brandon + + The term `awk' refers to a particular program as well as to the +language you use to tell this program what to do. When we need to be +careful, we call the program "the `awk' utility" and the language "the +`awk' language." This Info file explains both the `awk' language and +how to run the `awk' utility. The term "`awk' program" refers to a +program written by you in the `awk' programming language. + + Primarily, this Info file explains the features of `awk', as defined +in the POSIX standard. It does so in the context of the `gawk' +implementation. While doing so, it also attempts to describe important +differences between `gawk' and other `awk' implementations.(1) Finally, +any `gawk' features that are not in the POSIX standard for `awk' are +noted. + + There are subsections labelled as *Advanced Notes* scattered +throughout the Info file. They add a more complete explanation of +points that are relevant, but not likely to be of interest on first +reading. All appear in the index, under the heading "advanced notes." + + Most of the time, the examples use complete `awk' programs. In some +of the more advanced sections, only the part of the `awk' program that +illustrates the concept currently being described is shown. - Using `awk' you can: + While this Info file is aimed principally at people who have not been +exposed to `awk', there is a lot of information here that even the `awk' +expert should find useful. In particular, the description of POSIX +`awk' and the example programs in *Note A Library of `awk' Functions: +Library Functions, and in *Note Practical `awk' Programs: Sample +Programs, should be of interest. - * manage small, personal databases + *Note Getting Started with `awk': Getting Started, provides the +essentials you need to know to begin using `awk'. - * generate reports + *Note Regular Expressions: Regexp, introduces regular expressions in +general, and in particular the flavors supported by POSIX `awk' and +`gawk'. - * validate data + *Note Reading Input Files: Reading Files, describes how `awk' reads +your data. It introduces the concepts of records and fields, as well +as the `getline' command. I/O redirection is first described here. - * produce indexes, and perform other document preparation tasks + *Note Printing Output: Printing, describes how `awk' programs can +produce output with `print' and `printf'. - * even experiment with algorithms that can be adapted later to other - computer languages + *Note Expressions::, describes expressions, which are the basic +building blocks for getting most things done in a program. -* Menu: + *Note Patterns Actions and Variables: Patterns and Actions, +describes how to write patterns for matching records, actions for doing +something when a record is matched, and the built-in variables `awk' +and `gawk' use. -* This Manual:: Using this Info file. Includes sample - input files that you can use. -* Conventions:: Typographical Conventions. -* Sample Data Files:: Sample data files for use in the `awk' - programs illustrated in this Info file. + *Note Arrays in `awk': Arrays, covers `awk''s one-and-only data +structure: associative arrays. Deleting array elements and whole +arrays is also described, as well as sorting arrays in `gawk'. - -File: gawk.info, Node: This Manual, Next: Conventions, Prev: What Is Awk, Up: What Is Awk + *Note Functions::, describes the built-in functions `awk' and `gawk' +provide for you, as well as how to define your own functions. -Using This Book -=============== + *Note Internationalization with `gawk': Internationalization, +describes special features in `gawk' for translating program messages +into different languages at runtime. - The term `awk' refers to a particular program, and to the language -you use to tell this program what to do. When we need to be careful, -we call the program "the `awk' utility" and the language "the `awk' -language." The term `gawk' refers to a version of `awk' developed as -part the GNU project. The purpose of this Info file is to explain both -the `awk' language and how to run the `awk' utility. + *Note Advanced Features of `gawk': Advanced Features, describes a +number of `gawk'-specific advanced features. Of particular note are +the abilities to have two-way communications with another process, +perform TCP/IP networking, and profile your `awk' programs. - The main purpose of the Info file is to explain the features of -`awk', as defined in the POSIX standard. It does so in the context of -one particular implementation, `gawk'. While doing so, it will also -attempt to describe important differences between `gawk' and other -`awk' implementations. Finally, any `gawk' features that are not in -the POSIX standard for `awk' will be noted. + *Note Running `awk' and `gawk': Invoking Gawk, describes how to run +`gawk', the meaning of its command-line options, and how it finds `awk' +program source files. - The term "`awk' program" refers to a program written by you in the -`awk' programming language. + *Note A Library of `awk' Functions: Library Functions, and *Note +Practical `awk' Programs: Sample Programs, provide many sample `awk' +programs. Reading them allows you to see `awk' being used for solving +real problems. - *Note Getting Started with `awk': Getting Started, for the bare -essentials you need to know to start using `awk'. + *Note The Evolution of the `awk' Language: Language History, +describes how the `awk' language has evolved since it was first +released to present. It also describes how `gawk' has acquired +features over time. - Some useful "one-liners" are included to give you a feel for the -`awk' language (*note Useful One Line Programs: One-liners.). + *Note Installing `gawk': Installation, describes how to get `gawk', +how to compile it under Unix, and how to compile and use it on different +non-Unix systems. It also describes how to report bugs in `gawk' and +where to get three other freely available implementations of `awk'. - Many sample `awk' programs have been provided for you (*note A -Library of `awk' Functions: Library Functions.; also *note Practical -`awk' Programs: Sample Programs.). + *Note Implementation Notes: Notes, describes how to disable `gawk''s +extensions, as well as how to contribute new code to `gawk', how to +write extension libraries, and some possible future directions for +`gawk' development. - The entire `awk' language is summarized for quick reference in *Note -`gawk' Summary: Gawk Summary. Look there if you just need to refresh -your memory about a particular feature. + *Note Basic Programming Concepts: Basic Concepts, provides some very +cursory background material for those who are completely unfamiliar +with computer programming. Also centralized there is a discussion of +some of the issues involved in using floating-point numbers. - If you find terms that you aren't familiar with, try looking them up -in the glossary (*note Glossary::). + The *Note Glossary::, defines most, if not all, the significant +terms used throughout the book. If you find terms that you aren't +familiar with, try looking them up. - Most of the time complete `awk' programs are used as examples, but in -some of the more advanced sections, only the part of the `awk' program -that illustrates the concept being described is shown. - - While this Info file is aimed principally at people who have not been -exposed to `awk', there is a lot of information here that even the `awk' -expert should find useful. In particular, the description of POSIX -`awk', and the example programs in *Note A Library of `awk' Functions: -Library Functions, and *Note Practical `awk' Programs: Sample Programs, -should be of interest. - -Dark Corners ------------- - - Who opened that window shade?!? - Count Dracula + *Note GNU General Public License: Copying, and *Note GNU Free +Documentation License::, present the licenses that cover the `gawk' +source code, and this Info file, respectively. + ---------- Footnotes ---------- - - Until the POSIX standard (and `The Gawk Manual'), many features of -`awk' were either poorly documented, or not documented at all. -Descriptions of such features (often called "dark corners") are noted -in this Info file with "(d.c.)". They also appear in the index under -the heading "dark corner." + (1) All such differences appear in the index under the heading +"differences between `gawk' and `awk'." -File: gawk.info, Node: Conventions, Next: Sample Data Files, Prev: This Manual, Up: What Is Awk +File: gawk.info, Node: Conventions, Next: Manual History, Prev: This Manual, Up: Preface Typographical Conventions ========================= This Info file is written using Texinfo, the GNU documentation formatting language. A single Texinfo source file is used to produce -both the printed and on-line versions of the documentation. This -section briefly documents the typographical conventions used in Texinfo. +both the printed and online versions of the documentation. This minor +node briefly documents the typographical conventions used in Texinfo. - Examples you would type at the command line are preceded by the + Examples you would type at the command-line are preceded by the common shell primary and secondary prompts, `$' and `>'. Output from the command is preceded by the glyph "-|". This typically represents the command's standard output. Error messages, and other output on the @@ -699,84 +829,204 @@ example: Characters that you type at the keyboard look `like this'. In particular, there are special characters called "control characters." These are characters that you type by holding down both the `CONTROL' -key and another key, at the same time. For example, a `Control-d' is -typed by first pressing and holding the `CONTROL' key, next pressing -the `d' key, and finally releasing both keys. +key and another key, at the same time. For example, a `Ctrl-d' is typed +by first pressing and holding the `CONTROL' key, next pressing the `d' +key and finally releasing both keys. + +Dark Corners +............ + + Dark corners are basically fractal -- no matter how much you + illuminate, there's always a smaller but darker one. + Brian Kernighan + + Until the POSIX standard (and `The Gawk Manual'), many features of +`awk' were either poorly documented or not documented at all. +Descriptions of such features (often called "dark corners") are noted +in this Info file with "(d.c.)". They also appear in the index under +the heading "dark corner." + + As noted by the opening quote, though, any coverage of dark corners +is, by definition, something that is incomplete. -File: gawk.info, Node: Sample Data Files, Prev: Conventions, Up: What Is Awk +File: gawk.info, Node: Manual History, Next: How To Contribute, Prev: Conventions, Up: Preface -Data Files for the Examples -=========================== +The GNU Project and This Book +============================= - Many of the examples in this Info file take their input from two -sample data files. The first, called `BBS-list', represents a list of -computer bulletin board systems together with information about those -systems. The second data file, called `inventory-shipped', contains -information about shipments on a monthly basis. In both files, each -line is considered to be one "record". + Software is like sex: it's better when it's free. + Linus Torvalds - In the file `BBS-list', each record contains the name of a computer -bulletin board, its phone number, the board's baud rate(s), and a code -for the number of hours it is operational. An `A' in the last column -means the board operates 24 hours a day. A `B' in the last column -means the board operates evening and weekend hours, only. A `C' means -the board operates only on weekends. + The Free Software Foundation (FSF) is a non-profit organization +dedicated to the production and distribution of freely distributable +software. It was founded by Richard M. Stallman, the author of the +original Emacs editor. GNU Emacs is the most widely used version of +Emacs today. - aardvark 555-5553 1200/300 B - alpo-net 555-3412 2400/1200/300 A - barfly 555-7685 1200/300 A - bites 555-1675 2400/1200/300 A - camelot 555-0542 300 C - core 555-2912 1200/300 C - fooey 555-1234 2400/1200/300 B - foot 555-6699 1200/300 B - macfoo 555-6480 1200/300 A - sdace 555-3430 2400/1200/300 A - sabafoo 555-2127 1200/300 C + The GNU(1) Project is an ongoing effort on the part of the Free +Software Foundation to create a complete, freely distributable, +POSIX-compliant computing environment. The FSF uses the "GNU General +Public License" (GPL) to ensure that their software's source code is +always available to the end user. A copy of the GPL is included for +your reference (*note GNU General Public License: Copying.). The GPL +applies to the C language source code for `gawk'. To find out more +about the FSF and the GNU Project online, see the GNU Project's home +page (http://www.gnu.org). This Info file may also be read from their +web site (http://www.gnu.org/manual/gawk/). - The second data file, called `inventory-shipped', represents -information about shipments during the year. Each record contains the -month of the year, the number of green crates shipped, the number of -red boxes shipped, the number of orange bags shipped, and the number of -blue packages shipped, respectively. There are 16 entries, covering -the 12 months of one year and four months of the next year. + A shell, an editor (Emacs), highly portable optimizing C, C++, and +Objective-C compilers, a symbolic debugger and dozens of large and +small utilities (such as `gawk'), have all been completed and are +freely available. The GNU operating system kernel (the HURD), has been +released but is still in an early stage of development. - Jan 13 25 15 115 - Feb 15 32 24 226 - Mar 15 24 34 228 - Apr 31 52 63 420 - May 16 34 29 208 - Jun 31 42 75 492 - Jul 24 34 67 436 - Aug 15 34 47 316 - Sep 13 55 37 277 - Oct 29 54 68 525 - Nov 20 87 82 577 - Dec 17 35 61 401 - - Jan 21 36 64 620 - Feb 26 58 80 652 - Mar 24 75 70 495 - Apr 21 70 74 514 + Until the GNU operating system is more fully developed, you should +consider using GNU/Linux, a freely distributable, Unix-like operating +system for Intel 80386, DEC Alpha, Sun SPARC, IBM S/390, and other +systems.(2) There are many books on GNU/Linux. One that is freely +available is `Linux Installation and Getting Started', by Matt Welsh. +Many GNU/Linux distributions are often available in computer stores or +bundled on CD-ROMs with books about Linux. (There are three other +freely available, Unix-like operating systems for 80386 and other +systems: NetBSD, FreeBSD, and OpenBSD. All are based on the 4.4-Lite +Berkeley Software Distribution, and they use recent versions of `gawk' +for their versions of `awk'.) + + The Info file itself has gone through a number of previous editions. +Paul Rubin wrote the very first draft of `The GAWK Manual'; it was +around 40 pages in size. Diane Close and Richard Stallman improved it, +yielding a version that was around 90 pages long and barely described +the original, "old" version of `awk'. + + I started working with that version in the fall of 1988. As work on +it progressed, the FSF published several preliminary versions (numbered +0.X). In 1996, Edition 1.0 was released with `gawk' 3.0.0. The FSF +published the first two editions under the title `The GNU Awk User's +Guide'. + + This edition maintains the basic structure of Edition 1.0, but with +significant additional material, reflecting the host of new features in +`gawk' version 3.1. Of particular note is *Note Sorting Array Values +and Indices with `gawk': Array Sorting, as well as *Note Using `gawk''s +Bit Manipulation Functions: Bitwise Functions, *Note +Internationalization with `gawk': Internationalization, and also *Note +Advanced Features of `gawk': Advanced Features, and *Note Adding New +Built-in Functions to `gawk': Dynamic Extensions. + + `GAWK: Effective AWK Programming' will undoubtedly continue to +evolve. An electronic version comes with the `gawk' distribution from +the FSF. If you find an error in this Info file, please report it! +*Note Reporting Problems and Bugs: Bugs, for information on submitting +problem reports electronically, or write to me in care of the publisher. - If you are reading this in GNU Emacs using Info, you can copy the -regions of text showing these sample files into your own test files. -This way you can try out the examples shown in the remainder of this -document. You do this by using the command `M-x write-region' to copy -text from the Info file into a file for use with `awk' (*Note -Miscellaneous File Operations: (emacs)Misc File Ops, for more -information). Using this information, create your own `BBS-list' and -`inventory-shipped' files, and practice what you learn in this Info -file. + ---------- Footnotes ---------- - If you are using the stand-alone version of Info, see *Note -Extracting Programs from Texinfo Source Files: Extract Program, for an -`awk' program that will extract these data files from `gawk.texi', the -Texinfo source file for this Info file. + (1) GNU stands for "GNU's not Unix." + + (2) The terminology "GNU/Linux" is explained in the *Note Glossary::. + + +File: gawk.info, Node: How To Contribute, Next: Acknowledgments, Prev: Manual History, Up: Preface + +How to Contribute +================= + + As the maintainer of GNU `awk', I am starting a collection of +publicly available `awk' programs. For more information, see +`ftp://ftp.freefriends.org/arnold/Awkstuff'. If you have written an +interesting `awk' program, or have written a `gawk' extension that you +would like to share with the rest of the world, please contact me +(<arnold@gnu.org>). Making things available on the Internet helps keep +the `gawk' distribution down to manageable size. + + +File: gawk.info, Node: Acknowledgments, Prev: How To Contribute, Up: Preface + +Acknowledgments +=============== + + The initial draft of `The GAWK Manual' had the following +acknowledgments: + + Many people need to be thanked for their assistance in producing + this manual. Jay Fenlason contributed many ideas and sample + programs. Richard Mlynarik and Robert Chassell gave helpful + comments on drafts of this manual. The paper `A Supplemental + Document for `awk'' by John W. Pierce of the Chemistry Department + at UC San Diego, pinpointed several issues relevant both to `awk' + implementation and to this manual, that would otherwise have + escaped us. + + I would like to acknowledge Richard M. Stallman, for his vision of a +better world and for his courage in founding the FSF and starting the +GNU project. + + The following people (in alphabetical order) provided helpful +comments on various versions of this book, up to and including this +edition. Rick Adams, Nelson H.F. Beebe, Karl Berry, Dr. Michael +Brennan, Rich Burridge, Claire Coutier, Diane Close, Scott Deifik, +Christopher ("Topher") Eliot, Jeffrey Friedl, Dr. Darrel Hankerson, +Michal Jaegermann, Dr. Richard J. LeBlanc, Michael Lijewski, Pat Rankin, +Miriam Robbins, Mary Sheehan, and Chuck Toporek. + + Robert J. Chassell provided much valuable advice on the use of +Texinfo. He also deserves special thanks for convincing me _not_ to +title this Info file `How To Gawk Politely'. Karl Berry helped +significantly with the TeX part of Texinfo. + + I would like to thank Marshall and Elaine Hartholz of Seattle and +Dr. Bert and Rita Schreiber of Detroit for large amounts of quiet +vacation time in their homes, which allowed me to make significant +progress on this Info file and on `gawk' itself. + + Phil Hughes of SSC contributed in a very important way by loaning me +his laptop GNU/Linux system, not once, but twice, which allowed me to +do a lot of work while away from home. + + David Trueman deserves special credit; he has done a yeoman job of +evolving `gawk' so that it performs well and without bugs. Although he +is no longer involved with `gawk', working with him on this project was +a significant pleasure. + + The intrepid members of the GNITS mailing list, and most notably +Ulrich Drepper, provided invaluable help and feedback for the design of +the internationalization features. + + Nelson Beebe, Martin Brown, Scott Deifik, Darrel Hankerson, Michal +Jaegermann, Ju"rgen Kahrs, Pat Rankin, Kai Uwe Rommel, and Eli Zaretskii +(in alphabetical order) are long-time members of the `gawk' "crack +portability team." Without their hard work and help, `gawk' would not +be nearly the fine program it is today. It has been and continues to +be a pleasure working with this team of fine people. + + David and I would like to thank Brian Kernighan of Bell Laboratories +for invaluable assistance during the testing and debugging of `gawk', +and for help in clarifying numerous points about the language. We +could not have done nearly as good a job on either `gawk' or its +documentation without his help. + + Chuck Toporek, Mary Sheehan, and Claire Coutier of O'Reilly & +Associates contributed significant editorial help for this Info file +for the 3.1 release of `gawk'. + + I must thank my wonderful wife, Miriam, for her patience through the +many versions of this project, for her proof-reading, and for sharing +me with the computer. I would like to thank my parents for their love, +and for the grace with which they raised and educated me. Finally, I +also must acknowledge my gratitude to G-d, for the many opportunities +He has sent my way, as well as for the gifts He has given me with which +to take advantage of those opportunities. + + + +Arnold Robbins +Nof Ayalon +ISRAEL +March, 2001 -File: gawk.info, Node: Getting Started, Next: One-liners, Prev: What Is Awk, Up: Top +File: gawk.info, Node: Getting Started, Next: Regexp, Prev: Preface, Up: Top Getting Started with `awk' ************************** @@ -784,29 +1034,29 @@ Getting Started with `awk' The basic function of `awk' is to search files for lines (or other units of text) that contain certain patterns. When a line matches one of the patterns, `awk' performs specified actions on that line. `awk' -keeps processing input lines in this way until the end of the input -files are reached. +keeps processing input lines in this way until it reaches the end of +the input files. Programs in `awk' are different from programs in most other languages, because `awk' programs are "data-driven"; that is, you -describe the data you wish to work with, and then what to do when you +describe the data you want to work with and then what to do when you find it. Most other languages are "procedural"; you have to describe, in great detail, every step the program is to take. When working with procedural languages, it is usually much harder to clearly describe the data your program will process. For this reason, `awk' programs are -often refreshingly easy to both write and read. +often refreshingly easy to write and read. When you run `awk', you specify an `awk' "program" that tells `awk' what to do. The program consists of a series of "rules". (It may also -contain "function definitions", an advanced feature which we will -ignore for now. *Note User-defined Functions: User-defined.) Each -rule specifies one pattern to search for, and one action to perform -when that pattern is found. +contain "function definitions", an advanced feature that we will ignore +for now. *Note User-Defined Functions: User-defined.) Each rule +specifies one pattern to search for and one action to perform upon +finding the pattern. Syntactically, a rule consists of a pattern followed by an action. The action is enclosed in curly braces to separate it from the pattern. -Rules are usually separated by newlines. Therefore, an `awk' program -looks like this: +Newlines usually separate rules. Therefore, an `awk' program looks +like this: PATTERN { ACTION } PATTERN { ACTION } @@ -814,54 +1064,22 @@ looks like this: * Menu: -* Names:: What name to use to find `awk'. * Running gawk:: How to run `gawk' programs; includes - command line syntax. + command-line syntax. +* Sample Data Files:: Sample data files for use in the `awk' + programs illustrated in this Info file. * Very Simple:: A very simple example. -* Two Rules:: A less simple one-line example with two rules. +* Two Rules:: A less simple one-line example using two + rules. * More Complex:: A more complex example. * Statements/Lines:: Subdividing or combining statements into lines. * Other Features:: Other Features of `awk'. -* When:: When to use `gawk' and when to use other - things. - - -File: gawk.info, Node: Names, Next: Running gawk, Prev: Getting Started, Up: Getting Started - -A Rose By Any Other Name -======================== - - The `awk' language has evolved over the years. Full details are -provided in *Note The Evolution of the `awk' Language: Language History. -The language described in this Info file is often referred to as "new -`awk'." - - Because of this, many systems have multiple versions of `awk'. Some -systems have an `awk' utility that implements the original version of -the `awk' language, and a `nawk' utility for the new version. Others -have an `oawk' for the "old `awk'" language, and plain `awk' for the -new one. Still others only have one version, usually the new one.(1) - - All in all, this makes it difficult for you to know which version of -`awk' you should run when writing your programs. The best advice we -can give here is to check your local documentation. Look for `awk', -`oawk', and `nawk', as well as for `gawk'. Chances are, you will have -some version of new `awk' on your system, and that is what you should -use when running your programs. (Of course, if you're reading this -Info file, chances are good that you have `gawk'!) - - Throughout this Info file, whenever we refer to a language feature -that should be available in any complete implementation of POSIX `awk', -we simply use the term `awk'. When referring to a feature that is -specific to the GNU implementation, we use the term `gawk'. - - ---------- Footnotes ---------- - - (1) Often, these systems use `gawk' for their `awk' implementation! +* When:: When to use `gawk' and when to use + other things. -File: gawk.info, Node: Running gawk, Next: Very Simple, Prev: Names, Up: Getting Started +File: gawk.info, Node: Running gawk, Next: Sample Data Files, Prev: Getting Started, Up: Getting Started How to Run `awk' Programs ========================= @@ -872,29 +1090,31 @@ this: awk 'PROGRAM' INPUT-FILE1 INPUT-FILE2 ... -where PROGRAM consists of a series of patterns and actions, as -described earlier. (The reason for the single quotes is described -below, in *Note One-shot Throw-away `awk' Programs: One-shot.) - When the program is long, it is usually more convenient to put it in a file and run it with a command like this: awk -f PROGRAM-FILE INPUT-FILE1 INPUT-FILE2 ... + This minor node discusses both mechanisms, along with several +variations of each. + * Menu: -* One-shot:: Running a short throw-away `awk' program. +* One-shot:: Running a short throw-away `awk' + program. * Read Terminal:: Using no input files (input from terminal instead). * Long:: Putting permanent `awk' programs in files. * Executable Scripts:: Making self-contained `awk' programs. -* Comments:: Adding documentation to `gawk' programs. +* Comments:: Adding documentation to `gawk' + programs. +* Quoting:: More discussion of shell quoting issues. File: gawk.info, Node: One-shot, Next: Read Terminal, Prev: Running gawk, Up: Running gawk -One-shot Throw-away `awk' Programs +One-Shot Throw-Away `awk' Programs ---------------------------------- Once you are familiar with `awk', you will often type in simple @@ -908,55 +1128,48 @@ described earlier. This command format instructs the "shell", or command interpreter, to start `awk' and use the PROGRAM to process records in the input -file(s). There are single quotes around PROGRAM so that the shell -doesn't interpret any `awk' characters as special shell characters. -They also cause the shell to treat all of PROGRAM as a single argument -for `awk' and allow PROGRAM to be more than one line long. +file(s). There are single quotes around PROGRAM so the shell won't +interpret any `awk' characters as special shell characters. The quotes +also cause the shell to treat all of PROGRAM as a single argument for +`awk', and allow PROGRAM to be more than one line long. This format is also useful for running short or medium-sized `awk' programs from shell scripts, because it avoids the need for a separate file for the `awk' program. A self-contained shell script is more -reliable since there are no other files to misplace. +reliable because there are no other files to misplace. - *Note Useful One Line Programs: One-liners, presents several short, + *Note Some Simple Examples: Very Simple, presents several short, self-contained programs. - As an interesting side point, the command - - awk '/foo/' FILES ... - -is essentially the same as - - egrep foo FILES ... - File: gawk.info, Node: Read Terminal, Next: Long, Prev: One-shot, Up: Running gawk -Running `awk' without Input Files +Running `awk' Without Input Files --------------------------------- You can also run `awk' without any input files. If you type the -command line: +following command line: awk 'PROGRAM' -then `awk' applies the PROGRAM to the "standard input", which usually -means whatever you type on the terminal. This continues until you -indicate end-of-file by typing `Control-d'. (On other operating -systems, the end-of-file character may be different. For example, on -OS/2 and MS-DOS, it is `Control-z'.) +`awk' applies the PROGRAM to the "standard input", which usually means +whatever you type on the terminal. This continues until you indicate +end-of-file by typing `Ctrl-d'. (On other operating systems, the +end-of-file character may be different. For example, on OS/2 and +MS-DOS, it is `Ctrl-z'.) - For example, the following program prints a friendly piece of advice -(from Douglas Adams' `The Hitchhiker's Guide to the Galaxy'), to keep -you from worrying about the complexities of computer programming -(`BEGIN' is a feature we haven't discussed yet). + As an example, the following program prints a friendly piece of +advice (from Douglas Adams's `The Hitchhiker's Guide to the Galaxy'), +to keep you from worrying about the complexities of computer +programming. (`BEGIN' is a feature we haven't discussed yet.): $ awk "BEGIN { print \"Don't Panic!\" }" -| Don't Panic! This program does not read any input. The `\' before each of the -inner double quotes is necessary because of the shell's quoting rules, -in particular because it mixes both single quotes and double quotes. +inner double quotes is necessary because of the shell's quoting +rules--in particular because it mixes both single quotes and double +quotes.(1) This next simple `awk' program emulates the `cat' utility; it copies whatever you type at the keyboard to its standard output. (Why this @@ -971,7 +1184,13 @@ works is explained shortly.) -| Four score and seven years ago, ... What, me worry? -| What, me worry? - Control-d + Ctrl-d + + ---------- Footnotes ---------- + + (1) Although we generally recommend the use of single quotes around +the program text, double quotes are needed here in order to put the +single quote into the message. File: gawk.info, Node: Long, Next: Executable Scripts, Prev: Read Terminal, Up: Running gawk @@ -979,9 +1198,9 @@ File: gawk.info, Node: Long, Next: Executable Scripts, Prev: Read Terminal, Running Long Programs --------------------- - Sometimes your `awk' programs can be very long. In this case it is -more convenient to put the program into a separate file. To tell `awk' -to use that file for its program, you type: + Sometimes your `awk' programs can be very long. In this case, it is +more convenient to put the program into a separate file. In order to +tell `awk' to use that file for its program, you type: awk -f SOURCE-FILE INPUT-FILE1 INPUT-FILE2 ... @@ -999,7 +1218,7 @@ does the same thing as this one: awk "BEGIN { print \"Don't Panic!\" }" -which was explained earlier (*note Running `awk' without Input Files: +This was explained earlier (*note Running `awk' Without Input Files: Read Terminal.). Note that you don't usually need single quotes around the file name that you specify with `-f', because most file names don't contain any of the shell's special characters. Notice that in @@ -1009,7 +1228,7 @@ command line. If you want to identify your `awk' program files clearly as such, you can add the extension `.awk' to the file name. This doesn't affect -the execution of the `awk' program, but it does make "housekeeping" +the execution of the `awk' program but it does make "housekeeping" easier. @@ -1020,76 +1239,71 @@ Executable `awk' Programs Once you have learned `awk', you may want to write self-contained `awk' scripts, using the `#!' script mechanism. You can do this on -many Unix systems(1) (and someday on the GNU system). - - For example, you could update the file `advice' to look like this: +many Unix systems(1) as well as on the GNU system. For example, you +could update the file `advice' to look like this: #! /bin/awk -f - BEGIN { print "Don't Panic!" } + BEGIN { print "Don't Panic!" } -After making this file executable (with the `chmod' utility), you can -simply type `advice' at the shell, and the system will arrange to run -`awk'(2) as if you had typed `awk -f advice'. +After making this file executable (with the `chmod' utility), simply +type `advice' at the shell and the system arranges to run `awk'(2) as +if you had typed `awk -f advice': + $ chmod +x advice $ advice -| Don't Panic! Self-contained `awk' scripts are useful when you want to write a -program which users can invoke without their having to know that the +program that users can invoke without their having to know that the program is written in `awk'. - *Caution:* You should not put more than one argument on the `#!' -line after the path to `awk'. This will not work. The operating system -treats the rest of the line as a single agument, and passes it to `awk'. -Doing this will lead to confusing behavior: most likely a usage -diagnostic of some sort from `awk'. - - Some older systems do not support the `#!' mechanism. You can get a -similar effect using a regular shell script. It would look something -like this: +Advanced Notes: Portability Issues with `#!' +-------------------------------------------- - : The colon ensures execution by the standard shell. - awk 'PROGRAM' "$@" + Some systems limit the length of the interpreter name to 32 +characters. Often, this can be dealt with by using a symbolic link. - Using this technique, it is _vital_ to enclose the PROGRAM in single -quotes to protect it from interpretation by the shell. If you omit the -quotes, only a shell wizard can predict the results. + You should not put more than one argument on the `#!' line after the +path to `awk'. It does not work. The operating system treats the rest +of the line as a single argument and passes it to `awk'. Doing this +leads to confusing behavior--most likely a usage diagnostic of some +sort from `awk'. - The `"$@"' causes the shell to forward all the command line -arguments to the `awk' program, without interpretation. The first -line, which starts with a colon, is used so that this shell script will -work even if invoked by a user who uses the C shell. (Not all older -systems obey this convention, but many do.) + Finally, the value of `ARGV[0]' (*note Built-in Variables::) varies +depending upon your operating system. Some systems put `awk' there, +some put the full pathname of `awk' (such as `/bin/awk'), and some put +the name of your script (`advice'). Don't rely on the value of +`ARGV[0]' to provide your script name. ---------- Footnotes ---------- - (1) The `#!' mechanism works on Linux systems, Unix systems derived -from Berkeley Unix, System V Release 4, and some System V Release 3 + (1) The `#!' mechanism works on Linux systems, systems derived from +the 4.4-Lite Berkeley Software Distribution, and most commercial Unix systems. (2) The line beginning with `#!' lists the full file name of an -interpreter to be run, and an optional initial command line argument to +interpreter to run and an optional initial command-line argument to pass to that interpreter. The operating system then runs the interpreter with the given argument and the full argument list of the executed program. The first argument in the list is the full file name -of the `awk' program. The rest of the argument list will either be -options to `awk', or data files, or both. +of the `awk' program. The rest of the argument list is either options +to `awk', or data files, or both. -File: gawk.info, Node: Comments, Prev: Executable Scripts, Up: Running gawk +File: gawk.info, Node: Comments, Next: Quoting, Prev: Executable Scripts, Up: Running gawk Comments in `awk' Programs -------------------------- A "comment" is some text that is included in a program for the sake -of human readers; it is not really part of the program. Comments can -explain what the program does, and how it works. Nearly all -programming languages have provisions for comments, because programs are -typically hard to understand without their extra help. +of human readers; it is not really an executable part of the program. +Comments can explain what the program does and how it works. Nearly all +programming languages have provisions for comments, as programs are +typically hard to understand without them. In the `awk' language, a comment starts with the sharp sign -character, `#', and continues to the end of the line. The `#' does not +character (`#') and continues to the end of the line. The `#' does not have to be the first character on the line. The `awk' language ignores the rest of a line following a sharp sign. For example, we could have put the following into `advice': @@ -1099,47 +1313,230 @@ put the following into `advice': BEGIN { print "Don't Panic!" } You can put comment lines into keyboard-composed throw-away `awk' -programs also, but this usually isn't very useful; the purpose of a -comment is to help you or another person understand the program at a -later time. +programs, but this usually isn't very useful; the purpose of a comment +is to help you or another person understand the program when reading it +at a later time. - *Caution:* As mentioned in *Note One-shot Throw-away `awk' Programs: + *Caution:* As mentioned in *Note One-Shot Throw-Away `awk' Programs: One-shot, you can enclose small to medium programs in single quotes, in order to keep your shell scripts self-contained. When doing so, _don't_ put an apostrophe (i.e., a single quote) into a comment (or -anywhere else in your program). The shell will interpret the quote as -the closing quote for the entire program. As a result, usually the -shell will print a message about mismatched quotes, and if `awk' -actually runs, it will probably print strange messages about syntax -errors. For example: +anywhere else in your program). The shell interprets the quote as the +closing quote for the entire program. As a result, usually the shell +prints a message about mismatched quotes, and if `awk' actually runs, +it will probably print strange messages about syntax errors. For +example, look at the following: + + $ awk '{ print "hello" } # let's be cute' + > + + The shell sees that the first two quotes match, and that a new +quoted object begins at the end of the command-line. It therefore +prompts with the secondary prompt, waiting for more input. With Unix +`awk', closing the quoted string produces this result: - awk 'BEGIN { print "hello" } # let's be cute' + $ awk '{ print "hello" } # let's be cute' + > ' + error--> awk: can't open file be + error--> source line number 1 + + Putting a backslash before the single quote in `let's' wouldn't help, +since backslashes are not special inside single quotes. The next +node describes the shell's quoting rules. -File: gawk.info, Node: Very Simple, Next: Two Rules, Prev: Running gawk, Up: Getting Started +File: gawk.info, Node: Quoting, Prev: Comments, Up: Running gawk -A Very Simple Example -===================== +Shell Quoting Issues +-------------------- + + For short to medium length `awk' programs, it is most convenient to +enter the program on the `awk' command line. This is best done by +enclosing the entire program in single quotes. This is true whether +you are entering the program interactively at the shell prompt, or +writing it as part of a larger shell script: + + awk 'PROGRAM TEXT' INPUT-FILE1 INPUT-FILE2 ... + + Once you are working with the shell, it is helpful to have a basic +knowledge of shell quoting rules. The following rules apply only to +POSIX-compliant, Bourne-style shells (such as `bash', the GNU +Bourne-Again Shell). If you use `csh', you're on your own. + + * Quoted items can be concatenated with nonquoted items as well as + with other quoted items. The shell turns everything into one + argument for the command. + + * Preceding any single character with a backslash (`\') quotes that + character. The shell removes the backslash and passes the quoted + character on to the command. + + * Single quotes protect everything between the opening and closing + quotes. The shell does no interpretation of the quoted text, + passing it on verbatim to the command. It is _impossible_ to + embed a single quote inside single-quoted text. Refer back to + *Note Comments in `awk' Programs: Comments, for an example showing + what happens if you try. + + * Double quotes protect most things between the opening and closing + quotes. The shell does at least variable and command substitution + on the quoted text. Different shells may do additional kinds of + processing on double-quoted text. + + Since certain characters within double-quoted text are processed + by the shell, they must be "escaped" within the text. Of note are + the characters `$', ``', `\' and `"', all of which must be + preceded by a backslash within double-quoted text if they are to + be passed on literally to the program. (The leading backslash is + stripped first.) Thus, the example seen in *Note Running `awk' + Without Input Files: Read Terminal, is applicable: + + $ awk "BEGIN { print \"Don't Panic!\" }" + -| Don't Panic! + + Note that the single quote is not special within double quotes. + + * Null strings are removed when they occur as part of a non-null + command-line argument, while explicit non-null objects are kept. + For example, to specify that the field separator `FS' should be + set to the null string, use: + + awk -F "" 'PROGRAM' FILES # correct + + Don't use this: + + awk -F"" 'PROGRAM' FILES # wrong! + + In the second case, `awk' will attempt to use the text of the + program as the value of `FS', and the first file name as the text + of the program! This results in syntax errors at best, and + confusing behavior at worst. + + Mixing single and double quotes is difficult. You have to resort to +shell quoting tricks, like this: + + $ awk 'BEGIN { print "Here is a single quote <'"'"'>" }' + -| Here is a single quote <'> + +This program consists of three concatenated quoted strings. The first +and the third are single-quoted, the second is double-quoted. + + This can be "simplified" to: + + $ awk 'BEGIN { print "Here is a single quote <'\''>" }' + -| Here is a single quote <'> + +Judge for yourself which of these two is the more readable. + + Another option is to use double quotes, escaping the embedded, +`awk'-level double quotes: + + $ awk "BEGIN { print \"Here is a single quote <'>\" }" + -| Here is a single quote <'> + +This option is also painful, because double quotes, backslashes, and +dollar signs are very common in `awk' programs. + + If you really need both single and double quotes in your `awk' +program, it is probably best to move it into a separate file, where the +shell won't be part of the picture, and you can say what you mean. + + +File: gawk.info, Node: Sample Data Files, Next: Very Simple, Prev: Running gawk, Up: Getting Started + +Data Files for the Examples +=========================== + + Many of the examples in this Info file take their input from two +sample data files. The first, called `BBS-list', represents a list of +computer bulletin board systems together with information about those +systems. The second data file, called `inventory-shipped', contains +information about monthly shipments. In both files, each line is +considered to be one "record". + + In the file `BBS-list', each record contains the name of a computer +bulletin board, its phone number, the board's baud rate(s), and a code +for the number of hours it is operational. An `A' in the last column +means the board operates 24 hours a day. A `B' in the last column +means the board only operates on evening and weekend hours. A `C' +means the board operates only on weekends: + + aardvark 555-5553 1200/300 B + alpo-net 555-3412 2400/1200/300 A + barfly 555-7685 1200/300 A + bites 555-1675 2400/1200/300 A + camelot 555-0542 300 C + core 555-2912 1200/300 C + fooey 555-1234 2400/1200/300 B + foot 555-6699 1200/300 B + macfoo 555-6480 1200/300 A + sdace 555-3430 2400/1200/300 A + sabafoo 555-2127 1200/300 C + + The second data file, called `inventory-shipped', represents +information about shipments during the year. Each record contains the +month, the number of green crates shipped, the number of red boxes +shipped, the number of orange bags shipped, and the number of blue +packages shipped, respectively. There are 16 entries, covering the 12 +months of last year and the first four months of the current year. + + Jan 13 25 15 115 + Feb 15 32 24 226 + Mar 15 24 34 228 + Apr 31 52 63 420 + May 16 34 29 208 + Jun 31 42 75 492 + Jul 24 34 67 436 + Aug 15 34 47 316 + Sep 13 55 37 277 + Oct 29 54 68 525 + Nov 20 87 82 577 + Dec 17 35 61 401 + + Jan 21 36 64 620 + Feb 26 58 80 652 + Mar 24 75 70 495 + Apr 21 70 74 514 + + If you are reading this in GNU Emacs using Info, you can copy the +regions of text showing these sample files into your own test files. +This way you can try out the examples shown in the remainder of this +document. You do this by using the command `M-x write-region' to copy +text from the Info file into a file for use with `awk' (*Note +Miscellaneous File Operations: (emacs)Misc File Ops, for more +information). Using this information, create your own `BBS-list' and +`inventory-shipped' files and practice what you learn in this Info file. + + If you are using the stand-alone version of Info, see *Note +Extracting Programs from Texinfo Source Files: Extract Program, for an +`awk' program that extracts these data files from `gawk.texi', the +Texinfo source file for this Info file. + + +File: gawk.info, Node: Very Simple, Next: Two Rules, Prev: Sample Data Files, Up: Getting Started + +Some Simple Examples +==================== The following command runs a simple `awk' program that searches the -input file `BBS-list' for the string of characters: `foo'. (A string -of characters is usually called a "string". The term "string" is -perhaps based on similar usage in English, such as "a string of -pearls," or, "a string of cars in a train.") +input file `BBS-list' for the character string `foo'. (A string of +characters is usually called a "string". The term "string" is based on +similar usage in English, such as "a string of pearls," or, "a string +of cars in a train."): awk '/foo/ { print $0 }' BBS-list -When lines containing `foo' are found, they are printed, because +When lines containing `foo' are found, they are printed because `print $0' means print the current line. (Just `print' by itself means the same thing, so we could have written that instead.) - You will notice that slashes, `/', surround the string `foo' in the -`awk' program. The slashes indicate that `foo' is a pattern to search -for. This type of pattern is called a "regular expression", and is -covered in more detail later (*note Regular Expressions: Regexp.). The -pattern is allowed to match parts of words. There are single-quotes -around the `awk' program so that the shell won't interpret any of it as -special shell characters. + You will notice that slashes (`/') surround the string `foo' in the +`awk' program. The slashes indicate that `foo' is the pattern to +search for. This type of pattern is called a "regular expression", +which is covered in more detail later (*note Regular Expressions: +Regexp.). The pattern is allowed to match parts of words. There are +single quotes around the `awk' program so that the shell won't +interpret any of it as special shell characters. Here is what this program prints: @@ -1155,10 +1552,81 @@ for _every_ input line. If the action is omitted, the default action is to print all lines that match the pattern. Thus, we could leave out the action (the `print' statement and the -curly braces) in the above example, and the result would be the same: -all lines matching the pattern `foo' would be printed. By comparison, -omitting the `print' statement but retaining the curly braces makes an -empty action that does nothing; then no lines would be printed. +curly braces) in the above example and the result would be the same: all +lines matching the pattern `foo' are printed. By comparison, omitting +the `print' statement but retaining the curly braces makes an empty +action that does nothing (i.e., no lines are printed). + + Many practical `awk' programs are just a line or two. Following is a +collection of useful, short programs to get you started. Some of these +programs contain constructs that haven't been covered yet. (The +description of the program will give you a good idea of what is going +on, but please read the rest of the Info file to become an `awk' +expert!) Most of the examples use a data file named `data'. This is +just a placeholder; if you use these programs yourself, substitute your +own file names for `data'. For future reference, note that there is +often more than one way to do things in `awk'. At some point, you may +want to look back at these examples and see if you can come up with +different ways to do the same things shown here: + + * Print the length of the longest input line: + + awk '{ if (length($0) > max) max = length($0) } + END { print max }' data + + * Print every line that is longer than 80 characters: + + awk 'length($0) > 80' data + + The sole rule has a relational expression as its pattern and it + has no action--so the default action, printing the record, is used. + + * Print the length of the longest line in `data': + + expand data | awk '{ if (x < length()) x = length() } + END { print "maximum line length is " x }' + + The input is processed by the `expand' utility to change tabs into + spaces, so the widths compared are actually the right-margin + columns. + + * Print every line that has at least one field: + + awk 'NF > 0' data + + This is an easy way to delete blank lines from a file (or rather, + to create a new file similar to the old file but from which the + blank lines have been removed). + + * Print seven random numbers from 0 to 100, inclusive: + + awk 'BEGIN { for (i = 1; i <= 7; i++) + print int(101 * rand()) }' + + * Print the total number of bytes used by FILES: + + ls -l FILES | awk '{ x += $5 } + END { print "total bytes: " x }' + + * Print the total number of kilobytes used by FILES: + + ls -l FILES | awk '{ x += $5 } + END { print "total K-bytes: " (x + 1023)/1024 }' + + * Print a sorted list of the login names of all users: + + awk -F: '{ print $1 }' /etc/passwd | sort + + * Count lines in a file: + + awk 'END { print NR }' data + + * Print the even-numbered lines in the data file: + + awk 'NR % 2 == 0' data + + If you use the expression `NR % 2 == 1' instead, it would print + the odd-numbered lines. File: gawk.info, Node: Two Rules, Next: More Complex, Prev: Very Simple, Up: Getting Started @@ -1168,28 +1636,28 @@ An Example with Two Rules The `awk' utility reads the input files one line at a time. For each line, `awk' tries the patterns of each of the rules. If several -patterns match then several actions are run, in the order in which they +patterns match, then several actions are run in the order in which they appear in the `awk' program. If no patterns match, then no actions are run. - After processing all the rules (perhaps none) that match the line, -`awk' reads the next line (however, *note The `next' Statement: Next -Statement., and also *note The `nextfile' Statement: Nextfile -Statement.). This continues until the end of the file is reached. - - For example, the `awk' program: + After processing all the rules that match the line (and perhaps +there are none), `awk' reads the next line. (However, *note The `next' +Statement: Next Statement., and also *note Using `gawk''s `nextfile' +Statement: Nextfile Statement.). This continues until the end of the +file is reached. For example, the following `awk' program contains two +rules: /12/ { print $0 } /21/ { print $0 } -contains two rules. The first rule has the string `12' as the pattern -and `print $0' as the action. The second rule has the string `21' as -the pattern and also has `print $0' as the action. Each rule's action -is enclosed in its own pair of braces. +The first rule has the string `12' as the pattern and `print $0' as the +action. The second rule has the string `21' as the pattern and also +has `print $0' as the action. Each rule's action is enclosed in its +own pair of braces. - This `awk' program prints every line that contains the string `12' -_or_ the string `21'. If a line contains both strings, it is printed -twice, once by each rule. + This program prints every line that contains the string `12' _or_ +the string `21'. If a line contains both strings, it is printed twice, +once by each rule. This is what happens if we run this program on our two sample data files, `BBS-list' and `inventory-shipped', as shown here: @@ -1210,7 +1678,7 @@ files, `BBS-list' and `inventory-shipped', as shown here: -| Jan 21 36 64 620 -| Apr 21 70 74 514 -Note how the line in `BBS-list' beginning with `sabafoo' was printed +Note how the line beginning with `sabafoo' in `BBS-list' was printed twice, once for each rule. @@ -1219,34 +1687,29 @@ File: gawk.info, Node: More Complex, Next: Statements/Lines, Prev: Two Rules, A More Complex Example ====================== - Here is an example to give you an idea of what typical `awk' -programs do. This example shows how `awk' can be used to summarize, -select, and rearrange the output of another utility. It uses features -that haven't been covered yet, so don't worry if you don't understand -all the details. + Now that we've mastered some simple tasks, let's look at what +typical `awk' programs do. This example shows how `awk' can be used to +summarize, select, and rearrange the output of another utility. It uses +features that haven't been covered yet, so don't worry if you don't +understand all the details: - ls -lg | awk '$6 == "Nov" { sum += $5 } + ls -l | awk '$6 == "Nov" { sum += $5 } END { print sum }' This command prints the total number of bytes in all the files in the current directory that were last modified in November (of any year). -(In the C shell you would need to type a semicolon and then a backslash -at the end of the first line; in a POSIX-compliant shell, such as the -Bourne shell or Bash, the GNU Bourne-Again shell, you can type the -example as shown.) - - The `ls -lg' part of this example is a system command that gives you -a listing of the files in a directory, including file size and the date -the file was last modified. Its output looks like this: +(1) The `ls -l' part of this example is a system command that gives you +a listing of the files in a directory, including each file's size and +the date the file was last modified. Its output looks like this: -rw-r--r-- 1 arnold user 1933 Nov 7 13:05 Makefile - -rw-r--r-- 1 arnold user 10809 Nov 7 13:03 gawk.h - -rw-r--r-- 1 arnold user 983 Apr 13 12:14 gawk.tab.h - -rw-r--r-- 1 arnold user 31869 Jun 15 12:20 gawk.y - -rw-r--r-- 1 arnold user 22414 Nov 7 13:03 gawk1.c - -rw-r--r-- 1 arnold user 37455 Nov 7 13:03 gawk2.c - -rw-r--r-- 1 arnold user 27511 Dec 9 13:07 gawk3.c - -rw-r--r-- 1 arnold user 7989 Nov 7 13:03 gawk4.c + -rw-r--r-- 1 arnold user 10809 Nov 7 13:03 awk.h + -rw-r--r-- 1 arnold user 983 Apr 13 12:14 awk.tab.h + -rw-r--r-- 1 arnold user 31869 Jun 15 12:20 awk.y + -rw-r--r-- 1 arnold user 22414 Nov 7 13:03 awk1.c + -rw-r--r-- 1 arnold user 37455 Nov 7 13:03 awk2.c + -rw-r--r-- 1 arnold user 27511 Dec 9 13:07 awk3.c + -rw-r--r-- 1 arnold user 7989 Nov 7 13:03 awk4.c The first field contains read-write permissions, the second field contains the number of links to the file, and the third field @@ -1254,27 +1717,41 @@ identifies the owner of the file. The fourth field identifies the group of the file. The fifth field contains the size of the file in bytes. The sixth, seventh and eighth fields contain the month, day, and time, respectively, that the file was last modified. Finally, the ninth field -contains the name of the file. +contains the name of the file.(2) The `$6 == "Nov"' in our `awk' program is an expression that tests -whether the sixth field of the output from `ls -lg' matches the string +whether the sixth field of the output from `ls -l' matches the string `Nov'. Each time a line has the string `Nov' for its sixth field, the -action `sum += $5' is performed. This adds the fifth field (the file +action `sum += $5' is performed. This adds the fifth field (the file's size) to the variable `sum'. As a result, when `awk' has finished -reading all the input lines, `sum' is the sum of the sizes of files -whose lines matched the pattern. (This works because `awk' variables -are automatically initialized to zero.) +reading all the input lines, `sum' is the total of the sizes of the +files whose lines matched the pattern. (This works because `awk' +variables are automatically initialized to zero.) After the last line of output from `ls' has been processed, the -`END' rule is executed, and the value of `sum' is printed. In this -example, the value of `sum' would be 80600. +`END' rule executes and prints the value of `sum'. In this example, +the value of `sum' is 140963. These more advanced `awk' techniques are covered in later sections -(*note Overview of Actions: Action Overview.). Before you can move on -to more advanced `awk' programming, you have to know how `awk' -interprets your input and displays your output. By manipulating fields -and using `print' statements, you can produce some very useful and -impressive looking reports. +(*note Actions: Action Overview.). Before you can move on to more +advanced `awk' programming, you have to know how `awk' interprets your +input and displays your output. By manipulating fields and using +`print' statements, you can produce some very useful and impressive +looking reports. + + ---------- Footnotes ---------- + + (1) In the C shell (`csh'), you need to type a semicolon and then a +backslash at the end of the first line; see *Note `awk' Statements +Versus Lines: Statements/Lines, for an explanation as to why. In a +POSIX-compliant shell, such as the Bourne shell or `bash', you can type +the example as shown. If the command `echo $path' produces an empty +output line, you are most likely using a POSIX-compliant shell. +Otherwise, you are probably using the C shell or a shell derived from +it. + + (2) On some very old systems, you may need to use `ls -lg' to get +this output. File: gawk.info, Node: Statements/Lines, Next: Other Features, Prev: More Complex, Up: Getting Started @@ -1288,20 +1765,18 @@ separate rule, like this: awk '/12/ { print $0 } /21/ { print $0 }' BBS-list inventory-shipped - However, `gawk' will ignore newlines after any of the following: + However, `gawk' ignores newlines after any of the following symbols +and keywords: , { ? : || && do else -A newline at any other point is considered the end of the statement. -(Splitting lines after `?' and `:' is a minor `gawk' extension. The -`?' and `:' referred to here is the three operand conditional -expression described in *Note Conditional Expressions: Conditional Exp.) +A newline at any other point is considered the end of the statement.(1) If you would like to split a single statement into two lines at a point where a newline would terminate it, you can "continue" it by -ending the first line with a backslash character, `\'. The backslash -must be the final character on the line to be recognized as a -continuation character. This is allowed absolutely anywhere in the +ending the first line with a backslash character (`\'). The backslash +must be the final character on the line in order to be recognized as a +continuation character. A backslash is allowed anywhere in the statement, even in the middle of a string or regular expression. For example: @@ -1309,27 +1784,26 @@ example: on the next line/ { print $1 }' We have generally not used backslash continuation in the sample programs -in this Info file. Since in `gawk' there is no limit on the length of -a line, it is never strictly necessary; it just makes programs more -readable. For this same reason, as well as for clarity, we have kept -most statements short in the sample programs presented throughout the -Info file. Backslash continuation is most useful when your `awk' -program is in a separate source file, instead of typed in on the -command line. You should also note that many `awk' implementations are -more particular about where you may use backslash continuation. For -example, they may not allow you to split a string constant using -backslash continuation. Thus, for maximal portability of your `awk' -programs, it is best not to split your lines in the middle of a regular -expression or a string. - - *Caution: backslash continuation does not work as described above -with the C shell.* Continuation with backslash works for `awk' -programs in files, and also for one-shot programs _provided_ you are -using a POSIX-compliant shell, such as the Bourne shell or Bash, the -GNU Bourne-Again shell. But the C shell (`csh') behaves differently! -There, you must use two backslashes in a row, followed by a newline. -Note also that when using the C shell, _every_ newline in your awk -program must be escaped with a backslash. To illustrate: +in this Info file. In `gawk', there is no limit on the length of a +line, so backslash continuation is never strictly necessary; it just +makes programs more readable. For this same reason, as well as for +clarity, we have kept most statements short in the sample programs +presented throughout the Info file. Backslash continuation is most +useful when your `awk' program is in a separate source file instead of +entered from the command line. You should also note that many `awk' +implementations are more particular about where you may use backslash +continuation. For example, they may not allow you to split a string +constant using backslash continuation. Thus, for maximum portability +of your `awk' programs, it is best not to split your lines in the +middle of a regular expression or a string. + + *Caution:* _Backslash continuation does not work as described above +with the C shell._ It works for `awk' programs in files and for +one-shot programs, _provided_ you are using a POSIX-compliant shell, +such as the Unix Bourne shell or `bash'. But the C shell behaves +differently! There, you must use two backslashes in a row, followed by +a newline. Note also that when using the C shell, _every_ newline in +your awk program must be escaped with a backslash. To illustrate: % awk 'BEGIN { \ ? print \\ @@ -1340,14 +1814,23 @@ program must be escaped with a backslash. To illustrate: Here, the `%' and `?' are the C shell's primary and secondary prompts, analogous to the standard shell's `$' and `>'. + Compare the previous example to how it is done with a +POSIX-compliant shell: + + $ awk 'BEGIN { + > print \ + > "hello, world" + > }' + -| hello, world + `awk' is a line-oriented language. Each rule's action has to begin on the same line as the pattern. To have the pattern and action on -separate lines, you _must_ use backslash continuation--there is no +separate lines, you _must_ use backslash continuation; there is no other way. - Note that backslash continuation and comments do not mix. As soon as -`awk' sees the `#' that starts a comment, it ignores _everything_ on -the rest of the line. For example: + Another thing to keep in mind is that backslash continuation and +comments do not mix. As soon as `awk' sees the `#' that starts a +comment, it ignores _everything_ on the rest of the line. For example: $ gawk 'BEGIN { print "dont panic" # a friendly \ > BEGIN rule @@ -1355,23 +1838,31 @@ the rest of the line. For example: error--> gawk: cmd. line:2: BEGIN rule error--> gawk: cmd. line:2: ^ parse error -Here, it looks like the backslash would continue the comment onto the -next line. However, the backslash-newline combination is never even -noticed, since it is "hidden" inside the comment. Thus, the `BEGIN' is -noted as a syntax error. +In this case, it looks like the backslash would continue the comment +onto the next line. However, the backslash-newline combination is never +even noticed because it is "hidden" inside the comment. Thus, the +`BEGIN' is noted as a syntax error. When `awk' statements within one rule are short, you might want to -put more than one of them on a line. You do this by separating the -statements with a semicolon, `;'. - - This also applies to the rules themselves. Thus, the previous -program could have been written: +put more than one of them on a line. This is accomplished by +separating the statements with a semicolon (`;'). This also applies to +the rules themselves. Thus, the program shown at the start of this +minor node could also be written this way: /12/ { print $0 } ; /21/ { print $0 } -*Note:* the requirement that rules on the same line must be separated -with a semicolon was not in the original `awk' language; it was added -for consistency with the treatment of statements within an action. +*Note:* The requirement that states that rules on the same line must be +separated with a semicolon was not in the original `awk' language; it +was added for consistency with the treatment of statements within an +action. + + ---------- Footnotes ---------- + + (1) The `?' and `:' referred to here is the three-operand +conditional expression described in *Note Conditional Expressions: +Conditional Exp. Splitting lines after `?' and `:' is a minor `gawk' +extension; if `--posix' is specified (*note Command-Line Options: +Options.), then this extension is disabled. File: gawk.info, Node: Other Features, Next: When, Prev: Statements/Lines, Up: Getting Started @@ -1379,13 +1870,15 @@ File: gawk.info, Node: Other Features, Next: When, Prev: Statements/Lines, U Other Features of `awk' ======================= - The `awk' language provides a number of predefined, or built-in -variables, which your programs can use to get information from `awk'. -There are other variables your program can set to control how `awk' -processes your data. + The `awk' language provides a number of predefined, or "built-in", +variables that your programs can use to get information from `awk'. +There are other variables your program can set as well to control how +`awk' processes your data. In addition, `awk' provides a number of built-in functions for doing -common computational and string related operations. +common computational and string related operations. `gawk' provides +built-in functions for working with timestamps, performing bit +manipulation, and for runtime string translation. As we develop our presentation of the `awk' language, we introduce most of the variables and many of the functions. They are defined @@ -1398,24 +1891,24 @@ File: gawk.info, Node: When, Prev: Other Features, Up: Getting Started When to Use `awk' ================= - You might wonder how `awk' might be useful for you. Using utility -programs, advanced patterns, field separators, arithmetic statements, -and other selection criteria, you can produce much more complex output. -The `awk' language is very useful for producing reports from large -amounts of raw data, such as summarizing information from the output of -other utility programs like `ls'. (*Note A More Complex Example: More -Complex.) + Now that you've seen some of what `awk' can do, you might wonder how +`awk' could be useful for you. By using utility programs, advanced +patterns, field separators, arithmetic statements, and other selection +criteria, you can produce much more complex output. The `awk' language +is very useful for producing reports from large amounts of raw data, +such as summarizing information from the output of other utility +programs like `ls'. (*Note A More Complex Example: More Complex.) Programs written with `awk' are usually much smaller than they would be in other languages. This makes `awk' programs easy to compose and use. Often, `awk' programs can be quickly composed at your terminal, -used once, and thrown away. Since `awk' programs are interpreted, you +used once, and thrown away. Because `awk' programs are interpreted, you can avoid the (usually lengthy) compilation part of the typical edit-compile-test-debug cycle of software development. Complex programs have been written in `awk', including a complete retargetable assembler for eight-bit microprocessors (*note Glossary::, -for more information) and a microcode assembler for a special purpose +for more information), and a microcode assembler for a special purpose Prolog computer. However, `awk''s capabilities are strained by tasks of such complexity. @@ -1424,98 +1917,29 @@ hundred lines, you might consider using a different programming language. Emacs Lisp is a good choice if you need sophisticated string or pattern matching capabilities. The shell is also good at string and pattern matching; in addition, it allows powerful use of the system -utilities. More conventional languages, such as C, C++, and Lisp, offer +utilities. More conventional languages, such as C, C++, and Java, offer better facilities for system programming and for managing the complexity of large programs. Programs in these languages may require more lines of source code than the equivalent `awk' programs, but they are easier to maintain and usually run more efficiently. -File: gawk.info, Node: One-liners, Next: Regexp, Prev: Getting Started, Up: Top - -Useful One Line Programs -************************ - - Many useful `awk' programs are short, just a line or two. Here is a -collection of useful, short programs to get you started. Some of these -programs contain constructs that haven't been covered yet. The -description of the program will give you a good idea of what is going -on, but please read the rest of the Info file to become an `awk' expert! - - Most of the examples use a data file named `data'. This is just a -placeholder; if you were to use these programs yourself, you would -substitute your own file names for `data'. - - Since you are reading this in Info, each line of the example code is -enclosed in quotes, to represent text that you would type literally. -The examples themselves represent shell commands that use single quotes -to keep the shell from interpreting the contents of the program. When -reading the examples, focus on the text between the open and close -quotes. - -`awk '{ if (length($0) > max) max = length($0) }' -` END { print max }' data' - This program prints the length of the longest input line. - -`awk 'length($0) > 80' data' - This program prints every line that is longer than 80 characters. - The sole rule has a relational expression as its pattern, and has - no action (so the default action, printing the record, is used). - -`expand data | awk '{ if (x < length()) x = length() }' -` END { print "maximum line length is " x }'' - This program prints the length of the longest line in `data'. The - input is processed by the `expand' program to change tabs into - spaces, so the widths compared are actually the right-margin - columns. - -`awk 'NF > 0' data' - This program prints every line that has at least one field. This - is an easy way to delete blank lines from a file (or rather, to - create a new file similar to the old file but from which the blank - lines have been deleted). - -`awk 'BEGIN { for (i = 1; i <= 7; i++)' -` print int(101 * rand()) }'' - This program prints seven random numbers from zero to 100, - inclusive. - -`ls -lg FILES | awk '{ x += $5 } ; END { print "total bytes: " x }'' - This program prints the total number of bytes used by FILES. - -`ls -lg FILES | awk '{ x += $5 }' -` END { print "total K-bytes: " (x + 1023)/1024 }'' - This program prints the total number of kilobytes used by FILES. - -`awk -F: '{ print $1 }' /etc/passwd | sort' - This program prints a sorted list of the login names of all users. - -`awk 'END { print NR }' data' - This program counts lines in a file. - -`awk 'NR % 2 == 0' data' - This program prints the even numbered lines in the data file. If - you were to use the expression `NR % 2 == 1' instead, it would - print the odd numbered lines. - - -File: gawk.info, Node: Regexp, Next: Reading Files, Prev: One-liners, Up: Top +File: gawk.info, Node: Regexp, Next: Reading Files, Prev: Getting Started, Up: Top Regular Expressions ******************* A "regular expression", or "regexp", is a way of describing a set of strings. Because regular expressions are such a fundamental part of -`awk' programming, their format and use deserve a separate chapter. +`awk' programming, their format and use deserve a separate major node. A regular expression enclosed in slashes (`/') is an `awk' pattern -that matches every input record whose text belongs to that set. - - The simplest regular expression is a sequence of letters, numbers, or -both. Such a regexp matches any string that contains that sequence. -Thus, the regexp `foo' matches any string containing `foo'. Therefore, -the pattern `/foo/' matches any input record containing the three -characters `foo', _anywhere_ in the record. Other kinds of regexps let +that matches every input record whose text belongs to that set. The +simplest regular expression is a sequence of letters, numbers, or both. +Such a regexp matches any string that contains that sequence. Thus, +the regexp `foo' matches any string containing `foo'. Therefore, the +pattern `/foo/' matches any input record containing the three +characters `foo' _anywhere_ in the record. Other kinds of regexps let you specify more complicated classes of strings. * Menu: @@ -1523,6 +1947,7 @@ you specify more complicated classes of strings. * Regexp Usage:: How to Use Regular Expressions. * Escape Sequences:: How to write non-printing characters. * Regexp Operators:: Regular Expression Operators. +* Character Lists:: What can go between `[...]'. * GNU Regexp Operators:: Operators specific to GNU software. * Case-sensitivity:: How to do case-insensitive matching. * Leftmost Longest:: How much text matches. @@ -1537,8 +1962,9 @@ How to Use Regular Expressions A regular expression can be used as a pattern by enclosing it in slashes. Then the regular expression is tested against the entire text of each record. (Normally, it only needs to match some part of the -text in order to succeed.) For example, this prints the second field -of each record that contains the three characters `foo' anywhere in it: +text in order to succeed.) For example, the following prints the +second field of each record that contains the string `foo' anywhere in +it: $ awk '/foo/ { print $2 }' BBS-list -| 555-1234 @@ -1548,43 +1974,46 @@ of each record that contains the three characters `foo' anywhere in it: Regular expressions can also be used in matching expressions. These expressions allow you to specify the string to match against; it need -not be the entire current input record. The two operators, `~' and -`!~', perform regular expression comparisons. Expressions using these -operators can be used as patterns or in `if', `while', `for', and `do' -statements. (*Note Control Statements in Actions: Statements.) - -`EXP ~ /REGEXP/' - This is true if the expression EXP (taken as a string) is matched - by REGEXP. The following example matches, or selects, all input - records with the upper-case letter `J' somewhere in the first - field: - - $ awk '$1 ~ /J/' inventory-shipped - -| Jan 13 25 15 115 - -| Jun 31 42 75 492 - -| Jul 24 34 67 436 - -| Jan 21 36 64 620 - - So does this: - - awk '{ if ($1 ~ /J/) print }' inventory-shipped - -`EXP !~ /REGEXP/' - This is true if the expression EXP (taken as a character string) - is _not_ matched by REGEXP. The following example matches, or - selects, all input records whose first field _does not_ contain - the upper-case letter `J': - - $ awk '$1 !~ /J/' inventory-shipped - -| Feb 15 32 24 226 - -| Mar 15 24 34 228 - -| Apr 31 52 63 420 - -| May 16 34 29 208 - ... +not be the entire current input record. The two operators `~' and `!~' +perform regular expression comparisons. Expressions using these +operators can be used as patterns, or in `if', `while', `for', and `do' +statements. (*Note Control Statements in Actions: Statements.) For +example: - When a regexp is written enclosed in slashes, like `/foo/', we call -it a "regexp constant", much like `5.27' is a numeric constant, and -`"foo"' is a string constant. + EXP ~ /REGEXP/ + +is true if the expression EXP (taken as a string) matches REGEXP. The +following example matches, or selects, all input records with the +uppercase letter `J' somewhere in the first field: + + $ awk '$1 ~ /J/' inventory-shipped + -| Jan 13 25 15 115 + -| Jun 31 42 75 492 + -| Jul 24 34 67 436 + -| Jan 21 36 64 620 + + So does this: + + awk '{ if ($1 ~ /J/) print }' inventory-shipped + + This next example is true if the expression EXP (taken as a +character string) does _not_ match REGEXP: + + EXP !~ /REGEXP/ + + The following example matches, or selects, all input records whose +first field _does not_ contain the uppercase letter `J': + + $ awk '$1 !~ /J/' inventory-shipped + -| Feb 15 32 24 226 + -| Mar 15 24 34 228 + -| Apr 31 52 63 420 + -| May 16 34 29 208 + ... + + When a regexp is enclosed in slashes, such as `/foo/', we call it a +"regexp constant", much like `5.27' is a numeric constant and `"foo"' +is a string constant. File: gawk.info, Node: Escape Sequences, Next: Regexp Operators, Prev: Regexp Usage, Up: Regexp @@ -1593,393 +2022,259 @@ Escape Sequences ================ Some characters cannot be included literally in string constants -(`"foo"') or regexp constants (`/foo/'). You represent them instead -with "escape sequences", which are character sequences beginning with a -backslash (`\'). - - One use of an escape sequence is to include a double-quote character -in a string constant. Since a plain double-quote would end the string, -you must use `\"' to represent an actual double-quote character as a -part of the string. For example: +(`"foo"') or regexp constants (`/foo/'). Instead, they should be +represented with "escape sequences", which are character sequences +beginning with a backslash (`\'). One use of an escape sequence is to +include a double quote character in a string constant. Because a plain +double quote ends the string, you must use `\"' to represent an actual +double quote character as a part of the string. For example: $ awk 'BEGIN { print "He said \"hi!\" to her." }' -| He said "hi!" to her. The backslash character itself is another character that cannot be -included normally; you write `\\' to put one backslash in the string or -regexp. Thus, the string whose contents are the two characters `"' and -`\' must be written `"\"\\"'. +included normally; you must write `\\' to put one backslash in the +string or regexp. Thus, the string whose contents are the two +characters `"' and `\' must be written `"\"\\"'. Another use of backslash is to represent unprintable characters such as tab or newline. While there is nothing to stop you from entering most unprintable characters directly in a string constant or regexp constant, they may look ugly. - Here is a table of all the escape sequences used in `awk', and what -they represent. Unless noted otherwise, all of these escape sequences -apply to both string constants and regexp constants. + The following table lists all the escape sequences used in `awk' and +what they represent. Unless noted otherwise, all these escape sequences +apply to both string constants and regexp constants: `\\' A literal backslash, `\'. `\a' - The "alert" character, `Control-g', ASCII code 7 (BEL). + The "alert" character, `Ctrl-g', ASCII code 7 (BEL). (This + usually makes some sort of audible noise.) `\b' - Backspace, `Control-h', ASCII code 8 (BS). + Backspace, `Ctrl-h', ASCII code 8 (BS). `\f' - Formfeed, `Control-l', ASCII code 12 (FF). + Formfeed, `Ctrl-l', ASCII code 12 (FF). `\n' - Newline, `Control-j', ASCII code 10 (LF). + Newline, `Ctrl-j', ASCII code 10 (LF). `\r' - Carriage return, `Control-m', ASCII code 13 (CR). + Carriage return, `Ctrl-m', ASCII code 13 (CR). `\t' - Horizontal tab, `Control-i', ASCII code 9 (HT). + Horizontal tab, `Ctrl-i', ASCII code 9 (HT). `\v' - Vertical tab, `Control-k', ASCII code 11 (VT). + Vertical tab, `Ctrl-k', ASCII code 11 (VT). `\NNN' - The octal value NNN, where NNN are one to three digits between `0' - and `7'. For example, the code for the ASCII ESC (escape) + The octal value NNN, where NNN stands for 1 to 3 digits between + `0' and `7'. For example, the code for the ASCII ESC (escape) character is `\033'. `\xHH...' - The hexadecimal value HH, where HH are hexadecimal digits (`0' - through `9' and either `A' through `F' or `a' through `f'). Like - the same construct in ANSI C, the escape sequence continues until - the first non-hexadecimal digit is seen. However, using more than - two hexadecimal digits produces undefined results. (The `\x' - escape sequence is not allowed in POSIX `awk'.) + The hexadecimal value HH, where HH stands for a sequence of + hexadecimal digits (`0' through `9', and either `A' through `F' or + `a' through `f'). Like the same construct in ISO C, the escape + sequence continues until the first non-hexadecimal digit is seen. + However, using more than two hexadecimal digits produces undefined + results. (The `\x' escape sequence is not allowed in POSIX `awk'.) `\/' - A literal slash (necessary for regexp constants only). You use - this when you wish to write a regexp constant that contains a - slash. Since the regexp is delimited by slashes, you need to - escape the slash that is part of the pattern, in order to tell - `awk' to keep processing the rest of the regexp. + A literal slash (necessary for regexp constants only). This + expression is used when you want to write a regexp constant that + contains a slash. Because the regexp is delimited by slashes, you + need to escape the slash that is part of the pattern, in order to + tell `awk' to keep processing the rest of the regexp. `\"' - A literal double-quote (necessary for string constants only). You - use this when you wish to write a string constant that contains a - double-quote. Since the string is delimited by double-quotes, you - need to escape the quote that is part of the string, in order to - tell `awk' to keep processing the rest of the string. - - In `gawk', there are additional two character sequences that begin -with backslash that have special meaning in regexps. *Note Additional -Regexp Operators Only in `gawk': GNU Regexp Operators. - - In a string constant, what happens if you place a backslash before -something that is not one of the characters listed above? POSIX `awk' -purposely leaves this case undefined. There are two choices. - - * Strip the backslash out. This is what Unix `awk' and `gawk' both - do. For example, `"a\qc"' is the same as `"aqc"'. + A literal double quote (necessary for string constants only). + This expression is used when you want to write a string constant + that contains a double quote. Because the string is delimited by + double quotes, you need to escape the quote that is part of the + string, in order to tell `awk' to keep processing the rest of the + string. - * Leave the backslash alone. Some other `awk' implementations do - this. In such implementations, `"a\qc"' is the same as if you had - typed `"a\\qc"'. + In `gawk', a number of additional two-character sequences that begin +with a backslash have special meaning in regexps. *Note +`gawk'-Specific Regexp Operators: GNU Regexp Operators. In a regexp, a backslash before any character that is not in the -above table, and not listed in *Note Additional Regexp Operators Only -in `gawk': GNU Regexp Operators, means that the next character should -be taken literally, even if it would normally be a regexp operator. -E.g., `/a\+b/' matches the three characters `a+b'. +above table and not listed in *Note `gawk'-Specific Regexp Operators: +GNU Regexp Operators, means that the next character should be taken +literally, even if it would normally be a regexp operator. For +example, `/a\+b/' matches the three characters `a+b'. For complete portability, do not use a backslash before any -character not listed in the table above. - - Another interesting question arises. Suppose you use an octal or -hexadecimal escape to represent a regexp metacharacter (*note Regular -Expression Operators: Regexp Operators.). Does `awk' treat the -character as a literal character, or as a regexp operator? - - It turns out that historically, such characters were taken literally -(d.c.). However, the POSIX standard indicates that they should be -treated as real metacharacters, and this is what `gawk' does. However, -in compatibility mode (*note Command Line Options: Options.), `gawk' -treats the characters represented by octal and hexadecimal escape -sequences literally when used in regexp constants. Thus, `/a\52b/' is -equivalent to `/a\*b/'. +character not shown in the table above. To summarize: - 1. The escape sequences in the table above are always processed first, + * The escape sequences in the table above are always processed first, for both string constants and regexp constants. This happens very early, as soon as `awk' reads your program. - 2. `gawk' processes both regexp constants and dynamic regexps (*note + * `gawk' processes both regexp constants and dynamic regexps (*note Using Dynamic Regexps: Computed Regexps.), for the special - operators listed in *Note Additional Regexp Operators Only in - `gawk': GNU Regexp Operators. + operators listed in *Note `gawk'-Specific Regexp Operators: GNU + Regexp Operators. - 3. A backslash before any other character means to treat that + * A backslash before any other character means to treat that character literally. +Advanced Notes: Backslash Before Regular Characters +--------------------------------------------------- + + If you place a backslash in a string constant before something that +is not one of the characters listed above, POSIX `awk' purposely leaves +what happens as undefined. There are two choices: + +Strip the backslash out + This is what Unix `awk' and `gawk' both do. For example, `"a\qc"' + is the same as `"aqc"'. (Because this is such an easy bug to both + introduce and to miss, `gawk' warns you about it.) Consider `FS = + "[ \t]+\|[ \t]+"' to use vertical bars surrounded by whitespace as + the field separator. There should be two backslashes in the + string, `FS = "[ \t]+\\|[ \t]+"'.) + +Leave the backslash alone + Some other `awk' implementations do this. In such + implementations, `"a\qc"' is the same as if you had typed + `"a\\qc"'. + +Advanced Notes: Escape Sequences for Metacharacters +--------------------------------------------------- + + Suppose you use an octal or hexadecimal escape to represent a regexp +metacharacter (*note Regular Expression Operators: Regexp Operators.). +Does `awk' treat the character as a literal character or as a regexp +operator? + + Historically, such characters were taken literally. (d.c.) +However, the POSIX standard indicates that they should be treated as +real metacharacters, which is what `gawk' does. In compatibility mode +(*note Command-Line Options: Options.), `gawk' treats the characters +represented by octal and hexadecimal escape sequences literally when +used in regexp constants. Thus, `/a\52b/' is equivalent to `/a\*b/'. + -File: gawk.info, Node: Regexp Operators, Next: GNU Regexp Operators, Prev: Escape Sequences, Up: Regexp +File: gawk.info, Node: Regexp Operators, Next: Character Lists, Prev: Escape Sequences, Up: Regexp Regular Expression Operators ============================ - You can combine regular expressions with the following characters, -called "regular expression operators", or "metacharacters", to increase -the power and versatility of regular expressions. + You can combine regular expressions with special characters, called +"regular expression operators" or "metacharacters", to increase the +power and versatility of regular expressions. The escape sequences described in *Note Escape Sequences::, are -valid inside a regexp. They are introduced by a `\'. They are +valid inside a regexp. They are introduced by a `\', and are recognized and converted into the corresponding real characters as the very first step in processing regexps. - Here is a table of metacharacters. All characters that are not -escape sequences and that are not listed in the table stand for -themselves. + Here is a list of metacharacters. All characters that are not escape +sequences and that are not listed in the table stand for themselves: `\' This is used to suppress the special meaning of a character when - matching. For example: - - \$ - - matches the character `$'. + matching. For example, `\$' matches the character `$'. `^' - This matches the beginning of a string. For example: - - ^@chapter - - matches the `@chapter' at the beginning of a string, and can be - used to identify chapter beginnings in Texinfo source files. The - `^' is known as an "anchor", since it anchors the pattern to - matching only at the beginning of the string. + This matches the beginning of a string. For example, `^@chapter' + matches `@chapter' at the beginning of a string, and can be used + to identify chapter beginnings in Texinfo source files. The `^' + is known as an "anchor", because it anchors the pattern to match + only at the beginning of the string. It is important to realize that `^' does not match the beginning of - a line embedded in a string. In this example the condition is not - true: + a line embedded in a string. The condition is not true in the + following example: if ("line1\nLINE 2" ~ /^L/) ... `$' - This is similar to `^', but it matches only at the end of a string. - For example: - - p$ - - matches a record that ends with a `p'. The `$' is also an anchor, - and also does not match the end of a line embedded in a string. - In this example the condition is not true: + This is similar to `^' but it matches only at the end of a string. + For example, `p$' matches a record that ends with a `p'. The `$' + is an anchor and does not match the end of a line embedded in a + string. The condition is not true in the following example: if ("line1\nLINE 2" ~ /1$/) ... `.' - The period, or dot, matches any single character, _including_ the - newline character. For example: - - .P - - matches any single character followed by a `P' in a string. Using - concatenation we can make a regular expression like `U.A', which - matches any three-character sequence that begins with `U' and ends - with `A'. + This matches any single character, _including_ the newline + character. For example, `.P' matches any single character + followed by a `P' in a string. Using concatenation, we can make a + regular expression such as `U.A', that matches any three-character + sequence that begins with `U' and ends with `A'. - In strict POSIX mode (*note Command Line Options: Options.), `.' + In strict POSIX mode (*note Command-Line Options: Options.), `.' does not match the NUL character, which is a character with all bits equal to zero. Otherwise, NUL is just another character. Other versions of `awk' may not be able to match the NUL character. `[...]' - This is called a "character list". It matches any _one_ of the - characters that are enclosed in the square brackets. For example: - - [MVX] - - matches any one of the characters `M', `V', or `X' in a string. - - Ranges of characters are indicated by using a hyphen between the - beginning and ending characters, and enclosing the whole thing in - brackets. For example: - - [0-9] - - matches any digit. Multiple ranges are allowed. E.g., the list - `[A-Za-z0-9]' is a common way to express the idea of "all - alphanumeric characters." - - To include one of the characters `\', `]', `-' or `^' in a - character list, put a `\' in front of it. For example: - - [d\]] - - matches either `d', or `]'. - - This treatment of `\' in character lists is compatible with other - `awk' implementations, and is also mandated by POSIX. The regular - expressions in `awk' are a superset of the POSIX specification for - Extended Regular Expressions (EREs). POSIX EREs are based on the - regular expressions accepted by the traditional `egrep' utility. - - "Character classes" are a new feature introduced in the POSIX - standard. A character class is a special notation for describing - lists of characters that have a specific attribute, but where the - actual characters themselves can vary from country to country - and/or from character set to character set. For example, the - notion of what is an alphabetic character differs in the USA and - in France. - - A character class is only valid in a regexp _inside_ the brackets - of a character list. Character classes consist of `[:', a keyword - denoting the class, and `:]'. Here are the character classes - defined by the POSIX standard. - - `[:alnum:]' - Alphanumeric characters. - - `[:alpha:]' - Alphabetic characters. - - `[:blank:]' - Space and tab characters. - - `[:cntrl:]' - Control characters. - - `[:digit:]' - Numeric characters. - - `[:graph:]' - Characters that are printable and are also visible. (A space - is printable, but not visible, while an `a' is both.) - - `[:lower:]' - Lower-case alphabetic characters. - - `[:print:]' - Printable characters (characters that are not control - characters.) - - `[:punct:]' - Punctuation characters (characters that are not letter, - digits, control characters, or space characters). - - `[:space:]' - Space characters (such as space, tab, and formfeed, to name a - few). - - `[:upper:]' - Upper-case alphabetic characters. - - `[:xdigit:]' - Characters that are hexadecimal digits. - - For example, before the POSIX standard, to match alphanumeric - characters, you had to write `/[A-Za-z0-9]/'. If your character - set had other alphabetic characters in it, this would not match - them. With the POSIX character classes, you can write - `/[[:alnum:]]/', and this will match _all_ the alphabetic and - numeric characters in your character set. - - Two additional special sequences can appear in character lists. - These apply to non-ASCII character sets, which can have single - symbols (called "collating elements") that are represented with - more than one character, as well as several characters that are - equivalent for "collating", or sorting, purposes. (E.g., in - French, a plain "e" and a grave-accented "e`" are equivalent.) - - Collating Symbols - A "collating symbol" is a multi-character collating element - enclosed in `[.' and `.]'. For example, if `ch' is a - collating element, then `[[.ch.]]' is a regexp that matches - this collating element, while `[ch]' is a regexp that matches - either `c' or `h'. - - Equivalence Classes - An "equivalence class" is a locale-specific name for a list of - characters that are equivalent. The name is enclosed in `[=' - and `=]'. For example, the name `e' might be used to - represent all of "e," "e`," and "e'." In this case, `[[=e]]' - is a regexp that matches any of `e', `e'', or `e`'. - - These features are very valuable in non-English speaking locales. - - *Caution:* The library functions that `gawk' uses for regular - expression matching currently only recognize POSIX character - classes; they do not recognize collating symbols or equivalence - classes. + This is called a "character list".(1) It matches any _one_ of the + characters that are enclosed in the square brackets. For example, + `[MVX]' matches any one of the characters `M', `V', or `X', in a + string. A full discussion of what can be inside the square + brackets of a character list is given in *Note Using Character + Lists: Character Lists. `[^ ...]' This is a "complemented character list". The first character after the `[' _must_ be a `^'. It matches any characters _except_ those - in the square brackets. For example: - - [^0-9] - - matches any character that is not a digit. + in the square brackets. For example, `[^awk]' matches any + character that is not an `a', a `w', or a `k'. `|' - This is the "alternation operator", and it is used to specify - alternatives. For example: - - ^P|[0-9] - - matches any string that matches either `^P' or `[0-9]'. This - means it matches any string that starts with `P' or contains a - digit. + This is the "alternation operator" and it is used to specify + alternatives. The `|' has the lowest precedence of all the regular + expression operators. For example, `^P|[[:digit:]]' matches any + string that matches either `^P' or `[[:digit:]]'. This means it + matches any string that starts with `P' or contains a digit. The alternation applies to the largest possible regexps on either - side. In other words, `|' has the lowest precedence of all the - regular expression operators. + side. `(...)' - Parentheses are used for grouping in regular expressions as in - arithmetic. They can be used to concatenate regular expressions + Parentheses are used for grouping in regular expressions, similar + to arithmetic. They can be used to concatenate regular expressions containing the alternation operator, `|'. For example, - `@(samp|code)\{[^}]+\}' matches both `@code{foo}' and - `@samp{bar}'. (These are Texinfo formatting control sequences.) + `@(samp|code)\{[^}]+\}' matches both `@code{foo}' and `@samp{bar}'. + (These are Texinfo formatting control sequences.) `*' - This symbol means that the preceding regular expression is to be - repeated as many times as necessary to find a match. For example: - - ph* - - applies the `*' symbol to the preceding `h' and looks for matches - of one `p' followed by any number of `h's. This will also match - just `p' if no `h's are present. + This symbol means that the preceding regular expression should be + repeated as many times as necessary to find a match. For example, + `ph*' applies the `*' symbol to the preceding `h' and looks for + matches of one `p' followed by any number of `h's. This also + matches just `p' if no `h's are present. The `*' repeats the _smallest_ possible preceding expression. - (Use parentheses if you wish to repeat a larger expression.) It - finds as many repetitions as possible. For example: - - awk '/\(c[ad][ad]*r x\)/ { print }' sample - - prints every record in `sample' containing a string of the form - `(car x)', `(cdr x)', `(cadr x)', and so on. Notice the escaping - of the parentheses by preceding them with backslashes. + (Use parentheses if you want to repeat a larger expression.) It + finds as many repetitions as possible. For example, `awk + '/\(c[ad][ad]*r x\)/ { print }' sample' prints every record in + `sample' containing a string of the form `(car x)', `(cdr x)', + `(cadr x)', and so on. Notice the escaping of the parentheses by + preceding them with backslashes. `+' - This symbol is similar to `*', but the preceding expression must be - matched at least once. This means that: - - wh+y - - would match `why' and `whhy' but not `wy', whereas `wh*y' would - match all three of these strings. This is a simpler way of - writing the last `*' example: + This symbol is similar to `*' except that the preceding expression + must be matched at least once. This means that `wh+y' would match + `why' and `whhy', but not `wy', whereas `wh*y' would match all + three of these strings. The following is a simpler way of writing + the last `*' example: awk '/\(c[ad]+r x\)/ { print }' sample `?' - This symbol is similar to `*', but the preceding expression can be - matched either once or not at all. For example: - - fe?d - - will match `fed' and `fd', but nothing else. + This symbol is similar to `*' except that the preceding expression + can be matched either once or not at all. For example, `fe?d' + matches `fed' and `fd', but nothing else. `{N}' `{N,}' @@ -1989,111 +2284,212 @@ themselves. repeated N times. If there are two numbers separated by a comma, the preceding regexp is repeated N to M times. If there is one number followed by a comma, then the preceding regexp is repeated - at least N times. + at least N times: `wh{3}y' - matches `whhhy' but not `why' or `whhhhy'. + Matches `whhhy', but not `why' or `whhhhy'. `wh{3,5}y' - matches `whhhy' or `whhhhy' or `whhhhhy', only. + Matches `whhhy', `whhhhy', or `whhhhhy', only. `wh{2,}y' - matches `whhy' or `whhhy', and so on. + Matches `whhy' or `whhhy', and so on. Interval expressions were not traditionally available in `awk'. - As part of the POSIX standard they were added, to make `awk' and + They were added as part of the POSIX standard to make `awk' and `egrep' consistent with each other. - However, since old programs may use `{' and `}' in regexp + However, because old programs may use `{' and `}' in regexp constants, by default `gawk' does _not_ match interval expressions in regexps. If either `--posix' or `--re-interval' are specified - (*note Command Line Options: Options.), then interval expressions + (*note Command-Line Options: Options.), then interval expressions are allowed in regexps. + For new programs that use `{' and `}' in regexp constants, it is + good practice to always escape them with a backslash. Then the + regexp constants are valid and work the way you want them to, using + any version of `awk'.(2) + In regular expressions, the `*', `+', and `?' operators, as well as the braces `{' and `}', have the highest precedence, followed by concatenation, and finally by `|'. As in arithmetic, parentheses can change how operators are grouped. - If `gawk' is in compatibility mode (*note Command Line Options: -Options.), character classes and interval expressions are not available -in regular expressions. + In POSIX `awk' and `gawk', the `*', `+', and `?' operators stand for +themselves when there is nothing in the regexp that precedes them. For +example, `/+/' matches a literal plus sign. However, many other +versions of `awk' treat such a usage as a syntax error. + + If `gawk' is in compatibility mode (*note Command-Line Options: +Options.), POSIX character classes and interval expressions are not +available in regular expressions. + + ---------- Footnotes ---------- + + (1) In other literature, you may see a character list referred to as +either a "character set", a "character class" or a "bracket expression". - The next node discusses the GNU-specific regexp operators, and -provides more detail concerning how command line options affect the way -`gawk' interprets the characters in regular expressions. + (2) Use two backslashes if you're using a string constant with a +regexp operator or function. -File: gawk.info, Node: GNU Regexp Operators, Next: Case-sensitivity, Prev: Regexp Operators, Up: Regexp +File: gawk.info, Node: Character Lists, Next: GNU Regexp Operators, Prev: Regexp Operators, Up: Regexp -Additional Regexp Operators Only in `gawk' -========================================== +Using Character Lists +===================== + + Within a character list, a "range expression" consists of two +characters separated by a hyphen. It matches any single character that +sorts between the two characters, using the locale's collating sequence +and character set. For example, in the default C locale, `[a-dx-z]' is +equivalent to `[abcdxyz]'. Many locales sort characters in dictionary +order, and in these locales, `[a-dx-z]' is typically not equivalent to +`[abcdxyz]'; instead it might be equivalent to `[aBbCcDdxXyYz]', for +example. To obtain the traditional interpretation of bracket +expressions, you can use the C locale by setting the `LC_ALL' +environment variable to the value `C'. + + To include one of the characters `\', `]', `-', or `^' in a +character list, put a `\' in front of it. For example: + + [d\]] + +matches either `d' or `]'. + + This treatment of `\' in character lists is compatible with other +`awk' implementations and is also mandated by POSIX. The regular +expressions in `awk' are a superset of the POSIX specification for +Extended Regular Expressions (EREs). POSIX EREs are based on the +regular expressions accepted by the traditional `egrep' utility. + + "Character classes" are a new feature introduced in the POSIX +standard. A character class is a special notation for describing lists +of characters that have a specific attribute, but the actual characters +can vary from country to country and/or from character set to character +set. For example, the notion of what is an alphabetic character +differs between the United States and France. + + A character class is only valid in a regexp _inside_ the brackets of +a character list. Character classes consist of `[:', a keyword +denoting the class, and `:]'. Here are the character classes defined +by the POSIX standard: + +`[:alnum:]' Alphanumeric characters. +`[:alpha:]' Alphabetic characters. +`[:blank:]' Space and tab characters. +`[:cntrl:]' Control characters. +`[:digit:]' Numeric characters. +`[:graph:]' Characters that are both printable and visible. (A space is + printable but not visible, whereas an `a' is both.) +`[:lower:]' Lowercase alphabetic characters. +`[:print:]' Printable characters (characters that are not control + characters). +`[:punct:]' Punctuation characters (characters that are not letters, + digits, control characters, or space characters). +`[:space:]' Space characters (such as space, tab, and formfeed, to name a + few). +`[:upper:]' Uppercase alphabetic characters. +`[:xdigit:]' Characters that are hexadecimal digits. + + For example, before the POSIX standard, you had to write +`/[A-Za-z0-9]/' to match alphanumeric characters. If your character +set had other alphabetic characters in it, this would not match them, +and if your character set collated differently from ASCII, this might +not even match the ASCII alphanumeric characters. With the POSIX +character classes, you can write `/[[:alnum:]]/' to match the alphabetic +and numeric characters in your character set. + + Two additional special sequences can appear in character lists. +These apply to non-ASCII character sets, which can have single symbols +(called "collating elements") that are represented with more than one +character. They can also have several characters that are equivalent for +"collating", or sorting, purposes. (For example, in French, a plain "e" +and a grave-accented "e`" are equivalent.) + +Collating Symbols + A "collating symbol" is a multicharacter collating element + enclosed between `[.' and `.]'. For example, if `ch' is a + collating element, then `[[.ch.]]' is a regexp that matches this + collating element, whereas `[ch]' is a regexp that matches either + `c' or `h'. + +Equivalence Classes + An "equivalence class" is a locale-specific name for a list of + characters that are equal. The name is enclosed between `[=' and + `=]'. For example, the name `e' might be used to represent all of + "e," "e`," and "e'." In this case, `[[=e=]]' is a regexp that + matches any of `e', `e'', or `e`'. + + These features are very valuable in non-English speaking locales. + + *Caution:* The library functions that `gawk' uses for regular +expression matching currently only recognize POSIX character classes; +they do not recognize collating symbols or equivalence classes. + + +File: gawk.info, Node: GNU Regexp Operators, Next: Case-sensitivity, Prev: Character Lists, Up: Regexp + +`gawk'-Specific Regexp Operators +================================ GNU software that deals with regular expressions provides a number of additional regexp operators. These operators are described in this -section, and are specific to `gawk'; they are not available in other -`awk' implementations. - - Most of the additional operators are for dealing with word matching. -For our purposes, a "word" is a sequence of one or more letters, digits, -or underscores (`_'). +minor node and are specific to `gawk'; they are not available in other +`awk' implementations. Most of the additional operators deal with word +matching. For our purposes, a "word" is a sequence of one or more +letters, digits, or underscores (`_'): `\w' - This operator matches any word-constituent character, i.e. any - letter, digit, or underscore. Think of it as a short-hand for + Matches any word-constituent character--that is, it matches any + letter, digit, or underscore. Think of it as short-hand for `[[:alnum:]_]'. `\W' - This operator matches any character that is not word-constituent. - Think of it as a short-hand for `[^[:alnum:]_]'. + Matches any character that is not word-constituent. Think of it + as short-hand for `[^[:alnum:]_]'. `\<' - This operator matches the empty string at the beginning of a word. - For example, `/\<away/' matches `away', but not `stowaway'. + Matches the empty string at the beginning of a word. For example, + `/\<away/' matches `away' but not `stowaway'. `\>' - This operator matches the empty string at the end of a word. For - example, `/stow\>/' matches `stow', but not `stowaway'. + Matches the empty string at the end of a word. For example, + `/stow\>/' matches `stow' but not `stowaway'. `\y' - This operator matches the empty string at either the beginning or - the end of a word (the word boundar*y*). For example, `\yballs?\y' - matches either `ball' or `balls' as a separate word. + Matches the empty string at either the beginning or the end of a + word (i.e., the word boundar*y*). For example, `\yballs?\y' + matches either `ball' or `balls', as a separate word. `\B' - This operator matches the empty string within a word. In other - words, `\B' matches the empty string that occurs between two - word-constituent characters. For example, `/\Brat\B/' matches - `crate', but it does not match `dirty rat'. `\B' is essentially - the opposite of `\y'. + Matches the empty string that occurs between two word-constituent + characters. For example, `/\Brat\B/' matches `crate' but it does + not match `dirty rat'. `\B' is essentially the opposite of `\y'. There are two other operators that work on buffers. In Emacs, a -"buffer" is, naturally, an Emacs buffer. For other programs, the -regexp library routines that `gawk' uses consider the entire string to -be matched as the buffer. - - For `awk', since `^' and `$' always work in terms of the beginning -and end of strings, these operators don't add any new capabilities. -They are provided for compatibility with other GNU software. +"buffer" is, naturally, an Emacs buffer. For other programs, `gawk''s +regexp library routines consider the entire string to match as the +buffer. `\`' - This operator matches the empty string at the beginning of the - buffer. + Matches the empty string at the beginning of a buffer (string). `\'' - This operator matches the empty string at the end of the buffer. + Matches the empty string at the end of a buffer (string). - In other GNU software, the word boundary operator is `\b'. However, -that conflicts with the `awk' language's definition of `\b' as -backspace, so `gawk' uses a different letter. + Because `^' and `$' always work in terms of the beginning and end of +strings, these operators don't add any new capabilities for `awk'. +They are provided for compatibility with other GNU software. - An alternative method would have been to require two backslashes in -the GNU operators, but this was deemed to be too confusing, and the -current method of using `\y' for the GNU `\b' appears to be the lesser -of two evils. + In other GNU software, the word-boundary operator is `\b'. However, +that conflicts with the `awk' language's definition of `\b' as +backspace, so `gawk' uses a different letter. An alternative method +would have been to require two backslashes in the GNU operators, but +this was deemed too confusing. The current method of using `\y' for the +GNU `\b' appears to be the lesser of two evils. - The various command line options (*note Command Line Options: -Options.) control how `gawk' interprets characters in regexps. + The various command-line options (*note Command-Line Options: +Options.) control how `gawk' interprets characters in regexps: No options In the default case, `gawk' provides all the facilities of POSIX @@ -2102,16 +2498,16 @@ No options expressions are not supported. `--posix' - Only POSIX regexps are supported, the GNU operators are not special + Only POSIX regexps are supported; the GNU operators are not special (e.g., `\w' matches a literal `w'). Interval expressions are allowed. `--traditional' Traditional Unix `awk' regexps are matched. The GNU operators are - not special, interval expressions are not available, and neither - are the POSIX character classes (`[[:alnum:]]' and so on). - Characters described by octal and hexadecimal escape sequences are - treated literally, even if they represent regexp metacharacters. + not special, interval expressions are not available, nor are the + POSIX character classes (`[[:alnum:]]' and so on). Characters + described by octal and hexadecimal escape sequences are treated + literally, even if they represent regexp metacharacters. `--re-interval' Allow interval expressions in regexps, even if `--traditional' has @@ -2120,36 +2516,36 @@ No options File: gawk.info, Node: Case-sensitivity, Next: Leftmost Longest, Prev: GNU Regexp Operators, Up: Regexp -Case-sensitivity in Matching +Case Sensitivity in Matching ============================ Case is normally significant in regular expressions, both when -matching ordinary characters (i.e. not metacharacters), and inside -character sets. Thus a `w' in a regular expression matches only a -lower-case `w' and not an upper-case `W'. +matching ordinary characters (i.e., not metacharacters) and inside +character sets. Thus, a `w' in a regular expression matches only a +lowercase `w' and not an uppercase `W'. The simplest way to do a case-independent match is to use a character -list: `[Ww]'. However, this can be cumbersome if you need to use it -often; and it can make the regular expressions harder to read. There -are two alternatives that you might prefer. - - One way to do a case-insensitive match at a particular point in the -program is to convert the data to a single case, using the `tolower' or -`toupper' built-in string functions (which we haven't discussed yet; -*note Built-in Functions for String Manipulation: String Functions.). +list--for example, `[Ww]'. However, this can be cumbersome if you need +to use it often and it can make the regular expressions harder to read. +There are two alternatives that you might prefer. + + One way to perform a case-insensitive match at a particular point in +the program is to convert the data to a single case, using the +`tolower' or `toupper' built-in string functions (which we haven't +discussed yet; *note String Manipulation Functions: String Functions.). For example: tolower($1) ~ /foo/ { ... } -converts the first field to lower-case before matching against it. -This will work in any POSIX-compliant implementation of `awk'. +converts the first field to lowercase before matching against it. This +works in any POSIX-compliant `awk'. Another method, specific to `gawk', is to set the variable -`IGNORECASE' to a non-zero value (*note Built-in Variables::). When +`IGNORECASE' to a nonzero value (*note Built-in Variables::). When `IGNORECASE' is not zero, _all_ regexp and string operations ignore case. Changing the value of `IGNORECASE' dynamically controls the case -sensitivity of your program as it runs. Case is significant by default -because `IGNORECASE' (like most variables) is initialized to zero. +sensitivity of the program as it runs. Case is significant by default +because `IGNORECASE' (like most variables) is initialized to zero: x = "aB" if (x ~ /ab/) ... # this test will fail @@ -2158,66 +2554,70 @@ because `IGNORECASE' (like most variables) is initialized to zero. if (x ~ /ab/) ... # now it will succeed In general, you cannot use `IGNORECASE' to make certain rules -case-insensitive and other rules case-sensitive, because there is no way -to set `IGNORECASE' just for the pattern of a particular rule. To do -this, you must use character lists or `tolower'. However, one thing -you can do only with `IGNORECASE' is turn case-sensitivity on or off -dynamically for all the rules at once. - - `IGNORECASE' can be set on the command line, or in a `BEGIN' rule -(*note Other Command Line Arguments: Other Arguments.; also *note +case-insensitive and other rules case-sensitive, because there is no +straightforward way to set `IGNORECASE' just for the pattern of a +particular rule.(1) To do this, use either character lists or +`tolower'. However, one thing you can do with `IGNORECASE' only is +dynamically turn case-sensitivity on or off for all the rules at once. + + `IGNORECASE' can be set on the command line or in a `BEGIN' rule +(*note Other Command-Line Arguments: Other Arguments.; also *note Startup and Cleanup Actions: Using BEGIN/END.). Setting `IGNORECASE' from the command line is a way to make a program case-insensitive without having to edit it. - Prior to version 3.0 of `gawk', the value of `IGNORECASE' only -affected regexp operations. It did not affect string comparison with -`==', `!=', and so on. Beginning with version 3.0, both regexp and -string comparison operations are affected by `IGNORECASE'. + Prior to `gawk' 3.0, the value of `IGNORECASE' affected regexp +operations only. It did not affect string comparison with `==', `!=', +and so on. Beginning with version 3.0, both regexp and string +comparison operations are also affected by `IGNORECASE'. - Beginning with version 3.0 of `gawk', the equivalences between -upper-case and lower-case characters are based on the ISO-8859-1 (ISO -Latin-1) character set. This character set is a superset of the -traditional 128 ASCII characters, that also provides a number of -characters suitable for use with European languages. + Beginning with `gawk' 3.0, the equivalences between upper- and +lowercase characters are based on the ISO-8859-1 (ISO Latin-1) +character set. This character set is a superset of the traditional 128 +ASCII characters, that also provides a number of characters suitable +for use with European languages. The value of `IGNORECASE' has no effect if `gawk' is in -compatibility mode (*note Command Line Options: Options.). Case is +compatibility mode (*note Command-Line Options: Options.). Case is always significant in compatibility mode. + ---------- Footnotes ---------- + + (1) Experienced C and C++ programmers will note that it is possible, +using something like `IGNORECASE = 1 && /foObAr/ { ... }' and +`IGNORECASE = 0 || /foobar/ { ... }'. However, this is somewhat +obscure and we don't recommend it. + File: gawk.info, Node: Leftmost Longest, Next: Computed Regexps, Prev: Case-sensitivity, Up: Regexp How Much Text Matches? ====================== - Consider the following example: + Consider the following: echo aaaabcd | awk '{ sub(/a+/, "<A>"); print }' - This example uses the `sub' function (which we haven't discussed yet, -*note Built-in Functions for String Manipulation: String Functions.) -to make a change to the input record. Here, the regexp `/a+/' indicates -"one or more `a' characters," and the replacement text is `<A>'. - - The input contains four `a' characters. What will the output be? -In other words, how many is "one or more"--will `awk' match two, three, -or all four `a' characters? + This example uses the `sub' function (which we haven't discussed yet; +*note String Manipulation Functions: String Functions.) to make a +change to the input record. Here, the regexp `/a+/' indicates "one or +more `a' characters," and the replacement text is `<A>'. - The answer is, `awk' (and POSIX) regular expressions always match -the leftmost, _longest_ sequence of input characters that can match. -Thus, in this example, all four `a' characters are replaced with `<A>'. + The input contains four `a' characters. `awk' (and POSIX) regular +expressions always match the leftmost, _longest_ sequence of input +characters that can match. Thus, all four `a' characters are replaced +with `<A>' in this example: $ echo aaaabcd | awk '{ sub(/a+/, "<A>"); print }' -| <A>bcd For simple match/no-match tests, this is not so important. But when doing text matching and substitutions with the `match', `sub', `gsub', -and `gensub' functions, it is very important. *Note Built-in Functions -for String Manipulation: String Functions, for more information on -these functions. Understanding this principle is also important for -regexp-based record and field splitting (*note How Input is Split into -Records: Records., and also *note Specifying How Fields are Separated: +and `gensub' functions, it is very important. *Note String +Manipulation Functions: String Functions, for more information on these +functions. Understanding this principle is also important for +regexp-based record and field splitting (*note How Input Is Split into +Records: Records., and also *note Specifying How Fields Are Separated: Field Separators.). @@ -2226,27 +2626,27 @@ File: gawk.info, Node: Computed Regexps, Prev: Leftmost Longest, Up: Regexp Using Dynamic Regexps ===================== - The right hand side of a `~' or `!~' operator need not be a regexp -constant (i.e. a string of characters between slashes). It may be any -expression. The expression is evaluated, and converted if necessary to -a string; the contents of the string are used as the regexp. A regexp -that is computed in this way is called a "dynamic regexp". For example: + The righthand side of a `~' or `!~' operator need not be a regexp +constant (i.e., a string of characters between slashes). It may be any +expression. The expression is evaluated and converted to a string if +necessary; the contents of the string are used as the regexp. A regexp +that is computed in this way is called a "dynamic regexp": - BEGIN { identifier_regexp = "[A-Za-z_][A-Za-z_0-9]*" } - $0 ~ identifier_regexp { print } + BEGIN { digits_regexp = "[[:digit:]]+" } + $0 ~ digits_regexp { print } -sets `identifier_regexp' to a regexp that describes `awk' variable -names, and tests if the input record matches this regexp. +This sets `digits_regexp' to a regexp that describes one or more digits, +and tests whether the input record matches this regexp. - *Caution:* When using the `~' and `!~' operators, there is a -difference between a regexp constant enclosed in slashes, and a string -constant enclosed in double quotes. If you are going to use a string -constant, you have to understand that the string is in essence scanned -_twice_; the first time when `awk' reads your program, and the second -time when it goes to match the string on the left-hand side of the -operator with the pattern on the right. This is true of any string -valued expression (such as `identifier_regexp' above), not just string -constants. + When using the `~' and `!~' *Caution:* When using the `~' and `!~' +operators, there is a difference between a regexp constant enclosed in +slashes and a string constant enclosed in double quotes. If you are +going to use a string constant, you have to understand that the string +is, in essence, scanned _twice_: the first time when `awk' reads your +program, and the second time when it goes to match the string on the +lefthand side of the operator with the pattern on the right. This is +true of any string valued expression (such as `digits_regexp' shown +previously), not just string constants. What difference does it make if the string is scanned twice? The answer has to do with escape sequences, and particularly with @@ -2254,28 +2654,51 @@ backslashes. To get a backslash into a regular expression inside a string, you have to type two backslashes. For example, `/\*/' is a regexp constant for a literal `*'. Only -one backslash is needed. To do the same thing with a string, you would -have to type `"\\*"'. The first backslash escapes the second one, so -that the string actually contains the two characters `\' and `*'. +one backslash is needed. To do the same thing with a string, you have +to type `"\\*"'. The first backslash escapes the second one so that +the string actually contains the two characters `\' and `*'. Given that you can use both regexp and string constants to describe regular expressions, which should you use? The answer is "regexp -constants," for several reasons. +constants," for several reasons: - 1. String constants are more complicated to write, and more difficult + * String constants are more complicated to write and more difficult to read. Using regexp constants makes your programs less error-prone. Not understanding the difference between the two kinds of constants is a common source of errors. - 2. It is also more efficient to use regexp constants: `awk' can note - that you have supplied a regexp and store it internally in a form - that makes pattern matching more efficient. When using a string + * It is more efficient to use regexp constants. `awk' can note that + you have supplied a regexp, and store it internally in a form that + makes pattern matching more efficient. When using a string constant, `awk' must first convert the string into this internal - form, and then perform the pattern matching. + form and then perform the pattern matching. - 3. Using regexp constants is better style; it shows clearly that you + * Using regexp constants is better form; it shows clearly that you intend a regexp match. +Advanced Notes: Using `\n' in Character Lists of Dynamic Regexps +---------------------------------------------------------------- + + Some commercial versions of `awk' do not allow the newline character +to be used inside a character list for a dynamic regexp: + + $ awk '$0 ~ "[ \t\n]"' + error--> awk: newline in character class [ + error--> ]... + error--> source line number 1 + error--> context is + error--> >>> <<< + + But a newline in a regexp constant works with no problem: + + $ awk '$0 ~ /[ \t\n]/' + here is a sample line + -| here is a sample line + Ctrl-d + + `gawk' does not have this problem, and it isn't likely to occur +often in practice, but it's worth noting for future reference. + File: gawk.info, Node: Reading Files, Next: Printing, Prev: Regexp, Up: Top @@ -2283,20 +2706,20 @@ Reading Input Files ******************* In the typical `awk' program, all input is read either from the -standard input (by default the keyboard, but often a pipe from another -command) or from files whose names you specify on the `awk' command -line. If you specify input files, `awk' reads them in order, reading -all the data from one before going on to the next. The name of the -current input file can be found in the built-in variable `FILENAME' -(*note Built-in Variables::). - - The input is read in units called "records", and processed by the +standard input (by default, this is the keyboard but often it is a pipe +from another command), or from files whose names you specify on the +`awk' command line. If you specify input files, `awk' reads them in +order, processing all the data from one before going on to the next. +The name of the current input file can be found in the built-in variable +`FILENAME' (*note Built-in Variables::). + + The input is read in units called "records", and is processed by the rules of your program one record at a time. By default, each record is one line. Each record is automatically split into chunks called "fields". This makes it more convenient for programs to work on the parts of a record. - On rare occasions you will need to use the `getline' command. The + On rare occasions, you may need to use the `getline' command. The `getline' command is valuable, both because it can do explicit input from any number of files, and because the files used with it do not have to be named on the `awk' command line (*note Explicit Input with @@ -2317,38 +2740,47 @@ have to be named on the `awk' command line (*note Explicit Input with File: gawk.info, Node: Records, Next: Fields, Prev: Reading Files, Up: Reading Files -How Input is Split into Records +How Input Is Split into Records =============================== The `awk' utility divides the input for your `awk' program into -records and fields. Records are separated by a character called the -"record separator". By default, the record separator is the newline -character. This is why records are, by default, single lines. You can -use a different character for the record separator by assigning the -character to the built-in variable `RS'. - - You can change the value of `RS' in the `awk' program, like any -other variable, with the assignment operator, `=' (*note Assignment +records and fields. `awk' keeps track of the number of records that +have been read so far from the current input file. This value is +stored in a built-in variable called `FNR'. It is reset to zero when a +new file is started. Another built-in variable, `NR', is the total +number of input records read so far from all data files. It starts at +zero, but is never automatically reset to zero. + + Records are separated by a character called the "record separator". +By default, the record separator is the newline character. This is why +records are, by default, single lines. A different character can be +used for the record separator by assigning the character to the +built-in variable `RS'. + + Like any other variable, the value of `RS' can be changed in the +`awk' program with the assignment operator, `=' (*note Assignment Expressions: Assignment Ops.). The new record-separator character should be enclosed in quotation marks, which indicate a string constant. Often the right time to do this is at the beginning of -execution, before any input has been processed, so that the very first -record will be read with the proper separator. To do this, use the -special `BEGIN' pattern (*note The `BEGIN' and `END' Special Patterns: -BEGIN/END.). For example: +execution, before any input is processed, so that the very first record +is read with the proper separator. To do this, use the special `BEGIN' +pattern (*note The `BEGIN' and `END' Special Patterns: BEGIN/END.). +For example: - awk 'BEGIN { RS = "/" } ; { print $0 }' BBS-list + awk 'BEGIN { RS = "/" } + { print $0 }' BBS-list changes the value of `RS' to `"/"', before reading any input. This is a string whose first character is a slash; as a result, records are separated by slashes. Then the input file is read, and the second rule in the `awk' program (the action with no pattern) prints each record. -Since each `print' statement adds a newline at the end of its output, +Because each `print' statement adds a newline at the end of its output, the effect of this `awk' program is to copy the input with each slash changed to a newline. Here are the results of running the program on `BBS-list': - $ awk 'BEGIN { RS = "/" } ; { print $0 }' BBS-list + $ awk 'BEGIN { RS = "/" } + > { print $0 }' BBS-list -| aardvark 555-5553 1200 -| 300 B -| alpo-net 555-3412 2400 @@ -2382,11 +2814,15 @@ Files.), the line looks like this: camelot 555-0542 300 C -It only has one baud rate; there are no slashes in the record. +It has one baud rate only, so there are no slashes in the record, +unlike the others which have two or more baud rates. In fact, this +record is treated as part of the record for the `core' BBS; the newline +separating them in the output is the original newline in the data file, +not the one added by `awk' when it printed the record! Another way to change the record separator is on the command line, -using the variable-assignment feature (*note Other Command Line -Arguments: Other Arguments.). +using the variable-assignment feature (*note Other Command-Line +Arguments: Other Arguments.): awk '{ print $0 }' RS="/" BBS-list @@ -2394,50 +2830,49 @@ This sets `RS' to `/' before processing `BBS-list'. Using an unusual character such as `/' for the record separator produces correct behavior in the vast majority of cases. However, the -following (extreme) pipeline prints a surprising `1'. There is one -field, consisting of a newline. The value of the built-in variable -`NF' is the number of fields in the current record. +following (extreme) pipeline prints a surprising `1': $ echo | awk 'BEGIN { RS = "a" } ; { print NF }' -| 1 -Reaching the end of an input file terminates the current input record, -even if the last character in the file is not the character in `RS' -(d.c.). + There is one field, consisting of a newline. The value of the +built-in variable `NF' is the number of fields in the current record. - The empty string, `""' (a string of no characters), has a special -meaning as the value of `RS': it means that records are separated by -one or more blank lines, and nothing else. *Note Multiple-Line -Records: Multiple Line, for more details. + Reaching the end of an input file terminates the current input +record, even if the last character in the file is not the character in +`RS'. (d.c.) + + The empty string `""' (a string without any characters) has a +special meaning as the value of `RS'. It means that records are +separated by one or more blank lines and nothing else. *Note +Multiple-Line Records: Multiple Line, for more details. If you change the value of `RS' in the middle of an `awk' run, the new value is used to delimit subsequent records, but the record -currently being processed (and records already processed) are not +currently being processed, as well as records already processed, are not affected. After the end of the record has been determined, `gawk' sets the -variable `RT' to the text in the input that matched `RS'. - - The value of `RS' is in fact not limited to a one-character string. -It can be any regular expression (*note Regular Expressions: Regexp.). -In general, each record ends at the next string that matches the -regular expression; the next record starts at the end of the matching -string. This general rule is actually at work in the usual case, where -`RS' contains just a newline: a record ends at the beginning of the -next matching string (the next newline in the input) and the following +variable `RT' to the text in the input that matched `RS'. When using +`gawk', the value of `RS' is not limited to a one-character string. It +can be any regular expression (*note Regular Expressions: Regexp.). In +general, each record ends at the next string that matches the regular +expression; the next record starts at the end of the matching string. +This general rule is actually at work in the usual case, where `RS' +contains just a newline: a record ends at the beginning of the next +matching string (the next newline in the input) and the following record starts just after the end of this string (at the first character -of the following line). The newline, since it matches `RS', is not +of the following line). The newline, because it matches `RS', is not part of either record. - When `RS' is a single character, `RT' will contain the same single -character. However, when `RS' is a regular expression, then `RT' -becomes more useful; it contains the actual input text that matched the -regular expression. + When `RS' is a single character, `RT' contains the same single +character. However, when `RS' is a regular expression, `RT' contains +the actual input text that matched the regular expression. The following example illustrates both of these features. It sets -`RS' equal to a regular expression that matches either a newline, or a -series of one or more upper-case letters with optional leading and/or -trailing white space (*note Regular Expressions: Regexp.). +`RS' equal to a regular expression that matches either a newline or a +series of one or more uppercase letters with optional leading and/or +trailing whitespace: $ echo record 1 AAAA record 2 BBBB record 3 | > gawk 'BEGIN { RS = "\n|( *[[:upper:]]+ *)" } @@ -2448,24 +2883,47 @@ trailing white space (*note Regular Expressions: Regexp.). -| The final line of output has an extra blank line. This is because the -value of `RT' is a newline, and then the `print' statement supplies its -own terminating newline. - - *Note A Simple Stream Editor: Simple Sed, for a more useful example -of `RS' as a regexp and `RT'. +value of `RT' is a newline, and the `print' statement supplies its own +terminating newline. *Note A Simple Stream Editor: Simple Sed, for a +more useful example of `RS' as a regexp and `RT'. The use of `RS' as a regular expression and the `RT' variable are `gawk' extensions; they are not available in compatibility mode (*note -Command Line Options: Options.). In compatibility mode, only the first +Command-Line Options: Options.). In compatibility mode, only the first character of the value of `RS' is used to determine the end of the record. - The `awk' utility keeps track of the number of records that have -been read so far from the current input file. This value is stored in a -built-in variable called `FNR'. It is reset to zero when a new file is -started. Another built-in variable, `NR', is the total number of input -records read so far from all data files. It starts at zero but is -never automatically reset to zero. +Advanced Notes: `RS = "\0"' Is Not Portable +------------------------------------------- + + There are times when you might want to treat an entire data file as a +single record. The only way to make this happen is to give `RS' a +value that you know doesn't occur in the input file. This is hard to +do in a general way, such that a program always works for arbitrary +input files. + + You might think that for text files, the NUL character, which +consists of a character with all bits equal to zero, is a good value to +use for `RS' in this case: + + BEGIN { RS = "\0" } # whole file becomes one record? + + `gawk' in fact accepts this, and uses the NUL character for the +record separator. However, this usage is _not_ portable to other `awk' +implementations. + + All other `awk' implementations(1) store strings internally as +C-style strings. C strings use the NUL character as the string +terminator. In effect, this means that `RS = "\0"' is the same as `RS += ""'. (d.c.) + + The best way to treat a whole file as a single record is to simply +read the file in, one record at a time, concatenating each record onto +the end of the previous ones. + + ---------- Footnotes ---------- + + (1) At least that we know about. File: gawk.info, Node: Fields, Next: Non-Constant Fields, Prev: Records, Up: Reading Files @@ -2475,45 +2933,42 @@ Examining Fields When `awk' reads an input record, the record is automatically separated or "parsed" by the interpreter into chunks called "fields". -By default, fields are separated by whitespace, like words in a line. -Whitespace in `awk' means any string of one or more spaces, tabs or -newlines;(1) other characters such as formfeed, and so on, that are -considered whitespace by other languages are _not_ considered +By default, fields are separated by "whitespace", like words in a line. +Whitespace in `awk' means any string of one or more spaces, tabs, or +newlines;(1) other characters, such as formfeed, vertical tab, etc. +that are considered whitespace by other languages, are _not_ considered whitespace by `awk'. The purpose of fields is to make it more convenient for you to refer to these pieces of the record. You don't have to use them--you can -operate on the whole record if you wish--but fields are what make +operate on the whole record if you want--but fields are what make simple `awk' programs so powerful. - To refer to a field in an `awk' program, you use a dollar-sign, `$', + A dollar-sign (`$') is used to refer to a field in an `awk' program, followed by the number of the field you want. Thus, `$1' refers to the -first field, `$2' to the second, and so on. For example, suppose the -following is a line of input: +first field, `$2' to the second, and so on. (Unlike the Unix shells, +the field numbers are not limited to single digits. `$127' is the one +hundred and twenty-seventh field in the record.) For example, suppose +the following is a line of input: This seems like a pretty nice example. -Here the first field, or `$1', is `This'; the second field, or `$2', is -`seems'; and so on. Note that the last field, `$7', is `example.'. +Here the first field, or `$1', is `This', the second field, or `$2', is +`seems', and so on. Note that the last field, `$7', is `example.'. Because there is no space between the `e' and the `.', the period is considered part of the seventh field. `NF' is a built-in variable whose value is the number of fields in -the current record. `awk' updates the value of `NF' automatically, -each time a record is read. +the current record. `awk' automatically updates the value of `NF' each +time it reads a record. No matter how many fields there are, the last +field in a record can be represented by `$NF'. So, `$NF' is the same +as `$7', which is `example.'. If you try to reference a field beyond +the last one (such as `$8' when the record has only seven fields), you +get the empty string. (If used in a numeric operation, you get zero.) - No matter how many fields there are, the last field in a record can -be represented by `$NF'. So, in the example above, `$NF' would be the -same as `$7', which is `example.'. Why this works is explained below -(*note Non-constant Field Numbers: Non-Constant Fields.). If you try -to reference a field beyond the last one, such as `$8' when the record -has only seven fields, you get the empty string. - - `$0', which looks like a reference to the "zeroth" field, is a -special case: it represents the whole input record. `$0' is used when -you are not interested in fields. - - Here are some more examples: + The use of `$0', which looks like a reference to the "zeroth" field, +is a special case: it represents the whole input record when you are +not interested in specific fields. Here are some more examples: $ awk '$1 ~ /foo/ { print $0 }' BBS-list -| fooey 555-1234 2400/1200/300 B @@ -2528,8 +2983,8 @@ Usage.); it tests whether a string (here, the field `$1') matches a given regular expression. By contrast, the following example looks for `foo' in _the entire -record_ and prints the first field and the last field for each input -record containing a match. +record_ and prints the first field and the last field for each matching +input record: $ awk '/foo/ { print $1, $NF }' BBS-list -| fooey B @@ -2545,7 +3000,7 @@ separating fields. File: gawk.info, Node: Non-Constant Fields, Next: Changing Fields, Prev: Fields, Up: Reading Files -Non-constant Field Numbers +Non-Constant Field Numbers ========================== The number of a field does not need to be a constant. Any @@ -2560,13 +3015,12 @@ Recall that `NR' is the number of records read so far: one in the first record, two in the second, etc. So this example prints the first field of the first record, the second field of the second record, and so on. For the twentieth record, field number 20 is printed; most likely, the -record has fewer than 20 fields, so this prints a blank line. - - Here is another example of using expressions as field numbers: +record has fewer than 20 fields, so this prints a blank line. Here is +another example of using expressions as field numbers: awk '{ print $(2*2) }' BBS-list - `awk' must evaluate the expression `(2*2)' and use its value as the + `awk' evaluates the expression `(2*2)' and uses its value as the number of the field to print. The `*' sign represents multiplication, so the expression `2*2' evaluates to four. The parentheses are used so that the multiplication is done before the `$' operation; they are @@ -2578,16 +3032,15 @@ Operator Precedence (How Operators Nest): Precedence.) If the field number you compute is zero, you get the entire record. Thus, `$(2-2)' has the same value as `$0'. Negative field numbers are -not allowed; trying to reference one will usually terminate your -running `awk' program. (The POSIX standard does not define what -happens when you reference a negative field number. `gawk' will notice -this and terminate your program. Other `awk' implementations may -behave differently.) - - As mentioned in *Note Examining Fields: Fields, the number of fields -in the current record is stored in the built-in variable `NF' (also +not allowed; trying to reference one usually terminates the program. +(The POSIX standard does not define what happens when you reference a +negative field number. `gawk' notices this and terminates your +program. Other `awk' implementations may behave differently.) + + As mentioned in *Note Examining Fields: Fields, `awk' stores the +current record's number of fields in the built-in variable `NF' (also *note Built-in Variables::). The expression `$NF' is not a special -feature: it is the direct consequence of evaluating `NF' and using its +feature--it is the direct consequence of evaluating `NF' and using its value as a field number. @@ -2596,36 +3049,38 @@ File: gawk.info, Node: Changing Fields, Next: Field Separators, Prev: Non-Con Changing the Contents of a Field ================================ - You can change the contents of a field as seen by `awk' within an + The contents of a field, as seen by `awk', can be changed within an `awk' program; this changes what `awk' perceives as the current input record. (The actual input is untouched; `awk' _never_ modifies the -input file.) - - Consider this example and its output: +input file.) Consider this example and its output: - $ awk '{ $3 = $2 - 10; print $2, $3 }' inventory-shipped + $ awk '{ nboxes = $3 ; $3 = $3 - 10 + > print nboxes, $3 }' inventory-shipped -| 13 3 -| 15 5 -| 15 5 ... -The `-' sign represents subtraction, so this program reassigns field -three, `$3', to be the value of field two minus ten, `$2 - 10'. (*Note -Arithmetic Operators: Arithmetic Ops.) Then field two, and the new -value for field three, are printed. - - In order for this to work, the text in field `$2' must make sense as -a number; the string of characters must be converted to a number in -order for the computer to do arithmetic on it. The number resulting -from the subtraction is converted back to a string of characters which -then becomes field three. *Note Conversion of Strings and Numbers: +The program first saves the original value of field three in the +variable `nboxes'. The `-' sign represents subtraction, so this +program reassigns field three, `$3', as the original value of field +three minus ten: `$3 - 10'. (*Note Arithmetic Operators: Arithmetic +Ops.) Then it prints the original and new values for field three. +(Someone in the warehouse made a consistent mistake while inventorying +the red boxes.) + + For this to work, the text in field `$2' must make sense as a +number; the string of characters must be converted to a number for the +computer to do arithmetic on it. The number resulting from the +subtraction is converted back to a string of characters that then +becomes field three. *Note Conversion of Strings and Numbers: Conversion. - When you change the value of a field (as perceived by `awk'), the + When the value of a field is changed (as perceived by `awk'), the text of the input record is recalculated to contain the new field where -the old one was. Therefore, `$0' changes to reflect the altered field. -Thus, this program prints a copy of the input file, with 10 subtracted -from the second field of each line. +the old one was. In other words, `$0' changes to reflect the altered +field. Thus, this program prints a copy of the input file, with 10 +subtracted from the second field of each line: $ awk '{ $2 = $2 - 10; print $0 }' inventory-shipped -| Jan 3 25 15 115 @@ -2633,8 +3088,8 @@ from the second field of each line. -| Mar 5 24 34 228 ... - You can also assign contents to fields that are out of range. For -example: + It is also possible to also assign contents to fields that are out +of range. For example: $ awk '{ $6 = ($5 + $4 + $3 + $2) > print $6 }' inventory-shipped @@ -2649,16 +3104,17 @@ We've just created `$6', whose value is the sum of fields `$2', `$3', shipped for a particular month. Creating a new field changes `awk''s internal copy of the current -input record--the value of `$0'. Thus, if you do `print $0' after -adding a field, the record printed includes the new field, with the -appropriate number of field separators between it and the previously +input record, which is the value of `$0'. Thus, if you do `print $0' +after adding a field, the record printed includes the new field, with +the appropriate number of field separators between it and the previously existing fields. This recomputation affects and is affected by `NF' (the number of -fields; *note Examining Fields: Fields.), and by a feature that has not -been discussed yet, the "output field separator", `OFS', which is used -to separate the fields (*note Output Separators::). For example, the -value of `NF' is set to the number of the highest field you create. +fields; *note Examining Fields: Fields.). It is also affected by a +feature that has not been discussed yet: the "output field separator", +`OFS', used to separate the fields (*note Output Separators::). For +example, the value of `NF' is set to the number of the highest field +you create. Note, however, that merely _referencing_ an out-of-range field does _not_ change the value of either `$0' or `NF'. Referencing an @@ -2676,130 +3132,120 @@ and Comparison Expressions: Typing and Comparison, for more information about the `!=' operator.) It is important to note that making an assignment to an existing -field will change the value of `$0', but will not change the value of -`NF', even when you assign the empty string to a field. For example: +field changes the value of `$0' but does not change the value of `NF', +even when you assign the empty string to a field. For example: $ echo a b c d | awk '{ OFS = ":"; $2 = "" > print $0; print NF }' -| a::c:d -| 4 -The field is still there; it just has an empty value. You can tell -because there are two colons in a row. - - This example shows what happens if you create a new field. +The field is still there; it just has an empty value, denoted by the +two colons between `a' and `c'. This example shows what happens if you +create a new field: $ echo a b c d | awk '{ OFS = ":"; $2 = ""; $6 = "new" > print $0; print NF }' -| a::c:d::new -| 6 -The intervening field, `$5' is created with an empty value (indicated +The intervening field, `$5', is created with an empty value (indicated by the second pair of adjacent colons), and `NF' is updated with the value six. - Finally, decrementing `NF' will lose the values of the fields after -the new value of `NF', and `$0' will be recomputed. Here is an example: + Decrementing `NF' throws away the values of the fields after the new +value of `NF' and recomputes `$0'. (d.c.) Here is an example: - $ echo a b c d e f | ../gawk '{ print "NF =", NF; - > NF = 3; print $0 }' + $ echo a b c d e f | awk '{ print "NF =", NF; + > NF = 3; print $0 }' -| NF = 6 -| a b c + *Caution:* Some versions of `awk' don't rebuild `$0' when `NF' is +decremented. Caveat emptor. + File: gawk.info, Node: Field Separators, Next: Constant Size, Prev: Changing Fields, Up: Reading Files -Specifying How Fields are Separated +Specifying How Fields Are Separated =================================== - This section is rather long; it describes one of the most fundamental -operations in `awk'. - * Menu: -* Basic Field Splitting:: How fields are split with single characters - or simple strings. * Regexp Field Splitting:: Using regexps as the field separator. * Single Character Fields:: Making each character a separate field. -* Command Line Field Separator:: Setting `FS' from the command line. +* Command Line Field Separator:: Setting `FS' from the command-line. * Field Splitting Summary:: Some final points and a summary table. - -File: gawk.info, Node: Basic Field Splitting, Next: Regexp Field Splitting, Prev: Field Separators, Up: Field Separators - -The Basics of Field Separating ------------------------------- - The "field separator", which is either a single character or a regular expression, controls the way `awk' splits an input record into fields. `awk' scans the input record for character sequences that match the separator; the fields themselves are the text between the matches. - In the examples below, we use the bullet symbol "*" to represent -spaces in the output. - - If the field separator is `oo', then the following line: + In the examples that follow, we use the bullet symbol (*) to +represent spaces in the output. If the field separator is `oo', then +the following line: moo goo gai pan -would be split into three fields: `m', `*g' and `*gai*pan'. Note the +is split into three fields: `m', `*g', and `*gai*pan'. Note the leading spaces in the values of the second and third fields. The field separator is represented by the built-in variable `FS'. -Shell programmers take note! `awk' does _not_ use the name `IFS' which -is used by the POSIX compatible shells (such as the Bourne shell, `sh', -or the GNU Bourne-Again Shell, Bash). +Shell programmers take note: `awk' does _not_ use the name `IFS' that +is used by the POSIX-compliant shells (such as the Unix Bourne shell, +`sh', or `bash'). - You can change the value of `FS' in the `awk' program with the + The value of `FS' can be changed in the `awk' program with the assignment operator, `=' (*note Assignment Expressions: Assignment -Ops.). Often the right time to do this is at the beginning of -execution, before any input has been processed, so that the very first -record will be read with the proper separator. To do this, use the -special `BEGIN' pattern (*note The `BEGIN' and `END' Special Patterns: -BEGIN/END.). For example, here we set the value of `FS' to the string -`","': +Ops.). Often the right time to do this is at the beginning of execution +before any input has been processed, so that the very first record is +read with the proper separator. To do this, use the special `BEGIN' +pattern (*note The `BEGIN' and `END' Special Patterns: BEGIN/END.). +For example, here we set the value of `FS' to the string `","': awk 'BEGIN { FS = "," } ; { print $2 }' -Given the input line, +Given the input line: John Q. Smith, 29 Oak St., Walamazoo, MI 42139 this `awk' program extracts and prints the string `*29*Oak*St.'. - Sometimes your input data will contain separator characters that -don't separate fields the way you thought they would. For instance, the + Sometimes the input data contains separator characters that don't +separate fields the way you thought they would. For instance, the person's name in the example we just used might have a title or suffix -attached, such as `John Q. Smith, LXIX'. From input containing such a -name: +attached, such as: John Q. Smith, LXIX, 29 Oak St., Walamazoo, MI 42139 -the above program would extract `*LXIX', instead of `*29*Oak*St.'. If +The same program would extract `*LXIX', instead of `*29*Oak*St.'. If you were expecting the program to print the address, you would be -surprised. The moral is: choose your data layout and separator -characters carefully to prevent such problems. - - Normally, fields are separated by whitespace sequences (spaces, tabs -and newlines), not by single spaces: two spaces in a row do not delimit -an empty field. The default value of the field separator `FS' is a -string containing a single space, `" "'. If this value were -interpreted in the usual way, each space character would separate +surprised. The moral is to choose your data layout and separator +characters carefully to prevent such problems. (If the data is not in +a form that is easy to process, perhaps you can massage it first with a +separate `awk' program.) + + Fields are normally separated by whitespace sequences (spaces, tabs, +and newlines), not by single spaces. Two spaces in a row do not +delimit an empty field. The default value of the field separator `FS' +is a string containing a single space, `" "'. If `awk' interpreted +this value in the usual way, each space character would separate fields, so two spaces in a row would make an empty field between them. The reason this does not happen is that a single space as the value of -`FS' is a special case: it is taken to specify the default manner of +`FS' is a special case--it is taken to specify the default manner of delimiting fields. If `FS' is any other single character, such as `","', then each occurrence of that character separates two fields. Two consecutive occurrences delimit an empty field. If the character occurs at the beginning or the end of the line, that too delimits an empty field. The -space character is the only single character which does not follow these +space character is the only single character that does not follow these rules. -File: gawk.info, Node: Regexp Field Splitting, Next: Single Character Fields, Prev: Basic Field Splitting, Up: Field Separators +File: gawk.info, Node: Regexp Field Splitting, Next: Single Character Fields, Prev: Field Separators, Up: Field Separators Using Regular Expressions to Separate Fields -------------------------------------------- @@ -2813,26 +3259,24 @@ example, the assignment: FS = ", \t" makes every area of an input line that consists of a comma followed by a -space and a tab, into a field separator. (`\t' is an "escape sequence" +space and a tab into a field separator. (`\t' is an "escape sequence" that stands for a tab; *note Escape Sequences::, for the complete list of similar escape sequences.) - For a less trivial example of a regular expression, suppose you want -single spaces to separate fields the way single commas were used above. -You can set `FS' to `"[ ]"' (left bracket, space, right bracket). This -regular expression matches a single space and nothing else (*note -Regular Expressions: Regexp.). + For a less trivial example of a regular expression, try using single +spaces to separate fields the way single commas are used. `FS' can be +set to `"[ ]"' (left bracket, space, right bracket). This regular +expression matches a single space and nothing else (*note Regular +Expressions: Regexp.). There is an important difference between the two cases of `FS = " "' -(a single space) and `FS = "[ \t\n]+"' (left bracket, space, backslash, -"t", backslash, "n", right bracket, which is a regular expression -matching one or more spaces, tabs, or newlines). For both values of -`FS', fields are separated by runs of spaces, tabs and/or newlines. -However, when the value of `FS' is `" "', `awk' will first strip -leading and trailing whitespace from the record, and then decide where -the fields are. - - For example, the following pipeline prints `b': +(a single space) and `FS = "[ \t\n]+"' (a regular expression matching +one or more spaces, tabs, or newlines). For both values of `FS', +fields are separated by "runs" (multiple adjacent occurrences) of +spaces, tabs, and/or newlines. However, when the value of `FS' is +`" "', `awk' first strips leading and trailing whitespace from the +record and then decides where the fields are. For example, the +following pipeline prints `b': $ echo ' a b c d ' | awk '{ print $2 }' -| b @@ -2840,11 +3284,11 @@ the fields are. However, this pipeline prints `a' (note the extra spaces around each letter): - $ echo ' a b c d ' | awk 'BEGIN { FS = "[ \t]+" } + $ echo ' a b c d ' | awk 'BEGIN { FS = "[ \t\n]+" } > { print $2 }' -| a -In this case, the first field is "null", or empty. +In this case, the first field is "null" or empty. The stripping of leading and trailing whitespace also comes into play whenever `$0' is recomputed. For instance, study this pipeline: @@ -2856,8 +3300,8 @@ play whenever `$0' is recomputed. For instance, study this pipeline: The first `print' statement prints the record as it was read, with leading whitespace intact. The assignment to `$2' rebuilds `$0' by concatenating `$1' through `$NF' together, separated by the value of -`OFS'. Since the leading whitespace was ignored when finding `$1', it -is not part of the new `$0'. Finally, the last `print' statement +`OFS'. Because the leading whitespace was ignored when finding `$1', +it is not part of the new `$0'. Finally, the last `print' statement prints the new `$0'. @@ -2867,9 +3311,9 @@ Making Each Character a Separate Field -------------------------------------- There are times when you may want to examine each character of a -record separately. In `gawk', this is easy to do, you simply assign -the null string (`""') to `FS'. In this case, each individual character -in the record will become a separate field. Here is an example: +record separately. This can be done in `gawk' by simply assigning the +null string (`""') to `FS'. In this case, each individual character in +the record becomes a separate field. For example: $ echo a b | gawk 'BEGIN { FS = "" } > { @@ -2880,11 +3324,11 @@ in the record will become a separate field. Here is an example: -| Field 2 is -| Field 3 is b - Traditionally, the behavior for `FS' equal to `""' was not defined. -In this case, Unix `awk' would simply treat the entire record as only -having one field (d.c.). In compatibility mode (*note Command Line -Options: Options.), if `FS' is the null string, then `gawk' will also -behave this way. + Traditionally, the behavior of `FS' equal to `""' was not defined. +In this case, most versions of Unix `awk' simply treat the entire record +as only having one field. (d.c.) In compatibility mode (*note +Command-Line Options: Options.), if `FS' is the null string, then +`gawk' also behaves this way. File: gawk.info, Node: Command Line Field Separator, Next: Field Splitting Summary, Prev: Single Character Fields, Up: Field Separators @@ -2892,47 +3336,46 @@ File: gawk.info, Node: Command Line Field Separator, Next: Field Splitting Sum Setting `FS' from the Command Line ---------------------------------- - `FS' can be set on the command line. You use the `-F' option to do -so. For example: + `FS' can be set on the command line. Use the `-F' option to do so. +For example: awk -F, 'PROGRAM' INPUT-FILES -sets `FS' to be the `,' character. Notice that the option uses a -capital `F'. Contrast this with `-f', which specifies a file -containing an `awk' program. Case is significant in command line -options: the `-F' and `-f' options have nothing to do with each other. -You can use both options at the same time to set the `FS' variable -_and_ get an `awk' program from a file. +sets `FS' to the `,' character. Notice that the option uses a capital +`F' instead of a lowercase `-f', which specifies a file containing an +`awk' program. Case is significant in command-line options: the `-F' +and `-f' options have nothing to do with each other. You can use both +options at the same time to set the `FS' variable _and_ get an `awk' +program from a file. The value used for the argument to `-F' is processed in exactly the -same way as assignments to the built-in variable `FS'. This means that -if the field separator contains special characters, they must be escaped -appropriately. For example, to use a `\' as the field separator, you +same way as assignments to the built-in variable `FS'. Any special +characters in the field separator must be escaped appropriately. For +example, to use a `\' as the field separator on the command line, you would have to type: # same as FS = "\\" awk -F\\\\ '...' files ... -Since `\' is used for quoting in the shell, `awk' will see `-F\\'. -Then `awk' processes the `\\' for escape characters (*note Escape -Sequences::), finally yielding a single `\' to be used for the field +Because `\' is used for quoting in the shell, `awk' sees `-F\\'. Then +`awk' processes the `\\' for escape characters (*note Escape +Sequences::), finally yielding a single `\' to use for the field separator. - As a special case, in compatibility mode (*note Command Line + As a special case, in compatibility mode (*note Command-Line Options: Options.), if the argument to `-F' is `t', then `FS' is set to -the tab character. This is because if you type `-F\t' at the shell, -without any quotes, the `\' gets deleted, so `awk' figures that you -really want your fields to be separated with tabs, and not `t's. Use -`-v FS="t"' on the command line if you really do want to separate your -fields with `t's (*note Command Line Options: Options.). +the tab character. If you type `-F\t' at the shell, without any +quotes, the `\' gets deleted, so `awk' figures that you really want +your fields to be separated with tabs and not `t's. Use `-v FS="t"' or +`-F"[t]"' on the command line if you really do want to separate your +fields with `t's. For example, let's use an `awk' program file called `baud.awk' that -contains the pattern `/300/', and the action `print $1'. Here is the -program: +contains the pattern `/300/' and the action `print $1': /300/ { print $1 } - Let's also set `FS' to be the `-' character, and run the program on + Let's also set `FS' to be the `-' character and run the program on the file `BBS-list'. The following command prints a list of the names of the bulletin boards that operate at 300 baud and the first three digits of their phone numbers: @@ -2941,10 +3384,17 @@ digits of their phone numbers: -| aardvark 555 -| alpo -| barfly 555 - ... - -Note the second line of output. In the original file (*note Data Files -for the Examples: Sample Data Files.), the second line looked like this: + -| bites 555 + -| camelot 555 + -| core 555 + -| fooey 555 + -| foot 555 + -| macfoo 555 + -| sdace 555 + -| sabafoo 555 + +Note the second line of output. The second line in the original file +looked like this: alpo-net 555-3412 2400/1200/300 A @@ -2953,15 +3403,17 @@ separator, instead of the `-' in the phone number that was originally intended. This demonstrates why you have to be careful in choosing your field and record separators. - On many Unix systems, each user has a separate entry in the system -password file, one line per user. The information in these lines is -separated by colons. The first field is the user's logon name, and the -second is the user's encrypted password. A password file entry might + Perhaps the most common use of a single character as the field +separator occurs when processing the Unix system password file. On +many Unix systems, each user has a separate entry in the system password +file, one line per user. The information in these lines is separated +by colons. The first field is the user's logon name and the second is +the user's (encrypted or shadow) password. A password file entry might look like this: - arnold:xyzzy:2076:10:Arnold Robbins:/home/arnold:/bin/sh + arnold:xyzzy:2076:10:Arnold Robbins:/home/arnold:/bin/bash - The following program searches the system password file, and prints + The following program searches the system password file and prints the entries for users who have no password: awk -F: '$2 == ""' /etc/passwd @@ -2972,30 +3424,6 @@ File: gawk.info, Node: Field Splitting Summary, Prev: Command Line Field Separ Field Splitting Summary ----------------------- - According to the POSIX standard, `awk' is supposed to behave as if -each record is split into fields at the time that it is read. In -particular, this means that you can change the value of `FS' after a -record is read, and the value of the fields (i.e. how they were split) -should reflect the old value of `FS', not the new one. - - However, many implementations of `awk' do not work this way. -Instead, they defer splitting the fields until a field is actually -referenced. The fields will be split using the _current_ value of -`FS'! (d.c.) This behavior can be difficult to diagnose. The following -example illustrates the difference between the two methods. (The -`sed'(1) command prints just the first line of `/etc/passwd'.) - - sed 1q /etc/passwd | awk '{ FS = ":" ; print $1 }' - -will usually print - - root - -on an incorrect implementation of `awk', while `gawk' will print -something like - - root:nSijPlPhZZwgE:0:0:Root:/: - The following table summarizes how fields are split, based on the value of `FS'. (`==' means "is equal to.") @@ -3016,6 +3444,35 @@ value of `FS'. (`==' means "is equal to.") `FS == ""' Each individual character in the record becomes a separate field. + (This is a `gawk' extension; it is not specified by the POSIX + standard.) + +Advanced Notes: Changing `FS' Does Not Affect the Fields +-------------------------------------------------------- + + According to the POSIX standard, `awk' is supposed to behave as if +each record is split into fields at the time it is read. In +particular, this means that if you change the value of `FS' after a +record is read, the value of the fields (i.e., how they were split) +should reflect the old value of `FS', not the new one. + + However, many implementations of `awk' do not work this way. +Instead, they defer splitting the fields until a field is actually +referenced. The fields are split using the _current_ value of `FS'! +(d.c.) This behavior can be difficult to diagnose. The following +example illustrates the difference between the two methods. (The +`sed'(1) command prints just the first line of `/etc/passwd'.) + + sed 1q /etc/passwd | awk '{ FS = ":" ; print $1 }' + +which usually prints: + + root + +on an incorrect implementation of `awk', while `gawk' prints something +like: + + root:nSijPlPhZZwgE:0:0:Root:/: ---------- Footnotes ---------- @@ -3025,35 +3482,35 @@ defined by the POSIX standard. File: gawk.info, Node: Constant Size, Next: Multiple Line, Prev: Field Separators, Up: Reading Files -Reading Fixed-width Data +Reading Fixed-Width Data ======================== - (This section discusses an advanced, experimental feature. If you -are a novice `awk' user, you may wish to skip it on the first reading.) + (This minor node discusses an advanced feature of `awk'. If you are +a novice `awk' user, you might want to skip it on the first reading.) - `gawk' version 2.13 introduced a new facility for dealing with -fixed-width fields with no distinctive field separator. Data of this -nature arises, for example, in the input for old FORTRAN programs where -numbers are run together; or in the output of programs that did not + `gawk' version 2.13 introduced a facility for dealing with +fixed-width fields with no distinctive field separator. For example, +data of this nature arises in the input for old Fortran programs where +numbers are run together, or in the output of programs that did not anticipate the use of their output as input for other programs. An example of the latter is a table where all the columns are lined up by the use of a variable number of spaces and _empty fields are just -spaces_. Clearly, `awk''s normal field splitting based on `FS' will +spaces_. Clearly, `awk''s normal field splitting based on `FS' does not work well in this case. Although a portable `awk' program can use -a series of `substr' calls on `$0' (*note Built-in Functions for String -Manipulation: String Functions.), this is awkward and inefficient for a +a series of `substr' calls on `$0' (*note String Manipulation +Functions: String Functions.), this is awkward and inefficient for a large number of fields. The splitting of an input record into fixed-width fields is specified by assigning a string containing space-separated numbers to the built-in variable `FIELDWIDTHS'. Each number specifies the width -of the field _including_ columns between fields. If you want to ignore -the columns between fields, you can specify the width as a separate -field that is subsequently ignored. - - The following data is the output of the Unix `w' utility. It is -useful to illustrate the use of `FIELDWIDTHS'. +of the field, _including_ columns between fields. If you want to +ignore the columns between fields, you can specify the width as a +separate field that is subsequently ignored. It is a fatal error to +supply a field width that is not a positive number. The following data +is the output of the Unix `w' utility. It is useful to illustrate the +use of `FIELDWIDTHS': 10:06pm up 21 days, 14:04, 23 users User tty login idle JCPU PCPU what @@ -3067,9 +3524,11 @@ useful to illustrate the use of `FIELDWIDTHS'. dave ttyq4 26Jun9115days 46 46 wnewmail The following program takes the above input, converts the idle time -to number of seconds and prints out the first two fields and the -calculated idle time. (This program uses a number of `awk' features -that haven't been introduced yet.) +to number of seconds, and prints out the first two fields and the +calculated idle time. + + *Note:* This program uses a number of `awk' features that haven't +been introduced yet. BEGIN { FIELDWIDTHS = "9 6 10 6 7 7 35" } NR > 2 { @@ -3087,7 +3546,7 @@ that haven't been introduced yet.) print $1, $2, idle } - Here is the result of running the program on the data: + Running the program on the data produces the following results: hzuo ttyV0 0 hzang ttyV3 50 @@ -3099,10 +3558,10 @@ that haven't been introduced yet.) dave ttyq4 1296000 Another (possibly more practical) example of fixed-width input data -would be the input from a deck of balloting cards. In some parts of -the United States, voters mark their choices by punching holes in -computer cards. These cards are then processed to count the votes for -any particular candidate or on any particular issue. Since a voter may +is the input from a deck of balloting cards. In some parts of the +United States, voters mark their choices by punching holes in computer +cards. These cards are then processed to count the votes for any +particular candidate or on any particular issue. Because a voter may choose not to vote on some issue, any column on the card may be empty. An `awk' program for processing such data could use the `FIELDWIDTHS' feature to simplify reading the data. (Of course, getting `gawk' to @@ -3110,11 +3569,21 @@ run on a system with card readers is another story!) Assigning a value to `FS' causes `gawk' to return to using `FS' for field splitting. Use `FS = FS' to make this happen, without having to -know the current value of `FS'. +know the current value of `FS'. In order to tell which kind of field +splitting is in effect, use `PROCINFO["FS"]' (*note Built-in Variables +That Convey Information: Auto-set.). The value is `"FS"' if regular +field splitting is being used, or it is `"FIELDWIDTHS"' if fixed-width +field splitting is being used: + + if (PROCINFO["FS"] == "FS") + REGULAR FIELD SPLITTING ... + else + FIXED-WIDTH FIELD SPLITTING ... - This feature is still experimental, and may evolve over time. Note -that in particular, `gawk' does not attempt to verify the sanity of the -values used in the value of `FIELDWIDTHS'. + This information is useful when writing a function that needs to +temporarily change `FS' or `FIELDWIDTHS', read some records, and then +restore the original settings (*note Reading the User Database: Passwd +Functions., for an example of such a function). File: gawk.info, Node: Multiple Line, Next: Getline, Prev: Constant Size, Up: Reading Files @@ -3122,13 +3591,9 @@ File: gawk.info, Node: Multiple Line, Next: Getline, Prev: Constant Size, Up Multiple-Line Records ===================== - In some data bases, a single line cannot conveniently hold all the -information in one entry. In such cases, you can use multi-line -records. - - The first step in doing this is to choose your data format: when -records are not defined as single lines, how do you want to define them? -What should separate records? + In some databases, a single line cannot conveniently hold all the +information in one entry. In such cases, you can use multiline +records. The first step in doing this is to choose your data format. One technique is to use an unusual character or string to separate records. For example, you could use the formfeed character (written @@ -3139,49 +3604,49 @@ well be used, as long as it won't be part of the data in a record. Another technique is to have blank lines separate records. By a special dispensation, an empty string as the value of `RS' indicates -that records are separated by one or more blank lines. If you set `RS' -to the empty string, a record always ends at the first blank line -encountered. And the next record doesn't start until the first -non-blank line that follows--no matter how many blank lines appear in a -row, they are considered one record-separator. +that records are separated by one or more blank lines. When `RS' is set +to the empty string, each record always ends at the first blank line +encountered. The next record doesn't start until the first non-blank +line that follows. No matter how many blank lines appear in a row, they +all act as one record separator. (Blank lines must be completely +empty; lines that contain only whitespace do not count.) You can achieve the same effect as `RS = ""' by assigning the string `"\n\n+"' to `RS'. This regexp matches the newline at the end of the -record, and one or more blank lines after the record. In addition, a +record and one or more blank lines after the record. In addition, a regular expression always matches the longest possible sequence when there is a choice (*note How Much Text Matches?: Leftmost Longest.). So the next record doesn't start until the first non-blank line that follows--no matter how many blank lines appear in a row, they are -considered one record-separator. +considered one record separator. There is an important difference between `RS = ""' and `RS = "\n\n+"'. In the first case, leading newlines in the input data file are ignored, and if a file ends without extra blank lines after the last record, the final newline is removed from the record. In the -second case, this special processing is not done (d.c.). +second case, this special processing is not done. (d.c.) Now that the input is separated into records, the second step is to separate the fields in the record. One way to do this is to divide each of the lines into fields in the normal manner. This happens by default -as the result of a special feature: when `RS' is set to the empty +as the result of a special feature. When `RS' is set to the empty string, the newline character _always_ acts as a field separator. This is in addition to whatever field separations result from `FS'. The original motivation for this special exception was probably to -provide useful behavior in the default case (i.e. `FS' is equal to +provide useful behavior in the default case (i.e., `FS' is equal to `" "'). This feature can be a problem if you really don't want the -newline character to separate fields, since there is no way to prevent -it. However, you can work around this by using the `split' function to -break up the record manually (*note Built-in Functions for String -Manipulation: String Functions.). +newline character to separate fields, because there is no way to +prevent it. However, you can work around this by using the `split' +function to break up the record manually (*note String Manipulation +Functions: String Functions.). Another way to separate fields is to put each field on a separate line: to do this, just set the variable `FS' to the string `"\n"'. -(This simple regular expression matches a single newline.) - - A practical example of a data file organized this way might be a -mailing list, where each entry is separated by blank lines. If we have -a mailing list in a file named `addresses', that looks like this: +(This simple regular expression matches a single newline.) A practical +example of a data file organized this way might be a mailing list, +where each entry is separated by blank lines. Consider a mailing list +in a file named `addresses', that looks like this: Jane Doe 123 Main Street @@ -3192,7 +3657,7 @@ a mailing list in a file named `addresses', that looks like this: Smallville, MW 98765-4321 ... -A simple program to process this file would look like this: +A simple program to process this file is as follows: # addrs.awk --- simple mailing list program @@ -3221,10 +3686,9 @@ A simple program to process this file would look like this: ... *Note Printing Mailing Labels: Labels Program, for a more realistic -program that deals with address lists. - - The following table summarizes how records are split, based on the -value of `RS'. (`==' means "is equal to.") +program that deals with address lists. The following table summarizes +how records are split, based on the value of `RS'. (`==' means "is +equal to.") `RS == "\n"' Records are separated by the newline character (`\n'). In effect, @@ -3244,7 +3708,8 @@ value of `RS'. (`==' means "is equal to.") `RS == REGEXP' Records are separated by occurrences of characters that match REGEXP. Leading and trailing matches of REGEXP delimit empty - records. + records. (This is a `gawk' extension, it is not specified by the + POSIX standard.) In all cases, `gawk' sets `RT' to the input text that matched the value specified by `RS'. @@ -3261,43 +3726,40 @@ output from another program) or from the files specified on the command line. The `awk' language has a special built-in command called `getline' that can be used to read input under your explicit control. -* Menu: - -* Getline Intro:: Introduction to the `getline' function. -* Plain Getline:: Using `getline' with no arguments. -* Getline/Variable:: Using `getline' into a variable. -* Getline/File:: Using `getline' from a file. -* Getline/Variable/File:: Using `getline' into a variable from a - file. -* Getline/Pipe:: Using `getline' from a pipe. -* Getline/Variable/Pipe:: Using `getline' into a variable from a - pipe. -* Getline Summary:: Summary Of `getline' Variants. - - -File: gawk.info, Node: Getline Intro, Next: Plain Getline, Prev: Getline, Up: Getline - -Introduction to `getline' -------------------------- + The `getline' command is used in several different ways and should +_not_ be used by beginners. The examples that follow the explanation +of the `getline' command include material that has not been covered +yet. Therefore, come back and study the `getline' command _after_ you +have reviewed the rest of this Info file and have a good knowledge of +how `awk' works. - This command is used in several different ways, and should _not_ be -used by beginners. It is covered here because this is the chapter on -input. The examples that follow the explanation of the `getline' -command include material that has not been covered yet. Therefore, -come back and study the `getline' command _after_ you have reviewed the -rest of this Info file and have a good knowledge of how `awk' works. - - `getline' returns one if it finds a record, and zero if the end of -the file is encountered. If there is some error in getting a record, -such as a file that cannot be opened, then `getline' returns -1. In -this case, `gawk' sets the variable `ERRNO' to a string describing the -error that occurred. + The `getline' command returns one if it finds a record and zero if +the end of the file is encountered. If there is some error in getting +a record, such as a file that cannot be opened, then `getline' returns +-1. In this case, `gawk' sets the variable `ERRNO' to a string +describing the error that occurred. In the following examples, COMMAND stands for a string value that represents a shell command. +* Menu: + +* Plain Getline:: Using `getline' with no arguments. +* Getline/Variable:: Using `getline' into a variable. +* Getline/File:: Using `getline' from a file. +* Getline/Variable/File:: Using `getline' into a variable from a + file. +* Getline/Pipe:: Using `getline' from a pipe. +* Getline/Variable/Pipe:: Using `getline' into a variable from a + pipe. +* Getline/Coprocess:: Using `getline' from a coprocess. +* Getline/Variable/Coprocess:: Using `getline' into a variable from a + coprocess. +* Getline Notes:: Important things to know about `getline'. +* Getline Summary:: Summary of `getline' Variants. + -File: gawk.info, Node: Plain Getline, Next: Getline/Variable, Prev: Getline Intro, Up: Getline +File: gawk.info, Node: Plain Getline, Next: Getline/Variable, Prev: Getline, Up: Getline Using `getline' with No Arguments --------------------------------- @@ -3305,12 +3767,12 @@ Using `getline' with No Arguments The `getline' command can be used without arguments to read input from the current input file. All it does in this case is read the next input record and split it up into fields. This is useful if you've -finished processing the current record, but you want to do some special +finished processing the current record, but want to do some special processing _right now_ on the next record. Here's an example: - awk '{ + { if ((t = index($0, "/*")) != 0) { - # value will be "" if t is 1 + # value of `tmp' will be "" if t is 1 tmp = substr($0, 1, t - 1) u = index(substr($0, t + 2), "*/") while (u == 0) { @@ -3325,70 +3787,65 @@ processing _right now_ on the next record. Here's an example: } # substr expression will be "" if */ # occurred at end of line - $0 = tmp substr($0, t + u + 3) + $0 = tmp substr($0, u + 2) } print $0 - }' + } - This `awk' program deletes all C-style comments, `/* ... */', from + This `awk' program deletes all C-style comments (`/* ... */') from the input. By replacing the `print $0' with other statements, you could perform more complicated processing on the decommented input, -like searching for matches of a regular expression. This program has a -subtle problem--it does not work if one comment ends and another begins -on the same line. +such as searching for matches of a regular expression. (This program +has a subtle problem--it does not work if one comment ends and another +begins on the same line.) - This form of the `getline' command sets `NF' (the number of fields; -*note Examining Fields: Fields.), `NR' (the number of records read so -far; *note How Input is Split into Records: Records.), `FNR' (the -number of records read from this input file), and the value of `$0'. + This form of the `getline' command sets `NF', `NR', `FNR', and the +value of `$0'. - *Note:* the new value of `$0' is used in testing the patterns of any + *Note:* The new value of `$0' is used to test the patterns of any subsequent rules. The original value of `$0' that triggered the rule -which executed `getline' is lost (d.c.). By contrast, the `next' -statement reads a new record but immediately begins processing it -normally, starting with the first rule in the program. *Note The -`next' Statement: Next Statement. +that executed `getline' is lost. By contrast, the `next' statement +reads a new record but immediately begins processing it normally, +starting with the first rule in the program. *Note The `next' +Statement: Next Statement. File: gawk.info, Node: Getline/Variable, Next: Getline/File, Prev: Plain Getline, Up: Getline -Using `getline' Into a Variable +Using `getline' into a Variable ------------------------------- You can use `getline VAR' to read the next record from `awk''s input -into the variable VAR. No other processing is done. +into the variable VAR. No other processing is done. For example, +suppose the next line is a comment or a special string, and you want to +read it without triggering any rules. This form of `getline' allows +you to read that line and store it in a variable so that the main +read-a-line-and-check-each-rule loop of `awk' never sees it. The +following example swaps every two lines of input. The program is as +follows: - For example, suppose the next line is a comment, or a special string, -and you want to read it, without triggering any rules. This form of -`getline' allows you to read that line and store it in a variable so -that the main read-a-line-and-check-each-rule loop of `awk' never sees -it. + { + if ((getline tmp) > 0) { + print tmp + print $0 + } else + print $0 + } - The following example swaps every two lines of input. For example, -given: +It takes the following list: wan tew free phore -it outputs: +and produces these results: tew wan phore free -Here's the program: - - awk '{ - if ((getline tmp) > 0) { - print tmp - print $0 - } else - print $0 - }' - The `getline' command used in this way sets only the variables `NR' and `FNR' (and of course, VAR). The record is not split into fields, so the values of the fields (including `$0') and the value of `NF' do @@ -3400,68 +3857,59 @@ File: gawk.info, Node: Getline/File, Next: Getline/Variable/File, Prev: Getli Using `getline' from a File --------------------------- - Use `getline < FILE' to read the next record from the file FILE. -Here FILE is a string-valued expression that specifies the file name. -`< FILE' is called a "redirection" since it directs input to come from -a different place. + Use `getline < FILE' to read the next record from FILE. Here FILE +is a string-valued expression that specifies the file name. `< FILE' +is called a "redirection" because it directs input to come from a +different place. For example, the following program reads its input +record from the file `secondary.input' when it encounters a first field +with a value equal to 10 in the current input file: - For example, the following program reads its input record from the -file `secondary.input' when it encounters a first field with a value -equal to 10 in the current input file. - - awk '{ + { if ($1 == 10) { getline < "secondary.input" print } else print - }' + } - Since the main input stream is not used, the values of `NR' and -`FNR' are not changed. But the record read is split into fields in the -normal manner, so the values of `$0' and other fields are changed. So -is the value of `NF'. + Because the main input stream is not used, the values of `NR' and +`FNR' are not changed. However, the record it reads is split into +fields in the normal manner, so the values of `$0' and the other fields +are changed, resulting in a new value of `NF'. According to POSIX, `getline < EXPRESSION' is ambiguous if EXPRESSION contains unparenthesized operators other than `$'; for example, `getline < dir "/" file' is ambiguous because the -concatenation operator is not parenthesized, and you should write it as +concatenation operator is not parenthesized. You should write it as `getline < (dir "/" file)' if you want your program to be portable to -other `awk' implementations. +other `awk' implementations. (It happens that `gawk' gets it right, +but you should not rely on this. Parentheses make it easier to read.) File: gawk.info, Node: Getline/Variable/File, Next: Getline/Pipe, Prev: Getline/File, Up: Getline -Using `getline' Into a Variable from a File +Using `getline' into a Variable from a File ------------------------------------------- - Use `getline VAR < FILE' to read input the file FILE and put it in -the variable VAR. As above, FILE is a string-valued expression that -specifies the file from which to read. + Use `getline VAR < FILE' to read input from the file FILE, and put +it in the variable VAR. As above, FILE is a string-valued expression +that specifies the file from which to read. In this version of `getline', none of the built-in variables are -changed, and the record is not split into fields. The only variable -changed is VAR. +changed and the record is not split into fields. The only variable +changed is VAR. For example, the following program copies all the +input files to the output, except for records that say +`@include FILENAME'. Such a record is replaced by the contents of the +file FILENAME: - According to POSIX, `getline VAR < EXPRESSION' is ambiguous if -EXPRESSION contains unparenthesized operators other than `$'; for -example, `getline < dir "/" file' is ambiguous because the -concatenation operator is not parenthesized, and you should write it as -`getline < (dir "/" file)' if you want your program to be portable to -other `awk' implementations. - - For example, the following program copies all the input files to the -output, except for records that say `@include FILENAME'. Such a record -is replaced by the contents of the file FILENAME. - - awk '{ + { if (NF == 2 && $1 == "@include") { while ((getline line < $2) > 0) print line close($2) } else print - }' + } Note here how the name of the extra input file is not built into the program; it is taken directly from the data, from the second field on @@ -3469,13 +3917,13 @@ the `@include' line. The `close' function is called to ensure that if two identical `@include' lines appear in the input, the entire specified file is -included twice. *Note Closing Input and Output Files and Pipes: Close +included twice. *Note Closing Input and Output Redirections: Close Files And Pipes. One deficiency of this program is that it does not process nested -`@include' statements (`@include' statements in included files) the way -a true macro preprocessor would. *Note An Easy Way to Use Library -Functions: Igawk Program, for a program that does handle nested +`@include' statements (i.e., `@include' statements in included files) +the way a true macro preprocessor would. *Note An Easy Way to Use +Library Functions: Igawk Program, for a program that does handle nested `@include' statements. @@ -3484,16 +3932,15 @@ File: gawk.info, Node: Getline/Pipe, Next: Getline/Variable/Pipe, Prev: Getli Using `getline' from a Pipe --------------------------- - You can pipe the output of a command into `getline', using `COMMAND -| getline'. In this case, the string COMMAND is run as a shell command -and its output is piped into `awk' to be used as input. This form of -`getline' reads one record at a time from the pipe. - - For example, the following program copies its input to its output, -except for lines that begin with `@execute', which are replaced by the -output produced by running the rest of the line as a shell command: + The output of a command can also be piped into `getline', using +`COMMAND | getline'. In this case, the string COMMAND is run as a +shell command and its output is piped into `awk' to be used as input. +This form of `getline' reads one record at a time from the pipe. For +example, the following program copies its input to its output, except +for lines that begin with `@execute', which are replaced by the output +produced by running the rest of the line as a shell command: - awk '{ + { if ($1 == "@execute") { tmp = substr($0, 10) while ((tmp | getline) > 0) @@ -3501,13 +3948,12 @@ output produced by running the rest of the line as a shell command: close(tmp) } else print - }' + } The `close' function is called to ensure that if two identical `@execute' lines appear in the input, the command is run for each one. -*Note Closing Input and Output Files and Pipes: Close Files And Pipes. - - Given the input: +*Note Closing Input and Output Redirections: Close Files And Pipes. +Given the input: foo bar @@ -3527,97 +3973,147 @@ the program might produce: Notice that this program ran the command `who' and printed the result. (If you try this program yourself, you will of course get different -results, showing you who is logged in on your system.) +results, depending upon who is logged in on your system.) This variation of `getline' splits the record into fields, sets the value of `NF' and recomputes the value of `$0'. The values of `NR' and `FNR' are not changed. According to POSIX, `EXPRESSION | getline' is ambiguous if -EXPRESSION contains unparenthesized operators other than `$'; for +EXPRESSION contains unparenthesized operators other than `$'--for example, `"echo " "date" | getline' is ambiguous because the -concatenation operator is not parenthesized, and you should write it as +concatenation operator is not parenthesized. You should write it as `("echo " "date") | getline' if you want your program to be portable to other `awk' implementations. (It happens that `gawk' gets it right, but you should not rely on this. Parentheses make it easier to read, anyway.) -File: gawk.info, Node: Getline/Variable/Pipe, Next: Getline Summary, Prev: Getline/Pipe, Up: Getline +File: gawk.info, Node: Getline/Variable/Pipe, Next: Getline/Coprocess, Prev: Getline/Pipe, Up: Getline -Using `getline' Into a Variable from a Pipe +Using `getline' into a Variable from a Pipe ------------------------------------------- - When you use `COMMAND | getline VAR', the output of the command -COMMAND is sent through a pipe to `getline' and into the variable VAR. -For example, the following program reads the current date and time into -the variable `current_time', using the `date' utility, and then prints -it. + When you use `COMMAND | getline VAR', the output of COMMAND is sent +through a pipe to `getline' and into the variable VAR. For example, the +following program reads the current date and time into the variable +`current_time', using the `date' utility, and then prints it: - awk 'BEGIN { + BEGIN { "date" | getline current_time close("date") print "Report printed on " current_time - }' + } In this version of `getline', none of the built-in variables are -changed, and the record is not split into fields. +changed and the record is not split into fields. According to POSIX, `EXPRESSION | getline VAR' is ambiguous if EXPRESSION contains unparenthesized operators other than `$'; for example, `"echo " "date" | getline VAR' is ambiguous because the -concatenation operator is not parenthesized, and you should write it as +concatenation operator is not parenthesized. You should write it as `("echo " "date") | getline VAR' if you want your program to be portable to other `awk' implementations. (It happens that `gawk' gets it right, but you should not rely on this. Parentheses make it easier to read, anyway.) -File: gawk.info, Node: Getline Summary, Prev: Getline/Variable/Pipe, Up: Getline +File: gawk.info, Node: Getline/Coprocess, Next: Getline/Variable/Coprocess, Prev: Getline/Variable/Pipe, Up: Getline -Summary of `getline' Variants ------------------------------ +Using `getline' from a Coprocess +-------------------------------- - With all the forms of `getline', even though `$0' and `NF', may be -updated, the record will not be tested against all the patterns in the -`awk' program, in the way that would happen if the record were read -normally by the main processing loop of `awk'. However the new record -is tested against any subsequent rules. - - Many `awk' implementations limit the number of pipelines an `awk' -program may have open to just one! In `gawk', there is no such limit. -You can open as many pipelines as the underlying operating system will -permit. - - An interesting side-effect occurs if you use `getline' (without a -redirection) inside a `BEGIN' rule. Since an unredirected `getline' -reads from the command line data files, the first `getline' command -causes `awk' to set the value of `FILENAME'. Normally, `FILENAME' does -not have a value inside `BEGIN' rules, since you have not yet started -to process the command line data files (d.c.). (*Note The `BEGIN' and -`END' Special Patterns: BEGIN/END, also *note Built-in Variables that -Convey Information: Auto-set..) - - The following table summarizes the six variants of `getline', -listing which built-in variables are set by each one. + Input into `getline' from a pipe is a one-way operation. The +command that is started with `COMMAND | getline' only sends data _to_ +your `awk' program. + + On occasion, you might want to send data to another program for +processing and then read the results back. `gawk' allows you start a +"coprocess", with which two-way communications are possible. This is +done with the `|&' operator. Typically, you write data to the +coprocess first, and then read results back, as shown in the following: -`getline' - sets `$0', `NF', `FNR', and `NR'. + print "SOME QUERY" |& "db_server" + "db_server" |& getline -`getline VAR' - sets VAR, `FNR', and `NR'. +which sends a query to `db_server' and then reads the results. -`getline < FILE' - sets `$0', and `NF'. + The values of `NR' and `FNR' are not changed, because the main input +stream is not used. However, the record is split into fields in the +normal manner, thus changing the values of `$0', the other fields, and +of `NF'. -`getline VAR < FILE' - sets VAR. + Coprocesses are an advanced feature. They are discussed here only +because this is the minor node on `getline'. *Note Two-Way +Communications with Another Process: Two-way I/O, where coprocesses are +discussed in more detail. -`COMMAND | getline' - sets `$0', and `NF'. + +File: gawk.info, Node: Getline/Variable/Coprocess, Next: Getline Notes, Prev: Getline/Coprocess, Up: Getline + +Using `getline' into a Variable from a Coprocess +------------------------------------------------ + + When you use `COMMAND |& getline VAR', the output from the coprocess +COMMAND is sent through a two-way pipe to `getline' and into the +variable VAR. + + In this version of `getline', none of the built-in variables are +changed and the record is not split into fields. The only variable +changed is VAR. + + Coprocesses are an advanced feature. They are discussed here only +because this is the minor node on `getline'. *Note Two-Way +Communications with Another Process: Two-way I/O, where coprocesses are +discussed in more detail. + + +File: gawk.info, Node: Getline Notes, Next: Getline Summary, Prev: Getline/Variable/Coprocess, Up: Getline + +Points About `getline' to Remember +---------------------------------- + + Here are some miscellaneous points about `getline' that you should +bear in mind: + + * When `getline' changes the value of `$0' and `NF', `awk' does + _not_ automatically jump to the start of the program and start + testing the new record against every pattern. However, the new + record is tested against any subsequent rules. + + * Many `awk' implementations limit the number of pipelines that an + `awk' program may have open to just one. In `gawk', there is no + such limit. You can open as many pipelines (and coprocesses) as + the underlying operating system permits. + + * An interesting side effect occurs if you use `getline' without a + redirection inside a `BEGIN' rule. Because an unredirected + `getline' reads from the command-line data files, the first + `getline' command causes `awk' to set the value of `FILENAME'. + Normally, `FILENAME' does not have a value inside `BEGIN' rules, + because you have not yet started to process the command-line data + files. (d.c.) (*Note The `BEGIN' and `END' Special Patterns: + BEGIN/END, also *note Built-in Variables That Convey Information: + Auto-set..) + + +File: gawk.info, Node: Getline Summary, Prev: Getline Notes, Up: Getline -`COMMAND | getline VAR' - sets VAR. +Summary of `getline' Variants +----------------------------- + + The following table summarizes the eight variants of `getline', +listing which built-in variables are set by each one. + +`getline' Sets `$0', `NF', `FNR' and `NR' +`getline' VAR Sets VAR, `FNR' and `NR' +`getline <' FILE Sets `$0' and `NF' +`getline VAR < FILE' Sets VAR +COMMAND `| getline' Sets `$0' and `NF' +COMMAND `| getline' VAR Sets VAR +COMMAND `|& getline' Sets `$0' and `NF' (this is a `gawk' + extension) +COMMAND `|& getline' VAR Sets VAR (this is a `gawk' extension) File: gawk.info, Node: Printing, Next: Expressions, Prev: Reading Files, Up: Top @@ -3625,10 +4121,21 @@ File: gawk.info, Node: Printing, Next: Expressions, Prev: Reading Files, Up: Printing Output *************** - One of the most common actions is to "print", or output, some or all -of the input. You use the `print' statement for simple output. You -use the `printf' statement for fancier formatting. Both are described -in this chapter. + One of the most common programming actions is to "print" or output, +some or all of the input. Use the `print' statement for simple output, +and the `printf' statement for fancier formatting. The `print' +statement is not limited when computing _which_ values to print. +However, with two exceptions, you cannot specify _how_ to print +them--how many columns, whether to use exponential notation or not, and +so on. (For the exceptions, *note Output Separators::, and *Note +Controlling Numeric Output with `print': OFMT.) For that, you need the +`printf' statement (*note Using `printf' Statements for Fancier +Printing: Printf.). + + Besides basic and formatted printing, this major node also covers +I/O redirections to files and pipes, introduces the special file names +that `gawk' processes internally, and discusses the `close' built-in +function. * Menu: @@ -3650,44 +4157,29 @@ File: gawk.info, Node: Print, Next: Print Examples, Prev: Printing, Up: Prin The `print' Statement ===================== - The `print' statement does output with simple, standardized -formatting. You specify only the strings or numbers to be printed, in a -list separated by commas. They are output, separated by single spaces, -followed by a newline. The statement looks like this: + The `print' statement is used to produce output with simple, +standardized formatting. Specify only the strings or numbers to print, +in a list separated by commas. They are output, separated by single +spaces, followed by a newline. The statement looks like this: print ITEM1, ITEM2, ... -The entire list of items may optionally be enclosed in parentheses. The +The entire list of items may be optionally enclosed in parentheses. The parentheses are necessary if any of the item expressions uses the `>' relational operator; otherwise it could be confused with a redirection (*note Redirecting Output of `print' and `printf': Redirection.). - The items to be printed can be constant strings or numbers, fields -of the current record (such as `$1'), variables, or any `awk' -expressions. Numeric values are converted to strings, and then printed. - - The `print' statement is completely general for computing _what_ -values to print. However, with two exceptions, you cannot specify _how_ -to print them--how many columns, whether to use exponential notation or -not, and so on. (For the exceptions, *note Output Separators::, and -*Note Controlling Numeric Output with `print': OFMT.) For that, you -need the `printf' statement (*note Using `printf' Statements for -Fancier Printing: Printf.). + The items to print can be constant strings or numbers, fields of the +current record (such as `$1'), variables, or any `awk' expression. +Numeric values are converted to strings and then printed. The simple statement `print' with no items is equivalent to `print $0': it prints the entire current record. To print a blank line, use -`print ""', where `""' is the empty string. - - To print a fixed piece of text, use a string constant such as -`"Don't Panic"' as one item. If you forget to use the double-quote -characters, your text will be taken as an `awk' expression, and you -will probably get an error. Keep in mind that a space is printed -between any two items. - - Each `print' statement makes at least one line of output. But it -isn't limited to one line. If an item value is a string that contains a -newline, the newline is output along with the rest of the string. A -single `print' can make any number of lines this way. +`print ""', where `""' is the empty string. To print a fixed piece of +text, use a string constant, such as `"Don't Panic"', as one item. If +you forget to use the double quote characters, your text is taken as an +`awk' expression and you will probably get an error. Keep in mind that +a space is printed between any two items. File: gawk.info, Node: Print Examples, Next: Output Separators, Prev: Print, Up: Printing @@ -3695,17 +4187,24 @@ File: gawk.info, Node: Print Examples, Next: Output Separators, Prev: Print, Examples of `print' Statements ============================== - Here is an example of printing a string that contains embedded -newlines (the `\n' is an escape sequence, used to represent the newline -character; *note Escape Sequences::): + Each `print' statement makes at least one line of output. However, +it isn't limited to only one line. If an item value is a string that +contains a newline, the newline is output along with the rest of the +string. A single `print' statement can make any number of lines this +way. + + The following is an example of printing a string that contains +embedded newlines (the `\n' is an escape sequence, used to represent +the newline character; *note Escape Sequences::): $ awk 'BEGIN { print "line one\nline two\nline three" }' -| line one -| line two -| line three - Here is an example that prints the first two fields of each input -record, with a space between them: + The next example, which is run on the `inventory-shipped' file, +prints the first two fields of each input record, with a space between +them: $ awk '{ print $1, $2 }' inventory-shipped -| Jan 13 @@ -3725,19 +4224,18 @@ Here is the same program, without the comma: -| Mar15 ... - To someone unfamiliar with the file `inventory-shipped', neither + To someone unfamiliar with the `inventory-shipped' file, neither example's output makes much sense. A heading line at the beginning would make it clearer. Let's add some headings to our table of months (`$1') and green crates shipped (`$2'). We do this using the `BEGIN' -pattern (*note The `BEGIN' and `END' Special Patterns: BEGIN/END.) to -force the headings to be printed only once: +pattern (*note The `BEGIN' and `END' Special Patterns: BEGIN/END.) so +that the headings are only printed once: awk 'BEGIN { print "Month Crates" print "----- ------" } { print $1, $2 }' inventory-shipped -Did you already guess what happens? When run, the program prints the -following: +When run, the program prints the following: Month Crates ----- ------ @@ -3746,23 +4244,24 @@ following: Mar 15 ... -The headings and the table data don't line up! We can fix this by -printing some spaces between the two fields: +The only problem, however, is that the headings and the table data +don't line up! We can fix this by printing some spaces between the two +fields: awk 'BEGIN { print "Month Crates" print "----- ------" } { print $1, " ", $2 }' inventory-shipped - You can imagine that this way of lining up columns can get pretty -complicated when you have many columns to fix. Counting spaces for two -or three columns can be simple, but more than this and you can get lost -quite easily. This is why the `printf' statement was created (*note -Using `printf' Statements for Fancier Printing: Printf.); one of its -specialties is lining up columns of data. + Lining up columns this way can get pretty complicated when there are +many columns to fix. Counting spaces for two or three columns is +simple, but any more than this can take up a lot of time. This is why +the `printf' statement was created (*note Using `printf' Statements for +Fancier Printing: Printf.); one of its specialties is lining up columns +of data. - As a side point, you can continue either a `print' or `printf' -statement simply by putting a newline after any comma (*note `awk' -Statements Versus Lines: Statements/Lines.). + *Note:* You can continue either a `print' or `printf' statement +simply by putting a newline after any comma (*note `awk' Statements +Versus Lines: Statements/Lines.). File: gawk.info, Node: Output Separators, Next: OFMT, Prev: Print Examples, Up: Printing @@ -3771,31 +4270,28 @@ Output Separators ================= As mentioned previously, a `print' statement contains a list of -items, separated by commas. In the output, the items are normally -separated by single spaces. This need not be the case; a single space -is only the default. You can specify any string of characters to use -as the "output field separator" by setting the built-in variable `OFS'. -The initial value of this variable is the string `" "', that is, a -single space. +items separated by commas. In the output, the items are normally +separated by single spaces. However, this doesn't need to be the case; +a single space is only the default. Any string of characters may be +used as the "output field separator" by setting the built-in variable +`OFS'. The initial value of this variable is the string `" "'--that +is, a single space. The output from an entire `print' statement is called an "output -record". Each `print' statement outputs one output record and then -outputs a string called the "output record separator". The built-in -variable `ORS' specifies this string. The initial value of `ORS' is -the string `"\n"', i.e. a newline character; thus, normally each -`print' statement makes a separate line. - - You can change how output fields and records are separated by -assigning new values to the variables `OFS' and/or `ORS'. The usual -place to do this is in the `BEGIN' rule (*note The `BEGIN' and `END' -Special Patterns: BEGIN/END.), so that it happens before any input is -processed. You may also do this with assignments on the command line, -before the names of your input files, or using the `-v' command line -option (*note Command Line Options: Options.). - - The following example prints the first and second fields of each -input record separated by a semicolon, with a blank line added after -each line: +record". Each `print' statement outputs one output record, and then +outputs a string called the "output record separator" (or `ORS'). The +initial value of `ORS' is the string `"\n"'; i.e., a newline character. +Thus, each `print' statement normally makes a separate line. + + In order to change how output fields and records are separated, +assign new values to the variables `OFS' and `ORS'. The usual place to +do this is in the `BEGIN' rule (*note The `BEGIN' and `END' Special +Patterns: BEGIN/END.), so that it happens before any input is +processed. It can also be done with assignments on the command line, +before the names of the input files, or using the `-v' command-line +option (*note Command-Line Options: Options.). The following example +prints the first and second fields of each input record, separated by a +semicolon, with a blank line added after each newline: $ awk 'BEGIN { OFS = ";"; ORS = "\n\n" } > { print $1, $2 }' BBS-list @@ -3806,9 +4302,8 @@ each line: -| barfly;555-7685 ... - If the value of `ORS' does not contain a newline, all your output -will be run together on a single line, unless you output newlines some -other way. + If the value of `ORS' does not contain a newline, the program's +output is run together on a single line. File: gawk.info, Node: OFMT, Next: Printf, Prev: Output Separators, Up: Printing @@ -3816,31 +4311,31 @@ File: gawk.info, Node: OFMT, Next: Printf, Prev: Output Separators, Up: Prin Controlling Numeric Output with `print' ======================================= - When you use the `print' statement to print numeric values, `awk' -internally converts the number to a string of characters, and prints + When the `print' statement is used to print numeric values, `awk' +internally converts the number to a string of characters and prints that string. `awk' uses the `sprintf' function to do this conversion -(*note Built-in Functions for String Manipulation: String Functions.). -For now, it suffices to say that the `sprintf' function accepts a -"format specification" that tells it how to format numbers (or -strings), and that there are a number of different ways in which -numbers can be formatted. The different format specifications are -discussed more fully in *Note Format-Control Letters: Control Letters. +(*note String Manipulation Functions: String Functions.). For now, it +suffices to say that the `sprintf' function accepts a "format +specification" that tells it how to format numbers (or strings), and +that there are a number of different ways in which numbers can be +formatted. The different format specifications are discussed more +fully in *Note Format-Control Letters: Control Letters. The built-in variable `OFMT' contains the default format specification that `print' uses with `sprintf' when it wants to convert a number to a string for printing. The default value of `OFMT' is -`"%.6g"'. By supplying different format specifications as the value of -`OFMT', you can change how `print' will print your numbers. As a brief -example: +`"%.6g"'. The way `print' prints numbers can be changed by supplying +different format specifications as the value of `OFMT', as shown in the +following example: $ awk 'BEGIN { > OFMT = "%.0f" # print numbers as integers (rounds) - > print 17.23 }' - -| 17 + > print 17.23, 17.54 }' + -| 17 18 -According to the POSIX standard, `awk''s behavior will be undefined if -`OFMT' contains anything but a floating point conversion specification -(d.c.). +According to the POSIX standard, `awk''s behavior is undefined if +`OFMT' contains anything but a floating-point conversion specification. +(d.c.) File: gawk.info, Node: Printf, Next: Redirection, Prev: OFMT, Up: Printing @@ -3848,13 +4343,14 @@ File: gawk.info, Node: Printf, Next: Redirection, Prev: OFMT, Up: Printing Using `printf' Statements for Fancier Printing ============================================== - If you want more precise control over the output format than `print' -gives you, use `printf'. With `printf' you can specify the width to -use for each item, and you can specify various formatting choices for -numbers (such as what radix to use, whether to print an exponent, -whether to print a sign, and how many digits to print after the decimal -point). You do this by supplying a string, called the "format string", -which controls how and where to print the other arguments. + For more precise control over the output format than what is +normally provided by `print', use `printf'. `printf' can be used to +specify the width to use for each item, as well as various formatting +choices for numbers (such as what output base to use, whether to print +an exponent, whether to print a sign, and how many digits to print +after the decimal point). This is done by supplying a string, called +the "format string", that controls how and where to print the other +arguments. * Menu: @@ -3869,39 +4365,40 @@ File: gawk.info, Node: Basic Printf, Next: Control Letters, Prev: Printf, Up Introduction to the `printf' Statement -------------------------------------- - The `printf' statement looks like this: + A simple `printf' statement looks like this: printf FORMAT, ITEM1, ITEM2, ... The entire list of arguments may optionally be enclosed in parentheses. The parentheses are necessary if any of the item expressions use the -`>' relational operator; otherwise it could be confused with a -redirection (*note Redirecting Output of `print' and `printf': -Redirection.). +`>' relational operator; otherwise it can be confused with a redirection +(*note Redirecting Output of `print' and `printf': Redirection.). The difference between `printf' and `print' is the FORMAT argument. This is an expression whose value is taken as a string; it specifies how to output each of the other arguments. It is called the "format string". - The format string is very similar to that in the ANSI C library -function `printf'. Most of FORMAT is text to be output verbatim. -Scattered among this text are "format specifiers", one per item. Each + The format string is very similar to that in the ISO C library +function `printf'. Most of FORMAT is text to output verbatim. +Scattered among this text are "format specifiers"--one per item. Each format specifier says to output the next item in the argument list at that place in the format. - The `printf' statement does not automatically append a newline to its -output. It outputs only what the format string specifies. So if you -want a newline, you must include one in the format string. The output -separator variables `OFS' and `ORS' have no effect on `printf' + The `printf' statement does not automatically append a newline to +its output. It outputs only what the format string specifies. So if a +newline is needed, you must include one in the format string. The +output separator variables `OFS' and `ORS' have no effect on `printf' statements. For example: - BEGIN { - ORS = "\nOUCH!\n"; OFS = "!" - msg = "Don't Panic!"; printf "%s\n", msg - } + $ awk 'BEGIN { + > ORS = "\nOUCH!\n"; OFS = "+" + > msg = "Dont Panic!" + > printf "%s\n", msg + > }' + -| Dont Panic! - This program still prints the familiar `Don't Panic!' message. +Here, neither the `+' nor the `OUCH' appear when the message is printed. File: gawk.info, Node: Control Letters, Next: Format Modifiers, Prev: Basic Printf, Up: Printf @@ -3910,79 +4407,71 @@ Format-Control Letters ---------------------- A format specifier starts with the character `%' and ends with a -"format-control letter"; it tells the `printf' statement how to output -one item. (If you actually want to output a `%', write `%%'.) The -format-control letter specifies what kind of value to print. The rest -of the format specifier is made up of optional "modifiers" which are -parameters to use, such as the field width. - - Here is a list of the format-control letters: +"format-control letter"--it tells the `printf' statement how to output +one item. The format-control letter specifies what _kind_ of value to +print. The rest of the format specifier is made up of optional +"modifiers" that control _how_ to print the value, such as the field +width. Here is a list of the format-control letters: -`c' - This prints a number as an ASCII character. Thus, `printf "%c", - 65' outputs the letter `A'. The output for a string value is the - first character of the string. +`%c' + This prints a number as an ASCII character; thus, `printf "%c", + 65' outputs the letter `A'. (The output for a string value is the + first character of the string.) -`d' -`i' - These are equivalent. They both print a decimal integer. The `%i' - specification is for compatibility with ANSI C. +`%d, %i' + These are equivalent; they both print a decimal integer. (The + `%i' specification is for compatibility with ISO C.) -`e' -`E' - This prints a number in scientific (exponential) notation. For - example, +`%e, %E' + These print a number in scientific (exponential) notation; for + example: printf "%4.3e\n", 1950 - prints `1.950e+03', with a total of four significant figures of - which three follow the decimal point. The `4.3' are modifiers, - discussed below. `%E' uses `E' instead of `e' in the output. + prints `1.950e+03', with a total of four significant figures, + three of which follow the decimal point. (The `4.3' represents + two modifiers, discussed in the next node.) `%E' uses `E' instead + of `e' in the output. -`f' - This prints a number in floating point notation. For example, +`%f' + This prints a number in floating-point notation. For example: printf "%4.3f", 1950 - prints `1950.000', with a total of four significant figures of - which three follow the decimal point. The `4.3' are modifiers, - discussed below. + prints `1950.000', with a total of four significant figures, three + of which follow the decimal point. (The `4.3' represents two + modifiers, discussed in the next node.) -`g' -`G' - This prints a number in either scientific notation or floating - point notation, whichever uses fewer characters. If the result is - printed in scientific notation, `%G' uses `E' instead of `e'. +`%g, %G' + These print a number in either scientific notation or in + floating-point notation, whichever uses fewer characters; if the + result is printed in scientific notation, `%G' uses `E' instead of + `e'. -`o' - This prints an unsigned octal integer. (In octal, or base-eight - notation, the digits run from `0' to `7'; the decimal number eight - is represented as `10' in octal.) +`%o' + This prints an unsigned octal integer. -`s' +`%s' This prints a string. -`u' - This prints an unsigned decimal number. (This format is of - marginal use, since all numbers in `awk' are floating point. It +`%u' + This prints an unsigned decimal integer. (This format is of + marginal use, because all numbers in `awk' are floating-point; it is provided primarily for compatibility with C.) -`x' -`X' - This prints an unsigned hexadecimal integer. (In hexadecimal, or - base-16 notation, the digits are `0' through `9' and `a' through - `f'. The hexadecimal digit `f' represents the decimal number 15.) - `%X' uses the letters `A' through `F' instead of `a' through `f'. +`%x, %X' + These print an unsigned hexadecimal integer; `%X' uses the letters + `A' through `F' instead of `a' through `f'. -`%' - This isn't really a format-control letter, but it does have a - meaning when used after a `%': the sequence `%%' outputs one `%'. - It does not consume an argument, and it ignores any modifiers. +`%%' + This isn't a format-control letter but it does have meaning--the + sequence `%%' outputs one `%'; it does not consume an argument and + it ignores any modifiers. - When using the integer format-control letters for values that are -outside the range of a C `long' integer, `gawk' will switch to the `%g' -format specifier. Other versions of `awk' may print invalid values, or -do something else entirely (d.c.). + *Note:* When using the integer format-control letters for values +that are outside the range of a C `long' integer, `gawk' switches to the +`%g' format specifier. Other versions of `awk' may print invalid values +or do something else entirely. (d.c.) File: gawk.info, Node: Format Modifiers, Next: Printf Examples, Prev: Control Letters, Up: Printf @@ -3991,50 +4480,69 @@ Modifiers for `printf' Formats ------------------------------ A format specification can also include "modifiers" that can control -how much of the item's value is printed and how much space it gets. The -modifiers come between the `%' and the format-control letter. In the -examples below, we use the bullet symbol "*" to represent spaces in the -output. Here are the possible modifiers, in the order in which they may -appear: +how much of the item's value is printed, as well as how much space it +gets. The modifiers come between the `%' and the format-control letter. +We will use the bullet symbol "*" in the following examples to represent +spaces in the output. Here are the possible modifiers, in the order in +which they may appear: + +`N$' + An integer constant followed by a `$' is a "positional specifier". + Normally, format specifications are applied to arguments in the + order given in the format string. With a positional specifier, + the format specification is applied to a specific argument, + instead of what would be the next argument in the list. + Positional specifiers begin counting with one: + + printf "%s %s\n", "don't", "panic" + printf "%2$s %1$s\n", "panic", "don't" + + prints the famous friendly message twice. + + At first glance, this feature doesn't seem to be of much use. It + is in fact a `gawk' extension, intended for use in translating + messages at runtime. *Note Rearranging `printf' Arguments: Printf + Ordering, which describes how and why to use positional specifiers. + For now, we will not use them. `-' - The minus sign, used before the width modifier (see below), says - to left-justify the argument within its specified width. Normally - the argument is printed right-justified in the specified width. - Thus, + The minus sign, used before the width modifier (see further on in + this table), says to left-justify the argument within its + specified width. Normally, the argument is printed + right-justified in the specified width. Thus: printf "%-4s", "foo" prints `foo*'. `SPACE' - For numeric conversions, prefix positive values with a space, and + For numeric conversions, prefix positive values with a space and negative values with a minus sign. `+' - The plus sign, used before the width modifier (see below), says to - always supply a sign for numeric conversions, even if the data to - be formatted is positive. The `+' overrides the space modifier. + The plus sign, used before the width modifier (see further on in + this table), says to always supply a sign for numeric conversions, + even if the data to format is positive. The `+' overrides the + space modifier. `#' Use an "alternate form" for certain control letters. For `%o', - supply a leading zero. For `%x', and `%X', supply a leading `0x' - or `0X' for a non-zero result. For `%e', `%E', and `%f', the - result will always contain a decimal point. For `%g', and `%G', + supply a leading zero. For `%x' and `%X', supply a leading `0x' + or `0X' for a nonzero result. For `%e', `%E', and `%f', the + result always contains a decimal point. For `%g' and `%G', trailing zeros are not removed from the result. `0' - A leading `0' (zero) acts as a flag, that indicates output should - be padded with zeros instead of spaces. This applies even to - non-numeric output formats (d.c.). This flag only has an effect - when the field width is wider than the value to be printed. + A leading `0' (zero) acts as a flag that indicates that output + should be padded with zeros instead of spaces. This applies even + to non-numeric output formats. (d.c.) This flag only has an + effect when the field width is wider than the value to print. `WIDTH' This is a number specifying the desired minimum width of a field. - Inserting any number between the `%' sign and the format control - character forces the field to be expanded to this width. The - default way to do this is to pad with spaces on the left. For - example, + Inserting any number between the `%' sign and the format-control + character forces the field to expand to this width. The default + way to do this is to pad with spaces on the left. For example: printf "%4s", "foo" @@ -4042,7 +4550,7 @@ appear: The value of WIDTH is a minimum width, not a maximum. If the item value requires more than WIDTH characters, it can be as wide as - necessary. Thus, + necessary. Thus, the following: printf "%4s", "foobar" @@ -4052,14 +4560,24 @@ appear: padded with spaces on the right, instead of on the left. `.PREC' - This is a number that specifies the precision to use when printing. - For the `e', `E', and `f' formats, this specifies the number of - digits you want printed to the right of the decimal point. For - the `g', and `G' formats, it specifies the maximum number of - significant digits. For the `d', `o', `i', `u', `x', and `X' - formats, it specifies the minimum number of digits to print. For - a string, it specifies the maximum number of characters from the - string that should be printed. Thus, + A period followed by an integer constant specifies the precision + to use when printing. The meaning of the precision varies by + control letter: + + `%e', `%E', `%f' + Number of digits to the right of the decimal point. + + `%g', `%G' + Maximum number of significant digits. + + `%d', `%i', `%o', `%u', `%x', `%X' + Minimum number of digits to print. + + `%s' + Maximum number of characters from the string that should + print. + + Thus, the following: printf "%.4s", "foobar" @@ -4067,38 +4585,37 @@ appear: The C library `printf''s dynamic WIDTH and PREC capability (for example, `"%*.*s"') is supported. Instead of supplying explicit WIDTH -and/or PREC values in the format string, you pass them in the argument -list. For example: +and/or PREC values in the format string, they are passed in the +argument list. For example: w = 5 p = 3 s = "abcdefg" printf "%*.*s\n", w, p, s -is exactly equivalent to +is exactly equivalent to: s = "abcdefg" printf "%5.3s\n", s -Both programs output `**abc'. - - Earlier versions of `awk' did not support this capability. If you -must use such a version, you may simulate this feature by using -concatenation to build up the format string, like so: +Both programs output `**abc'. Earlier versions of `awk' did not +support this capability. If you must use such a version, you may +simulate this feature by using concatenation to build up the format +string, like so: w = 5 p = 3 s = "abcdefg" printf "%" w "." p "s\n", s -This is not particularly easy to read, but it does work. +This is not particularly easy to read but it does work. - C programmers may be used to supplying additional `l' and `h' flags -in `printf' format strings. These are not valid in `awk'. Most `awk' -implementations silently ignore these flags. If `--lint' is provided -on the command line (*note Command Line Options: Options.), `gawk' will -warn about their use. If `--posix' is supplied, their use is a fatal -error. + C programmers may be used to supplying additional `l', `L', and `h' +modifiers in `printf' format strings. These are not valid in `awk'. +Most `awk' implementations silently ignore these modifiers. If +`--lint' is provided on the command line (*note Command-Line Options: +Options.), `gawk' warns about their use. If `--posix' is supplied, +their use is a fatal error. File: gawk.info, Node: Printf Examples, Prev: Format Modifiers, Up: Printf @@ -4106,14 +4623,15 @@ File: gawk.info, Node: Printf Examples, Prev: Format Modifiers, Up: Printf Examples Using `printf' ----------------------- - Here is how to use `printf' to make an aligned table: + The following is a simple example of how to use `printf' to make an +aligned table: awk '{ printf "%-10s %s\n", $1, $2 }' BBS-list -prints the names of bulletin boards (`$1') of the file `BBS-list' as a -string of 10 characters, left justified. It also prints the phone -numbers (`$2') afterward on the line. This produces an aligned -two-column table of names and phone numbers: +This command prints the names of the bulletin boards (`$1') in the file +`BBS-list' as a string of 10 characters that are left-justified. It +also prints the phone numbers (`$2') next on the line. This produces +an aligned two-column table of names and phone numbers, as shown here: $ awk '{ printf "%-10s %s\n", $1, $2 }' BBS-list -| aardvark 555-5553 @@ -4128,35 +4646,34 @@ two-column table of names and phone numbers: -| sdace 555-3430 -| sabafoo 555-2127 - Did you notice that we did not specify that the phone numbers be -printed as numbers? They had to be printed as strings because the -numbers are separated by a dash. If we had tried to print the phone -numbers as numbers, all we would have gotten would have been the first -three digits, `555'. This would have been pretty confusing. + In this case, the phone numbers had to be printed as strings because +the numbers are separated by a dash. Printing the phone numbers as +numbers would have produced just the first three digits: `555'. This +would have been pretty confusing. - We did not specify a width for the phone numbers because they are the -last things on their lines. We don't need to put spaces after them. + It wasn't necessary to specify a width for the phone numbers because +they are last on their lines. They don't need to have spaces after +them. - We could make our table look even nicer by adding headings to the -tops of the columns. To do this, we use the `BEGIN' pattern (*note The -`BEGIN' and `END' Special Patterns: BEGIN/END.) to force the header to -be printed only once, at the beginning of the `awk' program: + The table could be made to look even nicer by adding headings to the +tops of the columns. This is done using the `BEGIN' pattern (*note The +`BEGIN' and `END' Special Patterns: BEGIN/END.) so that the headers +are only printed once, at the beginning of the `awk' program: awk 'BEGIN { print "Name Number" print "---- ------" } { printf "%-10s %s\n", $1, $2 }' BBS-list - Did you notice that we mixed `print' and `printf' statements in the -above example? We could have used just `printf' statements to get the -same results: + The above example mixed `print' and `printf' statements in the same +program. Using just `printf' statements can produce the same results: awk 'BEGIN { printf "%-10s %s\n", "Name", "Number" printf "%-10s %s\n", "----", "------" } { printf "%-10s %s\n", $1, $2 }' BBS-list -By printing each column heading with the same format specification used -for the elements of the column, we have made sure that the headings are -aligned just like the columns. +Printing each column heading with the same format specification used +for the column elements ensures that the headings are aligned just like +the columns. The fact that the same format specification is used three times can be emphasized by storing it in a variable, like this: @@ -4166,9 +4683,10 @@ be emphasized by storing it in a variable, like this: printf format, "----", "------" } { printf format, $1, $2 }' BBS-list - See if you can use the `printf' statement to line up the headings and -table data for our `inventory-shipped' example covered earlier in the -section on the `print' statement (*note The `print' Statement: Print.). + At this point, it would be a worthwhile exercise to use the `printf' +statement to line up the headings and table data for the +`inventory-shipped' example that was covered earlier in the minor node +on the `print' statement (*note The `print' Statement: Print.). File: gawk.info, Node: Redirection, Next: Special Files, Prev: Printf, Up: Printing @@ -4176,34 +4694,33 @@ File: gawk.info, Node: Redirection, Next: Special Files, Prev: Printf, Up: P Redirecting Output of `print' and `printf' ========================================== - So far we have been dealing only with output that prints to the -standard output, usually your terminal. Both `print' and `printf' can -also send their output to other places. This is called "redirection". + So far, the output from `print' and `printf' has gone to the standard +output, usually the terminal. Both `print' and `printf' can also send +their output to other places. This is called "redirection". A redirection appears after the `print' or `printf' statement. Redirections in `awk' are written just like redirections in shell commands, except that they are written inside the `awk' program. - There are three forms of output redirection: output to a file, -output appended to a file, and output through a pipe to another command. -They are all shown for the `print' statement, but they work identically -for `printf' also. + There are four forms of output redirection: output to a file, output +appended to a file, output through a pipe to another command, and output +to a coprocess. They are all shown for the `print' statement, but they +work identically for `printf': `print ITEMS > OUTPUT-FILE' This type of redirection prints the items into the output file - OUTPUT-FILE. The file name OUTPUT-FILE can be any expression. - Its value is changed to a string and then used as a file name - (*note Expressions::). + named OUTPUT-FILE. The file name OUTPUT-FILE can be any + expression. Its value is changed to a string and then used as a + file name (*note Expressions::). When this type of redirection is used, the OUTPUT-FILE is erased before the first output is written to it. Subsequent writes to the same OUTPUT-FILE do not erase OUTPUT-FILE, but append to it. - If OUTPUT-FILE does not exist, then it is created. - - For example, here is how an `awk' program can write a list of BBS - names to a file `name-list' and a list of phone numbers to a file - `phone-list'. Each output file contains one name or number per - line. + (This is different from how you use redirections in shell scripts.) + If OUTPUT-FILE does not exist, it is created. For example, here + is how an `awk' program can write a list of BBS names to one file + named `name-list', and a list of phone numbers to another file + named `phone-list': $ awk '{ print $2 > "phone-list" > print $1 > "name-list" }' BBS-list @@ -4216,9 +4733,11 @@ for `printf' also. -| alpo-net ... + Each output file contains one name or number per line. + `print ITEMS >> OUTPUT-FILE' This type of redirection prints the items into the pre-existing - output file OUTPUT-FILE. The difference between this and the + output file named OUTPUT-FILE. The difference between this and the single-`>' redirection is that the old contents (if any) of OUTPUT-FILE are not erased. Instead, the `awk' output is appended to the file. If OUTPUT-FILE does not exist, then it is created. @@ -4226,27 +4745,26 @@ for `printf' also. `print ITEMS | COMMAND' It is also possible to send output to another program through a pipe instead of into a file. This type of redirection opens a - pipe to COMMAND and writes the values of ITEMS through this pipe, + pipe to COMMAND, and writes the values of ITEMS through this pipe to another process created to execute COMMAND. The redirection argument COMMAND is actually an `awk' expression. - Its value is converted to a string, whose contents give the shell - command to be run. - - For example, this produces two files, one unsorted list of BBS - names and one list sorted in reverse alphabetical order: + Its value is converted to a string whose contents give the shell + command to be run. For example, the following produces two files, + one unsorted list of BBS names, and one list sorted in reverse + alphabetical order: awk '{ print $1 > "names.unsorted" command = "sort -r > names.sorted" print $1 | command }' BBS-list - Here the unsorted list is written with an ordinary redirection - while the sorted list is written by piping through the `sort' - utility. + The unsorted list is written with an ordinary redirection, while + the sorted list is written by piping through the `sort' utility. - This example uses redirection to mail a message to a mailing list - `bug-system'. This might be useful when trouble is encountered in - an `awk' script run periodically for system maintenance. + The next example uses redirection to mail a message to the mailing + list `bug-system'. This might be useful when trouble is + encountered in an `awk' script run periodically for system + maintenance: report = "mail bug-system" print "Awk script failed:", $0 | report @@ -4256,26 +4774,73 @@ for `printf' also. The message is built using string concatenation and saved in the variable `m'. It is then sent down the pipeline to the `mail' - program. + program. (The parentheses group the items to concatenate--see + *Note String Concatenation: Concatenation.) + + The `close' function is called here because it's a good idea to + close the pipe as soon as all the intended output has been sent to + it. *Note Closing Input and Output Redirections: Close Files And + Pipes, for more information on this. + + This example also illustrates the use of a variable to represent a + FILE or COMMAND--it is not necessary to always use a string + constant. Using a variable is generally a good idea, because + `awk' requires that the string value be spelled identically every + time. + +`print ITEMS |& COMMAND' + This type of redirection prints the items to the input of COMMAND. + The difference between this and the single-`|' redirection is that + the output from COMMAND can be read with `getline'. Thus COMMAND + is a "coprocess", that works together with, but subsidiary to, the + `awk' program. + + This feature is a `gawk' extension, and is not available in POSIX + `awk'. *Note Two-Way Communications with Another Process: Two-way + I/O, for a more complete discussion. + + Redirecting output using `>', `>>', `|', or `|&' asks the system to +open a file, pipe, or coprocess, only if the particular FILE or COMMAND +you specify has not already been written to by your program or if it +has been closed since it was last written to. + + It is a common error to use `>' redirection for the first `print' to +a file, and then to use `>>' for subsequent output: + + # clear the file + print "Don't panic" > "guide.txt" + ... + # append + print "Avoid improbability generators" >> "guide.txt" - We call the `close' function here because it's a good idea to close - the pipe as soon as all the intended output has been sent to it. - *Note Closing Input and Output Files and Pipes: Close Files And - Pipes, for more information on this. This example also - illustrates the use of a variable to represent a FILE or COMMAND: - it is not necessary to always use a string constant. Using a - variable is generally a good idea, since `awk' requires you to - spell the string value identically every time. +This is indeed how redirections must be used from the shell. But in +`awk', it isn't necessary. In this kind of case, a program should use +`>' for all the `print' statements, since the output file is only +opened once. - Redirecting output using `>', `>>', or `|' asks the system to open a -file or pipe only if the particular FILE or COMMAND you've specified -has not already been written to by your program, or if it has been -closed since it was last written to. + Many `awk' implementations limit the number of pipelines that an +`awk' program may have open to just one! In `gawk', there is no such +limit. `gawk' allows a program to open as many pipelines as the +underlying operating system permits. + +Advanced Notes: Piping into `sh' +-------------------------------- + + A particularly powerful way to use redirection is to build command +lines, and pipe them into the shell, `sh'. For example, suppose you +have a list of files brought over from a system where all the file names +are stored in uppercase, and you wish to rename them to have names in +all lowercase. The following program is both simple and efficient: + + { printf("mv %s %s\n", $0, tolower($0)) | "sh" } + + END { close("sh") } - Many `awk' implementations limit the number of pipelines an `awk' -program may have open to just one! In `gawk', there is no such limit. -You can open as many pipelines as the underlying operating system will -permit. + The `tolower' function returns its argument string with all +uppercase characters converted to lowercase (*note String Manipulation +Functions: String Functions.). The program builds up a list of command +lines, using the `mv' utility to rename the files. It then sends the +list to the shell for execution. File: gawk.info, Node: Special Files, Next: Close Files And Pipes, Prev: Redirection, Up: Printing @@ -4283,38 +4848,57 @@ File: gawk.info, Node: Special Files, Next: Close Files And Pipes, Prev: Redi Special File Names in `gawk' ============================ + `gawk' provides a number of special file names that it interprets +internally. These file names provide access to standard file +descriptors, process-related information, and TCP/IP networking. + +* Menu: + +* Special FD:: Special files for I/O. +* Special Process:: Special files for process information. +* Special Network:: Special files for network communications. +* Special Caveats:: Things to watch out for. + + +File: gawk.info, Node: Special FD, Next: Special Process, Prev: Special Files, Up: Special Files + +Special Files for Standard Descriptors +-------------------------------------- + Running programs conventionally have three input and output streams already available to them for reading and writing. These are known as the "standard input", "standard output", and "standard error output". These streams are, by default, connected to your terminal, but they are -often redirected with the shell, via the `<', `<<', `>', `>>', `>&' and -`|' operators. Standard error is typically used for writing error -messages; the reason we have two separate streams, standard output and -standard error, is so that they can be redirected separately. +often redirected with the shell, via the `<', `<<', `>', `>>', `>&', +and `|' operators. Standard error is typically used for writing error +messages; the reason there are two separate streams, standard output, +and standard error, is so that they can be redirected separately. In other implementations of `awk', the only way to write an error message to standard error in an `awk' program is as follows: print "Serious error detected!" | "cat 1>&2" -This works by opening a pipeline to a shell command which can access the -standard error stream which it inherits from the `awk' process. This -is far from elegant, and is also inefficient, since it requires a -separate process. So people writing `awk' programs often neglect to do +This works by opening a pipeline to a shell command that can access the +standard error stream that it inherits from the `awk' process. This is +far from elegant, and it is also inefficient, because it requires a +separate process. So people writing `awk' programs often don't do this. Instead, they send the error messages to the terminal, like this: print "Serious error detected!" > "/dev/tty" -This usually has the same effect, but not always: although the standard -error stream is usually the terminal, it can be redirected, and when -that happens, writing to the terminal is not correct. In fact, if -`awk' is run from a background job, it may not have a terminal at all. -Then opening `/dev/tty' will fail. +This usually has the same effect but not always: although the standard +error stream is usually the terminal, it can be redirected; when that +happens, writing to the terminal is not correct. In fact, if `awk' is +run from a background job, it may not have a terminal at all. Then +opening `/dev/tty' fails. `gawk' provides special file names for accessing the three standard -streams. When you redirect input or output in `gawk', if the file name -matches one of these special names, then `gawk' directly uses the -stream it stands for. +streams, as well as any other inherited open files. If the file name +matches one of these special names when `gawk' redirects input or +output, then it directly uses the stream that the file name stands for. +(These special file names work for all operating systems that `gawk' +has been ported to, not just those that are POSIX-compliant.): `/dev/stdin' The standard input (file descriptor 0). @@ -4326,39 +4910,46 @@ stream it stands for. The standard error output (file descriptor 2). `/dev/fd/N' - The file associated with file descriptor N. Such a file must have - been opened by the program initiating the `awk' execution - (typically the shell). Unless you take special pains in the shell - from which you invoke `gawk', only descriptors 0, 1 and 2 are - available. + The file associated with file descriptor N. Such a file must be + opened by the program initiating the `awk' execution (typically + the shell). Unless special pains are taken in the shell from which + `gawk' is invoked, only descriptors 0, 1, and 2 are available. The file names `/dev/stdin', `/dev/stdout', and `/dev/stderr' are -aliases for `/dev/fd/0', `/dev/fd/1', and `/dev/fd/2', respectively, -but they are more self-explanatory. - - The proper way to write an error message in a `gawk' program is to -use `/dev/stderr', like this: +aliases for `/dev/fd/0', `/dev/fd/1', and `/dev/fd/2', respectively. +However, they are more self-explanatory. The proper way to write an +error message in a `gawk' program is to use `/dev/stderr', like this: print "Serious error detected!" > "/dev/stderr" + Note the use of quotes around the file name. Like any other +redirection, the value must be a string. It is a common error to omit +the quotes, which leads to confusing results. + + +File: gawk.info, Node: Special Process, Next: Special Network, Prev: Special FD, Up: Special Files + +Special Files for Process-Related Information +--------------------------------------------- + `gawk' also provides special file names that give access to information about the running `gawk' process. Each of these "files" provides a single record of information. To read them more than once, -you must first close them with the `close' function (*note Closing -Input and Output Files and Pipes: Close Files And Pipes.). The -filenames are: +they must first be closed with the `close' function (*note Closing +Input and Output Redirections: Close Files And Pipes.). The file names +are: `/dev/pid' Reading this file returns the process ID of the current process, - in decimal, terminated with a newline. + in decimal form, terminated with a newline. `/dev/ppid' Reading this file returns the parent process ID of the current - process, in decimal, terminated with a newline. + process, in decimal form, terminated with a newline. `/dev/pgrpid' Reading this file returns the process group ID of the current - process, in decimal, terminated with a newline. + process, in decimal form, terminated with a newline. `/dev/user' Reading this file returns a single record terminated with a @@ -4382,56 +4973,103 @@ filenames are: group ID number). If there are any additional fields, they are the group IDs - returned by `getgroups' system call. (Multiple groups may not be - supported on all systems.) + returned by the `getgroups' system call. (Multiple groups may not + be supported on all systems.) These special file names may be used on the command line as data files, as well as for I/O redirections within an `awk' program. They may not be used as source files with the `-f' option. - Recognition of these special file names is disabled if `gawk' is in -compatibility mode (*note Command Line Options: Options.). + *Note:* The special files that provide process-related information +are now considered obsolete and will disappear entirely in the next +release of `gawk'. `gawk' prints a warning message every time you use +one of these files. To obtain process-related information, use the +`PROCINFO' array. *Note Built-in Variables That Convey Information: +Auto-set. + + +File: gawk.info, Node: Special Network, Next: Special Caveats, Prev: Special Process, Up: Special Files + +Special Files for Network Communications +---------------------------------------- + + Starting with version 3.1 of `gawk', `awk' programs can open a +two-way TCP/IP connection, acting as either a client or server. This +is done using a special file name of the form: - *Caution*: Unless your system actually has a `/dev/fd' directory -(or any of the other above listed special files), the interpretation of -these file names is done by `gawk' itself. For example, using -`/dev/fd/4' for output will actually write on file descriptor 4, and -not on a new file descriptor that was `dup''ed from file descriptor 4. -Most of the time this does not matter; however, it is important to -_not_ close any of the files related to file descriptors 0, 1, and 2. -If you do close one of these files, unpredictable behavior will result. + `/inet/PROTOCOL/LOCAL-PORT/REMOTE-HOST/REMOTE-PORT' - The special files that provide process-related information will -disappear in a future version of `gawk'. *Note Probable Future -Extensions: Future Extensions. + The PROTOCOL is one of `tcp', `udp', or `raw', and the other fields +represent the other essential pieces of information for making a +networking connection. These file names are used with the `|&' +operator for communicating with a coprocess (*note Two-Way +Communications with Another Process: Two-way I/O.). This is an +advanced feature, mentioned here only for completeness. Full +discussion is delayed until *Note Using `gawk' for Network Programming: +TCP/IP Networking. + + +File: gawk.info, Node: Special Caveats, Prev: Special Network, Up: Special Files + +Special File Name Caveats +------------------------- + + Here is a list of things to bear in mind when using the special file +names that `gawk' provides. + + * Recognition of these special file names is disabled if `gawk' is in + compatibility mode (*note Command-Line Options: Options.). + + * The special files that provide process-related information are now + considered obsolete and will disappear entirely in the next + release of `gawk'. `gawk' prints a warning message every time you + use one of these files. To obtain process-related information, + use the `PROCINFO' array. *Note Built-in Variables::. + + * Starting with version 3.1, `gawk' _always_ interprets these + special file names.(1) For example, using `/dev/fd/4' for output + actually writes on file descriptor 4, and not on a new file + descriptor that is `dup''ed from file descriptor 4. Most of the + time this does not matter; however, it is important to _not_ close + any of the files related to file descriptors 0, 1, and 2. Doing + so results in unpredictable behavior. + + ---------- Footnotes ---------- + + (1) Older versions of `gawk' would only interpret these names +internally if the system did not actually have a a `/dev/fd' directory +or any of the other above listed special files. Usually this didn't +make a difference, but sometimes it did; thus, it was decided to make +`gawk''s behavior consistent on all systems and to have it always +interpret the special file names itself. File: gawk.info, Node: Close Files And Pipes, Prev: Special Files, Up: Printing -Closing Input and Output Files and Pipes -======================================== +Closing Input and Output Redirections +===================================== If the same file name or the same shell command is used with -`getline' (*note Explicit Input with `getline': Getline.) more than -once during the execution of an `awk' program, the file is opened (or -the command is executed) only the first time. At that time, the first +`getline' more than once during the execution of an `awk' program +(*note Explicit Input with `getline': Getline.), the file is opened (or +the command is executed) the first time only. At that time, the first record of input is read from that file or command. The next time the -same file or command is used in `getline', another record is read from -it, and so on. +same file or command is used with `getline', another record is read +from it, and so on. - Similarly, when a file or pipe is opened for output, the file name -or command associated with it is remembered by `awk' and subsequent + Similarly, when a file or pipe is opened for output, the file name or +command associated with it is remembered by `awk', and subsequent writes to the same file or command are appended to the previous writes. The file or pipe stays open until `awk' exits. - This implies that if you want to start reading the same file again -from the beginning, or if you want to rerun a shell command (rather than -reading more output from the command), you must take special steps. -What you must do is use the `close' function, as follows: + This implies that special steps are necessary in order to read the +same file again from the beginning, or to rerun a shell command (rather +than reading more output from the same command). The `close' function +makes these things possible: close(FILENAME) -or +or: close(COMMAND) @@ -4448,12 +5086,11 @@ then you must close it with this: Once this function call is executed, the next `getline' from that file or command, or the next `print' or `printf' to that file or -command, will reopen the file or rerun the command. - - Because the expression that you use to close a file or pipeline must -exactly match the expression used to open the file or run the command, -it is good practice to use a variable to store the file name or command. -The previous example would become +command, reopens the file or reruns the command. Because the +expression that you use to close a file or pipeline must exactly match +the expression used to open the file or run the command, it is good +practice to use a variable to store the file name or command. The +previous example becomes the following: sortcom = "sort -r names" sortcom | getline foo @@ -4461,45 +5098,120 @@ The previous example would become close(sortcom) This helps avoid hard-to-find typographical errors in your `awk' -programs. - - Here are some reasons why you might need to close an output file: +programs. Here are some of the reasons for closing an output file: * To write a file and read it back later on in the same `awk' - program. Close the file when you are finished writing it; then - you can start reading it with `getline'. + program. Close the file after writing it, then begin reading it + with `getline'. * To write numerous files, successively, in the same `awk' program. - If you don't close the files, eventually you may exceed a system - limit on the number of open files in one process. So close each - one when you are finished writing it. + If the files aren't closed, eventually `awk' may exceed a system + limit on the number of open files in one process. It is best to + close each one when the program has finished writing it. - * To make a command finish. When you redirect output through a pipe, - the command reading the pipe normally continues to try to read - input as long as the pipe is open. Often this means the command - cannot really do its work until the pipe is closed. For example, - if you redirect output to the `mail' program, the message is not - actually sent until the pipe is closed. + * To make a command finish. When output is redirected through a + pipe, the command reading the pipe normally continues to try to + read input as long as the pipe is open. Often this means the + command cannot really do its work until the pipe is closed. For + example, if output is redirected to the `mail' program, the + message is not actually sent until the pipe is closed. * To run the same program a second time, with the same arguments. This is not the same thing as giving more input to the first run! - For example, suppose you pipe output to the `mail' program. If you - output several lines redirected to this pipe without closing it, - they make a single message of several lines. By contrast, if you - close the pipe after each line of output, then each line makes a - separate message. - - `close' returns a value of zero if the close succeeded. Otherwise, -the value will be non-zero. In this case, `gawk' sets the variable -`ERRNO' to a string describing the error that occurred. + For example, suppose a program pipes output to the `mail' program. + If it outputs several lines redirected to this pipe without closing + it, they make a single message of several lines. By contrast, if + the program closes the pipe after each line of output, then each + line makes a separate message. If you use more files than the system allows you to have open, -`gawk' will attempt to multiplex the available open files among your -data files. `gawk''s ability to do this depends upon the facilities of -your operating system: it may not always work. It is therefore both -good practice and good portability advice to always use `close' on your -files when you are done with them. +`gawk' attempts to multiplex the available open files among your data +files. `gawk''s ability to do this depends upon the facilities of your +operating system, so it may not always work. It is therefore both good +practice and good portability advice to always use `close' on your +files when you are done with them. In fact, if you are using a lot of +pipes, it is essential that you close commands when done. For example, +consider something like this: + + { + ... + command = ("grep " $1 " /some/file | my_prog -q " $3) + while ((command | getline) > 0) { + PROCESS OUTPUT OF command + } + # need close(command) here + } + + This example creates a new pipeline based on data in _each_ record. +Without the call to `close' indicated in the comment, `awk' creates +child processes to run the commands, until it eventually runs out of +file descriptors for more pipelines. + + Even though each command has finished (as indicated by the +end-of-file return status from `getline'), the child process is not +terminated;(1) more importantly, the file descriptor for the pipe is +not closed and released until `close' is called or `awk' exits. + + `close' will silently do nothing if given an argument that does not +represent a file, pipe or coprocess that was opened with a redirection. + + When using the `|&' operator to communicate with a coprocess, it is +occasionally useful to be able to close one end of the two-way pipe +without closing the other. This is done by supplying a second argument +to `close'. As in any other call to `close', the first argument is the +name of the command or special file used to start the coprocess. The +second argument should be a string, with either of the values `"to"' or +`"from"'. Case does not matter. As this is an advanced feature, a +more complete discussion is delayed until *Note Two-Way Communications +with Another Process: Two-way I/O, which discusses it in more detail +and gives an example. + +Advanced Notes: Using `close''s Return Value +-------------------------------------------- + + In many versions of Unix `awk', the `close' function is actually a +statement. It is a syntax error to try and use the return value from +`close': (d.c.) + + command = "..." + command | getline info + retval = close(command) # syntax error in most Unix awks + + `gawk' treats `close' as a function. The return value is -1 if the +argument names something that was never opened with a redirection, or +if there is a system problem closing the file or process. In these +cases, `gawk' sets the built-in variable `ERRNO' to a string describing +the problem. + + In `gawk', when closing a pipe or coprocess, the return value is the +exit status of the command. Otherwise, it is the return value from the +system's `close' or `fclose' C functions when closing input or output +files, respectively. This value is zero if the close succeeds, or -1 if +it fails. + + The return value for closing a pipeline is particularly useful. It +allows you to get the output from a command as well as its exit status. + + For POSIX-compliant systems, if the exit status is a number above +128, then the program was terminated by a signal. Subtract 128 to get +the signal number: + + exit_val = close(command) + if (exit_val > 128) + print command, "died with signal", exit_val - 128 + else + print command, "exited with code", exit_val + + Currently, in `gawk', this only works for commands piping into +`getline'. For commands piped into from `print' or `printf', the +return value from `close' is that of the library's `pclose' function. + + ---------- Footnotes ---------- + + (1) The technical terminology is rather morbid. The finished child +is called a "zombie," and cleaning up after it is referred to as +"reaping." File: gawk.info, Node: Expressions, Next: Patterns and Actions, Prev: Printing, Up: Top @@ -4508,20 +5220,20 @@ Expressions *********** Expressions are the basic building blocks of `awk' patterns and -actions. An expression evaluates to a value, which you can print, test, -store in a variable or pass to a function. Additionally, an expression -can assign a new value to a variable or a field, with an assignment -operator. +actions. An expression evaluates to a value that you can print, test, +or pass to a function. Additionally, an expression can assign a new +value to a variable or a field by using an assignment operator. An expression can serve as a pattern or action statement on its own. -Most other kinds of statements contain one or more expressions which -specify data on which to operate. As in other languages, expressions -in `awk' include variables, array references, constants, and function -calls, as well as combinations of these with various operators. +Most other kinds of statements contain one or more expressions that +specify the data on which to operate. As in other languages, +expressions in `awk' include variables, array references, constants, +and function calls, as well as combinations of these with various +operators. * Menu: -* Constants:: String, numeric, and regexp constants. +* Constants:: String, numeric and regexp constants. * Using Constant Regexps:: When and how to use a regexp constant. * Variables:: Variables give names to values for later use. * Conversion:: The conversion of strings to numbers and vice @@ -4532,7 +5244,7 @@ calls, as well as combinations of these with various operators. * Assignment Ops:: Changing the value of a variable or a field. * Increment Ops:: Incrementing the numeric value of a variable. * Truth Values:: What is ``true'' and what is ``false''. -* Typing and Comparison:: How variables acquire types, and how this +* Typing and Comparison:: How variables acquire types and how this affects comparison of numbers and strings with `<', etc. * Boolean Ops:: Combining comparison expressions using boolean @@ -4551,46 +5263,129 @@ Constant Expressions ==================== The simplest type of expression is the "constant", which always has -the same value. There are three types of constants: numeric constants, -string constants, and regular expression constants. +the same value. There are three types of constants: numeric, string, +and regular expression. + + Each is used in the appropriate context when you need a data value +that isn't going to change. Numeric constants can have different +forms, but are stored identically internally. * Menu: * Scalar Constants:: Numeric and string constants. +* Non-decimal-numbers:: What are octal and hex numbers. * Regexp Constants:: Regular Expression constants. -File: gawk.info, Node: Scalar Constants, Next: Regexp Constants, Prev: Constants, Up: Constants +File: gawk.info, Node: Scalar Constants, Next: Non-decimal-numbers, Prev: Constants, Up: Constants Numeric and String Constants ---------------------------- A "numeric constant" stands for a number. This number can be an integer, a decimal fraction, or a number in scientific (exponential) -notation.(1) Here are some examples of numeric constants, which all -have the same value: +notation.(1) Here are some examples of numeric constants that all have +the same value: 105 1.05e+2 1050e-1 A string constant consists of a sequence of characters enclosed in -double-quote marks. For example: +double quote marks. For example: "parrot" represents the string whose contents are `parrot'. Strings in `gawk' -can be of any length and they can contain any of the possible eight-bit -ASCII characters including ASCII NUL (character code zero). Other `awk' -implementations may have difficulty with some character codes. +can be of any length, and they can contain any of the possible +eight-bit ASCII characters including ASCII NUL (character code zero). +Other `awk' implementations may have difficulty with some character +codes. ---------- Footnotes ---------- - (1) The internal representation uses double-precision floating point -numbers. If you don't know what that means, then don't worry about it. + (1) The internal representation of all numbers, including integers, +uses double-precision floating-point numbers. On most modern systems, +these are in IEEE 754 standard format. -File: gawk.info, Node: Regexp Constants, Prev: Scalar Constants, Up: Constants +File: gawk.info, Node: Non-decimal-numbers, Next: Regexp Constants, Prev: Scalar Constants, Up: Constants + +Octal and Hexadecimal Numbers +----------------------------- + + In `awk', all numbers are in decimal; i.e., base 10. Many other +programming languages allow you to specify numbers in other bases, often +octal (base 8) and hexadecimal (base 16). In octal, the numbers go 0, +1, 2, 3, 4, 5, 6, 7, 10, 11, 12, etc.. Just as `11' in decimal is 1 +times 10 plus 1, so `11' in octal is 1 times 8, plus 1. This equals +nine in decimal. In hexadecimal, there are 16 digits. Since the +everyday decimal number system only has ten digits (`0'--`9'), the +letters `a' through `f' are used to represent the rest. (Case in the +letters is usually irrelevant; hexadecimal `a' and `A' have the same +value.) Thus, `11' in hexadecimal is 1 times 16 plus 1, which equals +17 in decimal. + + Just by looking at plain `11', you can't tell what base it's in. +So, in C, C++, and other languages derived from C, there is a special +notation to help signify the base. Octal numbers start with a leading +`0', and hexadecimal numbers start with a leading `0x' or `0X': + +`11' + Decimal 11. + +`011' + Octal 11, decimal value 9. + +`0x11' + Hexadecimal 11, decimal value 17. + + This example shows the difference: + + $ gawk 'BEGIN { printf "%d, %d, %d\n", 011, 11, 0x11 }' + -| 9, 11, 17 + + Being able to use octal and hexadecimal constants in your programs +is most useful when working with data that cannot be represented +conveniently as characters or as regular numbers, such as binary data +of various sorts. + + `gawk' allows the use of octal and hexadecimal constants in your +program text. However, such numbers in the input data are not treated +differently; doing so by default would break old programs. (If you +really need to do this, use the `--non-decimal-data' command-line +option, *note Allowing Non-Decimal Input Data: Non-decimal Data..) If +you have octal or hexadecimal data, you can use the `strtonum' function +(*note String Manipulation Functions: String Functions.) to convert +the data into a number. Most of the time, you will want to use octal +or hexadecimal constants when working with the built-in bit +manipulation functions; see *Note Using `gawk''s Bit Manipulation +Functions: Bitwise Functions, for more information. + + Unlike some early C implementations, `8' and `9' are not valid in +octal constants; e.g., `gawk' treats `018' as decimal 18. + + $ gawk 'BEGIN { print "021 is", 021 ; print 018 }' + -| 021 is 17 + -| 18 + + Octal and hexadecimal source code constants are a `gawk' extension. +If `gawk' is in compatibility mode (*note Command-Line Options: +Options.), they are not available. + +Advanced Notes: A Constant's Base Does Not Affect Its Value +----------------------------------------------------------- + + Once a numeric constant has been converted internally into a number, +`gawk' no longer remembers what the original form of the constant was; +the internal value is always used. This has particular consequences +for conversion of numbers to strings: + + $ gawk 'BEGIN { printf "0x11 is <%s>\n", 0x11 }' + -| 0x11 is <17> + + +File: gawk.info, Node: Regexp Constants, Prev: Non-decimal-numbers, Up: Constants Regular Expression Constants ---------------------------- @@ -4607,28 +5402,25 @@ File: gawk.info, Node: Using Constant Regexps, Next: Variables, Prev: Constan Using Regular Expression Constants ================================== - When used on the right hand side of the `~' or `!~' operators, a + When used on the righthand side of the `~' or `!~' operators, a regexp constant merely stands for the regexp that is to be matched. - - Regexp constants (such as `/foo/') may be used like simple +However, regexp constants (such as `/foo/') may be used like simple expressions. When a regexp constant appears by itself, it has the same -meaning as if it appeared in a pattern, i.e. `($0 ~ /foo/)' (d.c.) -(*note Expressions as Patterns: Expression Patterns.). This means that -the two code segments, +meaning as if it appeared in a pattern, i.e.; `($0 ~ /foo/)' (d.c.) +*Note Expressions as Patterns: Expression Patterns. This means that +the following two code segments: if ($0 ~ /barfly/ || $0 ~ /camelot/) print "found" -and +and: if (/barfly/ || /camelot/) print "found" -are exactly equivalent. - - One rather bizarre consequence of this rule is that the following -boolean expression is valid, but does not do what the user probably -intended: +are exactly equivalent. One rather bizarre consequence of this rule is +that the following Boolean expression is valid, but does not do what +the user probably intended: # note that /foo/ is on the left of the ~ if (/foo/ ~ $1) print "found foo" @@ -4636,34 +5428,27 @@ intended: This code is "obviously" testing `$1' for a match against the regexp `/foo/'. But in fact, the expression `/foo/ ~ $1' actually means `($0 ~ /foo/) ~ $1'. In other words, first match the input record against -the regexp `/foo/'. The result will be either zero or one, depending -upon the success or failure of the match. Then match that result -against the first field in the record. - - Since it is unlikely that you would ever really wish to make this -kind of test, `gawk' will issue a warning when it sees this construct in -a program. - - Another consequence of this rule is that the assignment statement +the regexp `/foo/'. The result is either zero or one, depending upon +the success or failure of the match. That result is then matched +against the first field in the record. Because it is unlikely that you +would ever really want to make this kind of test, `gawk' issues a +warning when it sees this construct in a program. Another consequence +of this rule is that the assignment statement: matches = /foo/ -will assign either zero or one to the variable `matches', depending -upon the contents of the current input record. - - This feature of the language was never well documented until the -POSIX specification. +assigns either zero or one to the variable `matches', depending upon +the contents of the current input record. This feature of the language +has never been well documented until the POSIX specification. Constant regular expressions are also used as the first argument for -the `gensub', `sub' and `gsub' functions, and as the second argument of -the `match' function (*note Built-in Functions for String Manipulation: -String Functions.). Modern implementations of `awk', including `gawk', -allow the third argument of `split' to be a regexp constant, while some -older implementations do not (d.c.). - - This can lead to confusion when attempting to use regexp constants -as arguments to user defined functions (*note User-defined Functions: -User-defined.). For example: +the `gensub', `sub', and `gsub' functions, and as the second argument +of the `match' function (*note String Manipulation Functions: String +Functions.). Modern implementations of `awk', including `gawk', allow +the third argument of `split' to be a regexp constant, but some older +implementations do not. (d.c.) This can lead to confusion when +attempting to use regexp constants as arguments to user defined +functions (*note User-Defined Functions: User-defined.). For example: function mysub(pat, repl, str, global) { @@ -4681,15 +5466,13 @@ User-defined.). For example: ... } - In this example, the programmer wishes to pass a regexp constant to -the user-defined function `mysub', which will in turn pass it on to -either `sub' or `gsub'. However, what really happens is that the `pat' -parameter will be either one or zero, depending upon whether or not -`$0' matches `/hi/'. - - As it is unlikely that you would ever really wish to pass a truth -value in this way, `gawk' will issue a warning when it sees a regexp -constant used as a parameter to a user-defined function. + In this example, the programmer wants to pass a regexp constant to +the user-defined function `mysub', which in turn passes it on to either +`sub' or `gsub'. However, what really happens is that the `pat' +parameter is either one or zero, depending upon whether or not `$0' +matches `/hi/'. `gawk' issues a warning when it sees a regexp constant +used as a parameter to a user-defined function, since passing a truth +value in this way is probably not what was intended. File: gawk.info, Node: Variables, Next: Conversion, Prev: Using Constant Regexps, Up: Expressions @@ -4698,15 +5481,15 @@ Variables ========= Variables are ways of storing values at one point in your program for -use later in another part of your program. You can manipulate them -entirely within your program text, and you can also assign values to -them on the `awk' command line. +use later in another part of your program. They can be manipulated +entirely within the program text, and they can also be assigned values +on the `awk' command line. * Menu: * Using Variables:: Using variables in your programs. -* Assignment Options:: Setting variables on the command line and a - summary of command line syntax. This is an +* Assignment Options:: Setting variables on the command-line and a + summary of command-line syntax. This is an advanced method of input. @@ -4715,29 +5498,31 @@ File: gawk.info, Node: Using Variables, Next: Assignment Options, Prev: Varia Using Variables in a Program ---------------------------- - Variables let you give names to values and refer to them later. You -have already seen variables in many of the examples. The name of a -variable must be a sequence of letters, digits and underscores, but it -may not begin with a digit. Case is significant in variable names; `a' -and `A' are distinct variables. + Variables let you give names to values and refer to them later. +Variables have already been used in many of the examples. The name of +a variable must be a sequence of letters, digits, or underscores, and +it may not begin with a digit. Case is significant in variable names; +`a' and `A' are distinct variables. A variable name is a valid expression by itself; it represents the variable's current value. Variables are given new values with -"assignment operators", "increment operators" and "decrement operators". -*Note Assignment Expressions: Assignment Ops. +"assignment operators", "increment operators", and "decrement +operators". *Note Assignment Expressions: Assignment Ops. - A few variables have special built-in meanings, such as `FS', the -field separator, and `NF', the number of fields in the current input -record. *Note Built-in Variables::, for a list of them. These -built-in variables can be used and assigned just like all other -variables, but their values are also used or changed automatically by -`awk'. All built-in variables names are entirely upper-case. + A few variables have special built-in meanings, such as `FS' (the +field separator), and `NF' (the number of fields in the current input +record). *Note Built-in Variables::, for a list of the built-in +variables. These built-in variables can be used and assigned just like +all other variables, but their values are also used or changed +automatically by `awk'. All built-in variables' names are entirely +uppercase. Variables in `awk' can be assigned either numeric or string values. -By default, variables are initialized to the empty string, which is -zero if converted to a number. There is no need to "initialize" each -variable explicitly in `awk', the way you would in C and in most other -traditional languages. +The kind of value a variable holds can change over the life of a +program. By default, variables are initialized to the empty string, +which is zero if converted to a number. There is no need to +"initialize" each variable explicitly in `awk', which is what you would +do in C and in most other traditional languages. File: gawk.info, Node: Assignment Options, Prev: Using Variables, Up: Variables @@ -4745,28 +5530,26 @@ File: gawk.info, Node: Assignment Options, Prev: Using Variables, Up: Variabl Assigning Variables on the Command Line --------------------------------------- - You can set any `awk' variable by including a "variable assignment" -among the arguments on the command line when you invoke `awk' (*note -Other Command Line Arguments: Other Arguments.). Such an assignment has -this form: + Any `awk' variable can be set by including a "variable assignment" +among the arguments on the command line when `awk' is invoked (*note +Other Command-Line Arguments: Other Arguments.). Such an assignment +has the following form: VARIABLE=TEXT -With it, you can set a variable either at the beginning of the `awk' -run or in between input files. - - If you precede the assignment with the `-v' option, like this: +With it, a variable is set either at the beginning of the `awk' run or +in between input files. When the assignment is preceded with the `-v' +option, as in the following: -v VARIABLE=TEXT -then the variable is set at the very beginning, before even the `BEGIN' +the variable is set at the very beginning, even before the `BEGIN' rules are run. The `-v' option and its assignment must precede all the -file name arguments, as well as the program text. (*Note Command Line +file name arguments, as well as the program text. (*Note Command-Line Options: Options, for more information about the `-v' option.) - - Otherwise, the variable assignment is performed at a time determined -by its position among the input file arguments: after the processing of -the preceding input file argument. For example: +Otherwise, the variable assignment is performed at a time determined by +its position among the input file arguments--after the processing of the +preceding input file argument. For example: awk '{ print $n }' n=4 inventory-shipped n=2 BBS-list @@ -4775,7 +5558,7 @@ first file is read, the command line sets the variable `n' equal to four. This causes the fourth field to be printed in lines from the file `inventory-shipped'. After the first file has finished, but before the second file is started, `n' is set to two, so that the -second field is printed in lines from `BBS-list'. +second field is printed in lines from `BBS-list': $ awk '{ print $n }' n=4 inventory-shipped n=2 BBS-list -| 15 @@ -4785,12 +5568,10 @@ second field is printed in lines from `BBS-list'. -| 555-3412 ... - Command line arguments are made available for explicit examination by + Command-line arguments are made available for explicit examination by the `awk' program in an array named `ARGV' (*note Using `ARGC' and -`ARGV': ARGC and ARGV.). - - `awk' processes the values of command line assignments for escape -sequences (d.c.) (*note Escape Sequences::). +`ARGV': ARGC and ARGV.). `awk' processes the values of command-line +assignments for escape sequences (d.c.) (*note Escape Sequences::). File: gawk.info, Node: Conversion, Next: Arithmetic Ops, Prev: Variables, Up: Expressions @@ -4798,68 +5579,72 @@ File: gawk.info, Node: Conversion, Next: Arithmetic Ops, Prev: Variables, Up Conversion of Strings and Numbers ================================= - Strings are converted to numbers, and numbers to strings, if the -context of the `awk' program demands it. For example, if the value of -either `foo' or `bar' in the expression `foo + bar' happens to be a -string, it is converted to a number before the addition is performed. -If numeric values appear in string concatenation, they are converted to -strings. Consider this: + Strings are converted to numbers and numbers are converted to +strings, if the context of the `awk' program demands it. For example, +if the value of either `foo' or `bar' in the expression `foo + bar' +happens to be a string, it is converted to a number before the addition +is performed. If numeric values appear in string concatenation, they +are converted to strings. Consider the following: two = 2; three = 3 print (two three) + 4 This prints the (numeric) value 27. The numeric values of the variables `two' and `three' are converted to strings and concatenated -together, and the resulting string is converted back to the number 23, -to which four is then added. +together. The resulting string is converted back to the number 23, to +which four is then added. If, for some reason, you need to force a number to be converted to a string, concatenate the empty string, `""', with that number. To force -a string to be converted to a number, add zero to that string. - - A string is converted to a number by interpreting any numeric prefix -of the string as numerals: `"2.5"' converts to 2.5, `"1e3"' converts to +a string to be converted to a number, add zero to that string. A +string is converted to a number by interpreting any numeric prefix of +the string as numerals: `"2.5"' converts to 2.5, `"1e3"' converts to 1000, and `"25fix"' has a numeric value of 25. Strings that can't be -interpreted as valid numbers are converted to zero. +interpreted as valid numbers convert to zero. The exact manner in which numbers are converted into strings is controlled by the `awk' built-in variable `CONVFMT' (*note Built-in -Variables::). Numbers are converted using the `sprintf' function -(*note Built-in Functions for String Manipulation: String Functions.) -with `CONVFMT' as the format specifier. +Variables::). Numbers are converted using the `sprintf' function with +`CONVFMT' as the format specifier (*note String Manipulation Functions: +String Functions.). `CONVFMT''s default value is `"%.6g"', which prints a value with at -least six significant digits. For some applications you will want to -change it to specify more precision. On most modern machines, you must -print 17 digits to capture a floating point number's value exactly. - - Strange results can happen if you set `CONVFMT' to a string that -doesn't tell `sprintf' how to format floating point numbers in a useful -way. For example, if you forget the `%' in the format, all numbers -will be converted to the same constant string. - - As a special case, if a number is an integer, then the result of -converting it to a string is _always_ an integer, no matter what the -value of `CONVFMT' may be. Given the following code fragment: +least six significant digits. For some applications, you might want to +change it to specify more precision. On most modern machines, 17 +digits is enough to capture a floating-point number's value exactly, +most of the time.(1) + + Strange results can occur if you set `CONVFMT' to a string that +doesn't tell `sprintf' how to format floating-point numbers in a useful +way. For example, if you forget the `%' in the format, `awk' converts +all numbers to the same constant string. As a special case, if a +number is an integer, then the result of converting it to a string is +_always_ an integer, no matter what the value of `CONVFMT' may be. +Given the following code fragment: CONVFMT = "%2.2f" a = 12 b = a "" -`b' has the value `"12"', not `"12.00"' (d.c.). - - Prior to the POSIX standard, `awk' specified that the value of -`OFMT' was used for converting numbers to strings. `OFMT' specifies -the output format to use when printing numbers with `print'. `CONVFMT' -was introduced in order to separate the semantics of conversion from -the semantics of printing. Both `CONVFMT' and `OFMT' have the same -default value: `"%.6g"'. In the vast majority of cases, old `awk' -programs will not change their behavior. However, this use of `OFMT' -is something to keep in mind if you must port your program to other -implementations of `awk'; we recommend that instead of changing your -programs, you just port `gawk' itself! *Note The `print' Statement: +`b' has the value `"12"', not `"12.00"'. (d.c.) + + Prior to the POSIX standard, `awk' used the value of `OFMT' for +converting numbers to strings. `OFMT' specifies the output format to +use when printing numbers with `print'. `CONVFMT' was introduced in +order to separate the semantics of conversion from the semantics of +printing. Both `CONVFMT' and `OFMT' have the same default value: +`"%.6g"'. In the vast majority of cases, old `awk' programs do not +change their behavior. However, these semantics for `OFMT' are +something to keep in mind if you must port your new style program to +older implementations of `awk'. We recommend that instead of changing +your programs, just port `gawk' itself. *Note The `print' Statement: Print, for more information on the `print' statement. + ---------- Footnotes ---------- + + (1) Pathological cases can require up to 752 digits (!), but we +doubt that you need to worry about this. + File: gawk.info, Node: Arithmetic Ops, Next: Concatenation, Prev: Conversion, Up: Expressions @@ -4868,19 +5653,18 @@ Arithmetic Operators The `awk' language uses the common arithmetic operators when evaluating expressions. All of these arithmetic operators follow normal -precedence rules, and work as you would expect them to. Arithmetic -operations are evaluated using double precision floating point, which -has the usual problems of inexactness and exceptions.(1) +precedence rules and work as you would expect them to. - Here is a file `grades' containing a list of student names and three -test scores per student (it's a small class): + The following example uses a file named `grades', which contains a +list of student names as well as three test scores per student (it's a +small class): Pat 100 97 58 Sandy 84 72 93 Chris 72 92 89 -This programs takes the file `grades', and prints the average of the -scores. +This programs takes the file `grades' and prints the average of the +scores: $ awk '{ sum = $2 + $3 + $4 ; avg = sum / 3 > print $1, avg }' grades @@ -4888,44 +5672,34 @@ scores. -| Sandy 83 -| Chris 84.3333 - This table lists the arithmetic operators in `awk', in order from -highest precedence to lowest: + The following list provides the arithmetic operators in `awk', in +order from the highest precedence to the lowest: `- X' Negation. `+ X' - Unary plus. The expression is converted to a number. + Unary plus; the expression is converted to a number. `X ^ Y' `X ** Y' - Exponentiation: X raised to the Y power. `2 ^ 3' has the value - eight. The character sequence `**' is equivalent to `^'. (The - POSIX standard only specifies the use of `^' for exponentiation.) + Exponentiation; X raised to the Y power. `2 ^ 3' has the value + eight; the character sequence `**' is equivalent to `^'. `X * Y' Multiplication. `X / Y' - Division. Since all numbers in `awk' are floating point numbers, - the result is not rounded to an integer: `3 / 4' has the value - 0.75. + Division; because all numbers in `awk' are floating-point + numbers, the result is _not_ rounded to an integer--`3 / 4' has + the value 0.75. (It is a common mistake, especially for C + programmers, to forget that _all_ numbers in `awk' are + floating-point, and that division of integer-looking constants + produces a real number, not an integer.) `X % Y' - Remainder. The quotient is rounded toward zero to an integer, - multiplied by Y and this result is subtracted from X. This - operation is sometimes known as "trunc-mod." The following - relation always holds: - - b * int(a / b) + (a % b) == a - - One possibly undesirable effect of this definition of remainder is - that `X % Y' is negative if X is negative. Thus, - - -17 % 8 = -1 - - In other `awk' implementations, the signedness of the remainder - may be machine dependent. + Remainder; further discussion is provided in the text, just after + this list. `X + Y' Addition. @@ -4933,17 +5707,27 @@ highest precedence to lowest: `X - Y' Subtraction. - For maximum portability, do not use the `**' operator. - Unary plus and minus have the same precedence, the multiplication operators all have the same precedence, and addition and subtraction have the same precedence. - ---------- Footnotes ---------- + When computing the remainder of `X % Y', the quotient is rounded +toward zero to an integer and multiplied by Y. This result is +subtracted from X; this operation is sometimes known as "trunc-mod." +The following relation always holds: + + b * int(a / b) + (a % b) == a + + One possibly undesirable effect of this definition of remainder is +that `X % Y' is negative if X is negative. Thus: - (1) David Goldberg, `What Every Computer Scientist Should Know About -Floating-point Arithmetic' (http://www.validgh.com/goldberg/paper.ps), -`ACM Computing Surveys' *23*, 1 (1991-03), 5-48. + -17 % 8 = -1 + + In other `awk' implementations, the signedness of the remainder may +be machine dependent. + + *Note:* The POSIX standard only specifies the use of `^' for +exponentiation. For maximum portability, do not use the `**' operator. File: gawk.info, Node: Concatenation, Next: Assignment Ops, Prev: Arithmetic Ops, Up: Expressions @@ -4954,8 +5738,6 @@ String Concatenation It seemed like a good idea at the time. Brian Kernighan - - There is only one string operation: concatenation. It does not have a specific operator to represent it. Instead, concatenation is performed by writing expressions next to one another, with no operator. @@ -4967,16 +5749,16 @@ For example: ... Without the space in the string constant after the `:', the line -would run together. For example: +runs together. For example: $ awk '{ print "Field number one:" $1 }' BBS-list -| Field number one:aardvark -| Field number one:alpo-net ... - Since string concatenation does not have an explicit operator, it is -often necessary to insure that it happens where you want it to by using -parentheses to enclose the items to be concatenated. For example, the + Because string concatenation does not have an explicit operator, it +is often necessary to insure that it happens at the right time by using +parentheses to enclose the items to concatenate. For example, the following code fragment does not concatenate `file' and `name' as you might expect: @@ -4988,8 +5770,45 @@ It is necessary to use the following: print "something meaningful" > (file name) - We recommend that you use parentheses around concatenation in all -but the most common contexts (such as on the right-hand side of `='). + Parentheses should be used around concatenation in all but the most +common contexts, such as on the righthand side of `='. Be careful +about the kinds of expressions used in string concatenation. In +particular, the order of evaluation of expressions used for +concatenation is undefined in the `awk' language. Consider this +example: + + BEGIN { + a = "don't" + print (a " " (a = "panic")) + } + +It is not defined whether the assignment to `a' happens before or after +the value of `a' is retrieved for producing the concatenated value. +The result could be either `don't panic', or `panic panic'. The +precedence of concatenation, when mixed with other operators, is often +counter-intuitive. Consider this example: + + $ awk 'BEGIN { print -12 " " -24 }' + -| -12-24 + + This "obviously" is concatenating -12, a space, and -24. But where +did the space disappear to? The answer lies in the combination of +operator precedences and `awk''s automatic conversion rules. To get +the desired result, write the program in the following manner: + + $ awk 'BEGIN { print -12 " " (-24) }' + -| -12 -24 + + This forces `awk' to treat the `-' on the `-24' as unary. +Otherwise, it's parsed as follows: + + -12 (`" "' - 24) + => -12 (0 - 24) + => -12 (-24) + => -12-24 + + As mentioned earlier, when doing concatenation, _parenthesize_. +Otherwise, you're never quite sure what you'll get. File: gawk.info, Node: Assignment Ops, Next: Increment Ops, Prev: Concatenation, Up: Expressions @@ -4997,46 +5816,44 @@ File: gawk.info, Node: Assignment Ops, Next: Increment Ops, Prev: Concatenati Assignment Expressions ====================== - An "assignment" is an expression that stores a new value into a -variable. For example, let's assign the value one to the variable `z': + An "assignment" is an expression that stores a (usually different) +value into a variable. For example, let's assign the value one to the +variable `z': z = 1 After this expression is executed, the variable `z' has the value one. Whatever old value `z' had before the assignment is forgotten. - Assignments can store string values also. For example, this would -store the value `"this food is good"' in the variable `message': + Assignments can also store string values. For example, the +following stores the value `"this food is good"' in the variable +`message': thing = "food" predicate = "good" message = "this " thing " is " predicate -(This also illustrates string concatenation.) - - The `=' sign is called an "assignment operator". It is the simplest -assignment operator because the value of the right-hand operand is -stored unchanged. +This also illustrates string concatenation. The `=' sign is called an +"assignment operator". It is the simplest assignment operator because +the value of the righthand operand is stored unchanged. Most operators +(addition, concatenation, and so on) have no effect except to compute a +value. If the value isn't used, there's no reason to use the operator. +An assignment operator is different; it does produce a value, but even +if you ignore it, the assignment still makes itself felt through the +alteration of the variable. We call this a "side effect". - Most operators (addition, concatenation, and so on) have no effect -except to compute a value. If you ignore the value, you might as well -not use the operator. An assignment operator is different; it does -produce a value, but even if you ignore the value, the assignment still -makes itself felt through the alteration of the variable. We call this -a "side effect". - - The left-hand operand of an assignment need not be a variable (*note + The lefthand operand of an assignment need not be a variable (*note Variables::); it can also be a field (*note Changing the Contents of a Field: Changing Fields.) or an array element (*note Arrays in `awk': Arrays.). These are all called "lvalues", which means they can appear -on the left-hand side of an assignment operator. The right-hand -operand may be any expression; it produces the new value which the -assignment stores in the specified variable, field or array element. -(Such values are called "rvalues"). +on the lefthand side of an assignment operator. The righthand operand +may be any expression; it produces the new value that the assignment +stores in the specified variable, field, or array element. (Such values +are called "rvalues"). It is important to note that variables do _not_ have permanent types. -The type of a variable is simply the type of whatever value it happens -to hold at the moment. In the following program fragment, the variable +A variable's type is simply the type of whatever value it happens to +hold at the moment. In the following program fragment, the variable `foo' has a numeric value at first, and a string value later on: foo = 1 @@ -5048,38 +5865,39 @@ When the second assignment gives `foo' a string value, the fact that it previously had a numeric value is forgotten. String values that do not begin with a digit have a numeric value of -zero. After executing this code, the value of `foo' is five: +zero. After executing the following code, the value of `foo' is five: foo = "a string" foo = foo + 5 -(Note that using a variable as a number and then later as a string can -be confusing and is poor programming style. The above examples +*Note:* Using a variable as a number and then later as a string can be +confusing and is poor programming style. The previous two examples illustrate how `awk' works, _not_ how you should write your own -programs!) +programs! - An assignment is an expression, so it has a value: the same value -that is assigned. Thus, `z = 1' as an expression has the value one. + An assignment is an expression, so it has a value--the same value +that is assigned. Thus, `z = 1' is an expression with the value one. One consequence of this is that you can write multiple assignments -together: +together, such as: - x = y = z = 0 + x = y = z = 5 -stores the value zero in all three variables. It does this because the -value of `z = 0', which is zero, is stored into `y', and then the value -of `y = z = 0', which is zero, is stored into `x'. +This example stores the value five in all three variables (`x', `y', +and `z'). It does so because the value of `z = 5', which is five, is +stored into `y' and then the value of `y = z = 5', which is five, is +stored into `x'. - You can use an assignment anywhere an expression is called for. For -example, it is valid to write `x != (y = 1)' to set `y' to one and then -test whether `x' equals one. But this style tends to make programs -hard to read; except in a one-shot program, you should not use such -nesting of assignments. + Assignments may be used anywhere an expression is called for. For +example, it is valid to write `x != (y = 1)' to set `y' to one, and +then test whether `x' equals one. But this style tends to make +programs hard to read; such nesting of assignments should be avoided, +except perhaps in a one-shot program. Aside from `=', there are several other assignment operators that do arithmetic with the old value of the variable. For example, the -operator `+=' computes a new value by adding the right-hand value to -the old value of the variable. Thus, the following assignment adds -five to the value of `foo': +operator `+=' computes a new value by adding the righthand value to the +old value of the variable. Thus, the following assignment adds five to +the value of `foo': foo += 5 @@ -5087,11 +5905,11 @@ This is equivalent to the following: foo = foo + 5 -Use whichever one makes the meaning of your program clearer. +Use whichever makes the meaning of your program clearer. There are situations where using `+=' (or any assignment operator) -is _not_ the same as simply repeating the left-hand operand in the -right-hand expression. For example: +is _not_ the same as simply repeating the lefthand operand in the +righthand expression. For example: # Thanks to Pat Rankin for this example BEGIN { @@ -5104,17 +5922,14 @@ right-hand expression. For example: print x, bar[x] } -The indices of `bar' are guaranteed to be different, because `rand' -will return different values each time it is called. (Arrays and the -`rand' function haven't been covered yet. *Note Arrays in `awk': -Arrays, and see *Note Numeric Built-in Functions: Numeric Functions, -for more information). This example illustrates an important fact -about the assignment operators: the left-hand expression is only -evaluated _once_. - - It is also up to the implementation as to which expression is -evaluated first, the left-hand one or the right-hand one. Consider -this example: +The indices of `bar' are practically guaranteed to be different, because +`rand' returns different values each time it is called. (Arrays and +the `rand' function haven't been covered yet. *Note Arrays in `awk': +Arrays, and see *Note Numeric Functions::, for more information). This +example illustrates an important fact about assignment operators: the +lefthand expression is only evaluated _once_. It is up to the +implementation as to which expression is evaluated first, the lefthand +or the righthand. Consider this example: i = 1 a[i += 2] = i + 1 @@ -5122,31 +5937,41 @@ this example: The value of `a[3]' could be either two or four. Here is a table of the arithmetic assignment operators. In each -case, the right-hand operand is an expression whose value is converted +case, the righthand operand is an expression whose value is converted to a number. -`LVALUE += INCREMENT' - Adds INCREMENT to the value of LVALUE to make the new value of - LVALUE. +LVALUE `+=' INCREMENT Adds INCREMENT to the value of LVALUE. +LVALUE `-=' DECREMENT Subtracts DECREMENT from the value of LVALUE. +LVALUE `*=' Multiplies the value of LVALUE by COEFFICIENT. +COEFFICIENT +LVALUE `/=' DIVISOR Divides the value of LVALUE by DIVISOR. +LVALUE `%=' MODULUS Sets LVALUE to its remainder by MODULUS. +LVALUE `^=' POWER +LVALUE `**=' POWER Raises LVALUE to the power POWER. + + *Note:* Only the `^=' operator is specified by POSIX. For maximum +portability, do not use the `**=' operator. -`LVALUE -= DECREMENT' - Subtracts DECREMENT from the value of LVALUE. +Advanced Notes: Syntactic Ambiguities Between `/=' and Regular Expressions +-------------------------------------------------------------------------- -`LVALUE *= COEFFICIENT' - Multiplies the value of LVALUE by COEFFICIENT. + There is a syntactic ambiguity between the `/=' assignment operator +and regexp constants whose first character is an `='. (d.c.) This is +most notable in commercial `awk' versions. For example: -`LVALUE /= DIVISOR' - Divides the value of LVALUE by DIVISOR. + $ awk /==/ /dev/null + error--> awk: syntax error at source line 1 + error--> context is + error--> >>> /= <<< + error--> awk: bailing out at source line 1 -`LVALUE %= MODULUS' - Sets LVALUE to its remainder by MODULUS. +A workaround is: -`LVALUE ^= POWER' -`LVALUE **= POWER' - Raises LVALUE to the power POWER. (Only the `^=' operator is - specified by POSIX.) + awk '/[=]=/' /dev/null - For maximum portability, do not use the `**=' operator. + `gawk' does not have this problem, nor do the other freely-available +versions described in *Note Other Freely Available `awk' +Implementations: Other Versions. File: gawk.info, Node: Increment Ops, Next: Truth Values, Prev: Assignment Ops, Up: Expressions @@ -5155,44 +5980,41 @@ Increment and Decrement Operators ================================= "Increment" and "decrement operators" increase or decrease the value -of a variable by one. You could do the same thing with an assignment -operator, so the increment operators add no power to the `awk' -language; but they are convenient abbreviations for very common -operations. - - The operator to add one is written `++'. It can be used to increment -a variable either before or after taking its value. - - To pre-increment a variable V, write `++V'. This adds one to the -value of V and that new value is also the value of this expression. -The assignment expression `V += 1' is completely equivalent. - - Writing the `++' after the variable specifies post-increment. This -increments the variable value just the same; the difference is that the -value of the increment expression itself is the variable's _old_ value. -Thus, if `foo' has the value four, then the expression `foo++' has the -value four, but it changes the value of `foo' to five. - - The post-increment `foo++' is nearly equivalent to writing `(foo += -1) - 1'. It is not perfectly equivalent because all numbers in `awk' -are floating point: in floating point, `foo + 1 - 1' does not -necessarily equal `foo'. But the difference is minute as long as you -stick to numbers that are fairly small (less than 10e12). - - Any lvalue can be incremented. Fields and array elements are -incremented just like variables. (Use `$(i++)' when you wish to do a -field reference and a variable increment at the same time. The -parentheses are necessary because of the precedence of the field -reference operator, `$'.) - - The decrement operator `--' works just like `++' except that it -subtracts one instead of adding. Like `++', it can be used before the -lvalue to pre-decrement or after it to post-decrement. - - Here is a summary of increment and decrement expressions. +of a variable by one. An assignment operator can do the same thing, so +the increment operators add no power to the `awk' language; however they +are convenient abbreviations for very common operations. + + The operator used for adding one is written `++'. It can be used to +increment a variable either before or after taking its value. To +pre-increment a variable `v', write `++v'. This adds one to the value +of `v'--that new value is also the value of the expression. (The +assignment expression `v += 1' is completely equivalent.) Writing the +`++' after the variable specifies post-increment. This increments the +variable value just the same; the difference is that the value of the +increment expression itself is the variable's _old_ value. Thus, if +`foo' has the value four, then the expression `foo++' has the value +four, but it changes the value of `foo' to five. In other words, the +operator returns the old value of the variable, but with the side +effect of incrementing it. + + The post-increment `foo++' is nearly the same as writing `(foo += 1) +- 1'. It is not perfectly equivalent because all numbers in `awk' are +floating-point--in floating-point, `foo + 1 - 1' does not necessarily +equal `foo'. But the difference is minute as long as you stick to +numbers that are fairly small (less than 10e12). + + Fields and array elements are incremented just like variables. (Use +`$(i++)' when you want to do a field reference and a variable increment +at the same time. The parentheses are necessary because of the +precedence of the field reference operator `$'.) + + The decrement operator `--' works just like `++', except that it +subtracts one instead of adding it. As with `++', it can be used before +the lvalue to pre-decrement or after it to post-decrement. Following +is a summary of increment and decrement expressions: `++LVALUE' - This expression increments LVALUE and the new value becomes the + This expression increments LVALUE, and the new value becomes the value of the expression. `LVALUE++' @@ -5200,13 +6022,42 @@ lvalue to pre-decrement or after it to post-decrement. is the _old_ value of LVALUE. `--LVALUE' - Like `++LVALUE', but instead of adding, it subtracts. It - decrements LVALUE and delivers the value that results. + This expression is like `++LVALUE', but instead of adding, it + subtracts. It decrements LVALUE and delivers the value that is + the result. `LVALUE--' - Like `LVALUE++', but instead of adding, it subtracts. It - decrements LVALUE. The value of the expression is the _old_ value - of LVALUE. + This expression is like `LVALUE++', but instead of adding, it + subtracts. It decrements LVALUE. The value of the expression is + the _old_ value of LVALUE. + +Advanced Notes: Operator Evaluation Order +----------------------------------------- + + Doctor, doctor! It hurts when I do this! + So don't do that! + Groucho Marx + +What happens for something like the following? + + b = 6 + print b += b++ + +Or something even stranger? + + b = 6 + b += ++b + b++ + print b + + In other words, when do the various side effects prescribed by the +postfix operators (`b++') take effect? When side effects happen is +"implementation defined". In other words, it is up to the particular +version of `awk'. The result for the first example may be 12 or 13, +and for the second, it may be 22 or 23. + + In short, doing things like this is not recommended and definitely +not anything that you can rely upon for portability. You should avoid +such things in your own programs. File: gawk.info, Node: Truth Values, Next: Typing and Comparison, Prev: Increment Ops, Up: Expressions @@ -5216,13 +6067,12 @@ True and False in `awk' Many programming languages have a special representation for the concepts of "true" and "false." Such languages usually use the special -constants `true' and `false', or perhaps their upper-case equivalents. - - `awk' is different. It borrows a very simple concept of true and -false from C. In `awk', any non-zero numeric value, _or_ any non-empty -string value is true. Any other value (zero or the null string, `""') -is false. The following program will print `A strange truth value' -three times: +constants `true' and `false', or perhaps their uppercase equivalents. +However, `awk' is different. It borrows a very simple concept of true +and false from C. In `awk', any nonzero numeric value _or_ any +non-empty string value is true. Any other value (zero or the null +string `""') is false. The following program prints `A strange truth +value' three times: BEGIN { if (3.1415927) @@ -5233,8 +6083,9 @@ three times: print "A strange truth value" } - There is a surprising consequence of the "non-zero or non-null" rule: -The string constant `"0"' is actually true, since it is non-null (d.c.). + There is a surprising consequence of the "nonzero or non-null" rule: +the string constant `"0"' is actually true, because it is non-null. +(d.c.) File: gawk.info, Node: Typing and Comparison, Next: Boolean Ops, Prev: Truth Values, Up: Expressions @@ -5245,40 +6096,35 @@ Variable Typing and Comparison Expressions The Guide is definitive. Reality is frequently inaccurate. The Hitchhiker's Guide to the Galaxy - - Unlike other programming languages, `awk' variables do not have a fixed type. Instead, they can be either a number or a string, depending upon the value that is assigned to them. The 1992 POSIX standard introduced the concept of a "numeric -string", which is simply a string that looks like a number, for +string", which is simply a string that looks like a number--for example, `" +2"'. This concept is used for determining the type of a -variable. - - The type of the variable is important, since the types of two -variables determine how they are compared. +variable. The type of the variable is important because the types of +two variables determine how they are compared. In `gawk', variable +typing follows these rules: - In `gawk', variable typing follows these rules. - - 1. A numeric literal or the result of a numeric operation has the + * A numeric constant or the result of a numeric operation has the NUMERIC attribute. - 2. A string literal or the result of a string operation has the STRING - attribute. + * A string constant or the result of a string operation has the + STRING attribute. - 3. Fields, `getline' input, `FILENAME', `ARGV' elements, `ENVIRON' - elements and the elements of an array created by `split' that are + * Fields, `getline' input, `FILENAME', `ARGV' elements, `ENVIRON' + elements, and the elements of an array created by `split' that are numeric strings have the STRNUM attribute. Otherwise, they have the STRING attribute. Uninitialized variables also have the STRNUM attribute. - 4. Attributes propagate across assignments, but are not changed by - any use. + * Attributes propagate across assignments but are not changed by any + use. The last rule is particularly important. In the following program, `a' has numeric type, even though it is later used in a string -operation. +operation: BEGIN { a = 12.345 @@ -5287,23 +6133,29 @@ operation. } When two operands are compared, either string comparison or numeric -comparison may be used, depending on the attributes of the operands, -according to the following, symmetric, matrix: +comparison may be used. This depends upon the attributes of the +operands, according to the following symmetric matrix: - +---------------------------------------------- - | STRING NUMERIC STRNUM + +---------------------------------------------- + | STRING NUMERIC STRNUM --------+---------------------------------------------- - | - STRING | string string string - | - NUMERIC | string numeric numeric - | - STRNUM | string numeric numeric + | + STRING | string string string + | + NUMERIC | string numeric numeric + | + STRNUM | string numeric numeric --------+---------------------------------------------- - The basic idea is that user input that looks numeric, and _only_ -user input, should be treated as numeric, even though it is actually -made of characters, and is therefore also a string. + The basic idea is that user input that looks numeric--and _only_ +user input--should be treated as numeric, even though it is actually +made of characters and is therefore also a string. Thus, for example, +the string constant `" +3.14"' is a string, even though it looks +numeric, and is _never_ treated as number for comparison purposes. + + In short, when one operand is a "pure" string, such as a string +constant, then a string comparison is performed. Otherwise, a numeric +comparison is performed.(1) "Comparison expressions" compare strings or numbers for relationships such as equality. They are written using "relational @@ -5339,20 +6191,19 @@ them: SUBSCRIPT. Comparison expressions have the value one if true and zero if false. - - When comparing operands of mixed types, numeric operands are -converted to strings using the value of `CONVFMT' (*note Conversion of -Strings and Numbers: Conversion.). +When comparing operands of mixed types, numeric operands are converted +to strings using the value of `CONVFMT' (*note Conversion of Strings +and Numbers: Conversion.). Strings are compared by comparing the first character of each, then -the second character of each, and so on. Thus `"10"' is less than +the second character of each, and so on. Thus, `"10"' is less than `"9"'. If there are two strings where one is a prefix of the other, -the shorter string is less than the longer one. Thus `"abc"' is less +the shorter string is less than the longer one. Thus, `"abc"' is less than `"abcd"'. - It is very easy to accidentally mistype the `==' operator, and leave -off one of the `='s. The result is still valid `awk' code, but the -program will not do what you mean: + It is very easy to accidentally mistype the `==' operator and leave +off one of the `=' characters. The result is still valid `awk' code, +but the program does not do what is intended: if (a = b) # oops! should be a == b ... @@ -5360,11 +6211,11 @@ program will not do what you mean: ... Unless `b' happens to be zero or the null string, the `if' part of the -test will always succeed. Because the operators are so similar, this -kind of error is very difficult to spot when scanning the source code. +test always succeeds. Because the operators are so similar, this kind +of error is very difficult to spot when scanning the source code. - Here are some sample expressions, how `gawk' compares them, and what -the result of the comparison is. + The following table of expressions illustrates the kind of comparison +`gawk' performs, as well as what the result of the comparison is: `1.5 <= 2.0' numeric comparison (true) @@ -5383,50 +6234,55 @@ the result of the comparison is. string comparison (true) `a = 2; b = " +2"' + `a == b' string comparison (false) - In this example, + In the next example: $ echo 1e2 3 | awk '{ print ($1 < $2) ? "true" : "false" }' -| false -the result is `false' since both `$1' and `$2' are numeric strings and -thus both have the STRNUM attribute, dictating a numeric comparison. - - The purpose of the comparison rules and the use of numeric strings is -to attempt to produce the behavior that is "least surprising," while -still "doing the right thing." - - String comparisons and regular expression comparisons are very -different. For example, +the result is `false' because both `$1' and `$2' are user input. They +are numeric strings--therefore both have the STRNUM attribute, +dictating a numeric comparison. The purpose of the comparison rules +and the use of numeric strings is to attempt to produce the behavior +that is "least surprising," while still "doing the right thing." +String comparisons and regular expression comparisons are very +different. For example: x == "foo" -has the value of one, or is true, if the variable `x' is precisely -`foo'. By contrast, +has the value one, or is true if the variable `x' is precisely `foo'. +By contrast: x ~ /foo/ has the value one if `x' contains `foo', such as `"Oh, what a fool am I!"'. - The right hand operand of the `~' and `!~' operators may be either a -regexp constant (`/.../'), or an ordinary expression, in which case the -value of the expression as a string is used as a dynamic regexp (*note -How to Use Regular Expressions: Regexp Usage.; also *note Using Dynamic -Regexps: Computed Regexps.). + The righthand operand of the `~' and `!~' operators may be either a +regexp constant (`/.../') or an ordinary expression. In the latter +case, the value of the expression as a string is used as a dynamic +regexp (*note How to Use Regular Expressions: Regexp Usage.; also *note +Using Dynamic Regexps: Computed Regexps.). - In recent implementations of `awk', a constant regular expression in + In modern implementations of `awk', a constant regular expression in slashes by itself is also an expression. The regexp `/REGEXP/' is an -abbreviation for this comparison expression: +abbreviation for the following comparison expression: $0 ~ /REGEXP/ One special place where `/foo/' is _not_ an abbreviation for `$0 ~ -/foo/' is when it is the right-hand operand of `~' or `!~'! *Note -Using Regular Expression Constants: Using Constant Regexps, where this -is discussed in more detail. +/foo/' is when it is the righthand operand of `~' or `!~'. *Note Using +Regular Expression Constants: Using Constant Regexps, where this is +discussed in more detail. + + ---------- Footnotes ---------- + + (1) The POSIX standard is under revision. The revised standard's +rules for typing and comparison are the same as just described for +`gawk'. File: gawk.info, Node: Boolean Ops, Next: Conditional Exp, Prev: Typing and Comparison, Up: Expressions @@ -5434,42 +6290,41 @@ File: gawk.info, Node: Boolean Ops, Next: Conditional Exp, Prev: Typing and C Boolean Expressions =================== - A "boolean expression" is a combination of comparison expressions or -matching expressions, using the boolean operators "or" (`||'), "and" + A "Boolean expression" is a combination of comparison expressions or +matching expressions, using the Boolean operators "or" (`||'), "and" (`&&'), and "not" (`!'), along with parentheses to control nesting. -The truth value of the boolean expression is computed by combining the +The truth value of the Boolean expression is computed by combining the truth values of the component expressions. Boolean expressions are also referred to as "logical expressions". The terms are equivalent. Boolean expressions can be used wherever comparison and matching -expressions can be used. They can be used in `if', `while', `do' and +expressions can be used. They can be used in `if', `while', `do', and `for' statements (*note Control Statements in Actions: Statements.). -They have numeric values (one if true, zero if false), which come into -play if the result of the boolean expression is stored in a variable, or +They have numeric values (one if true, zero if false), that come into +play if the result of the Boolean expression is stored in a variable or used in arithmetic. - In addition, every boolean expression is also a valid pattern, so -you can use one as a pattern to control the execution of rules. - - Here are descriptions of the three boolean operators, with examples. + In addition, every Boolean expression is also a valid pattern, so +you can use one as a pattern to control the execution of rules. The +Boolean operators are: `BOOLEAN1 && BOOLEAN2' True if both BOOLEAN1 and BOOLEAN2 are true. For example, the following statement prints the current input record if it contains - both `2400' and `foo'. + both `2400' and `foo': if ($0 ~ /2400/ && $0 ~ /foo/) print The subexpression BOOLEAN2 is evaluated only if BOOLEAN1 is true. This can make a difference when BOOLEAN2 contains expressions that - have side effects: in the case of `$0 ~ /foo/ && ($2 == bar++)', - the variable `bar' is not incremented if there is no `foo' in the - record. + have side effects. In the case of `$0 ~ /foo/ && ($2 == bar++)', + the variable `bar' is not incremented if there is no substring + `foo' in the record. `BOOLEAN1 || BOOLEAN2' True if at least one of BOOLEAN1 or BOOLEAN2 is true. For example, the following statement prints all records in the input - that contain _either_ `2400' or `foo', or both. + that contain _either_ `2400' or `foo' or both: if ($0 ~ /2400/ || $0 ~ /foo/) print @@ -5479,81 +6334,88 @@ you can use one as a pattern to control the execution of rules. `! BOOLEAN' True if BOOLEAN is false. For example, the following program - prints all records in the input file `BBS-list' that do _not_ - contain the string `foo'. + prints `no home!' in the unusual event that the `HOME' environment + variable is not defined: + + BEGIN { if (! ("HOME" in ENVIRON)) + print "no home!" } - awk '{ if (! ($0 ~ /foo/)) print }' BBS-list + (The `in' operator is described in *Note Referring to an Array + Element: Reference to Elements.) The `&&' and `||' operators are called "short-circuit" operators because of the way they work. Evaluation of the full expression is "short-circuited" if the result can be determined part way through its evaluation. - You can continue a statement that uses `&&' or `||' simply by -putting a newline after them. But you cannot put a newline in front of -either of these operators without using backslash continuation (*note -`awk' Statements Versus Lines: Statements/Lines.). - - The actual value of an expression using the `!' operator will be -either one or zero, depending upon the truth value of the expression it -is applied to. + Statements that use `&&' or `||' can be continued simply by putting +a newline after them. But you cannot put a newline in front of either +of these operators without using backslash continuation (*note `awk' +Statements Versus Lines: Statements/Lines.). - The `!' operator is often useful for changing the sense of a flag -variable from false to true and back again. For example, the following -program is one way to print lines in between special bracketing lines: + The actual value of an expression using the `!' operator is either +one or zero, depending upon the truth value of the expression it is +applied to. The `!' operator is often useful for changing the sense of +a flag variable from false to true and back again. For example, the +following program is one way to print lines in between special +bracketing lines: - $1 == "START" { interested = ! interested } + $1 == "START" { interested = ! interested; next } interested == 1 { print } - $1 == "END" { interested = ! interested } + $1 == "END" { interested = ! interested; next } -The variable `interested', like all `awk' variables, starts out +The variable `interested', as with all `awk' variables, starts out initialized to zero, which is also false. When a line is seen whose first field is `START', the value of `interested' is toggled to true, using `!'. The next rule prints lines as long as `interested' is true. When a line is seen whose first field is `END', `interested' is toggled back to false. + *Note:* The `next' statement is discussed in *Note The `next' +Statement: Next Statement. `next' tells `awk' to skip the rest of the +rules, get the next record, and start processing the rules over again +at the top. The reason it's there is to avoid printing the bracketing +`START' and `END' lines. + File: gawk.info, Node: Conditional Exp, Next: Function Calls, Prev: Boolean Ops, Up: Expressions Conditional Expressions ======================= - A "conditional expression" is a special kind of expression with + A "conditional expression" is a special kind of expression that has three operands. It allows you to use one expression's value to select -one of two other expressions. - - The conditional expression is the same as in the C language: +one of two other expressions. The conditional expression is the same +as in the C language, as shown here: SELECTOR ? IF-TRUE-EXP : IF-FALSE-EXP There are three subexpressions. The first, SELECTOR, is always -computed first. If it is "true" (not zero and not null) then +computed first. If it is "true" (not zero or not null), then IF-TRUE-EXP is computed next and its value becomes the value of the whole expression. Otherwise, IF-FALSE-EXP is computed next and its -value becomes the value of the whole expression. - - For example, this expression produces the absolute value of `x': +value becomes the value of the whole expression. For example, the +following expression produces the absolute value of `x': - x > 0 ? x : -x + x >= 0 ? x : -x - Each time the conditional expression is computed, exactly one of + Each time the conditional expression is computed, only one of IF-TRUE-EXP and IF-FALSE-EXP is used; the other is ignored. This is important when the expressions have side effects. For example, this conditional expression examines element `i' of either array `a' or -array `b', and increments `i'. +array `b', and increments `i': x == y ? a[i++] : b[i++] This is guaranteed to increment `i' exactly once, because each time -only one of the two increment expressions is executed, and the other is +only one of the two increment expressions is executed and the other is not. *Note Arrays in `awk': Arrays, for more information about arrays. - As a minor `gawk' extension, you can continue a statement that uses -`?:' simply by putting a newline after either character. However, you -cannot put a newline in front of either character without using -backslash continuation (*note `awk' Statements Versus Lines: -Statements/Lines.). If `--posix' is specified (*note Command Line + As a minor `gawk' extension, a statement that uses `?:' can be +continued simply by putting a newline after either character. However, +putting a newline in front of either character does not work without +using backslash continuation (*note `awk' Statements Versus Lines: +Statements/Lines.). If `--posix' is specified (*note Command-Line Options: Options.), then this extension is disabled. @@ -5562,58 +6424,55 @@ File: gawk.info, Node: Function Calls, Next: Precedence, Prev: Conditional Ex Function Calls ============== - A "function" is a name for a particular calculation. Because it has -a name, you can ask for it by name at any point in the program. For -example, the function `sqrt' computes the square root of a number. + A "function" is a name for a particular calculation. This enables +you to ask for it by name at any point in the program. For example, +the function `sqrt' computes the square root of a number. A fixed set of functions are "built-in", which means they are available in every `awk' program. The `sqrt' function is one of these. *Note Built-in Functions: Built-in, for a list of built-in functions -and their descriptions. In addition, you can define your own functions -for use in your program. *Note User-defined Functions: User-defined, -for how to do this. +and their descriptions. In addition, you can define functions for use +in your program. *Note User-Defined Functions: User-defined, for +instructions on how to do this. The way to use a function is with a "function call" expression, which consists of the function name followed immediately by a list of -"arguments" in parentheses. The arguments are expressions which -provide the raw materials for the function's calculations. When there -is more than one argument, they are separated by commas. If there are -no arguments, write just `()' after the function name. Here are some -examples: +"arguments" in parentheses. The arguments are expressions that provide +the raw materials for the function's calculations. When there is more +than one argument, they are separated by commas. If there are no +arguments, just write `()' after the function name. The following +examples show function calls with and without arguments: sqrt(x^2 + y^2) one argument atan2(y, x) two arguments rand() no arguments - *Do not put any space between the function name and the -open-parenthesis!* A user-defined function name looks just like the -name of a variable, and space would make the expression look like + *Caution:* Do not put any space between the function name and the +open-parenthesis! A user-defined function name looks just like the +name of a variable--a space would make the expression look like concatenation of a variable with an expression inside parentheses. -Space before the parenthesis is harmless with built-in functions, but -it is best not to get into the habit of using space to avoid mistakes -with user-defined functions. - Each function expects a particular number of arguments. For -example, the `sqrt' function must be called with a single argument, the -number to take the square root of: + With built-in functions, space before the parenthesis is harmless, +but it is best not to get into the habit of using space to avoid +mistakes with user-defined functions. Each function expects a +particular number of arguments. For example, the `sqrt' function must +be called with a single argument: the number to take the square root of: sqrt(ARGUMENT) - Some of the built-in functions allow you to omit the final argument. -If you do so, they use a reasonable default. *Note Built-in Functions: -Built-in, for full details. If arguments are omitted in calls to -user-defined functions, then those arguments are treated as local -variables, initialized to the empty string (*note User-defined -Functions: User-defined.). + Some of the built-in functions have one or more optional arguments. +If those arguments are not supplied, the functions use a reasonable +default value. *Note Built-in Functions: Built-in, for full details. +If arguments are omitted in calls to user-defined functions, then those +arguments are treated as local variables and initialized to the empty +string (*note User-Defined Functions: User-defined.). Like every other expression, the function call has a value, which is computed by the function based on the arguments you give it. In this example, the value of `sqrt(ARGUMENT)' is the square root of ARGUMENT. A function can also have side effects, such as assigning values to -certain variables or doing I/O. - - Here is a command to read numbers, one number per line, and print the -square root of each one: +certain variables or doing I/O. The following program reads numbers, +one number per line, and prints the square root of each one: $ awk '{ print "The square root of", $1, "is", sqrt($1) }' 1 @@ -5622,7 +6481,7 @@ square root of each one: -| The square root of 3 is 1.73205 5 -| The square root of 5 is 2.23607 - Control-d + Ctrl-d File: gawk.info, Node: Precedence, Prev: Function Calls, Up: Expressions @@ -5630,36 +6489,34 @@ File: gawk.info, Node: Precedence, Prev: Function Calls, Up: Expressions Operator Precedence (How Operators Nest) ======================================== - "Operator precedence" determines how operators are grouped, when + "Operator precedence" determines how operators are grouped when different operators appear close by in one expression. For example, `*' has higher precedence than `+'; thus, `a + b * c' means to multiply -`b' and `c', and then add `a' to the product (i.e. `a + (b * c)'). +`b' and `c', and then add `a' to the product (i.e., `a + (b * c)'). - You can overrule the precedence of the operators by using -parentheses. You can think of the precedence rules as saying where the -parentheses are assumed to be if you do not write parentheses yourself. -In fact, it is wise to always use parentheses whenever you have an -unusual combination of operators, because other people who read the -program may not remember what the precedence is in this case. You -might forget, too; then you could make a mistake. Explicit parentheses -will help prevent any such mistake. + The normal precedence of the operators can be overruled by using +parentheses. Think of the precedence rules as saying where the +parentheses are assumed to be. In fact, it is wise to always use +parentheses whenever there is an unusual combination of operators, +because other people who read the program may not remember what the +precedence is in this case. Even experienced programmers occasionally +forget the exact rules, which leads to mistakes. Explicit parentheses +help prevent any such mistakes. When operators of equal precedence are used together, the leftmost -operator groups first, except for the assignment, conditional and +operator groups first, except for the assignment, conditional, and exponentiation operators, which group in the opposite order. Thus, `a -- b + c' groups as `(a - b) + c', and `a = b = c' groups as `a = (b = +- b + c' groups as `(a - b) + c' and `a = b = c' groups as `a = (b = c)'. The precedence of prefix unary operators does not matter as long as only unary operators are involved, because there is only one way to -interpret them--innermost first. Thus, `$++i' means `$(++i)' and +interpret them: innermost first. Thus, `$++i' means `$(++i)' and `++$x' means `++($x)'. However, when another operator follows the -operand, then the precedence of the unary operators can matter. Thus, -`$x^2' means `($x)^2', but `-x^2' means `-(x^2)', because `-' has lower -precedence than `^' while `$' has higher precedence. - - Here is a table of `awk''s operators, in order from highest -precedence to lowest: +operand, then the precedence of the unary operators can matter. `$x^2' +means `($x)^2', but `-x^2' means `-(x^2)', because `-' has lower +precedence than `^', whereas `$' has higher precedence. This table +presents `awk''s operators, in order of highest precedence to lowest: `(...)' Grouping. @@ -5671,11 +6528,10 @@ precedence to lowest: Increment, decrement. `^ **' - Exponentiation. These operators group right-to-left. (The `**' - operator is not specified by POSIX.) + Exponentiation. These operators group right-to-left. `+ - !' - Unary plus, minus, logical "not". + Unary plus, minus, logical "not." `* / %' Multiplication, division, modulus. @@ -5683,25 +6539,26 @@ precedence to lowest: `+ -' Addition, subtraction. -`Concatenation' - No special token is used to indicate concatenation. The operands - are simply written side by side. +`String Concatenation' + No special symbol is used to indicate concatenation. The operands + are simply written side by side (*note String Concatenation: + Concatenation.). `< <= == !=' -`> >= >> |' - Relational, and redirection. The relational operators and the +`> >= >> | |&' + Relational and redirection. The relational operators and the redirections have the same precedence level. Characters such as `>' serve both as relationals and as redirections; the context distinguishes between the two meanings. Note that the I/O redirection operators in `print' and `printf' statements belong to the statement level, not to expressions. The - redirection does not produce an expression which could be the + redirection does not produce an expression that could be the operand of another operator. As a result, it does not make sense to use a redirection operator near another operator of lower - precedence, without parentheses. Such combinations, for example - `print foo > a ? b : c', result in syntax errors. The correct way - to write this statement is `print foo > (a ? b : c)'. + precedence without parentheses. Such combinations (for example + `print foo > a ? b : c'), result in syntax errors. The correct + way to write this statement is `print foo > (a ? b : c)'. `~ !~' Matching, non-matching. @@ -5720,71 +6577,73 @@ precedence to lowest: `= += -= *=' `/= %= ^= **=' - Assignment. These operators group right-to-left. (The `**=' - operator is not specified by POSIX.) + Assignment. These operators group right-to-left. + + *Note:* The `|&', `**', and `**=' operators are not specified by +POSIX. For maximum portability, do not use them. -File: gawk.info, Node: Patterns and Actions, Next: Statements, Prev: Expressions, Up: Top +File: gawk.info, Node: Patterns and Actions, Next: Arrays, Prev: Expressions, Up: Top -Patterns and Actions -******************** +Patterns, Actions, and Variables +******************************** As you have already seen, each `awk' statement consists of a pattern -with an associated action. This chapter describes how you build -patterns and actions. +with an associated action. This major node describes how you build +patterns and actions, what kinds of things you can do within actions, +and `awk''s built-in variables. + + The pattern-action rules and the statements available for use within +actions form the core of `awk' programming. In a sense, everything +covered up to here has been the foundation that programs are built on +top of. Now it's time to start building something useful. * Menu: * Pattern Overview:: What goes into a pattern. +* Using Shell Variables:: How to use shell variables with `awk'. * Action Overview:: What goes into an action. +* Statements:: Describes the various control statements in + detail. +* Built-in Variables:: Summarizes the built-in variables. -File: gawk.info, Node: Pattern Overview, Next: Action Overview, Prev: Patterns and Actions, Up: Patterns and Actions +File: gawk.info, Node: Pattern Overview, Next: Using Shell Variables, Prev: Patterns and Actions, Up: Patterns and Actions Pattern Elements ================ - Patterns in `awk' control the execution of rules: a rule is executed -when its pattern matches the current input record. This section -explains all about how to write patterns. - * Menu: -* Kinds of Patterns:: A list of all kinds of patterns. * Regexp Patterns:: Using regexps as patterns. * Expression Patterns:: Any expression can be used as a pattern. * Ranges:: Pairs of patterns specify record ranges. * BEGIN/END:: Specifying initialization and cleanup rules. * Empty:: The empty pattern, which matches every record. - -File: gawk.info, Node: Kinds of Patterns, Next: Regexp Patterns, Prev: Pattern Overview, Up: Pattern Overview - -Kinds of Patterns ------------------ - - Here is a summary of the types of patterns supported in `awk'. + Patterns in `awk' control the execution of rules--a rule is executed +when its pattern matches the current input record. The following is a +summary of the types of patterns in `awk': `/REGULAR EXPRESSION/' - A regular expression as a pattern. It matches when the text of the - input record fits the regular expression. (*Note Regular - Expressions: Regexp.) + A regular expression. It matches when the text of the input record + fits the regular expression. (*Note Regular Expressions: Regexp.) `EXPRESSION' - A single expression. It matches when its value is non-zero (if a + A single expression. It matches when its value is nonzero (if a number) or non-null (if a string). (*Note Expressions as Patterns: Expression Patterns.) `PAT1, PAT2' A pair of patterns separated by a comma, specifying a range of records. The range includes both the initial record that matches - PAT1, and the final record that matches PAT2. (*Note Specifying + PAT1 and the final record that matches PAT2. (*Note Specifying Record Ranges with Patterns: Ranges.) `BEGIN' `END' - Special patterns for you to supply start-up or clean-up actions - for your `awk' program. (*Note The `BEGIN' and `END' Special + Special patterns for you to supply startup or cleanup actions for + your `awk' program. (*Note The `BEGIN' and `END' Special Patterns: BEGIN/END.) `EMPTY' @@ -5792,13 +6651,13 @@ Kinds of Patterns Pattern: Empty.) -File: gawk.info, Node: Regexp Patterns, Next: Expression Patterns, Prev: Kinds of Patterns, Up: Pattern Overview +File: gawk.info, Node: Regexp Patterns, Next: Expression Patterns, Prev: Pattern Overview, Up: Pattern Overview Regular Expressions as Patterns ------------------------------- - We have been using regular expressions as patterns since our early -examples. This kind of pattern is simply a regexp constant in the + Regular expressions are one of the first kinds of patterns presented +in this book. This kind of pattern is simply a regexp constant in the pattern part of a rule. Its meaning is `$0 ~ /PATTERN/'. The pattern matches when the input record matches the regexp. For example: @@ -5811,35 +6670,29 @@ File: gawk.info, Node: Expression Patterns, Next: Ranges, Prev: Regexp Patter Expressions as Patterns ----------------------- - Any `awk' expression is valid as an `awk' pattern. Then the pattern -matches if the expression's value is non-zero (if a number) or non-null -(if a string). - - The expression is reevaluated each time the rule is tested against a -new input record. If the expression uses fields such as `$1', the -value depends directly on the new input record's text; otherwise, it -depends only on what has happened so far in the execution of the `awk' -program, but that may still be useful. - - A very common kind of expression used as a pattern is the comparison -expression, using the comparison operators described in *Note Variable -Typing and Comparison Expressions: Typing and Comparison. - - Regexp matching and non-matching are also very common expressions. -The left operand of the `~' and `!~' operators is a string. The right -operand is either a constant regular expression enclosed in slashes -(`/REGEXP/'), or any expression, whose string value is used as a -dynamic regular expression (*note Using Dynamic Regexps: Computed -Regexps.). - - The following example prints the second field of each input record -whose first field is precisely `foo'. + Any `awk' expression is valid as an `awk' pattern. The pattern +matches if the expression's value is nonzero (if a number) or non-null +(if a string). The expression is reevaluated each time the rule is +tested against a new input record. If the expression uses fields such +as `$1', the value depends directly on the new input record's text; +otherwise it depends on only what has happened so far in the execution +of the `awk' program. + + Comparison expressions, using the comparison operators described in +*Note Variable Typing and Comparison Expressions: Typing and Comparison, +are a very common kind of pattern. Regexp matching and non-matching +are also very common expressions. The left operand of the `~' and `!~' +operators is a string. The right operand is either a constant regular +expression enclosed in slashes (`/REGEXP/'), or any expression whose +string value is used as a dynamic regular expression (*note Using +Dynamic Regexps: Computed Regexps.). The following example prints the +second field of each input record whose first field is precisely `foo': $ awk '$1 == "foo" { print $2 }' BBS-list -(There is no output, since there is no BBS site named "foo".) Contrast -this with the following regular expression match, which would accept -any record with a first field that contains `foo': +(There is no output, because there is no BBS site with the exact name +`foo'.) Contrast this with the following regular expression match, +which accepts any record with a first field that contains `foo': $ awk '$1 ~ /foo/ { print $2 }' BBS-list -| 555-1234 @@ -5847,18 +6700,21 @@ any record with a first field that contains `foo': -| 555-6480 -| 555-2127 + A regexp constant as a pattern is also a special case of an +expression pattern. The expression `/foo/' has the value one if `foo' +appears in the current input record. Thus, as a pattern, `/foo/' +matches any record containing `foo'. + Boolean expressions are also commonly used as patterns. Whether the pattern matches an input record depends on whether its subexpressions -match. - - For example, the following command prints all records in `BBS-list' -that contain both `2400' and `foo'. +match. For example, the following command prints all the records in +`BBS-list' that contain both `2400' and `foo': $ awk '/2400/ && /foo/' BBS-list -| fooey 555-1234 2400/1200/300 B The following command prints all records in `BBS-list' that contain -_either_ `2400' or `foo', or both. +_either_ `2400' or `foo' (or both, of course): $ awk '/2400/ || /foo/' BBS-list -| alpo-net 555-3412 2400/1200/300 A @@ -5870,7 +6726,7 @@ _either_ `2400' or `foo', or both. -| sabafoo 555-2127 1200/300 C The following command prints all records in `BBS-list' that do _not_ -contain the string `foo'. +contain the string `foo': $ awk '! /foo/' BBS-list -| aardvark 555-5553 1200/300 B @@ -5881,17 +6737,12 @@ contain the string `foo'. -| core 555-2912 1200/300 C -| sdace 555-3430 2400/1200/300 A - The subexpressions of a boolean operator in a pattern can be + The subexpressions of a Boolean operator in a pattern can be constant regular expressions, comparisons, or any other `awk' expressions. Range patterns are not expressions, so they cannot appear -inside boolean patterns. Likewise, the special patterns `BEGIN' and +inside Boolean patterns. Likewise, the special patterns `BEGIN' and `END', which never match any input record, are not expressions and -cannot appear inside boolean patterns. - - A regexp constant as a pattern is also a special case of an -expression pattern. `/foo/' as an expression has the value one if `foo' -appears in the current input record; thus, as a pattern, `/foo/' -matches any record containing `foo'. +cannot appear inside Boolean patterns. File: gawk.info, Node: Ranges, Next: BEGIN/END, Prev: Expression Patterns, Up: Pattern Overview @@ -5899,60 +6750,67 @@ File: gawk.info, Node: Ranges, Next: BEGIN/END, Prev: Expression Patterns, U Specifying Record Ranges with Patterns -------------------------------------- - A "range pattern" is made of two patterns separated by a comma, of -the form `BEGPAT, ENDPAT'. It matches ranges of consecutive input -records. The first pattern, BEGPAT, controls where the range begins, -and the second one, ENDPAT, controls where it ends. For example, + A "range pattern" is made of two patterns separated by a comma, in +the form `BEGPAT, ENDPAT'. It is used to match ranges of consecutive +input records. The first pattern, BEGPAT, controls where the range +begins, while ENDPAT controls where the pattern ends. For example, the +following: - awk '$1 == "on", $1 == "off"' + awk '$1 == "on", $1 == "off"' myfile -prints every record between `on'/`off' pairs, inclusive. +prints every record in `myfile' between `on'/`off' pairs, inclusive. A range pattern starts out by matching BEGPAT against every input -record; when a record matches BEGPAT, the range pattern becomes "turned -on". The range pattern matches this record. As long as it stays -turned on, it automatically matches every input record read. It also -matches ENDPAT against every input record; when that succeeds, the -range pattern is turned off again for the following record. Then it -goes back to checking BEGPAT against each record. +record. When a record matches BEGPAT, the range pattern is "turned on" +and the range pattern matches this record as well. As long as the +range pattern stays turned on, it automatically matches every input +record read. The range pattern also matches ENDPAT against every input +record; when this succeeds, the range pattern is turned off again for +the following record. Then the range pattern goes back to checking +BEGPAT against each record. The record that turns on the range pattern and the one that turns it off both match the range pattern. If you don't want to operate on these records, you can write `if' statements in the rule's action to distinguish them from the records you are interested in. - It is possible for a pattern to be turned both on and off by the same -record, if the record satisfies both conditions. Then the action is -executed for just that record. - - For example, suppose you have text between two identical markers (say -the `%' symbol) that you wish to ignore. You might try to combine a + It is possible for a pattern to be turned on and off by the same +record. If the record satisfies both conditions, then the action is +executed for just that record. For example, suppose there is text +between two identical markers (say the `%' symbol), each on its own +line, that should be ignored. A first attempt would be to combine a range pattern that describes the delimited text with the `next' statement (not discussed yet, *note The `next' Statement: Next -Statement.), which causes `awk' to skip any further processing of the +Statement.). This causes `awk' to skip any further processing of the current record and start over again with the next input record. Such a -program would look like this: +program looks like this: /^%$/,/^%$/ { next } { print } This program fails because the range pattern is both turned on and -turned off by the first line with just a `%' on it. To accomplish this -task, you must write the program this way, using a flag: +turned off by the first line, which just has a `%' on it. To +accomplish this task, write the program in the following manner, using +a flag: /^%$/ { skip = ! skip; next } skip == 1 { next } # skip lines with `skip' set - Note that in a range pattern, the `,' has the lowest precedence (is -evaluated last) of all the operators. Thus, for example, the following -program attempts to combine a range pattern with another, simpler test. + In a range pattern, the comma (`,') has the lowest precedence of all +the operators (i.e., it is evaluated last). Thus, the following +program attempts to combine a range pattern with another simpler test: echo Yes | awk '/1/,/2/ || /Yes/' - The author of this program intended it to mean `(/1/,/2/) || /Yes/'. -However, `awk' interprets this as `/1/, (/2/ || /Yes/)'. This cannot -be changed or worked around; range patterns do not combine with other -patterns. + The intent of this program is `(/1/,/2/) || /Yes/'. However, `awk' +interprets this as `/1/, (/2/ || /Yes/)'. This cannot be changed or +worked around; range patterns do not combine with other patterns: + + $ echo yes | gawk '(/1/,/2/) || /Yes/' + error--> gawk: cmd. line:1: (/1/,/2/) || /Yes/ + error--> gawk: cmd. line:1: ^ parse error + error--> gawk: cmd. line:2: (/1/,/2/) || /Yes/ + error--> gawk: cmd. line:2: ^ unexpected newline File: gawk.info, Node: BEGIN/END, Next: Empty, Prev: Ranges, Up: Pattern Overview @@ -5960,9 +6818,13 @@ File: gawk.info, Node: BEGIN/END, Next: Empty, Prev: Ranges, Up: Pattern Ove The `BEGIN' and `END' Special Patterns -------------------------------------- - `BEGIN' and `END' are special patterns. They are not used to match -input records. Rather, they supply start-up or clean-up actions for -your `awk' script. + All the patterns described so far are for matching input records. +The `BEGIN' and `END' special patterns are different. They supply +startup and cleanup actions for `awk' programs. `BEGIN' and `END' +rules must have actions; there is no default action for these rules +because there is no current record when they run. `BEGIN' and `END' +rules are often referred to as "`BEGIN' and `END' blocks" by long-time +`awk' programmers. * Menu: @@ -5975,61 +6837,59 @@ File: gawk.info, Node: Using BEGIN/END, Next: I/O And BEGIN/END, Prev: BEGIN/ Startup and Cleanup Actions ........................... - A `BEGIN' rule is executed, once, before the first input record has -been read. An `END' rule is executed, once, after all the input has -been read. For example: + A `BEGIN' rule is executed once only, before the first input record +is read. Likewise, an `END' rule is executed once only, after all the +input is read. For example: $ awk ' > BEGIN { print "Analysis of \"foo\"" } > /foo/ { ++n } - > END { print "\"foo\" appears " n " times." }' BBS-list + > END { print "\"foo\" appears", n, "times." }' BBS-list -| Analysis of "foo" -| "foo" appears 4 times. This program finds the number of records in the input file `BBS-list' that contain the string `foo'. The `BEGIN' rule prints a title for the report. There is no need to use the `BEGIN' rule to initialize the -counter `n' to zero, as `awk' does this automatically (*note -Variables::). - - The second rule increments the variable `n' every time a record -containing the pattern `foo' is read. The `END' rule prints the value -of `n' at the end of the run. +counter `n' to zero, since `awk' does this automatically (*note +Variables::). The second rule increments the variable `n' every time a +record containing the pattern `foo' is read. The `END' rule prints the +value of `n' at the end of the run. The special patterns `BEGIN' and `END' cannot be used in ranges or -with boolean operators (indeed, they cannot be used with any operators). - - An `awk' program may have multiple `BEGIN' and/or `END' rules. They -are executed in the order they appear, all the `BEGIN' rules at -start-up and all the `END' rules at termination. `BEGIN' and `END' +with Boolean operators (indeed, they cannot be used with any operators). +An `awk' program may have multiple `BEGIN' and/or `END' rules. They +are executed in the order in which they appear: all the `BEGIN' rules +at startup and all the `END' rules at termination. `BEGIN' and `END' rules may be intermixed with other rules. This feature was added in -the 1987 version of `awk', and is included in the POSIX standard. The -original (1978) version of `awk' required you to put the `BEGIN' rule -at the beginning of the program, and the `END' rule at the end, and -only allowed one of each. This is no longer required, but it is a good -idea in terms of program organization and readability. +the 1987 version of `awk' and is included in the POSIX standard. The +original (1978) version of `awk' required the `BEGIN' rule to be placed +at the beginning of the program, the `END' rule to be placed at the +end, and only allowed one of each. This is no longer required, but it +is a good idea to follow this template in terms of program organization +and readability. Multiple `BEGIN' and `END' rules are useful for writing library -functions, since each library file can have its own `BEGIN' and/or -`END' rule to do its own initialization and/or cleanup. Note that the -order in which library functions are named on the command line controls -the order in which their `BEGIN' and `END' rules are executed. -Therefore you have to be careful to write such rules in library files -so that the order in which they are executed doesn't matter. *Note -Command Line Options: Options, for more information on using library +functions, because each library file can have its own `BEGIN' and/or +`END' rule to do its own initialization and/or cleanup. The order in +which library functions are named on the command line controls the +order in which their `BEGIN' and `END' rules are executed. Therefore +you have to be careful when writing such rules in library files so that +the order in which they are executed doesn't matter. *Note +Command-Line Options: Options, for more information on using library functions. *Note A Library of `awk' Functions: Library Functions, for a number of useful library functions. - If an `awk' program only has a `BEGIN' rule, and no other rules, -then the program exits after the `BEGIN' rule has been run. (The -original version of `awk' used to keep reading and ignoring input until -end of file was seen.) However, if an `END' rule exists, then the -input will be read, even if there are no other rules in the program. -This is necessary in case the `END' rule checks the `FNR' and `NR' -variables (d.c.). + If an `awk' program only has a `BEGIN' rule and no other rules, then +the program exits after the `BEGIN' rule is run.(1) However, if an +`END' rule exists, then the input is read, even if there are no other +rules in the program. This is necessary in case the `END' rule checks +the `FNR' and `NR' variables. - `BEGIN' and `END' rules must have actions; there is no default -action for these rules since there is no current record when they run. + ---------- Footnotes ---------- + + (1) The original version of `awk' used to keep reading and ignoring +input until end of file was seen. File: gawk.info, Node: I/O And BEGIN/END, Prev: Using BEGIN/END, Up: BEGIN/END @@ -6037,38 +6897,42 @@ File: gawk.info, Node: I/O And BEGIN/END, Prev: Using BEGIN/END, Up: BEGIN/EN Input/Output from `BEGIN' and `END' Rules ......................................... - There are several (sometimes subtle) issues involved when doing I/O -from a `BEGIN' or `END' rule. - - The first has to do with the value of `$0' in a `BEGIN' rule. Since -`BEGIN' rules are executed before any input is read, there simply is no -input record, and therefore no fields, when executing `BEGIN' rules. -References to `$0' and the fields yield a null string or zero, -depending upon the context. One way to give `$0' a real value is to -execute a `getline' command without a variable (*note Explicit Input -with `getline': Getline.). Another way is to simply assign a value to -it. - - The second point is similar to the first, but from the other -direction. Inside an `END' rule, what is the value of `$0' and `NF'? -Traditionally, due largely to implementation issues, `$0' and `NF' were -_undefined_ inside an `END' rule. The POSIX standard specified that -`NF' was available in an `END' rule, containing the number of fields -from the last input record. Due most probably to an oversight, the -standard does not say that `$0' is also preserved, although logically -one would think that it should be. In fact, `gawk' does preserve the -value of `$0' for use in `END' rules. Be aware, however, that Unix -`awk', and possibly other implementations, do not. - - The third point follows from the first two. What is the meaning of -`print' inside a `BEGIN' or `END' rule? The meaning is the same as -always, `print $0'. If `$0' is the null string, then this prints an -empty line. Many long time `awk' programmers use `print' in `BEGIN' -and `END' rules, to mean `print ""', relying on `$0' being null. While -you might generally get away with this in `BEGIN' rules, in `gawk' at -least, it is a very bad idea in `END' rules. It is also poor style, -since if you want an empty line in the output, you should say so -explicitly in your program. + There are several (sometimes subtle) points to remember when doing +I/O from a `BEGIN' or `END' rule. The first has to do with the value +of `$0' in a `BEGIN' rule. Because `BEGIN' rules are executed before +any input is read, there simply is no input record, and therefore no +fields, when executing `BEGIN' rules. References to `$0' and the fields +yield a null string or zero, depending upon the context. One way to +give `$0' a real value is to execute a `getline' command without a +variable (*note Explicit Input with `getline': Getline.). Another way +is to simply assign a value to `$0'. + + The second point is similar to the first but from the other +direction. Traditionally, due largely to implementation issues, `$0' +and `NF' were _undefined_ inside an `END' rule. The POSIX standard +specifies that `NF' is available in an `END' rule. It contains the +number of fields from the last input record. Most probably due to an +oversight, the standard does not say that `$0' is also preserved, +although logically one would think that it should be. In fact, `gawk' +does preserve the value of `$0' for use in `END' rules. Be aware, +however, that Unix `awk', and possibly other implementations, do not. + + The third point follows from the first two. The meaning of `print' +inside a `BEGIN' or `END' rule is the same as always: `print $0'. If +`$0' is the null string, then this prints an empty line. Many long +time `awk' programmers use an unadorned `print' in `BEGIN' and `END' +rules, to mean `print ""', relying on `$0' being null. Although one +might generally get away with this in `BEGIN' rules, it is a very bad +idea in `END' rules, at least in `gawk'. It is also poor style, since +if an empty line is needed in the output, the program should print one +explicitly. + + Finally, the `next' and `nextfile' statements are not allowed in a +`BEGIN' rule, because the implicit +read-a-record-and-match-against-the-rules loop has not started yet. +Similarly, those statements are not valid in an `END' rule, since all +the input has been read. (*Note The `next' Statement: Next Statement, +and see *Note Using `gawk''s `nextfile' Statement: Nextfile Statement.) File: gawk.info, Node: Empty, Prev: BEGIN/END, Up: Pattern Overview @@ -6076,7 +6940,7 @@ File: gawk.info, Node: Empty, Prev: BEGIN/END, Up: Pattern Overview The Empty Pattern ----------------- - An empty (i.e. non-existent) pattern is considered to match _every_ + An empty (i.e., non-existent) pattern is considered to match _every_ input record. For example, the program: awk '{ print $1 }' BBS-list @@ -6084,19 +6948,70 @@ input record. For example, the program: prints the first field of every record. -File: gawk.info, Node: Action Overview, Prev: Pattern Overview, Up: Patterns and Actions +File: gawk.info, Node: Using Shell Variables, Next: Action Overview, Prev: Pattern Overview, Up: Patterns and Actions -Overview of Actions -=================== +Using Shell Variables in Programs +================================= - An `awk' program or script consists of a series of rules and -function definitions, interspersed. (Functions are described later. -*Note User-defined Functions: User-defined.) + `awk' programs are often used as components in larger programs +written in shell. For example, it is very common to use a shell +variable to hold a pattern that the `awk' program searches for. There +are two ways to get the value of the shell variable into the body of +the `awk' program. + + The most common method is to use shell quoting to substitute the +variable's value into the program inside the script. For example, in +the following program: + + echo -n "Enter search pattern: " + read pattern + awk "/$pattern/ "'{ nmatches++ } + END { print nmatches, "found" }' /path/to/data + +the `awk' program consists of two pieces of quoted text that are +concatenated together to form the program. The first part is +double-quoted, which allows substitution of the `pattern' variable +inside the quotes. The second part is single-quoted. + + Variable substitution via quoting works, but can be potentially +messy. It requires a good understanding of the shell's quoting rules +(*note Shell Quoting Issues: Quoting.), and it's often difficult to +correctly match up the quotes when reading the program. + + A better method is to use `awk''s variable assignment feature (*note +Assigning Variables on the Command Line: Assignment Options.) to +assign the shell variable's value to an `awk' variable's value. Then +use dynamic regexps to match the pattern (*note Using Dynamic Regexps: +Computed Regexps.). The following shows how to redo the previous +example using this technique: + + echo -n "Enter search pattern: " + read pattern + awk -v pat="$pattern" '$0 ~ pat { nmatches++ } + END { print nmatches, "found" }' /path/to/data + +Now, the `awk' program is just one single-quoted string. The +assignment `-v pat="$pattern"' still requires double quotes, in case +there is whitespace in the value of `$pattern'. The `awk' variable +`pat' could be named `pattern' too, but that would be more confusing. +Using a variable also provides more flexibility, since the variable can +be used anywhere inside the program--for printing, as an array +subscript, or for any other use--without requiring the quoting tricks +at every point in the program. - A rule contains a pattern and an action, either of which (but not -both) may be omitted. The purpose of the "action" is to tell `awk' -what to do once a match for the pattern is found. Thus, in outline, an -`awk' program generally looks like this: + +File: gawk.info, Node: Action Overview, Next: Statements, Prev: Using Shell Variables, Up: Patterns and Actions + +Actions +======= + + An `awk' program or script consists of a series of rules and +function definitions interspersed. (Functions are described later. +*Note User-Defined Functions: User-defined.) A rule contains a pattern +and an action, either of which (but not both) may be omitted. The +purpose of the "action" is to tell `awk' what to do once a match for +the pattern is found. Thus, in outline, an `awk' program generally +looks like this: [PATTERN] [{ ACTION }] [PATTERN] [{ ACTION }] @@ -6105,18 +7020,17 @@ what to do once a match for the pattern is found. Thus, in outline, an ... An action consists of one or more `awk' "statements", enclosed in -curly braces (`{' and `}'). Each statement specifies one thing to be -done. The statements are separated by newlines or semicolons. - - The curly braces around an action must be used even if the action -contains only one statement, or even if it contains no statements at -all. However, if you omit the action entirely, omit the curly braces as -well. An omitted action is equivalent to `{ print $0 }'. +curly braces (`{' and `}'). Each statement specifies one thing to do. +The statements are separated by newlines or semicolons. The curly +braces around an action must be used even if the action contains only +one statement, or if it contains no statements at all. However, if you +omit the action entirely, omit the curly braces as well. An omitted +action is equivalent to `{ print $0 }': - /foo/ { } # match foo, do nothing - empty action - /foo/ # match foo, print the record - omitted action + /foo/ { } match `foo', do nothing -- empty action + /foo/ match `foo', print the record -- omitted action - Here are the kinds of statements supported in `awk': + The following types of statements are supported in `awk': * Expressions, which can call functions or assign values to variables (*note Expressions::). Executing this kind of statement simply @@ -6132,38 +7046,36 @@ well. An omitted action is equivalent to `{ print $0 }'. * Compound statements, which consist of one or more statements enclosed in curly braces. A compound statement is used in order to put several statements together in the body of an `if', - `while', `do' or `for' statement. + `while', `do', or `for' statement. - * Input statements, using the `getline' command (*note Explicit - Input with `getline': Getline.), the `next' statement (*note The - `next' Statement: Next Statement.), and the `nextfile' statement - (*note The `nextfile' Statement: Nextfile Statement.). + * Input statements using the `getline' command (*note Explicit Input + with `getline': Getline.), the `next' statement (*note The `next' + Statement: Next Statement.), and the `nextfile' statement (*note + Using `gawk''s `nextfile' Statement: Nextfile Statement.). - * Output statements, `print' and `printf'. *Note Printing Output: - Printing. + * Output statements, such as `print' and `printf'. *Note Printing + Output: Printing. - * Deletion statements, for deleting array elements. *Note The + * Deletion statements for deleting array elements. *Note The `delete' Statement: Delete. -File: gawk.info, Node: Statements, Next: Built-in Variables, Prev: Patterns and Actions, Up: Top +File: gawk.info, Node: Statements, Next: Built-in Variables, Prev: Action Overview, Up: Patterns and Actions Control Statements in Actions -***************************** +============================= - "Control statements" such as `if', `while', and so on control the + "Control statements", such as `if', `while', and so on, control the flow of execution in `awk' programs. Most of the control statements in `awk' are patterned on similar statements in C. - All the control statements start with special keywords such as `if' -and `while', to distinguish them from simple expressions. - - Many control statements contain other statements; for example, the -`if' statement contains another statement which may or may not be -executed. The contained statement is called the "body". If you want -to include more than one statement in the body, group them into a -single "compound statement" with curly braces, separating them with -newlines or semicolons. + All the control statements start with special keywords, such as `if' +and `while', to distinguish them from simple expressions. Many control +statements contain other statements. For example, the `if' statement +contains another statement that may or may not be executed. The +contained statement is called the "body". To include more than one +statement in the body, group them into a single "compound statement" +with curly braces, separating them with newlines or semicolons. * Menu: @@ -6185,7 +7097,7 @@ newlines or semicolons. File: gawk.info, Node: If Statement, Next: While Statement, Prev: Statements, Up: Statements The `if'-`else' Statement -========================= +------------------------- The `if'-`else' statement is `awk''s decision-making statement. It looks like this: @@ -6193,68 +7105,58 @@ looks like this: if (CONDITION) THEN-BODY [else ELSE-BODY] The CONDITION is an expression that controls what the rest of the -statement will do. If CONDITION is true, THEN-BODY is executed; +statement does. If the CONDITION is true, THEN-BODY is executed; otherwise, ELSE-BODY is executed. The `else' part of the statement is optional. The condition is considered false if its value is zero or -the null string, and true otherwise. - - Here is an example: +the null string; otherwise the condition is true. Refer to the +following: if (x % 2 == 0) print "x is even" else print "x is odd" - In this example, if the expression `x % 2 == 0' is true (that is, + In this example, if the expression `x % 2 == 0' is true (that is, if the value of `x' is evenly divisible by two), then the first `print' -statement is executed, otherwise the second `print' statement is -executed. - - If the `else' appears on the same line as THEN-BODY, and THEN-BODY -is not a compound statement (i.e. not surrounded by curly braces), then -a semicolon must separate THEN-BODY from `else'. To illustrate this, -let's rewrite the previous example: +statement is executed; otherwise the second `print' statement is +executed. If the `else' keyword appears on the same line as THEN-BODY +and THEN-BODY is not a compound statement (i.e., not surrounded by +curly braces), then a semicolon must separate THEN-BODY from the `else'. +To illustrate this, the previous example can be rewritten as: if (x % 2 == 0) print "x is even"; else print "x is odd" -If you forget the `;', `awk' won't be able to interpret the statement, -and you will get a syntax error. - - We would not actually write this example this way, because a human -reader might fail to see the `else' if it were not the first thing on -its line. +If the `;' is left out, `awk' can't interpret the statement and it +produces a syntax error. Don't actually write programs this way, +because a human reader might fail to see the `else' if it is not the +first thing on its line. File: gawk.info, Node: While Statement, Next: Do Statement, Prev: If Statement, Up: Statements The `while' Statement -===================== - - In programming, a "loop" means a part of a program that can be -executed two or more times in succession. +--------------------- - The `while' statement is the simplest looping statement in `awk'. -It repeatedly executes a statement as long as a condition is true. It -looks like this: + In programming, a "loop" is a part of a program that can be executed +two or more times in succession. The `while' statement is the simplest +looping statement in `awk'. It repeatedly executes a statement as long +as a condition is true. For example: while (CONDITION) BODY -Here BODY is a statement that we call the "body" of the loop, and -CONDITION is an expression that controls how long the loop keeps -running. - - The first thing the `while' statement does is test CONDITION. If +BODY is a statement called the "body" of the loop, and CONDITION is an +expression that controls how long the loop keeps running. The first +thing the `while' statement does is test the CONDITION. If the CONDITION is true, it executes the statement BODY. (The CONDITION is true when the value is not zero and not a null string.) After BODY has been executed, CONDITION is tested again, and if it is still true, BODY -is executed again. This process repeats until CONDITION is no longer -true. If CONDITION is initially false, the body of the loop is never -executed, and `awk' continues with the statement following the loop. - - This example prints the first three fields of each record, one per -line. +is executed again. This process repeats until the CONDITION is no +longer true. If the CONDITION is initially false, the body of the loop +is never executed and `awk' continues with the statement following the +loop. This example prints the first three fields of each record, one +per line: awk '{ i = 1 while (i <= 3) { @@ -6263,64 +7165,61 @@ line. } }' inventory-shipped -Here the body of the loop is a compound statement enclosed in braces, -containing two statements. +The body of this loop is a compound statement enclosed in braces, +containing two statements. The loop works in the following manner: +first, the value of `i' is set to one. Then, the `while' statement +tests whether `i' is less than or equal to three. This is true when +`i' equals one, so the `i'-th field is printed. Then the `i++' +increments the value of `i' and the loop repeats. The loop terminates +when `i' reaches four. - The loop works like this: first, the value of `i' is set to one. -Then, the `while' tests whether `i' is less than or equal to three. -This is true when `i' equals one, so the `i'-th field is printed. Then -the `i++' increments the value of `i' and the loop repeats. The loop -terminates when `i' reaches four. - - As you can see, a newline is not required between the condition and -the body; but using one makes the program clearer unless the body is a -compound statement or is very simple. The newline after the open-brace -that begins the compound statement is not required either, but the -program would be harder to read without it. + A newline is not required between the condition and the body; +however using one makes the program clearer unless the body is a +compound statement or else is very simple. The newline after the +open-brace that begins the compound statement is not required either, +but the program is harder to read without it. File: gawk.info, Node: Do Statement, Next: For Statement, Prev: While Statement, Up: Statements The `do'-`while' Statement -========================== +-------------------------- The `do' loop is a variation of the `while' looping statement. The -`do' loop executes the BODY once, and then repeats BODY as long as -CONDITION is true. It looks like this: +`do' loop executes the BODY once and then repeats the BODY as long as +the CONDITION is true. It looks like this: do BODY while (CONDITION) - Even if CONDITION is false at the start, BODY is executed at least -once (and only once, unless executing BODY makes CONDITION true). + Even if the CONDITION is false at the start, the BODY is executed at +least once (and only once, unless executing BODY makes CONDITION true). Contrast this with the corresponding `while' statement: while (CONDITION) BODY -This statement does not execute BODY even once if CONDITION is false to -begin with. - - Here is an example of a `do' statement: +This statement does not execute BODY even once if the CONDITION is +false to begin with. The following is an example of a `do' statement: - awk '{ i = 1 + { i = 1 do { print $0 i++ } while (i <= 10) - }' + } -This program prints each input record ten times. It isn't a very -realistic example, since in this case an ordinary `while' would do just -as well. But this reflects actual experience; there is only -occasionally a real use for a `do' statement. +This program prints each input record ten times. However, it isn't a +very realistic example, since in this case an ordinary `while' would do +just as well. This situation reflects actual experience; only +occasionally is there a real use for a `do' statement. File: gawk.info, Node: For Statement, Next: Break Statement, Prev: Do Statement, Up: Statements The `for' Statement -=================== +------------------- The `for' statement makes it more convenient to count iterations of a loop. The general form of the `for' statement looks like this: @@ -6328,48 +7227,47 @@ loop. The general form of the `for' statement looks like this: for (INITIALIZATION; CONDITION; INCREMENT) BODY -The INITIALIZATION, CONDITION and INCREMENT parts are arbitrary `awk' +The INITIALIZATION, CONDITION, and INCREMENT parts are arbitrary `awk' expressions, and BODY stands for any `awk' statement. The `for' statement starts by executing INITIALIZATION. Then, as -long as CONDITION is true, it repeatedly executes BODY and then -INCREMENT. Typically INITIALIZATION sets a variable to either zero or +long as the CONDITION is true, it repeatedly executes BODY and then +INCREMENT. Typically, INITIALIZATION sets a variable to either zero or one, INCREMENT adds one to it, and CONDITION compares it against the -desired number of iterations. - - Here is an example of a `for' statement: +desired number of iterations. For example: awk '{ for (i = 1; i <= 3; i++) print $i }' inventory-shipped -This prints the first three fields of each input record, one field per -line. +This prints the first three fields of each input record, with one field +per line. - You cannot set more than one variable in the INITIALIZATION part -unless you use a multiple assignment statement such as `x = y = 0', -which is possible only if all the initial values are equal. (But you -can initialize additional variables by writing their assignments as -separate statements preceding the `for' loop.) + It isn't possible to set more than one variable in the +INITIALIZATION part without using a multiple assignment statement such +as `x = y = 0'. This makes sense only if all the initial values are +equal. (But it is possible to initialize additional variables by +writing their assignments as separate statements preceding the `for' +loop.) - The same is true of the INCREMENT part; to increment additional -variables, you must write separate statements at the end of the loop. -The C compound expression, using C's comma operator, would be useful in -this context, but it is not supported in `awk'. + The same is true of the INCREMENT part. Incrementing additional +variables requires separate statements at the end of the loop. The C +compound expression, using C's comma operator, is useful in this +context but it is not supported in `awk'. - Most often, INCREMENT is an increment expression, as in the example -above. But this is not required; it can be any expression whatever. -For example, this statement prints all the powers of two between one -and 100: + Most often, INCREMENT is an increment expression, as in the previous +example. But this is not required; it can be any expression +whatsoever. For example, the following statement prints all the powers +of two between 1 and 100: for (i = 1; i <= 100; i *= 2) print i - Any of the three expressions in the parentheses following the `for' -may be omitted if there is nothing to be done there. Thus, + If there is nothing to be done, any of the three expressions in the +parentheses following the `for' keyword may be omitted. Thus, `for (; x > 0;)' is equivalent to `while (x > 0)'. If the CONDITION is -omitted, it is treated as TRUE, effectively yielding an "infinite loop" -(i.e. a loop that will never terminate). +omitted, it is treated as true, effectively yielding an "infinite loop" +(i.e., a loop that never terminates). In most cases, a `for' loop is an abbreviation for a `while' loop, as shown here: @@ -6381,10 +7279,16 @@ as shown here: } The only exception is when the `continue' statement (*note The -`continue' Statement: Continue Statement.) is used inside the loop; -changing a `for' statement to a `while' statement in this way can +`continue' Statement: Continue Statement.) is used inside the loop. +Changing a `for' statement to a `while' statement in this way can change the effect of the `continue' statement inside the loop. + The `awk' language has a `for' statement in addition to a `while' +statement because a `for' loop is often both less work to type and more +natural to think of. Counting the number of iterations is very common +in loops. It can be easier to think of this counting as part of +looping rather than as something to do inside the loop. + There is an alternate version of the `for' loop, for iterating over all the indices of an array: @@ -6394,102 +7298,95 @@ all the indices of an array: *Note Scanning All Elements of an Array: Scanning an Array, for more information on this version of the `for' loop. - The `awk' language has a `for' statement in addition to a `while' -statement because often a `for' loop is both less work to type and more -natural to think of. Counting the number of iterations is very common -in loops. It can be easier to think of this counting as part of -looping rather than as something to do inside the loop. - - The next section has more complicated examples of `for' loops. - File: gawk.info, Node: Break Statement, Next: Continue Statement, Prev: For Statement, Up: Statements The `break' Statement -===================== +--------------------- The `break' statement jumps out of the innermost `for', `while', or `do' loop that encloses it. The following example finds the smallest divisor of any integer, and also identifies prime numbers: - awk '# find smallest divisor of num - { num = $1 - for (div = 2; div*div <= num; div++) - if (num % div == 0) - break - if (num % div == 0) - printf "Smallest divisor of %d is %d\n", num, div - else - printf "%d is prime\n", num - }' + # find smallest divisor of num + { + num = $1 + for (div = 2; div*div <= num; div++) + if (num % div == 0) + break + if (num % div == 0) + printf "Smallest divisor of %d is %d\n", num, div + else + printf "%d is prime\n", num + } When the remainder is zero in the first `if' statement, `awk' immediately "breaks out" of the containing `for' loop. This means that `awk' proceeds immediately to the statement following the loop and continues processing. (This is very different from the `exit' -statement which stops the entire `awk' program. *Note The `exit' +statement, which stops the entire `awk' program. *Note The `exit' Statement: Exit Statement.) - Here is another program equivalent to the previous one. It -illustrates how the CONDITION of a `for' or `while' could just as well -be replaced with a `break' inside an `if': - - awk '# find smallest divisor of num - { num = $1 - for (div = 2; ; div++) { - if (num % div == 0) { - printf "Smallest divisor of %d is %d\n", num, div - break - } - if (div*div > num) { - printf "%d is prime\n", num - break - } - } - }' + Th following program illustrates how the CONDITION of a `for' or +`while' statement could be replaced with a `break' inside an `if': - As described above, the `break' statement has no meaning when used -outside the body of a loop. However, although it was never documented, -historical implementations of `awk' have treated the `break' statement -outside of a loop as if it were a `next' statement (*note The `next' -Statement: Next Statement.). Recent versions of Unix `awk' no longer -allow this usage. `gawk' will support this use of `break' only if -`--traditional' has been specified on the command line (*note Command -Line Options: Options.). Otherwise, it will be treated as an error, -since the POSIX standard specifies that `break' should only be used -inside the body of a loop (d.c.). + # find smallest divisor of num + { + num = $1 + for (div = 2; ; div++) { + if (num % div == 0) { + printf "Smallest divisor of %d is %d\n", num, div + break + } + if (div*div > num) { + printf "%d is prime\n", num + break + } + } + } + + The `break' statement has no meaning when used outside the body of a +loop. However, although it was never documented, historical +implementations of `awk' treated the `break' statement outside of a +loop as if it were a `next' statement (*note The `next' Statement: Next +Statement.). Recent versions of Unix `awk' no longer allow this usage. +`gawk' supports this use of `break' only if `--traditional' has been +specified on the command line (*note Command-Line Options: Options.). +Otherwise, it is treated as an error, since the POSIX standard +specifies that `break' should only be used inside the body of a loop. +(d.c.) File: gawk.info, Node: Continue Statement, Next: Next Statement, Prev: Break Statement, Up: Statements The `continue' Statement -======================== +------------------------ - The `continue' statement, like `break', is used only inside `for', + As with `break', the `continue' statement is used only inside `for', `while', and `do' loops. It skips over the rest of the loop body, causing the next cycle around the loop to begin immediately. Contrast this with `break', which jumps out of the loop altogether. The `continue' statement in a `for' loop directs `awk' to skip the -rest of the body of the loop, and resume execution with the +rest of the body of the loop and resume execution with the increment-expression of the `for' statement. The following program illustrates this fact: - awk 'BEGIN { + BEGIN { for (x = 0; x <= 20; x++) { if (x == 5) continue printf "%d ", x } print "" - }' + } -This program prints all the numbers from zero to 20, except for five, -for which the `printf' is skipped. Since the increment `x++' is not +This program prints all the numbers from 0 to 20--except for five, for +which the `printf' is skipped. Because the increment `x++' is not skipped, `x' does not remain stuck at five. Contrast the `for' loop -above with this `while' loop: +from the previous example with the following `while' loop: - awk 'BEGIN { + BEGIN { x = 0 while (x <= 20) { if (x == 5) @@ -6498,48 +7395,48 @@ above with this `while' loop: x++ } print "" - }' + } -This program loops forever once `x' gets to five. +This program loops forever once `x' reaches five. - As described above, the `continue' statement has no meaning when -used outside the body of a loop. However, although it was never -documented, historical implementations of `awk' have treated the -`continue' statement outside of a loop as if it were a `next' statement -(*note The `next' Statement: Next Statement.). Recent versions of Unix -`awk' no longer allow this usage. `gawk' will support this use of -`continue' only if `--traditional' has been specified on the command -line (*note Command Line Options: Options.). Otherwise, it will be -treated as an error, since the POSIX standard specifies that `continue' -should only be used inside the body of a loop (d.c.). + The `continue' statement has no meaning when used outside the body of +a loop. Historical versions of `awk' treated a `continue' statement +outside a loop the same way they treated a `break' statement outside a +loop: as if it were a `next' statement (*note The `next' Statement: +Next Statement.). Recent versions of Unix `awk' no longer work this +way, and `gawk' allows it only if `--traditional' is specified on the +command line (*note Command-Line Options: Options.). Just like the +`break' statement, the POSIX standard specifies that `continue' should +only be used inside the body of a loop. (d.c.) File: gawk.info, Node: Next Statement, Next: Nextfile Statement, Prev: Continue Statement, Up: Statements The `next' Statement -==================== +-------------------- The `next' statement forces `awk' to immediately stop processing the current record and go on to the next record. This means that no -further rules are executed for the current record. The rest of the -current rule's action is not executed either. +further rules are executed for the current record, and the rest of the +current rule's action isn't executed. Contrast this with the effect of the `getline' function (*note -Explicit Input with `getline': Getline.). That too causes `awk' to +Explicit Input with `getline': Getline.). That also causes `awk' to read the next record immediately, but it does not alter the flow of -control in any way. So the rest of the current action executes with a -new input record. +control in any way (i.e., the rest of the current action executes with +a new input record). At the highest level, `awk' program execution is a loop that reads an input record and then tests each rule's pattern against it. If you think of this loop as a `for' statement whose body contains the rules, -then the `next' statement is analogous to a `continue' statement: it -skips to the end of the body of this implicit loop, and executes the +then the `next' statement is analogous to a `continue' statement. It +skips to the end of the body of this implicit loop and executes the increment (which reads another record). - For example, if your `awk' program works only on records with four -fields, and you don't want it to fail when given bad input, you might -use this rule near the beginning of the program: + For example, suppose an `awk' program works only on records with +four fields, and it shouldn't fail when given bad input. To avoid +complicating the rest of the program, write a "weed out" rule near the +beginning, in the following manner: NF != 4 { err = sprintf("%s:%d: skipped: NF != 4\n", FILENAME, FNR) @@ -6547,107 +7444,117 @@ use this rule near the beginning of the program: next } -so that the following rules will not see the bad record. The error -message is redirected to the standard error output stream, as error -messages should be. *Note Special File Names in `gawk': Special Files. +Because of the `next' statement, the program's subsequent rules won't +see the bad record. The error message is redirected to the standard +error output stream, as error messages should be. *Note Special File +Names in `gawk': Special Files. According to the POSIX standard, the behavior is undefined if the -`next' statement is used in a `BEGIN' or `END' rule. `gawk' will treat -it as a syntax error. Although POSIX permits it, some other `awk' +`next' statement is used in a `BEGIN' or `END' rule. `gawk' treats it +as a syntax error. Although POSIX permits it, some other `awk' implementations don't allow the `next' statement inside function bodies -(*note User-defined Functions: User-defined.). Just as any other -`next' statement, a `next' inside a function body reads the next record -and starts processing it with the first rule in the program. - - If the `next' statement causes the end of the input to be reached, -then the code in any `END' rules will be executed. *Note The `BEGIN' -and `END' Special Patterns: BEGIN/END. - - *Caution:* Some `awk' implementations generate a run-time error if -you use the `next' statement inside a user-defined function (*note -User-defined Functions: User-defined.). `gawk' does not have this -problem. +(*note User-Defined Functions: User-defined.). Just as with any other +`next' statement, a `next' statement inside a function body reads the +next record and starts processing it with the first rule in the program. +If the `next' statement causes the end of the input to be reached, then +the code in any `END' rules is executed. *Note The `BEGIN' and `END' +Special Patterns: BEGIN/END. File: gawk.info, Node: Nextfile Statement, Next: Exit Statement, Prev: Next Statement, Up: Statements -The `nextfile' Statement -======================== +Using `gawk''s `nextfile' Statement +----------------------------------- `gawk' provides the `nextfile' statement, which is similar to the `next' statement. However, instead of abandoning processing of the current record, the `nextfile' statement instructs `gawk' to stop processing the current data file. + The `nextfile' statement is a `gawk' extension. In most other `awk' +implementations, or if `gawk' is in compatibility mode (*note +Command-Line Options: Options.), `nextfile' is not special. + Upon execution of the `nextfile' statement, `FILENAME' is updated to the name of the next data file listed on the command line, `FNR' is reset to one, `ARGIND' is incremented, and processing starts over with -the first rule in the progam. *Note Built-in Variables::. - - If the `nextfile' statement causes the end of the input to be -reached, then the code in any `END' rules will be executed. *Note The -`BEGIN' and `END' Special Patterns: BEGIN/END. - - The `nextfile' statement is a `gawk' extension; it is not -(currently) available in any other `awk' implementation. *Note -Implementing `nextfile' as a Function: Nextfile Function, for a -user-defined function you can use to simulate the `nextfile' statement. - - The `nextfile' statement would be useful if you have many data files -to process, and you expect that you would not want to process every -record in every file. Normally, in order to move on to the next data -file, you would have to continue scanning the unwanted records. The -`nextfile' statement accomplishes this much more efficiently. +the first rule in the program. (`ARGIND' hasn't been introduced yet. +*Note Built-in Variables::.) If the `nextfile' statement causes the +end of the input to be reached, then the code in any `END' rules is +executed. *Note The `BEGIN' and `END' Special Patterns: BEGIN/END. + + The `nextfile' statement is useful when there are many data files to +process but it isn't necessary to process every record in every file. +Normally, in order to move on to the next data file, a program has to +continue scanning the unwanted records. The `nextfile' statement +accomplishes this much more efficiently. + + While one might think that `close(FILENAME)' would accomplish the +same as `nextfile', this isn't true. `close' is reserved for closing +files, pipes, and coprocesses that are opened with redirections. It is +not related to the main processing that `awk' does with the files +listed in `ARGV'. + + If it's necessary to use an `awk' version that doesn't support +`nextfile', see *Note Implementing `nextfile' as a Function: Nextfile +Function, for a user-defined function that simulates the `nextfile' +statement. + + The current version of the Bell Laboratories `awk' (*note Other +Freely Available `awk' Implementations: Other Versions.) also supports +`nextfile'. However, it doesn't allow the `nextfile' statement inside +function bodies (*note User-Defined Functions: User-defined.). `gawk' +does; a `nextfile' inside a function body reads the next record and +starts processing it with the first rule in the program, just as any +other `nextfile' statement. *Caution:* Versions of `gawk' prior to 3.0 used two words (`next -file') for the `nextfile' statement. This was changed in 3.0 to one -word, since the treatment of `file' was inconsistent. When it appeared -after `next', it was a keyword. Otherwise, it was a regular -identifier. The old usage is still accepted. However, `gawk' will -generate a warning message, and support for `next file' will eventually -be discontinued in a future version of `gawk'. +file') for the `nextfile' statement. In version 3.0, this was changed +to one word, because the treatment of `file' was inconsistent. When it +appeared after `next', `file' was a keyword; otherwise, it was a +regular identifier. The old usage is no longer accepted; `next file' +generates a syntax error. File: gawk.info, Node: Exit Statement, Prev: Nextfile Statement, Up: Statements The `exit' Statement -==================== +-------------------- The `exit' statement causes `awk' to immediately stop executing the current rule and to stop processing input; any remaining input is -ignored. It looks like this: +ignored. The `exit' statement is written as follows: exit [RETURN CODE] - If an `exit' statement is executed from a `BEGIN' rule the program -stops processing everything immediately. No input records are read. -However, if an `END' rule is present, it is executed (*note The `BEGIN' -and `END' Special Patterns: BEGIN/END.). - - If `exit' is used as part of an `END' rule, it causes the program to -stop immediately. + When an `exit' statement is executed from a `BEGIN' rule, the +program stops processing everything immediately. No input records are +read. However, if an `END' rule is present, as part of executing the +`exit' statement, the `END' rule is executed (*note The `BEGIN' and +`END' Special Patterns: BEGIN/END.). If `exit' is used as part of an +`END' rule, it causes the program to stop immediately. An `exit' statement that is not part of a `BEGIN' or `END' rule stops the execution of any further automatic rules for the current record, skips reading any remaining input records, and executes the `END' rule if there is one. - If you do not want the `END' rule to do its job in this case, you -can set a variable to non-zero before the `exit' statement, and check -that variable in the `END' rule. *Note Assertions: Assert Function, -for an example that does this. + In such a case, if you don't want the `END' rule to do its job, set +a variable to nonzero before the `exit' statement and check that +variable in the `END' rule. *Note Assertions: Assert Function, for an +example that does this. If an argument is supplied to `exit', its value is used as the exit status code for the `awk' process. If no argument is supplied, `exit' returns status zero (success). In the case where an argument is supplied to a first `exit' statement, and then `exit' is called a -second time with no argument, the previously supplied exit value is -used (d.c.). +second time from an `END' rule with no argument, `awk' uses the +previously supplied exit value. (d.c.) - For example, let's say you've discovered an error condition you -really don't know how to handle. Conventionally, programs report this -by exiting with a non-zero status. Your `awk' program can do this -using an `exit' statement with a non-zero argument. Here is an example: + For example, suppose an error condition occurs that is difficult or +impossible to handle. Conventionally, programs report this by exiting +with a nonzero status. An `awk' program can do this using an `exit' +statement with a nonzero argument, as shown in the following example: BEGIN { if (("date" | getline date_now) <= 0) { @@ -6659,69 +7566,88 @@ using an `exit' statement with a non-zero argument. Here is an example: } -File: gawk.info, Node: Built-in Variables, Next: Arrays, Prev: Statements, Up: Top +File: gawk.info, Node: Built-in Variables, Prev: Statements, Up: Patterns and Actions Built-in Variables -****************** +================== Most `awk' variables are available for you to use for your own -purposes; they never change except when your program assigns values to -them, and never affect anything except when your program examines them. -However, a few variables in `awk' have special built-in meanings. Some -of them `awk' examines automatically, so that they enable you to tell -`awk' how to do certain things. Others are set automatically by `awk', -so that they carry information from the internal workings of `awk' to -your program. - - This chapter documents all the built-in variables of `gawk'. Most -of them are also documented in the chapters describing their areas of +purposes; they never change unless your program assigns values to them, +and they never affect anything unless your program examines them. +However, a few variables in `awk' have special built-in meanings. +`awk' examines some of these automatically, so that they enable you to +tell `awk' how to do certain things. Others are set automatically by +`awk', so that they carry information from the internal workings of +`awk' to your program. + + This minor node documents all the built-in variables of `gawk', most +of which are also documented in the chapters describing their areas of activity. * Menu: * User-modified:: Built-in variables that you change to control `awk'. -* Auto-set:: Built-in variables where `awk' gives you - information. +* Auto-set:: Built-in variables where `awk' gives + you information. * ARGC and ARGV:: Ways to use `ARGC' and `ARGV'. File: gawk.info, Node: User-modified, Next: Auto-set, Prev: Built-in Variables, Up: Built-in Variables -Built-in Variables that Control `awk' -===================================== +Built-in Variables That Control `awk' +------------------------------------- - This is an alphabetical list of the variables which you can change to -control how `awk' does certain things. Those variables that are -specific to `gawk' are marked with an asterisk, `*'. + The following is an alphabetical list of variables that you can +change to control how `awk' does certain things. The variables that are +specific to `gawk' are marked with a pound sign (`#'). + +`BINMODE #' + On non-POSIX systems, this variable specifies use of "binary" mode + for all I/O. Numeric values of one, two, or three, specify that + input files, output files, or all files, respectively, should use + binary I/O. Alternatively, string values of `"r"' or `"w"' + specify that input files and output files, respectively, should + use binary I/O. A string value of `"rw"' or `"wr"' indicates that + all files should use binary I/O. Any other string value is + equivalent to `"rw"', but `gawk' generates a warning message. + `BINMODE' is described in more detail in *Note Using `gawk' on PC + Operating Systems: PC Using. + + This variable is a `gawk' extension. In other `awk' + implementations (except `mawk', *note Other Freely Available `awk' + Implementations: Other Versions.), or if `gawk' is in + compatibility mode (*note Command-Line Options: Options.), it is + not special. `CONVFMT' This string controls conversion of numbers to strings (*note Conversion of Strings and Numbers: Conversion.). It works by being passed, in effect, as the first argument to the `sprintf' - function (*note Built-in Functions for String Manipulation: String - Functions.). Its default value is `"%.6g"'. `CONVFMT' was - introduced by the POSIX standard. - -`FIELDWIDTHS *' - This is a space separated list of columns that tells `gawk' how to - split input with fixed, columnar boundaries. It is an - experimental feature. Assigning to `FIELDWIDTHS' overrides the - use of `FS' for field splitting. *Note Reading Fixed-width Data: - Constant Size, for more information. - - If `gawk' is in compatibility mode (*note Command Line Options: - Options.), then `FIELDWIDTHS' has no special meaning, and field - splitting operations are done based exclusively on the value of + function (*note String Manipulation Functions: String Functions.). + Its default value is `"%.6g"'. `CONVFMT' was introduced by the + POSIX standard. + +`FIELDWIDTHS #' + This is a space-separated list of columns that tells `gawk' how to + split input with fixed columnar boundaries. Assigning a value to + `FIELDWIDTHS' overrides the use of `FS' for field splitting. + *Note Reading Fixed-Width Data: Constant Size, for more + information. + + If `gawk' is in compatibility mode (*note Command-Line Options: + Options.), then `FIELDWIDTHS' has no special meaning, and + field-splitting operations occur based exclusively on the value of `FS'. `FS' - `FS' is the input field separator (*note Specifying How Fields are + This is the input field separator (*note Specifying How Fields Are Separated: Field Separators.). The value is a single-character string or a multi-character regular expression that matches the separations between fields in an input record. If the value is the null string (`""'), then each character in the record becomes - a separate field. + a separate field. (This behavior is a `gawk' extension. POSIX + `awk' does not specify the behavior when `FS' is the null string.) The default value is `" "', a string consisting of a single space. As a special exception, this value means that any sequence of @@ -6734,61 +7660,94 @@ specific to `gawk' are marked with an asterisk, `*'. awk -F, 'PROGRAM' INPUT-FILES - If `gawk' is using `FIELDWIDTHS' for field-splitting, assigning a - value to `FS' will cause `gawk' to return to the normal, - `FS'-based, field splitting. An easy way to do this is to simply - say `FS = FS', perhaps with an explanatory comment. - -`IGNORECASE *' - If `IGNORECASE' is non-zero or non-null, then all string - comparisons, and all regular expression matching are - case-independent. Thus, regexp matching with `~' and `!~', and - the `gensub', `gsub', `index', `match', `split' and `sub' - functions, record termination with `RS', and field splitting with - `FS' all ignore case when doing their particular regexp operations. - The value of `IGNORECASE' does _not_ affect array subscripting. - *Note Case-sensitivity in Matching: Case-sensitivity. - - If `gawk' is in compatibility mode (*note Command Line Options: - Options.), then `IGNORECASE' has no special meaning, and string + If `gawk' is using `FIELDWIDTHS' for field splitting, assigning a + value to `FS' causes `gawk' to return to the normal, `FS'-based + field splitting. An easy way to do this is to simply say `FS = + FS', perhaps with an explanatory comment. + +`IGNORECASE #' + If `IGNORECASE' is nonzero or non-null, then all string comparisons + and all regular expression matching are case-independent. Thus, + regexp matching with `~' and `!~', as well as the `gensub', + `gsub', `index', `match', `split', and `sub' functions, record + termination with `RS', and field splitting with `FS', all ignore + case when doing their particular regexp operations. However, the + value of `IGNORECASE' does _not_ affect array subscripting. *Note + Case Sensitivity in Matching: Case-sensitivity. + + If `gawk' is in compatibility mode (*note Command-Line Options: + Options.), then `IGNORECASE' has no special meaning. Thus, string and regexp operations are always case-sensitive. +`LINT #' + When this variable is true (nonzero or non-null), `gawk' behaves + as if the `--lint' command-line option is in effect. (*note + Command-Line Options: Options.). With a value of `"fatal"', lint + warnings become fatal errors. Any other true value prints + non-fatal warnings. Assigning a false value to `LINT' turns off + the lint warnings. + + This variable is a `gawk' extension. It is not special in other + `awk' implementations. Unlike the other special variables, + changing `LINT' does affect the production of lint warnings, even + if `gawk' is in compatibility mode. Much as the `--lint' and + `--traditional' options independently control different aspects of + `gawk''s behavior, the control of lint warnings during program + execution is independent of the flavor of `awk' being executed. + `OFMT' This string controls conversion of numbers to strings (*note Conversion of Strings and Numbers: Conversion.) for printing with - the `print' statement. It works by being passed, in effect, as - the first argument to the `sprintf' function (*note Built-in - Functions for String Manipulation: String Functions.). Its - default value is `"%.6g"'. Earlier versions of `awk' also used - `OFMT' to specify the format for converting numbers to strings in - general expressions; this is now done by `CONVFMT'. + the `print' statement. It works by being passed as the first + argument to the `sprintf' function (*note String Manipulation + Functions: String Functions.). Its default value is `"%.6g"'. + Earlier versions of `awk' also used `OFMT' to specify the format + for converting numbers to strings in general expressions; this is + now done by `CONVFMT'. `OFS' This is the output field separator (*note Output Separators::). - It is output between the fields output by a `print' statement. Its - default value is `" "', a string consisting of a single space. + It is output between the fields printed by a `print' statement. + Its default value is `" "', a string consisting of a single space. `ORS' This is the output record separator. It is output at the end of - every `print' statement. Its default value is `"\n"'. (*Note - Output Separators::.) + every `print' statement. Its default value is `"\n"', the newline + character. (*Note Output Separators::.) `RS' This is `awk''s input record separator. Its default value is a string containing a single newline character, which means that an input record consists of a single line of text. It can also be the null string, in which case records are separated by runs of - blank lines, or a regexp, in which case records are separated by - matches of the regexp in the input text. (*Note How Input is - Split into Records: Records.) + blank lines. If it is a regexp, records are separated by matches + of the regexp in the input text. (*Note How Input Is Split into + Records: Records.) + + The ability for `RS' to be a regular expression is a `gawk' + extension. In most other `awk' implementations, or if `gawk' is + in compatibility mode (*note Command-Line Options: Options.), just + the first character of `RS''s value is used. `SUBSEP' - `SUBSEP' is the subscript separator. It has the default value of - `"\034"', and is used to separate the parts of the indices of a - multi-dimensional array. Thus, the expression `foo["A", "B"]' - really accesses `foo["A\034B"]' (*note Multi-dimensional Arrays: + This is the subscript separator. It has the default value of + `"\034"' and is used to separate the parts of the indices of a + multidimensional array. Thus, the expression `foo["A", "B"]' + really accesses `foo["A\034B"]' (*note Multidimensional Arrays: Multi-dimensional.). +`TEXTDOMAIN #' + This variable is used for internationalization of programs at the + `awk' level. It sets the default text domain for specially marked + string constants in the source text, as well as for the + `dcgettext' and `bindtextdomain' functions (*note + Internationalization with `gawk': Internationalization.). The + default value of `TEXTDOMAIN' is `"messages"'. + + This variable is a `gawk' extension. In other `awk' + implementations, or if `gawk' is in compatibility mode (*note + Command-Line Options: Options.), it is not special. + ---------- Footnotes ---------- (1) In POSIX `awk', newline does not count as whitespace. @@ -6796,136 +7755,184 @@ specific to `gawk' are marked with an asterisk, `*'. File: gawk.info, Node: Auto-set, Next: ARGC and ARGV, Prev: User-modified, Up: Built-in Variables -Built-in Variables that Convey Information -========================================== +Built-in Variables That Convey Information +------------------------------------------ - This is an alphabetical list of the variables that are set -automatically by `awk' on certain occasions in order to provide -information to your program. Those variables that are specific to -`gawk' are marked with an asterisk, `*'. + The following is an alphabetical list of variables that `awk' sets +automatically on certain occasions in order to provide information to +your program. The variables that are specific to `gawk' are marked +with an asterisk (`*'). -`ARGC' -`ARGV' +`ARGC, ARGV' The command-line arguments available to `awk' programs are stored in an array called `ARGV'. `ARGC' is the number of command-line - arguments present. *Note Other Command Line Arguments: Other - Arguments. Unlike most `awk' arrays, `ARGV' is indexed from zero - to `ARGC' - 1. For example: + arguments present. *Note Other Command-Line Arguments: Other + Arguments. Unlike most `awk' arrays, `ARGV' is indexed from 0 to + `ARGC' - 1. In the following example: $ awk 'BEGIN { - > for (i = 0; i < ARGC; i++) - > print ARGV[i] + > for (i = 0; i < ARGC; i++) + > print ARGV[i] > }' inventory-shipped BBS-list -| awk -| inventory-shipped -| BBS-list - In this example, `ARGV[0]' contains `"awk"', `ARGV[1]' contains - `"inventory-shipped"', and `ARGV[2]' contains `"BBS-list"'. The + `ARGV[0]' contains `"awk"', `ARGV[1]' contains + `"inventory-shipped"' and `ARGV[2]' contains `"BBS-list"'. The value of `ARGC' is three, one more than the index of the last - element in `ARGV', since the elements are numbered from zero. + element in `ARGV', because the elements are numbered from zero. The names `ARGC' and `ARGV', as well as the convention of indexing - the array from zero to `ARGC' - 1, are derived from the C - language's method of accessing command line arguments. *Note - Using `ARGC' and `ARGV': ARGC and ARGV, for information about how - `awk' uses these variables. - -`ARGIND *' - The index in `ARGV' of the current file being processed. Every - time `gawk' opens a new data file for processing, it sets `ARGIND' - to the index in `ARGV' of the file name. When `gawk' is - processing the input files, it is always true that `FILENAME == - ARGV[ARGIND]'. + the array from 0 to `ARGC' - 1, are derived from the C language's + method of accessing command-line arguments. + + The value of `ARGV[0]' can vary from system to system. Also, you + should note that the program text is _not_ included in `ARGV', nor + are any of `awk''s command-line options. *Note Using `ARGC' and + `ARGV': ARGC and ARGV, for information about how `awk' uses these + variables. + +`ARGIND #' + This is the index in `ARGV' of the current file being processed. + Every time `gawk' opens a new data file for processing, it sets + `ARGIND' to the index in `ARGV' of the file name. When `gawk' is + processing the input files, `FILENAME == ARGV[ARGIND]' is always + true. This variable is useful in file processing; it allows you to tell - how far along you are in the list of data files, and to - distinguish between successive instances of the same filename on + how far along you are in the list of data files as well as to + distinguish between successive instances of the same file name on the command line. While you can change the value of `ARGIND' within your `awk' - program, `gawk' will automatically set it to a new value when the - next file is opened. + program, `gawk' automatically sets it to a new value when the next + file is opened. - This variable is a `gawk' extension. In other `awk' + This variable is a `gawk' extension. In other `awk' implementations, or if `gawk' is in compatibility mode (*note - Command Line Options: Options.), it is not special. + Command-Line Options: Options.), it is not special. `ENVIRON' An associative array that contains the values of the environment. - The array indices are the environment variable names; the values + The array indices are the environment variable names; the elements are the values of the particular environment variables. For example, `ENVIRON["HOME"]' might be `/home/arnold'. Changing this array does not affect the environment passed on to any programs that `awk' may spawn via redirection or the `system' function. - (In a future version of `gawk', it may do so.) Some operating systems may not have environment variables. On such systems, the `ENVIRON' array is empty (except for - `ENVIRON["AWKPATH"]'). + `ENVIRON["AWKPATH"]', *note The `AWKPATH' Environment Variable: + AWKPATH Variable.). -`ERRNO *' - If a system error occurs either doing a redirection for `getline', +`ERRNO #' + If a system error occurs during a redirection for `getline', during a read for `getline', or during a `close' operation, then - `ERRNO' will contain a string describing the error. + `ERRNO' contains a string describing the error. - This variable is a `gawk' extension. In other `awk' + This variable is a `gawk' extension. In other `awk' implementations, or if `gawk' is in compatibility mode (*note - Command Line Options: Options.), it is not special. + Command-Line Options: Options.), it is not special. `FILENAME' This is the name of the file that `awk' is currently reading. When no data files are listed on the command line, `awk' reads - from the standard input, and `FILENAME' is set to `"-"'. + from the standard input and `FILENAME' is set to `"-"'. `FILENAME' is changed each time a new file is read (*note Reading Input Files: Reading Files.). Inside a `BEGIN' rule, the value of `FILENAME' is `""', since there are no input files being processed - yet.(1) (d.c.) + yet.(1) (d.c.) Note though, that using `getline' (*note Explicit + Input with `getline': Getline.) inside a `BEGIN' rule can give + `FILENAME' a value. `FNR' - `FNR' is the current record number in the current file. `FNR' is + This is the current record number in the current file. `FNR' is incremented each time a new record is read (*note Explicit Input with `getline': Getline.). It is reinitialized to zero each time a new input file is started. `NF' - `NF' is the number of fields in the current input record. `NF' is - set each time a new record is read, when a new field is created, - or when `$0' changes (*note Examining Fields: Fields.). + This is the number of fields in the current input record. `NF' is + set each time a new record is read, when a new field is created or + when `$0' changes (*note Examining Fields: Fields.). `NR' This is the number of input records `awk' has processed since the - beginning of the program's execution (*note How Input is Split - into Records: Records.). `NR' is set each time a new record is - read. + beginning of the program's execution (*note How Input Is Split + into Records: Records.). `NR' is incremented each time a new + record is read. + +`PROCINFO #' + The elements of this array provide access to information about the + running `awk' program. The following elements (listed + alphabetically) are guaranteed to be available: + + `PROCINFO["egid"]' + The value of the `getegid' system call. + + `PROCINFO["euid"]' + The value of the `geteuid' system call. + + `PROCINFO["FS"]' + This is `"FS"' if field splitting with `FS' is in effect, or + it is `"FIELDWIDTHS"' if field splitting with `FIELDWIDTHS' + is in effect. + + `PROCINFO["gid"]' + The value of the `getgid' system call. + + `PROCINFO["pgrpid"]' + The process group ID of the current process. + + `PROCINFO["pid"]' + The process ID of the current process. + + `PROCINFO["ppid"]' + The parent process ID of the current process. + + `PROCINFO["uid"]' + The value of the `getuid' system call. + + On some systems, there may be elements in the array, `"group1"' + through `"groupN"' for some N. N is the number of supplementary + groups that the process has. Use the `in' operator to test for + these elements (*note Referring to an Array Element: Reference to + Elements.). + + This array is a `gawk' extension. In other `awk' implementations, + or if `gawk' is in compatibility mode (*note Command-Line Options: + Options.), it is not special. `RLENGTH' - `RLENGTH' is the length of the substring matched by the `match' - function (*note Built-in Functions for String Manipulation: String - Functions.). `RLENGTH' is set by invoking the `match' function. - Its value is the length of the matched string, or -1 if no match - was found. + This is the length of the substring matched by the `match' function + (*note String Manipulation Functions: String Functions.). + `RLENGTH' is set by invoking the `match' function. Its value is + the length of the matched string, or -1 if no match is found. `RSTART' - `RSTART' is the start-index in characters of the substring matched - by the `match' function (*note Built-in Functions for String - Manipulation: String Functions.). `RSTART' is set by invoking the + This is the start-index in characters of the substring that is + matched by the `match' function (*note String Manipulation + Functions: String Functions.). `RSTART' is set by invoking the `match' function. Its value is the position of the string where the matched substring starts, or zero if no match was found. -`RT *' - `RT' is set each time a record is read. It contains the input text +`RT #' + This is set each time a record is read. It contains the input text that matched the text denoted by `RS', the record separator. - This variable is a `gawk' extension. In other `awk' + This variable is a `gawk' extension. In other `awk' implementations, or if `gawk' is in compatibility mode (*note - Command Line Options: Options.), it is not special. + Command-Line Options: Options.), it is not special. + +Advanced Notes: Changing `NR' and `FNR' +--------------------------------------- - A side note about `NR' and `FNR'. `awk' simply increments both of -these variables each time it reads a record, instead of setting them to -the absolute value of the number of records read. This means that your -program can change these variables, and their new values will be -incremented for each record (d.c.). For example: + `awk' increments `NR' and `FNR' each time it reads a record, instead +of setting them to the absolute value of the number of records read. +This means that a program can change these variables and their new +values are incremented for each record. (d.c.) This is demonstrated +in the following example: $ echo '1 > 2 @@ -6938,7 +7945,7 @@ incremented for each record (d.c.). For example: -| 19 Before `FNR' was added to the `awk' language (*note Major Changes -between V7 and SVR3.1: V7/SVR3.1.), many `awk' programs used this +Between V7 and SVR3.1: V7/SVR3.1.), many `awk' programs used this feature to track the number of records in a file by resetting `NR' to zero when `FILENAME' changed. @@ -6946,17 +7953,17 @@ zero when `FILENAME' changed. (1) Some early implementations of Unix `awk' initialized `FILENAME' to `"-"', even if there were data files to be processed. This behavior -was incorrect, and should not be relied upon in your programs. +was incorrect and should not be relied upon in your programs. File: gawk.info, Node: ARGC and ARGV, Prev: Auto-set, Up: Built-in Variables Using `ARGC' and `ARGV' -======================= +----------------------- - In *Note Built-in Variables that Convey Information: Auto-set, you -saw this program describing the information contained in `ARGC' and -`ARGV': + *Note Built-in Variables That Convey Information: Auto-set, +presented the following program describing the information contained in +`ARGC' and `ARGV': $ awk 'BEGIN { > for (i = 0; i < ARGC; i++) @@ -6966,15 +7973,14 @@ saw this program describing the information contained in `ARGC' and -| inventory-shipped -| BBS-list -In this example, `ARGV[0]' contains `"awk"', `ARGV[1]' contains -`"inventory-shipped"', and `ARGV[2]' contains `"BBS-list"'. - - Notice that the `awk' program is not entered in `ARGV'. The other -special command line options, with their arguments, are also not -entered. This includes variable assignments done with the `-v' option -(*note Command Line Options: Options.). Normal variable assignments on -the command line _are_ treated as arguments, and do show up in the -`ARGV' array. +In this example, `ARGV[0]' contains `awk', `ARGV[1]' contains +`inventory-shipped', and `ARGV[2]' contains `BBS-list'. Notice that +the `awk' program is not entered in `ARGV'. The other special +command-line options, with their arguments, are also not entered. This +includes variable assignments done with the `-v' option (*note +Command-Line Options: Options.). Normal variable assignments on the +command line _are_ treated as arguments and do show up in the `ARGV' +array: $ cat showargs.awk -| BEGIN { @@ -6985,38 +7991,35 @@ the command line _are_ treated as arguments, and do show up in the -| END { printf "A=%d, B=%d\n", A, B } $ awk -v A=1 -f showargs.awk B=2 /dev/null -| A=1, B=0 - -| ARGV[0] = awk - -| ARGV[1] = B=2 - -| ARGV[2] = /dev/null + -| ARGV[0] = awk + -| ARGV[1] = B=2 + -| ARGV[2] = /dev/null -| A=1, B=2 - Your program can alter `ARGC' and the elements of `ARGV'. Each time + A program can alter `ARGC' and the elements of `ARGV'. Each time `awk' reaches the end of an input file, it uses the next element of `ARGV' as the name of the next input file. By storing a different -string there, your program can change which files are read. You can -use `"-"' to represent the standard input. By storing additional -elements and incrementing `ARGC' you can cause additional files to be -read. +string there, a program can change which files are read. Use `"-"' to +represent the standard input. Storing additional elements and +incrementing `ARGC' causes additional files to be read. - If you decrease the value of `ARGC', that eliminates input files + If the value of `ARGC' is decreased, that eliminates input files from the end of the list. By recording the old value of `ARGC' -elsewhere, your program can treat the eliminated arguments as something +elsewhere, a program can treat the eliminated arguments as something other than file names. To eliminate a file from the middle of the list, store the null string (`""') into `ARGV' in place of the file's name. As a special feature, `awk' ignores file names that have been replaced with the null -string. You may also use the `delete' statement to remove elements from -`ARGV' (*note The `delete' Statement: Delete.). +string. Another option is to use the `delete' statement to remove +elements from `ARGV' (*note The `delete' Statement: Delete.). - All of these actions are typically done from the `BEGIN' rule, -before actual processing of the input begins. *Note Splitting a Large -File Into Pieces: Split Program, and see *Note Duplicating Output Into -Multiple Files: Tee Program, for an example of each way of removing -elements from `ARGV'. - - The following fragment processes `ARGV' in order to examine, and -then remove, command line options. + All of these actions are typically done in the `BEGIN' rule, before +actual processing of the input begins. *Note Splitting a Large File +into Pieces: Split Program, and see *Note Duplicating Output into +Multiple Files: Tee Program, for examples of each way of removing +elements from `ARGV'. The following fragment processes `ARGV' in order +to examine, and then remove, command-line options: BEGIN { for (i = 1; i < ARGC; i++) { @@ -7034,36 +8037,44 @@ then remove, command line options. } } - To actually get the options into the `awk' program, you have to end -the `awk' options with `--', and then supply your options, like so: + To actually get the options into the `awk' program, end the `awk' +options with `--' and then supply the `awk' program's options, in the +following manner: awk -f myprog -- -v -d file1 file2 ... - This is not necessary in `gawk': Unless `--posix' has been + This is not necessary in `gawk'. Unless `--posix' has been specified, `gawk' silently puts any unrecognized options into `ARGV' -for the `awk' program to deal with. - - As soon as it sees an unknown option, `gawk' stops looking for other -options it might otherwise recognize. The above example with `gawk' -would be: +for the `awk' program to deal with. As soon as it sees an unknown +option, `gawk' stops looking for other options that it might otherwise +recognize. The previous example with `gawk' would be: gawk -f myprog -d -v file1 file2 ... -Since `-d' is not a valid `gawk' option, the following `-v' is passed -on to the `awk' program. +Because `-d' is not a valid `gawk' option, it and the following `-v' +are passed on to the `awk' program. -File: gawk.info, Node: Arrays, Next: Built-in, Prev: Built-in Variables, Up: Top +File: gawk.info, Node: Arrays, Next: Functions, Prev: Patterns and Actions, Up: Top Arrays in `awk' *************** - An "array" is a table of values, called "elements". The elements of + An "array" is a table of values called "elements". The elements of an array are distinguished by their indices. "Indices" may be either -numbers or strings. `awk' maintains a single set of names that may be -used for naming variables, arrays and functions (*note User-defined -Functions: User-defined.). Thus, you cannot have a variable and an -array with the same name in the same `awk' program. +numbers or strings. + + This major node describes how arrays work in `awk', how to use array +elements, how to scan through every element in an array, and how to +remove array elements. It also describes how `awk' simulates +multidimensional arrays, as well as some of the less obvious points +about array usage. The major node finishes with a discussion of +`gawk''s facility for sorting an array based on its indices. + + `awk' maintains a single set of names that may be used for naming +variables, arrays, and functions (*note User-Defined Functions: +User-defined.). Thus, you cannot have a variable and an array with the +same name in the same `awk' program. * Menu: @@ -7079,10 +8090,10 @@ array with the same name in the same `awk' program. * Numeric Array Subscripts:: How to use numbers as subscripts in `awk'. * Uninitialized Subscripts:: Using Uninitialized variables as subscripts. -* Multi-dimensional:: Emulating multi-dimensional arrays in +* Multi-dimensional:: Emulating multidimensional arrays in `awk'. -* Multi-scanning:: Scanning multi-dimensional arrays. -* Array Efficiency:: Implementation-specific tips. +* Multi-scanning:: Scanning multidimensional arrays. +* Array Sorting:: Sorting array values and indices. File: gawk.info, Node: Array Intro, Next: Reference to Elements, Prev: Arrays, Up: Arrays @@ -7090,74 +8101,75 @@ File: gawk.info, Node: Array Intro, Next: Reference to Elements, Prev: Arrays Introduction to Arrays ====================== - The `awk' language provides one-dimensional "arrays" for storing -groups of related strings or numbers. - - Every `awk' array must have a name. Array names have the same -syntax as variable names; any valid variable name would also be a valid -array name. But you cannot use one name in both ways (as an array and -as a variable) in one `awk' program. + The `awk' language provides one-dimensional arrays for storing +groups of related strings or numbers. Every `awk' array must have a +name. Array names have the same syntax as variable names; any valid +variable name would also be a valid array name. But one name cannot be +used in both ways (as an array and as a variable) in the same `awk' +program. Arrays in `awk' superficially resemble arrays in other programming -languages; but there are fundamental differences. In `awk', you don't -need to specify the size of an array before you start to use it. -Additionally, any number or string in `awk' may be used as an array -index, not just consecutive integers. - - In most other languages, you have to "declare" an array and specify -how many elements or components it contains. In such languages, the -declaration causes a contiguous block of memory to be allocated for that -many elements. An index in the array usually must be a positive -integer; for example, the index zero specifies the first element in the -array, which is actually stored at the beginning of the block of -memory. Index one specifies the second element, which is stored in -memory right after the first element, and so on. It is impossible to -add more elements to the array, because it has room for only as many -elements as you declared. (Some languages allow arbitrary starting and -ending indices, e.g., `15 .. 27', but the size of the array is still -fixed when the array is declared.) - - A contiguous array of four elements might look like this, -conceptually, if the element values are eight, `"foo"', `""' and 30: +languages, but there are fundamental differences. In `awk', it isn't +necessary to specify the size of an array before starting to use it. +Additionally, any number or string in `awk', not just consecutive +integers, may be used as an array index. + + In most other languages, arrays must be "declared" before use, +including a specification of how many elements or components they +contain. In such languages, the declaration causes a contiguous block +of memory to be allocated for that many elements. Usually, an index in +the array must be a positive integer. For example, the index zero +specifies the first element in the array, which is actually stored at +the beginning of the block of memory. Index one specifies the second +element, which is stored in memory right after the first element, and +so on. It is impossible to add more elements to the array, because it +has room only for as many elements as given in the declaration. (Some +languages allow arbitrary starting and ending indices--e.g., `15 .. +27'--but the size of the array is still fixed when the array is +declared.) + + A contiguous array of four elements might look like the following +example, conceptually, if the element values are 8, `"foo"', `""', and +30: +---------+---------+--------+---------+ - | 8 | "foo" | "" | 30 | value + | 8 | "foo" | "" | 30 | Value +---------+---------+--------+---------+ - 0 1 2 3 index + 0 1 2 3 Index Only the values are stored; the indices are implicit from the order of -the values. Eight is the value at index zero, because eight appears in -the position with zero elements before it. +the values. 8 is the value at index zero, because 8 appears in the +position with zero elements before it. - Arrays in `awk' are different: they are "associative". This means + Arrays in `awk' are different--they are "associative". This means that each array is a collection of pairs: an index, and its corresponding array element value: - Element 4 Value 30 - Element 2 Value "foo" - Element 1 Value 8 - Element 3 Value "" + Element 3 Value 30 + Element 1 Value "foo" + Element 0 Value 8 + Element 2 Value "" -We have shown the pairs in jumbled order because their order is -irrelevant. +The pairs are shown in jumbled order because their order is irrelevant. One advantage of associative arrays is that new pairs can be added -at any time. For example, suppose we add to the above array a tenth -element whose value is `"number ten"'. The result is this: +at any time. For example, suppose a tenth element is added to the array +whose value is `"number ten"'. The result is: Element 10 Value "number ten" - Element 4 Value 30 - Element 2 Value "foo" - Element 1 Value 8 - Element 3 Value "" + Element 3 Value 30 + Element 1 Value "foo" + Element 0 Value 8 + Element 2 Value "" -Now the array is "sparse", which just means some indices are missing: -it has elements 1-4 and 10, but doesn't have elements 5, 6, 7, 8, or 9. +Now the array is "sparse", which just means some indices are missing. +It has elements 0-3 and 10, but doesn't have elements 4, 5, 6, 7, 8, or +9. Another consequence of associative arrays is that the indices don't have to be positive integers. Any number, or even a string, can be an -index. For example, here is an array which translates words from -English into French: +index. For example, the following is an array that translates words +from English into French: Element "dog" Value "chien" Element "cat" Value "chat" @@ -7166,17 +8178,20 @@ English into French: Here we decided to translate the number one in both spelled-out and numeric form--thus illustrating that a single array can have both -numbers and strings as indices. (In fact, array subscripts are always +numbers and strings as indices. In fact, array subscripts are always strings; this is discussed in more detail in *Note Using Numbers to -Subscript Arrays: Numeric Array Subscripts.) +Subscript Arrays: Numeric Array Subscripts. Here, the number `1' isn't +double-quoted, since `awk' automatically converts it to a string. The value of `IGNORECASE' has no effect upon array subscripting. -You must use the exact same string value to retrieve an array element -as you used to store it. +The identical string value used to store an array element must be used +to retrieve it. When `awk' creates an array (e.g., with the `split' +built-in function), that array's indices are consecutive integers +starting at one. (*Note String Manipulation Functions: String +Functions.) - When `awk' creates an array for you, e.g., with the `split' built-in -function, that array's indices are consecutive integers starting at one. -(*Note Built-in Functions for String Manipulation: String Functions.) + `awk''s arrays are efficient--the time to access an element is +independent of the number of elements in the array. File: gawk.info, Node: Reference to Elements, Next: Assigning Elements, Prev: Array Intro, Up: Arrays @@ -7184,47 +8199,44 @@ File: gawk.info, Node: Reference to Elements, Next: Assigning Elements, Prev: Referring to an Array Element ============================= - The principal way of using an array is to refer to one of its -elements. An array reference is an expression which looks like this: + The principal way to use an array is to refer to one of its elements. +An array reference is an expression as follows: ARRAY[INDEX] Here, ARRAY is the name of an array. The expression INDEX is the index -of the element of the array that you want. +of the desired element of the array. The value of the array reference is the current value of that array element. For example, `foo[4.3]' is an expression for the element of array `foo' at index `4.3'. - If you refer to an array element that has no recorded value, the -value of the reference is `""', the null string. This includes elements -to which you have not assigned any value, and elements that have been -deleted (*note The `delete' Statement: Delete.). Such a reference + A reference to an array element that has no recorded value yields a +value of `""', the null string. This includes elements that have not +been assigned any value as well as elements that have been deleted +(*note The `delete' Statement: Delete.). Such a reference automatically creates that array element, with the null string as its value. (In some cases, this is unfortunate, because it might waste memory inside `awk'.) - You can find out if an element exists in an array at a certain index -with the expression: + To determine whether an element exists in an array at a certain +index, use the following expression: INDEX in ARRAY This expression tests whether or not the particular index exists, without the side effect of creating that element if it is not present. -The expression has the value one (true) if `ARRAY[INDEX]' exists, and -zero (false) if it does not exist. - - For example, to test whether the array `frequencies' contains the -index `2', you could write this statement: +The expression has the value one (true) if `ARRAY[INDEX]' exists and +zero (false) if it does not exist. For example, this statement tests +whether the array `frequencies' contains the index `2': if (2 in frequencies) print "Subscript 2 is present." - Note that this is _not_ a test of whether or not the array -`frequencies' contains an element whose _value_ is two. (There is no -way to do that except to scan all the elements.) Also, this _does not_ -create `frequencies[2]', while the following (incorrect) alternative -would do so: + Note that this is _not_ a test of whether the array `frequencies' +contains an element whose _value_ is two. There is no way to do that +except to scan all the elements. Also, this _does not_ create +`frequencies[2]', while the following (incorrect) alternative does: if (frequencies[2] != "") print "Subscript 2 is present." @@ -7235,15 +8247,13 @@ File: gawk.info, Node: Assigning Elements, Next: Array Example, Prev: Referen Assigning Array Elements ======================== - Array elements are lvalues: they can be assigned values just like -`awk' variables: + Array elements can be assigned values just like `awk' variables: ARRAY[SUBSCRIPT] = VALUE -Here ARRAY is the name of your array. The expression SUBSCRIPT is the -index of the element of the array that you want to assign a value. The -expression VALUE is the value you are assigning to that element of the -array. +ARRAY is the name of an array. The expression SUBSCRIPT is the index +of the element of the array that is assigned a value. The expression +VALUE is the value to assign to that element of the array. File: gawk.info, Node: Array Example, Next: Scanning an Array, Prev: Assigning Elements, Up: Arrays @@ -7253,12 +8263,12 @@ Basic Array Example The following program takes a list of lines, each beginning with a line number, and prints them out in order of line number. The line -numbers are not in order, however, when they are first read: they are +numbers are not in order when they are first read--instead they are scrambled. This program sorts the lines by making an array using the -line numbers as subscripts. It then prints out the lines in sorted -order of their numbers. It is a very simple program, and gets confused -if it encounters repeated numbers, gaps, or lines that don't begin with -a number. +line numbers as subscripts. The program then prints out the lines in +sorted order of their numbers. It is a very simple program and gets +confused upon encountering repeated numbers, gaps, or lines that don't +begin with a number: { if ($1 > max) @@ -7273,12 +8283,9 @@ a number. The first rule keeps track of the largest line number seen so far; it also stores each line into the array `arr', at an index that is the -line's number. - - The second rule runs after all the input has been read, to print out -all the lines. - - When this program is run with the following input: +line's number. The second rule runs after all the input has been read, +to print out all the lines. When this program is run with the +following input: 5 I am the Five man 2 Who are you? The new number two! @@ -7286,7 +8293,7 @@ all the lines. 1 Who is number one? 3 I three you. -its output is this: +its output is: 1 Who is number one? 2 Who are you? The new number two! @@ -7295,10 +8302,8 @@ its output is this: 5 I am the Five man If a line number is repeated, the last line with a given number -overrides the others. - - Gaps in the line numbers can be handled with an easy improvement to -the program's `END' rule: +overrides the others. Gaps in the line numbers can be handled with an +easy improvement to the program's `END' rule, as follows: END { for (x = 1; x <= max; x++) @@ -7312,36 +8317,36 @@ File: gawk.info, Node: Scanning an Array, Next: Delete, Prev: Array Example, Scanning All Elements of an Array ================================= - In programs that use arrays, you often need a loop that executes -once for each element of an array. In other languages, where arrays are -contiguous and indices are limited to positive integers, this is easy: -you can find all the valid indices by counting from the lowest index up -to the highest. This technique won't do the job in `awk', since any -number or string can be an array index. So `awk' has a special kind of -`for' statement for scanning an array: + In programs that use arrays, it is often necessary to use a loop that +executes once for each element of an array. In other languages, where +arrays are contiguous and indices are limited to positive integers, +this is easy: all the valid indices can be found by counting from the +lowest index up to the highest. This technique won't do the job in +`awk', because any number or string can be an array index. So `awk' +has a special kind of `for' statement for scanning an array: for (VAR in ARRAY) BODY -This loop executes BODY once for each index in ARRAY that your program +This loop executes BODY once for each index in ARRAY that the program has previously used, with the variable VAR set to that index. - Here is a program that uses this form of the `for' statement. The + The following program uses this form of the `for' statement. The first rule scans the input records and notes which words appear (at least once) in the input, by storing a one into the array `used' with the word as index. The second rule scans the elements of `used' to find all the distinct words that appear in the input. It prints each -word that is more than 10 characters long, and also prints the number of -such words. *Note Built-in Functions for String Manipulation: String -Functions, for more information on the built-in function `length'. +word that is more than 10 characters long and also prints the number of +such words. *Note String Manipulation Functions: String Functions, for +more information on the built-in function `length'. - # Record a 1 for each word that is used at least once. + # Record a 1 for each word that is used at least once { for (i = 1; i <= NF; i++) used[$i] = 1 } - # Find number of distinct words more than 10 characters long. + # Find number of distinct words more than 10 characters long END { for (x in used) if (length(x) > 10) { @@ -7358,7 +8363,7 @@ example of this type. statement is determined by the internal arrangement of the array elements within `awk' and cannot be controlled or changed. This can lead to problems if new elements are added to ARRAY by statements in -the loop body; you cannot predict whether or not the `for' loop will +the loop body; it is not predictable whether or not the `for' loop will reach them. Similarly, changing VAR inside the loop may produce strange results. It is best to avoid such things. @@ -7368,83 +8373,84 @@ File: gawk.info, Node: Delete, Next: Numeric Array Subscripts, Prev: Scanning The `delete' Statement ====================== - You can remove an individual element of an array using the `delete' + To remove an individual element of an array, use the `delete' statement: delete ARRAY[INDEX] - Once you have deleted an array element, you can no longer obtain any -value the element once had. It is as if you had never referred to it -and had never given it any value. - - Here is an example of deleting elements in an array: + Once an array element has been deleted, any value the element once +had is no longer available. It is as if the element had never been +referred to or had been given a value. The following is an example of +deleting elements in an array: for (i in frequencies) delete frequencies[i] This example removes all the elements from the array `frequencies'. - - If you delete an element, a subsequent `for' statement to scan the -array will not report that element, and the `in' operator to check for -the presence of that element will return zero (i.e. false): +Once an element is deleted, a subsequent `for' statement to scan the +array does not report that element and the `in' operator to check for +the presence of that element returns zero (i.e., false): delete foo[4] if (4 in foo) print "This will never be printed" It is important to note that deleting an element is _not_ the same -as assigning it a null value (the empty string, `""'). +as assigning it a null value (the empty string, `""'). For example: foo[4] = "" if (4 in foo) print "This is printed, even though foo[4] is empty" - It is not an error to delete an element that does not exist. + It is not an error to delete an element that does not exist. If +`--lint' is provided on the command line (*note Command-Line Options: +Options.), `gawk' issues a warning message when an element that is not +in the array is deleted. - You can delete all the elements of an array with a single statement, -by leaving off the subscript in the `delete' statement. + All the elements of an array may be deleted with a single statement +by leaving off the subscript in the `delete' statement, as follows: delete ARRAY This ability is a `gawk' extension; it is not available in -compatibility mode (*note Command Line Options: Options.). +compatibility mode (*note Command-Line Options: Options.). Using this version of the `delete' statement is about three times more efficient than the equivalent loop that deletes each element one at a time. - The following statement provides a portable, but non-obvious way to -clear out an array. + The following statement provides a portable but non-obvious way to +clear out an array:(1) - # thanks to Michael Brennan for pointing this out split("", array) - The `split' function (*note Built-in Functions for String -Manipulation: String Functions.) clears out the target array first. -This call asks it to split apart the null string. Since there is no -data to split out, the function simply clears the array and then -returns. + The `split' function (*note String Manipulation Functions: String +Functions.) clears out the target array first. This call asks it to +split apart the null string. Because there is no data to split out, the +function simply clears the array and then returns. *Caution:* Deleting an array does not change its type; you cannot -delete an array and then use the array's name as a scalar. For example, -this will not work: +delete an array and then use the array's name as a scalar (i.e., a +regular variable). For example, the following does not work: a[1] = 3; delete a; a = 3 + ---------- Footnotes ---------- + + (1) Thanks to Michael Brennan for pointing this out. + File: gawk.info, Node: Numeric Array Subscripts, Next: Uninitialized Subscripts, Prev: Delete, Up: Arrays Using Numbers to Subscript Arrays ================================= - An important aspect of arrays to remember is that _array subscripts -are always strings_. If you use a numeric value as a subscript, it -will be converted to a string value before it is used for subscripting -(*note Conversion of Strings and Numbers: Conversion.). - - This means that the value of the built-in variable `CONVFMT' can -potentially affect how your program accesses elements of an array. For -example: + An important aspect about arrays to remember is that _array +subscripts are always strings_. When a numeric value is used as a +subscript, it is converted to a string value before being used for +subscripting (*note Conversion of Strings and Numbers: Conversion.). +This means that the value of the built-in variable `CONVFMT' can affect +how your program accesses elements of an array. For example: xyz = 12.153 data[xyz] = 1 @@ -7457,26 +8463,32 @@ example: This prints `12.15 is not in data'. The first statement gives `xyz' a numeric value. Assigning to `data[xyz]' subscripts `data' with the string value `"12.153"' (using the default conversion value of -`CONVFMT', `"%.6g"'), and assigns one to `data["12.153"]'. The program -then changes the value of `CONVFMT'. The test `(xyz in data)' -generates a new string value from `xyz', this time `"12.15"', since the -value of `CONVFMT' only allows two significant digits. This test fails, -since `"12.15"' is a different string from `"12.153"'. +`CONVFMT', `"%.6g"'). Thus, the array element `data["12.153"]' is +assigned the value one. The program then changes the value of +`CONVFMT'. The test `(xyz in data)' generates a new string value from +`xyz'--this time `"12.15"'--because the value of `CONVFMT' only allows +two significant digits. This test fails, since `"12.15"' is a +different string from `"12.153"'. According to the rules for conversions (*note Conversion of Strings and Numbers: Conversion.), integer values are always converted to strings as integers, no matter what the value of `CONVFMT' may happen -to be. So the usual case of: +to be. So the usual case of the following works: for (i = 1; i <= maxsub; i++) do something with array[i] -will work, no matter what the value of `CONVFMT'. + The "integer values always convert to strings as integers" rule has +an additional consequence for array indexing. Octal and hexadecimal +constants (*note Octal and Hexadecimal Numbers: Non-decimal-numbers.) +are converted internally into numbers and their original form is +forgotten. This means, for example, that `array[17]', `array[021]', and +`array[0x11]' all refer to the same element! - Like many things in `awk', the majority of the time things work as -you would expect them to work. But it is useful to have a precise -knowledge of the actual rules, since sometimes they can have a subtle -effect on your programs. + As with many things in `awk', the majority of the time things work +as one would expect them to. But it is useful to have a precise +knowledge of the actual rules which sometimes can have a subtle effect +on your programs. File: gawk.info, Node: Uninitialized Subscripts, Next: Multi-dimensional, Prev: Numeric Array Subscripts, Up: Arrays @@ -7484,9 +8496,9 @@ File: gawk.info, Node: Uninitialized Subscripts, Next: Multi-dimensional, Pre Using Uninitialized Variables as Subscripts =========================================== - Suppose you want to print your input data in reverse order. A -reasonable attempt at a program to do so (with some test data) might -look like this: + Suppose it's necessary to write a program to print the input data in +reverse order. A reasonable attempt to do so (with some test data) +might look like this: $ echo 'line 1 > line 2 @@ -7505,11 +8517,10 @@ the output! `lines' is uninitialized, and uninitialized variables have the numeric value zero. So, `awk' should have printed the value of `l[0]'. - The issue here is that subscripts for `awk' arrays are *always* -strings. And uninitialized variables, when used as strings, have the -value `""', not zero. Thus, `line 1' ended up stored in `l[""]'. - - The following version of the program works correctly: + The issue here is that subscripts for `awk' arrays are _always_ +strings. Uninitialized variables, when used as strings, have the value +`""', not zero. Thus, `line 1' ends up stored in `l[""]'. The +following version of the program works correctly: { l[lines++] = $0 } END { @@ -7518,37 +8529,37 @@ value `""', not zero. Thus, `line 1' ended up stored in `l[""]'. } Here, the `++' forces `lines' to be numeric, thus making the "old -value" numeric zero, which is then converted to `"0"' as the array +value" numeric zero. This is then converted to `"0"' as the array subscript. - As we have just seen, even though it is somewhat unusual, the null -string (`""') is a valid array subscript (d.c.). If `--lint' is provided -on the command line (*note Command Line Options: Options.), `gawk' will -warn about the use of the null string as a subscript. + Even though it is somewhat unusual, the null string (`""') is a +valid array subscript. (d.c.) `gawk' warns about the use of the null +string as a subscript if `--lint' is provided on the command line +(*note Command-Line Options: Options.). File: gawk.info, Node: Multi-dimensional, Next: Multi-scanning, Prev: Uninitialized Subscripts, Up: Arrays -Multi-dimensional Arrays -======================== +Multidimensional Arrays +======================= - A multi-dimensional array is an array in which an element is -identified by a sequence of indices, instead of a single index. For + A multidimensional array is an array in which an element is +identified by a sequence of indices instead of a single index. For example, a two-dimensional array requires two indices. The usual way (in most languages, including `awk') to refer to an element of a two-dimensional array named `grid' is with `grid[X,Y]'. - Multi-dimensional arrays are supported in `awk' through -concatenation of indices into one string. What happens is that `awk' -converts the indices into strings (*note Conversion of Strings and -Numbers: Conversion.) and concatenates them together, with a separator -between them. This creates a single string that describes the values -of the separate indices. The combined string is used as a single index -into an ordinary, one-dimensional array. The separator used is the -value of the built-in variable `SUBSEP'. + Multidimensional arrays are supported in `awk' through concatenation +of indices into one string. `awk' converts the indices into strings +(*note Conversion of Strings and Numbers: Conversion.) and concatenates +them together, with a separator between them. This creates a single +string that describes the values of the separate indices. The combined +string is used as a single index into an ordinary, one-dimensional +array. The separator used is the value of the built-in variable +`SUBSEP'. For example, suppose we evaluate the expression `foo[5,12] = "value"' -when the value of `SUBSEP' is `"@"'. The numbers five and 12 are +when the value of `SUBSEP' is `"@"'. The numbers 5 and 12 are converted to strings and concatenated with an `@' between them, yielding `"5@12"'; thus, the array element `foo["5@12"]' is set to `"value"'. @@ -7559,19 +8570,17 @@ expressions `foo[5,12]' and `foo[5 SUBSEP 12]' are always equivalent. The default value of `SUBSEP' is the string `"\034"', which contains a non-printing character that is unlikely to appear in an `awk' program -or in most input data. - - The usefulness of choosing an unlikely character comes from the fact -that index values that contain a string matching `SUBSEP' lead to -combined strings that are ambiguous. Suppose that `SUBSEP' were `"@"'; -then `foo["a@b", "c"]' and `foo["a", "b@c"]' would be indistinguishable -because both would actually be stored as `foo["a@b@c"]'. - - You can test whether a particular index-sequence exists in a -"multi-dimensional" array with the same operator `in' used for single -dimensional arrays. Instead of a single index as the left-hand operand, -write the whole sequence of indices, separated by commas, in -parentheses: +or in most input data. The usefulness of choosing an unlikely +character comes from the fact that index values that contain a string +matching `SUBSEP' can lead to combined strings that are ambiguous. +Suppose that `SUBSEP' is `"@"'; then `foo["a@b", "c"]' and +`foo["a", "b@c"]' are indistinguishable because both are actually +stored as `foo["a@b@c"]'. + + To test whether a particular index sequence exists in a +"multidimensional" array, use the same operator (`in') that is used for +single dimensional arrays. Write the whole sequence of indices in +parentheses, separated by commas, as the left operand: (SUBSCRIPT1, SUBSCRIPT2, ...) in ARRAY @@ -7579,7 +8588,7 @@ parentheses: fields; it rotates this array 90 degrees clockwise and prints the result. It assumes that all lines have the same number of elements. - awk '{ + { if (max_nf < NF) max_nf = NF max_nr = NR @@ -7593,7 +8602,7 @@ result. It assumes that all lines have the same number of elements. printf("%s ", vector[x, y]) printf("\n") } - }' + } When given the input: @@ -7602,7 +8611,7 @@ When given the input: 3 4 5 6 1 2 4 5 6 1 2 3 -it produces: +the program produces the following output: 4 3 2 1 5 4 3 2 @@ -7612,85 +8621,146 @@ it produces: 3 2 1 6 -File: gawk.info, Node: Multi-scanning, Next: Array Efficiency, Prev: Multi-dimensional, Up: Arrays +File: gawk.info, Node: Multi-scanning, Next: Array Sorting, Prev: Multi-dimensional, Up: Arrays -Scanning Multi-dimensional Arrays -================================= +Scanning Multidimensional Arrays +================================ There is no special `for' statement for scanning a -"multi-dimensional" array; there cannot be one, because in truth there -are no multi-dimensional arrays or elements; there is only a -multi-dimensional _way of accessing_ an array. +"multidimensional" array. There cannot be one, because in truth there +are no multidimensional arrays or elements--there is only a +multidimensional _way of accessing_ an array. However, if your program has an array that is always accessed as -multi-dimensional, you can get the effect of scanning it by combining +multidimensional, you can get the effect of scanning it by combining the scanning `for' statement (*note Scanning All Elements of an Array: -Scanning an Array.) with the `split' built-in function (*note Built-in -Functions for String Manipulation: String Functions.). It works like -this: +Scanning an Array.) with the built-in `split' function (*note String +Manipulation Functions: String Functions.). It works in the following +manner: for (combined in array) { - split(combined, separate, SUBSEP) - ... + split(combined, separate, SUBSEP) + ... } -This sets `combined' to each concatenated, combined index in the array, -and splits it into the individual indices by breaking it apart where -the value of `SUBSEP' appears. The split-out indices become the -elements of the array `separate'. +This sets the variable `combined' to each concatenated combined index +in the array, and splits it into the individual indices by breaking it +apart where the value of `SUBSEP' appears. The individual indices then +become the elements of the array `separate'. - Thus, suppose you have previously stored a value in `array[1, -"foo"]'; then an element with index `"1\034foo"' exists in `array'. -(Recall that the default value of `SUBSEP' is the character with code -034.) Sooner or later the `for' statement will find that index and do -an iteration with `combined' set to `"1\034foo"'. Then the `split' -function is called as follows: + Thus, if a value is previously stored in `array[1, "foo"]'; then an +element with index `"1\034foo"' exists in `array'. (Recall that the +default value of `SUBSEP' is the character with code 034.) Sooner or +later, the `for' statement finds that index and does an iteration with +the variable `combined' set to `"1\034foo"'. Then the `split' function +is called as follows: split("1\034foo", separate, "\034") -The result of this is to set `separate[1]' to `"1"' and `separate[2]' -to `"foo"'. Presto, the original sequence of separate indices has been +The result is to set `separate[1]' to `"1"' and `separate[2]' to +`"foo"'. Presto! The original sequence of separate indices is recovered. -File: gawk.info, Node: Array Efficiency, Prev: Multi-scanning, Up: Arrays +File: gawk.info, Node: Array Sorting, Prev: Multi-scanning, Up: Arrays -Using Array Memory Efficiently -============================== +Sorting Array Values and Indices with `gawk' +============================================ - This section applies just to `gawk'. + The order in which an array is scanned with a `for (i in array)' +loop is essentially arbitrary. In most `awk' implementations, sorting +an array requires writing a `sort' function. While this can be +educational for exploring different sorting algorithms, usually that's +not the point of the program. `gawk' provides the built-in `asort' +function (*note String Manipulation Functions: String Functions.) that +sorts an array. For example: + + POPULATE THE ARRAY data + n = asort(data) + for (i = 1; i <= n; i++) + DO SOMETHING WITH data[i] + + After the call to `asort', the array `data' is indexed from 1 to +some number N, the total number of elements in `data'. (This count is +`asort''s return value.) `data[1]' <= `data[2]' <= `data[3]', and so +on. The comparison of array elements is done using `gawk''s usual +comparison rules (*note Variable Typing and Comparison Expressions: +Typing and Comparison.). + + An important side effect of calling `asort' is that _the array's +original indices are irrevocably lost_. As this isn't always +desirable, `asort' accepts a second argument: + + POPULATE THE ARRAY source + n = asort(source, dest) + for (i = 1; i <= n; i++) + DO SOMETHING WITH dest[i] + + In this case, `gawk' copies the `source' array into the `dest' array +and then sorts `dest', destroying its indices. However, the `source' +array is not affected. + + Often, what's needed is to sort on the values of the _indices_ +instead of the values of the elements. To do this, use a helper array +to hold the sorted index values, and then access the original array's +elements. It works in the following way: + + POPULATE THE ARRAY data + # copy indices + j = 1 + for (i in data) { + ind[j] = i # index value becomes element value + j++ + } + n = asort(ind) # index values are now sorted + for (i = 1; i <= n; i++) + DO SOMETHING WITH data[ind[i]] - It is often useful to use the same bit of data as an index into -multiple arrays. Due to the way `gawk' implements associative arrays, -when you need to use input data as an index for multiple arrays, it is -much more effecient to assign the input field to a separate variable, -and then use that variable as the index. + Sorting the array by replacing the indices provides maximal +flexibility. To traverse the elements in decreasing order, use a loop +that goes from N down to 1, either over the elements or over the +indices. - { - name = $1 - ssn = $2 - nkids = $3 - ... - seniority[name]++ # better than seniority[$1]++ - kids[name] = nkids # better than kids[$1] = nkids - } + Copying array indices and elements isn't expensive in terms of +memory. Internally, `gawk' maintains "reference counts" to data. For +example, when `asort' copies the first array to the second one, there +is only one copy of the original array elements' data, even though both +arrays use the values. Similarly, when copying the indices from `data' +to `ind', there is only one copy of the actual index strings. + + As with array subscripts, the value of `IGNORECASE' does not affect +array sorting. + + +File: gawk.info, Node: Functions, Next: Internationalization, Prev: Arrays, Up: Top + +Functions +********* - Using separate variables with mnemonic names for the input fields -makes programs more readable, in any case. It is an eventual goal to -make `gawk''s array indexing as efficient as possible, no matter what -the source of the index value. + This major node describes `awk''s built-in functions, which fall +into three categories: numeric, string, and I/O. `gawk' provides +additional groups of functions to work with values that represent time, +do bit manipulation, and to internationalize and localize programs. + + Besides the built-in functions, `awk' has provisions for writing new +functions that the rest of a program can use. The second half of this +major node describes these "user-defined" functions. + +* Menu: + +* Built-in:: Summarizes the built-in functions. +* User-defined:: Describes User-defined functions in detail. -File: gawk.info, Node: Built-in, Next: User-defined, Prev: Arrays, Up: Top +File: gawk.info, Node: Built-in, Next: User-defined, Prev: Functions, Up: Functions Built-in Functions -****************** +================== - "Built-in" functions are functions that are always available for -your `awk' program to call. This chapter defines all the built-in -functions in `awk'; some of them are mentioned in other sections, but -they are summarized here for your convenience. (You can also define -new functions yourself. *Note User-defined Functions: User-defined.) + "Built-in" functions are always available for your `awk' program to +call. This minor node defines all the built-in functions in `awk'; +some of these are mentioned in other sections but are summarized here +for your convenience. * Menu: @@ -7698,26 +8768,27 @@ new functions yourself. *Note User-defined Functions: User-defined.) * Numeric Functions:: Functions that work with numbers, including `int', `sin' and `rand'. * String Functions:: Functions for string manipulation, such as - `split', `match', and - `sprintf'. + `split', `match' and `sprintf'. * I/O Functions:: Functions for files and shell commands. -* Time Functions:: Functions for dealing with time stamps. +* Time Functions:: Functions for dealing with timestamps. +* Bitwise Functions:: Functions for bitwise operations. +* I18N Functions:: Functions for string translation. File: gawk.info, Node: Calling Built-in, Next: Numeric Functions, Prev: Built-in, Up: Built-in Calling Built-in Functions -========================== +-------------------------- - To call a built-in function, write the name of the function followed -by arguments in parentheses. For example, `atan2(y + z, 1)' is a call -to the function `atan2', with two arguments. + To call one of `awk''s built-in functions, write the name of the +function followed by arguments in parentheses. For example, `atan2(y + +z, 1)' is a call to the function `atan2', and has two arguments. Whitespace is ignored between the built-in function name and the -open-parenthesis, but we recommend that you avoid using whitespace +open parenthesis, and it is good practice to avoid using whitespace there. User-defined functions do not permit whitespace in this way, and -you will find it easier to avoid mistakes by following a simple -convention which always works: no whitespace after a function name. +it is easier to avoid mistakes by following a simple convention that +always works--no whitespace after a function name. Each built-in function accepts a certain number of arguments. In some cases, arguments can be omitted. The defaults for omitted @@ -7727,88 +8798,86 @@ given to built-in functions are ignored. However, in `gawk', it is a fatal error to give extra arguments to a built-in function. When a function is called, expressions that create the function's -actual parameters are evaluated completely before the function call is -performed. For example, in the code fragment: +actual parameters are evaluated completely before the call is performed. +For example, in the following code fragment: i = 4 j = sqrt(i++) -the variable `i' is set to five before `sqrt' is called with a value of -four for its actual parameter. - - The order of evaluation of the expressions used for the function's -parameters is undefined. Thus, you should not write programs that -assume that parameters are evaluated from left to right or from right -to left. For example, +the variable `i' is incremented to the value five before `sqrt' is +called with a value of four for its actual parameter. The order of +evaluation of the expressions used for the function's parameters is +undefined. Thus, avoid writing programs that assume that parameters +are evaluated from left to right or from right to left. For example: i = 5 j = atan2(i++, i *= 2) If the order of evaluation is left to right, then `i' first becomes -six, and then 12, and `atan2' is called with the two arguments six and +six, and then 12, and `atan2' is called with the two arguments 6 and 12. But if the order of evaluation is right to left, `i' first becomes -10, and then 11, and `atan2' is called with the two arguments 11 and 10. +10, then 11, and `atan2' is called with the two arguments 11 and 10. File: gawk.info, Node: Numeric Functions, Next: String Functions, Prev: Calling Built-in, Up: Built-in -Numeric Built-in Functions -========================== +Numeric Functions +----------------- - Here is a full list of built-in functions that work with numbers. -Optional parameters are enclosed in square brackets ("[" and "]"). + The following list describes all of the built-in functions that work +with numbers. Optional parameters are enclosed in square brackets ([ +and ]): `int(X)' - This produces the nearest integer to X, located between X and zero, - truncated toward zero. + This returns the nearest integer to X, located between X and zero + and truncated toward zero. For example, `int(3)' is three, `int(3.9)' is three, `int(-3.9)' is -3, and `int(-3)' is -3 as well. `sqrt(X)' - This gives you the positive square root of X. It reports an error - if X is negative. Thus, `sqrt(4)' is two. + This returns the positive square root of X. `gawk' reports an + error if X is negative. Thus, `sqrt(4)' is two. `exp(X)' - This gives you the exponential of X (`e ^ X'), or reports an error - if X is out of range. The range of values X can have depends on - your machine's floating point representation. + This returns the exponential of X (`e ^ X') or reports an error if + X is out of range. The range of values X can have depends on your + machine's floating-point representation. `log(X)' - This gives you the natural logarithm of X, if X is positive; + This returns the natural logarithm of X, if X is positive; otherwise, it reports an error. `sin(X)' - This gives you the sine of X, with X in radians. + This returns the sine of X, with X in radians. `cos(X)' - This gives you the cosine of X, with X in radians. + This returns the cosine of X, with X in radians. `atan2(Y, X)' - This gives you the arctangent of `Y / X' in radians. + This returns the arctangent of `Y / X' in radians. `rand()' - This gives you a random number. The values of `rand' are - uniformly-distributed between zero and one. The value is never - zero and never one. + This returns a random number. The values of `rand' are uniformly + distributed between zero and one. The value is never zero and + never one.(1) - Often you want random integers instead. Here is a user-defined - function you can use to obtain a random non-negative integer less - than N: + Often random integers are needed instead. Following is a + user-defined function that can be used to obtain a random + non-negative integer less than N: function randint(n) { return int(n * rand()) } The multiplication produces a random number greater than zero and - less than `n'. We then make it an integer (using `int') between - zero and `n' - 1, inclusive. + less than `n'. Using `int', this result is made into an integer + between zero and `n' - 1, inclusive. - Here is an example where a similar function is used to produce - random integers between one and N. This program prints a new - random number for each input record. + The following example uses a similar function to produce random + integers between one and N. This program prints a new random + number for each input record. - awk ' # Function to roll a simulated die. function roll(n) { return 1 + int(rand() * n) } @@ -7817,37 +8886,47 @@ Optional parameters are enclosed in square brackets ("[" and "]"). { printf("%d points\n", roll(6)+roll(6)+roll(6)) - }' + } *Caution:* In most `awk' implementations, including `gawk', `rand' starts generating numbers from the same starting number, or - "seed", each time you run `awk'. Thus, a program will generate - the same results each time you run it. The numbers are random - within one `awk' run, but predictable from run to run. This is - convenient for debugging, but if you want a program to do - different things each time it is used, you must change the seed to - a value that will be different in each run. To do this, use - `srand'. + "seed", each time you run `awk'. Thus, a program generates the + same results each time you run it. The numbers are random within + one `awk' run but predictable from run to run. This is convenient + for debugging, but if you want a program to do different things + each time it is used, you must change the seed to a value that is + different in each run. To do this, use `srand'. `srand([X])' The function `srand' sets the starting point, or seed, for generating random numbers to the value X. Each seed value leads to a particular sequence of random - numbers.(1) Thus, if you set the seed to the same value a second - time, you will get the same sequence of random numbers again. + numbers.(2) Thus, if the seed is set to the same value a second + time, the same sequence of random numbers is produced again. + + Different `awk' implementations use different random number + generators internally. Don't expect the same `awk' program to + produce the same series of random numbers when executed by + different versions of `awk'. - If you omit the argument X, as in `srand()', then the current date - and time of day are used for a seed. This is the way to get random - numbers that are truly unpredictable. + If the argument X is omitted, as in `srand()', then the current + date and time of day are used for a seed. This is the way to get + random numbers that are truly unpredictable. The return value of `srand' is the previous seed. This makes it - easy to keep track of the seeds for use in consistently reproducing - sequences of random numbers. + easy to keep track of the seeds in case you need to consistently + reproduce sequences of random numbers. ---------- Footnotes ---------- - (1) Computer generated random numbers really are not truly random. + (1) The C version of `rand' is known to produce fairly poor +sequences of random numbers. However, nothing requires that an `awk' +implementation use the C `rand' to implement the `awk' version of +`rand'. In fact, `gawk' uses the BSD `random' function, which is +considerably better than `rand', to produce random numbers. + + (2) Computer generated random numbers really are not truly random. They are technically known as "pseudo-random." This means that while the numbers in a sequence appear to be random, you can in fact generate the same sequence of random numbers over and over again. @@ -7855,17 +8934,53 @@ the same sequence of random numbers over and over again. File: gawk.info, Node: String Functions, Next: I/O Functions, Prev: Numeric Functions, Up: Built-in -Built-in Functions for String Manipulation -========================================== +String Manipulation Functions +----------------------------- + + The functions in this minor node look at or change the text of one +or more strings. Optional parameters are enclosed in square brackets +([ and ]). Those functions that are specific to `gawk' are marked with +a pound sign (`#'): + +* Menu: + +* Gory Details:: More than you want to know about `\' and + `&' with `sub', `gsub', and + `gensub'. - The functions in this section look at or change the text of one or -more strings. Optional parameters are enclosed in square brackets ("[" -and "]"). +`asort(SOURCE [, DEST]) #' + `asort' is a `gawk'-specific extension, returning the number of + elements in the array SOURCE. The contents of SOURCE are sorted + using `gawk''s normal rules for comparing values, and the indices + of the sorted values of SOURCE are replaced with sequential + integers starting with one. If the optional array DEST is + specified, then SOURCE is duplicated into DEST. DEST is then + sorted, leaving the indices of SOURCE unchanged. For example, if + the contents of `a' are as follows: + + a["last"] = "de" + a["first"] = "sac" + a["middle"] = "cul" + + A call to `asort': + + asort(a) + + results in the following contents of `a': + + a[1] = "cul" + a[2] = "de" + a[3] = "sac" + + The `asort' function is described in more detail in *Note Sorting + Array Values and Indices with `gawk': Array Sorting. `asort' is a + `gawk' extension; it is not available in compatibility mode (*note + Command-Line Options: Options.). `index(IN, FIND)' This searches the string IN for the first occurrence of the string FIND, and returns the position in characters where that occurrence - begins in the string IN. For example: + begins in the string IN. Consider the following example: $ awk 'BEGIN { print index("peanut", "an") }' -| 3 @@ -7874,29 +8989,33 @@ and "]"). indices in `awk' start at one.) `length([STRING])' - This gives you the number of characters in STRING. If STRING is a + This returns the number of characters in STRING. If STRING is a number, the length of the digit string representing that number is - returned. For example, `length("abcde")' is five. By contrast, - `length(15 * 35)' works out to three. How? Well, 15 * 35 = 525, + returned. For example, `length("abcde")' is 5. By contrast, + `length(15 * 35)' works out to 3. In this example, 15 * 35 = 525, and 525 is then converted to the string `"525"', which has three characters. If no argument is supplied, `length' returns the length of `$0'. - In older versions of `awk', you could call the `length' function - without any parentheses. Doing so is marked as "deprecated" in the - POSIX standard. This means that while you can do this in your - programs, it is a feature that can eventually be removed from a - future version of the standard. Therefore, for maximal - portability of your `awk' programs, you should always supply the - parentheses. - -`match(STRING, REGEXP)' - The `match' function searches the string, STRING, for the longest, - leftmost substring matched by the regular expression, REGEXP. It - returns the character position, or "index", of where that - substring begins (one, if it starts at the beginning of STRING). - If no match is found, it returns zero. + *Note:* In older versions of `awk', the `length' function could be + called without any parentheses. Doing so is marked as + "deprecated" in the POSIX standard. This means that while a + program can do this, it is a feature that can eventually be + removed from a future version of the standard. Therefore, for + programs to be maximally portable, always supply the parentheses. + +`match(STRING, REGEXP [, ARRAY])' + The `match' function searches STRING for the longest leftmost + substring matched by the regular expression, REGEXP. It returns + the character position, or "index", where that substring begins + (one, if it starts at the beginning of STRING). If no match is + found, it returns zero. + + The order of the first two arguments is backwards from most other + string functions that work with regular expressions, such as `sub' + and `gsub'. It might help to remember that for `match', the order + is the same as for the `~' operator: `STRING ~ REGEXP'. The `match' function sets the built-in variable `RSTART' to the index. It also sets the built-in variable `RLENGTH' to the length @@ -7905,21 +9024,21 @@ and "]"). For example: - awk '{ + { if ($1 == "FIND") regex = $2 else { where = match($0, regex) if (where != 0) - print "Match of", regex, "found at", \ + print "Match of", regex, "found at", where, "in", $0 } - }' + } This program looks for lines that match the regular expression stored in the variable `regex'. This regular expression can be changed. If the first word on a line is `FIND', `regex' is - changed to be the second word on that line. Therefore, given: + changed to be the second word on that line. Therefore, if given: FIND ru+n My program runs @@ -7934,14 +9053,31 @@ and "]"). Match of ru+n found at 12 in My program runs Match of Melvin found at 1 in Melvin was here. + If ARRAY is present, it is cleared, and then the 0'th element of + ARRAY is set to the entire portion of STRING matched by REGEXP. + If REGEXP contains parentheses, the integer-indexed elements of + ARRAY are set to contain the portion of STRING matching the + corresponding parenthesized sub-expression. For example: + + $ echo foooobazbarrrrr | + > gawk '{ match($0, /(fo+).+(ba*r)/, arr) + > print arr[1], arr[2] }' + -| foooo barrrrr + + The ARRAY argument to `match' is a `gawk' extension. In + compatibility mode (*note Command-Line Options: Options.), using a + third argument is a fatal error. + `split(STRING, ARRAY [, FIELDSEP])' - This divides STRING into pieces separated by FIELDSEP, and stores - the pieces in ARRAY. The first piece is stored in `ARRAY[1]', the - second piece in `ARRAY[2]', and so forth. The string value of the - third argument, FIELDSEP, is a regexp describing where to split - STRING (much as `FS' can be a regexp describing where to split - input records). If the FIELDSEP is omitted, the value of `FS' is - used. `split' returns the number of elements created. + This function divides STRING into pieces separated by FIELDSEP, + and stores the pieces in ARRAY. The first piece is stored in + `ARRAY[1]', the second piece in `ARRAY[2]', and so forth. The + string value of the third argument, FIELDSEP, is a regexp + describing where to split STRING (much as `FS' can be a regexp + describing where to split input records). If the FIELDSEP is + omitted, the value of `FS' is used. `split' returns the number of + elements created. If STRING does not match FIELDSEP, ARRAY is + empty and `split' returns zero. The `split' function splits strings into pieces in a manner similar to the way input lines are split into fields. For example: @@ -7958,53 +9094,65 @@ and "]"). The value returned by this call to `split' is three. As with input field-splitting, when the value of FIELDSEP is - `" "', leading and trailing whitespace is ignored, and the elements - are separated by runs of whitespace. - - Also as with input field-splitting, if FIELDSEP is the null - string, each individual character in the string is split into its - own array element. (This is a `gawk'-specific extension.) + `" "', leading and trailing whitespace is ignored and the elements + are separated by runs of whitespace. Also as with input + field-splitting, if FIELDSEP is the null string, each individual + character in the string is split into its own array element. + (This is a `gawk'-specific extension.) - Recent implementations of `awk', including `gawk', allow the third - argument to be a regexp constant (`/abc/'), as well as a string - (d.c.). The POSIX standard allows this as well. + Modern implementations of `awk', including `gawk', allow the third + argument to be a regexp constant (`/abc/') as well as a string. + (d.c.) The POSIX standard allows this as well. Before splitting the string, `split' deletes any previously - existing elements in the array ARRAY (d.c.). + existing elements in the array ARRAY. If STRING does not match + FIELDSEP at all, ARRAY has one element only. The value of that + element is the original STRING. - If STRING does not match FIELDSEP at all, ARRAY will have one - element. The value of that element will be the original STRING. - -`sprintf(FORMAT, EXPRESSION1,...)' +`sprintf(FORMAT, EXPRESSION1, ...)' This returns (without printing) the string that `printf' would have printed out with the same arguments (*note Using `printf' Statements for Fancier Printing: Printf.). For example: - sprintf("pi = %.2f (approx.)", 22/7) + pival = sprintf("pi = %.2f (approx.)", 22/7) + + assigns the string `"pi = 3.14 (approx.)"' to the variable `pival'. + +`strtonum(STR) #' + Examines STR and returns its numeric value. If STR begins with a + leading `0', `strtonum' assumes that STR is an octal number. If + STR begins with a leading `0x' or `0X', `strtonum' assumes that + STR is a hexadecimal number. For example: - returns the string `"pi = 3.14 (approx.)"'. + $ echo 0x11 | + > gawk '{ printf "%d\n", strtonum($1) }' + -| 17 + + Using the `strtonum' function is _not_ the same as adding zero to + a string value; the automatic coercion of strings to numbers works + only for decimal data, not for octal or hexadecimal.(1) + + `strtonum' is a `gawk' extension; it is not available in + compatibility mode (*note Command-Line Options: Options.). `sub(REGEXP, REPLACEMENT [, TARGET])' The `sub' function alters the value of TARGET. It searches this value, which is treated as a string, for the leftmost longest - substring matched by the regular expression, REGEXP, extending - this match as far as possible. Then the entire string is changed - by replacing the matched text with REPLACEMENT. The modified - string becomes the new value of TARGET. + substring matched by the regular expression REGEXP. Then the + entire string is changed by replacing the matched text with + REPLACEMENT. The modified string becomes the new value of TARGET. This function is peculiar because TARGET is not simply used to - compute a value, and not just any expression will do: it must be a - variable, field or array element, so that `sub' can store a + compute a value, and not just any expression will do--it must be a + variable, field, or array element so that `sub' can store a modified value there. If this argument is omitted, then the - default is to use and alter `$0'. - - For example: + default is to use and alter `$0'. For example: str = "water, water, everywhere" sub(/at/, "ith", str) sets `str' to `"wither, water, everywhere"', by replacing the - leftmost, longest occurrence of `at' with `ith'. + leftmost longest occurrence of `at' with `ith'. The `sub' function returns the number of substitutions made (either one or zero). @@ -8014,21 +9162,19 @@ and "]"). can match more than one string, then this precise substring may vary.) For example: - awk '{ sub(/candidate/, "& and his wife"); print }' + { sub(/candidate/, "& and his wife"); print } changes the first occurrence of `candidate' to `candidate and his - wife' on each input line. + wife' on each input line. Here is another example: - Here is another example: - - awk 'BEGIN { - str = "daabaaa" - sub(/a+/, "C&C", str) - print str - }' + $ awk 'BEGIN { + > str = "daabaaa" + > sub(/a+/, "C&C", str) + > print str + > }' -| dCaaCbaaa - This shows how `&' can represent a non-constant string, and also + This shows how `&' can represent a non-constant string and also illustrates the "leftmost, longest" rule in regexp matching (*note How Much Text Matches?: Leftmost Longest.). @@ -8036,28 +9182,28 @@ and "]"). putting a backslash before it in the string. As usual, to insert one backslash in the string, you must write two backslashes. Therefore, write `\\&' in a string constant to include a literal - `&' in the replacement. For example, here is how to replace the - first `|' on each line with an `&': + `&' in the replacement. For example, following is shown how to + replace the first `|' on each line with an `&': - awk '{ sub(/\|/, "\\&"); print }' + { sub(/\|/, "\\&"); print } - *Note:* As mentioned above, the third argument to `sub' must be a - variable, field or array reference. Some versions of `awk' allow - the third argument to be an expression which is not an lvalue. In - such a case, `sub' would still search for the pattern and return - zero or one, but the result of the substitution (if any) would be - thrown away because there is no place to put it. Such versions of - `awk' accept expressions like this: + As mentioned, the third argument to `sub' must be a variable, + field or array reference. Some versions of `awk' allow the third + argument to be an expression that is not an lvalue. In such a + case, `sub' still searches for the pattern and returns zero or + one, but the result of the substitution (if any) is thrown away + because there is no place to put it. Such versions of `awk' + accept expressions such as the following: sub(/USA/, "United States", "the USA and Canada") - For historical compatibility, `gawk' will accept erroneous code, - such as in the above example. However, using any other - non-changeable object as the third parameter will cause a fatal - error, and your program will not run. + For historical compatibility, `gawk' accepts erroneous code, such + as in the previous example. However, using any other non-changeable + object as the third parameter causes a fatal error and your program + will not run. Finally, if the REGEXP is not a regexp constant, it is converted - into a string and then the value of that string is treated as the + into a string, and then the value of that string is treated as the regexp to match. `gsub(REGEXP, REPLACEMENT [, TARGET])' @@ -8066,34 +9212,32 @@ and "]"). substrings it can find. The `g' in `gsub' stands for "global," which means replace everywhere. For example: - awk '{ gsub(/Britain/, "United Kingdom"); print }' + { gsub(/Britain/, "United Kingdom"); print } replaces all occurrences of the string `Britain' with `United Kingdom' for all input records. The `gsub' function returns the number of substitutions made. If - the variable to be searched and altered, TARGET, is omitted, then - the entire input record, `$0', is used. + the variable to search and alter (TARGET) is omitted, then the + entire input record (`$0') is used. As in `sub', the characters + `&' and `\' are special, and the third argument must be assignable. - As in `sub', the characters `&' and `\' are special, and the third - argument must be an lvalue. - -`gensub(REGEXP, REPLACEMENT, HOW [, TARGET])' +`gensub(REGEXP, REPLACEMENT, HOW [, TARGET]) #' `gensub' is a general substitution function. Like `sub' and `gsub', it searches the target string TARGET for matches of the regular expression REGEXP. Unlike `sub' and `gsub', the modified - string is returned as the result of the function, and the original + string is returned as the result of the function and the original target string is _not_ changed. If HOW is a string beginning with `g' or `G', then it replaces all matches of REGEXP with - REPLACEMENT. Otherwise, HOW is a number indicating which match of - REGEXP to replace. If no TARGET is supplied, `$0' is used instead. + REPLACEMENT. Otherwise, HOW is treated as a number that indicates + which match of REGEXP to replace. If no TARGET is supplied, `$0' + is used. `gensub' provides an additional feature that is not available in `sub' or `gsub': the ability to specify components of a regexp in the replacement text. This is done by using parentheses in the - regexp to mark the components, and then specifying `\N' in the - replacement text, where N is a digit from one to nine. For - example: + regexp to mark the components and then specifying `\N' in the + replacement text, where N is a digit from 1 to 9. For example: $ gawk ' > BEGIN { @@ -8103,14 +9247,14 @@ and "]"). > }' -| def abc - As described above for `sub', you must type two backslashes in - order to get one into the string. + As with `sub', you must type two backslashes in order to get one + into the string. In the replacement text, the sequence `\0' represents the entire matched text, as does the character `&'. - This example shows how you can use the third argument to control - which match of the regexp should be changed. + The following example shows how you can use the third argument to + control which match of the regexp should be changed: $ echo a b c a b c | > gawk '{ print gensub(/a/, "AA", 2) }' @@ -8121,19 +9265,20 @@ and "]"). `print' for printing. If the HOW argument is a string that does not begin with `g' or - `G', or if it is a number that is less than zero, only one - substitution is performed. + `G', or if it is a number that is less than or equal to zero, only + one substitution is performed. If HOW is zero, `gawk' issues a + warning message. If REGEXP does not match TARGET, `gensub''s return value is the - original, unchanged value of TARGET. + original unchanged value of TARGET. `gensub' is a `gawk' extension; it is not available in - compatibility mode (*note Command Line Options: Options.). + compatibility mode (*note Command-Line Options: Options.). `substr(STRING, START [, LENGTH])' This returns a LENGTH-character-long substring of STRING, starting at character number START. The first character of a string is - character number one. For example, `substr("washington", 5, 3)' + character number one.(2) For example, `substr("washington", 5, 3)' returns `"ing"'. If LENGTH is not present, this function returns the whole suffix of @@ -8142,60 +9287,80 @@ and "]"). also returned if LENGTH is greater than the number of characters remaining in the string, counting from character number START. - *Note:* The string returned by `substr' _cannot_ be assigned to. - Thus, it is a mistake to attempt to change a portion of a string, - like this: + The string returned by `substr' _cannot_ be assigned. Thus, it is + a mistake to attempt to change a portion of a string, as shown in + the following example: string = "abcdef" # try to get "abCDEf", won't work substr(string, 3, 3) = "CDE" - or to use `substr' as the third agument of `sub' or `gsub': + It is also a mistake to use `substr' as the third argument of + `sub' or `gsub': gsub(/xyz/, "pdq", substr($0, 5, 20)) # WRONG + (Some commercial versions of `awk' do in fact let you use `substr' + this way, but doing so is not portable.) + + If you need to replace bits and pieces of a string, combine + `substr' with string concatenation, in the following manner: + + string = "abcdef" + ... + string = substr(string, 1, 2) "CDE" substr(string, 6) + `tolower(STRING)' - This returns a copy of STRING, with each upper-case character in - the string replaced with its corresponding lower-case character. + This returns a copy of STRING, with each uppercase character in + the string replaced with its corresponding lowercase character. Non-alphabetic characters are left unchanged. For example, `tolower("MiXeD cAsE 123")' returns `"mixed case 123"'. `toupper(STRING)' - This returns a copy of STRING, with each lower-case character in - the string replaced with its corresponding upper-case character. + This returns a copy of STRING, with each lowercase character in + the string replaced with its corresponding uppercase character. Non-alphabetic characters are left unchanged. For example, `toupper("MiXeD cAsE 123")' returns `"MIXED CASE 123"'. -More About `\' and `&' with `sub', `gsub' and `gensub' ------------------------------------------------------- + ---------- Footnotes ---------- + + (1) Unless you use the `--non-decimal-data' option, which isn't +recommended. *Note Allowing Non-Decimal Input Data: Non-decimal Data, +for more information. + + (2) This is different from C and C++, where the first character is +number zero. + + +File: gawk.info, Node: Gory Details, Prev: String Functions, Up: String Functions + +More About `\' and `&' with `sub', `gsub', and `gensub' +....................................................... - When using `sub', `gsub' or `gensub', and trying to get literal + When using `sub', `gsub', or `gensub', and trying to get literal backslashes and ampersands into the replacement text, you need to remember that there are several levels of "escape processing" going on. First, there is the "lexical" level, which is when `awk' reads your -program, and builds an internal copy of your program that can be -executed. - - Then there is the run-time level, when `awk' actually scans the +program and builds an internal copy of it that can be executed. Then +there is the runtime level, which is when `awk' actually scans the replacement string to determine what to generate. At both levels, `awk' looks for a defined set of characters that can come after a backslash. At the lexical level, it looks for the escape sequences listed in *Note Escape Sequences::. Thus, for every `\' that -`awk' will process at the run-time level, you type two `\'s at the +`awk' processes at the runtime level, type two backslashes at the lexical level. When a character that is not valid for an escape sequence follows the `\', Unix `awk' and `gawk' both simply remove the -initial `\', and put the following character into the string. Thus, for +initial `\' and put the next character into the string. Thus, for example, `"a\qb"' is treated as `"aqb"'. - At the run-time level, the various functions handle sequences of `\' + At the runtime level, the various functions handle sequences of `\' and `&' differently. The situation is (sadly) somewhat complex. - - Historically, the `sub' and `gsub' functions treated the two -character sequence `\&' specially; this sequence was replaced in the -generated text with a single `&'. Any other `\' within the REPLACEMENT -string that did not precede an `&' was passed through unchanged. To +Historically, the `sub' and `gsub' functions treated the two character +sequence `\&' specially; this sequence was replaced in the generated +text with a single `&'. Any other `\' within the REPLACEMENT string +that did not precede an `&' was passed through unchanged. To illustrate with a table: You type `sub' sees `sub' generates @@ -8208,11 +9373,11 @@ illustrate with a table: `\\\\\\&' `\\\&' a literal `\\&' `\\q' `\q' a literal `\q' -This table shows both the lexical level processing, where an odd number -of backslashes becomes an even number at the run time level, and the -run-time processing done by `sub'. (For the sake of simplicity, the -rest of the tables below only show the case of even numbers of `\'s -entered at the lexical level.) +This table shows both the lexical-level processing, where an odd number +of backslashes becomes an even number at the runtime level, as well as +the runtime processing done by `sub'. (For the sake of simplicity, the +rest of the tables below only show the case of even numbers of +backslashes entered at the lexical level.) The problem with the historical approach is that there is no way to get a literal `\' followed by the matched text. @@ -8220,7 +9385,7 @@ get a literal `\' followed by the matched text. The 1992 POSIX standard attempted to fix this problem. The standard says that `sub' and `gsub' look for either a `\' or an `&' after the `\'. If either one follows a `\', that character is output literally. -The interpretation of `\' and `&' then becomes like this: +The interpretation of `\' and `&' then becomes: You type `sub' sees `sub' generates -------- ---------- --------------- @@ -8229,23 +9394,23 @@ The interpretation of `\' and `&' then becomes like this: `\\\\&' `\\&' a literal `\', then the matched text `\\\\\\&' `\\\&' a literal `\&' -This would appear to solve the problem. Unfortunately, the phrasing of -the standard is unusual. It says, in effect, that `\' turns off the -special meaning of any following character, but that for anything other -than `\' and `&', such special meaning is undefined. This wording -leads to two problems. +This appears to solve the problem. Unfortunately, the phrasing of the +standard is unusual. It says, in effect, that `\' turns off the special +meaning of any following character, but for anything other than `\' and +`&', such special meaning is undefined. This wording leads to two +problems: - 1. Backslashes must now be doubled in the REPLACEMENT string, breaking + * Backslashes must now be doubled in the REPLACEMENT string, breaking historical `awk' programs. - 2. To make sure that an `awk' program is portable, _every_ character + * To make sure that an `awk' program is portable, _every_ character in the REPLACEMENT string must be preceded with a backslash.(1) - The POSIX standard is under revision.(2) Because of the above -problems, proposed text for the revised standard reverts to rules that + The POSIX standard is under revision. Because of the problems just +listed, proposed text for the revised standard reverts to rules that correspond more closely to the original existing practice. The proposed rules have special cases that make it possible to produce a `\' -preceding the matched text. +preceding the matched text: You type `sub' sees `sub' generates -------- ---------- --------------- @@ -8254,24 +9419,24 @@ preceding the matched text. `\\&' `\&' a literal `&' `\\q' `\q' a literal `\q' - In a nutshell, at the run-time level, there are now three special -sequences of characters, `\\\&', `\\&' and `\&', whereas historically, + In a nutshell, at the runtime level, there are now three special +sequences of characters (`\\\&', `\\&' and `\&') whereas historically there was only one. However, as in the historical case, any `\' that -is not part of one of these three sequences is not special, and appears +is not part of one of these three sequences is not special and appears in the output literally. - `gawk' 3.0 follows these proposed POSIX rules for `sub' and `gsub'. -Whether these proposed rules will actually become codified into the -standard is unknown at this point. Subsequent `gawk' releases will -track the standard and implement whatever the final version specifies; -this Info file will be updated as well. + `gawk' 3.0 and 3.1 follow these proposed POSIX rules for `sub' and +`gsub'. Whether these proposed rules will actually become codified +into the standard is unknown at this point. Subsequent `gawk' releases +will track the standard and implement whatever the final version +specifies; this Info file will be updated as well.(2) - The rules for `gensub' are considerably simpler. At the run-time + The rules for `gensub' are considerably simpler. At the runtime level, whenever `gawk' sees a `\', if the following character is a digit, then the text that matched the corresponding parenthesized subexpression is placed in the generated output. Otherwise, no matter -what the character after the `\' is, that character will appear in the -generated text, and the `\' will not. +what the character after the `\' is, it appears in the generated text +and the `\' does not: You type `gensub' sees `gensub' generates -------- ------------- ------------------ @@ -8282,69 +9447,99 @@ generated text, and the `\' will not. `\\\\\\&' `\\\&' a literal `\&' `\\q' `\q' a literal `q' - Because of the complexity of the lexical and run-time level -processing, and the special cases for `sub' and `gsub', we recommend -the use of `gawk' and `gensub' for when you have to do substitutions. + Because of the complexity of the lexical and runtime level processing +and the special cases for `sub' and `gsub', we recommend the use of +`gawk' and `gensub' when you have to do substitutions. + +Advanced Notes: Matching the Null String +---------------------------------------- + + In `awk', the `*' operator can match the null string. This is +particularly important for the `sub', `gsub', and `gensub' functions. +For example: + + $ echo abc | awk '{ gsub(/m*/, "X"); print }' + -| XaXbXcX + +Although this makes a certain amount of sense, it can be surprising. ---------- Footnotes ---------- (1) This consequence was certainly unintended. - (2) As of July, 2000, with final approval and publication as part of -the Austin Group Standards hopefully sometime in 2001. + (2) As this Info file was being finalized, we learned that the POSIX +standard will not use these rules. However, it was too late to change +`gawk' for the 3.1 release. `gawk' behaves as described here. File: gawk.info, Node: I/O Functions, Next: Time Functions, Prev: String Functions, Up: Built-in -Built-in Functions for Input/Output -=================================== - - The following functions are related to Input/Output (I/O). Optional -parameters are enclosed in square brackets ("[" and "]"). +Input/Output Functions +---------------------- -`close(FILENAME)' - Close the file FILENAME, for input or output. The argument may - alternatively be a shell command that was used for redirecting to - or from a pipe; then the pipe is closed. *Note Closing Input and - Output Files and Pipes: Close Files And Pipes, for more - information. + The following functions relate to Input/Output (I/O). Optional +parameters are enclosed in square brackets ([ and ]): + +`close(FILENAME [, HOW])' + Close the file FILENAME for input or output. Alternatively, the + argument may be a shell command that was used for creating a + coprocess, or for redirecting to or from a pipe; then the + coprocess or pipe is closed. *Note Closing Input and Output + Redirections: Close Files And Pipes, for more information. + + When closing a coprocess, it is occasionally useful to first close + one end of the two-way pipe, and then to close the other. This is + done by providing a second argument to `close'. This second + argument should be one of the two string values `"to"' or `"from"', + indicating which end of the pipe to close. Case in the string does + not matter. *Note Two-Way Communications with Another Process: + Two-way I/O, which discusses this feature in more detail and gives + an example. `fflush([FILENAME])' - Flush any buffered output associated FILENAME, which is either a - file opened for writing, or a shell command for redirecting output - to a pipe. - - Many utility programs will "buffer" their output; they save - information to be written to a disk file or terminal in memory, - until there is enough for it to be worthwhile to send the data to - the ouput device. This is often more efficient than writing every + Flush any buffered output associated with FILENAME, which is + either a file opened for writing or a shell command for + redirecting output to a pipe or coprocess. + + Many utility programs "buffer" their output; i.e., they save + information to write to a disk file or terminal in memory, until + there is enough for it to be worthwhile to send the data to the + output device. This is often more efficient than writing every little bit of information as soon as it is ready. However, sometimes it is necessary to force a program to "flush" its buffers; that is, write the information to its destination, even if a buffer is not full. This is the purpose of the `fflush' - function; `gawk' too buffers its output, and the `fflush' function - can be used to force `gawk' to flush its buffers. + function--`gawk' also buffers its output and the `fflush' function + forces `gawk' to flush its buffers. - `fflush' is a recent (1994) addition to the Bell Labs research - version of `awk'; it is not part of the POSIX standard, and will - not be available if `--posix' has been specified on the command - line (*note Command Line Options: Options.). + `fflush' was added to the Bell Laboratories research version of + `awk' in 1994; it is not part of the POSIX standard and is not + available if `--posix' has been specified on the command line + (*note Command-Line Options: Options.). `gawk' extends the `fflush' function in two ways. The first is to allow no argument at all. In this case, the buffer for the - standard output is flushed. The second way is to allow the null - string (`""') as the argument. In this case, the buffers for _all_ - open output files and pipes are flushed. + standard output is flushed. The second is to allow the null string + (`""') as the argument. In this case, the buffers for _all_ open + output files and pipes are flushed. + + `fflush' returns zero if the buffer is successfully flushed; + otherwise it returns -1. In the case where all buffers are + flushed, the return value is zero only if all buffers were flushed + successfully. Otherwise, it is -1, and `gawk' warns about the + FILENAME that had the problem. - `fflush' returns zero if the buffer was successfully flushed, and - nonzero otherwise. + `gawk' also issues a warning message if you attempt to flush a + file or pipe that was opened for reading (such as with `getline'), + or if FILENAME is not an open file, pipe, or coprocess. In such a + case, `fflush' returns -1 as well. `system(COMMAND)' The `system' function allows the user to execute operating system commands and then return to the `awk' program. The `system' function executes the command given by the string COMMAND. It - returns, as its value, the status returned by the command that was - executed. + returns the status returned by the command that was executed as + its value. For example, if the following fragment of code is put in your `awk' program: @@ -8353,12 +9548,12 @@ parameters are enclosed in square brackets ("[" and "]"). system("date | mail -s 'awk run done' root") } - the system administrator will be sent mail when the `awk' program + the system administrator is sent mail when the `awk' program finishes processing input and begins its end-of-input processing. Note that redirecting `print' or `printf' into a pipe is often enough to accomplish your task. If you need to run many commands, - it will be more efficient to simply print them to a pipe to the + it is more efficient to simply print them down a pipeline to the shell: while (MORE STUFF TO DO) @@ -8367,62 +9562,59 @@ parameters are enclosed in square brackets ("[" and "]"). However, if your `awk' program is interactive, `system' is useful for cranking up large self-contained programs, such as a shell or - an editor. + an editor. Some operating systems cannot implement the `system' + function. `system' causes a fatal error if it is not supported. - Some operating systems cannot implement the `system' function. - `system' causes a fatal error if it is not supported. +Advanced Notes: Interactive Versus Non-Interactive Buffering +------------------------------------------------------------ -Interactive vs. Non-Interactive Buffering ------------------------------------------ - - As a side point, buffering issues can be even more confusing -depending upon whether or not your program is "interactive", i.e., + As a side point, buffering issues can be even more confusing, +depending upon whether your program is "interactive"; i.e., communicating with a user sitting at a keyboard.(1) - Interactive programs generally "line buffer" their output; they + Interactive programs generally "line buffer" their output; i.e., they write out every line. Non-interactive programs wait until they have a -full buffer, which may be many lines of output. - - Here is an example of the difference. +full buffer, which may be many lines of output. Here is an example of +the difference: $ awk '{ print $1 + $2 }' 1 1 -| 2 2 3 -| 5 - Control-d + Ctrl-d Each line of output is printed immediately. Compare that behavior with -this example. +this example: $ awk '{ print $1 + $2 }' | cat 1 1 2 3 - Control-d + Ctrl-d -| 2 -| 5 -Here, no output is printed until after the `Control-d' is typed, since -it is all buffered, and sent down the pipe to `cat' in one shot. +Here, no output is printed until after the `Ctrl-d' is typed, because +it is all buffered and sent down the pipe to `cat' in one shot. -Controlling Output Buffering with `system' ------------------------------------------- +Advanced Notes: Controlling Output Buffering with `system' +---------------------------------------------------------- The `fflush' function provides explicit control over output buffering for individual files and pipes. However, its use is not portable to many other `awk' implementations. An alternative method to -flush output buffers is by calling `system' with a null string as its +flush output buffers is to call `system' with a null string as its argument: system("") # flush output -`gawk' treats this use of the `system' function as a special case, and +`gawk' treats this use of the `system' function as a special case and is smart enough not to run a shell (or other command interpreter) with the empty command. Therefore, with `gawk', this idiom is not only -useful, it is efficient. While this method should work with other -`awk' implementations, it will not necessarily avoid starting an +useful, it is also efficient. While this method should work with other +`awk' implementations, it does not necessarily avoid starting an unnecessary shell. (Other implementations may only flush the buffer -associated with the standard output, and not necessarily all buffered +associated with the standard output and not necessarily all buffered output.) If you think about what a programmer expects, it makes sense that @@ -8434,20 +9626,20 @@ output.) print "second print" } -must print +must print: first print system echo second print -and not +and not: system echo first print second print If `awk' did not flush its buffers before calling `system', the -latter (undesirable) output is what you would see. +latter (undesirable) output is what you see. ---------- Footnotes ---------- @@ -8455,57 +9647,89 @@ latter (undesirable) output is what you would see. a terminal device. -File: gawk.info, Node: Time Functions, Prev: I/O Functions, Up: Built-in +File: gawk.info, Node: Time Functions, Next: Bitwise Functions, Prev: I/O Functions, Up: Built-in -Functions for Dealing with Time Stamps -====================================== +Using `gawk''s Timestamp Functions +---------------------------------- A common use for `awk' programs is the processing of log files -containing time stamp information, indicating when a particular log -record was written. Many programs log their time stamp in the form +containing timestamp information, indicating when a particular log +record was written. Many programs log their timestamp in the form returned by the `time' system call, which is the number of seconds -since a particular epoch. On POSIX systems, it is the number of -seconds since Midnight, January 1, 1970, UTC. - - In order to make it easier to process such log files, and to produce -useful reports, `gawk' provides two functions for working with time -stamps. Both of these are `gawk' extensions; they are not specified in -the POSIX standard, nor are they in any other known version of `awk'. - - Optional parameters are enclosed in square brackets ("[" and "]"). +since a particular epoch. On POSIX-compliant systems, it is the number +of seconds since 1970-01-01 00:00:00 UTC, not counting leap seconds.(1) +All known POSIX-compliant systems support timestamps from 0 through +2^31 - 1, which is sufficient to represent times through 2038-01-19 +03:14:07 UTC. Many systems support a wider range of timestamps, +including negative timestamps that represent times before the epoch. + + In order to make it easier to process such log files and to produce +useful reports, `gawk' provides the following functions for working +with timestamps. They are `gawk' extensions; they are not specified in +the POSIX standard, nor are they in any other known version of `awk'.(2) +Optional parameters are enclosed in square brackets ([ and ]): `systime()' This function returns the current time as the number of seconds since the system epoch. On POSIX systems, this is the number of - seconds since Midnight, January 1, 1970, UTC. It may be a - different number on other systems. + seconds since 1970-01-01 00:00:00 UTC, not counting leap seconds. + It may be a different number on other systems. + +`mktime(DATESPEC)' + This function turns DATESPEC into a timestamp in the same form as + is returned by `systime'. It is similar to the function of the + same name in ISO C. The argument, DATESPEC, is a string of the + form `"YYYY MM DD HH MM SS [DST]"'. The string consists of six or + seven numbers representing, respectively, the full year including + century, the month from 1 to 12, the day of the month from 1 to + 31, the hour of the day from 0 to 23, the minute from 0 to 59, the + second from 0 to 60,(3) and an optional daylight savings flag. + + The values of these numbers need not be within the ranges + specified; for example, an hour of -1 means 1 hour before midnight. + The origin-zero Gregorian calendar is assumed, with year 0 + preceding year 1 and year -1 preceding year 0. The time is + assumed to be in the local timezone. If the daylight savings flag + is positive, the time is assumed to be daylight savings time; if + zero, the time is assumed to be standard time; and if negative + (the default), `mktime' attempts to determine whether daylight + savings time is in effect for the specified time. + + If DATESPEC does not contain enough elements or if the resulting + time is out of range, `mktime' returns -1. `strftime([FORMAT [, TIMESTAMP]])' This function returns a string. It is similar to the function of - the same name in ANSI C. The time specified by TIMESTAMP is used - to produce a string, based on the contents of the FORMAT string. - The TIMESTAMP is in the same format as the value returned by the + the same name in ISO C. The time specified by TIMESTAMP is used to + produce a string, based on the contents of the FORMAT string. The + TIMESTAMP is in the same format as the value returned by the `systime' function. If no TIMESTAMP argument is supplied, `gawk' - will use the current time of day as the time stamp. If no FORMAT + uses the current time of day as the timestamp. If no FORMAT argument is supplied, `strftime' uses `"%a %b %d %H:%M:%S %Z %Y"'. - This format string produces output (almost) equivalent to that of - the `date' utility. (Versions of `gawk' prior to 3.0 require the - FORMAT argument.) + This format string produces output that is (almost) equivalent to + that of the `date' utility. (Versions of `gawk' prior to 3.0 + require the FORMAT argument.) - The `systime' function allows you to compare a time stamp from a log + The `systime' function allows you to compare a timestamp from a log file with the current time of day. In particular, it is easy to determine how long ago a particular record was logged. It also allows you to produce log records using the "seconds since the epoch" format. - The `strftime' function allows you to easily turn a time stamp into + The `mktime' function allows you to convert a textual representation +of a date and time into a timestamp. This makes it easy to do +before/after comparisons of dates and times, particularly when dealing +with date and time data coming from an external source, such as a log +file. + + The `strftime' function allows you to easily turn a timestamp into human-readable information. It is similar in nature to the `sprintf' -function (*note Built-in Functions for String Manipulation: String -Functions.), in that it copies non-format specification characters -verbatim to the returned string, while substituting date and time -values for format specifications in the FORMAT string. +function (*note String Manipulation Functions: String Functions.), in +that it copies non-format specification characters verbatim to the +returned string, while substituting date and time values for format +specifications in the FORMAT string. - `strftime' is guaranteed by the ANSI C standard to support the -following date format specifications: + `strftime' is guaranteed by the 1999 ISO C standard(4) to support +the following date format specifications: `%a' The locale's abbreviated weekday name. @@ -8520,11 +9744,40 @@ following date format specifications: The locale's full month name. `%c' - The locale's "appropriate" date and time representation. + The locale's "appropriate" date and time representation. (This is + `%A %B %d %T %Y' in the `"C"' locale.) + +`%C' + The century. This is the year divided by 100 and truncated to the + next lower integer. `%d' The day of the month as a decimal number (01-31). +`%D' + Equivalent to specifying `%m/%d/%y'. + +`%e' + The day of the month, padded with a space if it is only one digit. + +`%F' + Equivalent to specifying `%Y-%m-%d'. This is the ISO 8601 date + format. + +`%g' + The year modulo 100 of the ISO week number, as a decimal number + (00-99). For example, January 1, 1993, is in week 53 of 1992. + Thus, the year of its ISO week number is 1992, even though its + year is 1993. Similarly, December 31, 1973, is in week 1 of 1974. + Thus, the year of its ISO week number is 1974, even though its + year is 1973. + +`%G' + The full year of the ISO week number, as a decimal number. + +`%h' + Equivalent to `%b'. + `%H' The hour (24-hour clock) as a decimal number (00-23). @@ -8540,17 +9793,44 @@ following date format specifications: `%M' The minute as a decimal number (00-59). +`%n' + A newline character (ASCII LF). + `%p' The locale's equivalent of the AM/PM designations associated with a 12-hour clock. +`%r' + The locale's 12-hour clock time. (This is `%I:%M:%S %p' in the + `"C"' locale.) + +`%R' + Equivalent to specifying `%H:%M'. + `%S' - The second as a decimal number (00-60).(1) + The second as a decimal number (00-60). + +`%t' + A tab character. + +`%T' + Equivalent to specifying `%H:%M:%S'. + +`%u' + The weekday as a decimal number (1-7). Monday is day one. `%U' The week number of the year (the first Sunday as the first day of week one) as a decimal number (00-53). +`%V' + The week number of the year (the first Monday as the first day of + week one) as a decimal number (01-53). The method for determining + the week number is as specified by ISO 8601. (To wit: if the week + containing January 1 has four or more days in the new year, then + it is week one, otherwise it is week 53 of the previous year and + the next week is week one.) + `%w' The weekday as a decimal number (0-6). Sunday is day zero. @@ -8559,65 +9839,54 @@ following date format specifications: week one) as a decimal number (00-53). `%x' - The locale's "appropriate" date representation. + The locale's "appropriate" date representation. (This is `%A %B + %d %Y' in the `"C"' locale.) `%X' - The locale's "appropriate" time representation. + The locale's "appropriate" time representation. (This is `%T' in + the `"C"' locale.) `%y' - The year without century as a decimal number (00-99). + The year modulo 100 as a decimal number (00-99). `%Y' - The year with century as a decimal number (e.g., 1995). + The full year as a decimal number (e.g., 1995). + +`%z' + The timezone offset in a +HHMM format (e.g., the format necessary + to produce RFC 822/RFC 1036 date headers). `%Z' - The time zone name or abbreviation, or no characters if no time - zone is determinable. + The time zone name or abbreviation; no characters if no time zone + is determinable. + +`%Ec %EC %Ex %EX %Ey %EY %Od %Oe %OH' +`%OI %Om %OM %OS %Ou %OU %OV %Ow %OW %Oy' + These are "alternate representations" for the specifications that + use only the second letter (`%c', `%C', and so on).(5) (These + facilitate compliance with the POSIX `date' utility.) `%%' A literal `%'. If a conversion specifier is not one of the above, the behavior is -undefined.(2) +undefined.(6) Informally, a "locale" is the geographic place in which a program is meant to run. For example, a common way to abbreviate the date -September 4, 1991 in the United States would be "9/4/91". In many -countries in Europe, however, it would be abbreviated "4.9.91". Thus, -the `%x' specification in a `"US"' locale might produce `9/4/91', while -in a `"EUROPE"' locale, it might produce `4.9.91'. The ANSI C standard +September 4, 1991 in the United States is "9/4/91." In many countries +in Europe, however, it is abbreviated "4.9.91." Thus, the `%x' +specification in a `"US"' locale might produce `9/4/91', while in a +`"EUROPE"' locale, it might produce `4.9.91'. The ISO C standard defines a default `"C"' locale, which is an environment that is typical of what most C programmers are used to. A public-domain C version of `strftime' is supplied with `gawk' for -systems that are not yet fully ANSI-compliant. If that version is used -to compile `gawk' (*note Installing `gawk': Installation.), then the +systems that are not yet fully standards-compliant. It supports all of +the just listed format specifications. If that version is used to +compile `gawk' (*note Installing `gawk': Installation.), then the following additional format specifications are available: -`%D' - Equivalent to specifying `%m/%d/%y'. - -`%e' - The day of the month, padded with a space if it is only one digit. - -`%h' - Equivalent to `%b', above. - -`%n' - A newline character (ASCII LF). - -`%r' - Equivalent to specifying `%I:%M:%S %p'. - -`%R' - Equivalent to specifying `%H:%M'. - -`%T' - Equivalent to specifying `%H:%M:%S'. - -`%t' - A tab character. - `%k' The hour (24-hour clock) as a decimal number (0-23). Single digit numbers are padded with a space. @@ -8626,66 +9895,41 @@ following additional format specifications are available: The hour (12-hour clock) as a decimal number (1-12). Single digit numbers are padded with a space. -`%C' - The century, as a number between 00 and 99. +`%N' + The "Emperor/Era" name. Equivalent to `%C'. -`%u' - The weekday as a decimal number [1 (Monday)-7]. - -`%V' - The week number of the year (the first Monday as the first day of - week one) as a decimal number (01-53). The method for determining - the week number is as specified by ISO 8601 (to wit: if the week - containing January 1 has four or more days in the new year, then - it is week one, otherwise it is week 53 of the previous year and - the next week is week one). - -`%G' - The year with century of the ISO week number, as a decimal number. - - For example, January 1, 1993, is in week 53 of 1992. Thus, the year - of its ISO week number is 1992, even though its year is 1993. - Similarly, December 31, 1973, is in week 1 of 1974. Thus, the year - of its ISO week number is 1974, even though its year is 1973. - -`%g' - The year without century of the ISO week number, as a decimal - number (00-99). +`%o' + The "Emperor/Era" year. Equivalent to `%y'. -`%Ec %EC %Ex %Ey %EY %Od %Oe %OH %OI' -`%Om %OM %OS %Ou %OU %OV %Ow %OW %Oy' - These are "alternate representations" for the specifications that - use only the second letter (`%c', `%C', and so on). They are - recognized, but their normal representations are used.(3) (These - facilitate compliance with the POSIX `date' utility.) +`%s' + The time as a decimal timestamp in seconds since the epoch. `%v' - The date in VMS format (e.g., 20-JUN-1991). + The date in VMS format (e.g., `20-JUN-1991'). -`%z' - The timezone offset in a +HHMM format (e.g., the format necessary - to produce RFC-822/RFC-1036 date headers). + Additionally, the alternate representations are recognized but their +normal representations are used. This example is an `awk' implementation of the POSIX `date' utility. Normally, the `date' utility prints the current date and time of day -in a well known format. However, if you provide an argument to it that -begins with a `+', `date' will copy non-format specifier characters to -the standard output, and will interpret the current time according to -the format specifiers in the string. For example: +in a well-known format. However, if you provide an argument to it that +begins with a `+', `date' copies non-format specifier characters to the +standard output and interprets the current time according to the format +specifiers in the string. For example: $ date '+Today is %A, %B %d, %Y.' - -| Today is Thursday, July 11, 1991. + -| Today is Thursday, September 14, 2000. Here is the `gawk' version of the `date' utility. It has a shell -"wrapper", to handle the `-u' option, which requires that `date' run as -if the time zone was set to UTC. +"wrapper" to handle the `-u' option, which requires that `date' run as +if the time zone is set to UTC: #! /bin/sh # # date --- approximate the P1003.2 'date' command case $1 in - -u) TZ=GMT0 # use UTC + -u) TZ=UTC0 # use UTC export TZ shift ;; esac @@ -8707,27 +9951,184 @@ if the time zone was set to UTC. ---------- Footnotes ---------- - (1) Occasionally there are minutes in a year with a leap second, + (1) *Note Glossary::, especially the entries for "Epoch" and "UTC." + + (2) The GNU `date' utility can also do many of the things described +here. It's use may be preferable for simple time-related operations in +shell scripts. + + (3) Occasionally there are minutes in a year with a leap second, which is why the seconds can go up to 60. - (2) This is because ANSI C leaves the behavior of the C version of -`strftime' undefined, and `gawk' will use the system's version of -`strftime' if it's there. Typically, the conversion specifier will -either not appear in the returned string, or it will appear literally. + (4) As this is a recent standard, not every system's `strftime' +necessarily supports all of the conversions listed here. - (3) If you don't understand any of this, don't worry about it; these + (5) If you don't understand any of this, don't worry about it; these facilities are meant to make it easier to "internationalize" programs. +Other internationalization features are described in *Note +Internationalization with `gawk': Internationalization. + + (6) This is because ISO C leaves the behavior of the C version of +`strftime' undefined and `gawk' uses the system's version of `strftime' +if it's there. Typically, the conversion specifier either does not +appear in the returned string or it appears literally. -File: gawk.info, Node: User-defined, Next: Invoking Gawk, Prev: Built-in, Up: Top +File: gawk.info, Node: Bitwise Functions, Next: I18N Functions, Prev: Time Functions, Up: Built-in + +Using `gawk''s Bit Manipulation Functions +----------------------------------------- + + I can explain it for you, but I can't understand it for you. + Anonymous + + Many languages provide the ability to perform "bitwise" operations +on two integer numbers. In other words, the operation is performed on +each successive pair of bits in the operands. Three common operations +are bitwise AND, OR, and XOR. The operations are described by the +following table: + + Bit Operator + | AND | OR | XOR + |---+---+---+---+---+--- + Operands | 0 | 1 | 0 | 1 | 0 | 1 + ----------+---+---+---+---+---+--- + 0 | 0 0 | 0 1 | 0 1 + 1 | 0 1 | 1 1 | 1 0 + + As you can see, the result of an AND operation is 1 only when _both_ +bits are 1. The result of an OR operation is 1 if _either_ bit is 1. +The result of an XOR operation is 1 if either bit is 1, but not both. +The next operation is the "complement"; the complement of 1 is 0 and +the complement of 0 is 1. Thus, this operation "flips" all the bits of +a given value. + + Finally, two other common operations are to shift the bits left or +right. For example, if you have a bit string `10111001' and you shift +it right by three bits, you end up with `00010111'.(1) If you start over +again with `10111001' and shift it left by three bits, you end up with +`11001000'. `gawk' provides built-in functions that implement the +bitwise operations just described. They are: + +`and(V1, V2)' Return the bitwise AND of the values provided by V1 + and V2. +`or(V1, V2)' Return the bitwise OR of the values provided by V1 and + V2. +`xor(V1, V2)' Return the bitwise XOR of the values provided by V1 + and V2. +`compl(VAL)' Return the bitwise complement of VAL. +`lshift(VAL, COUNT)' Return the value of VAL, shifted left by COUNT bits. +`rshift(VAL, COUNT)' Return the value of VAL, shifted right by COUNT bits. + + For all of these functions, first the double-precision +floating-point value is converted to a C `unsigned long', then the +bitwise operation is performed and then the result is converted back +into a C `double'. (If you don't understand this paragraph, don't worry +about it.) + + Here is a user-defined function (*note User-Defined Functions: +User-defined.) that illustrates the use of these functions: + + # bits2str --- turn a byte into readable 1's and 0's + + function bits2str(bits, data, mask) + { + if (bits == 0) + return "0" + + mask = 1 + for (; bits != 0; bits = rshift(bits, 1)) + data = (and(bits, mask) ? "1" : "0") data + + while ((length(data) % 8) != 0) + data = "0" data + + return data + } + + BEGIN { + printf "123 = %s\n", bits2str(123) + printf "0123 = %s\n", bits2str(0123) + printf "0x99 = %s\n", bits2str(0x99) + comp = compl(0x99) + printf "compl(0x99) = %#x = %s\n", comp, bits2str(comp) + shift = lshift(0x99, 2) + printf "lshift(0x99, 2) = %#x = %s\n", shift, bits2str(shift) + shift = rshift(0x99, 2) + printf "rshift(0x99, 2) = %#x = %s\n", shift, bits2str(shift) + } + +This program produces the following output when run: + + $ gawk -f testbits.awk + -| 123 = 01111011 + -| 0123 = 01010011 + -| 0x99 = 10011001 + -| compl(0x99) = 0xffffff66 = 11111111111111111111111101100110 + -| lshift(0x99, 2) = 0x264 = 0000001001100100 + -| rshift(0x99, 2) = 0x26 = 00100110 + + The `bits2str' function turns a binary number into a string. The +number `1' represents a binary value where the rightmost bit is set to +1. Using this mask, the function repeatedly checks the rightmost bit. +AND-ing the mask with the value indicates whether the rightmost bit is +1 or not. If so, a `"1"' is concatenated onto the front of the string. +Otherwise, a `"0"' is added. The value is then shifted right by one +bit and the loop continues until there are no more 1 bits. + + If the initial value is zero it returns a simple `"0"'. Otherwise, +at the end, it pads the value with zeros to represent multiples of +eight-bit quantities. This is typical in modern computers. + + The main code in the `BEGIN' rule shows the difference between the +decimal and octal values for the same numbers (*note Octal and +Hexadecimal Numbers: Non-decimal-numbers.), and then demonstrates the +results of the `compl', `lshift', and `rshift' functions. + + ---------- Footnotes ---------- + + (1) This example shows that 0's come in on the left side. For +`gawk', this is always true, but in some languages, it's possible to +have the left side fill with 1's. Caveat emptor. + + +File: gawk.info, Node: I18N Functions, Prev: Bitwise Functions, Up: Built-in + +Using `gawk''s String Translation Functions +------------------------------------------- + + `gawk' provides facilities for internationalizing `awk' programs. +These include the functions described in the following list. The +description here is purposely brief. *Note Internationalization with +`gawk': Internationalization, for the full story. Optional parameters +are enclosed in square brackets ([ and ]): + +`dcgettext(STRING [, DOMAIN [, CATEGORY]])' + This function returns the translation of STRING in text domain + DOMAIN for locale category CATEGORY. The default value for DOMAIN + is the current value of `TEXTDOMAIN'. The default value for + CATEGORY is `"LC_MESSAGES"'. -User-defined Functions -********************** +`bindtextdomain(DIRECTORY [, DOMAIN])' + This function allows you to specify the directory where `gawk' + will look for message translation files, in case they will not or + cannot be placed in the "standard" locations (e.g., during + testing). It returns the directory where DOMAIN is "bound." + + The default DOMAIN is the value of `TEXTDOMAIN'. If DIRECTORY is + the null string (`""'), then `bindtextdomain' returns the current + binding for the given DOMAIN. + + +File: gawk.info, Node: User-defined, Prev: Built-in, Up: Functions + +User-Defined Functions +====================== Complicated `awk' programs can often be simplified by defining your own functions. User-defined functions can be called just like built-in -ones (*note Function Calls::), but it is up to you to define them--to -tell `awk' what they should do. +ones (*note Function Calls::), but it is up to you to define them; +i.e., to tell `awk' what they should do. * Menu: @@ -8736,19 +10137,20 @@ tell `awk' what they should do. does. * Function Caveats:: Things to watch out for. * Return Statement:: Specifying the value a function returns. +* Dynamic Typing:: How variable types can change at runtime. File: gawk.info, Node: Definition Syntax, Next: Function Example, Prev: User-defined, Up: User-defined Function Definition Syntax -========================== +-------------------------- Definitions of functions can appear anywhere between the rules of an `awk' program. Thus, the general form of an `awk' program is extended to include sequences of rules _and_ user-defined function definitions. -There is no need in `awk' to put the definition of a function before -all uses of the function. This is because `awk' reads the entire -program before starting to execute any of it. +There is no need to put the definition of a function before all uses of +the function. This is because `awk' reads the entire program before +starting to execute any of it. The definition of a function named NAME looks like this: @@ -8757,39 +10159,41 @@ program before starting to execute any of it. BODY-OF-FUNCTION } -NAME is the name of the function to be defined. A valid function name -is like a valid variable name: a sequence of letters, digits and -underscores, not starting with a digit. Within a single `awk' program, -any particular name can only be used as a variable, array or function. +NAME is the name of the function to define. A valid function name is +like a valid variable name: a sequence of letters, digits, and +underscores, that doesn't start with a digit. Within a single `awk' +program, any particular name can only be used as a variable, array, or +function. PARAMETER-LIST is a list of the function's arguments and local variable names, separated by commas. When the function is called, the argument names are used to hold the argument values given in the call. The local variables are initialized to the empty string. A function -cannot have two parameters with the same name. +cannot have two parameters with the same name, nor may it have a +parameter with the same name as the function itself. The BODY-OF-FUNCTION consists of `awk' statements. It is the most important part of the definition, because it says what the function should actually _do_. The argument names exist to give the body a way -to talk about the arguments; local variables, to give the body places -to keep temporary values. +to talk about the arguments; local variables exist to give the body +places to keep temporary values. Argument names are not distinguished syntactically from local -variable names; instead, the number of arguments supplied when the +variable names. Instead, the number of arguments supplied when the function is called determines how many argument variables there are. Thus, if three argument values are given, the first three names in -PARAMETER-LIST are arguments, and the rest are local variables. +PARAMETER-LIST are arguments and the rest are local variables. It follows that if the number of arguments is not the same in all calls to the function, some of the names in PARAMETER-LIST may be arguments on some occasions and local variables on others. Another way to think of this is that omitted arguments default to the null string. - Usually when you write a function you know how many names you intend -to use for arguments and how many you intend to use as local variables. -It is conventional to place some extra space between the arguments and -the local variables, to document how your function is supposed to be -used. + Usually when you write a function, you know how many names you +intend to use for arguments and how many you intend to use as local +variables. It is conventional to place some extra space between the +arguments and the local variables, in order to document how your +function is supposed to be used. During execution of the function body, the arguments and local variable values hide or "shadow" any variables of the same names used @@ -8803,25 +10207,26 @@ in the function's body. body is executing. Once the body finishes, you can once again access the variables that were shadowed while the function was running. - The function body can contain expressions which call functions. They + The function body can contain expressions that call functions. They can even call this function, either directly or by way of another -function. When this happens, we say the function is "recursive". +function. When this happens, we say the function is "recursive". The +act of a function calling itself is called "recursion". In many `awk' implementations, including `gawk', the keyword `function' may be abbreviated `func'. However, POSIX only specifies the use of the keyword `function'. This actually has some practical -implications. If `gawk' is in POSIX-compatibility mode (*note Command -Line Options: Options.), then the following statement will _not_ define -a function: +implications. If `gawk' is in POSIX-compatibility mode (*note +Command-Line Options: Options.), then the following statement does +_not_ define a function: func foo() { a = sqrt($1) ; print a } Instead it defines a rule that, for each record, concatenates the value of the variable `func' with the return value of the function `foo'. If the resulting string is non-null, the action is executed. This is -probably not what was desired. (`awk' accepts this input as -syntactically valid, since functions may be used before they are defined -in `awk' programs.) +probably not what is desired. (`awk' accepts this input as +syntactically valid, because functions may be used before they are +defined in `awk' programs.) To ensure that your `awk' programs are portable, always use the keyword `function' when defining a function. @@ -8830,22 +10235,23 @@ keyword `function' when defining a function. File: gawk.info, Node: Function Example, Next: Function Caveats, Prev: Definition Syntax, Up: User-defined Function Definition Examples -============================ +---------------------------- Here is an example of a user-defined function, called `myprint', that -takes a number and prints it in a specific format. +takes a number and prints it in a specific format: function myprint(num) { printf "%6.3g\n", num } -To illustrate, here is an `awk' rule which uses our `myprint' function: +To illustrate, here is an `awk' rule that uses our `myprint' function: $3 > 0 { myprint($3) } This program prints, in our special format, all the third fields that -contain a positive number in our input. Therefore, when given: +contain a positive number in our input. Therefore, when given the +following: 1.2 3.4 5.6 7.8 9.10 11.12 -13.14 15.16 @@ -8856,7 +10262,7 @@ this program, using our function to format the results, prints: 5.6 21.2 - This function deletes all the elements in an array. + This function deletes all the elements in an array: function delarray(a, i) { @@ -8867,13 +10273,16 @@ this program, using our function to format the results, prints: When working with arrays, it is often necessary to delete all the elements in an array and start over with a new list of elements (*note The `delete' Statement: Delete.). Instead of having to repeat this -loop everywhere in your program that you need to clear out an array, -your program can just call `delarray'. (This guarantees portability. -The usage `delete ARRAY' to delete the contents of an entire array is a +loop everywhere that you need to clear out an array, your program can +just call `delarray'. (This guarantees portability. The use of +`delete ARRAY' to delete the contents of an entire array is a non-standard extension.) - Here is an example of a recursive function. It takes a string as an -input parameter, and returns the string in backwards order. + The following is an example of a recursive function. It takes a +string as an input parameter and returns the string in backwards order. +Recursive functions must always have a test that stops the recursion. +In this case, the recursion terminates when the starting position is +zero; i.e., when there are no more characters left in the string. function rev(str, start) { @@ -8883,18 +10292,17 @@ input parameter, and returns the string in backwards order. return (substr(str, start, 1) rev(str, start - 1)) } - If this function is in a file named `rev.awk', we can test it this + If this function is in a file named `rev.awk', it can be tested this way: $ echo "Don't Panic!" | > gawk --source '{ print rev($0, length($0)) }' -f rev.awk -| !cinaP t'noD - Here is an example that uses the built-in function `strftime'. -(*Note Functions for Dealing with Time Stamps: Time Functions, for more -information on `strftime'.) The C `ctime' function takes a timestamp -and returns it in a string, formatted in a well known fashion. Here is -an `awk' version: + The C `ctime' function takes a timestamp and returns it in a string, +formatted in a well-known fashion. The following example uses the +built-in `strftime' function (*note Using `gawk''s Timestamp Functions: +Time Functions.) to create an `awk' version of `ctime': # ctime.awk # @@ -8911,23 +10319,23 @@ an `awk' version: File: gawk.info, Node: Function Caveats, Next: Return Statement, Prev: Function Example, Up: User-defined -Calling User-defined Functions -============================== +Calling User-Defined Functions +------------------------------ "Calling a function" means causing the function to run and do its -job. A function call is an expression, and its value is the value +job. A function call is an expression and its value is the value returned by the function. A function call consists of the function name followed by the -arguments in parentheses. What you write in the call for the arguments -are `awk' expressions; each time the call is executed, these +arguments in parentheses. `awk' expressions are what you write in the +call for the arguments. Each time the call is executed, these expressions are evaluated, and the values are the actual arguments. For example, here is a call to `foo' with three arguments (the first being a string concatenation): foo(x y, "lose", 4 * z) - *Caution:* whitespace characters (spaces and tabs) are not allowed + *Caution:* Whitespace characters (spaces and tabs) are not allowed between the function name and the open-parenthesis of the argument list. If you write whitespace by mistake, `awk' might think that you mean to concatenate a variable with an expression in parentheses. However, it @@ -8937,18 +10345,17 @@ reports an error. When a function is called, it is given a _copy_ of the values of its arguments. This is known as "call by value". The caller may use a variable as the expression for the argument, but the called function -does not know this: it only knows what value the argument had. For -example, if you write this code: +does not know this--it only knows what value the argument had. For +example, if you write the following code: foo = "bar" z = myfunc(foo) then you should not think of the argument to `myfunc' as being "the -variable `foo'." Instead, think of the argument as the string value, -`"bar"'. - - If the function `myfunc' alters the values of its local variables, -this has no effect on any other variables. Thus, if `myfunc' does this: +variable `foo'." Instead, think of the argument as the string value +`"bar"'. If the function `myfunc' alters the values of its local +variables, this has no effect on any other variables. Thus, if `myfunc' +does this: function myfunc(str) { @@ -8957,9 +10364,9 @@ this has no effect on any other variables. Thus, if `myfunc' does this: print str } -to change its first argument variable `str', this _does not_ change the +to change its first argument variable `str', it _does not_ change the value of `foo' in the caller. The role of `foo' in calling `myfunc' -ended when its value, `"bar"', was computed. If `str' also exists +ended when its value (`"bar"') was computed. If `str' also exists outside of `myfunc', the function body cannot alter this outer value, because it is shadowed during the execution of `myfunc' and cannot be seen or changed from there. @@ -8968,7 +10375,9 @@ seen or changed from there. copied. Instead, the array itself is made available for direct manipulation by the function. This is usually called "call by reference". Changes made to an array parameter inside the body of a -function _are_ visible outside that function. This can be *very* +function _are_ visible outside that function. + + *Note:* Changing an array parameter inside a function can be very dangerous if you do not watch what you are doing. For example: function changeit(array, ind, nvalue) @@ -8987,7 +10396,7 @@ This program prints `a[1] = 1, a[2] = two, a[3] = 3', because `changeit' stores `"two"' in the second element of `a'. Some `awk' implementations allow you to call a function that has not -been defined, and only report a problem at run-time when the program +been defined. They only report a problem at runtime when the program actually tries to call the function. For example: BEGIN { @@ -8999,46 +10408,46 @@ actually tries to call the function. For example: function bar() { ... } # note that `foo' is not defined -Since the `if' statement will never be true, it is not really a problem -that `foo' has not been defined. Usually though, it is a problem if a -program calls an undefined function. +Because the `if' statement will never be true, it is not really a +problem that `foo' has not been defined. Usually though, it is a +problem if a program calls an undefined function. - If `--lint' has been specified (*note Command Line Options: -Options.), `gawk' will report about calls to undefined functions. + If `--lint' is specified (*note Command-Line Options: Options.), +`gawk' reports calls to undefined functions. - Some `awk' implementations generate a run-time error if you use the + Some `awk' implementations generate a runtime error if you use the `next' statement (*note The `next' Statement: Next Statement.) inside -a user-defined function. `gawk' does not have this problem. +a user-defined function. `gawk' does not have this limitation. -File: gawk.info, Node: Return Statement, Prev: Function Caveats, Up: User-defined +File: gawk.info, Node: Return Statement, Next: Dynamic Typing, Prev: Function Caveats, Up: User-defined The `return' Statement -====================== +---------------------- The body of a user-defined function can contain a `return' statement. -This statement returns control to the rest of the `awk' program. It -can also be used to return a value for use in the rest of the `awk' -program. It looks like this: +This statement returns control to the calling part of the `awk' +program. It can also be used to return a value for use in the rest of +the `awk' program. It looks like this: return [EXPRESSION] The EXPRESSION part is optional. If it is omitted, then the returned -value is undefined and, therefore, unpredictable. +value is undefined, and therefore, unpredictable. A `return' statement with no value expression is assumed at the end of every function definition. So if control reaches the end of the function body, then the function returns an unpredictable value. `awk' -will _not_ warn you if you use the return value of such a function. +does _not_ warn you if you use the return value of such a function. Sometimes, you want to write a function for what it does, not for what it returns. Such a function corresponds to a `void' function in C or to a `procedure' in Pascal. Thus, it may be appropriate to not -return any value; you should simply bear in mind that if you use the -return value of such a function, you do so at your own risk. +return any value; simply bear in mind that if you use the return value +of such a function, you do so at your own risk. - Here is an example of a user-defined function that returns a value -for the largest number among the elements of an array: + The following is an example of a user-defined function that returns +a value for the largest number among the elements of an array: function maxelt(vec, i, ret) { @@ -9057,11 +10466,10 @@ function parameter list indicates that `i' and `ret' are not supposed to be arguments. This is a convention that you should follow when you define functions. - Here is a program that uses our `maxelt' function. It loads an + The following program uses the `maxelt' function. It loads an array, calls `maxelt', and then reports the maximum number in that array: - awk ' function maxelt(vec, i, ret) { for (i in vec) { @@ -9079,7 +10487,7 @@ array: END { print maxelt(nums) - }' + } Given the following input: @@ -9089,64 +10497,1166 @@ array: -6 467 998 1101 99385 11 0 225 -our program tells us (predictably) that `99385' is the largest number -in our array. +the program reports (predictably) that `99385' is the largest number in +the array. -File: gawk.info, Node: Invoking Gawk, Next: Library Functions, Prev: User-defined, Up: Top +File: gawk.info, Node: Dynamic Typing, Prev: Return Statement, Up: User-defined -Running `awk' -************* +Functions and Their Effect on Variable Typing +--------------------------------------------- - There are two ways to run `awk': with an explicit program, or with -one or more program files. Here are templates for both of them; items -enclosed in `[...]' in these templates are optional. + `awk' is a very fluid language. It is possible that `awk' can't +tell if an identifier represents a regular variable or an array until +runtime. Here is an annotated sample program: - Besides traditional one-letter POSIX-style options, `gawk' also -supports GNU long options. + function foo(a) + { + a[1] = 1 # parameter is an array + } + + BEGIN { + b = 1 + foo(b) # invalid: fatal type mismatch + + foo(x) # x uninitialized, becomes an array dynamically + x = 1 # now not allowed, runtime error + } - awk [OPTIONS] -f progfile [`--'] FILE ... - awk [OPTIONS] [`--'] 'PROGRAM' FILE ... + Usually, such things aren't a big issue, but it's worth being aware +of them. - It is possible to invoke `awk' with an empty program: + +File: gawk.info, Node: Internationalization, Next: Advanced Features, Prev: Functions, Up: Top + +Internationalization with `gawk' +******************************** + + Once upon a time, computer makers wrote software that only worked in +English. Eventually, hardware and software vendors noticed that if +their systems worked in the native languages of non-English-speaking +countries, they were able to sell more systems. As a result, +internationalization and localization of programs and software systems +became a common practice. + + Until recently, the ability to provide internationalization was +largely restricted to programs written in C and C++. This major node +describes the underlying library `gawk' uses for internationalization, +as well as how `gawk' makes internationalization features available at +the `awk' program level. Having internationalization available at the +`awk' level gives software developers additional flexibility--they are +no longer required to write in C when internationalization is a +requirement. + +* Menu: + +* I18N and L10N:: Internationalization and Localization. +* Explaining gettext:: How GNU `gettext' works. +* Programmer i18n:: Features for the programmer. +* Translator i18n:: Features for the translator. +* I18N Example:: A simple i18n example. +* Gawk I18N:: `gawk' is also internationalized. + + +File: gawk.info, Node: I18N and L10N, Next: Explaining gettext, Prev: Internationalization, Up: Internationalization + +Internationalization and Localization +===================================== + + "Internationalization" means writing (or modifying) a program once, +in such a way that it can use multiple languages without requiring +further source code changes. "Localization" means providing the data +necessary for an internationalized program to work in a particular +language. Most typically, these terms refer to features such as the +language used for printing error messages, the language used to read +responses, and information related to how numerical and monetary values +are printed and read. + + +File: gawk.info, Node: Explaining gettext, Next: Programmer i18n, Prev: I18N and L10N, Up: Internationalization + +GNU `gettext' +============= + + The facilities in GNU `gettext' focus on messages; strings printed +by a program, either directly or via formatting with `printf' or +`sprintf'.(1) + + When using GNU `gettext', each application has its own "text +domain". This is a unique name such as `kpilot' or `gawk', that +identifies the application. A complete application may have multiple +components--programs written in C or C++, as well as scripts written in +`sh' or `awk'. All of the components use the same text domain. + + To make the discussion concrete, assume we're writing an application +named `guide'. Internationalization consists of the following steps, +in this order: + + 1. The programmer goes through the source for all of `guide''s + components and marks each string that is a candidate for + translation. For example, `"`-F': option required"' is a good + candidate for translation. A table with strings of option names + is not (e.g., `gawk''s `--profile' option should remain the same, + no matter what the local language). + + 2. The programmer indicates the application's text domain (`"guide"') + to the `gettext' library, by calling the `textdomain' function. + + 3. Messages from the application are extracted from the source code + and collected into a Portable Object file (`guide.po'), which + lists the strings and their translations. The translations are + initially empty. The original (usually English) messages serve as + the key for lookup of the translations. + + 4. For each language with a translator, `guide.po' is copied and + translations are created and shipped with the application. + + 5. Each language's `.po' file is converted into a binary message + object (`.mo') file. A message object file contains the original + messages and their translations in a binary format that allows + fast lookup of translations at runtime. + + 6. When `guide' is built and installed, the binary translation files + are installed in a standard place. + + 7. For testing and development, it is possible to tell `gettext' to + use `.mo' files in a different directory than the standard one by + using the `bindtextdomain' function. + + 8. At runtime, `guide' looks up each string via a call to `gettext'. + The returned string is the translated string if available, or the + original string if not. + + 9. If necessary, it is possible to access messages from a different + text domain than the one belonging to the application, without + having to switch the application's default text domain back and + forth. + + In C (or C++), the string marking and dynamic translation lookup are +accomplished by wrapping each string in a call to `gettext': + + printf(gettext("Don't Panic!\n")); + + The tools that extract messages from source code pull out all +strings enclosed in calls to `gettext'. + + The GNU `gettext' developers, recognizing that typing `gettext' over +and over again is both painful and ugly to look at, use the macro `_' +(an underscore) to make things easier: + + /* In the standard header file: */ + #define _(str) gettext(str) + + /* In the program text: */ + printf(_("Don't Panic!\n")); + +This reduces the typing overhead to just three extra characters per +string and is considerably easier to read as well. There are locale +"categories" for different types of locale-related information. The +defined locale categories that `gettext' knows about are: + +`LC_MESSAGES' + Text messages. This is the default category for `gettext' + operations, but it is possible to supply a different one + explicitly, if necessary. (It is almost never necessary to supply + a different category.) + +`LC_COLLATE' + Text collation information; i.e., how different characters and/or + groups of characters sort in a given language. + +`LC_CTYPE' + Character type information (alphabetic, digit, upper- or + lowercase, and so on). This information is accessed via the POSIX + character classes in regular expressions, such as `/[[:alnum:]]/' + (*note Regular Expression Operators: Regexp Operators.). + +`LC_MONETARY' + Monetary information, such as the currency symbol, and whether the + symbol goes before or after a number. + +`LC_NUMERIC' + Numeric information, such as which characters to use for the + decimal point and the thousands separator.(2) + +`LC_RESPONSE' + Response information, such as how "yes" and "no" appear in the + local language, and possibly other information as well. + +`LC_TIME' + Time and date related information, such as 12- or 24-hour clock, + month printed before or after day in a date, local month + abbreviations, and so on. + +`LC_ALL' + All of the above. (Not too useful in the context of `gettext'.) + + ---------- Footnotes ---------- + + (1) For some operating systems, the `gawk' port doesn't support GNU +`gettext'. This applies most notably to the PC operating systems. As +such, these features are not available if you are using one of those +operating systems. Sorry. + + (2) Americans use a comma every three decimal places and a period +for the decimal point, while many Europeans do exactly the opposite: +`1,234.56' vs. `1.234,56'. + + +File: gawk.info, Node: Programmer i18n, Next: Translator i18n, Prev: Explaining gettext, Up: Internationalization + +Internationalizing `awk' Programs +================================= + + `gawk' provides the following variables and functions for +internationalization: + +`TEXTDOMAIN' + This variable indicates the application's text domain. For + compatibility with GNU `gettext', the default value is + `"messages"'. + +`_"your message here"' + String constants marked with a leading underscore are candidates + for translation at runtime. String constants without a leading + underscore are not translated. + +`dcgettext(STRING [, DOMAIN [, CATEGORY]])' + This built-in function returns the translation of STRING in text + domain DOMAIN for locale category CATEGORY. The default value for + DOMAIN is the current value of `TEXTDOMAIN'. The default value + for CATEGORY is `"LC_MESSAGES"'. + + If you supply a value for CATEGORY, it must be a string equal to + one of the known locale categories described in *Note GNU + `gettext': Explaining gettext. You must also supply a text + domain. Use `TEXTDOMAIN' if you want to use the current domain. + + *Caution:* The order of arguments to the `awk' version of the + `dcgettext' function is purposely different from the order for the + C version. The `awk' version's order was chosen to be simple and + to allow for reasonable `awk'-style default arguments. + +`bindtextdomain(DIRECTORY [, DOMAIN])' + This built-in function allows you to specify the directory where + `gettext' looks for `.mo' files, in case they will not or cannot + be placed in the standard locations (e.g., during testing). It + returns the directory where DOMAIN is "bound." + + The default DOMAIN is the value of `TEXTDOMAIN'. If DIRECTORY is + the null string (`""'), then `bindtextdomain' returns the current + binding for the given DOMAIN. + + To use these facilities in your `awk' program, follow the steps +outlined in *Note GNU `gettext': Explaining gettext, like so: + + 1. Set the variable `TEXTDOMAIN' to the text domain of your program. + This is best done in a `BEGIN' rule (*note The `BEGIN' and `END' + Special Patterns: BEGIN/END.), or it can also be done via the `-v' + command-line option (*note Command-Line Options: Options.): + + BEGIN { + TEXTDOMAIN = "guide" + ... + } + + 2. Mark all translatable strings with a leading underscore (`_') + character. It _must_ be adjacent to the opening quote of the + string. For example: + + print _"hello, world" + x = _"you goofed" + printf(_"Number of users is %d\n", nusers) + + 3. If you are creating strings dynamically, you can still translate + them, using the `dcgettext' built-in function. + + message = nusers " users logged in" + message = dcgettext(message, "adminprog") + print message + + Here, the call to `dcgettext' supplies a different text domain + (`"adminprog"') in which to find the message, but it uses the + default `"LC_MESSAGES"' category. + + 4. During development, you might want to put the `.mo' file in a + private directory for testing. This is done with the + `bindtextdomain' built-in function: + + BEGIN { + TEXTDOMAIN = "guide" # our text domain + if (Testing) { + # where to find our files + bindtextdomain("testdir") + # joe is in charge of adminprog + bindtextdomain("../joe/testdir", "adminprog") + } + ... + } + + + *Note A Simple Internationalization Example: I18N Example, for an +example program showing the steps necessary to create and use +translations from `awk'. + + +File: gawk.info, Node: Translator i18n, Next: I18N Example, Prev: Programmer i18n, Up: Internationalization + +Translating `awk' Programs +========================== + + Once a program's translatable strings have been marked, they must be +extracted to create the initial `.po' file. As part of translation, it +is often helpful to rearrange the order in which arguments to `printf' +are output. + + `gawk''s `--gen-po' command-line option extracts the messages and is +discussed next. After that, `printf''s ability to rearrange the order +for `printf' arguments at runtime is covered. + +* Menu: + +* String Extraction:: Extracting marked strings. +* Printf Ordering:: Rearranging `printf' arguments. +* I18N Portability:: `awk'-level portability issues. + + +File: gawk.info, Node: String Extraction, Next: Printf Ordering, Prev: Translator i18n, Up: Translator i18n + +Extracting Marked Strings +------------------------- + + Once your `awk' program is working, and all the strings have been +marked and you've set (and perhaps bound) the text domain, it is time +to produce translations. First, use the `--gen-po' command-line option +to create the initial `.po' file: + + $ gawk --gen-po -f guide.awk > guide.po + + When run with `--gen-po', `gawk' does not execute your program. +Instead, it parses it as usual and prints all marked strings to +standard output in the format of a GNU `gettext' Portable Object file. +Also included in the output are any constant strings that appear as the +first argument to `dcgettext'.(1) *Note A Simple Internationalization +Example: I18N Example, for the full list of steps to go through to +create and test translations for `guide'. + + ---------- Footnotes ---------- + + (1) Eventually, the `xgettext' utility that comes with GNU `gettext' +will be taught to automatically run `gawk --gen-po' for `.awk' files, +freeing the translator from having to do it manually. + + +File: gawk.info, Node: Printf Ordering, Next: I18N Portability, Prev: String Extraction, Up: Translator i18n + +Rearranging `printf' Arguments +------------------------------ + + Format strings for `printf' and `sprintf' (*note Using `printf' +Statements for Fancier Printing: Printf.) present a special problem +for translation. Consider the following:(1) + + printf(_"String `%s' has %d characters\n", + string, length(string))) + + A possible German translation for this might be: + + "%d Zeichen lang ist die Zeichenkette `%s'\n" + + The problem should be obvious: the order of the format +specifications is different from the original! Even though `gettext' +can return the translated string at runtime, it cannot change the +argument order in the call to `printf'. + + To solve this problem, `printf' format specificiers may have an +additional optional element, which we call a "positional specifier". +For example: + + "%2$d Zeichen lang ist die Zeichenkette `%1$s'\n" + + Here, the positional specifier consists of an integer count, which +indicates which argument to use, and a `$'. Counts are one-based, and +the format string itself is _not_ included. Thus, in the following +example, `string' is the first argument and `length(string)' is the +second. + + $ gawk 'BEGIN { + > string = "Dont Panic" + > printf _"%2$d characters live in \"%1$s\"\n", + > string, length(string) + > }' + -| 10 characters live in "Dont Panic" + + If present, positional specifiers come first in the format +specification, before the flags, the field width, and/or the precision. + + Positional specifiers can be used with the dynamic field width and +precision capability: + + $ gawk 'BEGIN { + > printf("%*.*s\n", 10, 20, "hello") + > printf("%3$*2$.*1$s\n", 20, 10, "hello") + > }' + -| hello + -| hello + +*Note:* When using `*' with a positional specifier, the `*' comes +first, then the integer position, and then the `$'. This is somewhat +counter-intutive. + + `gawk' does not allow you to mix regular format specifiers and those +with positional specifiers in the same string: + + $ gawk 'BEGIN { printf _"%d %3$s\n", 1, 2, "hi" }' + error--> gawk: cmd. line:1: fatal: must use `count$' on all formats or none + + *Note:* There are some pathological cases that `gawk' may fail to +diagnose. In such cases, the output may not be what you expect. It's +still a bad idea to try mixing them, even if `gawk' doesn't detect it. + + Although positional specifiers can be used directly in `awk' +programs, their primary purpose is to help in producing correct +translations of format strings into languages different from the one in +which the program is first written. + + ---------- Footnotes ---------- + + (1) This example is borrowed from the GNU `gettext' manual. + + +File: gawk.info, Node: I18N Portability, Prev: Printf Ordering, Up: Translator i18n + +`awk' Portability Issues +------------------------ + + `gawk''s internationalization features were purposely chosen to have +as little impact as possible on the portability of `awk' programs that +use them to other versions of `awk'. Consider this program: + + BEGIN { + TEXTDOMAIN = "guide" + if (Test_Guide) # set with -v + bindtextdomain("/test/guide/messages") + print _"don't panic!" + } + +As written, it won't work on other versions of `awk'. However, it is +actually almost portable, requiring very little change. + + * Assignments to `TEXTDOMAIN' won't have any effect, since + `TEXTDOMAIN' is not special in other `awk' implementations. + + * Non-GNU versions of `awk' treat marked strings as the + concatenation of a variable named `_' with the string following + it.(1) Typically, the variable `_' has the null string (`""') as + its value, leaving the original string constant as the result. + + * By defining "dummy" functions to replace `dcgettext' and + `bindtextdomain', the `awk' program can be made to run, but all + the messages are output in the original language. For example: + + function bindtextdomain(dir, domain) + { + return dir + } + + function dcgettext(string, domain, category) + { + return string + } + + * The use of positional specifications in `printf' or `sprintf' is + _not_ portable. To support `gettext' at the C level, many + systems' C versions of `sprintf' do support positional specifiers. + But it works only if enough arguments are supplied in the + function call. Many versions of `awk' pass `printf' formats and + arguments unchanged to the underlying C library version of + `sprintf', but only one format and argument at a time. What + happens if a positional specification is used is anybody's guess. + However, since the positional specifications are primarily for use + in _translated_ format strings, and since non-GNU `awk's never + retrieve the translated string, this should not be a problem in + practice. + + ---------- Footnotes ---------- + + (1) This is good fodder for an "Obfuscated `awk'" contest. + + +File: gawk.info, Node: I18N Example, Next: Gawk I18N, Prev: Translator i18n, Up: Internationalization + +A Simple Internationalization Example +===================================== + + Now let's look at a step-by-step example of how to internationalize +and localize a simple `awk' program, using `guide.awk' as our original +source: + + BEGIN { + TEXTDOMAIN = "guide" + bindtextdomain(".") # for testing + print _"Don't Panic" + print _"The Answer Is", 42 + print "Pardon me, Zaphod who?" + } + +Run `gawk --gen-po' to create the `.po' file: + + $ gawk --gen-po -f guide.awk > guide.po + +This produces: + + #: guide.awk:4 + msgid "Don't Panic" + msgstr "" + + #: guide.awk:5 + msgid "The Answer Is" + msgstr "" + + This original portable object file is saved and reused for each +language into which the application is translated. The `msgid' is the +original string and the `msgstr' is the translation. + + *Note:* Strings not marked with a leading underscore do not appear +in the `guide.po' file. + + Next, the messages must be translated. Here is a translation to a +hypothetical dialect of English, called "Mellow":(1) + + $ cp guide.po guide-mellow.po + ADD TRANSLATIONS TO guide-mellow.po ... + +Following are the translations: + + #: guide.awk:4 + msgid "Don't Panic" + msgstr "Hey man, relax!" + + #: guide.awk:5 + msgid "The Answer Is" + msgstr "Like, the scoop is" + + The next step is to make the directory to hold the binary message +object file and then to create the `guide.mo' file. The directory +layout shown here is standard for GNU `gettext' on GNU/Linux systems. +Other versions of `gettext' may use a different layout: + + $ mkdir en_US en_US/LC_MESSAGES + + The `msgfmt' utility does the conversion from human-readable `.po' +file to machine-readable `.mo' file. By default, `msgfmt' creates a +file named `messages'. This file must be renamed and placed in the +proper directory so that `gawk' can find it: + + $ msgfmt guide-mellow.po + $ mv messages en_US/LC_MESSAGES/guide.mo + + Finally, we run the program to test it: + + $ gawk -f guide.awk + -| Hey man, relax! + -| Like, the scoop is 42 + -| Pardon me, Zaphod who? + + If the two replacement functions for `dcgettext' and `bindtextdomain' +(*note `awk' Portability Issues: I18N Portability.) are in a file +named `libintl.awk', then we can run `guide.awk' unchanged as follows: + + $ gawk --posix -f guide.awk -f libintl.awk + -| Don't Panic + -| The Answer Is 42 + -| Pardon me, Zaphod who? + + ---------- Footnotes ---------- + + (1) Perhaps it would be better if it were called "Hippy." Ah, well. + + +File: gawk.info, Node: Gawk I18N, Prev: I18N Example, Up: Internationalization + +`gawk' Can Speak Your Language +============================== + + As of version 3.1, `gawk' itself has been internationalized using +the GNU `gettext' package. (GNU `gettext' is described in complete +detail in *Note Top::.) As of this writing, the latest version of GNU +`gettext' is version 0.10.37 +(ftp://gnudist.gnu.org/gnu/gettext/gettext-0.10.37.tar.gz). + + If a translation of `gawk''s messages exists, then `gawk' produces +usage messages, warnings, and fatal errors in the local language. + + On systems that do not use version 2 (or later) of the GNU C +library, you should configure `gawk' with the `--with-included-gettext' +option before compiling and installing it. *Note Additional +Configuration Options::, for more information. + + +File: gawk.info, Node: Advanced Features, Next: Invoking Gawk, Prev: Internationalization, Up: Top + +Advanced Features of `gawk' +*************************** + + Write documentation as if whoever reads it is a violent psychopath + who knows where you live. + Steve English, as quoted by Peter Langston + + This major node discusses advanced features in `gawk'. It's a bit +of a "grab bag" of items that are otherwise unrelated to each other. +First, a command-line option allows `gawk' to recognize non-decimal +numbers in input data, not just in `awk' programs. Next, two-way I/O, +discussed briefly in earlier parts of this Info file, is described in +full detail, along with the basics of TCP/IP networking and BSD portal +files. Finally, `gawk' can "profile" an `awk' program, making it +possible to tune it for performance. + + *Note Adding New Built-in Functions to `gawk': Dynamic Extensions, +discusses the ability to dynamically add new built-in functions to +`gawk'. As this feature is still immature and likely to change, its +description is relegated to an appendix. + +* Menu: + +* Non-decimal Data:: Allowing non-decimal input data. +* Two-way I/O:: Two-way communications with another process. +* TCP/IP Networking:: Using `gawk' for network programming. +* Portal Files:: Using `gawk' with BSD portals. +* Profiling:: Profiling your `awk' programs. + + +File: gawk.info, Node: Non-decimal Data, Next: Two-way I/O, Prev: Advanced Features, Up: Advanced Features + +Allowing Non-Decimal Input Data +=============================== + + If you run `gawk' with the `--non-decimal-data' option, you can have +non-decimal constants in your input data: - $ awk '' datafile1 datafile2 + $ echo 0123 123 0x123 | + > gawk --non-decimal-data '{ printf "%d, %d, %d\n", + > $1, $2, $3 }' + -| 83, 123, 291 -Doing so makes little sense though; `awk' will simply exit silently -when given an empty program (d.c.). If `--lint' has been specified on -the command line, `gawk' will issue a warning that the program is empty. + For this feature to work, write your program so that `gawk' treats +your data as numeric: + + $ echo 0123 123 0x123 | gawk '{ print $1, $2, $3 }' + -| 0123 123 0x123 + +The `print' statement treats its expressions as strings. Although the +fields can act as numbers when necessary, they are still strings, so +`print' does not try to treat them numerically. You may need to add +zero to a field to force it to be treated as a number. For example: + + $ echo 0123 123 0x123 | gawk --non-decimal-data ' + > { print $1, $2, $3 + > print $1 + 0, $2 + 0, $3 + 0 }' + -| 0123 123 0x123 + -| 83 123 291 + + Because it is common to have decimal data with leading zeros, and +because using it could lead to surprising results, the default is to +leave this facility disabled. If you want it, you must explicitly +request it. + + *Caution:* _Use of this option is not recommended._ It can break old +programs very badly. Instead, use the `strtonum' function to convert +your data (*note Octal and Hexadecimal Numbers: Non-decimal-numbers.). +This makes your programs easier to write and easier to read, and leads +to less surprising results. + + +File: gawk.info, Node: Two-way I/O, Next: TCP/IP Networking, Prev: Non-decimal Data, Up: Advanced Features + +Two-Way Communications with Another Process +=========================================== + + From: brennan@whidbey.com (Mike Brennan) + Newsgroups: comp.lang.awk + Subject: Re: Learn the SECRET to Attract Women Easily + Date: 4 Aug 1997 17:34:46 GMT + Message-ID: <5s53rm$eca@news.whidbey.com> + + On 3 Aug 1997 13:17:43 GMT, Want More Dates??? + <tracy78@kilgrona.com> wrote: + >Learn the SECRET to Attract Women Easily + > + >The SCENT(tm) Pheromone Sex Attractant For Men to Attract Women + + The scent of awk programmers is a lot more attractive to women than + the scent of perl programmers. + -- + Mike Brennan + + It is often useful to be able to send data to a separate program for +processing and then read the result. This can always be done with +temporary files: + + # write the data for processing + tempfile = ("/tmp/mydata." PROCINFO["pid"]) + while (NOT DONE WITH DATA) + print DATA | ("subprogram > " tempfile) + close("subprogram > " tempfile) + + # read the results, remove tempfile when done + while ((getline newdata < tempfile) > 0) + PROCESS newdata APPROPRIATELY + close(tempfile) + system("rm " tempfile) + +This works, but not elegantly. + + Starting with version 3.1 of `gawk', it is possible to open a +_two-way_ pipe to another process. The second process is termed a +"coprocess", since it runs in parallel with `gawk'. The two-way +connection is created using the new `|&' operator (borrowed from the +Korn Shell, `ksh'):(1) + + do { + print DATA |& "subprogram" + "subprogram" |& getline results + } while (DATA LEFT TO PROCESS) + close("subprogram") + + The first time an I/O operation is executed using the `|&' operator, +`gawk' creates a two-way pipeline to a child process that runs the +other program. Output created with `print' or `printf' is written to +the program's standard input, and output from the program's standard +output can be read by the `gawk' program using `getline'. As is the +case with processes started by `|', the subprogram can be any program, +or pipeline of programs, that can be started by the shell. + + There are some cautionary items to be aware of: + + * As the code inside `gawk' currently stands, the coprocess's + standard error goes to the same place that the parent `gawk''s + standard error goes. It is not possible to read the child's + standard error separately. + + * I/O buffering may be a problem. `gawk' automatically flushes all + output down the pipe to the child process. However, if the + coprocess does not flush its output, `gawk' may hang when doing a + `getline' in order to read the coprocess's results. This could + lead to a situation known as "deadlock", where each process is + waiting for the other one to do something. + + It is possible to close just one end of the two-way pipe to a +coprocess, by supplying a second argument to the `close' function of +either `"to"' or `"from"' (*note Closing Input and Output Redirections: +Close Files And Pipes.). These strings tell `gawk' to close the end of +the pipe that sends data to the process or the end that reads from it, +respectively. + + This is particularly necessary in order to use the system `sort' +utility as part of a coprocess; `sort' must read _all_ of its input +data before it can produce any output. The `sort' program does not +receive an end-of-file indication until `gawk' closes the write end of +the pipe. + + When you have finished writing data to the `sort' utility, you can +close the `"to"' end of the pipe, and then start reading sorted data +via `getline'. For example: + + BEGIN { + command = "LC_ALL=C sort" + n = split("abcdefghijklmnopqrstuvwxyz", a, "") + + for (i = n; i > 0; i--) + print a[i] |& command + close(command, "to") + + while ((command |& getline line) > 0) + print "got", line + close(command) + } + + This program writes the letters of the alphabet in reverse order, one +per line, down the two-way pipe to `sort'. It then closes the write +end of the pipe, so that `sort' receives an end-of-file indication. +This causes `sort' to sort the data and write the sorted data back to +the `gawk' program. Once all of the data has been read, `gawk' +terminates the coprocess and exits. + + As a side note, the assignment `LC_ALL=C' in the `sort' command +ensures traditional Unix (ASCII) sorting from `sort'. + + ---------- Footnotes ---------- + + (1) This is very different from the same operator in the C shell, +`csh'. + + +File: gawk.info, Node: TCP/IP Networking, Next: Portal Files, Prev: Two-way I/O, Up: Advanced Features + +Using `gawk' for Network Programming +==================================== + + `EMISTERED': A host is a host from coast to coast, + and no-one can talk to host that's close, + unless the host that isn't close + is busy hung or dead. + + In addition to being able to open a two-way pipeline to a coprocess +on the same system (*note Two-Way Communications with Another Process: +Two-way I/O.), it is possible to make a two-way connection to another +process on another system across an IP networking connection. + + You can think of this as just a _very long_ two-way pipeline to a +coprocess. The way `gawk' decides that you want to use TCP/IP +networking is by recognizing special file names that begin with +`/inet/'. + + The full syntax of the special file name is +`/inet/PROTOCOL/LOCAL-PORT/REMOTE-HOST/REMOTE-PORT'. The meaning of +the components are: + +PROTOCOL + The protocol to use over IP. This must be either `tcp', `udp', or + `raw', for a TCP, UDP, or raw IP connection, respectively. The + use of TCP is recommended for most applications. + + *Caution:* The use of raw sockets is not currently supported in + version 3.1 of `gawk'. + +LOCAL-PORT + The local TCP or UDP port number to use. Use a port number of `0' + when you want the system to pick a port. This is what you should do + when writing a TCP or UDP client. You may also use a well-known + service name, such as `smtp' or `http', in which case `gawk' + attempts to determine the pre-defined port number using the C + `getservbyname' function. + +REMOTE-HOST + The IP address or fully-qualified domain name of the Internet host + to which you want to connect. + +REMOTE-PORT + The TCP or UDP port number to use on the given REMOTE-HOST. + Again, use `0' if you don't care, or else a well-known service + name. + + Consider the following very simple example: + + BEGIN { + Service = "/inet/tcp/0/localhost/daytime" + Service |& getline + print $0 + close(Service) + } + + This program reads the current date and time from the local system's +TCP `daytime' server. It then prints the results and closes the +connection. + + Because this topic is extensive, the use of `gawk' for TCP/IP +programming is documented separately. *Note Top::, for a much more +complete introduction and discussion, as well as extensive examples. + + +File: gawk.info, Node: Portal Files, Next: Profiling, Prev: TCP/IP Networking, Up: Advanced Features + +Using `gawk' with BSD Portals +============================= + + Similar to the `/inet' special files, if `gawk' is configured with +the `--enable-portals' option (*note Compiling `gawk' for Unix: Quick +Installation.), then `gawk' treats files whose pathnames begin with +`/p' as 4.4 BSD-style portals. + + When used with the `|&' operator, `gawk' opens the file for two-way +communications. The operating system's portal mechanism then manages +creating the process associated with the portal and the corresponding +communications with the portal's process. + + +File: gawk.info, Node: Profiling, Prev: Portal Files, Up: Advanced Features + +Profiling Your `awk' Programs +============================= + + Beginning with version 3.1 of `gawk', you may produce execution +traces of your `awk' programs. This is done with a specially compiled +version of `gawk', called `pgawk' ("profiling `gawk'"). + + `pgawk' is identical in every way to `gawk', except that when it has +finished running, it creates a profile of your program in a file named +`awkprof.out'. Because it is profiling, it also executes up to 45 +percent slower than `gawk' normally does. + + As shown in the following example, the `--profile' option can be +used to change the name of the file where `pgawk' will write the +profile: + + $ pgawk --profile=myprog.prof -f myprog.awk data1 data2 + +In the above example, `pgawk' places the profile in `myprog.prof' +instead of in `awkprof.out'. + + Regular `gawk' also accepts this option. When called with just +`--profile', `gawk' "pretty prints" the program into `awkprof.out', +without any execution counts. You may supply an option to `--profile' +to change the file name. Here is a sample session showing a simple +`awk' program, its input data, and the results from running `pgawk'. +First, the `awk' program: + + BEGIN { print "First BEGIN rule" } + + END { print "First END rule" } + + /foo/ { + print "matched /foo/, gosh" + for (i = 1; i <= 3; i++) + sing() + } + + { + if (/foo/) + print "if is true" + else + print "else is true" + } + + BEGIN { print "Second BEGIN rule" } + + END { print "Second END rule" } + + function sing( dummy) + { + print "I gotta be me!" + } + + Following is the input data: + + foo + bar + baz + foo + junk + + Here is the `awkprof.out' that results from running `pgawk' on this +program and data. (This example also illustrates that `awk' +programmers sometimes have to work late.): + + # gawk profile, created Sun Aug 13 00:00:15 2000 + + # BEGIN block(s) + + BEGIN { + 1 print "First BEGIN rule" + 1 print "Second BEGIN rule" + } + + # Rule(s) + + 5 /foo/ { # 2 + 2 print "matched /foo/, gosh" + 6 for (i = 1; i <= 3; i++) { + 6 sing() + } + } + + 5 { + 5 if (/foo/) { # 2 + 2 print "if is true" + 3 } else { + 3 print "else is true" + } + } + + # END block(s) + + END { + 1 print "First END rule" + 1 print "Second END rule" + } + + # Functions, listed alphabetically + + 6 function sing(dummy) + { + 6 print "I gotta be me!" + } + + The previous example illustrates many of the basic rules for +profiling output. The rules are as follows: + + * The program is printed in the order `BEGIN' rule, pattern/action + rules, `END' rule and functions, listed alphabetically. Multiple + `BEGIN' and `END' rules are merged together. + + * Pattern-action rules have two counts. The first count, to the + left of the rule, shows how many times the rule's pattern was + _tested_. The second count, to the right of the rule's opening + left brace in a comment, shows how many times the rule's action + was _executed_. The difference between the two indicates how many + times the rule's pattern evaluated to false. + + * Similarly, the count for an `if'-`else' statement shows how many + times the condition was tested. To the right of the opening left + brace for the `if''s body is a count showing how many times the + condition was true. The count for the `else' indicates how many + times the test failed. + + * The count for a loop header (such as `for' or `while') shows how + many times the loop test was executed. (Because of this, you + can't just look at the count on the first statement in a rule to + determine how many times the rule was executed. If the first + statement is a loop, the count is misleading.) + + * For user-defined functions, the count next to the `function' + keyword indicates how many times the function was called. The + counts next to the statements in the body show how many times + those statements were executed. + + * The layout uses "K&R" style using tabs. Braces are used + everywhere, even when the body of an `if', `else', or loop is only + a single statement. + + * Parentheses are used only where needed, as indicated by the + structure of the program and the precedence rules. For example, + `(3 + 5) * 4' means add three plus five, then multiply the total + by four. However, `3 + 5 * 4' has no parentheses, and means `3 + + (5 * 4)'. + + * All string concatenations are parenthesized too. (This could be + made a bit smarter.) + + * Parentheses are used around the arguments to `print' and `printf' + only when the `print' or `printf' statement is followed by a + redirection. Similarly, if the target of a redirection isn't a + scalar, it gets parenthesized. + + * `pgawk' supplies leading comments in front of the `BEGIN' and + `END' rules, the pattern/action rules, and the functions. + + + The profiled version of your program may not look exactly like what +you typed when you wrote it. This is because `pgawk' creates the +profiled version by "pretty printing" its internal representation of +the program. The advantage to this is that `pgawk' can produce a +standard representation. The disadvantage is that all source code +comments are lost, as are the distinctions among multiple `BEGIN' and +`END' rules. Also, things such as: + + /foo/ + +come out as: + + /foo/ { + print $0 + } + +which is correct, but possibly surprising. + + Besides creating profiles when a program has completed, `pgawk' can +produce a profile while it is running. This is useful if your `awk' +program goes into an infinite loop and you want to see what has been +executed. To use this feature, run `pgawk' in the background: + + $ pgawk -f myprog & + [1] 13992 + +The shell prints a job number and process ID number, in this case, +13992. Use the `kill' command to send the `USR1' signal to `pgawk': + + $ kill -USR1 13992 + +As usual, the profiled version of the program is written to +`awkprof.out', or to a different file if you use the `--profile' option. + + Along with the regular profile, as shown earlier, the profile +includes a trace of any active functions: + + # Function Call Stack: + + # 3. baz + # 2. bar + # 1. foo + # -- main -- + + You may send `pgawk' the `USR1' signal as many times as you like. +Each time, the profile and function call trace are appended to the +output profile file. + + If you use the `HUP' signal instead of the `USR1' signal, `pgawk' +produces the profile and the function call trace, and then exits. + + +File: gawk.info, Node: Invoking Gawk, Next: Library Functions, Prev: Advanced Features, Up: Top + +Running `awk' and `gawk' +************************ + + This major node covers how to run awk, both POSIX-standard and +`gawk'-specific command-line options, and what `awk' and `gawk' do with +non-option arguments. It then proceeds to cover how `gawk' searches +for source files, obsolete options and/or features, and known bugs in +`gawk'. This major node rounds out the discussion of `awk' as a +program and as a language. + + While a number of the options and features described here were +discussed in passing earlier in the book, this major node provides the +full details. * Menu: -* Options:: Command line options and their meanings. +* Command Line:: How to run `awk'. +* Options:: Command-line options and their meanings. * Other Arguments:: Input file names and variable assignments. -* AWKPATH Variable:: Searching directories for `awk' programs. +* AWKPATH Variable:: Searching directories for `awk' + programs. * Obsolete:: Obsolete Options and/or features. * Undocumented:: Undocumented Options and Features. * Known Bugs:: Known Bugs in `gawk'. -File: gawk.info, Node: Options, Next: Other Arguments, Prev: Invoking Gawk, Up: Invoking Gawk +File: gawk.info, Node: Command Line, Next: Options, Prev: Invoking Gawk, Up: Invoking Gawk + +Invoking `awk' +============== + + There are two ways to run `awk'--with an explicit program or with +one or more program files. Here are templates for both of them; items +enclosed in [...] in these templates are optional: + + awk [OPTIONS] -f progfile [`--'] FILE ... + awk [OPTIONS] [`--'] 'PROGRAM' FILE ... + + Besides traditional one-letter POSIX-style options, `gawk' also +supports GNU long options. + + It is possible to invoke `awk' with an empty program: -Command Line Options + awk '' datafile1 datafile2 + +Doing so makes little sense though; `awk' exits silently when given an +empty program. (d.c.) If `--lint' has been specified on the +command-line, `gawk' issues a warning that the program is empty. + + +File: gawk.info, Node: Options, Next: Other Arguments, Prev: Command Line, Up: Invoking Gawk + +Command-Line Options ==================== - Options begin with a dash, and consist of a single character. GNU -style long options consist of two dashes and a keyword. The keyword -can be abbreviated, as long the abbreviation allows the option to be -uniquely identified. If the option takes an argument, then the keyword -is either immediately followed by an equals sign (`=') and the -argument's value, or the keyword and the argument's value are separated -by whitespace. For brevity, the discussion below only refers to the -traditional short options; however the long and short options are -interchangeable in all contexts. + Options begin with a dash and consist of a single character. +GNU-style long options consist of two dashes and a keyword. The +keyword can be abbreviated, as long as the abbreviation allows the +option to be uniquely identified. If the option takes an argument, +then the keyword is either immediately followed by an equals sign (`=') +and the argument's value, or the keyword and the argument's value are +separated by whitespace. If a particular option with a value is given +more than once, it is the last value that counts. Each long option for `gawk' has a corresponding POSIX-style option. -The options and their meanings are as follows: +The long and short options are interchangeable in all contexts. The +options and their meanings are as follows: `-F FS' `--field-separator FS' - Sets the `FS' variable to FS (*note Specifying How Fields are + Sets the `FS' variable to FS (*note Specifying How Fields Are Separated: Field Separators.). `-f SOURCE-FILE' @@ -9156,119 +11666,177 @@ The options and their meanings are as follows: `-v VAR=VAL' `--assign VAR=VAL' - Sets the variable VAR to the value VAL *before* execution of the + Sets the variable VAR to the value VAL _before_ execution of the program begins. Such variable values are available inside the - `BEGIN' rule (*note Other Command Line Arguments: Other + `BEGIN' rule (*note Other Command-Line Arguments: Other Arguments.). - The `-v' option can only set one variable, but you can use it more + The `-v' option can only set one variable, but it can be used more than once, setting another variable each time, like this: `awk -v foo=1 -v bar=2 ...'. - *Caution:* Using `-v' to set the values of the builtin variables - may lead to suprising results. `awk' will reset the values of + *Caution:* Using `-v' to set the values of the built-in variables + may lead to surprising results. `awk' will reset the values of those variables as it needs to, possibly ignoring any predefined value you may have given. -`-mf NNN' -`-mr NNN' - Set various memory limits to the value NNN. The `f' flag sets the - maximum number of fields, and the `r' flag sets the maximum record - size. These two flags and the `-m' option are from the Bell Labs - research version of Unix `awk'. They are provided for - compatibility, but otherwise ignored by `gawk', since `gawk' has - no predefined limits. +`-mf N' +`-mr N' + Set various memory limits to the value N. The `f' flag sets the + maximum number of fields and the `r' flag sets the maximum record + size. These two flags and the `-m' option are from the Bell + Laboratories research version of Unix `awk'. They are provided + for compatibility but otherwise ignored by `gawk', since `gawk' + has no predefined limits. (The Bell Laboratories `awk' no longer + needs these options; it continues to accept them to avoid breaking + old programs.) `-W GAWK-OPT' - Following the POSIX standard, options that are implementation - specific are supplied as arguments to the `-W' option. These - options also have corresponding GNU style long options. See below. + Following the POSIX standard, implementation-specific options are + supplied as arguments to the `-W' option. These options also have + corresponding GNU-style long options. Note that the long options + may be abbreviated, as long as the abbreviations remain unique. + The full list of `gawk'-specific options is provided next. `--' - Signals the end of the command line options. The following + Signals the end of the command-line options. The following arguments are not treated as options even if they begin with `-'. This interpretation of `--' follows the POSIX argument parsing conventions. This is useful if you have file names that start with `-', or in shell scripts, if you have file names that will be specified by - the user which could start with `-'. + the user that could start with `-'. - The following `gawk'-specific options are available: + The previous list described options mandated by the POSIX standard, +as well as options available in the Bell Laboratories version of `awk'. +The following list describes `gawk'-specific options: -`-W traditional' `-W compat' -`--traditional' +`-W traditional' `--compat' +`--traditional' Specifies "compatibility mode", in which the GNU extensions to the `awk' language are disabled, so that `gawk' behaves just like the - Bell Labs research version of Unix `awk'. `--traditional' is the - preferred form of this option. *Note Extensions in `gawk' Not in - POSIX `awk': POSIX/GNU, which summarizes the extensions. Also see - *Note Downward Compatibility and Debugging: Compatibility Mode. + Bell Laboratories research version of Unix `awk'. `--traditional' + is the preferred form of this option. *Note Extensions in `gawk' + Not in POSIX `awk': POSIX/GNU, which summarizes the extensions. + Also see *Note Downward Compatibility and Debugging: Compatibility + Mode. -`-W copyleft' `-W copyright' -`--copyleft' `--copyright' - Print the short version of the General Public License, and then - exit. This option may disappear in a future version of `gawk'. + Print the short version of the General Public License and then + exit. + +`-W copyleft' +`--copyleft' + Just like `--copyright'. This option may disappear in a future + version of `gawk'. + +`-W dump-variables[=FILE]' +`--dump-variables[=FILE]' + Print a sorted list of global variables, their types, and final + values to FILE. If no FILE is provided, `gawk' prints this list + to a file named `awkvars.out' in the current directory. + + Having a list of all the global variables is a good way to look for + typographical errors in your programs. You would also use this + option if you have a large program with a lot of functions, and + you want to be sure that your functions don't inadvertently use + global variables that you meant to be local. (This is a + particularly easy mistake to make with simple variable names like + `i', `j', and so on.) + +`-W gen-po' +`--gen-po' + Analyze the source program and generate a GNU `gettext' Portable + Object file on standard output for all string constants that have + been marked for translation. *Note Internationalization with + `gawk': Internationalization, for information about this option. `-W help' `-W usage' `--help' `--usage' Print a "usage" message summarizing the short and long style - options that `gawk' accepts, and then exit. + options that `gawk' accepts and then exit. -`-W lint' -`--lint' +`-W lint[=fatal]' +`--lint[=fatal]' Warn about constructs that are dubious or non-portable to other `awk' implementations. Some warnings are issued when `gawk' first - reads your program. Others are issued at run-time, as your - program executes. + reads your program. Others are issued at runtime, as your program + executes. With an optional argument of `fatal', lint warnings + become fatal errors. This may be drastic but its use will + certainly encourage the development of cleaner `awk' programs. `-W lint-old' `--lint-old' Warn about constructs that are not available in the original - Version 7 Unix version of `awk' (*note Major Changes between V7 - and SVR3.1: V7/SVR3.1.). + version of `awk' from Version 7 Unix (*note Major Changes Between + V7 and SVR3.1: V7/SVR3.1.). + +`-W non-decimal-data' +`--non-decimal-data' + Enable automatic interpretation of octal and hexadecimal values in + input data (*note Allowing Non-Decimal Input Data: Non-decimal + Data.). + + *Caution:* This option can severely break old programs. Use with + care. `-W posix' `--posix' Operate in strict POSIX mode. This disables all `gawk' extensions - (just like `--traditional'), and adds the following additional + (just like `--traditional') and adds the following additional restrictions: * `\x' escape sequences are not recognized (*note Escape Sequences::). * Newlines do not act as whitespace to separate fields when - `FS' is equal to a single space. + `FS' is equal to a single space (*note Examining Fields: + Fields.). + + * Newlines are not allowed after `?' or `:' (*note Conditional + Expressions: Conditional Exp.). * The synonym `func' for the keyword `function' is not recognized (*note Function Definition Syntax: Definition Syntax.). - * The operators `**' and `**=' cannot be used in place of `^' + * The `**' and `**=' operators cannot be used in place of `^' and `^=' (*note Arithmetic Operators: Arithmetic Ops., and also *note Assignment Expressions: Assignment Ops.). - * Specifying `-Ft' on the command line does not set the value + * Specifying `-Ft' on the command-line does not set the value of `FS' to be a single tab character (*note Specifying How - Fields are Separated: Field Separators.). + Fields Are Separated: Field Separators.). * The `fflush' built-in function is not supported (*note - Built-in Functions for Input/Output: I/O Functions.). + Input/Output Functions: I/O Functions.). - If you supply both `--traditional' and `--posix' on the command - line, `--posix' will take precedence. `gawk' will also issue a + If you supply both `--traditional' and `--posix' on the + command-line, `--posix' takes precedence. `gawk' also issues a warning if both options are supplied. +`-W profile[=FILE]' +`--profile[=FILE]' + Enable profiling of `awk' programs (*note Profiling Your `awk' + Programs: Profiling.). By default, profiles are created in a file + named `awkprof.out'. The optional FILE argument allows you to + specify a different file name for the profile file. + + When run with `gawk', the profile is just a "pretty printed" + version of the program. When run with `pgawk', the profile + contains execution counts for each statement in the program in the + left margin, and function call counts for each function. + `-W re-interval' `--re-interval' Allow interval expressions (*note Regular Expression Operators: - Regexp Operators.), in regexps. Because interval expressions were + Regexp Operators.) in regexps. Because interval expressions were traditionally not available in `awk', `gawk' does not provide them by default. This prevents old `awk' programs from breaking. @@ -9276,73 +11844,76 @@ The options and their meanings are as follows: `--source PROGRAM-TEXT' Program source code is taken from the PROGRAM-TEXT. This option allows you to mix source code in files with source code that you - enter on the command line. This is particularly useful when you - have library functions that you wish to use from your command line + enter on the command-line. This is particularly useful when you + have library functions that you want to use from your command-line programs (*note The `AWKPATH' Environment Variable: AWKPATH Variable.). `-W version' `--version' - Prints version information for this particular copy of `gawk'. + Print version information for this particular copy of `gawk'. This allows you to determine if your copy of `gawk' is up to date with respect to whatever the Free Software Foundation is currently distributing. It is also useful for bug reports (*note Reporting Problems and Bugs: Bugs.). - Any other options are flagged as invalid with a warning message, but -are otherwise ignored. + As long as program text has been supplied, any other options are +flagged as invalid with a warning message but are otherwise ignored. In compatibility mode, as a special case, if the value of FS supplied to the `-F' option is `t', then `FS' is set to the tab character -(`"\t"'). This is only true for `--traditional', and not for `--posix' -(*note Specifying How Fields are Separated: Field Separators.). +(`"\t"'). This is only true for `--traditional' and not for `--posix' +(*note Specifying How Fields Are Separated: Field Separators.). - The `-f' option may be used more than once on the command line. If + The `-f' option may be used more than once on the command-line. If it is, `awk' reads its program source from all of the named files, as if they had been concatenated together into one big file. This is -useful for creating libraries of `awk' functions. Useful functions can -be written once, and then retrieved from a standard place, instead of -having to be included into each individual program. - - You can type in a program at the terminal and still use library -functions, by specifying `-f /dev/tty'. `awk' will read a file from -the terminal to use as part of the `awk' program. After typing your -program, type `Control-d' (the end-of-file character) to terminate it. -(You may also use `-f -' to read program source from the standard -input, but then you will not be able to also use the standard input as a +useful for creating libraries of `awk' functions. These functions can +be written once and then retrieved from a standard place, instead of +having to be included into each individual program. (As mentioned in +*Note Function Definition Syntax: Definition Syntax, function names +must be unique.) + + Library functions can still be used, even if the program is entered +at the terminal, by specifying `-f /dev/tty'. After typing your +program, type `Ctrl-d' (the end-of-file character) to terminate it. +(You may also use `-f -' to read program source from the standard input +but then you will not be able to also use the standard input as a source of data.) Because it is clumsy using the standard `awk' mechanisms to mix -source file and command line `awk' programs, `gawk' provides the +source file and command-line `awk' programs, `gawk' provides the `--source' option. This does not require you to pre-empt the standard -input for your source code, and allows you to easily mix command line +input for your source code; it allows you to easily mix command-line and library source code (*note The `AWKPATH' Environment Variable: AWKPATH Variable.). - If no `-f' or `--source' option is specified, then `gawk' will use -the first non-option command line argument as the text of the program + If no `-f' or `--source' option is specified, then `gawk' uses the +first non-option command-line argument as the text of the program source code. If the environment variable `POSIXLY_CORRECT' exists, then `gawk' -will behave in strict POSIX mode, exactly as if you had supplied the -`--posix' command line option. Many GNU programs look for this -environment variable to turn on strict POSIX mode. If you supply -`--lint' on the command line, and `gawk' turns on POSIX mode because of -`POSIXLY_CORRECT', then it will print a warning message indicating that -POSIX mode is in effect. - - You would typically set this variable in your shell's startup file. -For a Bourne compatible shell (such as Bash), you would add these lines -to the `.profile' file in your home directory. +behaves in strict POSIX mode, exactly as if you had supplied the +`--posix' command-line option. Many GNU programs look for this +environment variable to turn on strict POSIX mode. If `--lint' is +supplied on the command-line and `gawk' turns on POSIX mode because of +`POSIXLY_CORRECT', then it issues a warning message indicating that +POSIX mode is in effect. You would typically set this variable in your +shell's startup file. For a Bourne-compatible shell (such as `bash'), +you would add these lines to the `.profile' file in your home directory: POSIXLY_CORRECT=true export POSIXLY_CORRECT For a `csh' compatible shell,(1) you would add this line to the -`.login' file in your home directory. +`.login' file in your home directory: setenv POSIXLY_CORRECT true + Having `POSIXLY_CORRECT' set is not recommended for daily use, but +it is good for testing the portability of your programs to other +environments. + ---------- Footnotes ---------- (1) Not recommended. @@ -9350,16 +11921,18 @@ to the `.profile' file in your home directory. File: gawk.info, Node: Other Arguments, Next: AWKPATH Variable, Prev: Options, Up: Invoking Gawk -Other Command Line Arguments +Other Command-Line Arguments ============================ - Any additional arguments on the command line are normally treated as + Any additional arguments on the command-line are normally treated as input files to be processed in the order specified. However, an argument that has the form `VAR=VALUE', assigns the value VALUE to the -variable VAR--it does not specify a file at all. +variable VAR--it does not specify a file at all. (This was discussed +earlier in *Note Assigning Variables on the Command Line: Assignment +Options.) All these arguments are made available to your `awk' program in the -`ARGV' array (*note Built-in Variables::). Command line options and +`ARGV' array (*note Built-in Variables::). Command-line options and the program text (if present) are omitted from `ARGV'. All other arguments, including variable assignments, are included. As each element of `ARGV' is processed, `gawk' sets the variable `ARGIND' to @@ -9367,31 +11940,32 @@ the index in `ARGV' of the current element. The distinction between file name arguments and variable-assignment arguments is made when `awk' is about to open the next input file. At -that point in execution, it checks the "file name" to see whether it is +that point in execution, it checks the file name to see whether it is really a variable assignment; if so, `awk' sets the variable instead of reading a file. Therefore, the variables actually receive the given values after all previously specified files have been read. In particular, the values of variables assigned in this fashion are _not_ available inside a `BEGIN' -rule (*note The `BEGIN' and `END' Special Patterns: BEGIN/END.), since -such rules are run before `awk' begins scanning the argument list. +rule (*note The `BEGIN' and `END' Special Patterns: BEGIN/END.), +because such rules are run before `awk' begins scanning the argument +list. - The variable values given on the command line are processed for -escape sequences (d.c.) (*note Escape Sequences::). + The variable values given on the command-line are processed for +escape sequences (*note Escape Sequences::). (d.c.) In some earlier implementations of `awk', when a variable assignment occurred before any file names, the assignment would happen _before_ the `BEGIN' rule was executed. `awk''s behavior was thus inconsistent; -some command line assignments were available inside the `BEGIN' rule, -while others were not. However, some applications came to depend upon -this "feature." When `awk' was changed to be more consistent, the `-v' -option was added to accommodate applications that depended upon the old -behavior. +some command-line assignments were available inside the `BEGIN' rule, +while others were not. Unfortunately, some applications came to depend +upon this "feature." When `awk' was changed to be more consistent, the +`-v' option was added to accommodate applications that depended upon +the old behavior. The variable assignment feature is most useful for assigning to variables such as `RS', `OFS', and `ORS', which control input and -output formats, before scanning the data files. It is also useful for +output formats before scanning the data files. It is also useful for controlling state if multiple passes are needed over a data file. For example: @@ -9408,14 +11982,13 @@ File: gawk.info, Node: AWKPATH Variable, Next: Obsolete, Prev: Other Argument The `AWKPATH' Environment Variable ================================== - The previous section described how `awk' program files can be named -on the command line with the `-f' option. In most `awk' + The previous minor node described how `awk' program files can be +named on the command-line with the `-f' option. In most `awk' implementations, you must supply a precise path name for each program -file, unless the file is in the current directory. - - But in `gawk', if the file name supplied to the `-f' option does not -contain a `/', then `gawk' searches a list of directories (called the -"search path"), one by one, looking for a file with the specified name. +file, unless the file is in the current directory. But in `gawk', if +the file name supplied to the `-f' option does not contain a `/', then +`gawk' searches a list of directories (called the "search path"), one +by one, looking for a file with the specified name. The search path is a string consisting of directory names separated by colons. `gawk' gets its search path from the `AWKPATH' environment @@ -9424,40 +11997,44 @@ which is `.:/usr/local/share/awk'.(1) (Programs written for use by system administrators should use an `AWKPATH' variable that does not include the current directory, `.'.) - The search path feature is particularly useful for building up -libraries of useful `awk' functions. The library files can be placed -in a standard directory that is in the default path, and then specified -on the command line with a short file name. Otherwise, the full file -name would have to be typed for each file. + The search path feature is particularly useful for building libraries +of useful `awk' functions. The library files can be placed in a +standard directory in the default path and then specified on the +command-line with a short file name. Otherwise, the full file name +would have to be typed for each file. - By using both the `--source' and `-f' options, your command line + By using both the `--source' and `-f' options, your command-line `awk' programs can use facilities in `awk' library files. *Note A -Library of `awk' Functions: Library Functions. - - Path searching is not done if `gawk' is in compatibility mode. This -is true for both `--traditional' and `--posix'. *Note Command Line -Options: Options. +Library of `awk' Functions: Library Functions. Path searching is not +done if `gawk' is in compatibility mode. This is true for both +`--traditional' and `--posix'. *Note Command-Line Options: Options. - *Note:* if you want files in the current directory to be found, you + *Note:* If you want files in the current directory to be found, you must include the current directory in the path, either by including `.' -explicitly in the path, or by writing a null entry in the path. (A -null entry is indicated by starting or ending the path with a colon, or -by placing two colons next to each other (`::').) If the current +explicitly in the path or by writing a null entry in the path. (A null +entry is indicated by starting or ending the path with a colon or by +placing two colons next to each other (`::').) If the current directory is not included in the path, then files cannot be found in the current directory. This path search mechanism is identical to the shell's. Starting with version 3.0, if `AWKPATH' is not defined in the -environment, `gawk' will place its default search path into +environment, `gawk' places its default search path into `ENVIRON["AWKPATH"]'. This makes it easy to determine the actual search -path `gawk' will use. +path that `gawk' will use from within an `awk' program. + + While you can change `ENVIRON["AWKPATH"]' within your `awk' program, +this has no effect on the running program's behavior. This makes +sense: the `AWKPATH' environment variable is used to find the program +source files. Once your program is running, all the files have been +found, and `gawk' no longer needs to use `AWKPATH'. ---------- Footnotes ---------- (1) Your version of `gawk' may use a different directory; it will -depend upon how `gawk' was built and installed. The actual directory -will be the value of `$(datadir)' generated when `gawk' was configured. -You probably don't need to worry about this though. +depend upon how `gawk' was built and installed. The actual directory is +the value of `$(datadir)' generated when `gawk' was configured. You +probably don't need to worry about this though. File: gawk.info, Node: Obsolete, Next: Undocumented, Prev: AWKPATH Variable, Up: Invoking Gawk @@ -9465,15 +12042,23 @@ File: gawk.info, Node: Obsolete, Next: Undocumented, Prev: AWKPATH Variable, Obsolete Options and/or Features ================================ - This section describes features and/or command line options from + This minor node describes features and/or command-line options from previous releases of `gawk' that are either not available in the -current version, or that are still supported but deprecated (meaning -that they will _not_ be in the next release). - - For version 3.0.6 of `gawk', there are no command line options or -other deprecated features from the previous version of `gawk'. This -node is thus essentially a place holder, in case some option becomes -obsolete in a future version of `gawk'. +current version or that are still supported but deprecated (meaning that +they will _not_ be in the next release). + + For version 3.1 of `gawk', there are no deprecated command-line +options from the previous version of `gawk'. The use of `next file' +(two words) for `nextfile' was deprecated in `gawk' 3.0 but still +worked. Starting with version 3.1, the two word usage is no longer +accepted. + + The process-related special files described in *Note Special Files +for Process-Related Information: Special Process, work as described, but +are now considered deprecated. `gawk' prints a warning message every +time they are used. (Use `PROCINFO' instead; see *Note Built-in +Variables That Convey Information: Auto-set.) They will be removed +from the next release of `gawk'. File: gawk.info, Node: Undocumented, Next: Known Bugs, Prev: Obsolete, Up: Invoking Gawk @@ -9484,9 +12069,7 @@ Undocumented Options and Features Use the Source, Luke! Obi-Wan - - - This section intentionally left blank. + This minor node intentionally left blank. File: gawk.info, Node: Known Bugs, Prev: Undocumented, Up: Invoking Gawk @@ -9494,24 +12077,15 @@ File: gawk.info, Node: Known Bugs, Prev: Undocumented, Up: Invoking Gawk Known Bugs in `gawk' ==================== - * The `-F' option for changing the value of `FS' (*note Command Line - Options: Options.) is not necessary given the command line + * The `-F' option for changing the value of `FS' (*note Command-Line + Options: Options.) is not necessary given the command-line variable assignment feature; it remains only for backwards compatibility. - * If your system actually has support for `/dev/fd' and the - associated `/dev/stdin', `/dev/stdout', and `/dev/stderr' files, - you may get different output from `gawk' than you would get on a - system without those files. When `gawk' interprets these files - internally, it synchronizes output to the standard output with - output to `/dev/stdout', while on a system with those files, the - output is actually to different open files (*note Special File - Names in `gawk': Special Files.). - * Syntactically invalid single character programs tend to overflow the parse stack, generating a rather unhelpful message. Such programs are surprisingly difficult to diagnose in the completely - general case, and the effort to do so really is not worth it. + general case and the effort to do so really is not worth it. File: gawk.info, Node: Library Functions, Next: Sample Programs, Prev: Invoking Gawk, Up: Top @@ -9519,10 +12093,21 @@ File: gawk.info, Node: Library Functions, Next: Sample Programs, Prev: Invoki A Library of `awk' Functions **************************** - This chapter presents a library of useful `awk' functions. The -sample programs presented later (*note Practical `awk' Programs: Sample -Programs.) use these functions. The functions are presented here in a -progression from simple to complex. + *Note User-Defined Functions: User-defined, describes how to write +your own `awk' functions. Writing functions is important, because it +allows you to encapsulate algorithms and program tasks in a single +place. It simplifies programming, making program development more +manageable, and making programs more readable. + + One valuable way to learn a new programming language is to _read_ +programs in that language. To that end, this major node and *Note +Practical `awk' Programs: Sample Programs, provide a good-sized body of +code for you to read, and hopefully, to learn from. + + This major node presents a library of useful `awk' functions. Many +of the sample programs presented later in this Info file use these +functions. The functions are presented here in a progression from +simple to complex. *Note Extracting Programs from Texinfo Source Files: Extract Program, presents a program that you can use to extract the source code for @@ -9531,122 +12116,206 @@ for this Info file. (This has already been done as part of the `gawk' distribution.) If you have written one or more useful, general purpose `awk' -functions, and would like to contribute them for a subsequent edition -of this Info file, please contact the author. *Note Reporting Problems -and Bugs: Bugs, for information on doing this. Don't just send code, -as you will be required to either place your code in the public domain, -publish it under the GPL (*note GNU GENERAL PUBLIC LICENSE: Copying.), -or assign the copyright in it to the Free Software Foundation. +functions and would like to contribute them to the author's collection +of `awk' programs, see *Note How to Contribute: How To Contribute, for +more information. + + The programs in this major node and in *Note Practical `awk' +Programs: Sample Programs, freely use features that are `gawk'-specific. +It is straightforward to rewrite these programs for different +implementations of `awk'. + + Diagnostic error messages are sent to `/dev/stderr'. Use `| "cat +1>&2"' instead of `> "/dev/stderr"', if your system does not have a +`/dev/stderr' or if you cannot use `gawk'. + + A number of programs use `nextfile' (*note Using `gawk''s `nextfile' +Statement: Nextfile Statement.) to skip any remaining input in the +input file. *Note Implementing `nextfile' as a Function: Nextfile +Function, shows you how to write a function that does the same thing. + + Finally, some of the programs choose to ignore upper- and lowercase +distinctions in their input. They do so by assigning one to +`IGNORECASE'. You can achieve almost the same effect(1) by adding the +following rule to the beginning of the program: + + # ignore case + { $0 = tolower($0) } + +Also, verify that all regexp and string constants used in comparisons +only use lowercase letters. * Menu: -* Portability Notes:: What to do if you don't have `gawk'. -* Nextfile Function:: Two implementations of a `nextfile' - function. -* Assert Function:: A function for assertions in `awk' - programs. -* Round Function:: A function for rounding if `sprintf' does - not do it correctly. -* Ordinal Functions:: Functions for using characters as numbers and - vice versa. -* Join Function:: A function to join an array into a string. -* Mktime Function:: A function to turn a date into a timestamp. -* Gettimeofday Function:: A function to get formatted times. -* Filetrans Function:: A function for handling data file transitions. -* Getopt Function:: A function for processing command line +* Library Names:: How to best name private global variables in + library functions. +* General Functions:: Functions that are of general use. +* Data File Management:: Functions for managing command-line data + files. +* Getopt Function:: A function for processing command-line arguments. * Passwd Functions:: Functions for getting user information. * Group Functions:: Functions for getting group information. -* Library Names:: How to best name private global variables in - library functions. + + ---------- Footnotes ---------- + + (1) The effects are not identical. Output of the transformed record +will be in all lowercase, while `IGNORECASE' preserves the original +contents of the input record. -File: gawk.info, Node: Portability Notes, Next: Nextfile Function, Prev: Library Functions, Up: Library Functions +File: gawk.info, Node: Library Names, Next: General Functions, Prev: Library Functions, Up: Library Functions -Simulating `gawk'-specific Features -=================================== +Naming Library Function Global Variables +======================================== - The programs in this chapter and in *Note Practical `awk' Programs: -Sample Programs, freely use features that are specific to `gawk'. This -section briefly discusses how you can rewrite these programs for -different implementations of `awk'. + Due to the way the `awk' language evolved, variables are either +"global" (usable by the entire program) or "local" (usable just by a +specific function). There is no intermediate state analogous to +`static' variables in C. - Diagnostic error messages are sent to `/dev/stderr'. Use `| "cat -1>&2"' instead of `> "/dev/stderr"', if your system does not have a -`/dev/stderr', or if you cannot use `gawk'. + Library functions often need to have global variables that they can +use to preserve state information between calls to the function--for +example, `getopt''s variable `_opti' (*note Processing Command-Line +Options: Getopt Function.). Such variables are called "private", since +the only functions that need to use them are the ones in the library. - A number of programs use `nextfile' (*note The `nextfile' Statement: -Nextfile Statement.), to skip any remaining input in the input file. -*Note Implementing `nextfile' as a Function: Nextfile Function, shows -you how to write a function that will do the same thing. + When writing a library function, you should try to choose names for +your private variables that will not conflict with any variables used by +either another library function or a user's main program. For example, +a name like `i' or `j' is not a good choice, because user programs +often use variable names like these for their own purposes. - Finally, some of the programs choose to ignore upper-case and -lower-case distinctions in their input. They do this by assigning one -to `IGNORECASE'. You can achieve the same effect by adding the -following rule to the beginning of the program: + The example programs shown in this major node all start the names of +their private variables with an underscore (`_'). Users generally +don't use leading underscores in their variable names, so this +convention immediately decreases the chances that the variable name +will be accidentally shared with the user's program. - # ignore case - { $0 = tolower($0) } + In addition, several of the library functions use a prefix that helps +indicate what function or set of functions use the variables--for +example, `_pw_byname' in the user database routines (*note Reading the +User Database: Passwd Functions.). This convention is recommended, +since it even further decreases the chance of inadvertent conflict +among variable names. Note that this convention is used equally well +for variable names and for private function names as well.(1) -Also, verify that all regexp and string constants used in comparisons -only use lower-case letters. + As a final note on variable naming, if a function makes global +variables available for use by a main program, it is a good convention +to start that variable's name with a capital letter--for example, +`getopt''s `Opterr' and `Optind' variables (*note Processing +Command-Line Options: Getopt Function.). The leading capital letter +indicates that it is global, while the fact that the variable name is +not all capital letters indicates that the variable is not one of +`awk''s built-in variables, such as `FS'. + + It is also important that _all_ variables in library functions that +do not need to save state are, in fact, declared local.(2) If this is +not done, the variable could accidentally be used in the user's +program, leading to bugs that are very difficult to track down: + + function lib_func(x, y, l1, l2) + { + ... + USE VARIABLE some_var # some_var should be local + ... # but is not by oversight + } + + A different convention, common in the Tcl community, is to use a +single associative array to hold the values needed by the library +function(s), or "package." This significantly decreases the number of +actual global names in use. For example, the functions described in +*Note Reading the User Database: Passwd Functions, might have used +array elements `PW_data["inited"]', `PW_data["total"]', +`PW_data["count"]', and `PW_data["awklib"]', instead of `_pw_inited', +`_pw_awklib', `_pw_total', and `_pw_count'. + + The conventions presented in this minor node are exactly that: +conventions. You are not required to write your programs this way--we +merely recommend that you do so. + + ---------- Footnotes ---------- + + (1) While all the library routines could have been rewritten to use +this convention, this was not done, in order to show how my own `awk' +programming style has evolved, and to provide some basis for this +discussion. + + (2) `gawk''s `--dump-variables' command-line option is useful for +verifying this. -File: gawk.info, Node: Nextfile Function, Next: Assert Function, Prev: Portability Notes, Up: Library Functions +File: gawk.info, Node: General Functions, Next: Data File Management, Prev: Library Names, Up: Library Functions + +General Programming +=================== + + This minor node presents a number of functions that are of general +programming use. + +* Menu: + +* Nextfile Function:: Two implementations of a `nextfile' + function. +* Assert Function:: A function for assertions in `awk' + programs. +* Round Function:: A function for rounding if `sprintf' does + not do it correctly. +* Cliff Random Function:: The Cliff Random Number Generator. +* Ordinal Functions:: Functions for using characters as numbers and + vice versa. +* Join Function:: A function to join an array into a string. +* Gettimeofday Function:: A function to get formatted times. + + +File: gawk.info, Node: Nextfile Function, Next: Assert Function, Prev: General Functions, Up: General Functions Implementing `nextfile' as a Function -===================================== +------------------------------------- - The `nextfile' statement presented in *Note The `nextfile' -Statement: Nextfile Statement, is a `gawk'-specific extension. It is -not available in other implementations of `awk'. This section shows -two versions of a `nextfile' function that you can use to simulate -`gawk''s `nextfile' statement if you cannot use `gawk'. + The `nextfile' statement presented in *Note Using `gawk''s +`nextfile' Statement: Nextfile Statement, is a `gawk'-specific +extension--it is not available in most other implementations of `awk'. +This minor node shows two versions of a `nextfile' function that you +can use to simulate `gawk''s `nextfile' statement if you cannot use +`gawk'. - Here is a first attempt at writing a `nextfile' function. + A first attempt at writing a `nextfile' function is as follows: # nextfile --- skip remaining records in current file - # this should be read in before the "main" awk program function nextfile() { _abandon_ = FILENAME; next } - _abandon_ == FILENAME { next } - This file should be included before the main program, because it -supplies a rule that must be executed first. This rule compares the -current data file's name (which is always in the `FILENAME' variable) -to a private variable named `_abandon_'. If the file name matches, -then the action part of the rule executes a `next' statement, to go on -to the next record. (The use of `_' in the variable name is a -convention. It is discussed more fully in *Note Naming Library -Function Global Variables: Library Names.) + Because it supplies a rule that must be executed first, this file +should be included before the main program. This rule compares the +current data file's name (which is always in the `FILENAME' variable) to +a private variable named `_abandon_'. If the file name matches, then +the action part of the rule executes a `next' statement to go on to the +next record. (The use of `_' in the variable name is a convention. It +is discussed more fully in *Note Naming Library Function Global +Variables: Library Names.) The use of the `next' statement effectively creates a loop that reads -all the records from the current data file. Eventually, the end of the -file is reached, and a new data file is opened, changing the value of +all the records from the current data file. The end of the file is +eventually reached and a new data file is opened, changing the value of `FILENAME'. Once this happens, the comparison of `_abandon_' to -`FILENAME' fails, and execution continues with the first rule of the +`FILENAME' fails and execution continues with the first rule of the "real" program. The `nextfile' function itself simply sets the value of `_abandon_' -and then executes a `next' statement to start the loop going.(1) - - This initial version has a subtle problem. What happens if the same -data file is listed _twice_ on the command line, one right after the -other, or even with just a variable assignment between the two -occurrences of the file name? +and then executes a `next' statement to start the loop. - In such a case, this code will skip right through the file, a second -time, even though it should stop when it gets to the end of the first -occurrence. Here is a second version of `nextfile' that remedies this -problem. + This initial version has a subtle problem. If the same data file is +listed _twice_ on the commandline, one right after the other or even +with just a variable assignment between them, this code skips right +through the file, a second time, even though it should stop when it +gets to the end of the first occurrence. A second version of +`nextfile' that remedies this problem is shown here: # nextfile --- skip remaining records in current file # correctly handle successive occurrences of the same file - # Arnold Robbins, arnold@gnu.org, Public Domain - # May, 1993 - # this should be read in before the "main" awk program function nextfile() { _abandon_ = FILENAME; next } @@ -9658,56 +12327,46 @@ problem. next } - The `nextfile' function has not changed. It sets `_abandon_' equal -to the current file name and then executes a `next' satement. The -`next' statement reads the next record and increments `FNR', so `FNR' -is guaranteed to have a value of at least two. However, if `nextfile' -is called for the last record in the file, then `awk' will close the -current data file and move on to the next one. Upon doing so, -`FILENAME' will be set to the name of the new file, and `FNR' will be -reset to one. If this next file is the same as the previous one, -`_abandon_' will still be equal to `FILENAME'. However, `FNR' will be -equal to one, telling us that this is a new occurrence of the file, and -not the one we were reading when the `nextfile' function was executed. -In that case, `_abandon_' is reset to the empty string, so that further -executions of this rule will fail (until the next time that `nextfile' -is called). - - If `FNR' is not one, then we are still in the original data file, -and the program executes a `next' statement to skip through it. - - An important question to ask at this point is: "Given that the + The `nextfile' function has not changed. It makes `_abandon_' equal +to the current file name and then executes a `next' statement. The +`next' statement reads the next record and increments `FNR' so that +`FNR' is guaranteed to have a value of at least two. However, if +`nextfile' is called for the last record in the file, then `awk' closes +the current data file and moves on to the next one. Upon doing so, +`FILENAME' is set to the name of the new file and `FNR' is reset to +one. If this next file is the same as the previous one, `_abandon_' is +still equal to `FILENAME'. However, `FNR' is equal to one, telling us +that this is a new occurrence of the file and not the one we were +reading when the `nextfile' function was executed. In that case, +`_abandon_' is reset to the empty string, so that further executions of +this rule fail (until the next time that `nextfile' is called). + + If `FNR' is not one, then we are still in the original data file and +the program executes a `next' statement to skip through it. + + An important question to ask at this point is: given that the functionality of `nextfile' can be provided with a library file, why is -it built into `gawk'?" This is an important question. Adding features -for little reason leads to larger, slower programs that are harder to -maintain. - - The answer is that building `nextfile' into `gawk' provides -significant gains in efficiency. If the `nextfile' function is executed -at the beginning of a large data file, `awk' still has to scan the -entire file, splitting it up into records, just to skip over it. The -built-in `nextfile' can simply close the file immediately and proceed -to the next one, saving a lot of time. This is particularly important -in `awk', since `awk' programs are generally I/O bound (i.e. they -spend most of their time doing input and output, instead of performing -computations). - - ---------- Footnotes ---------- - - (1) Some implementations of `awk' do not allow you to execute `next' -from within a function body. Some other work-around will be necessary -if you use such a version. +it built into `gawk'? Adding features for little reason leads to +larger, slower programs that are harder to maintain. The answer is +that building `nextfile' into `gawk' provides significant gains in +efficiency. If the `nextfile' function is executed at the beginning of +a large data file, `awk' still has to scan the entire file, splitting +it up into records, just to skip over it. The built-in `nextfile' can +simply close the file immediately and proceed to the next one, which +saves a lot of time. This is particularly important in `awk', because +`awk' programs are generally I/O-bound (i.e., they spend most of their +time doing input and output, instead of performing computations). -File: gawk.info, Node: Assert Function, Next: Round Function, Prev: Nextfile Function, Up: Library Functions +File: gawk.info, Node: Assert Function, Next: Round Function, Prev: Nextfile Function, Up: General Functions Assertions -========== +---------- - When writing large programs, it is often useful to be able to know -that a condition or set of conditions is true. Before proceeding with a + When writing large programs, it is often useful to know that a +condition or set of conditions is true. Before proceeding with a particular computation, you make a statement about what you believe to -be the case. Such a statement is known as an "assertion." The C +be the case. Such a statement is known as an "assertion". The C language provides an `<assert.h>' header file and corresponding `assert' macro that the programmer can use to make assertions. If an assertion fails, the `assert' macro arranges to print a diagnostic @@ -9718,24 +12377,20 @@ not, and then it kills the program. In C, using `assert' looks this: int myfunc(int a, double b) { - assert(a <= 5 && b >= 17); + assert(a <= 5 && b >= 17.1); ... } - If the assertion failed, the program would print a message similar to -this: + If the assertion fails, the program prints a message similar to this: - prog.c:5: assertion failed: a <= 5 && b >= 17 + prog.c:5: assertion failed: a <= 5 && b >= 17.1 - The ANSI C language makes it possible to turn the condition into a -string for use in printing the diagnostic message. This is not -possible in `awk', so this `assert' function also requires a string -version of the condition that is being tested. + The C language makes it possible to turn the condition into a string +for use in printing the diagnostic message. This is not possible in +`awk', so this `assert' function also requires a string version of the +condition that is being tested. Following is the function: # assert --- assert that a condition is true. Otherwise exit. - # Arnold Robbins, arnold@gnu.org, Public Domain - # May, 1993 - function assert(condition, string) { if (! condition) { @@ -9754,60 +12409,57 @@ version of the condition that is being tested. The `assert' function tests the `condition' parameter. If it is false, it prints a message to standard error, using the `string' parameter to describe the failed condition. It then sets the variable -`_assert_exit' to one, and executes the `exit' statement. The `exit' +`_assert_exit' to one and executes the `exit' statement. The `exit' statement jumps to the `END' rule. If the `END' rules finds -`_assert_exit' to be true, then it exits immediately. - - The purpose of the `END' rule with its test is to keep any other -`END' rules from running. When an assertion fails, the program should -exit immediately. If no assertions fail, then `_assert_exit' will -still be false when the `END' rule is run normally, and the rest of the -program's `END' rules will execute. For all of this to work correctly, -`assert.awk' must be the first source file read by `awk'. +`_assert_exit' to be true, it then exits immediately. - You would use this function in your programs this way: + The purpose of the test in the `END' rule is to keep any other `END' +rules from running. When an assertion fails, the program should exit +immediately. If no assertions fail, then `_assert_exit' is still false +when the `END' rule is run normally, and the rest of the program's +`END' rules execute. For all of this to work correctly, `assert.awk' +must be the first source file read by `awk'. The function can be used +in a program in the following way: function myfunc(a, b) { - assert(a <= 5 && b >= 17, "a <= 5 && b >= 17") + assert(a <= 5 && b >= 17.1, "a <= 5 && b >= 17.1") ... } -If the assertion failed, you would see a message like this: +If the assertion fails, you see a message similar to the following: - mydata:1357: assertion failed: a <= 5 && b >= 17 + mydata:1357: assertion failed: a <= 5 && b >= 17.1 - There is a problem with this version of `assert', that it may not be -possible to work around with standard `awk'. An `END' rule is -automatically added to the program calling `assert'. Normally, if a -program consists of just a `BEGIN' rule, the input files and/or + There is a small problem with this version of `assert'. An `END' +rule is automatically added to the program calling `assert'. Normally, +if a program consists of just a `BEGIN' rule, the input files and/or standard input are not read. However, now that the program has an `END' -rule, `awk' will attempt to read the input data files, or standard input +rule, `awk' attempts to read the input data files or standard input (*note Startup and Cleanup Actions: Using BEGIN/END.), most likely -causing the program to hang, waiting for input. +causing the program to hang as it waits for input. + + There is a simple workaround to this: make sure the `BEGIN' rule +always ends with an `exit' statement. -File: gawk.info, Node: Round Function, Next: Ordinal Functions, Prev: Assert Function, Up: Library Functions +File: gawk.info, Node: Round Function, Next: Cliff Random Function, Prev: Assert Function, Up: General Functions Rounding Numbers -================ +---------------- The way `printf' and `sprintf' (*note Using `printf' Statements for -Fancier Printing: Printf.) do rounding will often depend upon the +Fancier Printing: Printf.) perform rounding often depends upon the system's C `sprintf' subroutine. On many machines, `sprintf' rounding is "unbiased," which means it doesn't always round a trailing `.5' up, contrary to naive expectations. In unbiased rounding, `.5' rounds to even, rather than always up, so 1.5 rounds to 2 but 4.5 rounds to 4. -The result is that if you are using a format that does rounding (e.g., -`"%.0f"') you should check what your system does. The following +This means that if you are using a format that does rounding (e.g., +`"%.0f"'), you should check what your system does. The following function does traditional rounding; it might be useful if your awk's -`printf' does unbiased rounding. +`printf' does unbiased rounding: # round --- do normal rounding - # - # Arnold Robbins, arnold@gnu.org, August, 1996 - # Public Domain - function round(x, ival, aval, fraction) { ival = int(x) # integer part, int() truncates @@ -9837,10 +12489,41 @@ function does traditional rounding; it might be useful if your awk's { print $0, round($0) } -File: gawk.info, Node: Ordinal Functions, Next: Join Function, Prev: Round Function, Up: Library Functions +File: gawk.info, Node: Cliff Random Function, Next: Ordinal Functions, Prev: Round Function, Up: General Functions + +The Cliff Random Number Generator +--------------------------------- + + The Cliff random number generator(1) is a very simple random number +generator that "passes the noise sphere test for randomness by showing +no structure." It is easily programmed, in less than 10 lines of `awk' +code: + + # cliff_rand.awk --- generate Cliff random numbers + BEGIN { _cliff_seed = 0.1 } + + function cliff_rand() + { + _cliff_seed = (100 * log(_cliff_seed)) % 1 + if (_cliff_seed < 0) + _cliff_seed = - _cliff_seed + return _cliff_seed + } + + This algorithm requires an initial "seed" of 0.1. Each new value +uses the current seed as input for the calculation. If the built-in +`rand' function (*note Numeric Functions::) isn't random enough, you +might try using this function instead. + + ---------- Footnotes ---------- + + (1) `http://mathworld.wolfram.com/CliffRandomNumberGenerator.hmtl' + + +File: gawk.info, Node: Ordinal Functions, Next: Join Function, Prev: Cliff Random Function, Up: General Functions Translating Between Characters and Numbers -========================================== +------------------------------------------ One commercial implementation of `awk' supplies a built-in function, `ord', which takes a character and returns the numeric value for that @@ -9849,23 +12532,14 @@ character in the machine's character set. If the string passed to The inverse of this function is `chr' (from the function of the same name in Pascal), which takes a number and returns the corresponding -character. - - Both functions can be written very nicely in `awk'; there is no real -reason to build them into the `awk' interpreter. +character. Both functions are written very nicely in `awk'; there is +no real reason to build them into the `awk' interpreter: # ord.awk --- do ord and chr - # + # Global identifiers: # _ord_: numerical values indexed by characters # _ord_init: function to initialize _ord_ - # - # Arnold Robbins - # arnold@gnu.org - # Public Domain - # 16 January, 1992 - # 20 July, 1992, revised - BEGIN { _ord_init() } function _ord_init( low, high, i, t) @@ -9891,15 +12565,15 @@ reason to build them into the `awk' interpreter. Some explanation of the numbers used by `chr' is worthwhile. The most prominent character set in use today is ASCII. Although an -eight-bit byte can hold 256 distinct values (from zero to 255), ASCII -only defines characters that use the values from zero to 127.(1) At -least one computer manufacturer that we know of uses ASCII, but with -mark parity, meaning that the leftmost bit in the byte is always one. -What this means is that on those systems, characters have numeric -values from 128 to 255. Finally, large mainframe systems use the -EBCDIC character set, which uses all 256 values. While there are other +eight-bit byte can hold 256 distinct values (from 0 to 255), ASCII only +defines characters that use the values from 0 to 127.(1) In the now +distant past, at least one minicomputer manufacturer used ASCII, but +with mark parity, meaning that the leftmost bit in the byte is always +1. This means that on those systems, characters have numeric values +from 128 to 255. Finally, large mainframe systems use the EBCDIC +character set, which uses all 256 values. While there are other character sets in use on some older systems, they are not really worth -worrying about. +worrying about: function ord(str, c) { @@ -9925,25 +12599,23 @@ worrying about. # } # } - An obvious improvement to these functions would be to move the code -for the `_ord_init' function into the body of the `BEGIN' rule. It was -written this way initially for ease of development. - - There is a "test program" in a `BEGIN' rule, for testing the -function. It is commented out for production use. + An obvious improvement to these functions is to move the code for the +`_ord_init' function into the body of the `BEGIN' rule. It was written +this way initially for ease of development. There is a "test program" +in a `BEGIN' rule, to test the function. It is commented out for +production use. ---------- Footnotes ---------- (1) ASCII has been extended in many countries to use the values from 128 to 255 for country-specific characters. If your system uses these -extensions, you can simplify `_ord_init' to simply loop from zero to -255. +extensions, you can simplify `_ord_init' to simply loop from 0 to 255. -File: gawk.info, Node: Join Function, Next: Mktime Function, Prev: Ordinal Functions, Up: Library Functions +File: gawk.info, Node: Join Function, Next: Gettimeofday Function, Prev: Ordinal Functions, Up: General Functions -Merging an Array Into a String -============================== +Merging an Array into a String +------------------------------ When doing string processing, it is often useful to be able to join all the strings in an array into one long string. The following @@ -9951,18 +12623,15 @@ function, `join', accomplishes this task. It is used later in several of the application programs (*note Practical `awk' Programs: Sample Programs.). - Good function design is important; this function needs to be -general, but it should also have a reasonable default behavior. It is -called with an array and the beginning and ending indices of the + Good function design is important; this function needs to be general +but it should also have a reasonable default behavior. It is called +with an array as well as the beginning and ending indices of the elements in the array to be merged. This assumes that the array indices are numeric--a reasonable assumption since the array was likely -created with `split' (*note Built-in Functions for String Manipulation: -String Functions.). +created with `split' (*note String Manipulation Functions: String +Functions.): # join.awk --- join an array into a string - # Arnold Robbins, arnold@gnu.org, Public Domain - # May 1993 - function join(array, start, end, sep, result, i) { if (sep == "") @@ -9977,318 +12646,38 @@ String Functions.). An optional additional argument is the separator to use when joining the strings back together. If the caller supplies a non-empty value, -`join' uses it. If it is not supplied, it will have a null value. In -this case, `join' uses a single blank as a default separator for the +`join' uses it; if it is not supplied, it has a null value. In this +case, `join' uses a single blank as a default separator for the strings. If the value is equal to `SUBSEP', then `join' joins the strings with no separator between them. `SUBSEP' serves as a "magic" value to indicate that there should be no separation between the -component strings. - - It would be nice if `awk' had an assignment operator for -concatenation. The lack of an explicit operator for concatenation -makes string operations more difficult than they really need to be. - - -File: gawk.info, Node: Mktime Function, Next: Gettimeofday Function, Prev: Join Function, Up: Library Functions - -Turning Dates Into Timestamps -============================= - - The `systime' function built in to `gawk' returns the current time -of day as a timestamp in "seconds since the Epoch." This timestamp can -be converted into a printable date of almost infinitely variable format -using the built-in `strftime' function. (For more information on -`systime' and `strftime', *note Functions for Dealing with Time Stamps: -Time Functions..) - - An interesting but difficult problem is to convert a readable -representation of a date back into a timestamp. The ANSI C library -provides a `mktime' function that does the basic job, converting a -canonical representation of a date into a timestamp. - - It would appear at first glance that `gawk' would have to supply a -`mktime' built-in function that was simply a "hook" to the C language -version. In fact though, `mktime' can be implemented entirely in -`awk'.(1) - - Here is a version of `mktime' for `awk'. It takes a simple -representation of the date and time, and converts it into a timestamp. - - The code is presented here intermixed with explanatory prose. In -*Note Extracting Programs from Texinfo Source Files: Extract Program, -you will see how the Texinfo source file for this Info file can be -processed to extract the code into a single source file. - - The program begins with a descriptive comment and a `BEGIN' rule -that initializes a table `_tm_months'. This table is a two-dimensional -array that has the lengths of the months. The first index is zero for -regular years, and one for leap years. The values are the same for all -the months in both kinds of years, except for February; thus the use of -multiple assignment. - - # mktime.awk --- convert a canonical date representation - # into a timestamp - # Arnold Robbins, arnold@gnu.org, Public Domain - # May 1993 - - BEGIN \ - { - # Initialize table of month lengths - _tm_months[0,1] = _tm_months[1,1] = 31 - _tm_months[0,2] = 28; _tm_months[1,2] = 29 - _tm_months[0,3] = _tm_months[1,3] = 31 - _tm_months[0,4] = _tm_months[1,4] = 30 - _tm_months[0,5] = _tm_months[1,5] = 31 - _tm_months[0,6] = _tm_months[1,6] = 30 - _tm_months[0,7] = _tm_months[1,7] = 31 - _tm_months[0,8] = _tm_months[1,8] = 31 - _tm_months[0,9] = _tm_months[1,9] = 30 - _tm_months[0,10] = _tm_months[1,10] = 31 - _tm_months[0,11] = _tm_months[1,11] = 30 - _tm_months[0,12] = _tm_months[1,12] = 31 - } - - The benefit of merging multiple `BEGIN' rules (*note The `BEGIN' and -`END' Special Patterns: BEGIN/END.) is particularly clear when writing -library files. Functions in library files can cleanly initialize their -own private data and also provide clean-up actions in private `END' -rules. - - The next function is a simple one that computes whether a given year -is or is not a leap year. If a year is evenly divisible by four, but -not evenly divisible by 100, or if it is evenly divisible by 400, then -it is a leap year. Thus, 1904 was a leap year, 1900 was not, but 2000 -will be. - - # decide if a year is a leap year - function _tm_isleap(year, ret) - { - ret = (year % 4 == 0 && year % 100 != 0) || - (year % 400 == 0) - - return ret - } - - This function is only used a few times in this file, and its -computation could have been written "in-line" (at the point where it's -used). Making it a separate function made the original development -easier, and also avoids the possibility of typing errors when -duplicating the code in multiple places. - - The next function is more interesting. It does most of the work of -generating a timestamp, which is converting a date and time into some -number of seconds since the Epoch. The caller passes an array (rather -imaginatively named `a') containing six values: the year including -century, the month as a number between one and 12, the day of the -month, the hour as a number between zero and 23, the minute in the -hour, and the seconds within the minute. - - The function uses several local variables to precompute the number of -seconds in an hour, seconds in a day, and seconds in a year. Often, -similar C code simply writes out the expression in-line, expecting the -compiler to do "constant folding". E.g., most C compilers would turn -`60 * 60' into `3600' at compile time, instead of recomputing it every -time at run time. Precomputing these values makes the function more -efficient. - - # convert a date into seconds - function _tm_addup(a, total, yearsecs, daysecs, - hoursecs, i, j) - { - hoursecs = 60 * 60 - daysecs = 24 * hoursecs - yearsecs = 365 * daysecs - - total = (a[1] - 1970) * yearsecs - - # extra day for leap years - for (i = 1970; i < a[1]; i++) - if (_tm_isleap(i)) - total += daysecs - - j = _tm_isleap(a[1]) - for (i = 1; i < a[2]; i++) - total += _tm_months[j, i] * daysecs - - total += (a[3] - 1) * daysecs - total += a[4] * hoursecs - total += a[5] * 60 - total += a[6] - - return total - } - - The function starts with a first approximation of all the seconds -between Midnight, January 1, 1970,(2) and the beginning of the current -year. It then goes through all those years, and for every leap year, -adds an additional day's worth of seconds. - - The variable `j' holds either one or zero, if the current year is or -is not a leap year. For every month in the current year prior to the -current month, it adds the number of seconds in the month, using the -appropriate entry in the `_tm_months' array. - - Finally, it adds in the seconds for the number of days prior to the -current day, and the number of hours, minutes, and seconds in the -current day. - - The result is a count of seconds since January 1, 1970. This value -is not yet what is needed though. The reason why is described shortly. - - The main `mktime' function takes a single character string argument. -This string is a representation of a date and time in a "canonical" -(fixed) form. This string should be `"YEAR MONTH DAY HOUR MINUTE -SECOND"'. - - # mktime --- convert a date into seconds, - # compensate for time zone - - function mktime(str, res1, res2, a, b, i, j, t, diff) - { - i = split(str, a, " ") # don't rely on FS - - if (i != 6) - return -1 - - # force numeric - for (j in a) - a[j] += 0 - - # validate - if (a[1] < 1970 || - a[2] < 1 || a[2] > 12 || - a[3] < 1 || a[3] > 31 || - a[4] < 0 || a[4] > 23 || - a[5] < 0 || a[5] > 59 || - a[6] < 0 || a[6] > 60 ) - return -1 - - res1 = _tm_addup(a) - t = strftime("%Y %m %d %H %M %S", res1) - - if (_tm_debug) - printf("(%s) -> (%s)\n", str, t) > "/dev/stderr" - - split(t, b, " ") - res2 = _tm_addup(b) - - diff = res1 - res2 - - if (_tm_debug) - printf("diff = %d seconds\n", diff) > "/dev/stderr" - - res1 += diff - - return res1 - } - - The function first splits the string into an array, using spaces and -tabs as separators. If there are not six elements in the array, it -returns an error, signaled as the value -1. Next, it forces each -element of the array to be numeric, by adding zero to it. The -following `if' statement then makes sure that each element is within an -allowable range. (This checking could be extended further, e.g., to -make sure that the day of the month is within the correct range for the -particular month supplied.) All of this is essentially preliminary -set-up and error checking. - - Recall that `_tm_addup' generated a value in seconds since Midnight, -January 1, 1970. This value is not directly usable as the result we -want, _since the calculation does not account for the local timezone_. -In other words, the value represents the count in seconds since the -Epoch, but only for UTC (Universal Coordinated Time). If the local -timezone is east or west of UTC, then some number of hours should be -either added to, or subtracted from the resulting timestamp. - - For example, 6:23 p.m. in Atlanta, Georgia (USA), is normally five -hours west of (behind) UTC. It is only four hours behind UTC if -daylight savings time is in effect. If you are calling `mktime' in -Atlanta, with the argument `"1993 5 23 18 23 12"', the result from -`_tm_addup' will be for 6:23 p.m. UTC, which is only 2:23 p.m. in -Atlanta. It is necessary to add another four hours worth of seconds to -the result. - - How can `mktime' determine how far away it is from UTC? This is -surprisingly easy. The returned timestamp represents the time passed to -`mktime' _as UTC_. This timestamp can be fed back to `strftime', which -will format it as a _local_ time; i.e. as if it already had the UTC -difference added in to it. This is done by giving -`"%Y %m %d %H %M %S"' to `strftime' as the format argument. It returns -the computed timestamp in the original string format. The result -represents a time that accounts for the UTC difference. When the new -time is converted back to a timestamp, the difference between the two -timestamps is the difference (in seconds) between the local timezone -and UTC. This difference is then added back to the original result. -An example demonstrating this is presented below. - - Finally, there is a "main" program for testing the function. - - BEGIN { - if (_tm_test) { - printf "Enter date as yyyy mm dd hh mm ss: " - getline _tm_test_date - t = mktime(_tm_test_date) - r = strftime("%Y %m %d %H %M %S", t) - printf "Got back (%s)\n", r - } - } - - The entire program uses two variables that can be set on the command -line to control debugging output and to enable the test in the final -`BEGIN' rule. Here is the result of a test run. (Note that debugging -output is to standard error, and test output is to standard output.) - - $ gawk -f mktime.awk -v _tm_test=1 -v _tm_debug=1 - -| Enter date as yyyy mm dd hh mm ss: 1993 5 23 15 35 10 - error--> (1993 5 23 15 35 10) -> (1993 05 23 11 35 10) - error--> diff = 14400 seconds - -| Got back (1993 05 23 15 35 10) - - The time entered was 3:35 p.m. (15:35 on a 24-hour clock), on May -23, 1993. The first line of debugging output shows the resulting time -as UTC--four hours ahead of the local time zone. The second line shows -that the difference is 14400 seconds, which is four hours. (The -difference is only four hours, since daylight savings time is in effect -during May.) The final line of test output shows that the timezone -compensation algorithm works; the returned time is the same as the -entered time. - - This program does not solve the general problem of turning an -arbitrary date representation into a timestamp. That problem is very -involved. However, the `mktime' function provides a foundation upon -which to build. Other software can convert month names into numeric -months, and AM/PM times into 24-hour clocks, to generate the -"canonical" format that `mktime' requires. +component strings.(1) ---------- Footnotes ---------- - (1) July, 2000: Actually, I was mistaken when I wrote this. The -version presented here doesn't always work correctly, and the next -major version of `gawk' will provide `mktime' as a built-in function. - - (2) This is the Epoch on POSIX systems. It may be different on -other systems. + (1) It would be nice if `awk' had an assignment operator for +concatenation. The lack of an explicit operator for concatenation +makes string operations more difficult than they really need to be. -File: gawk.info, Node: Gettimeofday Function, Next: Filetrans Function, Prev: Mktime Function, Up: Library Functions +File: gawk.info, Node: Gettimeofday Function, Prev: Join Function, Up: General Functions Managing the Time of Day -======================== +------------------------ - The `systime' and `strftime' functions described in *Note Functions -for Dealing with Time Stamps: Time Functions, provide the minimum + The `systime' and `strftime' functions described in *Note Using +`gawk''s Timestamp Functions: Time Functions, provide the minimum functionality necessary for dealing with the time of day in human readable form. While `strftime' is extensive, the control formats are not necessarily easy to remember or intuitively obvious when reading a program. The following function, `gettimeofday', populates a user-supplied -array with pre-formatted time information. It returns a string with -the current time formatted in the same way as the `date' utility. +array with preformatted time information. It returns a string with the +current time formatted in the same way as the `date' utility: - # gettimeofday --- get the time of day in a usable format - # Arnold Robbins, arnold@gnu.org, Public Domain, May 1993 - # + # gettimeofday.awk --- get the time of day in a usable format + # Returns a string in the format of output of date(1) # Populates the array argument time with individual values: # time["second"] -- seconds (0 - 59) @@ -10299,17 +12688,17 @@ the current time formatted in the same way as the `date' utility. # time["month"] -- month of year (1 - 12) # time["monthname"] -- name of the month # time["shortmonth"] -- short name of the month - # time["year"] -- year within century (0 - 99) - # time["fullyear"] -- year with century (19xx or 20xx) + # time["year"] -- year modulo 100 (0 - 99) + # time["fullyear"] -- full year # time["weekday"] -- day of week (Sunday = 0) # time["altweekday"] -- day of week (Monday = 0) - # time["weeknum"] -- week number, Sunday first day - # time["altweeknum"] -- week number, Monday first day # time["dayname"] -- name of weekday # time["shortdayname"] -- short name of weekday # time["yearday"] -- day of year (0 - 365) # time["timezone"] -- abbreviation of timezone name # time["ampm"] -- AM or PM designation + # time["weeknum"] -- week number, Sunday first day + # time["altweeknum"] -- week number, Monday first day function gettimeofday(time, ret, now, i) { @@ -10320,8 +12709,7 @@ the current time formatted in the same way as the `date' utility. ret = strftime("%a %b %d %H:%M:%S %Z %Y", now) # clear out target array - for (i in time) - delete time[i] + delete time # fill in values, force numeric values to be # numeric by adding 0 @@ -10350,34 +12738,49 @@ the current time formatted in the same way as the `date' utility. The string indices are easier to use and read than the various formats required by `strftime'. The `alarm' program presented in *Note -An Alarm Clock Program: Alarm Program, uses this function. +An Alarm Clock Program: Alarm Program, uses this function. A more +general design for the `gettimeofday' function would have allowed the +user to supply an optional timestamp value to use instead of the +current time. + + +File: gawk.info, Node: Data File Management, Next: Getopt Function, Prev: General Functions, Up: Library Functions - The `gettimeofday' function is presented above as it was written. A -more general design for this function would have allowed the user to -supply an optional timestamp value that would have been used instead of -the current time. +Data File Management +==================== + + This minor node presents functions that are useful for managing +command-line datafiles. + +* Menu: + +* Filetrans Function:: A function for handling data file transitions. +* Rewind Function:: A function for rereading the current file. +* File Checking:: Checking that data files are readable. +* Ignoring Assigns:: Treating assignments as file names. -File: gawk.info, Node: Filetrans Function, Next: Getopt Function, Prev: Gettimeofday Function, Up: Library Functions +File: gawk.info, Node: Filetrans Function, Next: Rewind Function, Prev: Data File Management, Up: Data File Management Noting Data File Boundaries -=========================== +--------------------------- The `BEGIN' and `END' rules are each executed exactly once, at the -beginning and end respectively of your `awk' program (*note The `BEGIN' -and `END' Special Patterns: BEGIN/END.). We (the `gawk' authors) once -had a user who mistakenly thought that the `BEGIN' rule was executed at -the beginning of each data file and the `END' rule was executed at the -end of each data file. When informed that this was not the case, the -user requested that we add new special patterns to `gawk', named -`BEGIN_FILE' and `END_FILE', that would have the desired behavior. He -even supplied us the code to do so. - - However, after a little thought, I came up with the following +beginning and end of your `awk' program, respectively (*note The +`BEGIN' and `END' Special Patterns: BEGIN/END.). We (the `gawk' +authors) once had a user who mistakenly thought that the `BEGIN' rule +is executed at the beginning of each data file and the `END' rule is +executed at the end of each data file. When informed that this was not +the case, the user requested that we add new special patterns to +`gawk', named `BEGIN_FILE' and `END_FILE', that would have the desired +behavior. He even supplied us the code to do so. + + Adding these special patterns to `gawk' wasn't necessary; the job +can be done cleanly in `awk' itself, as illustrated by the following library program. It arranges to call two user-supplied functions, `beginfile' and `endfile', at the beginning and end of each data file. Besides solving the problem in only nine(!) lines of code, it does so -_portably_; this will work with any implementation of `awk'. +_portably_; this works with any implementation of `awk': # transfile.awk # @@ -10386,9 +12789,6 @@ _portably_; this will work with any implementation of `awk'. # The user must supply functions beginfile() and endfile() # that each take the name of the file being started or # finished, respectively. - # - # Arnold Robbins, arnold@gnu.org, January 1992 - # Public Domain FILENAME != _oldfilename \ { @@ -10401,39 +12801,35 @@ _portably_; this will work with any implementation of `awk'. END { endfile(FILENAME) } This file must be loaded before the user's "main" program, so that -the rule it supplies will be executed first. +the rule it supplies is executed first. This rule relies on `awk''s `FILENAME' variable that automatically changes for each new data file. The current file name is saved in a private variable, `_oldfilename'. If `FILENAME' does not equal -`_oldfilename', then a new data file is being processed, and it is -necessary to call `endfile' for the old file. Since `endfile' should +`_oldfilename', then a new data file is being processed and it is +necessary to call `endfile' for the old file. Because `endfile' should only be called if a file has been processed, the program first checks to make sure that `_oldfilename' is not the null string. The program -then assigns the current file name to `_oldfilename', and calls -`beginfile' for the file. Since, like all `awk' variables, -`_oldfilename' will be initialized to the null string, this rule -executes correctly even for the first data file. +then assigns the current file name to `_oldfilename' and calls +`beginfile' for the file. Because, like all `awk' variables, +`_oldfilename' is initialized to the null string, this rule executes +correctly even for the first data file. - The program also supplies an `END' rule, to do the final processing -for the last file. Since this `END' rule comes before any `END' rules -supplied in the "main" program, `endfile' will be called first. Once -again the value of multiple `BEGIN' and `END' rules should be clear. + The program also supplies an `END' rule to do the final processing +for the last file. Because this `END' rule comes before any `END' rules +supplied in the "main" program, `endfile' is called first. Once again +the value of multiple `BEGIN' and `END' rules should be clear. This version has same problem as the first version of `nextfile' (*note Implementing `nextfile' as a Function: Nextfile Function.). If -the same data file occurs twice in a row on command line, then -`endfile' and `beginfile' will not be executed at the end of the first -pass and at the beginning of the second pass. This version solves the -problem. +the same data file occurs twice in a row on the command line, then +`endfile' and `beginfile' are not executed at the end of the first pass +and at the beginning of the second pass. The following version solves +the problem: # ftrans.awk --- handle data file transitions # # user supplies beginfile() and endfile() functions - # - # Arnold Robbins, arnold@gnu.org, November 1992 - # Public Domain - FNR == 1 { if (_filename_ != "") endfile(_filename_) @@ -10443,41 +12839,156 @@ problem. END { endfile(_filename_) } - In *Note Counting Things: Wc Program, you will see how this library -function can be used, and how it simplifies writing the main program. + *Note Counting Things: Wc Program, shows how this library function +can be used and how it simplifies writing the main program. + + +File: gawk.info, Node: Rewind Function, Next: File Checking, Prev: Filetrans Function, Up: Data File Management + +Rereading the Current File +-------------------------- + + Another request for a new built-in function was for a `rewind' +function that would make it possible to reread the current file. The +requesting user didn't want to have to use `getline' (*note Explicit +Input with `getline': Getline.) inside a loop. + + However, as long as you are not in the `END' rule, it is quite easy +to arrange to immediately close the current input file and then start +over with it from the top. For lack of a better name, we'll call it +`rewind': + + # rewind.awk --- rewind the current file and start over + function rewind( i) + { + # shift remaining arguments up + for (i = ARGC; i > ARGIND; i--) + ARGV[i] = ARGV[i-1] + + # make sure gawk knows to keep going + ARGC++ + + # make current file next to get done + ARGV[ARGIND+1] = FILENAME + + # do it + nextfile + } + + This code relies on the `ARGIND' variable (*note Built-in Variables +That Convey Information: Auto-set.), which is specific to `gawk'. If +you are not using `gawk', you can use ideas presented in *Note Noting +Data File Boundaries: Filetrans Function, to either update `ARGIND' on +your own or modify this code as appropriate. + + The `rewind' function also relies on the `nextfile' keyword (*note +Using `gawk''s `nextfile' Statement: Nextfile Statement.). *Note +Implementing `nextfile' as a Function: Nextfile Function, for a +function version of `nextfile'. + + +File: gawk.info, Node: File Checking, Next: Ignoring Assigns, Prev: Rewind Function, Up: Data File Management + +Checking for Readable Data Files +-------------------------------- + + Normally, if you give `awk' a data file that isn't readable, it +stops with a fatal error. There are times when you might want to just +ignore such files and keep going. You can do this by prepending the +following program to your `awk' program: + + # readable.awk --- library file to skip over unreadable files + BEGIN { + for (i = 1; i < ARGC; i++) { + if (ARGV[i] ~ /^[A-Za-z_][A-Za-z0-9_]*=.*/ \ + || ARGV[i] == "-") + continue # assignment or standard input + else if ((getline junk < ARGV[i]) < 0) # unreadable + delete ARGV[i] + else + close(ARGV[i]) + } + } + + In `gawk', the `getline' won't be fatal (unless `--posix' is in +force). Removing the element from `ARGV' with `delete' skips the file +(since it's no longer in the list). + + +File: gawk.info, Node: Ignoring Assigns, Prev: File Checking, Up: Data File Management + +Treating Assignments as File Names +---------------------------------- + + Occasionally, you might not want `awk' to process command-line +variable assignments (*note Assigning Variables on the Command Line: +Assignment Options.). In particular, if you have file names that +contain an `=' character, `awk' treats the file name as an assignment, +and does not process it. + + Some users have suggested an additional command-line option for +`gawk' to disable command-line assignments. However, some simple +programming with a library file does the trick: + + # noassign.awk --- library file to avoid the need for a + # special option that disables command-line assignments + function disable_assigns(argc, argv, i) + { + for (i = 1; i < argc; i++) + if (argv[i] ~ /^[A-Za-z_][A-Za-z_0-9]*=.*/) + argv[i] = ("./" argv[i]) + } + + BEGIN { + if (No_command_assign) + disable_assigns(ARGC, ARGV) + } + + You then run your program this way: + + awk -v No_command_assign=1 -f noassign.awk -f yourprog.awk * + + The function works by looping through the arguments. It prepends +`./' to any argument that matches the form of a variable assignment, +turning that argument into a file name. + + The use of `No_command_assign' allows you to disable command-line +assignments at invocation time, by giving the variable a true value. +When not set, it is initially zero (i.e., false), so the command-line +arguments are left alone. -File: gawk.info, Node: Getopt Function, Next: Passwd Functions, Prev: Filetrans Function, Up: Library Functions +File: gawk.info, Node: Getopt Function, Next: Passwd Functions, Prev: Data File Management, Up: Library Functions -Processing Command Line Options +Processing Command-Line Options =============================== - Most utilities on POSIX compatible systems take options or -"switches" on the command line that can be used to change the way a -program behaves. `awk' is an example of such a program (*note Command -Line Options: Options.). Often, options take "arguments", data that -the program needs to correctly obey the command line option. For -example, `awk''s `-F' option requires a string to use as the field -separator. The first occurrence on the command line of either `--' or a -string that does not begin with `-' ends the options. - - Most Unix systems provide a C function named `getopt' for processing -command line arguments. The programmer provides a string describing -the one letter options. If an option requires an argument, it is -followed in the string with a colon. `getopt' is also passed the count -and values of the command line arguments, and is called in a loop. -`getopt' processes the command line arguments for option letters. Each + Most utilities on POSIX compatible systems take options, or +"switches," on the command line that can be used to change the way a +program behaves. `awk' is an example of such a program (*note +Command-Line Options: Options.). Often, options take "arguments"; +i.e., data that the program needs to correctly obey the command-line +option. For example, `awk''s `-F' option requires a string to use as +the field separator. The first occurrence on the command line of +either `--' or a string that does not begin with `-' ends the options. + + Modern Unix systems provide a C function named `getopt' for +processing command-line arguments. The programmer provides a string +describing the one-letter options. If an option requires an argument, +it is followed in the string with a colon. `getopt' is also passed the +count and values of the command-line arguments and is called in a loop. +`getopt' processes the command-line arguments for option letters. Each time around the loop, it returns a single character representing the -next option letter that it found, or `?' if it found an invalid option. +next option letter that it finds, or `?' if it finds an invalid option. When it returns -1, there are no options left on the command line. When using `getopt', options that do not take arguments can be grouped together. Furthermore, options that take arguments require -that the argument be present. The argument can immediately follow the -option letter, or it can be a separate command line argument. +that the argument is present. The argument can immediately follow the +option letter or it can be a separate command-line argument. - Given a hypothetical program that takes three command line options, -`-a', `-b', and `-c', and `-b' requires an argument, all of the + Given a hypothetical program that takes three command-line options, +`-a', `-b', and `-c', where `-b' requires an argument, all of the following are valid ways of invoking the program: prog -a -b foo -c data1 data2 data3 @@ -10485,17 +12996,17 @@ following are valid ways of invoking the program: prog -acbfoo data1 data2 data3 Notice that when the argument is grouped with its option, the rest of -the command line argument is considered to be the option's argument. -In the above example, `-acbfoo' indicates that all of the `-a', `-b', -and `-c' options were supplied, and that `foo' is the argument to the -`-b' option. +the argument is considered to be the option's argument. In this +example, `-acbfoo' indicates that all of the `-a', `-b', and `-c' +options were supplied, and that `foo' is the argument to the `-b' +option. `getopt' provides four external variables that the programmer can -use. +use: `optind' The index in the argument value array (`argv') where the first - non-option command line argument can be found. + non-option command-line argument can be found. `optarg' The string value of the argument to an option. @@ -10503,14 +13014,13 @@ use. `opterr' Usually `getopt' prints an error message when it finds an invalid option. Setting `opterr' to zero disables this feature. (An - application might wish to print its own error message.) + application might want to print its own error message.) `optopt' - The letter representing the command line option. While not - usually documented, most versions supply this variable. + The letter representing the command-line option. - The following C fragment shows how `getopt' might process command -line arguments for `awk'. + The following C fragment shows how `getopt' might process +command-line arguments for `awk': int main(int argc, char *argv[]) @@ -10542,52 +13052,45 @@ line arguments for `awk'. } As a side point, `gawk' actually uses the GNU `getopt_long' function -to process both normal and GNU-style long options (*note Command Line +to process both normal and GNU-style long options (*note Command-Line Options: Options.). - The abstraction provided by `getopt' is very useful, and would be -quite handy in `awk' programs as well. Here is an `awk' version of + The abstraction provided by `getopt' is very useful and is quite +handy in `awk' programs as well. Following is an `awk' version of `getopt'. This function highlights one of the greatest weaknesses in `awk', which is that it is very poor at manipulating single characters. Repeated calls to `substr' are necessary for accessing individual -characters (*note Built-in Functions for String Manipulation: String -Functions.). +characters (*note String Manipulation Functions: String Functions.).(1) - The discussion walks through the code a bit at a time. + The discussion that follows walks through the code a bit at a time: - # getopt --- do C library getopt(3) function in awk - # - # arnold@gnu.org - # Public domain - # - # Initial version: March, 1991 - # Revised: May, 1993 - + # getopt.awk --- do C library getopt(3) function in awk # External variables: - # Optind -- index of ARGV for first non-option argument + # Optind -- index in ARGV of first non-option argument # Optarg -- string value of argument to current option - # Opterr -- if non-zero, print our own diagnostic + # Opterr -- if nonzero, print our own diagnostic # Optopt -- current option letter - # Returns + # Returns: # -1 at end of options # ? for unrecognized option # <c> a character representing the current option - # Private Data - # _opti index in multi-flag option, e.g., -abc + # Private Data: + # _opti -- index in multi-flag option, e.g., -abc + + The function starts out with a list of the global variables it uses, +what the return values are, what they mean, and any global variables +that are "private" to this library function. Such documentation is +essential for any program, and particularly for library functions. - The function starts out with some documentation: who wrote the code, -and when it was revised, followed by a list of the global variables it -uses, what the return values are and what they mean, and any global -variables that are "private" to this library function. Such -documentation is essential for any program, and particularly for -library functions. + The `getopt' function first checks that it was indeed called with a +string of options (the `options' parameter). If `options' has a zero +length, `getopt' immediately returns -1: - function getopt(argc, argv, options, optl, thisopt, i) + function getopt(argc, argv, options, thisopt, i) { - optl = length(options) - if (optl == 0) # no options given + if (length(options) == 0) # no options given return -1 if (argv[Optind] == "--") { # all done @@ -10599,21 +13102,17 @@ library functions. return -1 } - The function first checks that it was indeed called with a string of -options (the `options' parameter). If `options' has a zero length, -`getopt' immediately returns -1. - The next thing to check for is the end of the options. A `--' ends -the command line options, as does any command line argument that does +the command-line options, as does any command-line argument that does not begin with a `-'. `Optind' is used to step through the array of -command line arguments; it retains its value across calls to `getopt', -since it is a global variable. +command-line arguments; it retains its value across calls to `getopt', +because it is a global variable. - The regexp used, `/^-[^: \t\n\f\r\v\b]/', is perhaps a bit of -overkill; it checks for a `-' followed by anything that is not -whitespace and not a colon. If the current command line argument does -not match this pattern, it is not an option, and it ends option -processing. + The regular expression that is used, `/^-[^: \t\n\f\r\v\b]/', is +perhaps a bit of overkill; it checks for a `-' followed by anything +that is not whitespace and not a colon. If the current command-line +argument does not match this pattern, it is not an option, and it ends +option processing. if (_opti == 0) _opti = 2 @@ -10632,31 +13131,31 @@ processing. return "?" } - The `_opti' variable tracks the position in the current command line -argument (`argv[Optind]'). In the case that multiple options were -grouped together with one `-' (e.g., `-abx'), it is necessary to return -them to the user one at a time. + The `_opti' variable tracks the position in the current command-line +argument (`argv[Optind]'). If multiple options are grouped together +with one `-' (e.g., `-abx'), it is necessary to return them to the user +one at a time. - If `_opti' is equal to zero, it is set to two, the index in the -string of the next character to look at (we skip the `-', which is at -position one). The variable `thisopt' holds the character, obtained + If `_opti' is equal to zero, it is set to two, which is the index in +the string of the next character to look at (we skip the `-', which is +at position one). The variable `thisopt' holds the character, obtained with `substr'. It is saved in `Optopt' for the main program to use. If `thisopt' is not in the `options' string, then it is an invalid -option. If `Opterr' is non-zero, `getopt' prints an error message on +option. If `Opterr' is nonzero, `getopt' prints an error message on the standard error that is similar to the message from the C version of `getopt'. - Since the option is invalid, it is necessary to skip it and move on -to the next option character. If `_opti' is greater than or equal to -the length of the current command line argument, then it is necessary -to move on to the next one, so `Optind' is incremented and `_opti' is + Because the option is invalid, it is necessary to skip it and move +on to the next option character. If `_opti' is greater than or equal +to the length of the current command-line argument, it is necessary to +move on to the next argument, so `Optind' is incremented and `_opti' is reset to zero. Otherwise, `Optind' is left alone and `_opti' is merely incremented. - In any case, since the option was invalid, `getopt' returns `?'. + In any case, because the option is invalid, `getopt' returns `?'. The main program can examine `Optopt' if it needs to know what the -invalid option letter actually was. +invalid option letter actually is. Continuing on: if (substr(options, i + 1, 1) == ":") { # get option argument @@ -10670,11 +13169,11 @@ invalid option letter actually was. If the option requires an argument, the option letter is followed by a colon in the `options' string. If there are remaining characters in -the current command line argument (`argv[Optind]'), then the rest of -that string is assigned to `Optarg'. Otherwise, the next command line +the current command-line argument (`argv[Optind]'), then the rest of +that string is assigned to `Optarg'. Otherwise, the next command-line argument is used (`-xFOO' vs. `-x FOO'). In either case, `_opti' is -reset to zero, since there are no more characters left to examine in -the current command line argument. +reset to zero, because there are no more characters left to examine in +the current command-line argument. Continuing: if (_opti == 0 || _opti >= length(argv[Optind])) { Optind++ @@ -10685,12 +13184,18 @@ the current command line argument. } Finally, if `_opti' is either zero or greater than the length of the -current command line argument, it means this element in `argv' is +current command-line argument, it means this element in `argv' is through being processed, so `Optind' is incremented to point to the next element in `argv'. If neither condition is true, then only `_opti' is incremented, so that the next option letter can be processed on the next call to `getopt'. + The `BEGIN' rule initializes both `Opterr' and `Optind' to one. +`Opterr' is set to one, since the default behavior is for `getopt' to +print a diagnostic message upon seeing an invalid option. `Optind' is +set to one, since there's no reason to look at the program name, which +is in `ARGV[0]': + BEGIN { Opterr = 1 # default is to diagnose Optind = 1 # skip ARGV[0] @@ -10707,14 +13212,8 @@ on the next call to `getopt'. } } - The `BEGIN' rule initializes both `Opterr' and `Optind' to one. -`Opterr' is set to one, since the default behavior is for `getopt' to -print a diagnostic message upon seeing an invalid option. `Optind' is -set to one, since there's no reason to look at the program name, which -is in `ARGV[0]'. - The rest of the `BEGIN' rule is a simple test program. Here is the -result of two sample runs of the test program. +result of two sample runs of the test program: $ awk -f getopt.awk -v _getopt_test=1 -- -a -cbARG bax -x -| c = <a>, optarg = <> @@ -10732,61 +13231,56 @@ result of two sample runs of the test program. -| ARGV[4] = <xyz> -| ARGV[5] = <abc> - The first `--' terminates the arguments to `awk', so that it does -not try to interpret the `-a' etc. as its own options. - - Several of the sample programs presented in *Note Practical `awk' + In both runs, the first `--' terminates the arguments to `awk', so +that it does not try to interpret the `-a', etc., as its own options. +Several of the sample programs presented in *Note Practical `awk' Programs: Sample Programs, use `getopt' to process their arguments. + ---------- Footnotes ---------- + + (1) This function was written before `gawk' acquired the ability to +split strings into single characters using `""' as the separator. We +have left it alone, since using `substr' is more portable. + File: gawk.info, Node: Passwd Functions, Next: Group Functions, Prev: Getopt Function, Up: Library Functions Reading the User Database ========================= - The `/dev/user' special file (*note Special File Names in `gawk': -Special Files.) provides access to the current user's real and -effective user and group id numbers, and if available, the user's -supplementary group set. However, since these are numbers, they do not -provide very useful information to the average user. There needs to be -some way to find the user information associated with the user and -group numbers. This section presents a suite of functions for -retrieving information from the user database. *Note Reading the Group -Database: Group Functions, for a similar suite that retrieves -information from the group database. + The `PROCINFO' array (*note Built-in Variables::) provides access to +the current user's real and effective user and group id numbers, and if +available, the user's supplementary group set. However, because these +are numbers, they do not provide very useful information to the average +user. There needs to be some way to find the user information +associated with the user and group numbers. This minor node presents a +suite of functions for retrieving information from the user database. +*Note Reading the Group Database: Group Functions, for a similar suite +that retrieves information from the group database. The POSIX standard does not define the file where user information is kept. Instead, it provides the `<pwd.h>' header file and several C language subroutines for obtaining user information. The primary function is `getpwent', for "get password entry." The "password" comes -from the original user database file, `/etc/passwd', which kept user +from the original user database file, `/etc/passwd', which stores user information, along with the encrypted passwords (hence the name). - While an `awk' program could simply read `/etc/passwd' directly (the -format is well known), because of the way password files are handled on -networked systems, this file may not contain complete information about -the system's set of users. - - To be sure of being able to produce a readable, complete version of -the user database, it is necessary to write a small C program that -calls `getpwent'. `getpwent' is defined to return a pointer to a -`struct passwd'. Each time it is called, it returns the next entry in -the database. When there are no more entries, it returns `NULL', the -null pointer. When this happens, the C program should call `endpwent' -to close the database. Here is `pwcat', a C program that "cats" the -password database. + While an `awk' program could simply read `/etc/passwd' directly, +this file may not contain complete information about the system's set +of users.(1) To be sure you are able to produce a readable and complete +version of the user database, it is necessary to write a small C +program that calls `getpwent'. `getpwent' is defined as returning a +pointer to a `struct passwd'. Each time it is called, it returns the +next entry in the database. When there are no more entries, it returns +`NULL', the null pointer. When this happens, the C program should call +`endpwent' to close the database. Following is `pwcat', a C program +that "cats" the password database. /* * pwcat.c * * Generate a printable version of the password database - * - * Arnold Robbins - * arnold@gnu.org - * May 1993 - * Public Domain */ - #include <stdio.h> #include <pwd.h> @@ -10810,32 +13304,19 @@ password database. `pwcat' is the user database, in the traditional `/etc/passwd' format of colon-separated fields. The fields are: -Login name - The user's login name. - -Encrypted password - The user's encrypted password. This may not be available on some - systems. - -User-ID - The user's numeric user-id number. - -Group-ID - The user's numeric group-id number. - -Full name - The user's full name, and perhaps other information associated - with the user. - -Home directory - The user's login, or "home" directory (familiar to shell - programmers as `$HOME'). - -Login shell - The program that will be run when the user logs in. This is - usually a shell, such as Bash (the Gnu Bourne-Again shell). +Login name The user's login name. +Encrypted password The user's encrypted password. This may not be + available on some systems. +User-ID The user's numeric user-id number. +Group-ID The user's numeric group-id number. +Full name The user's full name, and perhaps other + information associated with the user. +Home directory The user's login (or "home") directory + (familiar to shell programmers as `$HOME'). +Login shell The program that is run when the user logs in. + This is usually a shell, such as `bash'. - Here are a few lines representative of `pwcat''s output. + A few lines representative of `pwcat''s output are as follows: $ pwcat -| root:3Ov02d5VaUPB6:0:1:Operator:/:/bin/sh @@ -10848,28 +13329,28 @@ Login shell -| andy:abcca2:113:10:Andy Jacobs:/home/andy:/bin/sh ... - With that introduction, here is a group of functions for getting user -information. There are several functions here, corresponding to the C -functions of the same name. + With that introduction, following is a group of functions for +getting user information. There are several functions here, +corresponding to the C functions of the same names: # passwd.awk --- access password file information - # Arnold Robbins, arnold@gnu.org, Public Domain - # May 1993 - BEGIN { # tailor this to suit your system _pw_awklib = "/usr/local/libexec/awk/" } - function _pw_init( oldfs, oldrs, olddol0, pwcat) + function _pw_init( oldfs, oldrs, olddol0, pwcat, using_fw) { if (_pw_inited) return + oldfs = FS oldrs = RS olddol0 = $0 + using_fw = (PROCINFO["FS"] == "FIELDWIDTHS") FS = ":" RS = "\n" + pwcat = _pw_awklib "pwcat" while ((pwcat | getline) > 0) { _pw_byname[$1] = $0 @@ -10880,34 +13361,46 @@ functions of the same name. _pw_count = 0 _pw_inited = 1 FS = oldfs + if (using_fw) + FIELDWIDTHS = FIELDWIDTHS RS = oldrs $0 = olddol0 } The `BEGIN' rule sets a private variable to the directory where -`pwcat' is stored. Since it is used to help out an `awk' library -routine, we have chosen to put it in `/usr/local/libexec/awk'. You -might want it to be in a different directory on your system. +`pwcat' is stored. Because it is used to help out an `awk' library +routine, we have chosen to put it in `/usr/local/libexec/awk'; however, +you might want it to be in a different directory on your system. The function `_pw_init' keeps three copies of the user information -in three associative arrays. The arrays are indexed by user name +in three associative arrays. The arrays are indexed by username (`_pw_byname'), by user-id number (`_pw_byuid'), and by order of -occurrence (`_pw_bycount'). - - The variable `_pw_inited' is used for efficiency; `_pw_init' only -needs to be called once. - - Since this function uses `getline' to read information from `pwcat', -it first saves the values of `FS', `RS', and `$0'. Doing so is -necessary, since these functions could be called from anywhere within a -user's program, and the user may have his or her own values for `FS' -and `RS'. +occurrence (`_pw_bycount'). The variable `_pw_inited' is used for +efficiency; `_pw_init' needs only to be called once. + + Because this function uses `getline' to read information from +`pwcat', it first saves the values of `FS', `RS', and `$0'. It notes +in the variable `using_fw' whether field splitting with `FIELDWIDTHS' +is in effect or not. Doing so is necessary, since these functions +could be called from anywhere within a user's program, and the user may +have his or her own way of splitting records and fields. + + The `using_fw' variable checks `PROCINFO["FS"]', which is +`"FIELDWIDTHS"' if field splitting is being done with `FIELDWIDTHS'. +This makes it possible to restore the correct field-splitting mechanism +later. The test can only be true for `gawk'. It is false if using +`FS' or on some other `awk' implementation. The main part of the function uses a loop to read database lines, split the line into fields, and then store the line into each array as necessary. When the loop is done, `_pw_init' cleans up by closing the -pipeline, setting `_pw_inited' to one, and restoring `FS', `RS', and -`$0'. The use of `_pw_count' will be explained below. +pipeline, setting `_pw_inited' to one, and restoring `FS' (and +`FIELDWIDTHS' if necessary), `RS', and `$0'. The use of `_pw_count' is +explained shortly. + + The `getpwnam' function takes a username as a string argument. If +that user is in the database, it returns the appropriate line. +Otherwise it returns the null string: function getpwnam(name) { @@ -10917,9 +13410,9 @@ pipeline, setting `_pw_inited' to one, and restoring `FS', `RS', and return "" } - The `getpwnam' function takes a user name as a string argument. If -that user is in the database, it returns the appropriate line. -Otherwise it returns the null string. + Similarly, the `getpwuid' function takes a user-id number argument. +If that user number is in the database, it returns the appropriate +line. Otherwise it returns the null string: function getpwuid(uid) { @@ -10929,9 +13422,9 @@ Otherwise it returns the null string. return "" } - Similarly, the `getpwuid' function takes a user-id number argument. -If that user number is in the database, it returns the appropriate -line. Otherwise it returns the null string. + The `getpwent' function simply steps through the database, one entry +at a time. It uses `_pw_count' to track its current position in the +`_pw_bycount' array: function getpwent() { @@ -10941,67 +13434,62 @@ line. Otherwise it returns the null string. return "" } - The `getpwent' function simply steps through the database, one entry -at a time. It uses `_pw_count' to track its current position in the -`_pw_bycount' array. + The `endpwent' function resets `_pw_count' to zero, so that +subsequent calls to `getpwent' start over again: function endpwent() { _pw_count = 0 } - The `endpwent' function resets `_pw_count' to zero, so that -subsequent calls to `getpwent' will start over again. - A conscious design decision in this suite is that each subroutine calls `_pw_init' to initialize the database arrays. The overhead of running a separate process to generate the user database, and the I/O -to scan it, will only be incurred if the user's main program actually -calls one of these functions. If this library file is loaded along -with a user's program, but none of the routines are ever called, then -there is no extra run-time overhead. (The alternative would be to move -the body of `_pw_init' into a `BEGIN' rule, which would always run -`pwcat'. This simplifies the code but runs an extra process that may -never be needed.) - - In turn, calling `_pw_init' is not too expensive, since the +to scan it, are only incurred if the user's main program actually calls +one of these functions. If this library file is loaded along with a +user's program, but none of the routines are ever called, then there is +no extra runtime overhead. (The alternative is move the body of +`_pw_init' into a `BEGIN' rule, which always runs `pwcat'. This +simplifies the code but runs an extra process that may never be needed.) + + In turn, calling `_pw_init' is not too expensive, because the `_pw_inited' variable keeps the program from reading the data more than once. If you are worried about squeezing every last cycle out of your `awk' program, the check of `_pw_inited' could be moved out of `_pw_init' and duplicated in all the other functions. In practice, -this is not necessary, since most `awk' programs are I/O bound, and it -would clutter up the code. +this is not necessary, since most `awk' programs are I/O-bound, and it +clutters up the code. - The `id' program in *Note Printing Out User Information: Id Program, + The `id' program in *Note Printing out User Information: Id Program, uses these functions. + ---------- Footnotes ---------- + + (1) It is often the case that password information is stored in a +network database. + -File: gawk.info, Node: Group Functions, Next: Library Names, Prev: Passwd Functions, Up: Library Functions +File: gawk.info, Node: Group Functions, Prev: Passwd Functions, Up: Library Functions Reading the Group Database ========================== Much of the discussion presented in *Note Reading the User Database: Passwd Functions, applies to the group database as well. Although -there has traditionally been a well known file, `/etc/group', in a well -known format, the POSIX standard only provides a set of C library +there has traditionally been a well-known file (`/etc/group') in a +well-known format, the POSIX standard only provides a set of C library routines (`<grp.h>' and `getgrent') for accessing the information. Even though this file may exist, it likely does not have complete information. Therefore, as with the user database, it is necessary to have a small C program that generates the group database as its output. - Here is `grcat', a C program that "cats" the group database. + `grcat', a C program that "cats" the group database, is as follows: /* * grcat.c * * Generate a printable version of the group database - * - * Arnold Robbins, arnold@gnu.org - * May 1993 - * Public Domain */ - #include <stdio.h> #include <grp.h> @@ -11027,27 +13515,23 @@ have a small C program that generates the group database as its output. exit(0); } - Each line in the group database represent one group. The fields are -separated with colons, and represent the following information. - -Group Name - The name of the group. - -Group Password - The encrypted group password. In practice, this field is never - used. It is usually empty, or set to `*'. - -Group ID Number - The numeric group-id number. This number should be unique within - the file. - -Group Member List - A comma-separated list of user names. These users are members of - the group. Most Unix systems allow users to be members of several - groups simultaneously. If your system does, then reading - `/dev/user' will return those group-id numbers in `$5' through - `$NF'. (Note that `/dev/user' is a `gawk' extension; *note - Special File Names in `gawk': Special Files..) + Each line in the group database represents one group. The fields are +separated with colons and represent the following information: + +Group name The group's name. +Group password The group's encrypted password. In practice, + this field is never used; it is usually empty + or set to `*'. +Group-ID The group's numeric group-id number; this + number should be unique within the file. +Group member list A comma-separated list of usernames. These + users are members of the group. Modern Unix + systems allow users to be members of several + groups simultaneously. If your system does, + then there are elements `"group1"' through + `"groupN"' in `PROCINFO' for those group-id + numbers. (Note that `PROCINFO' is a `gawk' + extension; *note Built-in Variables::.) Here is what running `grcat' might produce: @@ -11062,19 +13546,17 @@ Group Member List Here are the functions for obtaining information from the group database. There are several, modeled after the C library functions of -the same names. +the same names: # group.awk --- functions for dealing with the group file - # Arnold Robbins, arnold@gnu.org, Public Domain - # May 1993 - BEGIN \ { # Change to suit your system _gr_awklib = "/usr/local/libexec/awk/" } - function _gr_init( oldfs, oldrs, olddol0, grcat, n, a, i) + function _gr_init( oldfs, oldrs, olddol0, grcat, + using_fw, n, a, i) { if (_gr_inited) return @@ -11082,6 +13564,7 @@ the same names. oldfs = FS oldrs = RS olddol0 = $0 + using_fw = (PROCINFO["FS"] == "FIELDWIDTHS") FS = ":" RS = "\n" @@ -11110,45 +13593,52 @@ the same names. _gr_count = 0 _gr_inited++ FS = oldfs + if (using_fw) + FIELDWIDTHS = FIELDWIDTHS RS = oldrs $0 = olddol0 } The `BEGIN' rule sets a private variable to the directory where -`grcat' is stored. Since it is used to help out an `awk' library +`grcat' is stored. Because it is used to help out an `awk' library routine, we have chosen to put it in `/usr/local/libexec/awk'. You might want it to be in a different directory on your system. These routines follow the same general outline as the user database routines (*note Reading the User Database: Passwd Functions.). The `_gr_inited' variable is used to ensure that the database is scanned no -more than once. The `_gr_init' function first saves `FS', `RS', and -`$0', and then sets `FS' and `RS' to the correct values for scanning -the group information. +more than once. The `_gr_init' function first saves `FS', +`FIELDWIDTHS', `RS', and `$0', and then sets `FS' and `RS' to the +correct values for scanning the group information. The group information is stored is several associative arrays. The arrays are indexed by group name (`_gr_byname'), by group-id number (`_gr_bygid'), and by position in the database (`_gr_bycount'). There -is an additional array indexed by user name (`_gr_groupsbyuser'), that -is a space separated list of groups that each user belongs to. +is an additional array indexed by username (`_gr_groupsbyuser'), which +is a space-separated list of groups that each user belongs to. Unlike the user database, it is possible to have multiple records in the database for the same group. This is common when a group has a -large number of members. Such a pair of entries might look like: +large number of members. A pair of such entries might look like the +following: - tvpeople:*:101:johny,jay,arsenio + tvpeople:*:101:johnny,jay,arsenio tvpeople:*:101:david,conan,tom,joan For this reason, `_gr_init' looks to see if a group name or group-id -number has already been seen. If it has, then the user names are -simply concatenated onto the previous list of users. (There is -actually a subtle problem with the code presented above. Suppose that -the first time there were no names. This code adds the names with a -leading comma. It also doesn't check that there is a `$4'.) +number is already seen. If it is, then the usernames are simply +concatenated onto the previous list of users. (There is actually a +subtle problem with the code just presented. Suppose that the first +time there were no names. This code adds the names with a leading +comma. It also doesn't check that there is a `$4'.) - Finally, `_gr_init' closes the pipeline to `grcat', restores `FS', -`RS', and `$0', initializes `_gr_count' to zero (it is used later), and -makes `_gr_inited' non-zero. + Finally, `_gr_init' closes the pipeline to `grcat', restores `FS' +(and `FIELDWIDTHS' if necessary), `RS', and `$0', initializes +`_gr_count' to zero (it is used later), and makes `_gr_inited' nonzero. + + The `getgrnam' function takes a group name as its argument, and if +that group exists, it is returned. Otherwise, `getgrnam' returns the +null string: function getgrnam(group) { @@ -11158,9 +13648,8 @@ makes `_gr_inited' non-zero. return "" } - The `getgrnam' function takes a group name as its argument, and if -that group exists, it is returned. Otherwise, `getgrnam' returns the -null string. + The `getgrgid' function is similar, it takes a numeric group-id and +looks up the information associated with that group-id: function getgrgid(gid) { @@ -11170,8 +13659,8 @@ null string. return "" } - The `getgrgid' function is similar, it takes a numeric group-id, and -looks up the information associated with that group-id. + The `getgruser' function does not have a C counterpart. It takes a +username and returns the list of groups that have the user as a member: function getgruser(user) { @@ -11181,9 +13670,8 @@ looks up the information associated with that group-id. return "" } - The `getgruser' function does not have a C counterpart. It takes a -user name, and returns the list of groups that have the user as a -member. + The `getgrent' function steps through the database one entry at a +time. It uses `_gr_count' to track its position in the list: function getgrent() { @@ -11193,17 +13681,14 @@ member. return "" } - The `getgrent' function steps through the database one entry at a -time. It uses `_gr_count' to track its position in the list. + The `endgrent' function resets `_gr_count' to zero so that +`getgrent' can start over again: function endgrent() { _gr_count = 0 } - `endgrent' resets `_gr_count' to zero so that `getgrent' can start -over again. - As with the user database routines, each function calls `_gr_init' to initialize the arrays. Doing so only incurs the extra overhead of running `grcat' if these functions are used (as opposed to moving the @@ -11213,117 +13698,63 @@ body of `_gr_init' into a `BEGIN' rule). associative arrays. The functions that the user calls are themselves very simple, relying on `awk''s associative arrays to do work. - The `id' program in *Note Printing Out User Information: Id Program, + The `id' program in *Note Printing out User Information: Id Program, uses these functions. -File: gawk.info, Node: Library Names, Prev: Group Functions, Up: Library Functions - -Naming Library Function Global Variables -======================================== - - Due to the way the `awk' language evolved, variables are either -"global" (usable by the entire program), or "local" (usable just by a -specific function). There is no intermediate state analogous to -`static' variables in C. - - Library functions often need to have global variables that they can -use to preserve state information between calls to the function. For -example, `getopt''s variable `_opti' (*note Processing Command Line -Options: Getopt Function.), and the `_tm_months' array used by `mktime' -(*note Turning Dates Into Timestamps: Mktime Function.). Such -variables are called "private", since the only functions that need to -use them are the ones in the library. +File: gawk.info, Node: Sample Programs, Next: Language History, Prev: Library Functions, Up: Top - When writing a library function, you should try to choose names for -your private variables so that they will not conflict with any -variables used by either another library function or a user's main -program. For example, a name like `i' or `j' is not a good choice, -since user programs often use variable names like these for their own -purposes. +Practical `awk' Programs +************************ - The example programs shown in this chapter all start the names of -their private variables with an underscore (`_'). Users generally -don't use leading underscores in their variable names, so this -convention immediately decreases the chances that the variable name -will be accidentally shared with the user's program. + *Note A Library of `awk' Functions: Library Functions, presents the +idea that reading programs in a language contributes to learning that +language. This major node continues that theme, presenting a potpourri +of `awk' programs for your reading enjoyment. - In addition, several of the library functions use a prefix that helps -indicate what function or set of functions uses the variables. For -example, `_tm_months' in `mktime' (*note Turning Dates Into Timestamps: -Mktime Function.), and `_pw_byname' in the user data base routines -(*note Reading the User Database: Passwd Functions.). This convention -is recommended, since it even further decreases the chance of -inadvertent conflict among variable names. Note that this convention -can be used equally well both for variable names and for private -function names too. - - While I could have re-written all the library routines to use this -convention, I did not do so, in order to show how my own `awk' -programming style has evolved, and to provide some basis for this -discussion. + Many of these programs use the library functions presented in *Note +A Library of `awk' Functions: Library Functions. - As a final note on variable naming, if a function makes global -variables available for use by a main program, it is a good convention -to start that variable's name with a capital letter. For example, -`getopt''s `Opterr' and `Optind' variables (*note Processing Command -Line Options: Getopt Function.). The leading capital letter indicates -that it is global, while the fact that the variable name is not all -capital letters indicates that the variable is not one of `awk''s -built-in variables, like `FS'. +* Menu: - It is also important that _all_ variables in library functions that -do not need to save state are in fact declared local. If this is not -done, the variable could accidentally be used in the user's program, -leading to bugs that are very difficult to track down. +* Running Examples:: How to run these examples. +* Clones:: Clones of common utilities. +* Miscellaneous Programs:: Some interesting `awk' programs. - function lib_func(x, y, l1, l2) - { - ... - USE VARIABLE some_var # some_var could be local - ... # but is not by oversight - } + +File: gawk.info, Node: Running Examples, Next: Clones, Prev: Sample Programs, Up: Sample Programs - A different convention, common in the Tcl community, is to use a -single associative array to hold the values needed by the library -function(s), or "package." This significantly decreases the number of -actual global names in use. For example, the functions described in -*Note Reading the User Database: Passwd Functions, might have used -`PW_data["inited"]', `PW_data["total"]', `PW_data["count"]' and -`PW_data["awklib"]', instead of `_pw_inited', `_pw_awklib', `_pw_total', -and `_pw_count'. +Running the Example Programs +============================ - The conventions presented in this section are exactly that, -conventions. You are not required to write your programs this way, we -merely recommend that you do so. + To run a given program, you would typically do something like this: - -File: gawk.info, Node: Sample Programs, Next: Language History, Prev: Library Functions, Up: Top + awk -f PROGRAM -- OPTIONS FILES -Practical `awk' Programs -************************ +Here, PROGRAM is the name of the `awk' program (such as `cut.awk'), +OPTIONS are any command-line options for the program that start with a +`-', and FILES are the actual data files. - This chapter presents a potpourri of `awk' programs for your reading -enjoyment. + If your system supports the `#!' executable interpreter mechanism +(*note Executable `awk' Programs: Executable Scripts.), you can instead +run your program directly: - Many of these programs use the library functions presented in *Note -A Library of `awk' Functions: Library Functions. + cut.awk -c1-8 myfiles > results -* Menu: + If your `awk' is not `gawk', you may instead need to use this: -* Clones:: Clones of common utilities. -* Miscellaneous Programs:: Some interesting `awk' programs. + cut.awk -- -c1-8 myfiles > results -File: gawk.info, Node: Clones, Next: Miscellaneous Programs, Prev: Sample Programs, Up: Sample Programs +File: gawk.info, Node: Clones, Next: Miscellaneous Programs, Prev: Running Examples, Up: Sample Programs -Re-inventing Wheels for Fun and Profit -====================================== +Reinventing Wheels for Fun and Profit +===================================== - This section presents a number of POSIX utilities that are -implemented in `awk'. Re-inventing these programs in `awk' is often -enjoyable, since the algorithms can be very clearly expressed, and -usually the code is very concise and simple. This is true because + This minor node presents a number of POSIX utilities that are +implemented in `awk'. Reinventing these programs in `awk' is often +enjoyable, because the algorithms can be very clearly expressed, and +the code is usually very concise and simple. This is true because `awk' does so much for you. It should be noted that these programs are not necessarily intended @@ -11335,30 +13766,29 @@ tasks. * Menu: -* Cut Program:: The `cut' utility. -* Egrep Program:: The `egrep' utility. -* Id Program:: The `id' utility. -* Split Program:: The `split' utility. -* Tee Program:: The `tee' utility. -* Uniq Program:: The `uniq' utility. -* Wc Program:: The `wc' utility. +* Cut Program:: The `cut' utility. +* Egrep Program:: The `egrep' utility. +* Id Program:: The `id' utility. +* Split Program:: The `split' utility. +* Tee Program:: The `tee' utility. +* Uniq Program:: The `uniq' utility. +* Wc Program:: The `wc' utility. File: gawk.info, Node: Cut Program, Next: Egrep Program, Prev: Clones, Up: Clones -Cutting Out Fields and Columns +Cutting out Fields and Columns ------------------------------ - The `cut' utility selects, or "cuts," either characters or fields -from its standard input and sends them to its standard output. `cut' -can cut out either a list of characters, or a list of fields. By -default, fields are separated by tabs, but you may supply a command -line option to change the field "delimiter", i.e. the field separator -character. `cut''s definition of fields is less general than `awk''s. + The `cut' utility selects, or "cuts," characters or fields from its +standard input and sends them to its standard output. Fields are +separated by tabs by default, but you may supply a command-line option +to change the field "delimiter" (i.e., the field separator character). +`cut''s definition of fields is less general than `awk''s. A common use of `cut' might be to pull out just the login name of logged-on users from the output of `who'. For example, the following -pipeline generates a sorted, unique list of the logged on users: +pipeline generates a sorted, unique list of the logged-on users: who | cut -c1-8 | sort | uniq @@ -11368,7 +13798,7 @@ pipeline generates a sorted, unique list of the logged on users: Use LIST as the list of characters to cut out. Items within the list may be separated by commas, and ranges of characters can be separated with dashes. The list `1-8,15,22-35' specifies - characters one through eight, 15, and 22 through 35. + characters 1 through 8, 15, and 22 through 35. `-f LIST' Use LIST as the list of fields to cut out. @@ -11381,24 +13811,23 @@ pipeline generates a sorted, unique list of the logged on users: Suppress printing of lines that do not contain the field delimiter. The `awk' implementation of `cut' uses the `getopt' library function -(*note Processing Command Line Options: Getopt Function.), and the -`join' library function (*note Merging an Array Into a String: Join +(*note Processing Command-Line Options: Getopt Function.) and the +`join' library function (*note Merging an Array into a String: Join Function.). - The program begins with a comment describing the options and a -`usage' function which prints out a usage message and exits. `usage' -is called if invalid arguments are supplied. + The program begins with a comment describing the options, the library +functions needed, and a `usage' function that prints out a usage +message and exits. `usage' is called if invalid arguments are supplied: # cut.awk --- implement cut in awk - # Arnold Robbins, arnold@gnu.org, Public Domain - # May 1993 - # Options: - # -f list Cut fields - # -d c Field delimiter character - # -c list Cut characters + # -f list Cut fields + # -d c Field delimiter character + # -c list Cut characters # - # -s Suppress lines without the delimiter character + # -s Suppress lines without the delimiter + # + # Requires getopt and join library functions function usage( e1, e2) { @@ -11412,13 +13841,13 @@ is called if invalid arguments are supplied. The variables `e1' and `e2' are used so that the function fits nicely on the screen. - Next comes a `BEGIN' rule that parses the command line options. It -sets `FS' to a single tab character, since that is `cut''s default + Next comes a `BEGIN' rule that parses the command-line options. It +sets `FS' to a single tab character, because that is `cut''s default field separator. The output field separator is also set to be the same as the input field separator. Then `getopt' is used to step through -the command line options. One or the other of the variables +the command-line options. One or the other of the variables `by_fields' or `by_chars' is set to true, to indicate that processing -should be done by fields or by characters respectively. When cutting +should be done by fields or by characters, respectively. When cutting by characters, the output field separator is set to the null string. BEGIN \ @@ -11452,19 +13881,19 @@ by characters, the output field separator is set to the null string. for (i = 1; i < Optind; i++) ARGV[i] = "" - Special care is taken when the field delimiter is a space. Using -`" "' (a single space) for the value of `FS' is incorrect--`awk' would -separate fields with runs of spaces, tabs and/or newlines, and we want + Special care is taken when the field delimiter is a space. Using a +single space (`" "') for the value of `FS' is incorrect--`awk' would +separate fields with runs of spaces, tabs, and/or newlines, and we want them to be separated with individual spaces. Also, note that after `getopt' is through, we have to clear out all the elements of `ARGV' -from one to `Optind', so that `awk' will not try to process the command -line options as file names. +from 1 to `Optind', so that `awk' does not try to process the +command-line options as file names. - After dealing with the command line options, the program verifies + After dealing with the command-line options, the program verifies that the options make sense. Only one or the other of `-c' and `-f' -should be used, and both require a field list. Then either -`set_fieldlist' or `set_charlist' is called to pull apart the list of -fields or characters. +should be used, and both require a field list. Then the program calls +either `set_fieldlist' or `set_charlist' to pull apart the list of +fields or characters: if (by_fields && by_chars) usage() @@ -11483,14 +13912,13 @@ fields or characters. set_charlist() } - Here is `set_fieldlist'. It first splits the field list apart at -the commas, into an array. Then, for each element of the array, it -looks to see if it is actually a range, and if so splits it apart. The -range is verified to make sure the first number is smaller than the -second. Each number in the list is added to the `flist' array, which -simply lists the fields that will be printed. Normal field splitting -is used. The program lets `awk' handle the job of doing the field -splitting. + `set_fieldlist' is used to split the field list apart at the commas, +and into an array. Then, for each element of the array, it looks to +see if it is actually a range, and if so, splits it apart. The range is +verified to make sure the first number is smaller than the second. +Each number in the list is added to the `flist' array, which simply +lists the fields that will be printed. Normal field splitting is used. +The program lets `awk' handle the job of doing the field splitting: function set_fieldlist( n, m, i, j, k, f, g) { @@ -11514,20 +13942,19 @@ splitting. The `set_charlist' function is more complicated than `set_fieldlist'. The idea here is to use `gawk''s `FIELDWIDTHS' variable (*note Reading -Fixed-width Data: Constant Size.), which describes constant width +Fixed-Width Data: Constant Size.), which describes constant width input. When using a character list, that is exactly what we have. Setting up `FIELDWIDTHS' is more complicated than simply listing the fields that need to be printed. We have to keep track of the fields to -be printed, and also the intervening characters that have to be skipped. -For example, suppose you wanted characters one through eight, 15, and -22 through 35. You would use `-c 1-8,15,22-35'. The necessary value -for `FIELDWIDTHS' would be `"8 6 1 6 14"'. This gives us five fields, -and what should be printed are `$1', `$3', and `$5'. The intermediate -fields are "filler," stuff in between the desired data. - - `flist' lists the fields to be printed, and `t' tracks the complete -field list, including filler fields. +print and also the intervening characters that have to be skipped. For +example, suppose you wanted characters 1 through 8, 15, and 22 through +35. You would use `-c 1-8,15,22-35'. The necessary value for +`FIELDWIDTHS' is `"8 6 1 6 14"'. This yields five fields, and the +fields to print are `$1', `$3', and `$5'. The intermediate fields are +"filler", which is stuff in between the desired data. `flist' lists +the fields to print, and `t' tracks the complete field list, including +filler fields: function set_charlist( field, i, j, f, g, t, filler, last, len) @@ -11569,22 +13996,21 @@ field list, including filler fields. nfields = j - 1 } - Here is the rule that actually processes the data. If the `-s' -option was given, then `suppress' will be true. The first `if' -statement makes sure that the input record does have the field -separator. If `cut' is processing fields, `suppress' is true, and the -field separator character is not in the record, then the record is -skipped. + Next is the rule that actually processes the data. If the `-s' +option is given, then `suppress' is true. The first `if' statement +makes sure that the input record does have the field separator. If +`cut' is processing fields, `suppress' is true, and the field separator +character is not in the record, then the record is skipped. - If the record is valid, then at this point, `gawk' has split the data -into fields, either using the character in `FS' or using fixed-length -fields and `FIELDWIDTHS'. The loop goes through the list of fields -that should be printed. If the corresponding field has data in it, it -is printed. If the next field also has data, then the separator -character is written out in between the fields. + If the record is valid, then `gawk' has split the data into fields, +either using the character in `FS' or using fixed-length fields and +`FIELDWIDTHS'. The loop goes through the list of fields that should be +printed. The corresponding field is printed if it contains data. If +the next field also has data, then the separator character is written +out between the fields: { - if (by_fields && suppress && $0 !~ FS) + if (by_fields && suppress && index($0, FS) != 0) next for (i = 1; i <= nfields; i++) { @@ -11598,11 +14024,11 @@ character is written out in between the fields. } This version of `cut' relies on `gawk''s `FIELDWIDTHS' variable to -do the character-based cutting. While it would be possible in other -`awk' implementations to use `substr' (*note Built-in Functions for -String Manipulation: String Functions.), it would also be extremely -painful to do so. The `FIELDWIDTHS' variable supplies an elegant -solution to the problem of picking the input line apart by characters. +do the character-based cutting. While it is possible in other `awk' +implementations to use `substr' (*note String Manipulation Functions: +String Functions.), it is also extremely painful. The `FIELDWIDTHS' +variable supplies an elegant solution to the problem of picking the +input line apart by characters. File: gawk.info, Node: Egrep Program, Next: Id Program, Prev: Cut Program, Up: Clones @@ -11612,57 +14038,55 @@ Searching for Regular Expressions in Files The `egrep' utility searches files for patterns. It uses regular expressions that are almost identical to those available in `awk' -(*note Regular Expression Constants: Regexp Constants.). It is used -this way: +(*note Regular Expressions: Regexp.). It is used in the following +manner: egrep [ OPTIONS ] 'PATTERN' FILES ... - The PATTERN is a regexp. In typical usage, the regexp is quoted to -prevent the shell from expanding any of the special characters as file -name wildcards. Normally, `egrep' prints the lines that matched. If -multiple file names are provided on the command line, each output line -is preceded by the name of the file and a colon. + The PATTERN is a regular expression. In typical usage, the regular +expression is quoted to prevent the shell from expanding any of the +special characters as file name wildcards. Normally, `egrep' prints +the lines that matched. If multiple file names are provided on the +command line, each output line is preceded by the name of the file and +a colon. - The options are: + The options to `egrep' are as follows: `-c' Print out a count of the lines that matched the pattern, instead of the lines themselves. `-s' - Be silent. No output is produced, and the exit value indicates - whether or not the pattern was matched. + Be silent. No output is produced and the exit value indicates + whether the pattern was matched. `-v' Invert the sense of the test. `egrep' prints the lines that do - _not_ match the pattern, and exits successfully if the pattern was + _not_ match the pattern and exits successfully if the pattern is not matched. `-i' Ignore case distinctions in both the pattern and the input data. `-l' - Only print the names of the files that matched, not the lines that - matched. + Only print (list) the names of the files that matched, not the + lines that matched. `-e PATTERN' Use PATTERN as the regexp to match. The purpose of the `-e' option is to allow patterns that start with a `-'. This version uses the `getopt' library function (*note Processing -Command Line Options: Getopt Function.), and the file transition +Command-Line Options: Getopt Function.) and the file transition library program (*note Noting Data File Boundaries: Filetrans Function.). - The program begins with a descriptive comment, and then a `BEGIN' -rule that processes the command line arguments with `getopt'. The `-i' + The program begins with a descriptive comment and then a `BEGIN' rule +that processes the command-line arguments with `getopt'. The `-i' (ignore case) option is particularly easy with `gawk'; we just use the -`IGNORECASE' built in variable (*note Built-in Variables::). +`IGNORECASE' built-in variable (*note Built-in Variables::): # egrep.awk --- simulate egrep in awk - # Arnold Robbins, arnold@gnu.org, Public Domain - # May 1993 - # Options: # -c count of lines # -s silent - use exit value @@ -11670,6 +14094,8 @@ rule that processes the command line arguments with `getopt'. The `-i' # -i ignore case # -l print filenames only # -e argument is pattern + # + # Requires getopt and file transition library functions BEGIN { while ((c = getopt(ARGC, ARGV, "ce:svil")) != -1) { @@ -11689,17 +14115,13 @@ rule that processes the command line arguments with `getopt'. The `-i' usage() } - Next comes the code that handles the `egrep' specific behavior. If no -pattern was supplied with `-e', the first non-option on the command -line is used. The `awk' command line arguments up to `ARGV[Optind]' -are cleared, so that `awk' won't try to process them as files. If no -files were specified, the standard input is used, and if multiple files -were specified, we make sure to note this so that the file names can -precede the matched lines in the output. - - The last two lines are commented out, since they are not needed in -`gawk'. They should be uncommented if you have to use another version -of `awk'. + Next comes the code that handles the `egrep'-specific behavior. If no +pattern is supplied with `-e', the first non-option on the command line +is used. The `awk' command-line arguments up to `ARGV[Optind]' are +cleared, so that `awk' won't try to process them as files. If no files +are specified, the standard input is used, and if multiple files are +specified, we make sure to note this so that the file names can precede +the matched lines in the output: if (pattern == "") pattern = ARGV[Optind++] @@ -11716,10 +14138,14 @@ of `awk'. # pattern = tolower(pattern) } + The last two lines are commented out, since they are not needed in +`gawk'. They should be uncommented if you have to use another version +of `awk'. + The next set of lines should be uncommented if you are not using `gawk'. This rule translates all the characters in the input line into -lower-case if the `-i' option was specified. The rule is commented out -since it is not necessary with `gawk'. +lowercase if the `-i' option is specified.(1) The rule is commented out +since it is not necessary with `gawk': #{ # if (IGNORECASE) @@ -11729,7 +14155,9 @@ since it is not necessary with `gawk'. The `beginfile' function is called by the rule in `ftrans.awk' when each new file is processed. In this case, it is very simple; all it does is initialize a variable `fcount' to zero. `fcount' tracks how -many lines in the current file matched the pattern. +many lines in the current file matched the pattern. (Naming the +parameter `junk' shows we know that `beginfile' is called with a +parameter, but that we're not interested in its value.): function beginfile(junk) { @@ -11737,13 +14165,13 @@ many lines in the current file matched the pattern. } The `endfile' function is called after each file has been processed. -It is used only when the user wants a count of the number of lines that -matched. `no_print' will be true only if the exit status is desired. -`count_only' will be true if line counts are desired. `egrep' will -therefore only print line counts if printing and counting are enabled. -The output format must be adjusted depending upon the number of files -to be processed. Finally, `fcount' is added to `total', so that we -know how many lines altogether matched the pattern. +It affects the output only when the user wants a count of the number of +lines that matched. `no_print' is true only if the exit status is +desired. `count_only' is true if line counts are desired. `egrep' +therefore only prints line counts if printing and counting are enabled. +The output format must be adjusted depending upon the number of files to +process. Finally, `fcount' is added to `total', so that we know how +many lines altogether matched the pattern: function endfile(file) { @@ -11756,24 +14184,21 @@ know how many lines altogether matched the pattern. total += fcount } - This rule does most of the work of matching lines. The variable -`matches' will be true if the line matched the pattern. If the user -wants lines that did not match, the sense of the `matches' is inverted + The following rule does most of the work of matching lines. The +variable `matches' is true if the line matched the pattern. If the user +wants lines that did not match, the sense of `matches' is inverted using the `!' operator. `fcount' is incremented with the value of -`matches', which will be either one or zero, depending upon a -successful or unsuccessful match. If the line did not match, the -`next' statement just moves on to the next record. - - There are several optimizations for performance in the following few -lines of code. If the user only wants exit status (`no_print' is true), -and we don't have to count lines, then it is enough to know that one -line in this file matched, and we can skip on to the next file with -`nextfile'. Along similar lines, if we are only printing file names, -and we don't need to count lines, we can print the file name, and then -skip to the next file with `nextfile'. - - Finally, each line is printed, with a leading filename and colon if -necessary. +`matches', which is either one or zero, depending upon a successful or +unsuccessful match. If the line does not match, the `next' statement +just moves on to the next record. + + A number of additional tests are made, but they are only done if we +are not counting lines. First, if the user only wants exit status +(`no_print' is true), then it is enough to know that _one_ line in this +file matched, and we can skip on to the next file with `nextfile'. +Similarly, if we are only printing file names, we can print the file +name, and then skip to the next file with `nextfile'. Finally, each +line is printed, with a leading file name and colon if necessary: { matches = ($0 ~ pattern) @@ -11785,22 +14210,24 @@ necessary. if (! matches) next - if (no_print && ! count_only) - nextfile + if (! count_only) { + if (no_print) + nextfile - if (filenames_only && ! count_only) { - print FILENAME - nextfile - } + if (filenames_only) { + print FILENAME + nextfile + } - if (do_filenames && ! count_only) - print FILENAME ":" $0 - else if (! count_only) - print + if (do_filenames) + print FILENAME ":" $0 + else + print + } } The `END' rule takes care of producing the correct exit status. If -there were no matches, the exit status is one, otherwise it is zero. +there are no matches, the exit status is one, otherwise it is zero: END \ { @@ -11810,11 +14237,12 @@ there were no matches, the exit status is one, otherwise it is zero. } The `usage' function prints a usage message in case of invalid -options and then exits. +options, and then exits: function usage( e) { e = "Usage: egrep [-csvil] [-e pat] [files ...]" + e = e "\n\tegrep [-csvil] pat [files ...]" print e > "/dev/stderr" exit 1 } @@ -11822,69 +14250,62 @@ options and then exits. The variable `e' is used so that the function fits nicely on the printed page. - Just a note on programming style. You may have noticed that the `END' + Just a note on programming style: you may have noticed that the `END' rule uses backslash continuation, with the open brace on a line by itself. This is so that it more closely resembles the way functions -are written. Many of the examples use this style. You can decide for -yourself if you like writing your `BEGIN' and `END' rules this way, or -not. +are written. Many of the examples in this major node use this style. +You can decide for yourself if you like writing your `BEGIN' and `END' +rules this way or not. + + ---------- Footnotes ---------- + + (1) It also introduces a subtle bug; if a match happens, we output +the translated line, not the original. File: gawk.info, Node: Id Program, Next: Split Program, Prev: Egrep Program, Up: Clones -Printing Out User Information +Printing out User Information ----------------------------- The `id' utility lists a user's real and effective user-id numbers, real and effective group-id numbers, and the user's group set, if any. -`id' will only print the effective user-id and group-id if they are -different from the real ones. If possible, `id' will also supply the +`id' only prints the effective user-id and group-id if they are +different from the real ones. If possible, `id' also supplies the corresponding user and group names. The output might look like this: $ id -| uid=2076(arnold) gid=10(staff) groups=10(staff),4(tty) - This information is exactly what is provided by `gawk''s `/dev/user' -special file (*note Special File Names in `gawk': Special Files.). -However, the `id' utility provides a more palatable output than just a -string of numbers. + This information is part of what is provided by `gawk''s `PROCINFO' +array (*note Built-in Variables::). However, the `id' utility provides +a more palatable output than just individual numbers. Here is a simple version of `id' written in `awk'. It uses the user database library functions (*note Reading the User Database: Passwd -Functions.), and the group database library functions (*note Reading -the Group Database: Group Functions.). +Functions.) and the group database library functions (*note Reading +the Group Database: Group Functions.): The program is fairly straightforward. All the work is done in the -`BEGIN' rule. The user and group id numbers are obtained from -`/dev/user'. If there is no support for `/dev/user', the program gives -up. - - The code is repetitive. The entry in the user database for the real -user-id number is split into parts at the `:'. The name is the first -field. Similar code is used for the effective user-id number, and the -group numbers. +`BEGIN' rule. The user and group ID numbers are obtained from +`PROCINFO'. The code is repetitive. The entry in the user database +for the real user-id number is split into parts at the `:'. The name is +the first field. Similar code is used for the effective user-id number +and the group numbers. # id.awk --- implement id in awk - # Arnold Robbins, arnold@gnu.org, Public Domain - # May 1993 - + # + # Requires user and group library functions # output is: # uid=12(foo) euid=34(bar) gid=3(baz) \ # egid=5(blat) groups=9(nine),2(two),1(one) BEGIN \ { - if ((getline < "/dev/user") < 0) { - err = "id: no /dev/user support - cannot run" - print err > "/dev/stderr" - exit 1 - } - close("/dev/user") - - uid = $1 - euid = $2 - gid = $3 - egid = $4 + uid = PROCINFO["uid"] + euid = PROCINFO["euid"] + gid = PROCINFO["gid"] + egid = PROCINFO["egid"] printf("uid=%d", uid) pw = getpwuid(uid) @@ -11918,36 +14339,56 @@ group numbers. } } - if (NF > 4) { - printf(" groups="); - for (i = 5; i <= NF; i++) { - printf("%d", $i) - pw = getgrgid($i) - if (pw != "") { - split(pw, a, ":") - printf("(%s)", a[1]) - } - if (i < NF) - printf(",") + for (i = 1; ("group" i) in PROCINFO; i++) { + if (i == 1) + printf(" groups=") + group = PROCINFO["group" i] + printf("%d", group) + pw = getgrgid(group) + if (pw != "") { + split(pw, a, ":") + printf("(%s)", a[1]) } + if (("group" (i+1)) in PROCINFO) + printf(",") } + print "" } + The test in the `for' loop is worth noting. Any supplementary +groups in the `PROCINFO' array have the indices `"group1"' through +`"groupN"' for some N; i.e., the total number of supplementary groups. +The problem is, we don't know in advance how many of these groups there +are. + + This loop works by starting at one, concatenating the value with +`"group"', and then using `in' to see if that value is in the array. +Eventually, `i' is incremented past the last group in the array and the +loop exits. + + The loop is also correct if there are _no_ supplementary groups; +then the condition is false the first time it's tested, and the loop +body never executes. + File: gawk.info, Node: Split Program, Next: Tee Program, Prev: Id Program, Up: Clones -Splitting a Large File Into Pieces +Splitting a Large File into Pieces ---------------------------------- - The `split' program splits large text files into smaller pieces. By -default, the output files are named `xaa', `xab', and so on. Each file -has 1000 lines in it, with the likely exception of the last file. To -change the number of lines in each file, you supply a number on the -command line preceded with a minus, e.g., `-500' for files with 500 + The `split' program splits large text files into smaller pieces. +The usage is as follows: + + split [-COUNT] file [ PREFIX ] + + By default, the output files are named `xaa', `xab', and so on. Each +file has 1000 lines in it, with the likely exception of the last file. +To change the number of lines in each file, supply a number on the +command line preceded with a minus; e.g., `-500' for files with 500 lines in them instead of 1000. To change the name of the output files -to something like `myfileaa', `myfileab', and so on, you supply an -additional argument that specifies the filename. +to something like `myfileaa', `myfileab', and so on, supply an +additional argument that specifies the file name prefix. Here is a version of `split' in `awk'. It uses the `ord' and `chr' functions presented in *Note Translating Between Characters and @@ -11958,13 +14399,12 @@ there are not too many arguments. It then looks at each argument in turn. The first argument could be a minus followed by a number. If it is, this happens to look like a negative number, so it is made positive, and that is the count of lines. The data file name is -skipped over, and the final argument is used as the prefix for the -output file names. +skipped over and the final argument is used as the prefix for the +output file names: # split.awk --- do split in awk - # Arnold Robbins, arnold@gnu.org, Public Domain - # May 1993 - + # + # Requires ord and chr library functions # usage: split [-num] [file] [outname] BEGIN { @@ -11997,20 +14437,21 @@ it is greater than `count', it is time to close the current file and start a new one. `s1' and `s2' track the current suffixes for the file name. If they are both `z', the file is just too big. Otherwise, `s1' moves to the next letter in the alphabet and `s2' starts over again at -`a'. +`a': { if (++tcount > count) { close(out) if (s2 == "z") { if (s1 == "z") { - printf("split: %s is too large to split\n", \ + printf("split: %s is too large to split\n", FILENAME) > "/dev/stderr" exit 1 } s1 = chr(ord(s1) + 1) s2 = "a" - } else + } + else s2 = chr(ord(s2) + 1) out = (outfile s1 s2) tcount = 1 @@ -12018,7 +14459,7 @@ moves to the next letter in the alphabet and `s2' starts over again at print > out } - The `usage' function simply prints an error message and exits. +The `usage' function simply prints an error message and exits: function usage( e) { @@ -12030,39 +14471,37 @@ moves to the next letter in the alphabet and `s2' starts over again at The variable `e' is used so that the function fits nicely on the screen. This program is a bit sloppy; it relies on `awk' to close the last -file for it automatically, instead of doing it in an `END' rule. +file for it automatically, instead of doing it in an `END' rule. It +also assumes that letters are contiguous in the character set, which +isn't true for EBCDIC systems. File: gawk.info, Node: Tee Program, Next: Uniq Program, Prev: Split Program, Up: Clones -Duplicating Output Into Multiple Files +Duplicating Output into Multiple Files -------------------------------------- The `tee' program is known as a "pipe fitting." `tee' copies its -standard input to its standard output, and also duplicates it to the -files named on the command line. Its usage is: +standard input to its standard output and also duplicates it to the +files named on the command line. Its usage is as follows: tee [-a] file ... The `-a' option tells `tee' to append to the named files, instead of truncating them and starting over. - The `BEGIN' rule first makes a copy of all the command line -arguments, into an array named `copy'. `ARGV[0]' is not copied, since -it is not needed. `tee' cannot use `ARGV' directly, since `awk' will -attempt to process each file named in `ARGV' as input data. + The `BEGIN' rule first makes a copy of all the command-line arguments +into an array named `copy'. `ARGV[0]' is not copied, since it is not +needed. `tee' cannot use `ARGV' directly, since `awk' attempts to +process each file name in `ARGV' as input data. If the first argument is `-a', then the flag variable `append' is set to true, and both `ARGV[1]' and `copy[1]' are deleted. If `ARGC' is -less than two, then no file names were supplied, and `tee' prints a +less than two, then no file names were supplied and `tee' prints a usage message and exits. Finally, `awk' is forced to read the standard -input by setting `ARGV[1]' to `"-"', and `ARGC' to two. +input by setting `ARGV[1]' to `"-"' and `ARGC' to two: # tee.awk --- tee in awk - # Arnold Robbins, arnold@gnu.org, Public Domain - # May 1993 - # Revised December 1995 - BEGIN \ { for (i = 1; i < ARGC; i++) @@ -12085,7 +14524,7 @@ input by setting `ARGV[1]' to `"-"', and `ARGC' to two. The single rule does all the work. Since there is no pattern, it is executed for each line of input. The body of the rule simply prints the line into each file on the command line, and then to the standard -output. +output: { # moving the if outside the loop makes it run faster @@ -12098,7 +14537,7 @@ output. print } - It would have been possible to code the loop this way: +It is also possible to write the loop this way: for (i in copy) if (append) @@ -12106,14 +14545,13 @@ output. else print > copy[i] -This is more concise, but it is also less efficient. The `if' is -tested for each record and for each output file. By duplicating the -loop body, the `if' is only tested once for each input record. If -there are N input records and M input files, the first method only -executes N `if' statements, while the second would execute N`*'M `if' -statements. +This is more concise but it is also less efficient. The `if' is tested +for each record and for each output file. By duplicating the loop +body, the `if' is only tested once for each input record. If there are +N input records and M output files, the first method only executes N +`if' statements, while the second executes N`*'M `if' statements. - Finally, the `END' rule cleans up, by closing all the output files. + Finally, the `END' rule cleans up by closing all the output files: END \ { @@ -12124,13 +14562,13 @@ statements. File: gawk.info, Node: Uniq Program, Next: Wc Program, Prev: Tee Program, Up: Clones -Printing Non-duplicated Lines of Text +Printing Non-Duplicated Lines of Text ------------------------------------- The `uniq' utility reads sorted lines of data on its standard input, -and (by default) removes duplicate lines. In other words, only unique -lines are printed, hence the name. `uniq' has a number of options. The -usage is: +and by default removes duplicate lines. In other words, it only prints +unique lines--hence the name. `uniq' has a number of options. The +usage is as follows: uniq [-udc [-N]] [+N] [ INPUT FILE [ OUTPUT FILE ]] @@ -12163,36 +14601,32 @@ usage is: The generated output is sent to the named output file, instead of to the standard output. - Normally `uniq' behaves as if both the `-d' and `-u' options had -been provided. + Normally `uniq' behaves as if both the `-d' and `-u' options are +provided. - Here is an `awk' implementation of `uniq'. It uses the `getopt' -library function (*note Processing Command Line Options: Getopt -Function.), and the `join' library function (*note Merging an Array -Into a String: Join Function.). + `uniq' uses the `getopt' library function (*note Processing +Command-Line Options: Getopt Function.) and the `join' library function +(*note Merging an Array into a String: Join Function.). The program begins with a `usage' function and then a brief outline -of the options and their meanings in a comment. - - The `BEGIN' rule deals with the command line arguments and options. -It uses a trick to get `getopt' to handle options of the form `-25', -treating such an option as the option letter `2' with an argument of -`5'. If indeed two or more digits were supplied (`Optarg' looks like a -number), `Optarg' is concatenated with the option digit, and then -result is added to zero to make it into a number. If there is only one -digit in the option, then `Optarg' is not needed, and `Optind' must be -decremented so that `getopt' will process it next time. This code is -admittedly a bit tricky. - - If no options were supplied, then the default is taken, to print both +of the options and their meanings in a comment. The `BEGIN' rule deals +with the command-line arguments and options. It uses a trick to get +`getopt' to handle options of the form `-25', treating such an option +as the option letter `2' with an argument of `5'. If indeed two or more +digits are supplied (`Optarg' looks like a number), `Optarg' is +concatenated with the option digit and then the result is added to zero +to make it into a number. If there is only one digit in the option, +then `Optarg' is not needed. `Optind' must be decremented so that +`getopt' processes it next time. This code is admittedly a bit tricky. + + If no options are supplied, then the default is taken, to print both repeated and non-repeated lines. The output file, if provided, is -assigned to `outputfile'. Earlier, `outputfile' was initialized to the -standard output, `/dev/stdout'. +assigned to `outputfile'. Early on, `outputfile' is initialized to the +standard output, `/dev/stdout': # uniq.awk --- do uniq in awk - # Arnold Robbins, arnold@gnu.org, Public Domain - # May 1993 - + # + # Requires getopt and join library functions function usage( e) { e = "Usage: uniq [-udc [-n]] [+n] [ in [ out ]]" @@ -12250,22 +14684,17 @@ standard output, `/dev/stdout'. The following function, `are_equal', compares the current line, `$0', to the previous line, `last'. It handles skipping fields and -characters. - - If no field count and no character count were specified, `are_equal' -simply returns one or zero depending upon the result of a simple string -comparison of `last' and `$0'. Otherwise, things get more complicated. - - If fields have to be skipped, each line is broken into an array using -`split' (*note Built-in Functions for String Manipulation: String -Functions.), and then the desired fields are joined back into a line -using `join'. The joined lines are stored in `clast' and `cline'. If -no fields are skipped, `clast' and `cline' are set to `last' and `$0' -respectively. - - Finally, if characters are skipped, `substr' is used to strip off the -leading `charcount' characters in `clast' and `cline'. The two strings -are then compared, and `are_equal' returns the result. +characters. If no field count and no character count are specified, +`are_equal' simply returns one or zero depending upon the result of a +simple string comparison of `last' and `$0'. Otherwise, things get more +complicated. If fields have to be skipped, each line is broken into an +array using `split' (*note String Manipulation Functions: String +Functions.); the desired fields are then joined back into a line using +`join'. The joined lines are stored in `clast' and `cline'. If no +fields are skipped, `clast' and `cline' are set to `last' and `$0', +respectively. Finally, if characters are skipped, `substr' is used to +strip off the leading `charcount' characters in `clast' and `cline'. +The two strings are then compared and `are_equal' returns the result: function are_equal( n, m, clast, cline, alast, aline) { @@ -12294,20 +14723,20 @@ is executed only for the very first line of data. It sets `last' equal to `$0', so that subsequent lines of text have something to be compared to. - The second rule does the work. The variable `equal' will be one or -zero depending upon the results of `are_equal''s comparison. If `uniq' -is counting repeated lines, then the `count' variable is incremented if -the lines are equal. Otherwise the line is printed and `count' is -reset, since the two lines are not equal. + The second rule does the work. The variable `equal' is one or zero, +depending upon the results of `are_equal''s comparison. If `uniq' is +counting repeated lines, and the lines are equal, then it increments +the `count' variable. Otherwise it prints the line and resets `count', +since the two lines are not equal. - If `uniq' is not counting, `count' is incremented if the lines are -equal. Otherwise, if `uniq' is counting repeated lines, and more than -one line has been seen, or if `uniq' is counting non-repeated lines, -and only one line has been seen, then the line is printed, and `count' -is reset. + If `uniq' is not counting, and if the lines are equal, `count' is +incremented. Nothing is printed, since the point is to remove +duplicates. Otherwise, if `uniq' is counting repeated lines and more +than one line is seen, or if `uniq' is counting non-repeated lines and +only one line is seen, then the line is printed, and `count' is reset. Finally, similar logic is used in the `END' rule to print the final -line of input data. +line of input data: NR == 1 { last = $0 @@ -12354,13 +14783,14 @@ Counting Things --------------- The `wc' (word count) utility counts lines, words, and characters in -one or more input files. Its usage is: +one or more input files. Its usage is as follows: wc [-lwc] [ FILES ... ] If no files are specified on the command line, `wc' reads its -standard input. If there are multiple files, it will also print total -counts for all the files. The options and their meanings are: +standard input. If there are multiple files, it also prints total +counts for all the files. The options and their meanings are shown in +the following list: `-l' Only count lines. @@ -12375,27 +14805,24 @@ counts for all the files. The options and their meanings are: Only count characters. Implementing `wc' in `awk' is particularly elegant, since `awk' does -a lot of the work for us; it splits lines into words (i.e. fields) and -counts them, it counts lines (i.e. records) for us, and it can easily -tell us how long a line is. +a lot of the work for us; it splits lines into words (i.e., fields) and +counts them, it counts lines (i.e., records), and it can easily tell us +how long a line is. - This version uses the `getopt' library function (*note Processing -Command Line Options: Getopt Function.), and the file transition + This uses the `getopt' library function (*note Processing +Command-Line Options: Getopt Function.) and the file transition functions (*note Noting Data File Boundaries: Filetrans Function.). - This version has one major difference from traditional versions of -`wc'. Our version always prints the counts in the order lines, words, -and characters. Traditional versions note the order of the `-l', `-w', -and `-c' options on the command line, and print the counts in that -order. + This version has one notable difference from traditional versions of +`wc': it always prints the counts in the order lines, words, and +characters. Traditional versions note the order of the `-l', `-w', and +`-c' options on the command line, and print the counts in that order. The `BEGIN' rule does the argument processing. The variable -`print_total' will be true if more than one file was named on the -command line. +`print_total' is true if more than one file is named on the command +line: # wc.awk --- count lines, words, characters - # Arnold Robbins, arnold@gnu.org, Public Domain - # May 1993 # Options: # -l only count lines @@ -12403,6 +14830,8 @@ command line. # -c only count characters # # Default is to count lines, words, characters + # + # Requires getopt and file transition library functions BEGIN { # let getopt print a message about @@ -12427,18 +14856,19 @@ command line. The `beginfile' function is simple; it just resets the counts of lines, words, and characters to zero, and saves the current file name in -`fname'. +`fname': + + function beginfile(file) + { + chars = lines = words = 0 + fname = FILENAME + } The `endfile' function adds the current file's numbers to the running totals of lines, words, and characters. It then prints out those numbers for the file that was just read. It relies on `beginfile' to -reset the numbers for the following data file. +reset the numbers for the following data file: - function beginfile(file) { - chars = lines = words = 0 - fname = FILENAME - } - function endfile(file) { tchars += chars @@ -12454,13 +14884,12 @@ reset the numbers for the following data file. } There is one rule that is executed for each line. It adds the length -of the record to `chars'. It has to add one, since the newline -character separating records (the value of `RS') is not part of the -record itself. `lines' is incremented for each line read, and `words' -is incremented by the value of `NF', the number of "words" on this -line.(1) - - Finally, the `END' rule simply prints the totals for all the files. +of the record, plus one, to `chars'. Adding one plus the record length +is needed because the newline character separating records (the value +of `RS') is not part of the record itself, and thus not included in its +length. Next, `lines' is incremented for each line read, and `words' +is incremented by the value of `NF', which is the number of "words" on +this line:(1) # do per line { @@ -12468,7 +14897,9 @@ line.(1) lines++ words += NF } - + + Finally, the `END' rule simply prints the totals for all the files. + END { if (print_total) { if (do_lines) @@ -12483,9 +14914,10 @@ line.(1) ---------- Footnotes ---------- - (1) Examine the code in *Note Noting Data File Boundaries: Filetrans -Function. Why must `wc' use a separate `lines' variable, instead of -using the value of `FNR' in `endfile'? + (1) `wc' can't just use the value of `FNR' in `endfile'. If you +examine the code in *Note Noting Data File Boundaries: Filetrans +Function, you will see that `FNR' has already been reset by the time +`endfile' is called. File: gawk.info, Node: Miscellaneous Programs, Prev: Clones, Up: Sample Programs @@ -12493,22 +14925,23 @@ File: gawk.info, Node: Miscellaneous Programs, Prev: Clones, Up: Sample Progr A Grab Bag of `awk' Programs ============================ - This section is a large "grab bag" of miscellaneous programs. We + This minor node is a large "grab bag" of miscellaneous programs. We hope you find them both interesting and enjoyable. * Menu: -* Dupword Program:: Finding duplicated words in a document. -* Alarm Program:: An alarm clock. -* Translate Program:: A program similar to the `tr' utility. -* Labels Program:: Printing mailing labels. -* Word Sorting:: A program to produce a word usage count. -* History Sorting:: Eliminating duplicate entries from a history - file. -* Extract Program:: Pulling out programs from Texinfo source - files. -* Simple Sed:: A Simple Stream Editor. -* Igawk Program:: A wrapper for `awk' that includes files. +* Dupword Program:: Finding duplicated words in a document. +* Alarm Program:: An alarm clock. +* Translate Program:: A program similar to the `tr' utility. +* Labels Program:: Printing mailing labels. +* Word Sorting:: A program to produce a word usage count. +* History Sorting:: Eliminating duplicate entries from a history + file. +* Extract Program:: Pulling out programs from Texinfo source + files. +* Simple Sed:: A Simple Stream Editor. +* Igawk Program:: A wrapper for `awk' that includes + files. File: gawk.info, Node: Dupword Program, Next: Alarm Program, Prev: Miscellaneous Programs, Up: Miscellaneous Programs @@ -12517,30 +14950,37 @@ Finding Duplicated Words in a Document -------------------------------------- A common error when writing large amounts of prose is to accidentally -duplicate words. Often you will see this in text as something like "the -the program does the following ...." When the text is on-line, often -the duplicated words occur at the end of one line and the beginning of -another, making them very difficult to spot. +duplicate words. Typically you will see this in text as something like +"the the program does the following ...." When the text is online, +often the duplicated words occur at the end of one line and the +beginning of another, making them very difficult to spot. - This program, `dupword.awk', scans through a file one line at a time, + This program, `dupword.awk', scans through a file one line at a time and looks for adjacent occurrences of the same word. It also saves the last word on a line (in the variable `prev') for comparison with the first word on the next line. - The first two statements make sure that the line is all lower-case, + The first two statements make sure that the line is all lowercase, so that, for example, "The" and "the" compare equal to each other. The -second statement removes all non-alphanumeric and non-whitespace -characters from the line, so that punctuation does not affect the -comparison either. This sometimes leads to reports of duplicated words -that really are different, but this is unusual. - - # dupword --- find duplicate words in text - # Arnold Robbins, arnold@gnu.org, Public Domain - # December 1991 - +next statement replaces non-alphanumeric and non-whitespace characters +with spaces, so that punctuation does not affect the comparison either. +The characters are replaced with spaces so that formatting controls +don't create nonsense words (e.g., the Texinfo `@code{NF}' becomes +`codeNF' if punctuation is simply deleted). The record is then +re-split into fields, yielding just the actual words on the line, and +insuring that there are no empty fields. + + If there are no fields left after removing all the punctuation, the +current record is skipped. Otherwise, the program loops through each +word, comparing it to the previous one: + + # dupword.awk --- find duplicate words in text { $0 = tolower($0) - gsub(/[^A-Za-z0-9 \t]/, ""); + gsub(/[^[:alnum:][:blank:]]/, " "); + $0 = $0 # re-split + if (NF == 0) + next if ($1 == prev) printf("%s:%d: duplicate %s\n", FILENAME, FNR, $1) @@ -12557,28 +14997,30 @@ File: gawk.info, Node: Alarm Program, Next: Translate Program, Prev: Dupword An Alarm Clock Program ---------------------- + Nothing cures insomnia like a ringing alarm clock. + Arnold Robbins + The following program is a simple "alarm clock" program. You give -it a time of day, and an optional message. At the given time, it +it a time of day and an optional message. At the specified time, it prints the message on the standard output. In addition, you can give it -the number of times to repeat the message, and also a delay between +the number of times to repeat the message as well as a delay between repetitions. This program uses the `gettimeofday' function from *Note Managing the Time of Day: Gettimeofday Function. All the work is done in the `BEGIN' rule. The first part is argument -checking and setting of defaults; the delay, the count, and the message -to print. If the user supplied a message, but it does not contain the -ASCII BEL character (known as the "alert" character, `\a'), then it is -added to the message. (On many systems, printing the ASCII BEL -generates some sort of audible alert. Thus, when the alarm goes off, -the system calls attention to itself, in case the user is not looking -at their computer or terminal.) - - # alarm --- set an alarm - # Arnold Robbins, arnold@gnu.org, Public Domain - # May 1993 - +checking and setting of defaults: the delay, the count, and the message +to print. If the user supplied a message without the ASCII BEL +character (known as the "alert" character, `"\a"'), then it is added to +the message. (On many systems, printing the ASCII BEL generates some +sort of audible alert. Thus when the alarm goes off, the system calls +attention to itself in case the user is not looking at their computer +or terminal.): + + # alarm.awk --- set an alarm + # + # Requires gettimeofday library function # usage: alarm time [ "message" [ count [ delay ] ] ] BEGIN \ @@ -12588,7 +15030,8 @@ at their computer or terminal.) usage2 = sprintf("\t(%s) time ::= hh:mm", ARGV[1]) if (ARGC < 2) { - print usage > "/dev/stderr" + print usage1 > "/dev/stderr" + print usage2 > "/dev/stderr" exit 1 } else if (ARGC == 5) { delay = ARGV[4] + 0 @@ -12615,13 +15058,14 @@ at their computer or terminal.) else if (index(message, "\a") == 0) message = "\a" message "\a" - The next section of code turns the alarm time into hours and minutes, -and converts it if necessary to a 24-hour clock. Then it turns that -time into a count of the seconds since midnight. Next it turns the -current time into a count of seconds since midnight. The difference -between the two is how long to wait before setting off the alarm. + The next minor node of code turns the alarm time into hours and +minutes, converts it (if necessary) to a 24-hour clock, and then turns +that time into a count of the seconds since midnight. Next it turns +the current time into a count of seconds since midnight. The +difference between the two is how long to wait before setting off the +alarm: - # split up dest time + # split up alarm time split(ARGV[1], atime, ":") hour = atime[1] + 0 # force numeric minute = atime[2] + 0 # force numeric @@ -12649,13 +15093,13 @@ between the two is how long to wait before setting off the alarm. exit 1 } - Finally, the program uses the `system' function (*note Built-in -Functions for Input/Output: I/O Functions.) to call the `sleep' -utility. The `sleep' utility simply pauses for the given number of -seconds. If the exit status is not zero, the program assumes that -`sleep' was interrupted, and exits. If `sleep' exited with an OK status -(zero), then the program prints the message in a loop, again using -`sleep' to delay for however many seconds are necessary. + Finally, the program uses the `system' function (*note Input/Output +Functions: I/O Functions.) to call the `sleep' utility. The `sleep' +utility simply pauses for the given number of seconds. If the exit +status is not zero, the program assumes that `sleep' was interrupted +and exits. If `sleep' exited with an OK status (zero), then the program +prints the message in a loop, again using `sleep' to delay for however +many seconds are necessary: # zzzzzz..... go away if interrupted if (system(sprintf("sleep %d", naptime)) != 0) @@ -12680,35 +15124,32 @@ Transliterating Characters -------------------------- The system `tr' utility transliterates characters. For example, it -is often used to map upper-case letters into lower-case, for further -processing. - - GENERATE DATA | tr '[A-Z]' '[a-z]' | PROCESS DATA ... - - You give `tr' two lists of characters enclosed in square brackets. -Usually, the lists are quoted to keep the shell from attempting to do a -filename expansion.(1) When processing the input, the first character -in the first list is replaced with the first character in the second -list, the second character in the first list is replaced with the -second character in the second list, and so on. If there are more -characters in the "from" list than in the "to" list, the last character -of the "to" list is used for the remaining characters in the "from" -list. +is often used to map uppercase letters into lowercase for further +processing: + + GENERATE DATA | tr 'A-Z' 'a-z' | PROCESS DATA ... - Some time ago, a user proposed to us that we add a transliteration -function to `gawk'. Being opposed to "creeping featurism," I wrote the -following program to prove that character transliteration could be done -with a user-level function. This program is not as complete as the -system `tr' utility, but it will do most of the job. + `tr' requires two lists of characters.(1) When processing the +input, the first character in the first list is replaced with the first +character in the second list, the second character in the first list is +replaced with the second character in the second list, and so on. If +there are more characters in the "from" list than in the "to" list, the +last character of the "to" list is used for the remaining characters in +the "from" list. + + Some time ago, a user proposed that a transliteration function should +be added to `gawk'. The following program was written to prove that +character transliteration could be done with a user-level function. +This program is not as complete as the system `tr' utility but it does +most of the job. The `translate' program demonstrates one of the few weaknesses of standard `awk': dealing with individual characters is very painful, requiring repeated use of the `substr', `index', and `gsub' built-in -functions (*note Built-in Functions for String Manipulation: String -Functions.).(2) +functions (*note String Manipulation Functions: String Functions.).(2) There are two functions. The first, `stranslate', takes three -arguments. +arguments: `from' A list of characters to translate from. @@ -12727,17 +15168,14 @@ used to change it to the corresponding `to' character. The `translate' function simply calls `stranslate' using `$0' as the target. The main program sets two global variables, `FROM' and `TO', -from the command line, and then changes `ARGV' so that `awk' will read -from the standard input. +from the command line, and then changes `ARGV' so that `awk' reads from +the standard input. Finally, the processing rule simply calls `translate' for each -record. +record: - # translate --- do tr like stuff - # Arnold Robbins, arnold@gnu.org, Public Domain - # August 1989 - - # bugs: does not handle things like: tr A-Z a-z, it has + # translate.awk --- do tr-like stuff + # Bugs: does not handle things like: tr A-Z a-z, it has # to be spelled out. However, if `to' is shorter than `from', # the last character in `to' is used for the rest of `from'. @@ -12781,12 +15219,13 @@ record. } While it is possible to do character transliteration in a user-level -function, it is not necessarily efficient, and we started to consider -adding a built-in function. However, shortly after writing this -program, we learned that the System V Release 4 `awk' had added the -`toupper' and `tolower' functions. These functions handle the vast +function, it is not necessarily efficient, and we (the `gawk' authors) +started to consider adding a built-in function. However, shortly after +writing this program, we learned that the System V Release 4 `awk' had +added the `toupper' and `tolower' functions (*note String Manipulation +Functions: String Functions.). These functions handle the vast majority of the cases where character transliteration is necessary, and -so we chose to simply add those functions to `gawk' as well, and then +so we chose to simply add those functions to `gawk' as well and then leave well enough alone. An obvious improvement to this program would be to set up the `t_ar' @@ -12796,12 +15235,13 @@ program. ---------- Footnotes ---------- - (1) On older, non-POSIX systems, `tr' often does not require that -the lists be enclosed in square brackets and quoted. This is a feature. + (1) On some older System V systems, `tr' may require that the lists +be written as range expressions enclosed in square brackets (`[a-z]') +and quoted, to prevent the shell from attempting a file name expansion. +This is not a feature. (2) This program was written before `gawk' acquired the ability to -split each character in a string into separate array elements. How -might you use this new feature to simplify the program? +split each character in a string into separate array elements. File: gawk.info, Node: Labels Program, Next: Word Sorting, Prev: Translate Program, Up: Miscellaneous Programs @@ -12810,10 +15250,10 @@ Printing Mailing Labels ----------------------- Here is a "real world"(1) program. This script reads lists of names -and addresses, and generates mailing labels. Each page of labels has -20 labels on it, two across and ten down. The addresses are guaranteed -to be no more than five lines of data. Each address is separated from -the next by a blank line. +and addresses and generates mailing labels. Each page of labels has 20 +labels on it, two across and ten down. The addresses are guaranteed to +be no more than five lines of data. Each address is separated from the +next by a blank line. The basic idea is to read 20 labels worth of data. Each line of each label is stored in the `line' array. The single rule takes care @@ -12821,42 +15261,41 @@ of filling the `line' array and printing the page when 20 labels have been read. The `BEGIN' rule simply sets `RS' to the empty string, so that `awk' -will split records at blank lines (*note How Input is Split into -Records: Records.). It sets `MAXLINES' to 100, since `MAXLINE' is the -maximum number of lines on the page (20 * 5 = 100). +splits records at blank lines (*note How Input Is Split into Records: +Records.). It sets `MAXLINES' to 100, since 100 is the maximum number +of lines on the page (20 * 5 = 100). Most of the work is done in the `printpage' function. The label -lines are stored sequentially in the `line' array. But they have to be -printed horizontally; `line[1]' next to `line[6]', `line[2]' next to +lines are stored sequentially in the `line' array. But they have to +print horizontally; `line[1]' next to `line[6]', `line[2]' next to `line[7]', and so on. Two loops are used to accomplish this. The outer loop, controlled by `i', steps through every 10 lines of data; this is each row of labels. The inner loop, controlled by `j', goes -through the lines within the row. As `j' goes from zero to four, `i+j' -is the `j''th line in the row, and `i+j+5' is the entry next to it. -The output ends up looking something like this: +through the lines within the row. As `j' goes from 0 to 4, `i+j' is +the `j''th line in the row, and `i+j+5' is the entry next to it. The +output ends up looking something like this: line 1 line 6 line 2 line 7 line 3 line 8 line 4 line 9 line 5 line 10 + ... - As a final note, at lines 21 and 61, an extra blank line is printed, + As a final note, an extra blank line is printed at lines 21 and 61, to keep the output lined up on the labels. This is dependent on the particular brand of labels in use when the program was written. You will also note that there are two blank lines at the top and two blank lines at the bottom. The `END' rule arranges to flush the final page of labels; there may -not have been an even multiple of 20 labels in the data. +not have been an even multiple of 20 labels in the data: - # labels.awk - # Arnold Robbins, arnold@gnu.org, Public Domain - # June 1992 + # labels.awk --- print mailing labels - # Program to print labels. Each label is 5 lines of data - # that may have blank lines. The label sheets have 2 - # blank lines at the top and 2 at the bottom. + # Each label is 5 lines of data that may have blank lines. + # The label sheets have 2 blank lines at the top and 2 at + # the bottom. BEGIN { RS = "" ; MAXLINES = 100 } @@ -12917,13 +15356,12 @@ Generating Word Usage Counts The following `awk' program prints the number of occurrences of each word in its input. It illustrates the associative nature of `awk' -arrays by using strings as subscripts. It also demonstrates the `for X -in ARRAY' construction. Finally, it shows how `awk' can be used in +arrays by using strings as subscripts. It also demonstrates the `for +INDEX in ARRAY' mechanism. Finally, it shows how `awk' is used in conjunction with other utility programs to do a useful task of some complexity with a minimum of effort. Some explanations follow the -program listing. +program listing: - awk ' # Print list of word frequencies { for (i = 1; i <= NF; i++) @@ -12933,50 +15371,49 @@ program listing. END { for (word in freq) printf "%s\t%d\n", word, freq[word] - }' - - The first thing to notice about this program is that it has two -rules. The first rule, because it has an empty pattern, is executed on -every line of the input. It uses `awk''s field-accessing mechanism -(*note Examining Fields: Fields.) to pick out the individual words from -the line, and the built-in variable `NF' (*note Built-in Variables::) -to know how many fields are available. + } - For each input word, an element of the array `freq' is incremented to + This program has two rules. The first rule, because it has an empty +pattern, is executed for every input line. It uses `awk''s +field-accessing mechanism (*note Examining Fields: Fields.) to pick out +the individual words from the line, and the built-in variable `NF' +(*note Built-in Variables::) to know how many fields are available. +For each input word, it increments an element of the array `freq' to reflect that the word has been seen an additional time. The second rule, because it has the pattern `END', is not executed until the input has been exhausted. It prints out the contents of the -`freq' table that has been built up inside the first action. - - This program has several problems that would prevent it from being -useful by itself on real text files: +`freq' table that has been built up inside the first action. This +program has several problems that would prevent it from being useful by +itself on real text files: * Words are detected using the `awk' convention that fields are - separated by whitespace and that other characters in the input + separated just by whitespace. Other characters in the input (except newlines) don't have any special meaning to `awk'. This means that punctuation characters count as part of words. - * The `awk' language considers upper- and lower-case characters to be - distinct. Therefore, `bartender' and `Bartender' are not treated - as the same word. This is undesirable since, in normal text, words + * The `awk' language considers upper- and lowercase characters to be + distinct. Therefore, "bartender" and "Bartender" are not treated + as the same word. This is undesirable, since in normal text, words are capitalized if they begin sentences, and a frequency analyzer should not be sensitive to capitalization. * The output does not come out in any useful order. You're more - likely to be interested in which words occur most frequently, or + likely to be interested in which words occur most frequently or in having an alphabetized table of how frequently each word occurs. - The way to solve these problems is to use some of the more advanced -features of the `awk' language. First, we use `tolower' to remove case + The way to solve these problems is to use some of `awk''s more +advanced features. First, we use `tolower' to remove case distinctions. Next, we use `gsub' to remove punctuation characters. Finally, we use the system `sort' utility to process the output of the `awk' script. Here is the new version of the program: - # Print list of word frequencies + # wordfreq.awk --- print list of word frequencies + { $0 = tolower($0) # remove case distinctions - gsub(/[^a-z0-9_ \t]/, "", $0) # remove punctuation + # remove punctuation + gsub(/[^[:alnum:]_[:blank:]]/, "", $0) for (i = 1; i <= NF; i++) freq[$i]++ } @@ -12987,25 +15424,23 @@ Finally, we use the system `sort' utility to process the output of the } Assuming we have saved this program in a file named `wordfreq.awk', -and that the data is in `file1', the following pipeline +and that the data is in `file1', the following pipeline: awk -f wordfreq.awk file1 | sort +1 -nr produces a table of the words appearing in `file1' in order of -decreasing frequency. - - The `awk' program suitably massages the data and produces a word -frequency table, which is not ordered. +decreasing frequency. The `awk' program suitably massages the data and +produces a word frequency table, which is not ordered. The `awk' script's output is then sorted by the `sort' utility and -printed on the terminal. The options given to `sort' in this example -specify to sort using the second field of each input line (skipping one -field), that the sort keys should be treated as numeric quantities -(otherwise `15' would come before `5'), and that the sorting should be -done in descending (reverse) order. +printed on the terminal. The options given to `sort' specify a sort +that uses the second field of each input line (skipping one field), +that the sort keys should be treated as numeric quantities (otherwise +`15' would come before `5'), and that the sorting should be done in +descending (reverse) order. - We could have even done the `sort' from within the program, by -changing the `END' action to: + The `sort' could even be done from within the program, by changing +the `END' action to: END { sort = "sort +1 -nr" @@ -13014,11 +15449,10 @@ changing the `END' action to: close(sort) } - You would have to use this way of sorting on systems that do not -have true pipes. - - See the general operating system documentation for more information -on how to use the `sort' program. + This way of sorting must be used on systems that do not have true +pipes at the command-line (or batch-file) level. See the general +operating system documentation for more information on how to use the +`sort' program. File: gawk.info, Node: History Sorting, Next: Extract Program, Prev: Word Sorting, Up: Miscellaneous Programs @@ -13026,31 +15460,26 @@ File: gawk.info, Node: History Sorting, Next: Extract Program, Prev: Word Sor Removing Duplicates from Unsorted Text -------------------------------------- - The `uniq' program (*note Printing Non-duplicated Lines of Text: + The `uniq' program (*note Printing Non-Duplicated Lines of Text: Uniq Program.), removes duplicate lines from _sorted_ data. Suppose, however, you need to remove duplicate lines from a data -file, but that you wish to preserve the order the lines are in? A good +file but that you want to preserve the order the lines are in. A good example of this might be a shell history file. The history file keeps a copy of all the commands you have entered, and it is not unusual to -repeat a command several times in a row. Occasionally you might wish +repeat a command several times in a row. Occasionally you might want to compact the history by removing duplicate entries. Yet it is desirable to maintain the order of the original commands. This simple program does the job. It uses two arrays. The `data' array is indexed by the text of each line. For each line, `data[$0]' -is incremented. - - If a particular line has not been seen before, then `data[$0]' will -be zero. In that case, the text of the line is stored in +is incremented. If a particular line has not been seen before, then +`data[$0]' is zero. In this case, the text of the line is stored in `lines[count]'. Each element of `lines' is a unique command, and the -indices of `lines' indicate the order in which those lines were -encountered. The `END' rule simply prints out the lines, in order. +indices of `lines' indicate the order in which those lines are +encountered. The `END' rule simply prints out the lines, in order: # histsort.awk --- compact a shell history file - # Arnold Robbins, arnold@gnu.org, Public Domain - # May 1993 - # Thanks to Byron Rakitzis for the general idea { if (data[$0]++ == 0) @@ -13063,12 +15492,12 @@ encountered. The `END' rule simply prints out the lines, in order. } This program also provides a foundation for generating other useful -information. For example, using the following `print' satement in the -`END' rule would indicate how often a particular command was used. +information. For example, using the following `print' statement in the +`END' rule indicates how often a particular command is used: print data[lines[i]], lines[i] - This works because `data[$0]' was incremented each time a line was + This works because `data[$0]' is incremented each time a line is seen. @@ -13079,53 +15508,54 @@ Extracting Programs from Texinfo Source Files The nodes *Note A Library of `awk' Functions: Library Functions, and *Note Practical `awk' Programs: Sample Programs, are the top level -nodes for a large number of `awk' programs. If you wish to experiment +nodes for a large number of `awk' programs. If you want to experiment with these programs, it is tedious to have to type them in by hand. Here we present a program that can extract parts of a Texinfo input file into separate files. This Info file is written in Texinfo, the GNU project's document formatting language. A single Texinfo source file can be used to -produce both printed and on-line documentation. The Texinfo language -is described fully, starting with *Note Introduction: (texi)Top. +produce both printed and online documentation. The Texinfo language is +described fully, starting with *Note Top::. For our purposes, it is enough to know three things about Texinfo -input files. +input files: - * The "at" symbol, `@', is special in Texinfo, much like `\' in C or - `awk'. Literal `@' symbols are represented in Texinfo source - files as `@@'. + * The "at" symbol (`@') is special in Texinfo, much as the backslash + (`\') is in C or `awk'. Literal `@' symbols are represented in + Texinfo source files as `@@'. * Comments start with either `@c' or `@comment'. The file - extraction program will work by using special comments that start - at the beginning of a line. + extraction program works by using special comments that start at + the beginning of a line. - * Example text that should not be split across a page boundary is - bracketed between lines containing `@group' and `@end group' - commands. + * Lines containing `@group' and `@end group' commands bracket + example text that should not be split across a page boundary. + (Unfortunately, TeX isn't always smart enough to do things exactly + right and we have to give it some help.) The following program, `extract.awk', reads through a Texinfo source -file, and does two things, based on the special comments. Upon seeing +file and does two things, based on the special comments. Upon seeing `@c system ...', it runs a command, by extracting the command text from the control line and passing it on to the `system' function (*note -Built-in Functions for Input/Output: I/O Functions.). Upon seeing `@c -file FILENAME', each subsequent line is sent to the file FILENAME, -until `@c endfile' is encountered. The rules in `extract.awk' will -match either `@c' or `@comment' by letting the `omment' part be -optional. Lines containing `@group' and `@end group' are simply -removed. `extract.awk' uses the `join' library function (*note Merging -an Array Into a String: Join Function.). - - The example programs in the on-line Texinfo source for `Effective -AWK Programming' (`gawk.texi') have all been bracketed inside `file', -and `endfile' lines. The `gawk' distribution uses a copy of +Input/Output Functions: I/O Functions.). Upon seeing `@c file +FILENAME', each subsequent line is sent to the file FILENAME, until `@c +endfile' is encountered. The rules in `extract.awk' match either `@c' +or `@comment' by letting the `omment' part be optional. Lines +containing `@group' and `@end group' are simply removed. `extract.awk' +uses the `join' library function (*note Merging an Array into a String: +Join Function.). + + The example programs in the online Texinfo source for `GAWK: +Effective AWK Programming' (`gawk.texi') have all been bracketed inside +`file' and `endfile' lines. The `gawk' distribution uses a copy of `extract.awk' to extract the sample programs and install many of them -in a standard directory, where `gawk' can find them. The Texinfo file +in a standard directory where `gawk' can find them. The Texinfo file looks something like this: ... - This program has a @code{BEGIN} block, - which prints a nice message: + This program has a @code{BEGIN} rule, + that prints a nice message: @example @c file examples/messages.awk @@ -13143,16 +15573,14 @@ looks something like this: ... `extract.awk' begins by setting `IGNORECASE' to one, so that mixed -upper-case and lower-case letters in the directives won't matter. +upper- and lowercase letters in the directives won't matter. - The first rule handles calling `system', checking that a command was -given (`NF' is at least three), and also checking that the command -exited with a zero exit status, signifying OK. + The first rule handles calling `system', checking that a command is +given (`NF' is at least three) and also checking that the command exits +with a zero exit status, signifying OK: # extract.awk --- extract files and run programs # from texinfo files - # Arnold Robbins, arnold@gnu.org, Public Domain, May 1993 - BEGIN { IGNORECASE = 1 } /^@c(omment)?[ \t]+system/ \ @@ -13176,34 +15604,32 @@ exited with a zero exit status, signifying OK. The variable `e' is used so that the function fits nicely on the screen. The second rule handles moving data into files. It verifies that a -file name was given in the directive. If the file named is not the -current file, then the current file is closed. This means that an `@c -endfile' was not given for that file. (We should probably print a -diagnostic in this case, although at the moment we do not.) +file name is given in the directive. If the file named is not the +current file, then the current file is closed. Keeping the current file +open until a new file is encountered allows the use of the `>' +redirection for printing the contents, keeping open file management +simple. The `for' loop does the work. It reads lines using `getline' (*note Explicit Input with `getline': Getline.). For an unexpected end of file, it calls the `unexpected_eof' function. If the line is an "endfile" line, then it breaks out of the loop. If the line is an -`@group' or `@end group' line, then it ignores it, and goes on to the -next line. (These Texinfo control lines keep blocks of code together -on one page; unfortunately, TeX isn't always smart enough to do things -exactly right, and we have to give it some advice.) +`@group' or `@end group' line, then it ignores it and goes on to the +next line. Similarly, comments within examples are also ignored. Most of the work is in the following few lines. If the line has no -`@' symbols, it can be printed directly. Otherwise, each leading `@' -must be stripped off. - - To remove the `@' symbols, the line is split into separate elements -of the array `a', using the `split' function (*note Built-in Functions -for String Manipulation: String Functions.). Each element of `a' that -is empty indicates two successive `@' symbols in the original line. -For each two empty elements (`@@' in the original file), we have to add -back in a single `@' symbol. +`@' symbols, the program can print it directly. Otherwise, each +leading `@' must be stripped off. To remove the `@' symbols, the line +is split into separate elements of the array `a', using the `split' +function (*note String Manipulation Functions: String Functions.). The +`@' symbol is used as the separator character. Each element of `a' +that is empty indicates two successive `@' symbols in the original +line. For each two empty elements (`@@' in the original file), we have +to add a single `@' symbol back in. When the processing of the array is finished, `join' is called with the value of `SUBSEP', to rejoin the pieces back into a single line. -That line is then printed to the output file. +That line is then printed to the output file: /^@c(omment)?[ \t]+file/ \ { @@ -13225,6 +15651,8 @@ That line is then printed to the output file. break else if (line ~ /^@(end[ \t]+)?group/) continue + else if (line ~ /^@c(omment+)?[ \t]+/) + continue if (index(line, "@") == 0) { print line > curfile continue @@ -13246,19 +15674,17 @@ That line is then printed to the output file. An important thing to note is the use of the `>' redirection. Output done with `>' only opens the file once; it stays open and subsequent output is appended to the file (*note Redirecting Output of -`print' and `printf': Redirection.). This allows us to easily mix -program text and explanatory prose for the same sample source file (as -has been done here!) without any hassle. The file is only closed when -a new data file name is encountered, or at the end of the input file. +`print' and `printf': Redirection.). This makes it easy to mix program +text and explanatory prose for the same sample source file (as has been +done here!) without any hassle. The file is only closed when a new +data file name is encountered or at the end of the input file. Finally, the function `unexpected_eof' prints an appropriate error -message and then exits. - - The `END' rule handles the final cleanup, closing the open file. +message and then exits. The `END' rule handles the final cleanup, +closing the open file: - function unexpected_eof() - { - printf("%s:%d: unexpected EOF or error\n", \ + function unexpected_eof() { + printf("%s:%d: unexpected EOF or error\n", FILENAME, FNR) > "/dev/stderr" exit 1 } @@ -13275,32 +15701,26 @@ A Simple Stream Editor ---------------------- The `sed' utility is a "stream editor," a program that reads a -stream of data, makes changes to it, and passes the modified data on. -It is often used to make global changes to a large file, or to a stream -of data generated by a pipeline of commands. - - While `sed' is a complicated program in its own right, its most -common use is to perform global substitutions in the middle of a -pipeline: +stream of data, makes changes to it, and passes it on. It is often +used to make global changes to a large file or to a stream of data +generated by a pipeline of commands. While `sed' is a complicated +program in its own right, its most common use is to perform global +substitutions in the middle of a pipeline: command1 < orig.data | sed 's/old/new/g' | command2 > result - Here, the `s/old/new/g' tells `sed' to look for the regexp `old' on -each input line, and replace it with the text `new', globally (i.e. all -the occurrences on a line). This is similar to `awk''s `gsub' function -(*note Built-in Functions for String Manipulation: String Functions.). + Here, `s/old/new/g' tells `sed' to look for the regexp `old' on each +input line and globally replace it with the text `new', (i.e., all the +occurrences on a line). This is similar to `awk''s `gsub' function +(*note String Manipulation Functions: String Functions.). - The following program, `awksed.awk', accepts at least two command -line arguments; the pattern to look for and the text to replace it -with. Any additional arguments are treated as data file names to -process. If none are provided, the standard input is used. + The following program, `awksed.awk', accepts at least two +command-line arguments: the pattern to look for and the text to replace +it with. Any additional arguments are treated as data file names to +process. If none are provided, the standard input is used: # awksed.awk --- do s/foo/bar/g using just print # Thanks to Michael Brennan for the idea - - # Arnold Robbins, arnold@gnu.org, Public Domain - # August 1995 - function usage() { print "usage: awksed pat repl [files...]" > "/dev/stderr" @@ -13327,37 +15747,33 @@ process. If none are provided, the standard input is used. print } - The program relies on `gawk''s ability to have `RS' be a regexp and -on the setting of `RT' to the actual text that terminated the record -(*note How Input is Split into Records: Records.). + The program relies on `gawk''s ability to have `RS' be a regexp, as +well as on the setting of `RT' to the actual text that terminates the +record (*note How Input Is Split into Records: Records.). - The idea is to have `RS' be the pattern to look for. `gawk' will -automatically set `$0' to the text between matches of the pattern. -This is text that we wish to keep, unmodified. Then, by setting `ORS' -to the replacement text, a simple `print' statement will output the -text we wish to keep, followed by the replacement text. + The idea is to have `RS' be the pattern to look for. `gawk' +automatically sets `$0' to the text between matches of the pattern. +This is text that we want to keep, unmodified. Then, by setting `ORS' +to the replacement text, a simple `print' statement outputs the text we +want to keep, followed by the replacement text. There is one wrinkle to this scheme, which is what to do if the last -record doesn't end with text that matches `RS'? Using a `print' +record doesn't end with text that matches `RS'. Using a `print' statement unconditionally prints the replacement text, which is not -correct. - - However, if the file did not end in text that matches `RS', `RT' -will be set to the null string. In this case, we can print `$0' using +correct. However, if the file did not end in text that matches `RS', +`RT' is set to the null string. In this case, we can print `$0' using `printf' (*note Using `printf' Statements for Fancier Printing: Printf.). The `BEGIN' rule handles the setup, checking for the right number of -arguments, and calling `usage' if there is a problem. Then it sets `RS' -and `ORS' from the command line arguments, and sets `ARGV[1]' and -`ARGV[2]' to the null string, so that they will not be treated as file -names (*note Using `ARGC' and `ARGV': ARGC and ARGV.). - - The `usage' function prints an error message and exits. +arguments and calling `usage' if there is a problem. Then it sets `RS' +and `ORS' from the command-line arguments and sets `ARGV[1]' and +`ARGV[2]' to the null string, so that they are not treated as file names +(*note Using `ARGC' and `ARGV': ARGC and ARGV.). - Finally, the single rule handles the printing scheme outlined above, -using `print' or `printf' as appropriate, depending upon the value of -`RT'. + The `usage' function prints an error message and exits. Finally, +the single rule handles the printing scheme outlined above, using +`print' or `printf' as appropriate, depending upon the value of `RT'. File: gawk.info, Node: Igawk Program, Prev: Simple Sed, Up: Miscellaneous Programs @@ -13366,15 +15782,14 @@ An Easy Way to Use Library Functions ------------------------------------ Using library functions in `awk' can be very beneficial. It -encourages code re-use and the writing of general functions. Programs -are smaller, and therefore clearer. However, using library functions -is only easy when writing `awk' programs; it is painful when running -them, requiring multiple `-f' options. If `gawk' is unavailable, then -so too is the `AWKPATH' environment variable and the ability to put -`awk' functions into a library directory (*note Command Line Options: -Options.). - - It would be nice to be able to write programs like so: +encourages code reuse and the writing of general functions. Programs are +smaller and therefore clearer. However, using library functions is +only easy when writing `awk' programs; it is painful when running them, +requiring multiple `-f' options. If `gawk' is unavailable, then so too +is the `AWKPATH' environment variable and the ability to put `awk' +functions into a library directory (*note Command-Line Options: +Options.). It would be nice to be able to write programs in the +following manner: # library functions @include getopt.awk @@ -13389,16 +15804,16 @@ Options.). } The following program, `igawk.sh', provides this service. It -simulates `gawk''s searching of the `AWKPATH' variable, and also allows -"nested" includes; i.e. a file that has been included with `@include' -can contain further `@include' statements. `igawk' will make an effort -to only include files once, so that nested includes don't accidentally -include a library function twice. - - `igawk' should behave externally just like `gawk'. This means it -should accept all of `gawk''s command line arguments, including the +simulates `gawk''s searching of the `AWKPATH' variable and also allows +"nested" includes; i.e., a file that is included with `@include' can +contain further `@include' statements. `igawk' makes an effort to only +include files once, so that nested includes don't accidentally include +a library function twice. + + `igawk' should behave just like `gawk' externally. This means it +should accept all of `gawk''s command-line arguments, including the ability to have multiple source files specified via `-f', and the -ability to mix command line and library source files. +ability to mix command-line and library source files. The program is written using the POSIX Shell (`sh') command language. The way the program works is as follows: @@ -13407,16 +15822,16 @@ The way the program works is as follows: `awk' source code for later, when the expanded program is run. 2. For any arguments that do represent `awk' text, put the arguments - into a temporary file that will be expanded. There are two cases. + into a temporary file that will be expanded. There are two cases: a. Literal text, provided with `--source' or `--source='. This - text is just echoed directly. The `echo' program will - automatically supply a trailing newline. + text is just echoed directly. The `echo' program + automatically supplies a trailing newline. - b. File names provided with `-f'. We use a neat trick, and echo - `@include FILENAME' into the temporary file. Since the file - inclusion program will work the way `gawk' does, this will - get the text of the file included into the program at the + b. Source file names provided with `-f'. We use a neat trick + and echo `@include FILENAME' into the temporary file. Since + the file inclusion program works the way `gawk' does, this + gets the text of the file included into the program at the correct point. 3. Run an `awk' program (naturally) over the temporary file to expand @@ -13424,15 +15839,15 @@ The way the program works is as follows: temporary file. 4. Run the expanded program with `gawk' and any other original - command line arguments that the user supplied (such as the data + command-line arguments that the user supplied (such as the data file names). The initial part of the program turns on shell tracing if the first -argument was `debug'. Otherwise, a shell `trap' statement arranges to +argument is `debug'. Otherwise, a shell `trap' statement arranges to clean up any temporary files on program exit or upon an interrupt. - The next part loops through all the command line arguments. There -are several cases of interest. + The next part loops through all the command-line arguments. There +are several cases of interest: `--' This ends the arguments to `igawk'. Anything else should be @@ -13445,50 +15860,36 @@ are several cases of interest. programming trick. Don't worry about it if you are not familiar with `sh'.) -`-v' -`-F' +`-v, -F' These are saved and passed on to `gawk'. -`-f' -`--file' -`--file=' -`-Wfile=' +`-f, --file, --file=, -Wfile=' The file name is saved to the temporary file `/tmp/ig.s.$$' with an `@include' statement. The `sed' utility is used to remove the leading option part of the argument (e.g., `--file='). -`--source' -`--source=' -`-Wsource=' +`--source, --source=, -Wsource=' The source text is echoed into `/tmp/ig.s.$$'. -`--version' -`-Wversion' - `igawk' prints its version number, and runs `gawk --version' to - get the `gawk' version information, and then exits. - - If none of `-f', `--file', `-Wfile', `--source', or `-Wsource', were -supplied, then the first non-option argument should be the `awk' -program. If there are no command line arguments left, `igawk' prints -an error message and exits. Otherwise, the first argument is echoed -into `/tmp/ig.s.$$'. +`--version, -Wversion' + `igawk' prints its version number, runs `gawk --version' to get + the `gawk' version information, and then exits. - In any case, after the arguments have been processed, `/tmp/ig.s.$$' -contains the complete text of the original `awk' program. + If none of the `-f', `--file', `-Wfile', `--source', or `-Wsource' +arguments are supplied, then the first non-option argument should be +the `awk' program. If there are no command-line arguments left, +`igawk' prints an error message and exits. Otherwise, the first +argument is echoed into `/tmp/ig.s.$$'. In any case, after the +arguments have been processed, `/tmp/ig.s.$$' contains the complete +text of the original `awk' program. The `$$' in `sh' represents the current process ID number. It is often used in shell programs to generate unique temporary file names. This allows multiple users to run `igawk' without worrying that the -temporary file names will clash. - - Here's the program: +temporary file names will clash. The program is as follows: #! /bin/sh - # igawk --- like gawk but do @include processing - # Arnold Robbins, arnold@gnu.org, Public Domain - # July 1993 - if [ "$1" = debug ] then set -x @@ -13522,15 +15923,15 @@ temporary file names will clash. f=`echo "$1" | sed 's/-.file=//'` echo @include "$f" >> /tmp/ig.s.$$ ;; - -?file) # get arg, $2 + -?file) # get arg, $2 echo @include "$2" >> /tmp/ig.s.$$ shift;; - -?source=*) # -Wsource or --source + -?source=*) # -Wsource or --source t=`echo "$1" | sed 's/-.source=//'` echo "$t" >> /tmp/ig.s.$$ ;; - -?source) # get arg, $2 + -?source) # get arg, $2 echo "$2" >> /tmp/ig.s.$$ shift;; @@ -13539,7 +15940,7 @@ temporary file names will clash. gawk --version exit 0 ;; - -[W-]*) opts="$opts '$1'" ;; + -[W-]*) opts="$opts '$1'" ;; *) break;; esac @@ -13561,10 +15962,10 @@ temporary file names will clash. # at this point, /tmp/ig.s.$$ has the program The `awk' program to process `@include' directives reads through the -program, one line at a time using `getline' (*note Explicit Input with +program, one line at a time, using `getline' (*note Explicit Input with `getline': Getline.). The input file names and `@include' statements are managed using a stack. As each `@include' is encountered, the -current file name is "pushed" onto the stack, and the file named in the +current file name is "pushed" onto the stack and the file named in the `@include' directive becomes the current file name. As each file is finished, the stack is "popped," and the previous input file becomes the current input file again. The process is started by making the @@ -13575,10 +15976,10 @@ file. It simulates `gawk''s behavior when searching the `AWKPATH' environment variable (*note The `AWKPATH' Environment Variable: AWKPATH Variable.). If a file name has a `/' in it, no path search is done. Otherwise, the file name is concatenated with the name of each -directory in the path, and an attempt is made to open the generated file -name. The only way in `awk' to test if a file can be read is to go -ahead and try to read it with `getline'; that is what `pathto' does.(1) -If the file can be read, it is closed, and the file name is returned. +directory in the path, and an attempt is made to open the generated +file name. The only way to test if a file can be read in `awk' is to go +ahead and try to read it with `getline'; this is what `pathto' does.(1) +If the file can be read, it is closed and the file name is returned: gawk -- ' # process @include directives @@ -13602,7 +16003,7 @@ If the file can be read, it is closed, and the file name is returned. The main program is contained inside one `BEGIN' rule. The first thing it does is set up the `pathlist' array that `pathto' uses. After splitting the path on `:', null elements are replaced with `"."', which -represents the current directory. +represents the current directory: BEGIN { path = ENVIRON["AWKPATH"] @@ -13615,21 +16016,19 @@ represents the current directory. The stack is initialized with `ARGV[1]', which will be `/tmp/ig.s.$$'. The main loop comes next. Input lines are read in succession. Lines that do not start with `@include' are printed -verbatim. +verbatim. If the line does start with `@include', the file name is in +`$2'. `pathto' is called to generate the full path. If it cannot, +then we print an error message and continue. - If the line does start with `@include', the file name is in `$2'. -`pathto' is called to generate the full path. If it could not, then we -print an error message and continue. - - The next thing to check is if the file has been included already. -The `processed' array is indexed by the full file name of each included -file, and it tracks this information for us. If the file has been -seen, a warning message is printed. Otherwise, the new file name is -pushed onto the stack and processing continues. + The next thing to check is if the file is included already. The +`processed' array is indexed by the full file name of each included +file and it tracks this information for us. If the file is seen again, +a warning message is printed. Otherwise, the new file name is pushed +onto the stack and processing continues. Finally, when `getline' encounters the end of the input file, the file is closed and the stack is popped. When `stackptr' is less than -zero, the program is done. +zero, the program is done: stackptr = 0 input[stackptr] = ARGV[1] # ARGV[1] is first file @@ -13642,43 +16041,44 @@ zero, the program is done. } fpath = pathto($2) if (fpath == "") { - printf("igawk:%s:%d: cannot find %s\n", \ + printf("igawk:%s:%d: cannot find %s\n", input[stackptr], FNR, $2) > "/dev/stderr" continue } if (! (fpath in processed)) { processed[fpath] = input[stackptr] - input[++stackptr] = fpath + input[++stackptr] = fpath # push onto stack } else - print $2, "included in", input[stackptr], \ - "already included in", \ + print $2, "included in", input[stackptr], + "already included in", processed[fpath] > "/dev/stderr" } close(input[stackptr]) } }' /tmp/ig.s.$$ > /tmp/ig.e.$$ - The last step is to call `gawk' with the expanded program and the -original options and command line arguments that the user supplied. -`gawk''s exit status is passed back on to `igawk''s calling program. + The last step is to call `gawk' with the expanded program, along +with the original options and command-line arguments that the user +supplied. `gawk''s exit status is passed back on to `igawk''s calling +program: eval gawk -f /tmp/ig.e.$$ $opts -- "$@" exit $? This version of `igawk' represents my third attempt at this program. -There are three key simplifications that made the program work better. +There are three key simplifications that make the program work better: - 1. Using `@include' even for the files named with `-f' makes building + * Using `@include' even for the files named with `-f' makes building the initial collected `awk' program much simpler; all the `@include' processing can be done once. - 2. The `pathto' function doesn't try to save the line read with + * The `pathto' function doesn't try to save the line read with `getline' when testing for the file's accessibility. Trying to save this line for use with the main program complicates things considerably. - 3. Using a `getline' loop in the `BEGIN' rule does it all in one + * Using a `getline' loop in the `BEGIN' rule does it all in one place. It is not necessary to call out to a separate loop for processing nested `@include' statements. @@ -13694,15 +16094,15 @@ there is no real reason to build `@include' processing into `gawk' itself. As an additional example of this, consider the idea of having two -files in a directory in the search path. +files in a directory in the search path: `default.awk' - This file would contain a set of default library functions, such - as `getopt' and `assert'. + This file contains a set of default library functions, such as + `getopt' and `assert'. `site.awk' - This file would contain library functions that are specific to a - site or installation, i.e. locally developed functions. Having a + This file contains library functions that are specific to a site or + installation; i.e., locally developed functions. Having a separate file allows `default.awk' to change with new `gawk' releases, without requiring the system administrator to update it each time by adding the local functions. @@ -13716,22 +16116,23 @@ for the desired library functions. ---------- Footnotes ---------- (1) On some very old versions of `awk', the test `getline junk < t' -can loop forever if the file exists but is empty. Caveat Emptor. +can loop forever if the file exists but is empty. Caveat emptor. -File: gawk.info, Node: Language History, Next: Gawk Summary, Prev: Sample Programs, Up: Top +File: gawk.info, Node: Language History, Next: Installation, Prev: Sample Programs, Up: Top The Evolution of the `awk' Language *********************************** This Info file describes the GNU implementation of `awk', which -follows the POSIX specification. Many `awk' users are only familiar -with the original `awk' implementation in Version 7 Unix. (This -implementation was the basis for `awk' in Berkeley Unix, through -4.3-Reno. The 4.4 release of Berkeley Unix uses `gawk' 2.15.2 for its -version of `awk'.) This chapter briefly describes the evolution of the -`awk' language, with cross references to other parts of the Info file -where you can find more information. +follows the POSIX specification. Many long-time `awk' users learned +`awk' programming with the original `awk' implementation in Version 7 +Unix. (This implementation was the basis for `awk' in Berkeley Unix, +through 4.3-Reno. Subsequent versions of Berkeley Unix, and systems +derived from 4.4BSD-Lite, use various versions of `gawk' for their +`awk'.) This major node briefly describes the evolution of the `awk' +language, with cross references to other parts of the Info file where +you can find more information. * Menu: @@ -13744,37 +16145,38 @@ where you can find more information. version of `awk'. * POSIX/GNU:: The extensions in `gawk' not in POSIX `awk'. +* Contributors:: The major contributors to `gawk'. File: gawk.info, Node: V7/SVR3.1, Next: SVR4, Prev: Language History, Up: Language History -Major Changes between V7 and SVR3.1 +Major Changes Between V7 and SVR3.1 =================================== The `awk' language evolved considerably between the release of -Version 7 Unix (1978) and the new version first made generally -available in System V Release 3.1 (1987). This section summarizes the -changes, with cross-references to further details. +Version 7 Unix (1978) and the new version that was first made generally +available in System V Release 3.1 (1987). This minor node summarizes +the changes, with cross-references to further details: * The requirement for `;' to separate rules on a line (*note `awk' Statements Versus Lines: Statements/Lines.). - * User-defined functions, and the `return' statement (*note - User-defined Functions: User-defined.). + * User-defined functions and the `return' statement (*note + User-Defined Functions: User-defined.). * The `delete' statement (*note The `delete' Statement: Delete.). * The `do'-`while' statement (*note The `do'-`while' Statement: Do Statement.). - * The built-in functions `atan2', `cos', `sin', `rand' and `srand' - (*note Numeric Built-in Functions: Numeric Functions.). + * The built-in functions `atan2', `cos', `sin', `rand', and `srand' + (*note Numeric Functions::). - * The built-in functions `gsub', `sub', and `match' (*note Built-in - Functions for String Manipulation: String Functions.). + * The built-in functions `gsub', `sub', and `match' (*note String + Manipulation Functions: String Functions.). - * The built-in functions `close', and `system' (*note Built-in - Functions for Input/Output: I/O Functions.). + * The built-in functions `close' and `system' (*note Input/Output + Functions: I/O Functions.). * The `ARGC', `ARGV', `FNR', `RLENGTH', `RSTART', and `SUBSEP' built-in variables (*note Built-in Variables::). @@ -13790,17 +16192,17 @@ changes, with cross-references to further details. programs (*note Operator Precedence (How Operators Nest): Precedence.). - * Regexps as the value of `FS' (*note Specifying How Fields are - Separated: Field Separators.), and as the third argument to the - `split' function (*note Built-in Functions for String - Manipulation: String Functions.). + * Regexps as the value of `FS' (*note Specifying How Fields Are + Separated: Field Separators.) and as the third argument to the + `split' function (*note String Manipulation Functions: String + Functions.). * Dynamic regexps as operands of the `~' and `!~' operators (*note How to Use Regular Expressions: Regexp Usage.). * The escape sequences `\b', `\f', and `\r' (*note Escape Sequences::). (Some vendors have updated their old versions of - `awk' to recognize `\r', `\b', and `\f', but this is not something + `awk' to recognize `\b', `\f', and `\r', but this is not something you can rely on.) * Redirection of input for the `getline' function (*note Explicit @@ -13809,37 +16211,37 @@ changes, with cross-references to further details. * Multiple `BEGIN' and `END' rules (*note The `BEGIN' and `END' Special Patterns: BEGIN/END.). - * Multi-dimensional arrays (*note Multi-dimensional Arrays: + * Multidimensional arrays (*note Multidimensional Arrays: Multi-dimensional.). File: gawk.info, Node: SVR4, Next: POSIX, Prev: V7/SVR3.1, Up: Language History -Changes between SVR3.1 and SVR4 +Changes Between SVR3.1 and SVR4 =============================== - The System V Release 4 version of Unix `awk' added these features -(some of which originated in `gawk'): + The System V Release 4 (1989) version of Unix `awk' added these +features (some of which originated in `gawk'): * The `ENVIRON' variable (*note Built-in Variables::). - * Multiple `-f' options on the command line (*note Command Line + * Multiple `-f' options on the command line (*note Command-Line Options: Options.). * The `-v' option for assigning variables before program execution - begins (*note Command Line Options: Options.). + begins (*note Command-Line Options: Options.). - * The `--' option for terminating command line options. + * The `--' option for terminating command-line options. * The `\a', `\v', and `\x' escape sequences (*note Escape Sequences::). * A defined return value for the `srand' built-in function (*note - Numeric Built-in Functions: Numeric Functions.). + Numeric Functions::). * The `toupper' and `tolower' built-in string functions for case - translation (*note Built-in Functions for String Manipulation: - String Functions.). + translation (*note String Manipulation Functions: String + Functions.). * A cleaner specification for the `%c' format-control letter in the `printf' function (*note Format-Control Letters: Control Letters.). @@ -13848,26 +16250,31 @@ Changes between SVR3.1 and SVR4 (`"%*.*d"') in the argument list of the `printf' function (*note Format-Control Letters: Control Letters.). - * The use of regexp constants such as `/foo/' as expressions, where + * The use of regexp constants, such as `/foo/', as expressions, where they are equivalent to using the matching operator, as in `$0 ~ /foo/' (*note Using Regular Expression Constants: Using Constant Regexps.). + * Processing of escape sequences inside command-line variable + assignments (*note Assigning Variables on the Command Line: + Assignment Options.). + File: gawk.info, Node: POSIX, Next: BTL, Prev: SVR4, Up: Language History -Changes between SVR4 and POSIX `awk' +Changes Between SVR4 and POSIX `awk' ==================================== - The POSIX Command Language and Utilities standard for `awk' + The POSIX Command Language and Utilities standard for `awk' (1992) introduced the following changes into the language: - * The use of `-W' for implementation-specific options. + * The use of `-W' for implementation-specific options (*note + Command-Line Options: Options.). * The use of `CONVFMT' for controlling the conversion of numbers to strings (*note Conversion of Strings and Numbers: Conversion.). - * The concept of a numeric string, and tighter comparison rules to go + * The concept of a numeric string and tighter comparison rules to go with it (*note Variable Typing and Comparison Expressions: Typing and Comparison.). @@ -13881,21 +16288,24 @@ standard: Sequences::). * Newlines do not act as whitespace to separate fields when `FS' is - equal to a single space. + equal to a single space (*note Examining Fields: Fields.). + + * Newlines are not allowed after `?' or `:' (*note Conditional + Expressions: Conditional Exp.). * The synonym `func' for the keyword `function' is not recognized (*note Function Definition Syntax: Definition Syntax.). * The operators `**' and `**=' cannot be used in place of `^' and - `^=' (*note Arithmetic Operators: Arithmetic Ops., and also *note - Assignment Expressions: Assignment Ops.). + `^=' (*note Arithmetic Operators: Arithmetic Ops., and *Note + Assignment Expressions: Assignment Ops). * Specifying `-Ft' on the command line does not set the value of - `FS' to be a single tab character (*note Specifying How Fields are + `FS' to be a single tab character (*note Specifying How Fields Are Separated: Field Separators.). - * The `fflush' built-in function is not supported (*note Built-in - Functions for Input/Output: I/O Functions.). + * The `fflush' built-in function is not supported (*note + Input/Output Functions: I/O Functions.). File: gawk.info, Node: BTL, Next: POSIX/GNU, Prev: POSIX, Up: Language History @@ -13904,127 +16314,158 @@ Extensions in the Bell Laboratories `awk' ========================================= Brian Kernighan, one of the original designers of Unix `awk', has -made his version available via anonymous `ftp' (*note Other Freely -Available `awk' Implementations: Other Versions.). This section +made his version available via his home page (*note Other Freely +Available `awk' Implementations: Other Versions.). This minor node describes extensions in his version of `awk' that are not in POSIX `awk'. - * The `-mf NNN' and `-mr NNN' command line options to set the - maximum number of fields, and the maximum record size, respectively - (*note Command Line Options: Options.). + * The `-mf N' and `-mr N' command-line options to set the maximum + number of fields and the maximum record size, respectively (*note + Command-Line Options: Options.). As a side note, his `awk' no + longer needs these options; it continues to accept them to avoid + breaking old programs. * The `fflush' built-in function for flushing buffered output (*note - Built-in Functions for Input/Output: I/O Functions.). + Input/Output Functions: I/O Functions.). + + * The `**' and `**=' operators (*note Arithmetic Operators: + Arithmetic Ops. and *Note Assignment Expressions: Assignment Ops). + * The use of `func' as an abbreviation for `function' (*note + Function Definition Syntax: Definition Syntax.). + + + The Bell Laboratories `awk' also incorporates the following +extensions, originally developed for `gawk': + + * The `\x' escape sequence (*note Escape Sequences::). + + * The `/dev/stdin', `/dev/stdout', and `/dev/stderr' special files + (*note Special File Names in `gawk': Special Files.). + + * The ability for `FS' and for the third argument to `split' to be + null strings (*note Making Each Character a Separate Field: Single + Character Fields.). + + * The `nextfile' statement (*note Using `gawk''s `nextfile' + Statement: Nextfile Statement.). + + * The ability to delete all of an array at once with `delete ARRAY' + (*note The `delete' Statement: Delete.). -File: gawk.info, Node: POSIX/GNU, Prev: BTL, Up: Language History +File: gawk.info, Node: POSIX/GNU, Next: Contributors, Prev: BTL, Up: Language History Extensions in `gawk' Not in POSIX `awk' ======================================= - The GNU implementation, `gawk', adds a number of features. This -sections lists them in the order they were added to `gawk'. They can -all be disabled with either the `--traditional' or `--posix' options -(*note Command Line Options: Options.). + The GNU implementation, `gawk', adds a large number of features. +This minor node lists them in the order they were added to `gawk'. +They can all be disabled with either the `--traditional' or `--posix' +options (*note Command-Line Options: Options.). - Version 2.10 of `gawk' introduced these features: + Version 2.10 of `gawk' introduced the following features: * The `AWKPATH' environment variable for specifying a path search for - the `-f' command line option (*note Command Line Options: + the `-f' command-line option (*note Command-Line Options: Options.). - * The `IGNORECASE' variable and its effects (*note Case-sensitivity + * The `IGNORECASE' variable and its effects (*note Case Sensitivity in Matching: Case-sensitivity.). - * The `/dev/stdin', `/dev/stdout', `/dev/stderr', and `/dev/fd/N' - file name interpretation (*note Special File Names in `gawk': - Special Files.). + * The `/dev/stdin', `/dev/stdout', `/dev/stderr' and `/dev/fd/N' + special file names (*note Special File Names in `gawk': Special + Files.). - Version 2.13 of `gawk' introduced these features: + Version 2.13 of `gawk' introduced the following features: * The `FIELDWIDTHS' variable and its effects (*note Reading - Fixed-width Data: Constant Size.). + Fixed-Width Data: Constant Size.). * The `systime' and `strftime' built-in functions for obtaining and - printing time stamps (*note Functions for Dealing with Time - Stamps: Time Functions.). + printing timestamps (*note Using `gawk''s Timestamp Functions: + Time Functions.). - * The `-W lint' option to provide source code and run time error and - portability checking (*note Command Line Options: Options.). + * The `-W lint' option to provide error and portability checking for + both the source code and at runtime (*note Command-Line Options: + Options.). - * The `-W compat' option to turn off these extensions (*note Command - Line Options: Options.). + * The `-W compat' option to turn off the GNU extensions (*note + Command-Line Options: Options.). - * The `-W posix' option for full POSIX compliance (*note Command - Line Options: Options.). + * The `-W posix' option for full POSIX compliance (*note + Command-Line Options: Options.). - Version 2.14 of `gawk' introduced these features: + Version 2.14 of `gawk' introduced the following feature: * The `next file' statement for skipping to the next data file - (*note The `nextfile' Statement: Nextfile Statement.). + (*note Using `gawk''s `nextfile' Statement: Nextfile Statement.). - Version 2.15 of `gawk' introduced these features: + Version 2.15 of `gawk' introduced the following features: - * The `ARGIND' variable, that tracks the movement of `FILENAME' + * The `ARGIND' variable, which tracks the movement of `FILENAME' through `ARGV' (*note Built-in Variables::). - * The `ERRNO' variable, that contains the system error message when - `getline' returns -1, or when `close' fails (*note Built-in + * The `ERRNO' variable, which contains the system error message when + `getline' returns -1 or when `close' fails (*note Built-in Variables::). - * The ability to use GNU-style long named options that start with - `--' (*note Command Line Options: Options.). - - * The `--source' option for mixing command line and library file - source code (*note Command Line Options: Options.). - * The `/dev/pid', `/dev/ppid', `/dev/pgrpid', and `/dev/user' file name interpretation (*note Special File Names in `gawk': Special Files.). - Version 3.0 of `gawk' introduced these features: + * The ability to delete all of an array at once with `delete ARRAY' + (*note The `delete' Statement: Delete.). - * The `next file' statement became `nextfile' (*note The `nextfile' - Statement: Nextfile Statement.). + * The ability to use GNU-style long-named options that start with + `--' (*note Command-Line Options: Options.). - * The `--lint-old' option to warn about constructs that are not - available in the original Version 7 Unix version of `awk' (*note - Major Changes between V7 and SVR3.1: V7/SVR3.1.). + * The `--source' option for mixing command-line and library file + source code (*note Command-Line Options: Options.). - * The `--traditional' option was added as a better name for - `--compat' (*note Command Line Options: Options.). + Version 3.0 of `gawk' introduced the following features: - * The ability for `FS' to be a null string, and for the third - argument to `split' to be the null string (*note Making Each - Character a Separate Field: Single Character Fields.). + * `IGNORECASE' changed, now applying to string comparison as well as + regexp operations (*note Case Sensitivity in Matching: + Case-sensitivity.). - * The ability for `RS' to be a regexp (*note How Input is Split into - Records: Records.). + * The `RT' variable that contains the input text that matched `RS' + (*note How Input Is Split into Records: Records.). - * The `RT' variable (*note How Input is Split into Records: - Records.). + * Full support for both POSIX and GNU regexps (*note Regular + Expressions: Regexp.). * The `gensub' function for more powerful text manipulation (*note - Built-in Functions for String Manipulation: String Functions.). + String Manipulation Functions: String Functions.). * The `strftime' function acquired a default time format, allowing - it to be called with no arguments (*note Functions for Dealing - with Time Stamps: Time Functions.). + it to be called with no arguments (*note Using `gawk''s Timestamp + Functions: Time Functions.). - * Full support for both POSIX and GNU regexps (*note Regular - Expressions: Regexp.). + * The ability for `FS' and for the third argument to `split' to be + null strings (*note Making Each Character a Separate Field: Single + Character Fields.). + + * The ability for `RS' to be a regexp (*note How Input Is Split into + Records: Records.). + + * The `next file' statement became `nextfile' (*note Using `gawk''s + `nextfile' Statement: Nextfile Statement.). + + * The `--lint-old' option to warn about constructs that are not + available in the original Version 7 Unix version of `awk' (*note + Major Changes Between V7 and SVR3.1: V7/SVR3.1.). + + * The `-m' option and the `fflush' function from the Bell + Laboratories research version of `awk' (*note Command-Line + Options: Options.; also *note Input/Output Functions: I/O + Functions.). * The `--re-interval' option to provide interval expressions in regexps (*note Regular Expression Operators: Regexp Operators.). - * `IGNORECASE' changed, now applying to string comparison as well as - regexp operations (*note Case-sensitivity in Matching: - Case-sensitivity.). - - * The `-m' option and the `fflush' function from the Bell Labs - research version of `awk' (*note Command Line Options: Options.; - also *note Built-in Functions for Input/Output: I/O Functions.). + * The `--traditional' option was added as a better name for + `--compat' (*note Command-Line Options: Options.). * The use of GNU Autoconf to control the configuration process (*note Compiling `gawk' for Unix: Quick Installation.). @@ -14033,1295 +16474,202 @@ all be disabled with either the `--traditional' or `--posix' options Installation.). - -File: gawk.info, Node: Gawk Summary, Next: Installation, Prev: Language History, Up: Top + Version 3.1 of `gawk' introduced the following features: -`gawk' Summary -************** + * The `BINMODE' special variable for non-POSIX systems, which allows + binary I/O for input and/or output files (*note Using `gawk' on PC + Operating Systems: PC Using.). - This appendix provides a brief summary of the `gawk' command line -and the `awk' language. It is designed to serve as "quick reference." -It is therefore terse, but complete. + * The `LINT' special variable, which dynamically controls lint + warnings (*note Built-in Variables::). -* Menu: + * The `PROCINFO' array for providing process-related information + (*note Built-in Variables::). -* Command Line Summary:: Recapitulation of the command line. -* Language Summary:: A terse review of the language. -* Variables/Fields:: Variables, fields, and arrays. -* Rules Summary:: Patterns and Actions, and their component - parts. -* Actions Summary:: Quick overview of actions. -* Functions Summary:: Defining and calling functions. -* Historical Features:: Some undocumented but supported ``features''. + * The `TEXTDOMAIN' special variable for setting an application's + internationalization text domain (*note Built-in Variables::, and + *Note Internationalization with `gawk': Internationalization). - -File: gawk.info, Node: Command Line Summary, Next: Language Summary, Prev: Gawk Summary, Up: Gawk Summary + * The ability to use octal and hexadecimal constants in `awk' + program source code (*note Octal and Hexadecimal Numbers: + Non-decimal-numbers.). -Command Line Options Summary -============================ + * The `|&' operator for two-way I/O to a coprocess (*note Two-Way + Communications with Another Process: Two-way I/O.). - The command line consists of options to `gawk' itself, the `awk' -program text (if not supplied via the `-f' option), and values to be -made available in the `ARGC' and `ARGV' predefined `awk' variables: + * The `/inet' special files for TCP/IP networking using `|&' (*note + Using `gawk' for Network Programming: TCP/IP Networking.). - gawk [POSIX OR GNU STYLE OPTIONS] -f SOURCE-FILE [`--'] FILE ... - gawk [POSIX OR GNU STYLE OPTIONS] [`--'] 'PROGRAM' FILE ... + * The optional second argument to `close' that allows closing one end + of a two-way pipe to a coprocess (*note Two-Way Communications + with Another Process: Two-way I/O.). - The options that `gawk' accepts are: + * The optional third argument to the `match' function for capturing + text-matching subexpressions within a regexp (*note String + Manipulation Functions: String Functions.). -`-F FS' -`--field-separator FS' - Use FS for the input field separator (the value of the `FS' - predefined variable). + * Positional specifiers in `printf' formats for making translations + easier (*note Rearranging `printf' Arguments: Printf Ordering.). -`-f PROGRAM-FILE' -`--file PROGRAM-FILE' - Read the `awk' program source from the file PROGRAM-FILE, instead - of from the first command line argument. + * The `asort' function for sorting arrays (*note Sorting Array + Values and Indices with `gawk': Array Sorting.). -`-mf NNN' -`-mr NNN' - The `f' flag sets the maximum number of fields, and the `r' flag - sets the maximum record size. These options are ignored by - `gawk', since `gawk' has no predefined limits; they are only for - compatibility with the Bell Labs research version of Unix `awk'. + * The `bindtextdomain' and `dcgettext' functions for + internationalization (*note Internationalizing `awk' Programs: + Programmer i18n.). -`-v VAR=VAL' -`--assign VAR=VAL' - Assign the variable VAR the value VAL before program execution - begins. + * The `extension' built-in function and the ability to add new + built-in functions dynamically (*note Adding New Built-in + Functions to `gawk': Dynamic Extensions.). -`-W traditional' -`-W compat' -`--traditional' -`--compat' - Use compatibility mode, in which `gawk' extensions are turned off. + * The `mktime' built-in function for creating timestamps (*note + Using `gawk''s Timestamp Functions: Time Functions.). -`-W copyleft' -`-W copyright' -`--copyleft' -`--copyright' - Print the short version of the General Public License on the - standard output, and exit. This option may disappear in a future - version of `gawk'. + * The `and', `or', `xor', `compl', `lshift', `rshift', and + `strtonum' built-in functions (*note Using `gawk''s Bit + Manipulation Functions: Bitwise Functions.). -`-W help' -`-W usage' -`--help' -`--usage' - Print a relatively short summary of the available options on the - standard output, and exit. + * The support for `next file' as two words was removed completely + (*note Using `gawk''s `nextfile' Statement: Nextfile Statement.). -`-W lint' -`--lint' - Give warnings about dubious or non-portable `awk' constructs. + * The `--dump-variables' option to print a list of all global + variables (*note Command-Line Options: Options.). -`-W lint-old' -`--lint-old' - Warn about constructs that are not available in the original - Version 7 Unix version of `awk'. + * The `--gen-po' command-line option and the use of a leading + underscore to mark strings that should be translated (*note + Extracting Marked Strings: String Extraction.). -`-W posix' -`--posix' - Use POSIX compatibility mode, in which `gawk' extensions are - turned off and additional restrictions apply. + * The `--non-decimal-data' option to allow non-decimal input data + (*note Allowing Non-Decimal Input Data: Non-decimal Data.). -`-W re-interval' -`--re-interval' - Allow interval expressions (*note Regular Expression Operators: - Regexp Operators.), in regexps. + * The `--profile' option and `pgawk', the profiling version of + `gawk', for producing execution profiles of `awk' programs (*note + Profiling Your `awk' Programs: Profiling.). -`-W source=PROGRAM-TEXT' -`--source PROGRAM-TEXT' - Use PROGRAM-TEXT as `awk' program source code. This option allows - mixing command line source code with source code from files, and is - particularly useful for mixing command line programs with library - functions. + * The `--enable-portals' configuration option to enable special + treatment of pathnames that begin with `/p' as BSD portals (*note + Using `gawk' with BSD Portals: Portal Files.). -`-W version' -`--version' - Print version information for this particular copy of `gawk' on - the error output. - -`--' - Signal the end of options. This is useful to allow further - arguments to the `awk' program itself to start with a `-'. This - is mainly for consistency with POSIX argument parsing conventions. - - Any other options are flagged as invalid, but are otherwise ignored. -*Note Command Line Options: Options, for more details. - - -File: gawk.info, Node: Language Summary, Next: Variables/Fields, Prev: Command Line Summary, Up: Gawk Summary - -Language Summary -================ - - An `awk' program consists of a sequence of zero or more -pattern-action statements and optional function definitions. One or -the other of the pattern and action may be omitted. - - PATTERN { ACTION STATEMENTS } - PATTERN - { ACTION STATEMENTS } - - function NAME(PARAMETER LIST) { ACTION STATEMENTS } - - `gawk' first reads the program source from the PROGRAM-FILE(s), if -specified, or from the first non-option argument on the command line. -The `-f' option may be used multiple times on the command line. `gawk' -reads the program text from all the PROGRAM-FILE files, effectively -concatenating them in the order they are specified. This is useful for -building libraries of `awk' functions, without having to include them -in each new `awk' program that uses them. To use a library function in -a file from a program typed in on the command line, specify `--source -'PROGRAM'', and type your program in between the single quotes. *Note -Command Line Options: Options. - - The environment variable `AWKPATH' specifies a search path to use -when finding source files named with the `-f' option. The default -path, which is `.:/usr/local/share/awk'(1) is used if `AWKPATH' is not -set. If a file name given to the `-f' option contains a `/' character, -no path search is performed. *Note The `AWKPATH' Environment Variable: -AWKPATH Variable. - - `gawk' compiles the program into an internal form, and then proceeds -to read each file named in the `ARGV' array. The initial values of -`ARGV' come from the command line arguments. If there are no files -named on the command line, `gawk' reads the standard input. - - If a "file" named on the command line has the form `VAR=VAL', it is -treated as a variable assignment: the variable VAR is assigned the -value VAL. If any of the files have a value that is the null string, -that element in the list is skipped. - - For each record in the input, `gawk' tests to see if it matches any -PATTERN in the `awk' program. For each pattern that the record -matches, the associated ACTION is executed. - - ---------- Footnotes ---------- - - (1) The path may use a directory other than `/usr/local/share/awk', -depending upon how `gawk' was built and installed. - - -File: gawk.info, Node: Variables/Fields, Next: Rules Summary, Prev: Language Summary, Up: Gawk Summary - -Variables and Fields -==================== - - `awk' variables are not declared; they come into existence when they -are first used. Their values are either floating-point numbers or -strings. `awk' also has one-dimensional arrays; multiple-dimensional -arrays may be simulated. There are several predefined variables that -`awk' sets as a program runs; these are summarized below. - -* Menu: - -* Fields Summary:: Input field splitting. -* Built-in Summary:: `awk''s built-in variables. -* Arrays Summary:: Using arrays. -* Data Type Summary:: Values in `awk' are numbers or strings. - - -File: gawk.info, Node: Fields Summary, Next: Built-in Summary, Prev: Variables/Fields, Up: Variables/Fields + * The use of GNU Automake to help in standardizing the configuration + process (*note Compiling `gawk' for Unix: Quick Installation.). -Fields ------- + * The use of GNU `gettext' for `gawk''s own message output (*note + `gawk' Can Speak Your Language: Gawk I18N.). - As each input line is read, `gawk' splits the line into FIELDS, -using the value of the `FS' variable as the field separator. If `FS' -is a single character, fields are separated by that character. -Otherwise, `FS' is expected to be a full regular expression. In the -special case that `FS' is a single space, fields are separated by runs -of spaces, tabs and/or newlines.(1) If `FS' is the null string (`""'), -then each individual character in the record becomes a separate field. -Note that the value of `IGNORECASE' (*note Case-sensitivity in -Matching: Case-sensitivity.) also affects how fields are split when -`FS' is a regular expression. + * BeOS support (*note Installing `gawk' on BeOS: BeOS Installation.). - Each field in the input line may be referenced by its position, `$1', -`$2', and so on. `$0' is the whole line. The value of a field may be -assigned to as well. Field numbers need not be constants: - - n = 5 - print $n - -prints the fifth field in the input line. The variable `NF' is set to -the total number of fields in the input line. - - References to non-existent fields (i.e. fields after `$NF') return -the null string. However, assigning to a non-existent field (e.g., -`$(NF+2) = 5') increases the value of `NF', creates any intervening -fields with the null string as their value, and causes the value of -`$0' to be recomputed, with the fields being separated by the value of -`OFS'. Decrementing `NF' causes the values of fields past the new -value to be lost, and the value of `$0' to be recomputed, with the -fields being separated by the value of `OFS'. *Note Reading Input -Files: Reading Files. - - ---------- Footnotes ---------- - - (1) In POSIX `awk', newline does not separate fields. - - -File: gawk.info, Node: Built-in Summary, Next: Arrays Summary, Prev: Fields Summary, Up: Variables/Fields - -Built-in Variables ------------------- - - `gawk''s built-in variables are: - -`ARGC' - The number of elements in `ARGV'. See below for what is actually - included in `ARGV'. - -`ARGIND' - The index in `ARGV' of the current file being processed. When - `gawk' is processing the input data files, it is always true that - `FILENAME == ARGV[ARGIND]'. - -`ARGV' - The array of command line arguments. The array is indexed from - zero to `ARGC' - 1. Dynamically changing `ARGC' and the contents - of `ARGV' can control the files used for data. A null-valued - element in `ARGV' is ignored. `ARGV' does not include the options - to `awk' or the text of the `awk' program itself. - -`CONVFMT' - The conversion format to use when converting numbers to strings. - -`FIELDWIDTHS' - A space separated list of numbers describing the fixed-width input - data. - -`ENVIRON' - An array of environment variable values. The array is indexed by - variable name, each element being the value of that variable. - Thus, the environment variable `HOME' is `ENVIRON["HOME"]'. One - possible value might be `/home/arnold'. - - Changing this array does not affect the environment seen by - programs which `gawk' spawns via redirection or the `system' - function. (This may change in a future version of `gawk'.) - - Some operating systems do not have environment variables. The - `ENVIRON' array is empty when running on these systems. - -`ERRNO' - The system error message when an error occurs using `getline' or - `close'. - -`FILENAME' - The name of the current input file. If no files are specified on - the command line, the value of `FILENAME' is the null string. - -`FNR' - The input record number in the current input file. - -`FS' - The input field separator, a space by default. - -`IGNORECASE' - The case-sensitivity flag for string comparisons and regular - expression operations. If `IGNORECASE' has a non-zero value, then - pattern matching in rules, record separating with `RS', field - splitting with `FS', regular expression matching with `~' and - `!~', and the `gensub', `gsub', `index', `match', `split' and - `sub' built-in functions all ignore case when doing regular - expression operations, and all string comparisons are done - ignoring case. The value of `IGNORECASE' does _not_ affect array - subscripting. - -`NF' - The number of fields in the current input record. - -`NR' - The total number of input records seen so far. - -`OFMT' - The output format for numbers for the `print' statement, `"%.6g"' - by default. - -`OFS' - The output field separator, a space by default. - -`ORS' - The output record separator, by default a newline. - -`RS' - The input record separator, by default a newline. If `RS' is set - to the null string, then records are separated by blank lines. - When `RS' is set to the null string, then the newline character - always acts as a field separator, in addition to whatever value - `FS' may have. If `RS' is set to a multi-character string, it - denotes a regexp; input text matching the regexp separates records. - -`RT' - The input text that matched the text denoted by `RS', the record - separator. - -`RSTART' - The index of the first character last matched by `match'; zero if - no match. - -`RLENGTH' - The length of the string last matched by `match'; -1 if no match. - -`SUBSEP' - The string used to separate multiple subscripts in array elements, - by default `"\034"'. - - *Note Built-in Variables::, for more information. - - -File: gawk.info, Node: Arrays Summary, Next: Data Type Summary, Prev: Built-in Summary, Up: Variables/Fields - -Arrays ------- - - Arrays are subscripted with an expression between square brackets -(`[' and `]'). Array subscripts are _always_ strings; numbers are -converted to strings as necessary, following the standard conversion -rules (*note Conversion of Strings and Numbers: Conversion.). - - If you use multiple expressions separated by commas inside the square -brackets, then the array subscript is a string consisting of the -concatenation of the individual subscript values, converted to strings, -separated by the subscript separator (the value of `SUBSEP'). - - The special operator `in' may be used in a conditional context to -see if an array has an index consisting of a particular value. - - if (val in array) - print array[val] - - If the array has multiple subscripts, use `(i, j, ...) in ARRAY' to -test for existence of an element. - - The `in' construct may also be used in a `for' loop to iterate over -all the elements of an array. *Note Scanning All Elements of an Array: -Scanning an Array. - - You can remove an element from an array using the `delete' statement. - - You can clear an entire array using `delete ARRAY'. - - *Note Arrays in `awk': Arrays. - - -File: gawk.info, Node: Data Type Summary, Prev: Arrays Summary, Up: Variables/Fields - -Data Types ----------- - - The value of an `awk' expression is always either a number or a -string. - - Some contexts (such as arithmetic operators) require numeric values. -They convert strings to numbers by interpreting the text of the string -as a number. If the string does not look like a number, it converts to -zero. - - Other contexts (such as concatenation) require string values. They -convert numbers to strings by effectively printing them with `sprintf'. -*Note Conversion of Strings and Numbers: Conversion, for the details. - - To force conversion of a string value to a number, simply add zero -to it. If the value you start with is already a number, this does not -change it. - - To force conversion of a numeric value to a string, concatenate it -with the null string. - - Comparisons are done numerically if both operands are numeric, or if -one is numeric and the other is a numeric string. Otherwise one or -both operands are converted to strings and a string comparison is -performed. Fields, `getline' input, `FILENAME', `ARGV' elements, -`ENVIRON' elements and the elements of an array created by `split' are -the only items that can be numeric strings. String constants, such as -`"3.1415927"' are not numeric strings, they are string constants. The -full rules for comparisons are described in *Note Variable Typing and -Comparison Expressions: Typing and Comparison. - - Uninitialized variables have the string value `""' (the null, or -empty, string). In contexts where a number is required, this is -equivalent to zero. - - *Note Variables::, for more information on variable naming and -initialization; *note Conversion of Strings and Numbers: Conversion., -for more information on how variable values are interpreted. - - -File: gawk.info, Node: Rules Summary, Next: Actions Summary, Prev: Variables/Fields, Up: Gawk Summary - -Patterns -======== - -* Menu: - -* Pattern Summary:: Quick overview of patterns. -* Regexp Summary:: Quick overview of regular expressions. - - An `awk' program is mostly composed of rules, each consisting of a -pattern followed by an action. The action is enclosed in `{' and `}'. -Either the pattern may be missing, or the action may be missing, but -not both. If the pattern is missing, the action is executed for every -input record. A missing action is equivalent to `{ print }', which -prints the entire line. - - Comments begin with the `#' character, and continue until the end of -the line. Blank lines may be used to separate statements. Statements -normally end with a newline; however, this is not the case for lines -ending in a `,', `{', `?', `:', `&&', or `||'. Lines ending in `do' or -`else' also have their statements automatically continued on the -following line. In other cases, a line can be continued by ending it -with a `\', in which case the newline is ignored. - - Multiple statements may be put on one line by separating each one -with a `;'. This applies to both the statements within the action part -of a rule (the usual case), and to the rule statements. - - *Note Comments in `awk' Programs: Comments, for information on -`awk''s commenting convention; *note `awk' Statements Versus Lines: -Statements/Lines., for a description of the line continuation mechanism -in `awk'. - - -File: gawk.info, Node: Pattern Summary, Next: Regexp Summary, Prev: Rules Summary, Up: Rules Summary - -Pattern Summary ---------------- - - `awk' patterns may be one of the following: - - /REGULAR EXPRESSION/ - RELATIONAL EXPRESSION - PATTERN && PATTERN - PATTERN || PATTERN - PATTERN ? PATTERN : PATTERN - (PATTERN) - ! PATTERN - PATTERN1, PATTERN2 - BEGIN - END - - `BEGIN' and `END' are two special kinds of patterns that are not -tested against the input. The action parts of all `BEGIN' rules are -concatenated as if all the statements had been written in a single -`BEGIN' rule. They are executed before any of the input is read. -Similarly, all the `END' rules are concatenated, and executed when all -the input is exhausted (or when an `exit' statement is executed). -`BEGIN' and `END' patterns cannot be combined with other patterns in -pattern expressions. `BEGIN' and `END' rules cannot have missing -action parts. - - For `/REGULAR-EXPRESSION/' patterns, the associated statement is -executed for each input record that matches the regular expression. -Regular expressions are summarized below. - - A RELATIONAL EXPRESSION may use any of the operators defined below in -the section on actions. These generally test whether certain fields -match certain regular expressions. - - The `&&', `||', and `!' operators are logical "and," logical "or," -and logical "not," respectively, as in C. They do short-circuit -evaluation, also as in C, and are used for combining more primitive -pattern expressions. As in most languages, parentheses may be used to -change the order of evaluation. - - The `?:' operator is like the same operator in C. If the first -pattern matches, then the second pattern is matched against the input -record; otherwise, the third is matched. Only one of the second and -third patterns is matched. - - The `PATTERN1, PATTERN2' form of a pattern is called a range -pattern. It matches all input lines starting with a line that matches -PATTERN1, and continuing until a line that matches PATTERN2, inclusive. -A range pattern cannot be used as an operand of any of the pattern -operators. - - *Note Pattern Elements: Pattern Overview. - - -File: gawk.info, Node: Regexp Summary, Prev: Pattern Summary, Up: Rules Summary - -Regular Expressions -------------------- - - Regular expressions are based on POSIX EREs (extended regular -expressions). The escape sequences allowed in string constants are -also valid in regular expressions (*note Escape Sequences::). Regexps -are composed of characters as follows: - -`C' - matches the character C (assuming C is none of the characters - listed below). - -`\C' - matches the literal character C. - -`.' - matches any character, _including_ newline. In strict POSIX mode, - `.' does not match the NUL character, which is a character with - all bits equal to zero. - -`^' - matches the beginning of a string. - -`$' - matches the end of a string. - -`[ABC...]' - matches any of the characters ABC... (character list). - -`[[:CLASS:]]' - matches any character in the character class CLASS. Allowable - classes are `alnum', `alpha', `blank', `cntrl', `digit', `graph', - `lower', `print', `punct', `space', `upper', and `xdigit'. - -`[[.SYMBOL.]]' - matches the multi-character collating symbol SYMBOL. `gawk' does - not currently support collating symbols. - -`[[=CLASSNAME=]]' - matches any of the equivalent characters in the current locale - named by the equivalence class CLASSNAME. `gawk' does not - currently support equivalence classes. - -`[^ABC...]' - matches any character except ABC... (negated character list). - -`R1|R2' - matches either R1 or R2 (alternation). - -`R1R2' - matches R1, and then R2 (concatenation). - -`R+' - matches one or more R's. - -`R*' - matches zero or more R's. - -`R?' - matches zero or one R's. - -`(R)' - matches R (grouping). - -`R{N}' -`R{N,}' -`R{N,M}' - matches at least N, N to any number, or N to M occurrences of R - (interval expressions). - -`\y' - matches the empty string at either the beginning or the end of a - word. - -`\B' - matches the empty string within a word. - -`\<' - matches the empty string at the beginning of a word. - -`\>' - matches the empty string at the end of a word. - -`\w' - matches any word-constituent character (alphanumeric characters and - the underscore). - -`\W' - matches any character that is not word-constituent. - -`\`' - matches the empty string at the beginning of a buffer (same as a - string in `gawk'). - -`\'' - matches the empty string at the end of a buffer. - - The various command line options control how `gawk' interprets -characters in regexps. - -No options - In the default case, `gawk' provide all the facilities of POSIX - regexps and the GNU regexp operators described above. However, - interval expressions are not supported. - -`--posix' - Only POSIX regexps are supported, the GNU operators are not special - (e.g., `\w' matches a literal `w'). Interval expressions are - allowed. - -`--traditional' - Traditional Unix `awk' regexps are matched. The GNU operators are - not special, interval expressions are not available, and neither - are the POSIX character classes (`[[:alnum:]]' and so on). - Characters described by octal and hexadecimal escape sequences are - treated literally, even if they represent regexp metacharacters. - -`--re-interval' - Allow interval expressions in regexps, even if `--traditional' has - been provided. - - *Note Regular Expressions: Regexp. - - -File: gawk.info, Node: Actions Summary, Next: Functions Summary, Prev: Rules Summary, Up: Gawk Summary - -Actions -======= - - Action statements are enclosed in braces, `{' and `}'. A missing -action statement is equivalent to `{ print }'. - - Action statements consist of the usual assignment, conditional, and -looping statements found in most languages. The operators, control -statements, and Input/Output statements available are similar to those -in C. - - Comments begin with the `#' character, and continue until the end of -the line. Blank lines may be used to separate statements. Statements -normally end with a newline; however, this is not the case for lines -ending in a `,', `{', `?', `:', `&&', or `||'. Lines ending in `do' or -`else' also have their statements automatically continued on the -following line. In other cases, a line can be continued by ending it -with a `\', in which case the newline is ignored. - - Multiple statements may be put on one line by separating each one -with a `;'. This applies to both the statements within the action part -of a rule (the usual case), and to the rule statements. - - *Note Comments in `awk' Programs: Comments, for information on -`awk''s commenting convention; *note `awk' Statements Versus Lines: -Statements/Lines., for a description of the line continuation mechanism -in `awk'. - -* Menu: - -* Operator Summary:: `awk' operators. -* Control Flow Summary:: The control statements. -* I/O Summary:: The I/O statements. -* Printf Summary:: A summary of `printf'. -* Special File Summary:: Special file names interpreted internally. -* Built-in Functions Summary:: Built-in numeric and string functions. -* Time Functions Summary:: Built-in time functions. -* String Constants Summary:: Escape sequences in strings. - - -File: gawk.info, Node: Operator Summary, Next: Control Flow Summary, Prev: Actions Summary, Up: Actions Summary - -Operators ---------- - - The operators in `awk', in order of decreasing precedence, are: - -`(...)' - Grouping. - -`$' - Field reference. - -`++ --' - Increment and decrement, both prefix and postfix. - -`^' - Exponentiation (`**' may also be used, and `**=' for the assignment - operator, but they are not specified in the POSIX standard). - -`+ - !' - Unary plus, unary minus, and logical negation. - -`* / %' - Multiplication, division, and modulus. - -`+ -' - Addition and subtraction. - -`SPACE' - String concatenation. - -`< <= > >= != ==' - The usual relational operators. - -`~ !~' - Regular expression match, negated match. - -`in' - Array membership. - -`&&' - Logical "and". - -`||' - Logical "or". - -`?:' - A conditional expression. This has the form `EXPR1 ? EXPR2 : - EXPR3'. If EXPR1 is true, the value of the expression is EXPR2; - otherwise it is EXPR3. Only one of EXPR2 and EXPR3 is evaluated. - -`= += -= *= /= %= ^=' - Assignment. Both absolute assignment (`VAR=VALUE') and operator - assignment (the other forms) are supported. - - *Note Expressions::. - - -File: gawk.info, Node: Control Flow Summary, Next: I/O Summary, Prev: Operator Summary, Up: Actions Summary - -Control Statements ------------------- - - The control statements are as follows: - - if (CONDITION) STATEMENT [ else STATEMENT ] - while (CONDITION) STATEMENT - do STATEMENT while (CONDITION) - for (EXPR1; EXPR2; EXPR3) STATEMENT - for (VAR in ARRAY) STATEMENT - break - continue - delete ARRAY[INDEX] - delete ARRAY - exit [ EXPRESSION ] - { STATEMENTS } - - *Note Control Statements in Actions: Statements. - - -File: gawk.info, Node: I/O Summary, Next: Printf Summary, Prev: Control Flow Summary, Up: Actions Summary - -I/O Statements --------------- - - The Input/Output statements are as follows: - -`getline' - Set `$0' from next input record; set `NF', `NR', `FNR'. *Note - Explicit Input with `getline': Getline. - -`getline <FILE' - Set `$0' from next record of FILE; set `NF'. - -`getline VAR' - Set VAR from next input record; set `NR', `FNR'. - -`getline VAR <FILE' - Set VAR from next record of FILE. - -`COMMAND | getline' - Run COMMAND, piping its output into `getline'; sets `$0', `NF', - `NR'. - -`COMMAND | getline `var'' - Run COMMAND, piping its output into `getline'; sets VAR. - -`next' - Stop processing the current input record. The next input record - is read and processing starts over with the first pattern in the - `awk' program. If the end of the input data is reached, the `END' - rule(s), if any, are executed. *Note The `next' Statement: Next - Statement. - -`nextfile' - Stop processing the current input file. The next input record - read comes from the next input file. `FILENAME' is updated, `FNR' - is set to one, `ARGIND' is incremented, and processing starts over - with the first pattern in the `awk' program. If the end of the - input data is reached, the `END' rule(s), if any, are executed. - Earlier versions of `gawk' used `next file'; this usage is still - supported, but is considered to be deprecated. *Note The - `nextfile' Statement: Nextfile Statement. - -`print' - Prints the current record. *Note Printing Output: Printing. - -`print EXPR-LIST' - Prints expressions. - -`print EXPR-LIST > FILE' - Prints expressions to FILE. If FILE does not exist, it is created. - If it does exist, its contents are deleted the first time the - `print' is executed. - -`print EXPR-LIST >> FILE' - Prints expressions to FILE. The previous contents of FILE are - retained, and the output of `print' is appended to the file. - -`print EXPR-LIST | COMMAND' - Prints expressions, sending the output down a pipe to COMMAND. - The pipeline to the command stays open until the `close' function - is called. - -`printf FMT, EXPR-LIST' - Format and print. - -`printf FMT, EXPR-LIST > FILE' - Format and print to FILE. If FILE does not exist, it is created. - If it does exist, its contents are deleted the first time the - `printf' is executed. - -`printf FMT, EXPR-LIST >> FILE' - Format and print to FILE. The previous contents of FILE are - retained, and the output of `printf' is appended to the file. - -`printf FMT, EXPR-LIST | COMMAND' - Format and print, sending the output down a pipe to COMMAND. The - pipeline to the command stays open until the `close' function is - called. - - `getline' returns zero on end of file, and -1 on an error. In the -event of an error, `getline' will set `ERRNO' to the value of a -system-dependent string that describes the error. - - -File: gawk.info, Node: Printf Summary, Next: Special File Summary, Prev: I/O Summary, Up: Actions Summary - -`printf' Summary ----------------- - - Conversion specification have the form -`%'[FLAG][WIDTH][`.'PREC]FORMAT. Items in brackets are optional. - - The `awk' `printf' statement and `sprintf' function accept the -following conversion specification formats: - -`%c' - An ASCII character. If the argument used for `%c' is numeric, it - is treated as a character and printed. Otherwise, the argument is - assumed to be a string, and the only first character of that - string is printed. - -`%d' -`%i' - A decimal number (the integer part). - -`%e' -`%E' - A floating point number of the form `[-]d.dddddde[+-]dd'. The - `%E' format uses `E' instead of `e'. - -`%f' - A floating point number of the form [`-']`ddd.dddddd'. - -`%g' -`%G' - Use either the `%e' or `%f' formats, whichever produces a shorter - string, with non-significant zeros suppressed. `%G' will use `%E' - instead of `%e'. - -`%o' - An unsigned octal number (also an integer). - -`%u' - An unsigned decimal number (again, an integer). - -`%s' - A character string. - -`%x' -`%X' - An unsigned hexadecimal number (an integer). The `%X' format uses - `A' through `F' instead of `a' through `f' for decimal 10 through - 15. - -`%%' - A single `%' character; no argument is converted. - - There are optional, additional parameters that may lie between the -`%' and the control letter: - -`-' - The expression should be left-justified within its field. - -`SPACE' - For numeric conversions, prefix positive values with a space, and - negative values with a minus sign. - -`+' - The plus sign, used before the width modifier (see below), says to - always supply a sign for numeric conversions, even if the data to - be formatted is positive. The `+' overrides the space modifier. - -`#' - Use an "alternate form" for certain control letters. For `o', - supply a leading zero. For `x', and `X', supply a leading `0x' or - `0X' for a non-zero result. For `e', `E', and `f', the result - will always contain a decimal point. For `g', and `G', trailing - zeros are not removed from the result. - -`0' - A leading `0' (zero) acts as a flag, that indicates output should - be padded with zeros instead of spaces. This applies even to - non-numeric output formats. This flag only has an effect when the - field width is wider than the value to be printed. - -`WIDTH' - The field should be padded to this width. The field is normally - padded with spaces. If the `0' flag has been used, it is padded - with zeros. - -`.PREC' - A number that specifies the precision to use when printing. For - the `e', `E', and `f' formats, this specifies the number of digits - you want printed to the right of the decimal point. For the `g', - and `G' formats, it specifies the maximum number of significant - digits. For the `d', `o', `i', `u', `x', and `X' formats, it - specifies the minimum number of digits to print. For the `s' - format, it specifies the maximum number of characters from the - string that should be printed. - - Either or both of the WIDTH and PREC values may be specified as `*'. -In that case, the particular value is taken from the argument list. - - *Note Using `printf' Statements for Fancier Printing: Printf. - - -File: gawk.info, Node: Special File Summary, Next: Built-in Functions Summary, Prev: Printf Summary, Up: Actions Summary - -Special File Names ------------------- - - When doing I/O redirection from either `print' or `printf' into a -file, or via `getline' from a file, `gawk' recognizes certain special -file names internally. These file names allow access to open file -descriptors inherited from `gawk''s parent process (usually the shell). -The file names are: - -`/dev/stdin' - The standard input. - -`/dev/stdout' - The standard output. - -`/dev/stderr' - The standard error output. - -`/dev/fd/N' - The file denoted by the open file descriptor N. - - In addition, reading the following files provides process related -information about the running `gawk' program. All returned records are -terminated with a newline. - -`/dev/pid' - Returns the process ID of the current process. - -`/dev/ppid' - Returns the parent process ID of the current process. - -`/dev/pgrpid' - Returns the process group ID of the current process. - -`/dev/user' - At least four space-separated fields, containing the return values - of the `getuid', `geteuid', `getgid', and `getegid' system calls. - If there are any additional fields, they are the group IDs - returned by `getgroups' system call. (Multiple groups may not be - supported on all systems.) - -These file names may also be used on the command line to name data -files. These file names are only recognized internally if you do not -actually have files with these names on your system. - - *Note Special File Names in `gawk': Special Files, for a longer -description that provides the motivation for this feature. - - -File: gawk.info, Node: Built-in Functions Summary, Next: Time Functions Summary, Prev: Special File Summary, Up: Actions Summary - -Built-in Functions ------------------- - - `awk' provides a number of built-in functions for performing numeric -operations, string related operations, and I/O related operations. - - The built-in arithmetic functions are: - -`atan2(Y, X)' - the arctangent of Y/X in radians. - -`cos(EXPR)' - the cosine of EXPR, which is in radians. - -`exp(EXPR)' - the exponential function (`e ^ EXPR'). - -`int(EXPR)' - truncates to integer. - -`log(EXPR)' - the natural logarithm of `expr'. - -`rand()' - a random number between zero and one. - -`sin(EXPR)' - the sine of EXPR, which is in radians. - -`sqrt(EXPR)' - the square root function. - -`srand([EXPR])' - use EXPR as a new seed for the random number generator. If no EXPR - is provided, the time of day is used. The return value is the - previous seed for the random number generator. - - `awk' has the following built-in string functions: - -`gensub(REGEX, SUBST, HOW [, TARGET])' - If HOW is a string beginning with `g' or `G', then replace each - match of REGEX in TARGET with SUBST. Otherwise, replace the - HOW'th occurrence. If TARGET is not supplied, use `$0'. The - return value is the changed string; the original TARGET is not - modified. Within SUBST, `\N', where N is a digit from one to nine, - can be used to indicate the text that matched the N'th - parenthesized subexpression. This function is `gawk'-specific. - -`gsub(REGEX, SUBST [, TARGET])' - for each substring matching the regular expression REGEX in the - string TARGET, substitute the string SUBST, and return the number - of substitutions. If TARGET is not supplied, use `$0'. - -`index(STR, SEARCH)' - returns the index of the string SEARCH in the string STR, or zero - if SEARCH is not present. - -`length([STR])' - returns the length of the string STR. The length of `$0' is - returned if no argument is supplied. - -`match(STR, REGEX)' - returns the position in STR where the regular expression REGEX - occurs, or zero if REGEX is not present, and sets the values of - `RSTART' and `RLENGTH'. - -`split(STR, ARR [, REGEX])' - splits the string STR into the array ARR on the regular expression - REGEX, and returns the number of elements. If REGEX is omitted, - `FS' is used instead. REGEX can be the null string, causing each - character to be placed into its own array element. The array ARR - is cleared first. - -`sprintf(FMT, EXPR-LIST)' - prints EXPR-LIST according to FMT, and returns the resulting - string. - -`sub(REGEX, SUBST [, TARGET])' - just like `gsub', but only the first matching substring is - replaced. - -`substr(STR, INDEX [, LEN])' - returns the LEN-character substring of STR starting at INDEX. If - LEN is omitted, the rest of STR is used. - -`tolower(STR)' - returns a copy of the string STR, with all the upper-case - characters in STR translated to their corresponding lower-case - counterparts. Non-alphabetic characters are left unchanged. - -`toupper(STR)' - returns a copy of the string STR, with all the lower-case - characters in STR translated to their corresponding upper-case - counterparts. Non-alphabetic characters are left unchanged. - - The I/O related functions are: - -`close(EXPR)' - Close the open file or pipe denoted by EXPR. - -`fflush([EXPR])' - Flush any buffered output for the output file or pipe denoted by - EXPR. If EXPR is omitted, standard output is flushed. If EXPR is - the null string (`""'), all output buffers are flushed. - -`system(CMD-LINE)' - Execute the command CMD-LINE, and return the exit status. If your - operating system does not support `system', calling it will - generate a fatal error. - - `system("")' can be used to force `awk' to flush any pending - output. This is more portable, but less obvious, than calling - `fflush'. - - -File: gawk.info, Node: Time Functions Summary, Next: String Constants Summary, Prev: Built-in Functions Summary, Up: Actions Summary - -Time Functions --------------- + * Tandem support (*note Installing `gawk' on a Tandem: Tandem + Installation.). - The following two functions are available for getting the current -time of day, and for formatting time stamps. They are specific to -`gawk'. + * The Atari port became officially unsupported (*note Installing + `gawk' on the Atari ST: Atari Installation.). -`systime()' - returns the current time of day as the number of seconds since a - particular epoch (Midnight, January 1, 1970 UTC, on POSIX systems). + * The source code now uses new-style function definitions, with + `ansi2knr' to convert the code on systems with old compilers. -`strftime([FORMAT[, TIMESTAMP]])' - formats TIMESTAMP according to the specification in FORMAT. The - current time of day is used if no TIMESTAMP is supplied. A - default format equivalent to the output of the `date' utility is - used if no FORMAT is supplied. *Note Functions for Dealing with - Time Stamps: Time Functions, for the details on the conversion - specifiers that `strftime' accepts. -File: gawk.info, Node: String Constants Summary, Prev: Time Functions Summary, Up: Actions Summary - -String Constants ----------------- - - String constants in `awk' are sequences of characters enclosed in -double quotes (`"'). Within strings, certain "escape sequences" are -recognized, as in C. These are: +File: gawk.info, Node: Contributors, Prev: POSIX/GNU, Up: Language History -`\\' - A literal backslash. - -`\a' - The "alert" character; usually the ASCII BEL character. - -`\b' - Backspace. - -`\f' - Formfeed. - -`\n' - Newline. - -`\r' - Carriage return. - -`\t' - Horizontal tab. - -`\v' - Vertical tab. - -`\xHEX DIGITS' - The character represented by the string of hexadecimal digits - following the `\x'. As in ANSI C, all following hexadecimal - digits are considered part of the escape sequence. E.g., `"\x1B"' - is a string containing the ASCII ESC (escape) character. (The `\x' - escape sequence is not in POSIX `awk'.) - -`\DDD' - The character represented by the one, two, or three digit sequence - of octal digits. Thus, `"\033"' is also a string containing the - ASCII ESC (escape) character. +Major Contributors to `gawk' +============================ -`\C' - The literal character C, if C is not one of the above. + Always give credit where credit is due. + Anonymous - The escape sequences may also be used inside constant regular -expressions (e.g., the regexp `/[ \t\f\n\r\v]/' matches whitespace -characters). + This minor node names the major contributors to `gawk' and/or this +Info file, in approximate chronological order: - *Note Escape Sequences::. + * Dr. Alfred V. Aho, Dr. Peter J. Weinberger, and Dr. Brian W. + Kernighan, all of Bell Laboratories, designed and implemented Unix + `awk', from which `gawk' gets the majority of its feature set. - -File: gawk.info, Node: Functions Summary, Next: Historical Features, Prev: Actions Summary, Up: Gawk Summary + * Paul Rubin did the initial design and implementation in 1986, and + wrote the first draft (around 40 pages) of this Info file. -User-defined Functions -====================== + * Jay Fenlason finished the initial implementation. - Functions in `awk' are defined as follows: + * Diane Close revised the first draft of this Info file, bringing it + to around 90 pages. - function NAME(PARAMETER LIST) { STATEMENTS } + * Richard Stallman helped finish the implementation and the initial + draft of this Info file. He is also the founder of the FSF and + the GNU project. - Actual parameters supplied in the function call are used to -instantiate the formal parameters declared in the function. Arrays are -passed by reference, other variables are passed by value. + * John Woods contributed parts of the code (mostly fixes) in the + initial version of `gawk'. - If there are fewer arguments passed than there are names in -PARAMETER-LIST, the extra names are given the null string as their -value. Extra names have the effect of local variables. + * In 1988, David Trueman took over primary maintenance of `gawk', + making it compatible with "new" `awk', and greatly improving its + performance. - The open-parenthesis in a function call of a user-defined function -must immediately follow the function name, without any intervening -white space. This is to avoid a syntactic ambiguity with the -concatenation operator. + * Pat Rankin provided the VMS port and its documentation. - The word `func' may be used in place of `function' (but not in POSIX -`awk'). + * Conrad Kwok, Scott Garfinkle, and Kent Williams did the initial + ports to MS-DOS with various versions of MSC. - Use the `return' statement to return a value from a function. + * Hal Peterson provided help in porting `gawk' to Cray systems. - *Note User-defined Functions: User-defined. + * Kai Uwe Rommel provided the port to OS/2 and its documentation. - -File: gawk.info, Node: Historical Features, Prev: Functions Summary, Up: Gawk Summary + * Michal Jaegermann provided the port to Atari systems and its + documentation. He continues to provide portability checking with + DEC Alpha systems, and has done a lot of work to make sure `gawk' + works on non-32-bit systems. -Historical Features -=================== + * Fred Fish provided the port to Amiga systems and its documentation. - There are two features of historical `awk' implementations that -`gawk' supports. + * Scott Deifik currently maintains the MS-DOS port. - First, it is possible to call the `length' built-in function not only -with no arguments, but even without parentheses! + * Juan Grigera maintains the port to Win32 systems. - a = length + * Dr. Darrel Hankerson acts as coordinator for the various ports to + different PC platforms and creates binary distributions for + various PC operating systems. He is also instrumental in keeping + the documentation up to date for the various PC platforms. -is the same as either of + * Christos Zoulas provided the `extension' built-in function for + dynamically adding new modules. - a = length() - a = length($0) + * Ju"rgen Kahrs contributed the initial version of the TCP/IP + networking code and documentation, and motivated the inclusion of + the `|&' operator. -For example: + * Stephen Davies provided the port to Tandem systems and its + documentation. - $ echo abcdef | awk '{ print length }' - -| 6 + * Martin Brown provided the port to BeOS and its documentation. -This feature is marked as "deprecated" in the POSIX standard, and -`gawk' will issue a warning about its use if `--lint' is specified on -the command line. (The ability to use `length' this way was actually -an accident of the original Unix `awk' implementation. If any built-in -function used `$0' as its default argument, it was possible to call -that function without the parentheses. In particular, it was common -practice to use the `length' function in this fashion, and this usage -was documented in the `awk' manual page.) + * Arno Peters did the initial work to convert `gawk' to use GNU + Automake and `gettext'. - The other historical feature is the use of either the `break' -statement, or the `continue' statement outside the body of a `while', -`for', or `do' loop. Traditional `awk' implementations have treated -such usage as equivalent to the `next' statement. More recent versions -of Unix `awk' do not allow it. `gawk' supports this usage if -`--traditional' has been specified. + * Alan J. Broder provided the initial version of the `asort' function + as well as the code for the new optional third argument to the + `match' function. - *Note Command Line Options: Options, for more information about the -`--posix' and `--lint' options. + * Arnold Robbins has been working on `gawk' since 1988, at first + helping David Trueman, and as the primary maintainer since around + 1994. -File: gawk.info, Node: Installation, Next: Notes, Prev: Gawk Summary, Up: Top +File: gawk.info, Node: Installation, Next: Notes, Prev: Language History, Up: Top Installing `gawk' ***************** This appendix provides instructions for installing `gawk' on the various platforms that are supported by the developers. The primary -developers support Unix (and one day, GNU), while the other ports were -contributed. The file `ACKNOWLEDGMENT' in the `gawk' distribution -lists the electronic mail addresses of the people who did the -respective ports, and they are also provided in *Note Reporting -Problems and Bugs: Bugs. +developer supports GNU/Linux (and Unix), whereas the other ports are +contributed. *Note Reporting Problems and Bugs: Bugs, for the +electronic mail addresses of the people who did the respective ports. * Menu: * Gawk Distribution:: What is in the `gawk' distribution. -* Unix Installation:: Installing `gawk' under various versions - of Unix. -* VMS Installation:: Installing `gawk' on VMS. -* PC Installation:: Installing and Compiling `gawk' on MS-DOS - and OS/2 -* Atari Installation:: Installing `gawk' on the Atari ST. -* Amiga Installation:: Installing `gawk' on an Amiga. +* Unix Installation:: Installing `gawk' under various + versions of Unix. +* Non-Unix Installation:: Installation on Other Operating Systems. +* Unsupported:: Systems whose ports are no longer supported. * Bugs:: Reporting Problems and Bugs. * Other Versions:: Other freely available `awk' implementations. @@ -15332,8 +16680,8 @@ File: gawk.info, Node: Gawk Distribution, Next: Unix Installation, Prev: Inst The `gawk' Distribution ======================= - This section first describes how to get the `gawk' distribution, how -to extract it, and then what is in the various files and subdirectories. + This minor node describes how to get the `gawk' distribution, how to +extract it, and then what is in the various files and subdirectories. * Menu: @@ -15347,101 +16695,33 @@ File: gawk.info, Node: Getting, Next: Extracting, Prev: Gawk Distribution, U Getting the `gawk' Distribution ------------------------------- - There are three ways you can get GNU software. + There are three ways to get GNU software: - 1. You can copy it from someone else who already has it. + * Copy it from someone else who already has it. - 2. You can order `gawk' directly from the Free Software Foundation. - Software distributions are available for Unix, MS-DOS, and VMS, on - tape and CD-ROM. The address is: + * Order `gawk' directly from the Free Software Foundation. Software + distributions are available for Unix, MS-DOS, and VMS, on tape and + CD-ROM. Their address is: Free Software Foundation - 59 Temple Place--Suite 330 + 59 Temple Place, Suite 330 Boston, MA 02111-1307 USA Phone: +1-617-542-5942 Fax (including Japan): +1-617-542-2652 - Email: `gnu@gnu.org' + Email: <gnu@gnu.org> URL: `http://www.gnu.org/' Ordering from the FSF directly contributes to the support of the foundation and to the production of more free software. - 3. You can get `gawk' by using anonymous `ftp' to the Internet host + * Retrieve `gawk' by using anonymous `ftp' to the Internet host `gnudist.gnu.org', in the directory `/gnu/gawk'. - Here is a list of alternate `ftp' sites from which you can obtain - GNU software. When a site is listed as "SITE`:'DIRECTORY" the - DIRECTORY indicates the directory where GNU software is kept. You - should use a site that is geographically close to you. - - Asia: - - `cair-archive.kaist.ac.kr:/pub/gnu' - `ftp.cs.titech.ac.jp' - `ftp.nectec.or.th:/pub/mirrors/gnu' - `utsun.s.u-tokyo.ac.jp:/ftpsync/prep' - - Australia: - - `archie.au:/gnu' - (`archie.oz' or `archie.oz.au' for ACSnet) - - Africa: - - `ftp.sun.ac.za:/pub/gnu' - - Middle East: - - `ftp.technion.ac.il:/pub/unsupported/gnu' - - Europe: - - `archive.eu.net' - `ftp.denet.dk' - `ftp.eunet.ch' - `ftp.funet.fi:/pub/gnu' - `ftp.ieunet.ie:pub/gnu' - `ftp.informatik.rwth-aachen.de:/pub/gnu' - `ftp.informatik.tu-muenchen.de' - `ftp.luth.se:/pub/unix/gnu' - `ftp.mcc.ac.uk' - `ftp.stacken.kth.se' - `ftp.sunet.se:/pub/gnu' - `ftp.univ-lyon1.fr:pub/gnu' - `ftp.win.tue.nl:/pub/gnu' - `irisa.irisa.fr:/pub/gnu' - `isy.liu.se' - `nic.switch.ch:/mirror/gnu' - `src.doc.ic.ac.uk:/gnu' - `unix.hensa.ac.uk:/pub/uunet/systems/gnu' - - South America: - - `ftp.inf.utfsm.cl:/pub/gnu' - `ftp.unicamp.br:/pub/gnu' - - Western Canada: - - `ftp.cs.ubc.ca:/mirror2/gnu' - - USA: - - `col.hp.com:/mirrors/gnu' - `f.ms.uky.edu:/pub3/gnu' - `ftp.cc.gatech.edu:/pub/gnu' - `ftp.cs.columbia.edu:/archives/gnu/prep' - `ftp.digex.net:/pub/gnu' - `ftp.hawaii.edu:/mirrors/gnu' - `ftp.kpc.com:/pub/mirror/gnu' - - USA (continued): - `ftp.uu.net:/systems/gnu' - `gatekeeper.dec.com:/pub/GNU' - `jaguar.utah.edu:/gnustuff' - `labrea.stanford.edu' - `mrcnext.cso.uiuc.edu:/pub/gnu' - `vixen.cso.uiuc.edu:/gnu' - `wuarchive.wustl.edu:/systems/gnu' + The GNU software archive is mirrored around the world. The +up-to-date list of mirror sites is available from the main FSF web site +(http://www.gnu.org/order/ftp.html). Try to use one of the mirrors; +they will be less busy, and you can usually find one closer to your +site. File: gawk.info, Node: Extracting, Next: Distribution contents, Prev: Getting, Up: Gawk Distribution @@ -15452,29 +16732,26 @@ Extracting the Distribution `gawk' is distributed as a `tar' file compressed with the GNU Zip program, `gzip'. - Once you have the distribution (for example, `gawk-3.0.6.tar.gz'), -first use `gzip' to expand the file, and then use `tar' to extract it. -You can use the following pipeline to produce the `gawk' distribution: + Once you have the distribution (for example, `gawk-3.1.0.tar.gz'), +use `gzip' to expand the file and then use `tar' to extract it. You +can use the following pipeline to produce the `gawk' distribution: - # Under System V, add 'o' to the tar flags - gzip -d -c gawk-3.0.6.tar.gz | tar -xvpf - + # Under System V, add 'o' to the tar options + gzip -d -c gawk-3.1.0.tar.gz | tar -xvpf - -This will create a directory named `gawk-3.0.6' in the current -directory. +This creates a directory named `gawk-3.1.0' in the current directory. - The distribution file name is of the form `gawk-V.R.N.tar.gz'. The + The distribution file name is of the form `gawk-V.R.P.tar.gz'. The V represents the major version of `gawk', the R represents the current -release of version V, and the N represents a "patch level", meaning +release of version V, and the P represents a "patch level", meaning that minor bugs have been fixed in the release. The current patch -level is 6, but when retrieving distributions, you should get the -version with the highest version, release, and patch level. (Note that -release levels greater than or equal to 90 denote "beta," or -non-production software; you may not wish to retrieve such a version -unless you don't mind experimenting.) - - If you are not on a Unix system, you will need to make other -arrangements for getting and extracting the `gawk' distribution. You -should consult a local expert. +level is 0, but when retrieving distributions, you should get the +version with the highest version, release, and patch level. (Note, +however, that patch levels greater than or equal to 80 denote "beta" or +non-production software; you might not want to retrieve such a version +unless you don't mind experimenting.) If you are not on a Unix system, +you need to make other arrangements for getting and extracting the +`gawk' distribution. You should consult a local expert. File: gawk.info, Node: Distribution contents, Prev: Extracting, Up: Gawk Distribution @@ -15483,31 +16760,23 @@ Contents of the `gawk' Distribution ----------------------------------- The `gawk' distribution has a number of C source files, -documentation files, subdirectories and files related to the +documentation files, subdirectories, and files related to the configuration process (*note Compiling and Installing `gawk' on Unix: -Unix Installation.), and several subdirectories related to different, -non-Unix, operating systems. +Unix Installation.), as well as several subdirectories related to +different non-Unix operating systems: -various `.c', `.y', and `.h' files +Various `.c', `.y', and `.h' files: These files are the actual `gawk' source code. `README' `README_d/README.*' - Descriptive files: `README' for `gawk' under Unix, and the rest - for the various hardware and software combinations. + Descriptive files: `README' for `gawk' under Unix and the rest for + the various hardware and software combinations. `INSTALL' A file providing an overview of the configuration and installation process. -`PORTS' - A list of systems to which `gawk' has been ported, and which have - successfully run the test suite. - -`ACKNOWLEDGMENT' - A list of the people who contributed major parts of the code or - documentation. - `ChangeLog' A detailed list of source code changes as bugs are fixed or improvements made. @@ -15519,9 +16788,9 @@ various `.c', `.y', and `.h' files The GNU General Public License. `FUTURES' - A brief list of features and/or changes being contemplated for - future releases, with some indication of the time frame for the - feature, based on its difficulty. + A brief list of features and changes being contemplated for future + releases, with some indication of the time frame for the feature, + based on its difficulty. `LIMITATIONS' A list of those factors that limit `gawk''s performance. Most of @@ -15530,10 +16799,7 @@ various `.c', `.y', and `.h' files `POSIX.STD' A description of one area where the POSIX standard for `awk' is - incorrect, and how `gawk' handles the problem. - -`PROBLEMS' - A file describing known problems with the current release. + incorrect as well as how `gawk' handles the problem. `doc/awkforai.txt' A short article describing why `gawk' is a good language for AI @@ -15548,7 +16814,7 @@ various `.c', `.y', and `.h' files `doc/no.colors' `doc/setter.outline' The `troff' source for a five-color `awk' reference card. A - modern version of `troff', such as GNU Troff (`groff') is needed + modern version of `troff' such as GNU `troff' (`groff') is needed to produce the color version. See the file `README.card' for instructions if you have an older `troff'. @@ -15559,11 +16825,19 @@ various `.c', `.y', and `.h' files `doc/gawk.texi' The Texinfo source file for this Info file. It should be processed with TeX to produce a printed document, and with - `makeinfo' to produce an Info file. + `makeinfo' to produce an Info or HTML file. `doc/gawk.info' The generated Info file for this Info file. +`doc/gawkinet.texi' + The Texinfo source file for *Note Top::. It should be processed + with TeX to produce a printed document and with `makeinfo' to + produce an Info or HTML file. + +`doc/gawkinet.info' + The generated Info file for `TCP/IP Internetworking with `gawk''. + `doc/igawk.1' The `troff' source for a manual page describing the `igawk' program presented in *Note An Easy Way to Use Library Functions: @@ -15573,159 +16847,458 @@ various `.c', `.y', and `.h' files The input file used during the configuration process to generate the actual `Makefile' for creating the documentation. +`Makefile.am' +`*/Makefile.am' + Files used by the GNU `automake' software for generating the + `Makefile.in' files used by `autoconf' and `configure'. + `Makefile.in' `acconfig.h' +`acinclude.m4' `aclocal.m4' `configh.in' `configure.in' `configure' `custom.h' -`missing/*' - These files and subdirectory are used when configuring `gawk' for - various Unix systems. They are explained in detail in *Note - Compiling and Installing `gawk' on Unix: Unix Installation. +`missing_d/*' +`m4/*' + These files and subdirectories are used when configuring `gawk' + for various Unix systems. They are explained in *Note Compiling + and Installing `gawk' on Unix: Unix Installation. + +`intl/*' +`po/*' + The `intl' directory provides the GNU `gettext' library, which + implements `gawk''s internationalization features, while the `po' + library contains message translations. `awklib/extract.awk' +`awklib/Makefile.am' `awklib/Makefile.in' +`awklib/eg/*' The `awklib' directory contains a copy of `extract.awk' (*note Extracting Programs from Texinfo Source Files: Extract Program.), which can be used to extract the sample programs from the Texinfo - source file for this Info file, and a `Makefile.in' file, which - `configure' uses to generate a `Makefile'. As part of the process - of building `gawk', the library functions from *Note A Library of - `awk' Functions: Library Functions, and the `igawk' program from - *Note An Easy Way to Use Library Functions: Igawk Program, are - extracted into ready to use files. They are installed as part of - the installation process. - -`atari/*' - Files needed for building `gawk' on an Atari ST. *Note Installing - `gawk' on the Atari ST: Atari Installation, for details. + source file for this Info file. It also contains a `Makefile.in' + file, which `configure' uses to generate a `Makefile'. + `Makefile.am' is used by GNU Automake to create `Makefile.in'. + The library functions from *Note A Library of `awk' Functions: + Library Functions, and the `igawk' program from *Note An Easy Way + to Use Library Functions: Igawk Program, are included as + ready-to-use files in the `gawk' distribution. They are installed + as part of the installation process. The rest of the programs in + this Info file are available in appropriate subdirectories of + `awklib/eg'. + +`unsupported/atari/*' + Files needed for building `gawk' on an Atari ST (*note Installing + `gawk' on the Atari ST: Atari Installation., for details). + +`unsupported/tandem/*' + Files needed for building `gawk' on a Tandem (*note Installing + `gawk' on a Tandem: Tandem Installation., for details). + +`posix/*' + Files needed for building `gawk' on POSIX-compliant systems. `pc/*' - Files needed for building `gawk' under MS-DOS and OS/2. *Note - MS-DOS and OS/2 Installation and Compilation: PC Installation, for - details. + Files needed for building `gawk' under MS-DOS, MS Windows and OS/2 + (*note Installation on PC Operating Systems: PC Installation., for + details). `vms/*' - Files needed for building `gawk' under VMS. *Note How to Compile - and Install `gawk' on VMS: VMS Installation, for details. + Files needed for building `gawk' under VMS (*note How to Compile + and Install `gawk' on VMS: VMS Installation., for details). `test/*' - A test suite for `gawk'. You can use `make check' from the top - level `gawk' directory to run your version of `gawk' against the - test suite. If `gawk' successfully passes `make check' then you - can be confident of a successful port. + A test suite for `gawk'. You can use `make check' from the + top-level `gawk' directory to run your version of `gawk' against + the test suite. If `gawk' successfully passes `make check', then + you can be confident of a successful port. -File: gawk.info, Node: Unix Installation, Next: VMS Installation, Prev: Gawk Distribution, Up: Installation +File: gawk.info, Node: Unix Installation, Next: Non-Unix Installation, Prev: Gawk Distribution, Up: Installation Compiling and Installing `gawk' on Unix ======================================= Usually, you can compile and install `gawk' by typing only two -commands. However, if you do use an unusual system, you may need to +commands. However, if you use an unusual system, you may need to configure `gawk' for your system yourself. * Menu: -* Quick Installation:: Compiling `gawk' under Unix. -* Configuration Philosophy:: How it's all supposed to work. +* Quick Installation:: Compiling `gawk' under Unix. +* Additional Configuration Options:: Other compile-time options. +* Configuration Philosophy:: How it's all supposed to work. -File: gawk.info, Node: Quick Installation, Next: Configuration Philosophy, Prev: Unix Installation, Up: Unix Installation +File: gawk.info, Node: Quick Installation, Next: Additional Configuration Options, Prev: Unix Installation, Up: Unix Installation Compiling `gawk' for Unix ------------------------- After you have extracted the `gawk' distribution, `cd' to -`gawk-3.0.6'. Like most GNU software, `gawk' is configured +`gawk-3.1.0'. Like most GNU software, `gawk' is configured automatically for your Unix system by running the `configure' program. -This program is a Bourne shell script that was generated automatically +This program is a Bourne shell script that is generated automatically using GNU `autoconf'. (The `autoconf' software is described fully -starting with *Note Introduction: (autoconf)Top.) +starting with *Note Top::.) To configure `gawk', simply run `configure': sh ./configure This produces a `Makefile' and `config.h' tailored to your system. -The `config.h' file describes various facts about your system. You may -wish to edit the `Makefile' to change the `CFLAGS' variable, which -controls the command line options that are passed to the C compiler -(such as optimization levels, or compiling for debugging). +The `config.h' file describes various facts about your system. You +might want to edit the `Makefile' to change the `CFLAGS' variable, +which controls the command-line options that are passed to the C +compiler (such as optimization levels or compiling for debugging). - Alternatively, you can add your own values for most `make' -variables, such as `CC' and `CFLAGS', on the command line when running + Alternatively, you can add your own values for most `make' variables +on the command line, such as `CC' and `CFLAGS', when running `configure': CC=cc CFLAGS=-g sh ./configure See the file `INSTALL' in the `gawk' distribution for all the details. - After you have run `configure', and possibly edited the `Makefile', + After you have run `configure' and possibly edited the `Makefile', type: make -and shortly thereafter, you should have an executable version of `gawk'. -That's all there is to it! (If these steps do not work, please send in -a bug report; *note Reporting Problems and Bugs: Bugs..) +Shortly thereafter, you should have an executable version of `gawk'. +That's all there is to it! To verify that `gawk' is working properly, +run `make check'. All of the tests should succeed. If these steps do +not work, or if any of the tests fail, check the files in the +`README_d' directory to see if you've found a known problem. If the +failure is not described there, please send in a bug report (*note +Reporting Problems and Bugs: Bugs..) -File: gawk.info, Node: Configuration Philosophy, Prev: Quick Installation, Up: Unix Installation +File: gawk.info, Node: Additional Configuration Options, Next: Configuration Philosophy, Prev: Quick Installation, Up: Unix Installation + +Additional Configuration Options +-------------------------------- + + There are several additional options you may use on the `configure' +command line when compiling `gawk' from scratch. + +`--enable-portals' + This option causes `gawk' to treat pathnames that begin with `/p' + as BSD portal files when doing two-way I/O with the `|&' operator + (*note Using `gawk' with BSD Portals: Portal Files.). + +`--with-included-gettext' + Use the version of the `gettext' library that comes with `gawk'. + This option should be used on systems that do _not_ use version 2 + (or later) of the GNU C library. All known modern GNU/Linux + systems use Glibc 2. Use this option on any other system. + +`--disable-nls' + Disable all message translation facilities. This is usually not + desirable, but it may bring you some slight performance + improvement. You should also use this option if + `--with-included-gettext' doesn't work on your system. + + +File: gawk.info, Node: Configuration Philosophy, Prev: Additional Configuration Options, Up: Unix Installation The Configuration Process ------------------------- - (This section is of interest only if you know something about using -the C language and the Unix operating system.) + This minor node is of interest only if you know something about +using the C language and the Unix operating system. The source code for `gawk' generally attempts to adhere to formal standards wherever possible. This means that `gawk' uses library -routines that are specified by the ANSI C standard and by the POSIX -operating system interface standard. When using an ANSI C compiler, +routines that are specified by the ISO C standard and by the POSIX +operating system interface standard. When using an ISO C compiler, function prototypes are used to help improve the compile-time checking. - Many Unix systems do not support all of either the ANSI or the POSIX -standards. The `missing' subdirectory in the `gawk' distribution -contains replacement versions of those subroutines that are most likely + Many Unix systems do not support all of either the ISO or the POSIX +standards. The `missing_d' subdirectory in the `gawk' distribution +contains replacement versions of those functions that are most likely to be missing. - The `config.h' file that is created by the `configure' program -contains definitions that describe features of the particular operating -system where you are attempting to compile `gawk'. The three things -described by this file are what header files are available, so that -they can be correctly included, what (supposedly) standard functions -are actually available in your C libraries, and other miscellaneous -facts about your variant of Unix. For example, there may not be an -`st_blksize' element in the `stat' structure. In this case -`HAVE_ST_BLKSIZE' would be undefined. + The `config.h' file that `configure' creates contains definitions +that describe features of the particular operating system where you are +attempting to compile `gawk'. The three things described by this file +are: what header files are available, so that they can be correctly +included, what (supposedly) standard functions are actually available +in your C libraries, and various miscellaneous facts about your variant +of Unix. For example, there may not be an `st_blksize' element in the +`stat' structure. In this case, `HAVE_ST_BLKSIZE' is undefined. It is possible for your C compiler to lie to `configure'. It may do so by not exiting with an error when a library function is not -available. To get around this, you can edit the file `custom.h'. Use -an `#ifdef' that is appropriate for your system, and either `#define' -any constants that `configure' should have defined but didn't, or -`#undef' any constants that `configure' defined and should not have. -`custom.h' is automatically included by `config.h'. +available. To get around this, edit the file `custom.h'. Use an +`#ifdef' that is appropriate for your system, and either `#define' any +constants that `configure' should have defined but didn't, or `#undef' +any constants that `configure' defined and should not have. `custom.h' +is automatically included by `config.h'. It is also possible that the `configure' program generated by `autoconf' will not work on your system in some other fashion. If you do have a problem, the file `configure.in' is the input for `autoconf'. -You may be able to change this file, and generate a new version of -`configure' that will work on your system. *Note Reporting Problems -and Bugs: Bugs, for information on how to report problems in -configuring `gawk'. The same mechanism may be used to send in updates -to `configure.in' and/or `custom.h'. +You may be able to change this file and generate a new version of +`configure' that works on your system (*note Reporting Problems and +Bugs: Bugs., for information on how to report problems in configuring +`gawk'). The same mechanism may be used to send in updates to +`configure.in' and/or `custom.h'. -File: gawk.info, Node: VMS Installation, Next: PC Installation, Prev: Unix Installation, Up: Installation +File: gawk.info, Node: Non-Unix Installation, Next: Unsupported, Prev: Unix Installation, Up: Installation + +Installation on Other Operating Systems +======================================= + + This minor node describes how to install `gawk' on various non-Unix +systems. + +* Menu: + +* Amiga Installation:: Installing `gawk' on an Amiga. +* BeOS Installation:: Installing `gawk' on BeOS. +* PC Installation:: Installing and Compiling `gawk' on + MS-DOS and OS/2. +* VMS Installation:: Installing `gawk' on VMS. + + +File: gawk.info, Node: Amiga Installation, Next: BeOS Installation, Prev: Non-Unix Installation, Up: Non-Unix Installation + +Installing `gawk' on an Amiga +----------------------------- + + You can install `gawk' on an Amiga system using a Unix emulation +environment, available via anonymous `ftp' from `ftp.ninemoons.com' in +the directory `pub/ade/current'. This includes a shell based on +`pdksh'. The primary component of this environment is a Unix emulation +library, `ixemul.lib'. + + A more complete distribution for the Amiga is available on the Geek +Gadgets CD-ROM, available from: + + CRONUS + 1840 E. Warner Road #105-265 + Tempe, AZ 85284 USA + US Toll Free: (800) 804-0833 + Phone: +1-602-491-0442 + FAX: +1-602-491-0048 + Email: <info@ninemoons.com> + WWW: `http://www.ninemoons.com' + Anonymous `ftp' site: `ftp.ninemoons.com' + + Once you have the distribution, you can configure `gawk' simply by +running `configure': + + configure -v m68k-amigaos + + Then run `make' and you should be all set! If these steps do not +work, please send in a bug report (*note Reporting Problems and Bugs: +Bugs.). + + +File: gawk.info, Node: BeOS Installation, Next: PC Installation, Prev: Amiga Installation, Up: Non-Unix Installation + +Installing `gawk' on BeOS +------------------------- + + Since BeOS DR9, all the tools that you should need to build `gawk' +are included with BeOS. The process is basically identical to the Unix +process of running `configure' and then `make'. Full instructions are +given below. + + You can compile `gawk' under BeOS by extracting the standard sources +and running `configure'. You _must_ specify the location prefix for the +installation directory. For BeOS DR9 and beyond, the best directory to +use is `/boot/home/config', so the `configure' command is: + + configure --prefix=/boot/home/config + + This installs the compiled application into `/boot/home/config/bin', +which is already specified in the standard `PATH'. + + Once the configuration process is completed, you can run `make', and +then `make install': + + $ make + ... + $ make install + + BeOS uses `bash' as its shell; thus, you use `gawk' the same way you +would under Unix. If these steps do not work, please send in a bug +report (*note Reporting Problems and Bugs: Bugs.). + + +File: gawk.info, Node: PC Installation, Next: VMS Installation, Prev: BeOS Installation, Up: Non-Unix Installation + +Installation on PC Operating Systems +------------------------------------ + + This minor node covers installation and usage of `gawk' on x86 +machines running DOS, any version of Windows, or OS/2. In this minor +node, the term "Win32" refers to any of Windows-95/98/ME/NT/2000. + + The limitations of DOS (and DOS shells under Windows or OS/2) has +meant that various "DOS extenders" are often used with programs such as +`gawk'. The varying capabilities of Microsoft Windows 3.1 and Win32 +can add to the confusion. For an overview of the considerations, +please refer to `README_d/README.pc' in the distribution. + +* Menu: + +* PC Binary Installation:: Installing a prepared distribution. +* PC Compiling:: Compiling `gawk' for MS-DOS, Win32, + and OS/2. +* PC Using:: Running `gawk' on MS-DOS, Win32 and + OS/2. + + +File: gawk.info, Node: PC Binary Installation, Next: PC Compiling, Prev: PC Installation, Up: PC Installation + +Installing a Prepared Distribution for PC Systems +................................................. + + If you have received a binary distribution prepared by the DOS +maintainers, then `gawk' and the necessary support files appear under +the `gnu' directory, with executables in `gnu/bin', libraries in +`gnu/lib/awk', and manual pages under `gnu/man'. This is designed for +easy installation to a `/gnu' directory on your drive--however, the +files can be installed anywhere provided `AWKPATH' is set properly. +Regardless of the installation directory, the first line of `igawk.cmd' +and `igawk.bat' (in `gnu/bin') may need to be edited. + + The binary distribution contains a separate file describing the +contents. In particular, it may include more than one version of the +`gawk' executable. OS/2 binary distributions may have a different +arrangement, but installation is similar. + + +File: gawk.info, Node: PC Compiling, Next: PC Using, Prev: PC Binary Installation, Up: PC Installation + +Compiling `gawk' for PC Operating Systems +......................................... + + `gawk' can be compiled for MS-DOS, Win32, and OS/2 using the GNU +development tools from DJ Delorie (DJGPP; MS-DOS only) or Eberhard +Mattes (EMX; MS-DOS, Win32 and OS/2). Microsoft Visual C/C++ can be +used to build a Win32 version, and Microsoft C/C++ can be used to build +16-bit versions for MS-DOS and OS/2. The file `README_d/README.pc' in +the `gawk' distribution contains additional notes, and `pc/Makefile' +contains important information on compilation options. + + To build `gawk', copy the files in the `pc' directory (_except_ for +`ChangeLog') to the directory with the rest of the `gawk' sources. The +`Makefile' contains a configuration section with comments and may need +to be edited in order to work with your `make' utility. + + The `Makefile' contains a number of targets for building various +MS-DOS, Win32, and OS/2 versions. A list of targets is printed if the +`make' command is given without a target. As an example, to build `gawk' +using the DJGPP tools, enter `make djgpp'. + + Using `make' to run the standard tests and to install `gawk' +requires additional Unix-like tools, including `sh', `sed', and `cp'. +In order to run the tests, the `test/*.ok' files may need to be +converted so that they have the usual DOS-style end-of-line markers. +Most of the tests work properly with Stewartson's shell along with the +companion utilities or appropriate GNU utilities. However, some +editing of `test/Makefile' is required. It is recommended that you copy +the file `pc/Makefile.tst' over the file `test/Makefile' as a +replacement. Details can be found in `README_d/README.pc' and in the +file `pc/Makefile.tst'. + + +File: gawk.info, Node: PC Using, Prev: PC Compiling, Up: PC Installation + +Using `gawk' on PC Operating Systems +.................................... + + The OS/2 and MS-DOS versions of `gawk' search for program files as +described in *Note The `AWKPATH' Environment Variable: AWKPATH Variable. +However, semicolons (rather than colons) separate elements in the +`AWKPATH' variable. If `AWKPATH' is not set or is empty, then the +default search path is `".;c:/lib/awk;c:/gnu/lib/awk"'. + + An `sh'-like shell (as opposed to `command.com' under MS-DOS or +`cmd.exe' under OS/2) may be useful for `awk' programming. Ian +Stewartson has written an excellent shell for MS-DOS and OS/2, Daisuke +Aoyama has ported GNU `bash' to MS-DOS using the DJGPP tools, and +several shells are available for OS/2, including `ksh'. The file +`README_d/README.pc' in the `gawk' distribution contains information on +these shells. Users of Stewartson's shell on DOS should examine its +documentation for handling command lines; in particular, the setting +for `gawk' in the shell configuration may need to be changed and the +`ignoretype' option may also be of interest. + + Under OS/2 and DOS, `gawk' (and many other text programs) silently +translate end-of-line `"\r\n"' to `"\n"' on input and `"\n"' to +`"\r\n"' on output. A special `BINMODE' variable allows control over +these translations and is interpreted as follows. + + * If `BINMODE' is `"r"', or `(BINMODE & 1)' is nonzero, then binary + mode is set on read (i.e., no translations on reads). + + * If `BINMODE' is `"w"', or `(BINMODE & 2)' is nonzero, then binary + mode is set on write (i.e., no translations on writes). + + * If `BINMODE' is `"rw"' or `"wr"', binary mode is set for both read + and write (same as `(BINMODE & 3)'). + + * `BINMODE=NON-NULL-STRING' is the same as `BINMODE=3' (i.e., no + translations on reads or writes). However, `gawk' issues a warning + message if the string is not one of `"rw"' or `"wr"'. + +The modes for standard input and standard output are set one time only +(after the command line is read, but before processing any of the `awk' +program). Setting `BINMODE' for standard input or standard output is +accomplished by using an appropriate `-v BINMODE=N' option on the +command line. `BINMODE' is set at the time a file or pipe is opened +and cannot be changed mid-stream. + + The name `BINMODE' was chosen to match `mawk' (*note Other Freely +Available `awk' Implementations: Other Versions.). Both `mawk' and +`gawk' handle `BINMODE' similarly; however, `mawk' adds a `-W +BINMODE=N' option and an environment variable that can set `BINMODE', +`RS', and `ORS'. The files `binmode[1-3].awk' (under `gnu/lib/awk' in +some of the prepared distributions) have been chosen to match `mawk''s +`-W BINMODE=N' option. These can be changed or discarded; in +particular, the setting of `RS' giving the fewest "surprises" is open +to debate. `mawk' uses `RS = "\r\n"' if binary mode is set on read, +which is appropriate for files with the DOS-style end-of-line. + + To Illustrate, the following examples set binary mode on writes for +standard output and other files, and set `ORS' as the "usual" DOS-style +end-of-line: + + gawk -v BINMODE=2 -v ORS="\r\n" ... + +or: + + gawk -v BINMODE=w -f binmode2.awk ... + +These give the same result as the `-W BINMODE=2' option in `mawk'. The +following changes the record separator to `"\r\n"' and sets binary mode +on reads, but does not affect the mode on standard input: + + gawk -v RS="\r\n" --source "BEGIN { BINMODE = 1 }" ... + +or: + + gawk -f binmode1.awk ... + +With proper quoting, in the first example the setting of `RS' can be +moved into the `BEGIN' rule. + + +File: gawk.info, Node: VMS Installation, Prev: PC Installation, Up: Non-Unix Installation How to Compile and Install `gawk' on VMS -======================================== +---------------------------------------- - This section describes how to compile and install `gawk' under VMS. + This node describes how to compile and install `gawk' under VMS. * Menu: @@ -15738,16 +17311,16 @@ How to Compile and Install `gawk' on VMS File: gawk.info, Node: VMS Compilation, Next: VMS Installation Details, Prev: VMS Installation, Up: VMS Installation Compiling `gawk' on VMS ------------------------ +....................... To compile `gawk' under VMS, there is a `DCL' command procedure that -will issue all the necessary `CC' and `LINK' commands, and there is -also a `Makefile' for use with the `MMS' utility. From the source -directory, use either +issues all the necessary `CC' and `LINK' commands. There is also a +`Makefile' for use with the `MMS' utility. From the source directory, +use either: $ @[.VMS]VMSBUILD.COM -or +or: $ MMS/DESCRIPTION=[.VMS]DESCRIP.MMS GAWK @@ -15768,62 +17341,64 @@ VAX C V2.x GNU C Edit `vmsbuild.com' or `descrip.mms'; the changes are different - from those for VAX C V2.x, but equally straightforward. No - changes to `config.h' should be needed. + from those for VAX C V2.x but equally straightforward. No changes + to `config.h' are needed. DEC C Edit `vmsbuild.com' or `descrip.mms' according to their comments. - No changes to `config.h' should be needed. + No changes to `config.h' are needed. - `gawk' has been tested under VAX/VMS 5.5-1 using VAX C V3.2, GNU C -1.40 and 2.3. It should work without modifications for VMS V4.6 and up. + `gawk' has been tested under VAX/VMS 5.5-1 using VAX C V3.2, and GNU +C 1.40 and 2.3. It should work without modifications for VMS V4.6 and +up. File: gawk.info, Node: VMS Installation Details, Next: VMS Running, Prev: VMS Compilation, Up: VMS Installation Installing `gawk' on VMS ------------------------- +........................ To install `gawk', all you need is a "foreign" command, which is a `DCL' symbol whose value begins with a dollar sign. For example: $ GAWK :== $disk1:[gnubin]GAWK -(Substitute the actual location of `gawk.exe' for `$disk1:[gnubin]'.) -The symbol should be placed in the `login.com' of any user who wishes -to run `gawk', so that it will be defined every time the user logs on. +Substitute the actual location of `gawk.exe' for `$disk1:[gnubin]'. The +symbol should be placed in the `login.com' of any user who wants to run +`gawk', so that it is defined every time the user logs on. Alternatively, the symbol may be placed in the system-wide -`sylogin.com' procedure, which will allow all users to run `gawk'. +`sylogin.com' procedure, which allows all users to run `gawk'. Optionally, the help entry can be loaded into a VMS help library: $ LIBRARY/HELP SYS$HELP:HELPLIB [.VMS]GAWK.HLP (You may want to substitute a site-specific help library rather than -the standard VMS library `HELPLIB'.) After loading the help text, +the standard VMS library `HELPLIB'.) After loading the help text, the +command: $ HELP GAWK -will provide information about both the `gawk' implementation and the -`awk' programming language. +provides information about both the `gawk' implementation and the `awk' +programming language. The logical name `AWK_LIBRARY' can designate a default location for -`awk' program files. For the `-f' option, if the specified filename -has no device or directory path information in it, `gawk' will look in -the current directory first, then in the directory specified by the -translation of `AWK_LIBRARY' if the file was not found. If after -searching in both directories, the file still is not found, then `gawk' -appends the suffix `.awk' to the filename and the file search will be -re-tried. If `AWK_LIBRARY' is not defined, that portion of the file -search will fail benignly. +`awk' program files. For the `-f' option, if the specified file name +has no device or directory path information in it, `gawk' looks in the +current directory first, then in the directory specified by the +translation of `AWK_LIBRARY' if the file is not found. If, after +searching in both directories, the file still is not found, `gawk' +appends the suffix `.awk' to the filename and retries the file search. +If `AWK_LIBRARY' is not defined, that portion of the file search fails +benignly. File: gawk.info, Node: VMS Running, Next: VMS POSIX, Prev: VMS Installation Details, Up: VMS Installation Running `gawk' on VMS ---------------------- +..................... - Command line parsing and quoting conventions are significantly + Command-line parsing and quoting conventions are significantly different on VMS, so examples in this Info file or from other sources often need minor changes. They _are_ minor though, and all `awk' programs should run correctly. @@ -15834,168 +17409,122 @@ programs should run correctly. $ gawk -"W" version ! could also be -"W version" or "-W version" -Note that upper-case and mixed-case text must be quoted. +Note that uppercase and mixed-case text must be quoted. The VMS port of `gawk' includes a `DCL'-style interface in addition to the original shell-style interface (see the help entry for details). -One side-effect of dual command line parsing is that if there is only a +One side effect of dual command-line parsing is that if there is only a single parameter (as in the quoted string program above), the command becomes ambiguous. To work around this, the normally optional `--' flag is required to force Unix style rather than `DCL' parsing. If any -other dash-type options (or multiple parameters such as data files to be -processed) are present, there is no ambiguity and `--' can be omitted. +other dash-type options (or multiple parameters such as data files to +process) are present, there is no ambiguity and `--' can be omitted. - The default search path when looking for `awk' program files -specified by the `-f' option is `"SYS$DISK:[],AWK_LIBRARY:"'. The + The default search path, when looking for `awk' program files +specified by the `-f' option, is `"SYS$DISK:[],AWK_LIBRARY:"'. The logical name `AWKPATH' can be used to override this default. The format of `AWKPATH' is a comma-separated list of directory specifications. When defining it, the value should be quoted so that it retains a single -translation, and not a multi-translation `RMS' searchlist. +translation and not a multitranslation `RMS' searchlist. File: gawk.info, Node: VMS POSIX, Prev: VMS Running, Up: VMS Installation Building and Using `gawk' on VMS POSIX --------------------------------------- +...................................... Ignore the instructions above, although `vms/gawk.hlp' should still be made available in a help library. The source tree should be unpacked -into a container file subsystem rather than into the ordinary VMS file -system. Make sure that the two scripts, `configure' and +into a container file subsystem rather than into the ordinary VMS +filesystem. Make sure that the two scripts, `configure' and `vms/posix-cc.sh', are executable; use `chmod +x' on them if necessary. Then execute the following two commands: psx> CC=vms/posix-cc.sh configure psx> make CC=c89 gawk -The first command will construct files `config.h' and `Makefile' out of +The first command constructs files `config.h' and `Makefile' out of templates, using a script to make the C compiler fit `configure''s -expectations. The second command will compile and link `gawk' using -the C compiler directly; ignore any warnings from `make' about being -unable to redefine `CC'. `configure' will take a very long time to -execute, but at least it provides incremental feedback as it runs. +expectations. The second command compiles and links `gawk' using the C +compiler directly; ignore any warnings from `make' about being unable +to redefine `CC'. `configure' takes a very long time to execute, but +at least it provides incremental feedback as it runs. This has been tested with VAX/VMS V6.2, VMS POSIX V2.0, and DEC C V5.2. - Once built, `gawk' will work like any other shell utility. Unlike -the normal VMS port of `gawk', no special command line manipulation is + Once built, `gawk' works like any other shell utility. Unlike the +normal VMS port of `gawk', no special command-line manipulation is needed in the VMS POSIX environment. -File: gawk.info, Node: PC Installation, Next: Atari Installation, Prev: VMS Installation, Up: Installation - -MS-DOS and OS/2 Installation and Compilation -============================================ - - If you have received a binary distribution prepared by the DOS -maintainers, then `gawk' and the necessary support files will appear -under the `gnu' directory, with executables in `gnu/bin', libraries in -`gnu/lib/awk', and manual pages under `gnu/man'. This is designed for -easy installation to a `/gnu' directory on your drive, but the files -can be installed anywhere provided `AWKPATH' is set properly. -Regardless of the installation directory, the first line of `igawk.cmd' -and `igawk.bat' (in `gnu/bin') may need to be edited. +File: gawk.info, Node: Unsupported, Next: Bugs, Prev: Non-Unix Installation, Up: Installation - The binary distribution will contain a separate file describing the -contents. In particular, it may include more than one version of the -`gawk' executable. OS/2 binary distributions may have a different -arrangement, but installation is similar. - - The OS/2 and MS-DOS versions of `gawk' search for program files as -described in *Note The `AWKPATH' Environment Variable: AWKPATH Variable. -However, semicolons (rather than colons) separate elements in the -`AWKPATH' variable. If `AWKPATH' is not set or is empty, then the -default search path is `".;c:/lib/awk;c:/gnu/lib/awk"'. - - An `sh'-like shell (as opposed to `command.com' under MS-DOS or -`cmd.exe' under OS/2) may be useful for `awk' programming. Ian -Stewartson has written an excellent shell for MS-DOS and OS/2, and a -`ksh' clone and GNU Bash are available for OS/2. The file -`README_d/README.pc' in the `gawk' distribution contains information on -these shells. Users of Stewartson's shell on DOS should examine its -documentation on handling of command-lines. In particular, the setting -for `gawk' in the shell configuration may need to be changed, and the -`ignoretype' option may also be of interest. +Unsupported Operating System Ports +================================== - `gawk' can be compiled for MS-DOS and OS/2 using the GNU development -tools from DJ Delorie (DJGPP, MS-DOS-only) or Eberhard Mattes (EMX, -MS-DOS and OS/2). Microsoft C can be used to build 16-bit versions for -MS-DOS and OS/2. The file `README_d/README.pc' in the `gawk' -distribution contains additional notes, and `pc/Makefile' contains -important notes on compilation options. + This sections describes systems for which the `gawk' port is no +longer supported. - To build `gawk', copy the files in the `pc' directory (_except_ for -`ChangeLog') to the directory with the rest of the `gawk' sources. The -`Makefile' contains a configuration section with comments, and may need -to be edited in order to work with your `make' utility. - - The `Makefile' contains a number of targets for building various -MS-DOS and OS/2 versions. A list of targets will be printed if the -`make' command is given without a target. As an example, to build `gawk' -using the DJGPP tools, enter `make djgpp'. +* Menu: - Using `make' to run the standard tests and to install `gawk' -requires additional Unix-like tools, including `sh', `sed', and `cp'. -In order to run the tests, the `test/*.ok' files may need to be -converted so that they have the usual DOS-style end-of-line markers. -Most of the tests will work properly with Stewartson's shell along with -the companion utilities or appropriate GNU utilities. However, some -editing of `test/Makefile' is required. It is recommended that the file -`pc/Makefile.tst' be copied to `test/Makefile' as a replacement. -Details can be found in `README_d/README.pc'. +* Atari Installation:: Installing `gawk' on the Atari ST. +* Tandem Installation:: Installing `gawk' on a Tandem. -File: gawk.info, Node: Atari Installation, Next: Amiga Installation, Prev: PC Installation, Up: Installation +File: gawk.info, Node: Atari Installation, Next: Tandem Installation, Prev: Unsupported, Up: Unsupported Installing `gawk' on the Atari ST -================================= +--------------------------------- + + The Atari port is no longer supported. It is included for those who +might want to use it but it is no longer being actively maintained. There are no substantial differences when installing `gawk' on various Atari models. Compiled `gawk' executables do not require a -large amount of memory with most `awk' programs and should run on all -Motorola processor based models (called further ST, even if that is not +large amount of memory with most `awk' programs, and should run on all +Motorola processor-based models (called further ST, even if that is not exactly right). In order to use `gawk', you need to have a shell, either text or graphics, that does not map all the characters of a command line to -upper-case. Maintaining case distinction in option flags is very -important (*note Command Line Options: Options.). These days this is -the default, and it may only be a problem for some very old machines. -If your system does not preserve the case of option flags, you will -need to upgrade your tools. Support for I/O redirection is necessary -to make it easy to import `awk' programs from other environments. -Pipes are nice to have, but not vital. +uppercase. Maintaining case distinction in option flags is very +important (*note Command-Line Options: Options.). These days this is +the default and it may only be a problem for some very old machines. +If your system does not preserve the case of option flags, you need to +upgrade your tools. Support for I/O redirection is necessary to make +it easy to import `awk' programs from other environments. Pipes are +nice to have but not vital. * Menu: -* Atari Compiling:: Compiling `gawk' on Atari -* Atari Using:: Running `gawk' on Atari +* Atari Compiling:: Compiling `gawk' on Atari. +* Atari Using:: Running `gawk' on Atari. File: gawk.info, Node: Atari Compiling, Next: Atari Using, Prev: Atari Installation, Up: Atari Installation Compiling `gawk' on the Atari ST --------------------------------- +................................ A proper compilation of `gawk' sources when `sizeof(int)' differs -from `sizeof(void *)' requires an ANSI C compiler. An initial port was +from `sizeof(void *)' requires an ISO C compiler. An initial port was done with `gcc'. You may actually prefer executables where `int's are -four bytes wide, but the other variant works as well. +four bytes wide but the other variant works as well. You may need quite a bit of memory when trying to recompile the `gawk' sources, as some source files (`regex.c' in particular) are quite big. If you run out of memory compiling such a file, try reducing the -optimization level for this particular file; this may help. +optimization level for this particular file, which may help. - With a reasonable shell (Bash will do), and in particular if you run -Linux, MiNT or a similar operating system, you have a pretty good -chance that the `configure' utility will succeed. Otherwise sample -versions of `config.h' and `Makefile.st' are given in the `atari' -subdirectory and can be edited and copied to the corresponding files in -the main source directory. Even if `configure' produced something, it -might be advisable to compare its results with the sample versions and -possibly make adjustments. + With a reasonable shell (`bash' will do), you have a pretty good +chance that the `configure' utility will succeed, and in particular if +you run GNU/Linux, MiNT or a similar operating system. Otherwise +sample versions of `config.h' and `Makefile.st' are given in the +`atari' subdirectory and can be edited and copied to the corresponding +files in the main source directory. Even if `configure' produces +something, it might be advisable to compare its results with the sample +versions and possibly make adjustments. Some `gawk' source code fragments depend on a preprocessor define `atarist'. This basically assumes the TOS environment with `gcc'. @@ -16005,100 +17534,104 @@ environment. Also see the remarks about `AWKPATH' and `envsep' in As shipped, the sample `config.h' claims that the `system' function is missing from the libraries, which is not true, and an alternative -implementation of this function is provided in `atari/system.c'. -Depending upon your particular combination of shell and operating -system, you may wish to change the file to indicate that `system' is -available. +implementation of this function is provided in +`unsupported/atari/system.c'. Depending upon your particular +combination of shell and operating system, you might want to change the +file to indicate that `system' is available. File: gawk.info, Node: Atari Using, Prev: Atari Compiling, Up: Atari Installation Running `gawk' on the Atari ST ------------------------------- +.............................. An executable version of `gawk' should be placed, as usual, anywhere in your `PATH' where your shell can find it. - While executing, `gawk' creates a number of temporary files. When -using `gcc' libraries for TOS, `gawk' looks for either of the -environment variables `TEMP' or `TMPDIR', in that order. If either one -is found, its value is assumed to be a directory for temporary files. -This directory must exist, and if you can spare the memory, it is a -good idea to put it on a RAM drive. If neither `TEMP' nor `TMPDIR' are -found, then `gawk' uses the current directory for its temporary files. - - The ST version of `gawk' searches for its program files as described -in *Note The `AWKPATH' Environment Variable: AWKPATH Variable. The -default value for the `AWKPATH' variable is taken from `DEFPATH' + While executing, the Atari version of `gawk' creates a number of +temporary files. When using `gcc' libraries for TOS, `gawk' looks for +either of the environment variables, `TEMP' or `TMPDIR', in that order. +If either one is found, its value is assumed to be a directory for +temporary files. This directory must exist, and if you can spare the +memory, it is a good idea to put it on a RAM drive. If neither `TEMP' +nor `TMPDIR' are found, then `gawk' uses the current directory for its +temporary files. + + The ST version of `gawk' searches for its program files, as +described in *Note The `AWKPATH' Environment Variable: AWKPATH Variable. +The default value for the `AWKPATH' variable is taken from `DEFPATH' defined in `Makefile'. The sample `gcc'/TOS `Makefile' for the ST in the distribution sets `DEFPATH' to `".,c:\lib\awk,c:\gnu\lib\awk"'. The search path can be modified by explicitly setting `AWKPATH' to -whatever you wish. Note that colons cannot be used on the ST to -separate elements in the `AWKPATH' variable, since they have another, -reserved, meaning. Instead, you must use a comma to separate elements +whatever you want. Note that colons cannot be used on the ST to +separate elements in the `AWKPATH' variable, since they have another +reserved meaning. Instead, you must use a comma to separate elements in the path. When recompiling, the separating character can be -modified by initializing the `envsep' variable in `atari/gawkmisc.atr' -to another value. +modified by initializing the `envsep' variable in +`unsupported/atari/gawkmisc.atr' to another value. Although `awk' allows great flexibility in doing I/O redirections from within a program, this facility should be used with care on the ST -running under TOS. In some circumstances the OS routines for file -handle pool processing lose track of certain events, causing the -computer to crash, and requiring a reboot. Often a warm reboot is -sufficient. Fortunately, this happens infrequently, and in rather +running under TOS. In some circumstances, the OS routines for +file-handle pool processing lose track of certain events, causing the +computer to crash and requiring a reboot. Often a warm reboot is +sufficient. Fortunately, this happens infrequently and in rather esoteric situations. In particular, avoid having one part of an `awk' program using `print' statements explicitly redirected to -`"/dev/stdout"', while other `print' statements use the default -standard output, and a calling shell has redirected standard output to -a file. +`/dev/stdout', while other `print' statements use the default standard +output, and a calling shell has redirected standard output to a file. When `gawk' is compiled with the ST version of `gcc' and its usual -libraries, it will accept both `/' and `\' as path separators. While -this is convenient, it should be remembered that this removes one, -technically valid, character (`/') from your file names, and that it -may create problems for external programs, called via the `system' -function, which may not support this convention. Whenever it is -possible that a file created by `gawk' will be used by some other -program, use only backslashes. Also remember that in `awk', -backslashes in strings have to be doubled in order to get literal -backslashes (*note Escape Sequences::). +libraries, it accepts both `/' and `\' as path separators. While this +is convenient, it should be remembered that this removes one +technically valid character (`/') from your file name. It may also +create problems for external programs called via the `system' function, +which may not support this convention. Whenever it is possible that a +file created by `gawk' will be used by some other program, use only +backslashes. Also remember that in `awk', backslashes in strings have +to be doubled in order to get literal backslashes (*note Escape +Sequences::). -File: gawk.info, Node: Amiga Installation, Next: Bugs, Prev: Atari Installation, Up: Installation - -Installing `gawk' on an Amiga -============================= - - You can install `gawk' on an Amiga system using a Unix emulation -environment available via anonymous `ftp' from `ftp.ninemoons.com' in -the directory `pub/ade/current'. This includes a shell based on -`pdksh'. The primary component of this environment is a Unix emulation -library, `ixemul.lib'. - - A more complete distribution for the Amiga is available on the Geek -Gadgets CD-ROM from: - - CRONUS - 1840 E. Warner Road #105-265 - Tempe, AZ 85284 USA - US Toll Free: (800) 804-0833 - Phone: +1-602-491-0442 - FAX: +1-602-491-0048 - Email: `info@ninemoons.com' - WWW: `http://www.ninemoons.com' - Anonymous `ftp' site: `ftp.ninemoons.com' +File: gawk.info, Node: Tandem Installation, Prev: Atari Installation, Up: Unsupported - Once you have the distribution, you can configure `gawk' simply by -running `configure': - - configure -v m68k-amigaos +Installing `gawk' on a Tandem +----------------------------- - Then run `make', and you should be all set! (If these steps do not -work, please send in a bug report; *note Reporting Problems and Bugs: -Bugs..) + The Tandem port is only minimally supported. The port's contributor +no longer has access to a Tandem system. + + The Tandem port was done on a Cyclone machine running D20. The port +is pretty clean and all facilities seem to work except for the I/O +piping facilities (*note Using `getline' from a Pipe: Getline/Pipe., +*Note Using `getline' into a Variable from a Pipe: +Getline/Variable/Pipe, and *Note Redirecting Output of `print' and +`printf': Redirection), which is just too foreign a concept for Tandem. + + To build a Tandem executable from source, download all of the files +so that the file names on the Tandem box conform to the restrictions of +D20. For example, `array.c' becomes `ARRAYC', and `awk.h' becomes +`AWKH'. The totally Tandem-specific files are in the `tandem' +"subvolume" (`unsupported/tandem' in the `gawk' distribution) and +should be copied to the main source directory before building `gawk'. + + The file `compit' can then be used to compile and bind an executable. +Alas, there is no `configure' or `make'. + + Usage is the same as for Unix, except that D20 requires all `{' and +`}' characters to be escaped with `~' on the command line (but _not_ in +script files). Also, the standard Tandem syntax for `/in filename,out +filename/' must be used instead of the usual Unix `<' and `>' for file +redirection. (Redirection options on `getline', `print' etc., are +supported.) + + The `-mr VAL' option (*note Command-Line Options: Options.) has +been "stolen" to enable Tandem users to process fixed-length records +with no "end-of-line" character. That is, `-mr 74' tells `gawk' to read +the input file as fixed 74-byte records. -File: gawk.info, Node: Bugs, Next: Other Versions, Prev: Amiga Installation, Up: Installation +File: gawk.info, Node: Bugs, Next: Other Versions, Prev: Unsupported, Up: Installation Reporting Problems and Bugs =========================== @@ -16106,8 +17639,6 @@ Reporting Problems and Bugs There is nothing more dangerous than a bored archeologist. The Hitchhiker's Guide to the Galaxy - - If you have problems with `gawk' or think that you have found a bug, please report it to the developers; we cannot promise to do anything but we might well want to fix it. @@ -16121,56 +17652,52 @@ documentation! Before reporting a bug or trying to fix it yourself, try to isolate it to the smallest possible `awk' program and input data file that reproduces the problem. Then send us the program and data file, some -idea of what kind of Unix system you're using, and the exact results -`gawk' gave you. Also say what you expected to occur; this will help -us decide whether the problem was really in the documentation. +idea of what kind of Unix system you're using, the compiler you used to +compile `gawk', and the exact results `gawk' gave you. Also say what +you expected to occur; this helps us decide whether the problem is +really in the documentation. Once you have a precise problem, send email to <bug-gawk@gnu.org>. Please include the version number of `gawk' you are using. You can get this information with the command `gawk --version'. Using this -address will automatically send a carbon copy of your mail to Arnold -Robbins. If necessary, he can be reached directly at <arnold@gnu.org>. +address automatically sends a carbon copy of your mail to me. If +necessary, I can be reached directly at <arnold@gnu.org>. The bug +reporting address is preferred since the email list is archived at the +GNU Project. _All email should be in English, since that is my native +language._ - *Important!* Do _not_ try to report bugs in `gawk' by posting to the + *Caution:* Do _not_ try to report bugs in `gawk' by posting to the Usenet/Internet newsgroup `comp.lang.awk'. While the `gawk' developers do occasionally read this newsgroup, there is no guarantee that we will -see your posting. The steps described above are the official, +see your posting. The steps described above are the official recognized ways for reporting bugs. Non-bug suggestions are always welcome as well. If you have questions about things that are unclear in the documentation or are -just obscure features, ask Arnold Robbins; he will try to help you out, -although he may not have the time to fix the problem. You can send him -electronic mail at the Internet address above. +just obscure features, ask me; I will try to help you out, although I +may not have the time to fix the problem. You can send me electronic +mail at the Internet address noted previously. If you find bugs in one of the non-Unix ports of `gawk', please send an electronic mail message to the person who maintains that port. They -are listed below, and also in the `README' file in the `gawk' -distribution. Information in the `README' file should be considered -authoritative if it conflicts with this Info file. - - The people maintaining the non-Unix ports of `gawk' are: - -MS-DOS - Scott Deifik, `scottd@amgen.com', and Darrel Hankerson, - `hankedr@mail.auburn.edu'. - -OS/2 - Kai Uwe Rommel, `rommel@ars.de'. +are named in the following list, as well as in the `README' file in the +`gawk' distribution. Information in the `README' file should be +considered authoritative if it conflicts with this Info file. -VMS - Pat Rankin, `rankin@eql.caltech.edu'. + The people maintaining the non-Unix ports of `gawk' are as follows: -Atari ST - Michal Jaegermann, `michal@gortel.phys.ualberta.ca'. +Amiga Fred Fish, <fnf@ninemoons.com>. +BeOS Martin Brown, <mc@whoever.com>. +MS-DOS Scott Deifik, <scottd@amgen.com> and Darrel + Hankerson, <hankedr@mail.auburn.edu>. +MS-Windows Juan Grigera, <juan@biophnet.unlp.edu.ar>. +OS/2 Kai Uwe Rommel, <rommel@ars.de>. +Tandem Stephen Davies, <scldad@sdc.com.au>. +VMS Pat Rankin, <rankin@eql.caltech.edu>. -Amiga - Fred Fish, `fnf@ninemoons.com'. - - If your bug is also reproducible under Unix, please send copies of -your report to the general GNU bug list, as well as to Arnold Robbins, -at the addresses listed above. + If your bug is also reproducible under Unix, please send a copy of +your report to the <bug-gawk@gnu.org> email list as well. File: gawk.info, Node: Other Versions, Prev: Bugs, Up: Installation @@ -16179,33 +17706,36 @@ Other Freely Available `awk' Implementations ============================================ It's kind of fun to put comments like this in your awk code. - `// Do C++ comments work? answer: yes! of course' + `// Do C++ comments work? answer: yes! of course' Michael Brennan + There are three other freely available `awk' implementations. This +minor node briefly describes where to get them: +Unix `awk' + Brian Kernighan has made his implementation of `awk' freely + available. You can retrieve this version via the World Wide Web + from his home page.(1) It is available in several archive formats: - There are two other freely available `awk' implementations. This -section briefly describes where to get them. + Shell archive + `http://cm.bell-labs.com/who/bwk/awk.shar' -Unix `awk' - Brian Kernighan has been able to make his implementation of `awk' - freely available. You can get it via anonymous `ftp' to the host - `netlib.bell-labs.com'. Change directory to `/netlib/research'. - Use "binary" or "image" mode, and retrieve `awk.bundle.gz'. + Compressed `tar' file + `http://cm.bell-labs.com/who/bwk/awk.tar.gz' - This is a shell archive that has been compressed with the GNU - `gzip' utility. It can be uncompressed with the `gunzip' utility. + Zip file + `http://cm.bell-labs.com/who/bwk/awk.zip' - You can also retrieve this version via the World Wide Web from his - home page (http://cm.bell-labs.com/who/bwk). + This version requires an ISO C (1990 standard) compiler; the C + compiler from GCC (the GNU Compiler Collection) works quite nicely. - This version requires an ANSI C compiler; GCC (the GNU C compiler) - works quite nicely. + *Note Extensions in the Bell Laboratories `awk': BTL, for a list + of extensions in this `awk' that are not in POSIX `awk'. `mawk' Michael Brennan has written an independent implementation of `awk', - called `mawk'. It is available under the GPL (*note GNU GENERAL - PUBLIC LICENSE: Copying.), just as `gawk' is. + called `mawk'. It is available under the GPL (*note GNU General + Public License: Copying.), just as `gawk' is. You can get it via anonymous `ftp' to the host `ftp.whidbey.net'. Change directory to `/pub/brennan'. Use "binary" or "image" mode, @@ -16216,22 +17746,73 @@ Unix `awk' similar to `gawk''s (*note Compiling and Installing `gawk' on Unix: Unix Installation.). + `mawk' has the following extensions that are not in POSIX `awk': + + * The `fflush' built-in function for flushing buffered output + (*note Input/Output Functions: I/O Functions.). + + * The `**' and `**=' operators (*note Arithmetic Operators: + Arithmetic Ops. and also see *Note Assignment Expressions: + Assignment Ops). + + * The use of `func' as an abbreviation for `function' (*note + Function Definition Syntax: Definition Syntax.). + + * The `\x' escape sequence (*note Escape Sequences::). + + * The `/dev/stdout', and `/dev/stderr' special files (*note + Special File Names in `gawk': Special Files.). Use `"-"' + instead of `"/dev/stdin"' with `mawk'. + + * The ability for `FS' and for the third argument to `split' to + be null strings (*note Making Each Character a Separate + Field: Single Character Fields.). + + * The ability to delete all of an array at once with `delete + ARRAY' (*note The `delete' Statement: Delete.). + + * The ability for `RS' to be a regexp (*note How Input Is Split + into Records: Records.). + + * The `BINMODE' special variable for non-Unix operating systems + (*note Using `gawk' on PC Operating Systems: PC Using.). + + The next version of `mawk' will support `nextfile'. + +`awka' + Written by Andrew Sumner, `awka' translates `awk' programs into C, + compiles them, and links them with a library of functions that + provides the core `awk' functionality. It also has a number of + extensions. + + The `awk' translator is released under the GPL, and the library is + under the LGPL. + + To get `awka', go to `http://awka.sourceforge.net'. You can reach + Andrew Sumner at <andrew_sumner@bigfoot.com>. + + ---------- Footnotes ---------- + + (1) `http://cm.bell-labs.com/who/bwk' + -File: gawk.info, Node: Notes, Next: Glossary, Prev: Installation, Up: Top +File: gawk.info, Node: Notes, Next: Basic Concepts, Prev: Installation, Up: Top Implementation Notes ******************** This appendix contains information mainly of interest to implementors and maintainers of `gawk'. Everything in it applies -specifically to `gawk', and not to other implementations. +specifically to `gawk' and not to other implementations. * Menu: -* Compatibility Mode:: How to disable certain `gawk' extensions. +* Compatibility Mode:: How to disable certain `gawk' + extensions. * Additions:: Making Additions To `gawk'. +* Dynamic Extensions:: Adding new built-in functions to + `gawk'. * Future Extensions:: New features that may be implemented one day. -* Improvements:: Suggestions for improvements by volunteers. File: gawk.info, Node: Compatibility Mode, Next: Additions, Prev: Notes, Up: Notes @@ -16242,7 +17823,7 @@ Downward Compatibility and Debugging *Note Extensions in `gawk' Not in POSIX `awk': POSIX/GNU, for a summary of the GNU extensions to the `awk' language and program. All of these features can be turned off by invoking `gawk' with the -`--traditional' option, or with the `--posix' option. +`--traditional' option or with the `--posix' option. If `gawk' is compiled for debugging with `-DDEBUG', then there is one more option available on the command line: @@ -16252,28 +17833,30 @@ one more option available on the command line: Print out the parse stack information as the program is being parsed. - This option is intended only for serious `gawk' developers, and not + This option is intended only for serious `gawk' developers and not for the casual user. It probably has not even been compiled into your version of `gawk', since it slows down execution. -File: gawk.info, Node: Additions, Next: Future Extensions, Prev: Compatibility Mode, Up: Notes +File: gawk.info, Node: Additions, Next: Dynamic Extensions, Prev: Compatibility Mode, Up: Notes Making Additions to `gawk' ========================== - If you should find that you wish to enhance `gawk' in a significant + If you find that you want to enhance `gawk' in a significant fashion, you are perfectly free to do so. That is the point of having -free software; the source code is available, and you are free to change -it as you wish (*note GNU GENERAL PUBLIC LICENSE: Copying.). +free software; the source code is available and you are free to change +it as you want (*note GNU General Public License: Copying.). - This section discusses the ways you might wish to change `gawk', and -any considerations you should bear in mind. + This minor node discusses the ways you might want to change `gawk' +as well as any considerations you should bear in mind. * Menu: -* Adding Code:: Adding code to the main body of `gawk'. -* New Ports:: Porting `gawk' to a new operating system. +* Adding Code:: Adding code to the main body of + `gawk'. +* New Ports:: Porting `gawk' to a new operating + system. File: gawk.info, Node: Adding Code, Next: New Ports, Prev: Additions, Up: Additions @@ -16284,28 +17867,35 @@ Adding New Features You are free to add any new features you like to `gawk'. However, if you want your changes to be incorporated into the `gawk' distribution, there are several steps that you need to take in order to -make it possible for me to include your changes. +make it possible for me to include your changes: + + 1. Before building the new feature into `gawk' itself, consider + writing it as an extension module (*note Adding New Built-in + Functions to `gawk': Dynamic Extensions.). If that's not + possible, continue with the rest of the steps in this list. - 1. Get the latest version. It is much easier for me to integrate + 2. Get the latest version. It is much easier for me to integrate changes if they are relative to the most recent distributed version of `gawk'. If your version of `gawk' is very old, I may - not be able to integrate them at all. *Note Getting the `gawk' + not be able to integrate them at all. (*Note Getting the `gawk' Distribution: Getting, for information on getting the latest - version of `gawk'. + version of `gawk'.) - 2. See *note (Version)Top:: standards, GNU Coding Standards. This + 3. See *note (Version)Top:: standards, GNU Coding Standards. This document describes how GNU software should be written. If you haven't read it, please do so, preferably _before_ starting to - modify `gawk'. (The `GNU Coding Standards' are available as part - of the Autoconf distribution, from the FSF.) + modify `gawk'. (The `GNU Coding Standards' are available from the + GNU Project's `ftp' site, at + `ftp://gnudist.gnu.org/gnu/GNUInfo/standards.text'. Texinfo, + Info, and DVI versions are also available.) - 3. Use the `gawk' coding style. The C code for `gawk' follows the + 4. Use the `gawk' coding style. The C code for `gawk' follows the instructions in the `GNU Coding Standards', with minor exceptions. The code is formatted using the traditional "K&R" style, - particularly as regards the placement of braces and the use of - tabs. In brief, the coding rules for `gawk' are: + particularly as regards to the placement of braces and the use of + tabs. In brief, the coding rules for `gawk' are as follows: - * Use old style (non-prototype) function headers when defining + * Use ANSI/ISO style (prototype) function headers when defining functions. * Put the name of the function at the beginning of its own line. @@ -16314,34 +17904,35 @@ make it possible for me to include your changes. the line above the line with the name and arguments of the function. - * The declarations for the function arguments should not be - indented. - * Put spaces around parentheses used in control structures - (`if', `while', `for', `do', `switch' and `return'). + (`if', `while', `for', `do', `switch', and `return'). * Do not put spaces in front of parentheses used in function calls. - * Put spaces around all C operators, and after commas in + * Put spaces around all C operators and after commas in function calls. - * Do not use the comma operator to produce multiple - side-effects, except in `for' loop initialization and - increment parts, and in macro bodies. + * Do not use the comma operator to produce multiple side + effects, except in `for' loop initialization and increment + parts, and in macro bodies. * Use real tabs for indenting, not spaces. * Use the "K&R" brace layout style. * Use comparisons against `NULL' and `'\0'' in the conditions of - `if', `while' and `for' statements, and in the `case's of - `switch' statements, instead of just the plain pointer or + `if', `while', and `for' statements, as well as in the `case's + of `switch' statements, instead of just the plain pointer or character value. - * Use the `TRUE', `FALSE', and `NULL' symbolic constants, and - the character constant `'\0'' where appropriate, instead of - `1' and `0'. + * Use the `TRUE', `FALSE' and `NULL' symbolic constants and the + character constant `'\0'' where appropriate, instead of `1' + and `0'. + + * Use the `ISALPHA', `ISDIGIT', etc. macros, instead of the + traditional lowercase versions; these macros are better + behaved for non-ASCII character sets. * Provide one-line descriptive comments for each function. @@ -16349,54 +17940,54 @@ make it possible for me to include your changes. it. * Do not use the `alloca' function for allocating memory off - the stack. Its use causes more portability trouble than the - minor benefit of not having to free the storage. Instead, use - `malloc' and `free'. + the stack. Its use causes more portability trouble than is + worth the minor benefit of not having to free the storage. + Instead, use `malloc' and `free'. - If I have to reformat your code to follow the coding style used in - `gawk', I may not bother. + *Note:* If I have to reformat your code to follow the coding style + used in `gawk', I may not bother to integrate your changes at all. - 4. Be prepared to sign the appropriate paperwork. In order for the + 5. Be prepared to sign the appropriate paperwork. In order for the FSF to distribute your changes, you must either place those - changes in the public domain, and submit a signed statement to that + changes in the public domain and submit a signed statement to that effect, or assign the copyright in your changes to the FSF. Both - of these actions are easy to do, and _many_ people have done so + of these actions are easy to do and _many_ people have done so already. If you have questions, please contact me (*note Reporting - Problems and Bugs: Bugs.), or `gnu@gnu.org'. + Problems and Bugs: Bugs.), or <gnu@gnu.org>. - 5. Update the documentation. Along with your new code, please supply - new sections and or chapters for this Info file. If at all + 6. Update the documentation. Along with your new code, please supply + new sections and/or chapters for this Info file. If at all possible, please use real Texinfo, instead of just supplying unformatted ASCII text (although even that is better than no - documentation at all). Conventions to be followed in `Effective - AWK Programming' are provided after the `@bye' at the end of the - Texinfo source file. If possible, please update the man page as - well. + documentation at all). Conventions to be followed in `GAWK: + Effective AWK Programming' are provided after the `@bye' at the + end of the Texinfo source file. If possible, please update the + `man' page as well. You will also have to sign paperwork for your documentation changes. - 6. Submit changes as context diffs or unified diffs. Use `diff -c -r + 7. Submit changes as context diffs or unified diffs. Use `diff -c -r -N' or `diff -u -r -N' to compare the original `gawk' source tree - with your version. (I find context diffs to be more readable, but + with your version. (I find context diffs to be more readable but unified diffs are more compact.) I recommend using the GNU version of `diff'. Send the output produced by either run of - `diff' to me when you submit your changes. *Note Reporting - Problems and Bugs: Bugs, for the electronic mail information. + `diff' to me when you submit your changes. (*Note Reporting + Problems and Bugs: Bugs, for the electronic mail information.) Using this format makes it easy for me to apply your changes to the master version of the `gawk' source code (using `patch'). If I have to apply the changes manually, using a text editor, I may not do so, particularly if there are lots of changes. - 7. Include an entry for the `ChangeLog' file with your submission. - This further helps minimize the amount of work I have to do, + 8. Include an entry for the `ChangeLog' file with your submission. + This helps further minimize the amount of work I have to do, making it easier for me to accept patches. Although this sounds like a lot of work, please remember that while -you may write the new code, I have to maintain it and support it, and -if it isn't possible for me to do that with a minimum of extra work, -then I probably will not. +you may write the new code, I have to maintain it and support it. If it +isn't possible for me to do that with a minimum of extra work, then I +probably will not. File: gawk.info, Node: New Ports, Prev: Adding Code, Up: Additions @@ -16404,37 +17995,37 @@ File: gawk.info, Node: New Ports, Prev: Adding Code, Up: Additions Porting `gawk' to a New Operating System ---------------------------------------- - If you wish to port `gawk' to a new operating system, there are -several steps to follow. + If you want to port `gawk' to a new operating system, there are +several steps to follow: 1. Follow the guidelines in *Note Adding New Features: Adding Code, concerning coding style, submission of diffs, and so on. 2. When doing a port, bear in mind that your code must co-exist - peacefully with the rest of `gawk', and the other ports. Avoid + peacefully with the rest of `gawk' and the other ports. Avoid gratuitous changes to the system-independent parts of the code. If at all possible, avoid sprinkling `#ifdef's just for your port throughout the code. If the changes needed for a particular system affect too much of the code, I probably will not accept them. In such a case, you - will, of course, be able to distribute your changes on your own, - as long as you comply with the GPL (*note GNU GENERAL PUBLIC - LICENSE: Copying.). + can, of course, distribute your changes on your own, as long as + you comply with the GPL (*note GNU General Public License: + Copying.). 3. A number of the files that come with `gawk' are maintained by other people at the Free Software Foundation. Thus, you should not - change them unless it is for a very good reason. I.e. changes are - not out of the question, but changes to these files will be - scrutinized extra carefully. The files are `alloca.c', - `getopt.h', `getopt.c', `getopt1.c', `regex.h', `regex.c', `dfa.h', - `dfa.c', `install-sh', and `mkinstalldirs'. + change them unless it is for a very good reason; i.e., changes are + not out of the question, but changes to these files are + scrutinized extra carefully. The files are `getopt.h', `getopt.c', + `getopt1.c', `regex.h', `regex.c', `dfa.h', `dfa.c', `install-sh', + and `mkinstalldirs'. 4. Be willing to continue to maintain the port. Non-Unix operating systems are supported by volunteers who maintain the code needed - to compile and run `gawk' on their systems. If no-one volunteers - to maintain a port, that port becomes unsupported, and it may be - necessary to remove it from the distribution. + to compile and run `gawk' on their systems. If noone volunteers to + maintain a port, it becomes unsupported and it may be necessary to + remove it from the distribution. 5. Supply an appropriate `gawkmisc.???' file. Each port has its own `gawkmisc.???' that implements certain operating system specific @@ -16444,120 +18035,690 @@ several steps to follow. subdirectory. Be sure to update it as well. Each port's `gawkmisc.???' file has a suffix reminiscent of the - machine or operating system for the port. For example, + machine or operating system for the port--for example, `pc/gawkmisc.pc' and `vms/gawkmisc.vms'. The use of separate suffixes, instead of plain `gawkmisc.c', makes it possible to move files from a port's subdirectory into the main subdirectory, without accidentally destroying the real `gawkmisc.c' file. - (Currently, this is only an issue for the MS-DOS and OS/2 ports.) - - 6. Supply a `Makefile' and any other C source and header files that - are necessary for your operating system. All your code should be - in a separate subdirectory, with a name that is the same as, or - reminiscent of, either your operating system or the computer - system. If possible, try to structure things so that it is not - necessary to move files out of the subdirectory into the main - source directory. If that is not possible, then be sure to avoid - using names for your files that duplicate the names of files in - the main source directory. + (Currently, this is only an issue for the PC operating system + ports.) + + 6. Supply a `Makefile' as well as any other C source and header files + that are necessary for your operating system. All your code + should be in a separate subdirectory, with a name that is the same + as, or reminiscent of, either your operating system or the + computer system. If possible, try to structure things so that it + is not necessary to move files out of the subdirectory into the + main source directory. If that is not possible, then be sure to + avoid using names for your files that duplicate the names of files + in the main source directory. 7. Update the documentation. Please write a section (or sections) for this Info file describing the installation and compilation - steps needed to install and/or compile `gawk' for your system. + steps needed to compile and/or install `gawk' for your system. 8. Be prepared to sign the appropriate paperwork. In order for the FSF to distribute your code, you must either place your code in - the public domain, and submit a signed statement to that effect, - or assign the copyright in your code to the FSF. Both of these - actions are easy to do, and _many_ people have done so already. If - you have questions, please contact me, or `gnu@gnu.org'. + the public domain and submit a signed statement to that effect, or + assign the copyright in your code to the FSF. Both of these + actions are easy to do and _many_ people have done so already. If + you have questions, please contact me, or <gnu@gnu.org>. + + Following these steps makes it much easier to integrate your changes +into `gawk' and have them co-exist happily with other operating +systems' code that is already there. + + In the code that you supply and maintain, feel free to use a coding +style and brace layout that suits your taste. + + +File: gawk.info, Node: Dynamic Extensions, Next: Future Extensions, Prev: Additions, Up: Notes + +Adding New Built-in Functions to `gawk' +======================================= + + Danger Will Robinson! Danger!! + Warning! Warning! + The Robot + + Beginning with `gawk' 3.1, it is possible to add new built-in +functions to `gawk' using dynamically loaded libraries. This facility +is available on systems (such as GNU/Linux) that support the `dlopen' +and `dlsym' functions. This minor node describes how to write and use +dynamically loaded extentions for `gawk'. Experience with programming +in C or C++ is necessary when reading this minor node. + + *Caution:* The facilities described in this minor node are very much +subject to change in the next `gawk' release. Be aware that you may +have to re-do everything, perhaps from scratch, upon the next release. + +* Menu: + +* Internals:: A brief look at some `gawk' internals. +* Sample Library:: A example of new functions. + + +File: gawk.info, Node: Internals, Next: Sample Library, Prev: Dynamic Extensions, Up: Dynamic Extensions + +A Minimal Introduction to `gawk' Internals +------------------------------------------ + + The truth is that `gawk' was not designed for simple extensibility. +The facilities for adding functions using shared libraries work, but +are something of a "bag on the side." Thus, this tour is brief and +simplistic; would-be `gawk' hackers are encouraged to spend some time +reading the source code before trying to write extensions based on the +material presented here. Of particular note are the files `awk.h', +`builtin.c', and `eval.c'. Reading `awk.y' in order to see how the +parse tree is built would also be of use. + + With the disclaimers out of the way, the following types, structure +members, functions, and macros are declared in `awk.h' and are of use +when writing extensions. The next minor node shows how they are used: + +`AWKNUM' + An `AWKNUM' is the internal type of `awk' floating-point numbers. + Typically, it is a C `double'. + +`NODE' + Just about everything is done using objects of type `NODE'. These + contain both strings and numbers, as well as variables and arrays. + +`AWKNUM force_number(NODE *n)' + This macro forces a value to be numeric. It returns the actual + numeric value contained in the node. It may end up calling an + internal `gawk' function. + +`void force_string(NODE *n)' + This macro guarantees that a `NODE''s string value is current. It + may end up calling an internal `gawk' function. It also + guarantees that the string is zero-terminated. + +`n->param_cnt' + The number of parameters actually passed in a function call at + runtime. + +`n->stptr' +`n->stlen' + The data and length of a `NODE''s string value, respectively. The + string is _not_ guaranteed to be zero-terminated. If you need to + pass the string value to a C library function, save the value in + `n->stptr[n->stlen]', assign `'\0'' to it, call the routine, and + then restore the value. + +`n->type' + The type of the `NODE'. This is a C `enum'. Values should be + either `Node_var' or `Node_var_array' for function parameters. + +`n->vname' + The "variable name" of a node. This is not of much use inside + externally written extensions. + +`void assoc_clear(NODE *n)' + Clears the associative array pointed to by `n'. Make sure that + `n->type == Node_var_array' first. + +`NODE **assoc_lookup(NODE *symbol, NODE *subs, int reference)' + Finds, and installs if necessary, array elements. `symbol' is the + array, `subs' is the subscript. This is usually a value created + with `tmp_string' (see below). `reference' should be `TRUE' if it + is an error to use the value before it is created. Typically, + `FALSE' is the correct value to use from extension functions. + +`NODE *make_string(char *s, size_t len)' + Take a C string and turn it into a pointer to a `NODE' that can be + stored appropriately. This is permanent storage; understanding of + `gawk' memory management is helpful. + +`NODE *make_number(AWKNUM val)' + Take an `AWKNUM' and turn it into a pointer to a `NODE' that can + be stored appropriately. This is permanent storage; understanding + of `gawk' memory management is helpful. + +`NODE *tmp_string(char *s, size_t len);' + Take a C string and turn it into a pointer to a `NODE' that can be + stored appropriately. This is temporary storage; understanding of + `gawk' memory management is helpful. + +`NODE *tmp_number(AWKNUM val)' + Take an `AWKNUM' and turn it into a pointer to a `NODE' that can + be stored appropriately. This is temporary storage; understanding + of `gawk' memory management is helpful. + +`NODE *dupnode(NODE *n)' + Duplicate a node. In most cases, this increments an internal + reference count instead of actually duplicating the entire `NODE'; + understanding of `gawk' memory management is helpful. + +`void free_temp(NODE *n)' + This macro releases the memory associated with a `NODE' allocated + with `tmp_string' or `tmp_number'. Understanding of `gawk' memory + management is helpful. + +`void make_builtin(char *name, NODE *(*func)(NODE *), int count)' + Register a C function pointed to by `func' as new built-in + function `name'. `name' is a regular C string. `count' is the + maximum number of arguments that the function takes. The function + should be written in the following manner: + + /* do_xxx --- do xxx function for gawk */ + + NODE * + do_xxx(NODE *tree) + { + ... + } - Following these steps will make it much easier to integrate your -changes into `gawk', and have them co-exist happily with the code for -other operating systems that is already there. +`NODE *get_argument(NODE *tree, int i)' + This function is called from within a C extension function to get + the `i''th argument from the function call. The first argument is + argument zero. + +`void set_value(NODE *tree)' + This function is called from within a C extension function to set + the return value from the extension function. This value is what + the `awk' program sees as the return value from the new `awk' + function. + +`void update_ERRNO(void)' + This function is called from within a C extension function to set + the value of `gawk''s `ERRNO' variable, based on the current value + of the C `errno' variable. It is provided as a convenience. + + An argument that is supposed to be an array needs to be handled with +some extra code, in case the array being passed in is actually from a +function parameter. The following "boiler plate" code shows how to do +this: + + NODE *the_arg; + + the_arg = get_argument(tree, 2); /* assume need 3rd arg, 0-based */ + + /* if a parameter, get it off the stack */ + if (the_arg->type == Node_param_list) + the_arg = stack_ptr[the_arg->param_cnt]; + + /* parameter referenced an array, get it */ + if (the_arg->type == Node_array_ref) + the_arg = the_arg->orig_array; + + /* check type */ + if (the_arg->type != Node_var && the_arg->type != Node_var_array) + fatal("newfunc: third argument is not an array"); + + /* force it to be an array, if necessary, clear it */ + the_arg->type = Node_var_array; + assoc_clear(the_arg); - In the code that you supply, and that you maintain, feel free to use -a coding style and brace layout that suits your taste. + Again, you should spend time studying the `gawk' internals; don't +just blindly copy this code. -File: gawk.info, Node: Future Extensions, Next: Improvements, Prev: Additions, Up: Notes +File: gawk.info, Node: Sample Library, Prev: Internals, Up: Dynamic Extensions + +Directory and File Operation Built-ins +-------------------------------------- + + Two useful functions that are not in `awk' are `chdir' (so that an +`awk' program can change its directory) and `stat' (so that an `awk' +program can gather information about a file). This minor node +implements these functions for `gawk' in an external extension library. + +* Menu: + +* Internal File Description:: What the new functions will do. +* Internal File Ops:: The code for internal file operations. +* Using Internal File Ops:: How to use an external extension. + + +File: gawk.info, Node: Internal File Description, Next: Internal File Ops, Prev: Sample Library, Up: Sample Library + +Using `chdir' and `stat' +........................ + + This minor node shows how to use the new functions at the `awk' +level once they've been integrated into the running `gawk' interpreter. +Using `chdir' is very straightforward. It takes one argument, the new +directory to change to: + + ... + newdir = "/home/arnold/funstuff" + ret = chdir(newdir) + if (ret < 0) { + printf("could not change to %s: %s\n", + newdir, ERRNO) > "/dev/stderr" + exit 1 + } + ... + + The return value is negative if the `chdir' failed, and `ERRNO' +(*note Built-in Variables::) is set to a string indicating the error. + + Using `stat' is a bit more complicated. The C `stat' function fills +in a structure that has a fair amount of information. The right way to +model this in `awk' is to fill in an associative array with the +appropriate information: + + file = "/home/arnold/.profile" + fdata[1] = "x" # force `fdata' to be an array + ret = stat(file, fdata) + if (ret < 0) { + printf("could not stat %s: %s\n", + file, ERRNO) > "/dev/stderr" + exit 1 + } + printf("size of %s is %d bytes\n", file, fdata["size"]) + + The `stat' function always clears the data array, even if the `stat' +fails. It fills in the following elements: + +`"name"' + The name of the file that was `stat''ed. + +`"dev"' +`"ino"' + The file's device and inode numbers, respectively. + +`"mode"' + The file's mode, as a numeric value. This includes both the file's + type and its permissions. + +`"nlink"' + The number of hard links (directory entries) the file has. + +`"uid"' +`"gid"' + The numeric user and group ID numbers of the file's owner. + +`"size"' + The size in bytes of the file. + +`"blocks"' + The number of disk blocks the file actually occupies. This may not + be a function of the file's size if the file has holes. + +`"atime"' +`"mtime"' +`"ctime"' + The file's last access, modification, and inode update times, + respectively. These are numeric timestamps, suitable for + formatting with `strftime' (*note Built-in Functions: Built-in.). + +`"pmode"' + The file's "printable mode." This is a string representation of + the file's type and permissions, such as what is produced by `ls + -l'--for example, `"drwxr-xr-x"'. + +`"type"' + A printable string representation of the file's type. The value + is one of the following: + + `"blockdev"' + `"chardev"' + The file is a block or character device ("special file"). + + `"directory"' + The file is a directory. + + `"fifo"' + The file is a named-pipe (also known as a FIFO). + + `"file"' + The file is just a regular file. + + `"socket"' + The file is an `AF_UNIX' ("Unix domain") socket in the + filesystem. + + `"symlink"' + The file is a symbolic link. + + Several additional elements may be present depending upon the +operating system and the type of the file. You can test for them in +your `awk' program by using the `in' operator (*note Referring to an +Array Element: Reference to Elements.): + +`"blksize"' + The preferred block size for I/O to the file. This field is not + present on all POSIX-like systems in the C `stat' structure. + +`"linkval"' + If the file is a symbolic link, this element is the name of the + file the link points to (i.e., the value of the link). + +`"rdev"' +`"major"' +`"minor"' + If the file is a block or character device file, then these values + represent the numeric device number and the major and minor + components of that number, respectively. + + +File: gawk.info, Node: Internal File Ops, Next: Using Internal File Ops, Prev: Internal File Description, Up: Sample Library + +C Code for `chdir' and `stat' +............................. + + Here is the C code for these extensions. They were written for +GNU/Linux. The code needs some more work for complete portability to +other POSIX-compliant systems:(1) + + #include "awk.h" + + #include <sys/sysmacros.h> + + /* do_chdir --- provide dynamically loaded + chdir() builtin for gawk */ + + static NODE * + do_chdir(tree) + NODE *tree; + { + NODE *newdir; + int ret = -1; + + newdir = get_argument(tree, 0); + + The file includes the `"awk.h"' header file for definitions for the +`gawk' internals. It includes `<sys/sysmacros.h>' for access to the +`major' and `minor' macros. + + By convention, for an `awk' function `foo', the function that +implements it is called `do_foo'. The function should take a `NODE *' +argument, usually called `tree', that represents the argument list to +the function. The `newdir' variable represents the new directory to +change to, retrieved with `get_argument'. Note that the first argument +is numbered zero. + + This code actually accomplishes the `chdir'. It first forces the +argument to be a string and passes the string value to the `chdir' +system call. If the `chdir' fails, `ERRNO' is updated. The result of +`force_string' has to be freed with `free_temp': + + if (newdir != NULL) { + (void) force_string(newdir); + ret = chdir(newdir->stptr); + if (ret < 0) + update_ERRNO(); + + free_temp(newdir); + } + + Finally, the function returns the return value to the `awk' level, +using `set_value'. Then it must return a value from the call to the new +built-in (this value ignored by the interpreter): + + /* Set the return value */ + set_value(tmp_number((AWKNUM) ret)); + + /* Just to make the interpreter happy */ + return tmp_number((AWKNUM) 0); + } + + The `stat' built-in is more involved. First comes a function that +turns a numeric mode into a printable representation (e.g., 644 becomes +`-rw-r--r--'). This is omitted here for brevity: + + /* format_mode --- turn a stat mode field + into something readable */ + + static char * + format_mode(fmode) + unsigned long fmode; + { + ... + } + + Next comes the actual `do_stat' function itself. First come the +variable declarations and argument checking: + + /* do_stat --- provide a stat() function for gawk */ + + static NODE * + do_stat(tree) + NODE *tree; + { + NODE *file, *array; + struct stat sbuf; + int ret; + char *msg; + NODE **aptr; + char *pmode; /* printable mode */ + char *type = "unknown"; + + /* check arg count */ + if (tree->param_cnt != 2) + fatal( + "stat: called with %d arguments, should be 2", + tree->param_cnt); + + Then comes the actual work. First, we get the arguments. Then, we +always clear the array. To get the file information, we use `lstat', +in case the file is a symbolic link. If there's an error, we set +`ERRNO' and return: + + /* + * directory is first arg, + * array to hold results is second + */ + file = get_argument(tree, 0); + array = get_argument(tree, 1); + + /* empty out the array */ + assoc_clear(array); + + /* lstat the file, if error, set ERRNO and return */ + (void) force_string(file); + ret = lstat(file->stptr, & sbuf); + if (ret < 0) { + update_ERRNO(); + + set_value(tmp_number((AWKNUM) ret)); + + free_temp(file); + return tmp_number((AWKNUM) 0); + } + + Now comes the tedious part: filling in the array. Only a few of the +calls are shown here, since they all follow the same pattern: + + /* fill in the array */ + aptr = assoc_lookup(array, tmp_string("name", 4), FALSE); + *aptr = dupnode(file); + + aptr = assoc_lookup(array, tmp_string("mode", 4), FALSE); + *aptr = make_number((AWKNUM) sbuf.st_mode); + + aptr = assoc_lookup(array, tmp_string("pmode", 5), FALSE); + pmode = format_mode(sbuf.st_mode); + *aptr = make_string(pmode, strlen(pmode)); + + When done, we free the temporary value containing the file name, set +the return value, and return: + + free_temp(file); + + /* Set the return value */ + set_value(tmp_number((AWKNUM) ret)); + + /* Just to make the interpreter happy */ + return tmp_number((AWKNUM) 0); + } + + Finally, it's necessary to provide the "glue" that loads the new +function(s) into `gawk'. By convention, each library has a routine +named `dlload' that does the job: + + /* dlload --- load new builtins in this library */ + + NODE * + dlload(tree, dl) + NODE *tree; + void *dl; + { + make_builtin("chdir", do_chdir, 1); + make_builtin("stat", do_stat, 2); + return tmp_number((AWKNUM) 0); + } + + And that's it! As an exercise, consider adding functions to +implement system calls such as `chown', `chmod', and `umask'. + + ---------- Footnotes ---------- + + (1) This version is edited slightly for presentation. The complete +version can be found in `extension/filefuncs.c' in the `gawk' +distribution. + + +File: gawk.info, Node: Using Internal File Ops, Prev: Internal File Ops, Up: Sample Library + +Integrating the Extensions +.......................... + + Now that the code is written, it must be possible to add it at +runtime to the running `gawk' interpreter. First, the code must be +compiled. Assuming that the functions are in a file named +`filefuncs.c', and IDIR is the location of the `gawk' include files, +the following steps create a GNU/Linux shared library: + + $ gcc -shared -DHAVE_CONFIG_H -c -O -g -IIDIR filefuncs.c + $ ld -o filefuncs.so -shared filefuncs.o + + Once the library exists, it is loaded by calling the `extension' +built-in function. This function takes two arguments: the name of the +library to load and the name of a function to call when the library is +first loaded. This function adds the new functions to `gawk'. It +returns the value returned by the initialization function within the +shared library: + + # file testff.awk + BEGIN { + extension("./filefuncs.so", "dlload") + + chdir(".") # no-op + + data[1] = 1 # force `data' to be an array + print "Info for testff.awk" + ret = stat("testff.awk", data) + print "ret =", ret + for (i in data) + printf "data[\"%s\"] = %s\n", i, data[i] + print "testff.awk modified:", + strftime("%m %d %y %H:%M:%S", data["mtime"]) + } + + Here are the results of running the program: + + $ gawk -f testff.awk + -| Info for testff.awk + -| ret = 0 + -| data["blksize"] = 4096 + -| data["mtime"] = 932361936 + -| data["mode"] = 33188 + -| data["type"] = file + -| data["dev"] = 2065 + -| data["gid"] = 10 + -| data["ino"] = 878597 + -| data["ctime"] = 971431797 + -| data["blocks"] = 2 + -| data["nlink"] = 1 + -| data["name"] = testff.awk + -| data["atime"] = 971608519 + -| data["pmode"] = -rw-r--r-- + -| data["size"] = 607 + -| data["uid"] = 2076 + -| testff.awk modified: 07 19 99 08:25:36 + + +File: gawk.info, Node: Future Extensions, Prev: Dynamic Extensions, Up: Notes Probable Future Extensions ========================== AWK is a language similar to PERL, only considerably more elegant. Arnold Robbins - + Hey! Larry Wall + This minor node briefly lists extensions and possible improvements +that indicate the directions we are currently considering for `gawk'. +The file `FUTURES' in the `gawk' distribution lists these extensions as +well. + Following is a list of probable future changes visible at the `awk' +language level: - This section briefly lists extensions and possible improvements that -indicate the directions we are currently considering for `gawk'. The -file `FUTURES' in the `gawk' distributions lists these extensions as -well. +Loadable Module Interface + It is not clear that the `awk'-level interface to the modules + facility is as good as it should be. The interface needs to be + redesigned, particularly taking namespace issues into account, as + well as possibly including issues such as library search path order + and versioning. - This is a list of probable future changes that will be usable by the -`awk' language programmer. +`RECLEN' variable for fixed length records + Along with `FIELDWIDTHS', this would speed up the processing of + fixed-length records. `PROCINFO["RS"]' would be `"RS"' or + `"RECLEN"', depending upon which kind of record processing is in + effect. -Localization - The GNU project is starting to support multiple languages. It - will at least be possible to make `gawk' print its warnings and - error messages in languages other than English. It may be - possible for `awk' programs to also use the multiple language - facilities, separate from `gawk' itself. +Additional `printf' specifiers + The 1999 ISO C standard added a number of additional `printf' + format specifiers. These should be evaluated for possible + inclusion in `gawk'. Databases It may be possible to map a GDBM/NDBM/SDBM file into an `awk' array. -A `PROCINFO' Array - The special files that provide process-related information (*note - Special File Names in `gawk': Special Files.) will be superseded - by a `PROCINFO' array that would provide the same information, in - an easier to access fashion. +Large Character Sets + It would be nice if `gawk' could handle UTF-8 and other character + sets that are larger than eight bits. More `lint' warnings There are more things that could be checked for portability. -Control of subprocess environment - Changes made in `gawk' to the array `ENVIRON' may be propagated to - subprocesses run by `gawk'. + Following is a list of probable improvements that will make `gawk''s +source code easier to work with: + +Loadable Module Mechanics + The current extension mechanism works (*note Adding New Built-in + Functions to `gawk': Dynamic Extensions.), but is rather + primitive. It requires a fair amount of manual work to create and + integrate a loadable module. Nor is the current mechanism as + portable as might be desired. The GNU `libtool' package provides + a number of features that would make using loadable modules much + easier. `gawk' should be changed to use `libtool'. + +Loadable Module Internals + The API to its internals that `gawk' "exports" should be revised. + Too many things are needlessly exposed. A new API should be + designed and implemented to make module writing easier. + +Better Array Subscript Management + `gawk''s management of array subscript storage could use revamping, + so that using the same value to index multiple arrays only stores + one copy of the index value. - This is a list of probable improvements that will make `gawk' -perform better. +Integrating the DBUG Library + Integrating Fred Fish's DBUG library would be helpful during + development, but it's a lot of work to do. + + Following is a list of probable improvements that will make `gawk' +perform better: An Improved Version of `dfa' The `dfa' pattern matcher from GNU `grep' has some problems. Either a new version or a fixed one will deal with some important regexp matching issues. -Use of GNU `malloc' - The GNU version of `malloc' could potentially speed up `gawk', - since it relies heavily on the use of dynamic memory allocation. - - -File: gawk.info, Node: Improvements, Prev: Future Extensions, Up: Notes - -Suggestions for Improvements -============================ - - Here are some projects that would-be `gawk' hackers might like to -take on. They vary in size from a few days to a few weeks of -programming, depending on which one you choose and how fast a -programmer you are. Please send any improvements you write to the -maintainers at the GNU project. *Note Adding New Features: Adding Code, -for guidelines to follow when adding new features to `gawk'. *Note -Reporting Problems and Bugs: Bugs, for information on contacting the -maintainers. - - 1. Compilation of `awk' programs: `gawk' uses a Bison (YACC-like) - parser to convert the script given it into a syntax tree; the - syntax tree is then executed by a simple recursive evaluator. - This method incurs a lot of overhead, since the recursive - evaluator performs many procedure calls to do even the simplest - things. +Compilation of `awk' programs + `gawk' uses a Bison (YACC-like) parser to convert the script given + it into a syntax tree; the syntax tree is then executed by a + simple recursive evaluator. This method incurs a lot of overhead, + since the recursive evaluator performs many procedure calls to do + even the simplest things. It should be possible for `gawk' to convert the script's parse tree into a C program which the user would then compile, using the @@ -16565,21 +18726,330 @@ maintainers. needed functions (regexps, fields, associative arrays, type coercion, and so on). - An easier possibility might be for an intermediate phase of `awk' + An easier possibility might be for an intermediate phase of `gawk' to convert the parse tree into a linear byte code form like the one used in GNU Emacs Lisp. The recursive evaluator would then be replaced by a straight line byte code interpreter that would be intermediate in speed between running a compiled program and doing what `gawk' does now. - 2. The programs in the test suite could use documenting in this - Info file. + Finally, the programs in the test suite could use documenting in +this Info file. - 3. See the `FUTURES' file for more ideas. Contact us if you would - seriously like to tackle any of the items listed there. + *Note Making Additions to `gawk': Additions, if you are interested +in tackling any of these projects. -File: gawk.info, Node: Glossary, Next: Copying, Prev: Notes, Up: Top +File: gawk.info, Node: Basic Concepts, Next: Glossary, Prev: Notes, Up: Top + +Basic Programming Concepts +************************** + + This major node attempts to define some of the basic concepts and +terms that are used throughout the rest of this Info file. As this +Info file is specifically about `awk', and not about computer +programming in general, the coverage here is by necessity fairly +cursory and simplistic. (If you need more background, there are many +other introductory texts that you should refer to instead.) + +* Menu: + +* Basic High Level:: The high level view. +* Basic Data Typing:: A very quick intro to data types. +* Floating Point Issues:: Stuff to know about floating-point numbers. + + +File: gawk.info, Node: Basic High Level, Next: Basic Data Typing, Prev: Basic Concepts, Up: Basic Concepts + +What a Program Does +=================== + + At the most basic level, the job of a program is to process some +input data and produce results. + + _______ + +------+ / \ +---------+ + | Data | -----> < Program > -----> | Results | + +------+ \_______/ +---------+ + + The "program" in the figure can be either a compiled program(1) +(such as `ls'), or it may be "interpreted". In the latter case, a +machine-executable program such as `awk' reads your program, and then +uses the instructions in your program to process the data. + + When you write a program, it usually consists of the following, very +basic set of steps: + + ______ + +----------------+ / More \ No +----------+ + | Initialization | -------> < Data > -------> | Clean Up | + +----------------+ ^ \ ? / +----------+ + | +--+-+ + | | Yes + | | + | V + | +---------+ + +-----+ Process | + +---------+ + +Initialization + These are the things you do before actually starting to process + data, such as checking arguments, initializing any data you need + to work with, and so on. This step corresponds to `awk''s `BEGIN' + rule (*note The `BEGIN' and `END' Special Patterns: BEGIN/END.). + + If you were baking a cake, this might consist of laying out all the + mixing bowls and the baking pan, and making sure you have all the + ingredients that you need. + +Processing + This is where the actual work is done. Your program reads data, + one logical chunk at a time, and processes it as appropriate. + + In most programming languages, you have to manually manage the + reading of data, checking to see if there is more each time you + read a chunk. `awk''s pattern-action paradigm (*note Getting + Started with `awk': Getting Started.) handles the mechanics of + this for you. + + In baking a cake, the processing corresponds to the actual labor: + breaking eggs, mixing the flour, water, and other ingredients, and + then putting the cake into the oven. + +Clean Up + Once you've processed all the data, you may have things you need to + do before exiting. This step corresponds to `awk''s `END' rule + (*note The `BEGIN' and `END' Special Patterns: BEGIN/END.). + + After the cake comes out of the oven, you still have to wrap it in + plastic wrap to keep anyone from tasting it, as well as wash the + mixing bowls and other utensils. + + An "algorithm" is a detailed set of instructions necessary to +accomplish a task, or process data. It is much the same as a recipe +for baking a cake. Programs implement algorithms. Often, it is up to +you to design the algorithm and implement it, simultaneously. + + The "logical chunks" we talked about previously are called "records", +similar to the records a company keeps on employees, a school keeps for +students, or a doctor keeps for patients. Each record has many +component parts, such as first and last names, date of birth, address, +and so on. The component parts are referred to as the "fields" of the +record. + + The act of reading data is termed "input", and that of generating +results, not too surprisingly, is termed "output". They are often +referred to together as "Input/Output," and even more often, as "I/O" +for short. (You will also see "input" and "output" used as verbs.) + + `awk' manages the reading of data for you, as well as the breaking +it up into records and fields. Your program's job is to tell `awk' +what to with the data. You do this by describing "patterns" in the +data to look for, and "actions" to execute when those patterns are +seen. This "data-driven" nature of `awk' programs usually makes them +both easier to write and easier to read. + + ---------- Footnotes ---------- + + (1) Compiled programs are typically written in lower-level languages +such as C, C++, Fortran, or Ada, and then translated, or "compiled", +into a form that the computer can execute directly. + + +File: gawk.info, Node: Basic Data Typing, Next: Floating Point Issues, Prev: Basic High Level, Up: Basic Concepts + +Data Values in a Computer +========================= + + In a program, you keep track of information and values in things +called "variables". A variable is just a name for a given value, such +as `first_name', `last_name', `address', and so on. `awk' has several +pre-defined variables, and it has special names to refer to the current +input record and the fields of the record. You may also group multiple +associated values under one name, as an array. + + Data, particularly in `awk', consists of either numeric values, such +as 42 or 3.1415927, or string values. String values are essentially +anything that's not a number, such as a name. Strings are sometimes +referred to as "character data", since they store the individual +characters that comprise them. Individual variables, as well as +numeric and string variables, are referred to as "scalar" values. +Groups of values, such as arrays, are not scalars. + + Within computers, there are two kinds of numeric values: "integers", +and "floating-point". In school, integer values were referred to as +"whole" numbers--that is, numbers without any fractional part, such as +1, 42, or -17. The advantage to integer numbers is that they represent +values exactly. The disadvantage is that their range is limited. On +most modern systems, this range is -2,147,483,648 to 2,147,483,647. + + Integer values come in two flavors: "signed" and "unsigned". Signed +values may be negative or positive, with the range of values just +described. Unsigned values are always positive. On most modern +systems, the range is from 0 to 4,294,967,295. + + Floating-point numbers represent what are called "real" numbers; +i.e., those that do have a fractional part, such as 3.1415927. The +advantage to floating-point numbers is that they can represent a much +larger range of values. The disadvantage is that there are numbers +that they cannot represent exactly. `awk' uses "double-precision" +floating-point numbers, which can hold more digits than +"single-precision" floating-point numbers. Floating-point issues are +discussed more fully in *Note Floating-Point Number Caveats: Floating +Point Issues. + + At the very lowest level, computers store values as groups of binary +digits, or "bits". Modern computers group bits into groups of eight, +called "bytes". Advanced applications sometimes have to manipulate +bits directly, and `gawk' provides functions for doing so. + + While you are probably used to the idea of a number without a value +(i.e., zero), it takes a bit more getting used to the idea of +zero-length character data. Nevertheless, such a thing exists. It is +called the "null string". The null string is character data that has +no value. In other words, it is empty. It is written in `awk' programs +like this: `""'. + + Humans are used to working in decimal; i.e., base 10. In base 10, +numbers go from 0 to 9, and then "roll over" into the next column. +(Remember grade school? 42 is 4 times 10 plus 2.) + + There are other number bases though. Computers commonly use base 2 +or "binary", base 8 or "octal", and base 16 or "hexadecimal". In +binary, each column represents two times the value in the column to its +right. Each column may contain either a 0 or a 1. Thus, binary 1010 +represents 1 times 8, plus 0 times 4, plus 1 times 2, plus 0 times 1, +or decimal 10. Octal and hexadecimal are discussed more in *Note Octal +and Hexadecimal Numbers: Non-decimal-numbers. + + Programs are written in programming languages. Hundreds, if not +thousands, of programming languages exist. One of the most popular is +the C programming language. The C language had a very strong influence +on the design of the `awk' language. + + There have been several versions of C. The first is often referred +to as "K&R" C, after the initials of Brian Kernighan and Dennis Ritchie, +the authors of the first book on C. (Dennis Ritchie created the +language, and Brian Kernighan was one of the creators of `awk'.) + + In the mid-1980's, an effort began to produce an international +standard for C. This work culminated in 1989, with the production of +the ANSI standard for C. This standard became an ISO standard in 1990. +Where it makes sense, POSIX `awk' is compatible with 1990 ISO C. + + In 1999, a revised ISO C standard was approved and released. Future +versions of `gawk' will be as compatible as possible with this standard. + + +File: gawk.info, Node: Floating Point Issues, Prev: Basic Data Typing, Up: Basic Concepts + +Floating-Point Number Caveats +============================= + + As mentioned earlier, floating-point numbers represent what are +called "real" numbers; i.e., those that have a fractional part. `awk' +uses double-precision floating-point numbers to represent all numeric +values. This minor node describes some of the issues involved in using +floating-point numbers. + + There is a very nice paper on floating-point arithmetic by David +Goldberg, `What Every Computer Scientist Should Know About +Floating-point Arithmetic', `ACM Computing Surveys' *23*, 1 (1991-03), +5-48.(1) This is worth reading if you are interested in the details, +but it does require a background in Computer Science. + + Internally, `awk' keeps both the numeric value (double-precision +floating-point) and the string value for a variable. Separately, `awk' +keeps track of what type the variable has (*note Variable Typing and +Comparison Expressions: Typing and Comparison.), which plays a role in +how variables are used in comparisons. + + It is important to note that the string value for a number may not +reflect the full value (all the digits) that the numeric value actually +contains. The following program (`values.awk') illustrates this: + + { + $1 = $2 + $3 + # see it for what it is + printf("$1 = %.12g\n", $1) + # use CONVFMT + a = "<" $1 ">" + print "a =", a + # use OFMT + print "$1 =", $1 + } + +This program shows the full value of the sum of `$2' and `$3' using +`printf', and then prints the string values obtained from both +automatic conversion (via `CONVFMT') and from printing (via `OFMT'). + + Here is what happens when the program is run: + + $ echo 2 3.654321 1.2345678 | awk -f values.awk + -| $1 = 4.8888888 + -| a = <4.88889> + -| $1 = 4.88889 + + This makes it clear that the full numeric value is different from +what the default string representations show. + + `CONVFMT''s default value is `"%.6g"', which yields a value with at +least six significant digits. For some applications, you might want to +change it to specify more precision. On most modern machines, most of +the time, 17 digits is enough to capture a floating-point number's +value exactly.(2) + + Unlike numbers in the abstract sense (such as what you studied in +high school or college math), numbers stored in computers are limited +in certain ways. They cannot represent an infinite number of digits, +nor can they always represent things exactly. In particular, +floating-point numbers cannot always represent values exactly. Here is +an example: + + $ awk '{ printf("%010d\n", $1 * 100) }' + 515.79 + -| 0000051579 + 515.80 + -| 0000051579 + 515.81 + -| 0000051580 + 515.82 + -| 0000051582 + Ctrl-d + +This shows that some values can be represented exactly, whereas others +are only approximated. This is not a "bug" in `awk', but simply an +artifact of how computers represent numbers. + + Another peculiarity of floating-point numbers on modern systems is +that they often have more than one representation for the number zero! +In particular, it is possible to represent "minus zero" as well as +regular, or "positive" zero. + + This example shows that negative and positive zero are distinct +values when stored internally, but that they are in fact equal to each +other, as well as to "regular" zero: + + $ gawk 'BEGIN { mz = -0 ; pz = 0 + > printf "-0 = %g, +0 = %g, (-0 == +0) -> %d\n", mz, pz, mz == pz + > printf "mz == 0 -> %d, pz == 0 -> %d\n", mz == 0, pz == 0 + > }' + -| -0 = -0, +0 = 0, (-0 == +0) -> 1 + -| mz == 0 -> 1, pz == 0 -> 1 + + It helps to keep this in mind should you process numeric data that +contains negative zero values; the fact that the zero is negative is +noted and can affect comparisons. + + ---------- Footnotes ---------- + + (1) `http://www.validgh.com/goldberg/paper.ps' + + (2) Pathological cases can require up to 752 digits (!), but we +doubt that you need to worry about this. + + +File: gawk.info, Node: Glossary, Next: Copying, Prev: Basic Concepts, Up: Top Glossary ******** @@ -16587,25 +19057,42 @@ Glossary Action A series of `awk' statements attached to a rule. If the rule's pattern matches an input record, `awk' executes the rule's action. - Actions are always enclosed in curly braces. *Note Overview of - Actions: Action Overview. + Actions are always enclosed in curly braces. (*Note Actions: + Action Overview.) Amazing `awk' Assembler Henry Spencer at the University of Toronto wrote a retargetable - assembler completely as `awk' scripts. It is thousands of lines - long, including machine descriptions for several eight-bit + assembler completely as `sed' and `awk' scripts. It is thousands + of lines long, including machine descriptions for several eight-bit microcomputers. It is a good example of a program that would have - been better written in another language. + been better written in another language. You can get it from + `ftp://ftp.freefriends.org/arnold/Awkstuff/aaa.tgz'. Amazingly Workable Formatter (`awf') Henry Spencer at the University of Toronto wrote a formatter that accepts a large subset of the `nroff -ms' and `nroff -man' - formatting commands, using `awk' and `sh'. + formatting commands, using `awk' and `sh'. It is available over + the Internet from + `ftp://ftp.freefriends.org/arnold/Awkstuff/awf.tgz'. + +Anchor + The regexp metacharacters `^' and `$', which force the match to + the beginning or end of the string, respectively. ANSI The American National Standards Institute. This organization produces many standards, among them the standards for the C and - C++ programming languages. + C++ programming languages. These standards often become + international standards as well. See also "ISO." + +Array + A grouping of multiple values under the same name. Most languages + just provide sequential arrays. `awk' provides associative arrays. + +Assertion + A statement in a program that a condition is true at this point in + the program. Useful for reasoning about how a program is supposed + to behave. Assignment An `awk' expression that changes the value of some `awk' variable @@ -16613,6 +19100,10 @@ Assignment "lvalue". The assigned values are called "rvalues". *Note Assignment Expressions: Assignment Ops. +Associative Array + Arrays in which the indices may be numbers or strings, not just + sequential integers in a fixed range. + `awk' Language The language in which `awk' programs are written. @@ -16626,36 +19117,54 @@ Assignment Another name for an `awk' program. Bash - The GNU version of the standard shell (the Bourne-Again shell). - See "Bourne Shell." + The GNU version of the standard shell (the Bourne-Again SHell). + See also "Bourne Shell." BBS See "Bulletin Board System." +Bit + Short for "Binary Digit." All values in computer memory + ultimately reduce to binary digits: values that are either zero or + one. Groups of bits may be interpreted differently--as integers, + floating-point numbers, character data, addresses of other memory + objects, or other data. `awk' lets you work with floating-point + numbers and strings. `gawk' lets you manipulate bit values with + the built-in functions described in *Note Using `gawk''s Bit + Manipulation Functions: Bitwise Functions. + + Computers are often defined by how many bits they use to represent + integer values. Typical systems are 32-bit systems, but 64-bit + systems are becoming increasingly popular, and 16-bit systems are + waning in popularity. + Boolean Expression - Named after the English mathematician Boole. See "Logical + Named after the English mathematician Boole. See also "Logical Expression." Bourne Shell The standard shell (`/bin/sh') on Unix and Unix-like systems, - originally written by Steven R. Bourne. Many shells (Bash, `ksh', - `pdksh', `zsh') are generally upwardly compatible with the Bourne - shell. + originally written by Steven R. Bourne. Many shells (`bash', + `ksh', `pdksh', `zsh') are generally upwardly compatible with the + Bourne shell. Built-in Function The `awk' language provides built-in functions that perform various - numerical, time stamp related, and string computations. Examples - are `sqrt' (for the square root of a number) and `substr' (for a - substring of a string). *Note Built-in Functions: Built-in. + numerical, I/O-related, and string computations. Examples are + `sqrt' (for the square root of a number) and `substr' (for a + substring of a string). `gawk' provides functions for timestamp + management, bit manipulation, and runtime string translation. + (*Note Built-in Functions: Built-in.) Built-in Variable - `ARGC', `ARGIND', `ARGV', `CONVFMT', `ENVIRON', `ERRNO', - `FIELDWIDTHS', `FILENAME', `FNR', `FS', `IGNORECASE', `NF', `NR', - `OFMT', `OFS', `ORS', `RLENGTH', `RSTART', `RS', `RT', and - `SUBSEP', are the variables that have special meaning to `awk'. - Changing some of them affects `awk''s running environment. - Several of these variables are specific to `gawk'. *Note Built-in - Variables::. + `ARGC', `ARGV', `CONVFMT', `ENVIRON', `FILENAME', `FNR', `FS', + `NF', `NR', `OFMT', `OFS', `ORS', `RLENGTH', `RSTART', `RS', and + `SUBSEP' are the variables that have special meaning to `awk'. In + addition, `ARGIND', `BINMODE', `ERRNO', `FIELDWIDTHS', + `IGNORECASE', `LINT', `PROCINFO', `RT', and `TEXTDOMAIN' are the + variables that have special meaning to `gawk'. Changing some of + them affects `awk''s running environment. (*Note Built-in + Variables::.) Braces See "Curly Braces." @@ -16671,6 +19180,13 @@ C Info file points out similarities between `awk' and C when appropriate. + In general, `gawk' attempts to be as similar to the 1990 version + of ISO C as makes sense. Future versions of `gawk' may adopt + features from the newer 1999 standard, as appropriate. + +C++ + A popular object-oriented programming language derived from C. + Character Set The set of numeric codes used by a computer system to represent the characters (letters, numbers, punctuation, etc.) of a particular @@ -16683,33 +19199,42 @@ CHEM A preprocessor for `pic' that reads descriptions of molecules and produces `pic' input for drawing them. It was written in `awk' by Brian Kernighan and Jon Bentley, and is available from - <netlib@research.bell-labs.com>. + `http://cm.bell-labs.com/netlib/typesetting/chem.gz'. + +Coprocess + A subordinate program with which two-way communications is + possible. + +Compiler + A program that translates human-readable source code into + machine-executable object code. The object code is then executed + directly by the computer. See also "Interpreter." Compound Statement A series of `awk' statements, enclosed in curly braces. Compound - statements may be nested. *Note Control Statements in Actions: - Statements. + statements may be nested. (*Note Control Statements in Actions: + Statements.) Concatenation Concatenating two strings means sticking them together, one after - another, giving a new string. For example, the string `foo' + another, producing a new string. For example, the string `foo' concatenated with the string `bar' gives the string `foobar'. - *Note String Concatenation: Concatenation. + (*Note String Concatenation: Concatenation.) Conditional Expression An expression using the `?:' ternary operator, such as `EXPR1 ? EXPR2 : EXPR3'. The expression EXPR1 is evaluated; if the result - is true, the value of the whole expression is the value of EXPR2, + is true, the value of the whole expression is the value of EXPR2; otherwise the value is EXPR3. In either case, only one of EXPR2 - and EXPR3 is evaluated. *Note Conditional Expressions: - Conditional Exp. + and EXPR3 is evaluated. (*Note Conditional Expressions: + Conditional Exp.) Comparison Expression A relation that is either true or false, such as `(a < b)'. Comparison expressions are used in `if', `while', `do', and `for' statements, and in patterns to select which input records to - process. *Note Variable Typing and Comparison Expressions: Typing - and Comparison. + process. (*Note Variable Typing and Comparison Expressions: + Typing and Comparison.) Curly Braces The characters `{' and `}'. Curly braces are used in `awk' for @@ -16718,26 +19243,35 @@ Curly Braces Dark Corner An area in the language where specifications often were (or still are) not clear, leading to unexpected or undesirable behavior. - Such areas are marked in this Info file with "(d.c.)" in the text, + Such areas are marked in this Info file with "(d.c.)" in the text and are indexed under the heading "dark corner." +Data Driven + A description of `awk' programs, where you specify the data you + are interested in processing, and what to do when that data is + seen. + Data Objects These are numbers and strings of characters. Numbers are - converted into strings and vice versa, as needed. *Note - Conversion of Strings and Numbers: Conversion. + converted into strings and vice versa, as needed. (*Note + Conversion of Strings and Numbers: Conversion.) + +Deadlock + The situation in which two communicating processes are each waiting + for the other to perform an action. -Double Precision +Double-Precision An internal representation of numbers that can have fractional - parts. Double precision numbers keep track of more digits than do - single precision numbers, but operations on them are more - expensive. This is the way `awk' stores numeric values. It is - the C type `double'. + parts. Double-precision numbers keep track of more digits than do + single-precision numbers, but operations on them are sometimes + more expensive. This is the way `awk' stores numeric values. It + is the C type `double'. Dynamic Regular Expression A dynamic regular expression is a regular expression written as an ordinary expression. It could be a string constant, such as `"foo"', but it may also be an expression whose value can vary. - *Note Using Dynamic Regexps: Computed Regexps. + (*Note Using Dynamic Regexps: Computed Regexps.) Environment A collection of strings, of the form NAME`='VAL, that each program @@ -16748,36 +19282,58 @@ Environment Empty String See "Null String." +Epoch + The date used as the "beginning of time" for timestamps. Time + values in Unix systems are represented as seconds since the epoch, + with library functions available for converting these values into + standard date and time formats. + + The epoch on Unix and POSIX systems is 1970-01-01 00:00:00 UTC. + See also "GMT" and "UTC." + Escape Sequences A special sequence of characters used for describing non-printing - characters, such as `\n' for newline, or `\033' for the ASCII ESC - (escape) character. *Note Escape Sequences::. + characters, such as `\n' for newline or `\033' for the ASCII ESC + (Escape) character. (*Note Escape Sequences::.) + +FDL + See "Free Documentation License." Field When `awk' reads an input record, it splits the record into pieces - separated by whitespace (or by a separator regexp which you can + separated by whitespace (or by a separator regexp that you can change by setting the built-in variable `FS'). Such pieces are called fields. If the pieces are of fixed length, you can use the - built-in variable `FIELDWIDTHS' to describe their lengths. *Note - Specifying How Fields are Separated: Field Separators, and also see - *Note Reading Fixed-width Data: Constant Size. + built-in variable `FIELDWIDTHS' to describe their lengths. (*Note + Specifying How Fields Are Separated: Field Separators, and *Note + Reading Fixed-Width Data: Constant Size.) + +Flag + A variable whose truth value indicates the existence or + non-existence of some condition. -Floating Point Number - Often referred to in mathematical terms as a "rational" number, - this is just a number that can have a fractional part. See - "Double Precision" and "Single Precision." +Floating-Point Number + Often referred to in mathematical terms as a "rational" or real + number, this is just a number that can have a fractional part. + See also "Double-Precision" and "Single-Precision." Format Format strings are used to control the appearance of output in the - `printf' statement. Also, data conversions from numbers to strings + `strftime' and `sprintf' functions, and are used in the `printf' + statement as well. Also, data conversions from numbers to strings are controlled by the format string contained in the built-in - variable `CONVFMT'. *Note Format-Control Letters: Control Letters. + variable `CONVFMT'. (*Note Format-Control Letters: Control + Letters.) + +Free Documentation License + This document describes the terms under which this Info file is + published and may be copied. (*Note GNU Free Documentation + License::.) Function A specialized group of statements used to encapsulate general or program-specific tasks. `awk' has a number of built-in functions, - and also allows you to define your own. *Note Built-in Functions: - Built-in, and *Note User-defined Functions: User-defined. + and also allows you to define your own. (*Note Functions::.) FSF See "Free Software Foundation." @@ -16793,34 +19349,72 @@ Free Software Foundation General Public License This document describes the terms under which `gawk' and its source - code may be distributed. (*note GNU GENERAL PUBLIC LICENSE: + code may be distributed. (*Note GNU General Public License: Copying.) +GMT + "Greenwich Mean Time." This is the old term for UTC. It is the + time of day used as the epoch for Unix and POSIX systems. See + also "Epoch" and "UTC." + GNU "GNU's not Unix". An on-going project of the Free Software Foundation to create a complete, freely distributable, POSIX-compliant computing environment. +GNU/Linux + A variant of the GNU system using the Linux kernel, instead of the + Free Software Foundation's Hurd kernel. Linux is a stable, + efficient, full-featured clone of Unix that has been ported to a + variety of architectures. It is most popular on PC-class systems, + but runs well on a variety of other systems too. The Linux kernel + source code is available under the terms of the GNU General Public + License, which is perhaps its most important aspect. + GPL See "General Public License." Hexadecimal Base 16 notation, where the digits are `0'-`9' and `A'-`F', with - `A' representing 10, `B' representing 11, and so on up to `F' for + `A' representing 10, `B' representing 11, and so on, up to `F' for 15. Hexadecimal numbers are written in C using a leading `0x', to - indicate their base. Thus, `0x12' is 18 (one times 16 plus 2). + indicate their base. Thus, `0x12' is 18 (1 times 16 plus 2). I/O Abbreviation for "Input/Output," the act of moving data into and/or out of a running program. Input Record - A single chunk of data read in by `awk'. Usually, an `awk' input - record consists of one line of text. *Note How Input is Split - into Records: Records. + A single chunk of data that is read in by `awk'. Usually, an + `awk' input record consists of one line of text. (*Note How Input + Is Split into Records: Records.) Integer - A whole number, i.e. a number that does not have a fractional part. + A whole number, i.e., a number that does not have a fractional + part. + +Internationalization + The process of writing or modifying a program so that it can use + multiple languages without requiring further source code changes. + +Interpreter + A program that reads human-readable source code directly, and uses + the instructions in it to process data and produce results. `awk' + is typically (but not always) implemented as an interpreter. See + also "Compiler." + +Interval Expression + A component of a regular expression that lets you specify repeated + matches of some part of the regexp. Interval expressions were not + traditionally available in `awk' programs. + +ISO + The International Standards Organization. This organization + produces international standards for many things, including + programming languages, such as C and C++. In the computer arena, + important standards like those for C, C++, and POSIX become both + American national and ISO international standards simultaneously. + This Info file refers to Standard C as "ISO C" throughout. Keyword In the `awk' language, a keyword is a word that has special @@ -16831,6 +19425,21 @@ Keyword `do...while', `for', `for...in', `break', `continue', `delete', `next', `nextfile', `function', `func', and `exit'. +Lesser General Public License + This document describes the terms under which binary library + archives or shared objects, and their source code may be + distributed. + +Linux + See "GNU/Linux." + +LGPL + See "Lesser General Public License." + +Localization + The process of providing the data necessary for an + internationalized program to work in a particular language. + Logical Expression An expression using the operators for logic, AND, OR, and NOT, written `&&', `||', and `!' in `awk'. Often called Boolean @@ -16843,22 +19452,35 @@ Lvalue elements. In `awk', a field designator can also be used as an lvalue. +Matching + The act of testing a string against a regular expression. If the + regexp describes the contents of the string, it is said to "match" + it. + +Metacharacters + Characters used within a regexp that do not stand for themselves. + Instead, they denote regular expression operations, such as + repetition, grouping, or alternation. + Null String A string with no characters in it. It is represented explicitly in - `awk' programs by placing two double-quote characters next to each + `awk' programs by placing two double quote characters next to each other (`""'). It can appear in input data by having two successive occurrences of the field separator appear next to each other. Number - A numeric valued data object. The `gawk' implementation uses - double precision floating point to represent numbers. Very old - `awk' implementations use single precision floating point. + A numeric-valued data object. Modern `awk' implementations use + double-precision floating-point to represent numbers. Very old + `awk' implementations use single-precision floating-point. Octal Base-eight notation, where the digits are `0'-`7'. Octal numbers are written in C using a leading `0', to indicate their base. Thus, `013' is 11 (one times 8 plus 3). +P1003.2 + See "POSIX." + Pattern Patterns tell `awk' which input records are interesting to which rules. @@ -16866,43 +19488,48 @@ Pattern A pattern is an arbitrary conditional expression against which input is tested. If the condition is satisfied, the pattern is said to "match" the input record. A typical pattern might compare - the input record against a regular expression. *Note Pattern - Elements: Pattern Overview. + the input record against a regular expression. (*Note Pattern + Elements: Pattern Overview.) POSIX - The name for a series of standards being developed by the IEEE - that specify a Portable Operating System interface. The "IX" - denotes the Unix heritage of these standards. The main standard - of interest for `awk' users is `IEEE Standard for Information - Technology, Standard 1003.2-1992, Portable Operating System - Interface (POSIX) Part 2: Shell and Utilities'. Informally, this - standard is often referred to as simply "P1003.2." + The name for a series of standards that specify a Portable + Operating System interface. The "IX" denotes the Unix heritage of + these standards. The main standard of interest for `awk' users is + `IEEE Standard for Information Technology, Standard 1003.2-1992, + Portable Operating System Interface (POSIX) Part 2: Shell and + Utilities'. Informally, this standard is often referred to as + simply "P1003.2." + +Precedence + The order in which operations are performed when operators are used + without explicit parentheses. Private Variables and/or functions that are meant for use exclusively by - library functions, and not for the main `awk' program. Special - care must be taken when naming such variables and functions. - *Note Naming Library Function Global Variables: Library Names. + library functions and not for the main `awk' program. Special care + must be taken when naming such variables and functions. (*Note + Naming Library Function Global Variables: Library Names.) Range (of input lines) - A sequence of consecutive lines from the input file. A pattern - can specify ranges of input lines for `awk' to process, or it can - specify single lines. *Note Pattern Elements: Pattern Overview. + A sequence of consecutive lines from the input file(s). A pattern + can specify ranges of input lines for `awk' to process or it can + specify single lines. (*Note Pattern Elements: Pattern Overview.) Recursion When a function calls itself, either directly or indirectly. If this isn't clear, refer to the entry for "recursion." Redirection - Redirection means performing input from other than the standard - input stream, or output to other than the standard output stream. + Redirection means performing input from something other than the + standard input stream, or performing output to something other + than the standard output stream. You can redirect the output of the `print' and `printf' statements - to a file or a system command, using the `>', `>>', and `|' + to a file or a system command, using the `>', `>>', `|', and `|&' operators. You can redirect input to the `getline' statement using - the `<' and `|' operators. *Note Redirecting Output of `print' - and `printf': Redirection, and *Note Explicit Input with - `getline': Getline. + the `<', `|', and `|&' operators. (*Note Redirecting Output of + `print' and `printf': Redirection, and *Note Explicit Input with + `getline': Getline.) Regexp Short for "regular expression". A regexp is a pattern that @@ -16910,7 +19537,7 @@ Regexp the regexp `R.*xp' matches any string starting with the letter `R' and ending with the letters `xp'. In `awk', regexps are used in patterns and in conditional expressions. Regexps may contain - escape sequences. *Note Regular Expressions: Regexp. + escape sequences. (*Note Regular Expressions: Regexp.) Regular Expression See "regexp." @@ -16918,8 +19545,8 @@ Regular Expression Regular Expression Constant A regular expression constant is a regular expression written within slashes, such as `/foo/'. This regular expression is chosen - when you write the `awk' program, and cannot be changed doing its - execution. *Note How to Use Regular Expressions: Regexp Usage. + when you write the `awk' program and cannot be changed during its + execution. (*Note How to Use Regular Expressions: Regexp Usage.) Rule A segment of an `awk' program that specifies how to process single @@ -16933,77 +19560,111 @@ Rvalue operator. In `awk', essentially every expression has a value. These values are rvalues. +Scalar + A single value, be it a number or a string. Regular variables are + scalars; arrays and functions are not. + +Search Path + In `gawk', a list of directories to search for `awk' program + source files. In the shell, a list of directories to search for + executable programs. + +Seed + The initial value, or starting point, for a sequence of random + numbers. + `sed' See "Stream Editor." +Shell + The command interpreter for Unix and POSIX-compliant systems. The + shell works both interactively, and as a programming language for + batch files, or shell scripts. + Short-Circuit The nature of the `awk' logical operators `&&' and `||'. If the - value of the entire expression can be deduced from evaluating just - the left-hand side of these operators, the right-hand side will not - be evaluated (*note Boolean Expressions: Boolean Ops.). + value of the entire expression is determinable from evaluating just + the lefthand side of these operators, the righthand side is not + evaluated. (*Note Boolean Expressions: Boolean Ops.) Side Effect A side effect occurs when an expression has an effect aside from merely producing a value. Assignment expressions, increment and - decrement expressions and function calls have side effects. *Note - Assignment Expressions: Assignment Ops. + decrement expressions, and function calls have side effects. + (*Note Assignment Expressions: Assignment Ops.) -Single Precision +Single-Precision An internal representation of numbers that can have fractional - parts. Single precision numbers keep track of fewer digits than - do double precision numbers, but operations on them are less - expensive in terms of CPU time. This is the type used by some - very old versions of `awk' to store numeric values. It is the C - type `float'. + parts. Single-precision numbers keep track of fewer digits than + do double-precision numbers, but operations on them are sometimes + less expensive in terms of CPU time. This is the type used by + some very old versions of `awk' to store numeric values. It is + the C type `float'. Space The character generated by hitting the space bar on the keyboard. Special File A file name interpreted internally by `gawk', instead of being - handed directly to the underlying operating system. For example, - `/dev/stderr'. *Note Special File Names in `gawk': Special Files. + handed directly to the underlying operating system--for example, + `/dev/stderr'. (*Note Special File Names in `gawk': Special + Files.) Stream Editor A program that reads records from an input stream and processes them one or more at a time. This is in contrast with batch programs, which may expect to read their input files in entirety - before starting to do anything, and with interactive programs, - which require input from the user. + before starting to do anything, as well as with interactive + programs which require input from the user. String A datum consisting of a sequence of characters, such as `I am a - string'. Constant strings are written with double-quotes in the - `awk' language, and may contain escape sequences. *Note Escape - Sequences::. + string'. Constant strings are written with double quotes in the + `awk' language and may contain escape sequences. (*Note Escape + Sequences::.) Tab The character generated by hitting the `TAB' key on the keyboard. It usually expands to up to eight spaces upon output. +Text Domain + A unique name that identifies an application. Used for grouping + messages that are translated at runtime into the local language. + +Timestamp + A value in the "seconds since the epoch" format used by Unix and + POSIX systems. Used for the `gawk' functions `mktime', + `strftime', and `systime'. See also "Epoch" and "UTC." + Unix A computer operating system originally developed in the early 1970's at AT&T Bell Laboratories. It initially became popular in - universities around the world, and later moved into commercial - evnironments as a software development system and network server + universities around the world and later moved into commercial + environments as a software development system and network server system. There are many commercial versions of Unix, as well as several work-alike systems whose source code is freely available - (such as Linux, NetBSD, and FreeBSD). + (such as GNU/Linux, NetBSD, FreeBSD, and OpenBSD). + +UTC + The accepted abbreviation for "Universal Coordinated Time." This + is standard time in Greenwich, England, which is used as a + reference time for day and date calculations. See also "Epoch" + and "GMT." Whitespace A sequence of space, tab, or newline characters occurring inside an input record or a string. -File: gawk.info, Node: Copying, Next: Index, Prev: Glossary, Up: Top +File: gawk.info, Node: Copying, Next: GNU Free Documentation License, Prev: Glossary, Up: Top -GNU GENERAL PUBLIC LICENSE +GNU General Public License ************************** Version 2, June 1991 Copyright (C) 1989, 1991 Free Software Foundation, Inc. - 59 Temple Place --- Suite 330, Boston, MA 02111-1307, USA + 59 Temple Place, Suite 330, Boston, MA 02111, USA Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed. @@ -17156,7 +19817,7 @@ modification follow. c. Accompany it with the information you received as to the offer to distribute corresponding source code. (This alternative is - allowed only for non-commercial distribution and only if you + allowed only for noncommercial distribution and only if you received the program in object code or executable form with such an offer, in accord with Subsection b above.) @@ -17320,7 +19981,7 @@ the "copyright" line and a pointer to where the full notice is found. You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software - Foundation, Inc., 59 Temple Place --- Suite 330, Boston, MA 02111-1307, USA. + Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111, USA. Also add information on how to contact you by electronic and paper mail. @@ -17356,73 +20017,541 @@ if necessary. Here is a sample; alter the names: program into proprietary programs. If your program is a subroutine library, you may consider it more useful to permit linking proprietary applications with the library. If this is what you want to do, use the -GNU Library General Public License instead of this License. +GNU Lesser General Public License instead of this License. + + +File: gawk.info, Node: GNU Free Documentation License, Next: Index, Prev: Copying, Up: Top + +GNU Free Documentation License +****************************** + + Version 1.1, March 2000 + + Copyright (C) 2000 Free Software Foundation, Inc. + 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA + + Everyone is permitted to copy and distribute verbatim copies + of this license document, but changing it is not allowed. + + + + 0. PREAMBLE + + The purpose of this License is to make a manual, textbook, or other + written document "free" in the sense of freedom: to assure everyone + the effective freedom to copy and redistribute it, with or without + modifying it, either commercially or noncommercially. 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If + the Document does not specify a version number of this License, + you may choose any version ever published (not as a draft) by the + Free Software Foundation. + + +ADDENDUM: How to use this License for your documents +==================================================== + + To use this License in a document you have written, include a copy of +the License in the document and put the following copyright and license +notices just after the title page: + + + Copyright (C) YEAR YOUR NAME. + Permission is granted to copy, distribute and/or modify this document + under the terms of the GNU Free Documentation License, Version 1.1 + or any later version published by the Free Software Foundation; + with the Invariant Sections being LIST THEIR TITLES, with the + Front-Cover Texts being LIST, and with the Back-Cover Texts being LIST. + A copy of the license is included in the section entitled ``GNU + Free Documentation License''. +If you have no Invariant Sections, write "with no Invariant +Sections" instead of saying which ones are invariant. If you have no +Front-Cover Texts, write "no Front-Cover Texts" instead of "Front-Cover +Texts being LIST"; likewise for Back-Cover Texts. + + If your document contains nontrivial examples of program code, we +recommend releasing these examples in parallel under your choice of +free software license, such as the GNU General Public License, to +permit their use in free software. -File: gawk.info, Node: Index, Prev: Copying, Up: Top +File: gawk.info, Node: Index, Prev: GNU Free Documentation License, Up: Top Index ***** * Menu: +* ! operator <1>: Egrep Program. +* ! operator <2>: Ranges. +* ! operator <3>: Precedence. * ! operator: Boolean Ops. +* != operator <1>: Precedence. * != operator: Typing and Comparison. -* !~ operator <1>: Typing and Comparison. -* !~ operator <2>: Regexp Constants. -* !~ operator <3>: Computed Regexps. -* !~ operator <4>: Case-sensitivity. +* !~ operator <1>: Precedence. +* !~ operator <2>: Typing and Comparison. +* !~ operator <3>: Regexp Constants. +* !~ operator <4>: Computed Regexps. +* !~ operator <5>: Case-sensitivity. * !~ operator: Regexp Usage. * # (comment): Comments. * #! (executable scripts): Executable Scripts. -* $ (field operator): Fields. +* $ field operator <1>: Precedence. +* $ field operator: Fields. +* % operator: Precedence. +* %= operator <1>: Precedence. +* %= operator: Assignment Ops. +* && operator <1>: Precedence. * && operator: Boolean Ops. +* * operator: Precedence. +* ** operator: Precedence. +* **= operator <1>: Precedence. +* **= operator: Assignment Ops. +* *= operator <1>: Precedence. +* *= operator: Assignment Ops. +* + operator: Precedence. +* ++ operator <1>: Precedence. +* ++ operator: Increment Ops. +* += operator <1>: Precedence. +* += operator: Assignment Ops. +* - operator: Precedence. +* -- operator <1>: Precedence. +* -- operator: Increment Ops. * --assign option: Options. * --compat option: Options. * --copyleft option: Options. * --copyright option: Options. +* --disable-nls configuration option: Additional Configuration Options. +* --dump-variables option: Options. +* --enable-portals configuration option <1>: Additional Configuration Options. +* --enable-portals configuration option: Portal Files. * --field-separator option: Options. * --file option: Options. +* --gen-po option <1>: Options. +* --gen-po option: String Extraction. * --help option: Options. * --lint option: Options. * --lint-old option: Options. +* --non-decimal-data option <1>: Options. +* --non-decimal-data option: Non-decimal Data. * --posix option: Options. +* --profile option: Options. +* --re-interval option: Options. * --source option: Options. * --traditional option: Options. * --usage option: Options. * --version option: Options. +* --with-included-gettext configuration option <1>: Additional Configuration Options. +* --with-included-gettext configuration option: Gawk I18N. +* -= operator <1>: Precedence. +* -= operator: Assignment Ops. * -f option: Options. * -F option <1>: Options. * -F option: Command Line Field Separator. * -f option: Long. +* -mf option: Options. +* -mr option: Options. * -v option: Options. * -W option: Options. -* /dev/fd: Special Files. -* /dev/pgrpid: Special Files. -* /dev/pid: Special Files. -* /dev/ppid: Special Files. -* /dev/stderr: Special Files. -* /dev/stdin: Special Files. -* /dev/stdout: Special Files. -* /dev/user <1>: Passwd Functions. -* /dev/user: Special Files. +* / operator: Precedence. +* /= operator <1>: Precedence. +* /= operator: Assignment Ops. +* /= operator vs. /=.../ regexp constant: Assignment Ops. +* /dev/fd special files: Special FD. +* /dev/pgrpid special file: Special Process. +* /dev/pid special file: Special Process. +* /dev/ppid special file: Special Process. +* /dev/stderr special file: Special FD. +* /dev/stdin special file: Special FD. +* /dev/stdout special file: Special FD. +* /dev/user special file: Special Process. +* /inet special files: TCP/IP Networking. +* /p special files: Portal Files. +* < I/O operator: Getline/File. +* < operator <1>: Precedence. * < operator: Typing and Comparison. +* <= operator <1>: Precedence. * <= operator: Typing and Comparison. +* = operator: Assignment Ops. +* == operator <1>: Precedence. * == operator: Typing and Comparison. +* > I/O operator: Redirection. +* > operator <1>: Precedence. * > operator: Typing and Comparison. +* >= operator <1>: Precedence. * >= operator: Typing and Comparison. +* >> I/O operator <1>: Precedence. +* >> I/O operator: Redirection. +* ?: operator: Precedence. +* \" escape sequence: Escape Sequences. * \' regexp operator: GNU Regexp Operators. +* \/ escape sequence: Escape Sequences. * \< regexp operator: GNU Regexp Operators. * \> regexp operator: GNU Regexp Operators. * \` regexp operator: GNU Regexp Operators. +* \a escape sequence: Escape Sequences. +* \b escape sequence: Escape Sequences. * \B regexp operator: GNU Regexp Operators. +* \f escape sequence: Escape Sequences. +* \n escape sequence: Escape Sequences. +* \NNN escape sequence (octal): Escape Sequences. +* \r escape sequence: Escape Sequences. +* \t escape sequence: Escape Sequences. +* \v escape sequence: Escape Sequences. * \W regexp operator: GNU Regexp Operators. * \w regexp operator: GNU Regexp Operators. +* \x escape sequence: Escape Sequences. * \y regexp operator: GNU Regexp Operators. -* _gr_init: Group Functions. -* _pw_init: Passwd Functions. -* _tm_addup: Mktime Function. -* _tm_isleap: Mktime Function. +* ^ operator: Precedence. +* ^= operator <1>: Precedence. +* ^= operator: Assignment Ops. +* _ C macro (gettext): Explaining gettext. +* _gr_init user-defined function: Group Functions. +* _pw_init user-defined function: Passwd Functions. * accessing fields: Fields. * account information <1>: Group Functions. * account information: Passwd Functions. @@ -17434,91 +20563,165 @@ Index * action, separating statements: Action Overview. * adding new features: Adding Code. * addition: Arithmetic Ops. +* advanced features: Advanced Features. +* advanced notes <1>: I/O Functions. +* advanced notes <2>: Gory Details. +* advanced notes <3>: Auto-set. +* advanced notes <4>: Increment Ops. +* advanced notes <5>: Assignment Ops. +* advanced notes <6>: Non-decimal-numbers. +* advanced notes <7>: Close Files And Pipes. +* advanced notes <8>: Redirection. +* advanced notes <9>: Records. +* advanced notes <10>: Computed Regexps. +* advanced notes <11>: Escape Sequences. +* advanced notes: Executable Scripts. +* Aho, Alfred <1>: Contributors. * Aho, Alfred: History. * AI programming, using gawk: Distribution contents. -* alarm.awk: Alarm Program. +* alarm.awk program: Alarm Program. +* algorithm, definition of: Basic High Level. +* amazing awk assembler (aaa): Glossary. +* amazingly workable formatter (awf): Glossary. +* ambiguity, syntactic: /= operator vs. /=.../ regexp constant: Assignment Ops. * amiga: Amiga Installation. * anchors in regexps: Regexp Operators. -* and operator: Boolean Ops. -* anonymous ftp <1>: Other Versions. +* AND bitwise operation: Bitwise Functions. +* and built-in function: Bitwise Functions. +* AND logical operator: Boolean Ops. * anonymous ftp: Getting. -* applications of awk: When. -* ARGC: Auto-set. -* ARGIND <1>: Other Arguments. -* ARGIND: Auto-set. +* ANSI: Glossary. +* applications of awk <1>: When. +* applications of awk: Preface. +* archeologists: Bugs. +* ARGC variable: Auto-set. +* ARGIND variable <1>: Other Arguments. +* ARGIND variable: Auto-set. * argument processing: Getopt Function. * arguments in function call: Function Calls. -* arguments, command line: Invoking Gawk. -* ARGV <1>: Other Arguments. -* ARGV: Auto-set. +* arguments, command-line: Command Line. +* ARGV variable <1>: Other Arguments. +* ARGV variable: Auto-set. * arithmetic operators: Arithmetic Ops. * array assignment: Assigning Elements. * array reference: Reference to Elements. -* Array subscripts and IGNORECASE: Array Intro. -* array subscripts, uninitialized variables: Uninitialized Subscripts. * arrays: Array Intro. * arrays, associative: Array Intro. * arrays, definition of: Array Intro. * arrays, deleting an element: Delete. * arrays, deleting entire contents: Delete. -* arrays, multi-dimensional subscripts: Multi-dimensional. +* arrays, multidimensional subscripts: Multi-dimensional. * arrays, presence of elements: Reference to Elements. +* arrays, sorting: Array Sorting. +* arrays, sorting and IGNORECASE: Array Sorting. * arrays, sparse: Array Intro. * arrays, special for statement: Scanning an Array. +* arrays, subscripts, and IGNORECASE: Array Intro. +* arrays, subscripts, uninitialized variables: Uninitialized Subscripts. * arrays, the in operator: Reference to Elements. * artificial intelligence, using gawk: Distribution contents. * ASCII: Ordinal Functions. -* assert: Assert Function. -* assert, C version: Assert Function. +* asort built-in function <1>: String Functions. +* asort built-in function: Array Sorting. +* assert C library function: Assert Function. +* assert user-defined function: Assert Function. * assertions: Assert Function. * assignment operators: Assignment Ops. * assignment to fields: Changing Fields. +* assoc_clear internal function: Internals. +* assoc_lookup internal function: Internals. * associative arrays: Array Intro. -* atan2: Numeric Functions. +* atan2 built-in function: Numeric Functions. * atari: Atari Installation. * automatic initialization: More Complex. +* automatic warnings <1>: Options. +* automatic warnings <2>: I/O Functions. +* automatic warnings <3>: String Functions. +* automatic warnings <4>: Using Constant Regexps. +* automatic warnings <5>: Special Caveats. +* automatic warnings <6>: Special Process. +* automatic warnings: Escape Sequences. +* awf (amazingly workable formatter) program: Glossary. * awk language, POSIX version <1>: Definition Syntax. -* awk language, POSIX version <2>: String Functions. -* awk language, POSIX version <3>: User-modified. -* awk language, POSIX version <4>: Next Statement. -* awk language, POSIX version <5>: Continue Statement. -* awk language, POSIX version <6>: Break Statement. -* awk language, POSIX version <7>: Precedence. -* awk language, POSIX version <8>: Assignment Ops. -* awk language, POSIX version <9>: Arithmetic Ops. -* awk language, POSIX version <10>: Conversion. -* awk language, POSIX version <11>: Format Modifiers. -* awk language, POSIX version <12>: OFMT. -* awk language, POSIX version <13>: Field Splitting Summary. -* awk language, POSIX version <14>: Regexp Operators. +* awk language, POSIX version <2>: Gory Details. +* awk language, POSIX version <3>: String Functions. +* awk language, POSIX version <4>: User-modified. +* awk language, POSIX version <5>: Next Statement. +* awk language, POSIX version <6>: Continue Statement. +* awk language, POSIX version <7>: Break Statement. +* awk language, POSIX version <8>: Precedence. +* awk language, POSIX version <9>: Assignment Ops. +* awk language, POSIX version <10>: Arithmetic Ops. +* awk language, POSIX version <11>: Conversion. +* awk language, POSIX version <12>: Format Modifiers. +* awk language, POSIX version <13>: OFMT. +* awk language, POSIX version <14>: Field Splitting Summary. +* awk language, POSIX version <15>: Character Lists. +* awk language, POSIX version <16>: Regexp Operators. * awk language, POSIX version: Escape Sequences. * awk language, V.4 version <1>: SVR4. * awk language, V.4 version: Escape Sequences. +* awka compiler for awk programs: Other Versions. +* awka, source code: Other Versions. +* AWKNUM internal type: Internals. * AWKPATH environment variable: AWKPATH Variable. -* awksed: Simple Sed. +* awkprof.out profiling output file: Profiling. +* awksed.awk program: Simple Sed. +* awkvars.out global variable list output file: Options. * backslash continuation <1>: Egrep Program. * backslash continuation: Statements/Lines. -* backslash continuation and comments: Statements/Lines. -* backslash continuation in csh <1>: Statements/Lines. -* backslash continuation in csh: More Complex. +* backslash continuation, and comments: Statements/Lines. +* backslash continuation, in csh <1>: Statements/Lines. +* backslash continuation, in csh: More Complex. * basic function of awk: Getting Started. +* basic programming concepts: Basic Concepts. * BBS-list file: Sample Data Files. +* Beebe, Nelson: Acknowledgments. * BEGIN special pattern: BEGIN/END. -* beginfile: Filetrans Function. +* beginfile user-defined function: Filetrans Function. +* BeOS: BeOS Installation. +* Berry, Karl: Acknowledgments. +* binary I/O: User-modified. +* bindtextdomain built-in function <1>: Programmer i18n. +* bindtextdomain built-in function: I18N Functions. +* bindtextdomain C library function: Explaining gettext. +* bindtextdomain user-defined function: I18N Portability. +* BINMODE variable <1>: PC Using. +* BINMODE variable: User-modified. +* bits2str user-defined function: Bitwise Functions. +* bitwise complement: Bitwise Functions. +* bitwise operations: Bitwise Functions. +* bitwise shift: Bitwise Functions. +* blocks, BEGIN and END <1>: Profiling. +* blocks, BEGIN and END: BEGIN/END. * body of a loop: While Statement. * book, using this: This Manual. * boolean expressions: Boolean Ops. * boolean operators: Boolean Ops. +* bracket expression: Regexp Operators. +* Brandon, Dick: This Manual. * break statement: Break Statement. * break, outside of loops: Break Statement. * Brennan, Michael <1>: Other Versions. * Brennan, Michael <2>: Simple Sed. +* Brennan, Michael <3>: Two-way I/O. * Brennan, Michael: Delete. +* Broder, Alan J.: Contributors. +* Brown, Martin <1>: Bugs. +* Brown, Martin <2>: Contributors. +* Brown, Martin: Acknowledgments. +* BSD portal files: Portal Files. +* BSD-based operating systems <1>: Glossary. +* BSD-based operating systems <2>: Portal Files. +* BSD-based operating systems: Manual History. * buffer matching operators: GNU Regexp Operators. * buffering output: I/O Functions. * buffering, interactive vs. non-interactive: I/O Functions. * buffering, non-interactive vs. interactive: I/O Functions. * buffers, flushing: I/O Functions. +* bug reports: Bugs. +* bug reports, email address, bug-gawk@gnu.org: Bugs. +* bug-gawk@gnu.org bug reporting address: Bugs. * bugs, known in gawk: Known Bugs. * built-in functions: Built-in. * built-in variables: Built-in Variables. @@ -17532,91 +20735,180 @@ Index * case sensitivity: Case-sensitivity. * changing contents of a field: Changing Fields. * changing the record separator: Records. -* character classes: Regexp Operators. +* character class <1>: Character Lists. +* character class: Regexp Operators. * character encodings: Ordinal Functions. * character list: Regexp Operators. * character list, complemented: Regexp Operators. -* character sets: Ordinal Functions. -* chr: Ordinal Functions. -* close <1>: I/O Functions. -* close: Close Files And Pipes. +* character set (regexp component): Regexp Operators. +* character sets (machine character encodings) <1>: Glossary. +* character sets (machine character encodings): Ordinal Functions. +* Chassell, Robert J.: Acknowledgments. +* chem utility: Glossary. +* chr user-defined function: Ordinal Functions. +* Cliff random numbers: Cliff Random Function. +* cliff_rand user-defined function: Cliff Random Function. +* close built-in function <1>: I/O Functions. +* close built-in function: Close Files And Pipes. +* Close, Diane <1>: Contributors. +* Close, Diane: Manual History. +* close, return value: Close Files And Pipes. +* closing coprocesses: Close Files And Pipes. * closing input files and pipes: Close Files And Pipes. * closing output files and pipes: Close Files And Pipes. * coding style used in gawk: Adding Code. -* collating elements: Regexp Operators. -* collating symbols: Regexp Operators. -* command line: Invoking Gawk. -* command line formats: Running gawk. +* collating elements: Character Lists. +* collating symbols: Character Lists. +* comma operator, not supported: For Statement. +* command line: Command Line. * command line, setting FS on: Command Line Field Separator. +* command-line formats: Running gawk. +* command-line option, --assign: Options. +* command-line option, --compat: Options. +* command-line option, --copyleft: Options. +* command-line option, --copyright: Options. +* command-line option, --dump-variables: Options. +* command-line option, --field-separator: Options. +* command-line option, --file: Options. +* command-line option, --gen-po <1>: Options. +* command-line option, --gen-po: String Extraction. +* command-line option, --help: Options. +* command-line option, --lint: Options. +* command-line option, --lint-old: Options. +* command-line option, --non-decimal-data <1>: Options. +* command-line option, --non-decimal-data: Non-decimal Data. +* command-line option, --posix: Options. +* command-line option, --profile: Options. +* command-line option, --re-interval: Options. +* command-line option, --source: Options. +* command-line option, --traditional: Options. +* command-line option, --usage: Options. +* command-line option, --version: Options. +* command-line option, -f: Options. +* command-line option, -F <1>: Options. +* command-line option, -F: Command Line Field Separator. +* command-line option, -f: Long. +* command-line option, -mf: Options. +* command-line option, -mr: Options. +* command-line option, -v: Options. +* command-line option, -W: Options. * comments: Comments. * comments and backslash continuation: Statements/Lines. -* common mistakes <1>: Typing and Comparison. -* common mistakes <2>: Print Examples. -* common mistakes <3>: Basic Field Splitting. -* common mistakes: Computed Regexps. -* comp.lang.awk: Bugs. +* common mistakes <1>: Options. +* common mistakes <2>: String Functions. +* common mistakes <3>: Typing and Comparison. +* common mistakes <4>: Concatenation. +* common mistakes <5>: Arithmetic Ops. +* common mistakes <6>: Special FD. +* common mistakes <7>: Redirection. +* common mistakes <8>: Print Examples. +* common mistakes <9>: Field Separators. +* common mistakes <10>: Computed Regexps. +* common mistakes: Escape Sequences. +* comp.lang.awk Usenet news group: Bugs. * comparison expressions: Typing and Comparison. * comparisons, string vs. regexp: Typing and Comparison. * compatibility mode <1>: POSIX/GNU. * compatibility mode: Options. +* compiled programs <1>: Glossary. +* compiled programs: Basic High Level. +* compl built-in function: Bitwise Functions. +* complement, bitwise: Bitwise Functions. * complemented character list: Regexp Operators. * compound statement: Statements. * computed regular expressions: Computed Regexps. * concatenation: Concatenation. +* concatenation evaluation order: Concatenation. * conditional expression: Conditional Exp. +* configuration option, --disable-nls: Additional Configuration Options. +* configuration option, --enable-portals <1>: Additional Configuration Options. +* configuration option, --enable-portals: Portal Files. +* configuration option, --with-included-gettext <1>: Additional Configuration Options. +* configuration option, --with-included-gettext: Gawk I18N. * configuring gawk: Configuration Philosophy. * constants, types of: Constants. * continuation of lines: Statements/Lines. * continue statement: Continue Statement. * continue, outside of loops: Continue Statement. +* contributors to gawk: Contributors. * control statement: Statements. +* conventions, programming <1>: Internal File Ops. +* conventions, programming <2>: Nextfile Function. +* conventions, programming <3>: Library Names. +* conventions, programming <4>: Non-decimal Data. +* conventions, programming <5>: Return Statement. +* conventions, programming <6>: Definition Syntax. +* conventions, programming <7>: Calling Built-in. +* conventions, programming <8>: Auto-set. +* conventions, programming: Exit Statement. * conversion of case: String Functions. * conversion of strings and numbers: Conversion. * conversions, during subscripting: Numeric Array Subscripts. -* converting dates to timestamps: Mktime Function. -* CONVFMT <1>: Numeric Array Subscripts. -* CONVFMT <2>: User-modified. -* CONVFMT: Conversion. -* cos: Numeric Functions. +* converting dates to timestamps: Time Functions. +* CONVFMT variable <1>: Numeric Array Subscripts. +* CONVFMT variable <2>: User-modified. +* CONVFMT variable: Conversion. +* coprocess <1>: Two-way I/O. +* coprocess <2>: Close Files And Pipes. +* coprocess <3>: Redirection. +* coprocess: Getline/Coprocess. +* cos built-in function: Numeric Functions. +* csh utility <1>: Options. +* csh utility <2>: Two-way I/O. +* csh utility <3>: Statements/Lines. +* csh utility <4>: More Complex. +* csh utility: Quoting. * csh, backslash continuation <1>: Statements/Lines. * csh, backslash continuation: More Complex. * curly braces: Action Overview. * custom.h configuration file: Configuration Philosophy. * cut utility: Cut Program. -* cut.awk: Cut Program. -* d.c., see "dark corner": This Manual. -* dark corner <1>: Other Arguments. -* dark corner <2>: Invoking Gawk. -* dark corner <3>: String Functions. -* dark corner <4>: Uninitialized Subscripts. -* dark corner <5>: Auto-set. -* dark corner <6>: Exit Statement. -* dark corner <7>: Continue Statement. -* dark corner <8>: Break Statement. -* dark corner <9>: Using BEGIN/END. +* cut.awk program: Cut Program. +* d.c., see "dark corner": Conventions. +* dark corner <1>: Glossary. +* dark corner <2>: Other Arguments. +* dark corner <3>: Command Line. +* dark corner <4>: String Functions. +* dark corner <5>: Uninitialized Subscripts. +* dark corner <6>: Auto-set. +* dark corner <7>: Exit Statement. +* dark corner <8>: Continue Statement. +* dark corner <9>: Break Statement. * dark corner <10>: Truth Values. -* dark corner <11>: Conversion. -* dark corner <12>: Assignment Options. -* dark corner <13>: Using Constant Regexps. -* dark corner <14>: Format Modifiers. -* dark corner <15>: Control Letters. -* dark corner <16>: OFMT. -* dark corner <17>: Getline Summary. -* dark corner <18>: Plain Getline. -* dark corner <19>: Multiple Line. -* dark corner <20>: Field Splitting Summary. -* dark corner <21>: Single Character Fields. -* dark corner <22>: Records. -* dark corner <23>: Escape Sequences. -* dark corner: This Manual. +* dark corner <11>: Assignment Ops. +* dark corner <12>: Conversion. +* dark corner <13>: Assignment Options. +* dark corner <14>: Using Constant Regexps. +* dark corner <15>: Close Files And Pipes. +* dark corner <16>: Format Modifiers. +* dark corner <17>: Control Letters. +* dark corner <18>: OFMT. +* dark corner <19>: Getline Notes. +* dark corner <20>: Multiple Line. +* dark corner <21>: Field Splitting Summary. +* dark corner <22>: Single Character Fields. +* dark corner <23>: Changing Fields. +* dark corner <24>: Records. +* dark corner <25>: Escape Sequences. +* dark corner: Conventions. +* data files, non-readable, skipping: File Checking. +* data files, readable, checking: File Checking. +* data-driven languages <1>: Basic High Level. * data-driven languages: Getting Started. -* dates, converting to timestamps: Mktime Function. +* dates, converting to timestamps: Time Functions. +* Davies, Stephen <1>: Bugs. +* Davies, Stephen: Contributors. +* dcgettext built-in function <1>: Programmer i18n. +* dcgettext built-in function: I18N Functions. +* dcgettext user-defined function: I18N Portability. +* deadlock: Two-way I/O. * decrement operators: Increment Ops. * default action: Very Simple. * default pattern: Very Simple. * defining functions: Definition Syntax. * Deifik, Scott <1>: Bugs. -* Deifik, Scott: Acknowledgements. +* Deifik, Scott <2>: Contributors. +* Deifik, Scott: Acknowledgments. * delete statement: Delete. * deleting elements of arrays: Delete. * deleting entire arrays: Delete. @@ -17627,62 +20919,88 @@ Index * differences between gawk and awk <3>: Calling Built-in. * differences between gawk and awk <4>: Delete. * differences between gawk and awk <5>: ARGC and ARGV. -* differences between gawk and awk <6>: Nextfile Statement. -* differences between gawk and awk <7>: I/O And BEGIN/END. -* differences between gawk and awk <8>: Conditional Exp. -* differences between gawk and awk <9>: Arithmetic Ops. -* differences between gawk and awk <10>: Using Constant Regexps. -* differences between gawk and awk <11>: Scalar Constants. -* differences between gawk and awk <12>: Close Files And Pipes. -* differences between gawk and awk <13>: Special Files. -* differences between gawk and awk <14>: Redirection. -* differences between gawk and awk <15>: Getline Summary. -* differences between gawk and awk <16>: Getline Intro. -* differences between gawk and awk <17>: Single Character Fields. -* differences between gawk and awk <18>: Records. +* differences between gawk and awk <6>: User-modified. +* differences between gawk and awk <7>: Nextfile Statement. +* differences between gawk and awk <8>: I/O And BEGIN/END. +* differences between gawk and awk <9>: Conditional Exp. +* differences between gawk and awk <10>: Arithmetic Ops. +* differences between gawk and awk <11>: Using Constant Regexps. +* differences between gawk and awk <12>: Scalar Constants. +* differences between gawk and awk <13>: Close Files And Pipes. +* differences between gawk and awk <14>: Special FD. +* differences between gawk and awk <15>: Redirection. +* differences between gawk and awk <16>: Format Modifiers. +* differences between gawk and awk <17>: Getline Notes. +* differences between gawk and awk <18>: Getline/Coprocess. +* differences between gawk and awk <19>: Getline. +* differences between gawk and awk <20>: Single Character Fields. +* differences between gawk and awk <21>: Records. * differences between gawk and awk: Case-sensitivity. +* directory search <1>: VMS Running. +* directory search <2>: PC Using. +* directory search <3>: Igawk Program. * directory search: AWKPATH Variable. * division: Arithmetic Ops. +* do-while statement: Do Statement. +* documentation, online: Manual History. * documenting awk programs <1>: Library Names. * documenting awk programs: Comments. -* dupword.awk: Dupword Program. +* double-precision floating-point, definition of: Basic Data Typing. +* Drepper, Ulrich: Acknowledgments. +* dupnode internal function: Internals. +* dupword.awk program: Dupword Program. +* dynamic profiling: Profiling. * dynamic regular expressions: Computed Regexps. +* dynamic regular expressions with embedded newlines: Computed Regexps. * EBCDIC: Ordinal Functions. -* egrep <1>: Regexp Operators. -* egrep: One-shot. -* egrep utility: Egrep Program. -* egrep.awk: Egrep Program. +* egrep utility <1>: Egrep Program. +* egrep utility: Character Lists. +* egrep.awk program: Egrep Program. * element assignment: Assigning Elements. * element of array: Reference to Elements. +* emaill address for bug reports, bug-gawk@gnu.org: Bugs. +* embedded newlines, in dynamic regexps: Computed Regexps. +* EMISTERED: TCP/IP Networking. * empty action: Very Simple. * empty pattern: Empty. -* empty program: Invoking Gawk. +* empty program: Command Line. * empty string <1>: Truth Values. * empty string <2>: Conversion. * empty string <3>: Regexp Field Splitting. * empty string: Records. +* empty string, definition of: Basic Data Typing. * END special pattern: BEGIN/END. -* endfile: Filetrans Function. -* endgrent: Group Functions. -* endpwent: Passwd Functions. -* ENVIRON: Auto-set. +* endfile user-defined function: Filetrans Function. +* endgrent user-defined function: Group Functions. +* endpwent user-defined function: Passwd Functions. +* ENVIRON variable: Auto-set. * environment variable, AWKPATH: AWKPATH Variable. * environment variable, POSIXLY_CORRECT: Options. -* equivalence classes: Regexp Operators. -* ERRNO <1>: Auto-set. -* ERRNO <2>: Close Files And Pipes. -* ERRNO: Getline Intro. -* errors, common <1>: Typing and Comparison. -* errors, common <2>: Print Examples. -* errors, common <3>: Basic Field Splitting. -* errors, common: Computed Regexps. -* escape processing, sub et. al.: String Functions. +* epoch, definition of: Glossary. +* equivalence classes: Character Lists. +* ERRNO variable <1>: Auto-set. +* ERRNO variable: Getline. +* errors, common <1>: Options. +* errors, common <2>: String Functions. +* errors, common <3>: Typing and Comparison. +* errors, common <4>: Concatenation. +* errors, common <5>: Arithmetic Ops. +* errors, common <6>: Special FD. +* errors, common <7>: Redirection. +* errors, common <8>: Print Examples. +* errors, common <9>: Field Separators. +* errors, common <10>: Computed Regexps. +* errors, common: Escape Sequences. +* escape processing, sub et. al.: Gory Details. * escape sequence notation: Escape Sequences. -* evaluation, order of: Calling Built-in. +* evaluation, order of <1>: Calling Built-in. +* evaluation, order of <2>: Increment Ops. +* evaluation, order of: Concatenation. * examining fields: Fields. * executable scripts: Executable Scripts. * exit statement: Exit Statement. -* exp: Numeric Functions. +* exp built-in function: Numeric Functions. +* expand utility: Very Simple. * explicit input: Getline. * exponentiation: Arithmetic Ops. * expression: Expressions. @@ -17691,99 +21009,180 @@ Index * expression, comparison: Typing and Comparison. * expression, conditional: Conditional Exp. * expression, matching: Typing and Comparison. -* extract.awk: Extract Program. -* features, adding: Adding Code. -* fflush: I/O Functions. +* extension built-in function: Using Internal File Ops. +* extensions, Bell Laboratories awk: BTL. +* extensions, mawk: Other Versions. +* extract.awk program: Extract Program. +* extraction, of marked strings (internationalization): String Extraction. +* fatal errors <1>: File Checking. +* fatal errors <2>: Options. +* fatal errors <3>: I/O Functions. +* fatal errors <4>: String Functions. +* fatal errors <5>: Calling Built-in. +* fatal errors <6>: Format Modifiers. +* fatal errors: Constant Size. +* FDL: GNU Free Documentation License. +* features, adding to gawk: Adding Code. +* features, advanced: Advanced Features. +* features, undocumented: Undocumented. +* Fenlason, Jay <1>: Contributors. +* Fenlason, Jay: History. +* fflush built-in function: I/O Functions. * field operator $: Fields. -* field separator, choice of: Basic Field Splitting. -* field separator, FS: Basic Field Splitting. +* field separator, choice of: Field Separators. +* field separator, FS: Field Separators. * field separator, on command line: Command Line Field Separator. -* field, changing contents of: Changing Fields. * fields: Fields. -* fields, separating: Basic Field Splitting. -* FIELDWIDTHS: User-modified. -* file descriptors: Special Files. +* fields, changing contents of: Changing Fields. +* fields, definition of: Basic High Level. +* fields, separating: Field Separators. +* FIELDWIDTHS variable: User-modified. +* file descriptors: Special FD. * file, awk program: Long. -* FILENAME <1>: Auto-set. -* FILENAME <2>: Getline Summary. -* FILENAME: Reading Files. -* FILENAME, being set by getline: Getline Summary. -* Fish, Fred: Bugs. +* FILENAME variable <1>: Auto-set. +* FILENAME variable <2>: Getline Notes. +* FILENAME variable: Reading Files. +* FILENAME, being set by getline: Getline Notes. +* Fish, Fred <1>: Bugs. +* Fish, Fred: Contributors. +* flag variables <1>: Tee Program. +* flag variables <2>: Ranges. +* flag variables: Boolean Ops. +* floating-point, definition of: Basic Data Typing. +* floating-point, positive and negative values for zero: Floating Point Issues. +* floating-point, precision issues: Floating Point Issues. * flushing buffers: I/O Functions. -* FNR <1>: Auto-set. -* FNR: Records. -* for (x in ...): Scanning an Array. +* FNR variable <1>: Auto-set. +* FNR variable: Records. +* for (x in ...) statement: Scanning an Array. * for statement: For Statement. -* format specifier: Control Letters. +* force_number internal function: Internals. +* force_string internal function: Internals. +* format specifier, printf: Control Letters. +* format specifier, strftime: Time Functions. +* format specifiers, mixing regular with positional specifiers (printf): Printf Ordering. * format string: Basic Printf. * format, numeric output: OFMT. * formatted output: Printf. * formatted timestamps: Gettimeofday Function. -* Free Software Foundation <1>: Getting. +* Free Documentation License: GNU Free Documentation License. +* Free Software Foundation <1>: Glossary. +* Free Software Foundation <2>: Getting. * Free Software Foundation: Manual History. +* free_temp internal macro: Internals. +* FreeBSD <1>: Glossary. * FreeBSD: Manual History. -* Friedl, Jeffrey: Acknowledgements. -* FS <1>: User-modified. -* FS: Basic Field Splitting. -* ftp, anonymous <1>: Other Versions. +* FS variable <1>: User-modified. +* FS variable: Field Separators. +* FSF <1>: Glossary. +* FSF <2>: Getting. +* FSF: Manual History. * ftp, anonymous: Getting. * function call <1>: Function Caveats. * function call: Function Calls. * function definition: Definition Syntax. * function, recursive: Definition Syntax. +* function, user-defined: User-defined. * functions, undefined: Function Caveats. -* functions, user-defined: User-defined. -* gawk coding style: Adding Code. -* gensub: String Functions. -* getgrent: Group Functions. -* getgrent, C version: Group Functions. -* getgrgid: Group Functions. -* getgrnam: Group Functions. -* getgruser: Group Functions. -* getline: Getline. -* getline, return values: Getline Intro. -* getline, setting FILENAME: Getline Summary. -* getopt: Getopt Function. -* getopt, C version: Getopt Function. -* getpwent: Passwd Functions. -* getpwent, C version: Passwd Functions. -* getpwnam: Passwd Functions. -* getpwuid: Passwd Functions. -* gettimeofday: Gettimeofday Function. +* G-d: Acknowledgments. +* Garfinkle, Scott: Contributors. +* gawk, coding style: Adding Code. +* gawk, source code: Getting. +* General Public License <1>: Glossary. +* General Public License <2>: New Ports. +* General Public License <3>: Other Versions. +* General Public License: Manual History. +* gensub built-in function: String Functions. +* gensub, escape processing: Gory Details. +* get_argument internal function: Internals. +* getgrent C library function: Group Functions. +* getgrent user-defined function: Group Functions. +* getgrgid user-defined function: Group Functions. +* getgrnam user-defined function: Group Functions. +* getgruser user-defined function: Group Functions. +* getline built-in function: Getline. +* getline, return values: Getline. +* getline, setting FILENAME: Getline Notes. +* getopt C library function: Getopt Function. +* getopt user-defined function: Getopt Function. +* getpwent C library function: Passwd Functions. +* getpwent user-defined function: Passwd Functions. +* getpwnam user-defined function: Passwd Functions. +* getpwuid user-defined function: Passwd Functions. +* getservbyname C library function: TCP/IP Networking. +* gettext C library function: Explaining gettext. +* gettext, how it works: Explaining gettext. +* gettimeofday user-defined function: Gettimeofday Function. * getting gawk: Getting. +* GNITS mailing list: Acknowledgments. +* GNU Free Documentation License: GNU Free Documentation License. +* GNU General Public License <1>: Glossary. +* GNU General Public License <2>: New Ports. +* GNU General Public License <3>: Other Versions. +* GNU General Public License: Manual History. +* GNU Lesser General Public License <1>: Glossary. +* GNU Lesser General Public License: Other Versions. +* GNU Project <1>: Glossary. * GNU Project: Manual History. +* GNU/Linux <1>: Glossary. +* GNU/Linux <2>: Using Internal File Ops. +* GNU/Linux <3>: Internal File Ops. +* GNU/Linux <4>: Dynamic Extensions. +* GNU/Linux <5>: Atari Compiling. +* GNU/Linux <6>: Additional Configuration Options. +* GNU/Linux <7>: Installation. +* GNU/Linux <8>: I18N Example. +* GNU/Linux: Manual History. +* GPL <1>: Glossary. +* GPL <2>: New Ports. +* GPL <3>: Other Versions. +* GPL: Manual History. * grcat program: Group Functions. -* grcat.c: Group Functions. +* Grigera, Juan <1>: Bugs. +* Grigera, Juan: Contributors. * group file: Group Functions. * group information: Group Functions. -* gsub: String Functions. +* gsub built-in function: String Functions. +* gsub, escape processing: Gory Details. * gsub, third argument of: String Functions. * Hankerson, Darrel <1>: Bugs. -* Hankerson, Darrel: Acknowledgements. -* historical features <1>: Historical Features. -* historical features <2>: String Functions. -* historical features <3>: Continue Statement. -* historical features <4>: Break Statement. +* Hankerson, Darrel <2>: Contributors. +* Hankerson, Darrel: Acknowledgments. +* Hartholz, Elaine: Acknowledgments. +* Hartholz, Marshall: Acknowledgments. +* hexadecimal numbers: Non-decimal-numbers. +* historical features <1>: String Functions. +* historical features <2>: Continue Statement. +* historical features <3>: Break Statement. * historical features: Command Line Field Separator. * history of awk: History. -* histsort.awk: History Sorting. +* histsort.awk program: History Sorting. * how awk works: Two Rules. -* Hughes, Phil: Acknowledgements. -* I/O from BEGIN and END: I/O And BEGIN/END. +* Hughes, Phil: Acknowledgments. +* HUP signal: Profiling. +* I/O, binary: User-modified. +* I/O, from BEGIN and END: I/O And BEGIN/END. +* I/O, two-way: Two-way I/O. * id utility: Id Program. -* id.awk: Id Program. +* id.awk program: Id Program. * if-else statement: If Statement. -* igawk.sh: Igawk Program. -* IGNORECASE <1>: Array Intro. -* IGNORECASE <2>: User-modified. -* IGNORECASE: Case-sensitivity. -* IGNORECASE and array subscripts: Array Intro. +* igawk.sh program: Igawk Program. +* IGNORECASE variable <1>: Array Sorting. +* IGNORECASE variable <2>: Array Intro. +* IGNORECASE variable <3>: User-modified. +* IGNORECASE variable: Case-sensitivity. +* IGNORECASE, and array sorting: Array Sorting. +* IGNORECASE, and array subscripts: Array Intro. * ignoring case: Case-sensitivity. * implementation limits <1>: Redirection. -* implementation limits: Getline Summary. +* implementation limits: Getline Notes. +* in operator <1>: Id Program. +* in operator <2>: Scanning an Array. +* in operator <3>: For Statement. +* in operator <4>: Precedence. * in operator: Typing and Comparison. * increment operators: Increment Ops. -* index: String Functions. +* index built-in function: String Functions. * initialization, automatic: More Complex. * input: Reading Files. * input file, sample: Sample Data Files. @@ -17794,100 +21193,212 @@ Index * input, getline command: Getline. * input, multiple line records: Multiple Line. * input, standard: Read Terminal. +* insomnia, cure for: Alarm Program. * installation, amiga: Amiga Installation. * installation, atari: Atari Installation. -* installation, MS-DOS and OS/2: PC Installation. +* installation, beos: BeOS Installation. +* installation, pc operating systems: PC Installation. +* installation, tandem: Tandem Installation. * installation, unix: Quick Installation. * installation, vms: VMS Installation. -* int: Numeric Functions. +* int built-in function: Numeric Functions. +* integer, definition of: Basic Data Typing. +* integer, unsigned: Basic Data Typing. * interaction, awk and other programs: I/O Functions. * interactive buffering vs. non-interactive: I/O Functions. +* internal function, assoc_clear: Internals. +* internal function, assoc_lookup: Internals. +* internal function, dupnode: Internals. +* internal function, force_number: Internals. +* internal function, force_string: Internals. +* internal function, get_argument: Internals. +* internal function, make_builtin: Internals. +* internal function, make_number: Internals. +* internal function, make_string: Internals. +* internal function, set_value: Internals. +* internal function, tmp_number: Internals. +* internal function, tmp_string: Internals. +* internal function, update_ERRNO: Internals. +* internal macro, free_temp: Internals. +* internal type, AWKNUM: Internals. +* internal type, NODE: Internals. +* internal variable, param_cnt: Internals. +* internal variable, stlen: Internals. +* internal variable, stptr: Internals. +* internal variable, type: Internals. +* internal variable, vname: Internals. +* internationalization <1>: I18N and L10N. +* internationalization: User-modified. +* internationalization features in gawk: Internationalization. +* internationalization of awk programs, portability issues: I18N Portability. +* internationalization, marked strings: Programmer i18n. +* internationalizing a program: Explaining gettext. +* interpreted programs <1>: Glossary. +* interpreted programs: Basic High Level. * interval expressions: Regexp Operators. * inventory-shipped file: Sample Data Files. -* invocation of gawk: Invoking Gawk. +* invocation of gawk: Command Line. +* ISO: Glossary. * ISO 8601: Time Functions. * ISO 8859-1 <1>: Glossary. * ISO 8859-1: Case-sensitivity. * ISO Latin-1 <1>: Glossary. * ISO Latin-1: Case-sensitivity. -* Jaegermann, Michal <1>: Bugs. -* Jaegermann, Michal: Acknowledgements. -* join: Join Function. -* Kernighan, Brian <1>: Other Versions. -* Kernighan, Brian <2>: BTL. -* Kernighan, Brian <3>: Concatenation. -* Kernighan, Brian <4>: Acknowledgements. +* Jacobs, Andrew: Passwd Functions. +* Jaegermann, Michal <1>: Contributors. +* Jaegermann, Michal: Acknowledgments. +* Jedi knights: Undocumented. +* join user-defined function: Join Function. +* Kahrs, Ju"rgen <1>: Contributors. +* Kahrs, Ju"rgen: Acknowledgments. +* Kenobi, Obi-Wan: Undocumented. +* Kernighan, Brian <1>: Basic Data Typing. +* Kernighan, Brian <2>: Other Versions. +* Kernighan, Brian <3>: Contributors. +* Kernighan, Brian <4>: BTL. +* Kernighan, Brian <5>: Concatenation. +* Kernighan, Brian <6>: Acknowledgments. +* Kernighan, Brian <7>: Conventions. * Kernighan, Brian: History. +* kill command: Profiling. +* Knights, jedi: Undocumented. * known bugs: Known Bugs. -* labels.awk: Labels Program. +* Kwok, Conrad: Contributors. +* labels.awk program: Labels Program. * language, awk: This Manual. +* language, data-driven <1>: Basic High Level. * language, data-driven: Getting Started. * language, procedural: Getting Started. +* LC_ALL locale category: Explaining gettext. +* LC_COLLATE locale category: Explaining gettext. +* LC_CTYPE locale category: Explaining gettext. +* LC_MESSAGES locale category: Explaining gettext. +* LC_MONETARY locale category: Explaining gettext. +* LC_NUMERIC locale category: Explaining gettext. +* LC_RESPONSE locale category: Explaining gettext. +* LC_TIME locale category: Explaining gettext. +* left shift, bitwise: Bitwise Functions. * leftmost longest match <1>: Multiple Line. * leftmost longest match: Leftmost Longest. -* length: String Functions. +* length built-in function: String Functions. +* Lesser General Public License <1>: Glossary. +* Lesser General Public License: Other Versions. +* LGPL <1>: Glossary. +* LGPL: Other Versions. * limitations <1>: Redirection. -* limitations: Getline Summary. +* limitations: Getline Notes. * line break: Statements/Lines. * line continuation <1>: Conditional Exp. * line continuation <2>: Boolean Ops. * line continuation <3>: Print Examples. * line continuation: Statements/Lines. -* Linux <1>: Atari Compiling. +* lint checks <1>: Options. +* lint checks <2>: Command Line. +* lint checks <3>: Function Caveats. +* lint checks <4>: Uninitialized Subscripts. +* lint checks <5>: Delete. +* lint checks <6>: User-modified. +* lint checks: Format Modifiers. +* LINT variable: User-modified. +* Linux <1>: Glossary. +* Linux <2>: Using Internal File Ops. +* Linux <3>: Internal File Ops. +* Linux <4>: Dynamic Extensions. +* Linux <5>: Atari Compiling. +* Linux <6>: Additional Configuration Options. +* Linux <7>: Installation. +* Linux <8>: I18N Example. * Linux: Manual History. +* locale categories: Explaining gettext. * locale, definition of: Time Functions. -* log: Numeric Functions. +* localization: I18N and L10N. +* log built-in function: Numeric Functions. * logical false: Truth Values. -* logical operations: Boolean Ops. +* logical operators: Boolean Ops. * logical true: Truth Values. * login information: Passwd Functions. -* long options: Invoking Gawk. +* long options: Command Line. * loop: While Statement. * loops, exiting: Break Statement. +* Lost In Space: Dynamic Extensions. +* ls utility: More Complex. +* lshift built-in function: Bitwise Functions. * lvalue: Assignment Ops. +* make_builtin internal function: Internals. +* make_number internal function: Internals. +* make_string internal function: Internals. * mark parity: Ordinal Functions. -* match: String Functions. +* marked string extraction (internationalization): String Extraction. +* marked strings for internationalization: Programmer i18n. +* Marx, Groucho: Increment Ops. +* match built-in function: String Functions. * matching ranges of lines: Ranges. * matching, leftmost longest <1>: Multiple Line. * matching, leftmost longest: Leftmost Longest. -* mawk: Other Versions. +* matching, the null string: Gory Details. +* mawk, source code: Other Versions. * merging strings: Join Function. +* message object files (gettext): Explaining gettext. * metacharacters: Regexp Operators. -* mistakes, common <1>: Typing and Comparison. -* mistakes, common <2>: Print Examples. -* mistakes, common <3>: Basic Field Splitting. -* mistakes, common: Computed Regexps. -* mktime: Mktime Function. +* mistakes, common <1>: Options. +* mistakes, common <2>: String Functions. +* mistakes, common <3>: Typing and Comparison. +* mistakes, common <4>: Concatenation. +* mistakes, common <5>: Arithmetic Ops. +* mistakes, common <6>: Special FD. +* mistakes, common <7>: Redirection. +* mistakes, common <8>: Print Examples. +* mistakes, common <9>: Field Separators. +* mistakes, common <10>: Computed Regexps. +* mistakes, common: Escape Sequences. +* mktime built-in function: Time Functions. * modifiers (in format specifiers): Format Modifiers. -* multi-dimensional subscripts: Multi-dimensional. +* msgfmt utility: I18N Example. +* multidimensional subscripts: Multi-dimensional. * multiple line records: Multiple Line. * multiple passes over data: Other Arguments. * multiple statements on one line: Statements/Lines. * multiplication: Arithmetic Ops. -* names, use of: Definition Syntax. -* namespace issues in awk: Library Names. -* namespaces: Definition Syntax. +* mv utility: Redirection. +* names, use of <1>: Library Names. +* names, use of <2>: Definition Syntax. +* names, use of: Arrays. +* namespace issues in awk <1>: Library Names. +* namespace issues in awk <2>: Definition Syntax. +* namespace issues in awk: Arrays. +* negative zero: Floating Point Issues. +* NetBSD <1>: Glossary. * NetBSD: Manual History. +* networking, TCP/IP: TCP/IP Networking. * new awk: History. * new awk vs. old awk: Names. * newline: Statements/Lines. +* newlines, embedded in dynamic regexps: Computed Regexps. +* next file statement <1>: POSIX/GNU. * next file statement: Nextfile Statement. * next statement: Next Statement. * next, inside a user-defined function: Next Statement. -* nextfile function: Nextfile Function. * nextfile statement: Nextfile Statement. -* NF <1>: Auto-set. -* NF: Fields. +* nextfile user-defined function: Nextfile Function. +* nextfile, inside a user-defined function: Nextfile Statement. +* NF variable <1>: Auto-set. +* NF variable: Fields. +* noassign.awk program: Ignoring Assigns. +* NODE internal type: Internals. * non-interactive buffering vs. interactive: I/O Functions. -* not operator: Boolean Ops. -* NR <1>: Auto-set. -* NR: Records. +* non-readable data files, skipping: File Checking. +* NOT logical operator: Boolean Ops. +* NR variable <1>: Auto-set. +* NR variable: Records. * null string <1>: Truth Values. * null string <2>: Conversion. * null string: Regexp Field Splitting. * null string, as array subscript: Uninitialized Subscripts. +* null string, definition of: Basic Data Typing. * number of fields, NF: Fields. * number of records, NR, FNR: Records. +* numbers, hexadecimal: Non-decimal-numbers. +* numbers, octal: Non-decimal-numbers. * numbers, used as subscripts: Numeric Array Subscripts. * numeric character values: Ordinal Functions. * numeric constant: Scalar Constants. @@ -17896,33 +21407,42 @@ Index * numeric value: Scalar Constants. * obsolete features: Obsolete. * obsolete options: Obsolete. -* OFMT <1>: User-modified. -* OFMT <2>: Conversion. -* OFMT: OFMT. -* OFS <1>: User-modified. -* OFS: Output Separators. +* octal numbers: Non-decimal-numbers. +* OFMT variable <1>: User-modified. +* OFMT variable <2>: Conversion. +* OFMT variable: OFMT. +* OFS variable <1>: User-modified. +* OFS variable: Output Separators. * old awk: History. * old awk vs. new awk: Names. -* one-liners: One-liners. -* operations, logical: Boolean Ops. -* operator precedence: Precedence. +* one-liners: Very Simple. +* online documentation: Manual History. +* OpenBSD <1>: Glossary. +* OpenBSD: Manual History. +* operator precedence <1>: Precedence. +* operator precedence: Increment Ops. * operators, arithmetic: Arithmetic Ops. * operators, assignment: Assignment Ops. * operators, boolean: Boolean Ops. * operators, decrement: Increment Ops. * operators, increment: Increment Ops. +* operators, logical: Boolean Ops. * operators, regexp matching: Regexp Usage. * operators, relational: Typing and Comparison. * operators, short-circuit: Boolean Ops. * operators, string: Concatenation. * operators, string-matching: Regexp Usage. -* options, command line: Invoking Gawk. -* options, long: Invoking Gawk. -* or operator: Boolean Ops. -* ord: Ordinal Functions. +* options, command-line: Command Line. +* options, long: Command Line. +* OR bitwise operation: Bitwise Functions. +* or built-in function: Bitwise Functions. +* OR logical operator: Boolean Ops. +* ord user-defined function: Ordinal Functions. * order of evaluation: Calling Built-in. -* ORS <1>: User-modified. -* ORS: Output Separators. +* order of evaluation, concatenation: Concatenation. +* ORS variable <1>: User-modified. +* ORS variable: Output Separators. +* other awk implementations: Other Versions. * output: Printing. * output field separator, OFS: Output Separators. * output format specifier, OFMT: OFMT. @@ -17931,8 +21451,13 @@ Index * output, buffering: I/O Functions. * output, formatted: Printf. * output, piping: Redirection. +* P1003.2 POSIX standard: Glossary. +* param_cnt internal variable: Internals. * passes, multiple: Other Arguments. * password file: Passwd Functions. +* path, search <1>: VMS Running. +* path, search <2>: PC Using. +* path, search <3>: Igawk Program. * path, search: AWKPATH Variable. * pattern, BEGIN: BEGIN/END. * pattern, default: Very Simple. @@ -17941,485 +21466,747 @@ Index * pattern, END: BEGIN/END. * pattern, range: Ranges. * pattern, regular expressions: Regexp. -* patterns, types of: Kinds of Patterns. -* per file initialization and clean-up: Filetrans Function. +* patterns, types of: Pattern Overview. +* per file initialization and cleanup: Filetrans Function. * PERL: Future Extensions. +* Peters, Arno: Contributors. +* Peterson, Hal: Contributors. +* pgawk program: Profiling. * pipeline, input: Getline/Pipe. * pipes for output: Redirection. -* portability issues <1>: Portability Notes. -* portability issues <2>: Definition Syntax. -* portability issues <3>: I/O Functions. -* portability issues <4>: String Functions. -* portability issues <5>: Delete. -* portability issues <6>: Close Files And Pipes. -* portability issues <7>: Escape Sequences. -* portability issues: Statements/Lines. +* piping commands into the shell: Redirection. +* portability issues <1>: Library Functions. +* portability issues <2>: I18N Portability. +* portability issues <3>: Function Caveats. +* portability issues <4>: Definition Syntax. +* portability issues <5>: I/O Functions. +* portability issues <6>: String Functions. +* portability issues <7>: Delete. +* portability issues <8>: Precedence. +* portability issues <9>: Increment Ops. +* portability issues <10>: Assignment Ops. +* portability issues <11>: Arithmetic Ops. +* portability issues <12>: Close Files And Pipes. +* portability issues <13>: Changing Fields. +* portability issues <14>: Records. +* portability issues <15>: Escape Sequences. +* portability issues <16>: Statements/Lines. +* portability issues: Executable Scripts. +* portability issues, internationalization of awk programs: I18N Portability. +* portable object files (gettext): Explaining gettext. +* portal files: Portal Files. * porting gawk: New Ports. +* positional specifier, printf <1>: Printf Ordering. +* positional specifier, printf: Format Modifiers. +* positional specifiers, mixing with regular formats (printf): Printf Ordering. +* positive zero: Floating Point Issues. * POSIX awk <1>: Definition Syntax. -* POSIX awk <2>: String Functions. -* POSIX awk <3>: User-modified. -* POSIX awk <4>: Next Statement. -* POSIX awk <5>: Continue Statement. -* POSIX awk <6>: Break Statement. -* POSIX awk <7>: Precedence. -* POSIX awk <8>: Assignment Ops. -* POSIX awk <9>: Arithmetic Ops. -* POSIX awk <10>: Conversion. -* POSIX awk <11>: Format Modifiers. -* POSIX awk <12>: OFMT. -* POSIX awk <13>: Field Splitting Summary. -* POSIX awk <14>: Regexp Operators. +* POSIX awk <2>: Gory Details. +* POSIX awk <3>: String Functions. +* POSIX awk <4>: User-modified. +* POSIX awk <5>: Next Statement. +* POSIX awk <6>: Continue Statement. +* POSIX awk <7>: Break Statement. +* POSIX awk <8>: Precedence. +* POSIX awk <9>: Assignment Ops. +* POSIX awk <10>: Arithmetic Ops. +* POSIX awk <11>: Conversion. +* POSIX awk <12>: Format Modifiers. +* POSIX awk <13>: OFMT. +* POSIX awk <14>: Field Splitting Summary. +* POSIX awk <15>: Character Lists. +* POSIX awk <16>: Regexp Operators. * POSIX awk: Escape Sequences. * POSIX mode: Options. * POSIXLY_CORRECT environment variable: Options. -* precedence: Precedence. +* precedence <1>: Precedence. +* precedence: Increment Ops. * precedence, regexp operators: Regexp Operators. * print statement: Print. +* printf statement: Printf. * printf statement, syntax of: Basic Printf. * printf, format-control characters: Control Letters. +* printf, mixing positional specifiers with regular formats: Printf Ordering. * printf, modifiers: Format Modifiers. +* printf, positional specifier <1>: Printf Ordering. +* printf, positional specifier: Format Modifiers. * printing: Printing. +* problem reports: Bugs. * procedural languages: Getting Started. -* process information: Special Files. +* process information: Special Process. * processing arguments: Getopt Function. +* processing data: Basic High Level. +* PROCINFO variable: Auto-set. +* profiling awk programs: Profiling. +* profiling output file (awkprof.out): Profiling. +* profiling, dynamic: Profiling. * program file: Long. * program, awk: This Manual. * program, definition of: Getting Started. -* program, self contained: Executable Scripts. +* program, self-contained: Executable Scripts. +* programming concepts, basic: Basic Concepts. +* programming conventions <1>: Internal File Ops. +* programming conventions <2>: Nextfile Function. +* programming conventions <3>: Library Names. +* programming conventions <4>: Non-decimal Data. +* programming conventions <5>: Return Statement. +* programming conventions <6>: Definition Syntax. +* programming conventions <7>: Calling Built-in. +* programming conventions <8>: Auto-set. +* programming conventions: Exit Statement. +* programming language, recipe for: History. +* programming, basic steps: Basic High Level. +* programs, compiled: Basic High Level. * programs, documenting <1>: Library Names. * programs, documenting: Comments. +* programs, interpreted: Basic High Level. * pwcat program: Passwd Functions. -* pwcat.c: Passwd Functions. * quotient: Arithmetic Ops. -* quoting, shell <1>: Long. +* quoting rules, shell: Quoting. +* quoting, shell <1>: Comments. +* quoting, shell <2>: Long. * quoting, shell: Read Terminal. * Rakitzis, Byron: History Sorting. -* rand: Numeric Functions. +* rand built-in function: Numeric Functions. +* random numbers, Cliff: Cliff Random Function. * random numbers, seed of: Numeric Functions. * range pattern: Ranges. * Rankin, Pat <1>: Bugs. -* Rankin, Pat <2>: Assignment Ops. -* Rankin, Pat: Acknowledgements. +* Rankin, Pat <2>: Contributors. +* Rankin, Pat <3>: Assignment Ops. +* Rankin, Pat: Acknowledgments. +* readable data files, checking: File Checking. +* readable.awk program: File Checking. * reading files: Reading Files. * reading files, getline command: Getline. * reading files, multiple line records: Multiple Line. +* recipe for a programming language: History. * record separator, RS: Records. * record terminator, RT: Records. +* record, definition of <1>: Basic High Level. * record, definition of: Records. * records, multiple line: Multiple Line. * recursive function: Definition Syntax. * redirection of input: Getline/File. * redirection of output: Redirection. +* reference counting: Array Sorting. * reference to array: Reference to Elements. * regexp: Regexp. * regexp as expression: Typing and Comparison. * regexp comparison vs. string comparison: Typing and Comparison. * regexp constant: Regexp Usage. * regexp constants, difference between slashes and quotes: Computed Regexps. -* regexp match/non-match operators <1>: Typing and Comparison. -* regexp match/non-match operators: Regexp Usage. -* regexp matching operators: Regexp Usage. -* regexp operators: Regexp Operators. +* regexp operators <1>: Typing and Comparison. +* regexp operators <2>: Regexp Operators. +* regexp operators: Regexp Usage. * regexp operators, GNU specific: GNU Regexp Operators. * regexp operators, precedence of: Regexp Operators. * regexp, anchors: Regexp Operators. * regexp, dynamic: Computed Regexps. -* regexp, effect of command line options: GNU Regexp Operators. +* regexp, dynamic, with embedded newlines: Computed Regexps. +* regexp, effect of command-line options: GNU Regexp Operators. * regular expression: Regexp. * regular expression metacharacters: Regexp Operators. -* regular expressions as field separators: Basic Field Splitting. +* regular expressions as field separators: Field Separators. * regular expressions as patterns: Regexp. * regular expressions as record separators: Records. * regular expressions, computed: Computed Regexps. * relational operators: Typing and Comparison. * remainder: Arithmetic Ops. * removing elements of arrays: Delete. +* reporting bugs: Bugs. +* reporting problems: Bugs. * return statement: Return Statement. -* RFC-1036: Time Functions. -* RFC-822: Time Functions. -* RLENGTH <1>: String Functions. -* RLENGTH: Auto-set. -* Robbins, Miriam: Acknowledgements. +* return value from close: Close Files And Pipes. +* rewind user-defined function: Rewind Function. +* RFC 1036: Time Functions. +* RFC 822: Time Functions. +* right shift, bitwise: Bitwise Functions. +* Ritchie, Dennis: Basic Data Typing. +* RLENGTH variable <1>: String Functions. +* RLENGTH variable: Auto-set. +* Robbins, Arnold <1>: Future Extensions. +* Robbins, Arnold <2>: Bugs. +* Robbins, Arnold <3>: Contributors. +* Robbins, Arnold <4>: Alarm Program. +* Robbins, Arnold <5>: Passwd Functions. +* Robbins, Arnold <6>: Getline/Pipe. +* Robbins, Arnold: Command Line Field Separator. +* Robbins, Bill: Getline/Pipe. +* Robbins, Harry: Acknowledgments. +* Robbins, Jean: Acknowledgments. +* Robbins, Miriam <1>: Passwd Functions. +* Robbins, Miriam <2>: Getline/Pipe. +* Robbins, Miriam: Acknowledgments. +* Robinson, Will: Dynamic Extensions. +* robot, the: Dynamic Extensions. * Rommel, Kai Uwe <1>: Bugs. -* Rommel, Kai Uwe: Acknowledgements. -* round: Round Function. +* Rommel, Kai Uwe <2>: Contributors. +* Rommel, Kai Uwe: Acknowledgments. +* round user-defined function: Round Function. * rounding: Round Function. -* RS <1>: User-modified. -* RS: Records. -* RSTART <1>: String Functions. -* RSTART: Auto-set. -* RT <1>: Auto-set. -* RT <2>: Multiple Line. -* RT: Records. +* RS variable <1>: User-modified. +* RS variable: Records. +* rshift built-in function: Bitwise Functions. +* RSTART variable <1>: String Functions. +* RSTART variable: Auto-set. +* RT variable <1>: Auto-set. +* RT variable <2>: Multiple Line. +* RT variable: Records. +* Rubin, Paul <1>: Contributors. +* Rubin, Paul: History. * rule, definition of: Getting Started. * running awk programs: Running gawk. * running long programs: Long. * rvalue: Assignment Ops. -* sample input file: Sample Data Files. +* sample input files: Sample Data Files. +* scalar, definition of: Basic Data Typing. * scanning an array: Scanning an Array. +* Schreiber, Bert: Acknowledgments. +* Schreiber, Rita: Acknowledgments. * script, definition of: Getting Started. * scripts, executable: Executable Scripts. -* scripts, shell: Executable Scripts. +* search path <1>: VMS Running. +* search path <2>: PC Using. +* search path <3>: Igawk Program. * search path: AWKPATH Variable. +* search path, for source files <1>: VMS Running. +* search path, for source files <2>: PC Using. +* search path, for source files <3>: Igawk Program. * search path, for source files: AWKPATH Variable. -* sed utility <1>: Igawk Program. -* sed utility <2>: Simple Sed. +* sed utility <1>: Glossary. +* sed utility <2>: Igawk Program. +* sed utility <3>: Simple Sed. * sed utility: Field Splitting Summary. * seed for random numbers: Numeric Functions. -* self contained programs: Executable Scripts. -* shell quoting <1>: Long. +* self-contained programs: Executable Scripts. +* set_value internal function: Internals. +* sex, comparisons with <1>: Manual History. +* sex, comparisons with: This Manual. +* sex, programmer attractiveness: Two-way I/O. +* shell and awk interaction: Using Shell Variables. +* shell quoting <1>: Comments. +* shell quoting <2>: Long. * shell quoting: Read Terminal. -* shell scripts: Executable Scripts. +* shell quoting rules: Quoting. +* shell quoting, tricks: Quoting. +* shell varibles, using in awk programs: Using Shell Variables. +* shell, piping commands into: Redirection. +* shift, bitwise: Bitwise Functions. * short-circuit operators: Boolean Ops. -* side effect: Assignment Ops. +* side effects <1>: Array Sorting. +* side effects <2>: Reference to Elements. +* side effects <3>: Action Overview. +* side effects <4>: Function Calls. +* side effects <5>: Conditional Exp. +* side effects <6>: Boolean Ops. +* side effects <7>: Increment Ops. +* side effects <8>: Assignment Ops. +* side effects <9>: Concatenation. +* side effects: Getline Notes. +* SIGHUP signal: Profiling. +* signals, SIGHUP: Profiling. +* signals, SIGUSR1: Profiling. +* SIGUSR1 signal: Profiling. * simple stream editor: Simple Sed. -* sin: Numeric Functions. -* single character fields: Single Character Fields. +* sin built-in function: Numeric Functions. * single quotes, why needed: One-shot. +* single-character fields: Single Character Fields. +* single-precision floating-point, definition of: Basic Data Typing. * skipping input files: Nextfile Function. * skipping lines between markers: Ranges. +* Skywalker, Luke: Undocumented. +* sleep utility: Alarm Program. +* sort utility: Word Sorting. +* source code, awka: Other Versions. +* source code, gawk: Getting. +* source code, mawk: Other Versions. +* source code, Unix awk: Other Versions. * sparse arrays: Array Intro. -* split: String Functions. +* Spencer, Henry: Glossary. +* split built-in function: String Functions. * split utility: Split Program. -* split.awk: Split Program. -* sprintf: String Functions. -* sqrt: Numeric Functions. -* srand: Numeric Functions. -* Stallman, Richard <1>: Acknowledgements. +* split.awk program: Split Program. +* sprintf built-in function: String Functions. +* sqrt built-in function: Numeric Functions. +* srand built-in function: Numeric Functions. +* Stallman, Richard <1>: Glossary. +* Stallman, Richard <2>: Contributors. +* Stallman, Richard <3>: Acknowledgments. * Stallman, Richard: Manual History. -* standard error output: Special Files. -* standard input <1>: Special Files. +* standard error output: Special FD. +* standard input <1>: Special FD. * standard input <2>: Reading Files. * standard input: Read Terminal. -* standard output: Special Files. +* standard output: Special FD. * statement, compound: Statements. +* stlen internal variable: Internals. +* stptr internal variable: Internals. +* stream editor <1>: Igawk Program. +* stream editor <2>: Simple Sed. * stream editor: Field Splitting Summary. * stream editor, simple: Simple Sed. -* strftime: Time Functions. +* strftime built-in function: Time Functions. * string comparison vs. regexp comparison: Typing and Comparison. -* string constants: Constants. +* string constants: Scalar Constants. +* string extraction (internationalization): String Extraction. * string operators: Concatenation. * string-matching operators: Regexp Usage. -* sub: String Functions. +* strtonum built-in function: String Functions. +* sub built-in function: String Functions. +* sub, escape processing: Gory Details. * sub, third argument of: String Functions. * subscripts in arrays: Multi-dimensional. -* SUBSEP <1>: Multi-dimensional. -* SUBSEP: User-modified. -* substr: String Functions. +* SUBSEP variable <1>: Multi-dimensional. +* SUBSEP variable: User-modified. +* substr built-in function: String Functions. * subtraction: Arithmetic Ops. -* system: I/O Functions. -* systime: Time Functions. +* Sumner, Andrew: Other Versions. +* syntactic ambiguity: /= operator vs. /=.../ regexp constant: Assignment Ops. +* system built-in function: I/O Functions. +* systime built-in function: Time Functions. +* tandem: Tandem Installation. * Tcl: Library Names. +* TCP/IP networking <1>: Portal Files. +* TCP/IP networking: TCP/IP Networking. * tee utility: Tee Program. -* tee.awk: Tee Program. +* tee.awk program: Tee Program. * terminator, record: Records. +* testbits.awk program: Bitwise Functions. +* Texinfo <1>: Adding Code. +* Texinfo <2>: Distribution contents. +* Texinfo <3>: Extract Program. +* Texinfo <4>: Dupword Program. +* Texinfo <5>: Library Functions. +* Texinfo <6>: Regexp Operators. +* Texinfo <7>: Sample Data Files. +* Texinfo <8>: Acknowledgments. +* Texinfo: Conventions. +* textdomain C library function: Explaining gettext. +* TEXTDOMAIN variable <1>: Programmer i18n. +* TEXTDOMAIN variable: User-modified. * time of day: Time Functions. * timestamps: Time Functions. -* timestamps, converting from dates: Mktime Function. +* timestamps, converting from dates: Time Functions. * timestamps, formatted: Gettimeofday Function. -* tolower: String Functions. -* toupper: String Functions. -* translate.awk: Translate Program. -* Trueman, David: Acknowledgements. +* tmp_number internal function: Internals. +* tmp_string internal function: Internals. +* tolower built-in function: String Functions. +* Torvalds, Linus: Manual History. +* toupper built-in function: String Functions. +* tr utility: Translate Program. +* translate.awk program: Translate Program. +* Trueman, David <1>: Contributors. +* Trueman, David <2>: Acknowledgments. +* Trueman, David: History. * truth values: Truth Values. +* two-way I/O: Two-way I/O. * type conversion: Conversion. +* type internal variable: Internals. * types of variables <1>: Typing and Comparison. * types of variables: Assignment Ops. * undefined functions: Function Caveats. * undocumented features: Undocumented. * uninitialized variables, as array subscripts: Uninitialized Subscripts. * uniq utility: Uniq Program. -* uniq.awk: Uniq Program. +* uniq.awk program: Uniq Program. +* Unix: Glossary. +* Unix awk, source code: Other Versions. +* unsigned integers: Basic Data Typing. +* update_ERRNO internal function: Internals. * use of comments: Comments. * user information: Passwd Functions. * user-defined functions: User-defined. * user-defined variables: Using Variables. -* uses of awk: What Is Awk. +* uses of awk <1>: When. +* uses of awk: Preface. +* uses of gawk: Preface. +* using shell variables in awk programs: Using Shell Variables. * using this book: This Manual. +* USR1 signal: Profiling. * values of characters as numbers: Ordinal Functions. +* values, numeric: Basic Data Typing. +* values, string: Basic Data Typing. * variable shadowing: Definition Syntax. * variable typing: Typing and Comparison. +* variable, definition of: Basic Data Typing. * variables, user-defined: Using Variables. +* vname internal variable: Internals. +* w utility: Constant Size. * Wall, Larry: Future Extensions. +* warnings, automatic <1>: Options. +* warnings, automatic <2>: I/O Functions. +* warnings, automatic <3>: String Functions. +* warnings, automatic <4>: Using Constant Regexps. +* warnings, automatic <5>: Special Caveats. +* warnings, automatic <6>: Special Process. +* warnings, automatic: Escape Sequences. * wc utility: Wc Program. -* wc.awk: Wc Program. +* wc.awk program: Wc Program. +* Weinberger, Peter <1>: Contributors. * Weinberger, Peter: History. -* when to use awk: When. * while statement: While Statement. +* Williams, Kent: Contributors. +* Woods, John: Contributors. * word boundaries, matching: GNU Regexp Operators. * word, regexp definition of: GNU Regexp Operators. -* wordfreq.sh: Word Sorting. +* wordfreq.awk program: Word Sorting. +* xgettext utility: String Extraction. +* XOR bitwise operation: Bitwise Functions. +* xor built-in function: Bitwise Functions. +* Zaretskii, Eli: Acknowledgments. +* zero, negative vs. positive: Floating Point Issues. +* Zoulas, Christos: Contributors. +* | I/O operator <1>: Precedence. +* | I/O operator <2>: Redirection. +* | I/O operator: Getline/Pipe. +* |& I/O operator <1>: Two-way I/O. +* |& I/O operator <2>: Precedence. +* |& I/O operator <3>: Redirection. +* |& I/O operator: Getline/Coprocess. +* || operator <1>: Precedence. * || operator: Boolean Ops. -* ~ operator <1>: Typing and Comparison. -* ~ operator <2>: Regexp Constants. -* ~ operator <3>: Computed Regexps. -* ~ operator <4>: Case-sensitivity. +* ~ operator <1>: Precedence. +* ~ operator <2>: Typing and Comparison. +* ~ operator <3>: Regexp Constants. +* ~ operator <4>: Computed Regexps. +* ~ operator <5>: Case-sensitivity. * ~ operator: Regexp Usage. 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Extensions735742 +Node: Internals736758 +Node: Sample Library743097 +Node: Internal File Description743747 +Node: Internal File Ops747499 +Ref: Internal File Ops-Footnote-1752915 +Node: Using Internal File Ops753063 +Node: Future Extensions755084 +Node: Basic Concepts759427 +Node: Basic High Level760165 +Ref: Basic High Level-Footnote-1764332 +Node: Basic Data Typing764526 +Node: Floating Point Issues769020 +Ref: Floating Point Issues-Footnote-1772943 +Ref: Floating Point Issues-Footnote-2772994 +Node: Glossary773103 +Node: Copying797415 +Node: GNU Free Documentation License816614 +Node: Index836506 End Tag Table |