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diff --git a/gawk-info-2 b/gawk-info-2 deleted file mode 100644 index a228c5b9..00000000 --- a/gawk-info-2 +++ /dev/null @@ -1,1265 +0,0 @@ -Info file gawk-info, produced by Makeinfo, -*- Text -*- from input -file gawk.texinfo. - -This file documents `awk', a program that you can use to select -particular records in a file and perform operations upon them. - -Copyright (C) 1989 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 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. - -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. - - - -File: gawk-info, Node: Fields, Next: Non-Constant Fields, Prev: Records, Up: Reading Files - -Examining Fields -================ - -When `awk' reads an input record, the record is automatically -separated or "parsed" by the interpreter into pieces 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 and/or -tabs; other characters such as newline, formfeed, and so on, 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 -simple `awk' programs so powerful. - -To refer to a field in an `awk' program, you use a dollar--sign, `$', -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: - - 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, `$7', is -`example.'. Because there is no space between the `e' and the `.', -the period is considered part of the seventh field. - -No matter how many fields there are, the last field in a record can -be represented by `$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 Fields::.). If you try to refer to a field -beyond the last one, such as `$8' when the record has only 7 fields, -you get the empty string. - -Plain `NF', with no `$', is a special variable whose value is the -number of fields in the current record. - -`$0', which looks like an attempt to refer to the zeroth field, is a -special case: it represents the whole input record. This is what you -would use when you aren't interested in fields. - -Here are some more examples: - - awk '$1 ~ /foo/ { print $0 }' BBS-list - -This example contains the "matching" operator `~' (*note Comparison -Ops::.). Using this operator, all records in the file `BBS-list' -whose first field contains the string `foo' are printed. - -By contrast, the following example: - - awk '/foo/ { print $1, $NF }' BBS-list - -looks for the string `foo' in *the entire record* and prints the -first field and the last field for each input record containing the -pattern. - -The following program will search the system password file, and print -the entries for users who have no password. - - awk -F: '$2 == ""' /etc/passwd - -This program uses the `-F' option on the command line to set the file -separator. (Fields in `/etc/passwd' are separated by colons. The -second field represents a user's encrypted password, but if the field -is empty, that user has no password.) - - - -File: gawk-info, Node: Non-Constant Fields, Next: Changing Fields, Prev: Fields, Up: Reading Files - -Non-constant Field Numbers -========================== - -The number of a field does not need to be a constant. Any expression -in the `awk' language can be used after a `$' to refer to a field. -The `awk' utility evaluates the expression and uses the "numeric -value" as a field number. Consider this example: - - awk '{ print $NR }' - -Recall that `NR' is the number of records read so far: 1 in the first -record, 2 in the second, etc. So this example will print the first -field of the first record, the second field of the second record, and -so on. For the twentieth record, field number 20 will be printed; -most likely this will make a blank line, because the record will not -have 20 fields. - -Here is another example of using expressions as field numbers: - - awk '{ print $(2*2) }' BBS-list - -The `awk' language must evaluate the expression `(2*2)' and use its -value as the field number to print. The `*' sign represents -multiplication, so the expression `2*2' evaluates to 4. This -example, then, prints the hours of operation (the fourth field) for -every line of the file `BBS-list'. - -When you use non--constant field numbers, you may ask for a field -with a negative number. This always results in an empty string, just -like a field whose number is too large for the input record. For -example, `$(1-4)' would try to examine field number -3; it would -result in an empty string. - -If the field number you compute is zero, you get the entire record. - -The number of fields in the current record is stored in the special -variable `NF' (*note Special::.). The expression `$NF' is not a -special feature: it is the direct consequence of evaluating `NF' and -using its value as a field number. - - - -File: gawk-info, Node: Changing Fields, Next: Field Separators, Prev: Non-Constant Fields, Up: Reading Files - -Changing the Contents of a Field -================================ - -You can change the contents of a field as seen by `awk' 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.) - -Look at this example: - - awk '{ $3 = $2 - 10; print $2, $3 }' inventory-shipped - -The `-' sign represents subtraction, so this program reassigns field -three, `$3', to be the value of field two minus ten, ``$2' - 10'. -(*Note 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 3. *Note Conversion::. - -When you change the value of a field (as perceived by `awk'), the -text of the input record is recalculated to contain the new field -where the old one was. `$0' will from that time on reflect the -altered field. Thus, - - awk '{ $2 = $2 - 10; print $0 }' inventory-shipped - -will print a copy of the input file, with 10 subtracted from the -second field of each line. - -You can also assign contents to fields that are out of range. For -example: - - awk '{ $6 = ($5 + $4 + $3 + $2)/4) ; print $6 }' inventory-shipped - -We've just created `$6', whose value is the average of fields `$2', -`$3', `$4', and `$5'. The `+' sign represents addition, and the `/' -sign represents division. For the file `inventory-shipped' `$6' -represents the average number of parcels shipped for a particular -month. - -Creating a new field changes what `awk' interprets as the current -input record. The value of `$0' will be recomputed. This -recomputation affects and is affected by features not yet discussed, -in particular, the "Output Field Separator", `OFS', which is used to -separate the fields (*note Output Separators::.), and `NF' (the -number of fields; *note Fields::.). For example, the value of `NF' -will be set to the number of the highest out--of--range field you -create. - -Note, however, that merely *referencing* an out--of--range field will -*not* change the value of either `$0' or `NF'. Referencing an -out--of--range field merely produces a null string. For example: - - if ($(NF+1) != "") - print "can't happen" - else - print "everything is normal" - -should print `everything is normal'. (*Note If::, for more -information about `awk''s `if-else' statements.) - - - -File: gawk-info, Node: Field Separators, Next: Multiple, Prev: Changing Fields, Up: Reading Files - -Specifying How Fields Are Separated -=================================== - -You can change the way `awk' splits a record into fields by changing -the value of the "field separator". The field separator is -represented by the special variable `FS' in an `awk' program, and can -be set by `-F' on the command line. The `awk' language scans each -input line for the field separator character to determine the -positions of fields within that line. Shell programmers take note! -`awk' uses the variable `FS', not `IFS'. - -The default value of the field separator is a string containing a -single space. This value is actually a special case; as you know, by -default, fields are separated by whitespace sequences, not by single -spaces: two spaces in a row do not delimit an empty field. -``Whitespace'' is defined as sequences of one or more spaces or tab -characters. - -You change the value of `FS' by "assigning" it a new value. You can -do this using the special `BEGIN' pattern (*note BEGIN/END::.). This -pattern allows you to change the value of `FS' before any input is -read. The new value of `FS' is enclosed in quotations. For example, -set the value of `FS' to the string `","': - - awk 'BEGIN { FS = "," } ; { print $2 }' - -and use the input line: - - John Q. Smith, 29 Oak St., Walamazoo, MI 42139 - -This `awk' program will extract 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 person's name in the example we've been using might have a title -or suffix attached, such as `John Q. Smith, LXIX'. If you assigned -`FS' to be `,' then: - - awk 'BEGIN { FS = "," } ; { print $2 } - -would extract `LXIX', instead of `29 Oak St.'. If you were expecting -the program to print the address, you would be surprised. So, choose -your data layout and separator characters carefully to prevent -problems like this from happening. - -You can assign `FS' to be a series of characters. For 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' stands for a tab.) - -If `FS' is any single character other than a blank, then that -character is used as the field separator, and two successive -occurrences of that character do delimit an empty field. - -If you assign `FS' to a string longer than one character, that string -is evaluated as a "regular expression" (*note Regexp::.). The value -of the regular expression is used as a field separator. - -`FS' can be set on the command line. You use the `-F' argument to do -so. For example: - - awk -F, 'PROGRAM' INPUT-FILES - -sets `FS' to be the `,' character. Notice that the argument uses a -capital `F'. Contrast this with `-f', which specifies a file -containing an `awk' program. Case is significant in command 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' argument *and* -get an `awk' program from a file. - -As a special case, if the argument to `-F' is `t', then `FS' is set -to the tab character. (This is because if you type `-F\t', without -the quotes, at the shell, the `\' gets deleted, so `awk' figures that -you really want your fields to be separated with tabs, and not `t's. -Use `FS="t"' 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'. We'll use -the operating system utility `cat' to ``look'' at our program: - - % cat baud.awk - /300/ { print $1 } - -Let's also set `FS' to be the `-' character. We will apply all this -information to the file `BBS-list'. This `awk' program will now -print a list of the names of the bulletin boards that operate at 300 -baud and the first three digits of their phone numbers. - - awk -F- -f baud.awk BBS-list - -produces this output: - - aardvark 555 - alpo - barfly 555 - bites 555 - camelot 555 - core 555 - fooey 555 - foot 555 - macfoo 555 - sdace 555 - sabafoo 555 - -Note the second line of output. If you check the original file, you -will see that the second line looked like this: - - alpo-net 555-3412 2400/1200/300 A - -The `-' as part of the system's name was used as the field 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. - - - -File: gawk-info, Node: Multiple, Next: Assignment Options, Prev: Field Separators, Up: Reading Files - -Multiple--Line Records -====================== - -In some data bases, a single line cannot conveniently hold all the -information in one entry. Then you will want to 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 will you want to define -them? What should separate records? - -One technique is to use an unusual character or string to separate -records. For example, you could use the formfeed character (written -`\f' in `awk', as in C) to separate them, making each record a page -of the file. To do this, just set the variable `RS' to `"\f"' (a -string containing the formfeed character), or whatever string you -prefer to use. - -Another technique is to have blank lines separate records. By a -special dispensation, a null string as the value of `RS' indicates -that records are separated by one or more blank lines. If you set -`RS' to the null string, a record will always end at the first blank -line encountered. And the next record won't start until the first -nonblank line that follows--no matter how many blank lines appear in -a row, they will be considered one record--separator. - -The second step is to separate the fields in the record. One way to -do this 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.) Another idea is to divide each -of the lines into fields in the normal manner; the regular expression -`"[ \t\n]+"' will do this nicely by treating the newlines inside the -record just like spaces. - -When `RS' is set to the null string, the newline character *always* -acts as a field separator. This is in addition to whatever value -`FS' has. The probable reason for this rule is so that you get -rational behavior in the default case (i.e. `FS == " "'). This can -be a problem if you really don't want the newline character to -separate fields, since there is no way to do that. However, you can -work around this by using the `split' function to manually break up -your data (*note String Functions::.). - -Here is how to use records separated by blank lines and break each -line into fields normally: - - awk 'BEGIN { RS = ""; FS = "[ \t\n]+" } ; { print $0 }' BBS-list - - - -File: gawk-info, Node: Assignment Options, Next: Getline, Prev: Multiple, Up: Reading Files - -Assigning Variables on the Command Line -======================================= - -You can include variable "assignments" among the file names on the -command line used to invoke `awk' (*note Command Line::.). Such -assignments have the form: - - VARIABLE=TEXT - -and allow you to change variables either at the beginning of the -`awk' run or in between input files. 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 - -prints the value of field number `n' for all input records. Before -the first file is read, the command line sets the variable `n' equal -to 4. This causes the fourth field of the file `inventory-shipped' -to be printed. After the first file has finished, but before the -second file is started, `n' is set to 2, so that the second field of -the file `BBS-list' will be printed. - -Command line arguments are made available for explicit examination by -the `awk' program in an array named `ARGV' (*note Special::.). - - - -File: gawk-info, Node: Getline, Prev: Assignment Options, Up: Reading Files - -Explicit Input with `getline' -============================= - -So far we have been getting our input files from `awk''s main input -stream--either the standard input (usually your terminal) or the -files specified on the command line. The `awk' language has a -special built--in function called `getline' that can be used to read -input under your explicit control. - -This command is quite complex and should *not* be used by beginners. -The command (and its variations) is covered here because this is the -section about input. The examples that follow the explanation of the -`getline' command include material that has not been covered yet. -Therefore, come back and attempt the `getline' command *after* you -have reviewed the rest of this manual and have a good knowledge of -how `awk' works. - -When retrieving input, `getline' returns a 1 if it found a record, -and a 0 if the end of the file was encountered. If there was some -error in getting a record, such as a file that could not be opened, -then `getline' returns a -1. - -In the following examples, COMMAND stands for a string value that -represents a shell command. - -`getline' - The `getline' function can be used by itself, in an `awk' - program, to read input from the current input. 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 processing - *right now* on the next record. Here's an example: - - awk '{ - if (t = index($0, "/*")) { - if(t > 1) - tmp = substr($0, 1, t - 1) - else - tmp = "" - u = index(substr($0, t + 2), "*/") - while (! u) { - getline - t = -1 - u = index($0, "*/") - } - if(u <= length($0) - 2) - $0 = tmp substr($0, t + u + 3) - else - $0 = tmp - } - print $0 - }' - - This `awk' program deletes all comments, `/* ... */', from the - input. By replacing the `print $0' with other statements, you - could perform more complicated processing on the de--commented - input, such as search it for matches for a regular expression. - - This form of the `getline' command sets `NF' (the number of - fields; *note Fields::.), `NR' (the number of records read so - far), the `FNR' variable (*note Records::.), and the value of - `$0'. - - *Note:* The new value of `$0' will be used in testing the - patterns of any subsequent rules. The original value of `$0' - that triggered the rule which 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 Next::. - -`getline VAR' - This form of `getline' reads a record into the variable VAR. - This is useful when you want your program to read the next - record from the input file, but you don't want to subject the - record to the normal input processing. - - For example, suppose the next line is a comment, or a special - string, and you want to read it, but you must make certain that - it won't accidentally trigger any rules. This version of - `getline' will allow 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. For - example, given: - - wan - tew - free - phore - - it outputs: - - tew - wan - phore - free - - Here's the program: - - awk '{ - if ((getline tmp) > 0) { - print tmp - print $0 - } else - print $0 - }' - - The `getline' function used in this way sets only `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 not change. - -`getline < FILE' - This form of the `getline' function takes its input from the - file FILE. Here FILE is a string--valued expression that - specifies the file name. - - This form is useful if you want to read your input from a - particular file, instead of from the main input stream. For - example, the following program reads its input record from the - file `foo.input' when it encounters a first field with a value - equal to 10 in the current input file. - - awk '{ - if ($1 == 10) { - getline < "foo.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'. - - This does not cause the record to 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, just as when `getline' is used without a redirection. - -`getline VAR < FILE' - This form of the `getline' function takes its input from the - file FILE and puts it in the variable VAR. As above, FILE is a - string--valued expression that specifies the file to read from. - - 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. - - 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 from the data, from the second field on - the `@include' line. - - The `close' command is used to ensure that if two identical - `@include' lines appear in the input, the entire specified file - is included twice. *Note Close Input::. - - One deficiency of this program is that it does not process - nested `@include' statements the way a true macro preprocessor - would. - -`COMMAND | getline' - You can "pipe" the output of a command into `getline'. A pipe - is simply a way to link the output of one program to the input - of another. 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 from the pipe. - - For example, the following program copies input to 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) - print - close(tmp) - } else - print - }' - - The `close' command is used to ensure that if two identical - `@execute' lines appear in the input, the command is run again - for each one. *Note Close Input::. - - Given the input: - - foo - bar - baz - @execute who - bletch - - the program might produce: - - foo - bar - baz - hack ttyv0 Jul 13 14:22 - hack ttyp0 Jul 13 14:23 (gnu:0) - hack ttyp1 Jul 13 14:23 (gnu:0) - hack ttyp2 Jul 13 14:23 (gnu:0) - hack ttyp3 Jul 13 14:23 (gnu:0) - bletch - - Notice that this program ran the command `who' and printed the - result. (If you try this program yourself, you will get - different results, showing you logged in.) - - 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. - -`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 utility called `date', and then prints - it. - - awk '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. - - - -File: gawk-info, Node: Close Input, Up: Getline - -Closing Input Files -------------------- - -If the same file name or the same shell command is used with -`getline' more than once during the execution of the `awk' program, -the file is opened (or the command is executed) only the first time. -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. - -What this implies is that if you want to start reading the same file -again from the beginning, or if you want to rerun a shell command -(rather that reading more output from the command), you must take -special steps. What you can do is use the `close' statement: - - close (FILENAME) - -This statement closes a file or pipe, represented here by FILENAME. -The string value of FILENAME must be the same value as the string -used to open the file or pipe to begin with. - -Once this statement is executed, the next `getline' from that file or -command will reopen the file or rerun the command. - - - -File: gawk-info, Node: Printing, Next: One-liners, Prev: Reading Files, Up: Top - -Printing Output -*************** - -One of the most common things that actions do is to output or "print" -some or all of the input. For simple output, use the `print' -statement. For fancier formatting use the `printf' statement. Both -are described in this chapter. - -* Menu: - -* Print:: The `print' statement. -* Print Examples:: Simple examples of `print' statements. -* Output Separators:: The output separators and how to change them. - -* Redirection:: How to redirect output to multiple files and pipes. -* Close Output:: How to close output files and pipes. - -* Printf:: The `printf' statement. - - - -File: gawk-info, Node: Print, Next: Print Examples, Up: Printing - -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: - - print ITEM1, ITEM2, ... - - The entire list of items may optionally be enclosed in parentheses. -The parentheses are necessary if any of the item expressions uses a -relational operator; otherwise it could be confused with a -redirection (*note Redirection::.). The relational operators are -`==', `!=', `<', `>', `>=', `<=', `~' and `!~' (*note Comparison -Ops::.). - -The items printed can be constant strings or numbers, fields of the -current record (such as `$1'), variables, or any `awk' expressions. -The `print' statement is completely general for computing *what* -values to print. With one exception (*note Output Separators::.), -what you can't do is specify *how* to print them--how many columns to -use, whether to use exponential notation or not, and so on. For -that, you need the `printf' statement (*note Printf::.). - -To print a fixed piece of text, write a string constant as one item, -such as `"Hello there"'. 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 will be -printed between any two items. - -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 null, or empty, string. - -Most often, each `print' statement makes 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. - - - -File: gawk-info, Node: Print Examples, Next: Output Separators, Prev: Print, Up: Printing - -Examples of `print' Statements -============================== - -Here is an example that prints the first two fields of each input -record, with a space between them: - - awk '{ print $1, $2 }' inventory-shipped - -Its output looks like this: - - Jan 13 - Feb 15 - Mar 15 - ... - - A common mistake in using the `print' statement is to omit the comma -between two items. This often has the effect of making the items run -together in the output, with no space. The reason for this is that -juxtaposing two string expressions in `awk' means to concatenate -them. For example, without the comma: - - awk '{ print $1 $2 }' inventory-shipped - -prints: - - Jan13 - Feb15 - Mar15 - ... - - Neither example's output makes much sense to someone unfamiliar with -the file `inventory-shipped'. 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 BEGIN/END::.) to cause the headings to be printed only -once: - - awk 'BEGIN { print "Month Crates" - print "---- -----" } - { print $1, $2 }' inventory-shipped - -Did you already guess what will happen? This program prints the -following: - - Month Crates - ---- ----- - Jan 13 - Feb 15 - Mar 15 - ... - - 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 Printf::.); one of its specialties is lining up -columns of data. - - - -File: gawk-info, Node: Output Separators, Next: Redirection, Prev: Print Examples, Up: Printing - -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. But they do not have to be spaces; a -single space is only the default. You can specify any string of -characters to use as the "output field separator", by setting the -special variable `OFS'. The initial value of this variable is the -string `" "'. - -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 special -variable `ORS' specifies this string. The initial value of the -variable is the string `"\n"' containing 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 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. - -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: - - awk 'BEGIN { OFS = ";"; ORS = "\n\n" } - { print $1, $2 }' BBS-list - -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. - - - -File: gawk-info, Node: Redirection, Next: Printf, Prev: Output Separators, Up: Printing - -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 be told to 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. - -Here are the three forms of output redirection. They are all shown -for the `print' statement, but they work for `printf' also. - -`print ITEMS > OUTPUT-FILE' - This type of redirection prints the items onto 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 filename - (*note Expressions::.). - - When this type of redirection is used, the OUTPUT-FILE is erased - before the first output is written to it. Subsequent writes do - not erase OUTPUT-FILE, but append to it. If OUTPUT-FILE does - not exist, then it is created. - - For example, here is how one `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. - - awk '{ print $2 > "phone-list" - print $1 > "name-list" }' BBS-list - -`print ITEMS >> OUTPUT-FILE' - This type of redirection prints the items onto the output file - 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. - -`print ITEMS | COMMAND' - It is also possible to send output 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, 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: - - awk '{ print $1 > "names.unsorted" - print $1 | "sort -r > names.sorted" }' BBS-list - - Here the unsorted list is written with an ordinary redirection - while the sorted list is written by piping through the `sort' - utility. - - Here is an example that 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. - - print "Awk script failed:", $0 | "mail bug-system" - print "processing record number", FNR, "of", FILENAME | "mail bug-system" - close ("mail bug-system") - - We use a `close' statement here because it's a good idea to - close the pipe as soon as all the intended output has been sent - to it. *Note Close Output::, for more information on this. - -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. - - - -File: gawk-info, Node: Close Output, Up: Redirection - -Closing Output Files and Pipes ------------------------------- - -When a file or pipe is opened, the filename 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 is usually convenient. - -Sometimes there is a reason to close an output file or pipe earlier -than that. To do this, use the `close' command, as follows: - - close (FILENAME) - -or - - close (COMMAND) - -The argument FILENAME or COMMAND can be any expression. Its value -must exactly equal the string used to open the file or pipe to begin -with--for example, if you open a pipe with this: - - print $1 | "sort -r > names.sorted" - -then you must close it with this: - - close ("sort -r > names.sorted") - -Here are some reasons why you might need to close 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' (*note Getline::.). - - * To write numerous files, successively, in the same `awk' - program. If you don't close the files, eventually you will - exceed the system limit on the number of open files in one - process. So close each one when you are 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 will not actually be sent until the pipe is closed. - - * To run the same subprogram 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. - - - -File: gawk-info, Node: Printf, Prev: Redirection, 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 stylistic 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 specifying a "format string". - -* Menu: - -* Basic Printf:: Syntax of the `printf' statement. -* Format-Control:: Format-control letters. -* Modifiers:: Format--specification modifiers. -* Printf Examples:: Several examples. - - - -File: gawk-info, Node: Basic Printf, Next: Format-Control, Up: Printf - -Introduction to the `printf' Statement --------------------------------------- - -The `printf' statement looks like this: - - printf FORMAT, ITEM1, ITEM2, ... - - The entire list of items may optionally be enclosed in parentheses. -The parentheses are necessary if any of the item expressions uses a -relational operator; otherwise it could be confused with a -redirection (*note Redirection::.). The relational operators are -`==', `!=', `<', `>', `>=', `<=', `~' and `!~' (*note Comparison -Ops::.). - -The difference between `printf' and `print' is the argument FORMAT. -This is an expression whose value is taken as a string; its job is to -say how to output each of the other arguments. It is called the -"format string". - -The format string is essentially the same as in the C library -function `printf'. Most of FORMAT is text to be output verbatim. -Scattered among this text are "format specifiers", one per item. -Each format specifier says to output the next item at that place in -the format. - -The `printf' statement does not automatically append a newline to its -output. It outputs nothing but what the format specifies. So if you -want a newline, you must include one in the format. The output -separator variables `OFS' and `ORS' have no effect on `printf' -statements. - - - -File: gawk-info, Node: Format-Control, Next: Modifiers, Prev: Basic Printf, Up: Printf - -Format--Control Characters --------------------------- - -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 such as the field width to use. - -Here is a list of them: - -`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' - This prints a decimal integer. - -`e' - This prints a number in scientific (exponential) notation. For - example, - - printf "%4.3e", 1950 - - prints `1.950e+03', with a total of 4 significant figures of - which 3 follow the decimal point. The `4.3' are "modifiers", - discussed below. - -`f' - This prints a number in floating point notation. - -`g' - This prints either scientific notation or floating point - notation, whichever is shorter. - -`o' - This prints an unsigned octal integer. - -`s' - This prints a string. - -`x' - This prints an unsigned hexadecimal integer. - -`%' - 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. - - - -File: gawk-info, Node: Modifiers, Next: Printf Examples, Prev: Format-Control, Up: Printf - -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. -Here are the possible modifiers, in the order in which they may appear: - -`-' - The minus sign, used before the width modifier, says to - left--justify the argument within its specified width. Normally - the argument is printed right--justified in the specified width. - -`WIDTH' - This is a number representing the desired 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. - -`.PREC' - This is a number that specifies the precision to use when - printing. This specifies the number of digits you want printed - to the right of the decimal place. - -The C library `printf''s dynamic WIDTH and PREC capability (for -example, `"%*.*s"') is not supported. However, it can be easily -simulated using concatenation to dynamically build the format string. - - - -File: gawk-info, Node: Printf Examples, Prev: Modifiers, Up: Printf - -Examples of Using `printf' --------------------------- - -Here is 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 will produce an aligned -two--column table of names and phone numbers, like so: - - aardvark 555-5553 - alpo-net 555-3412 - barfly 555-7685 - bites 555-1675 - camelot 555-0542 - core 555-2912 - fooey 555-1234 - foot 555-6699 - macfoo 555-6480 - 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. This dash would be interpreted as a -"minus" sign if we had tried to print the phone numbers as numbers. -This would have led to some pretty confusing results. - -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. - -We could make our table look even nicer by adding headings to the -tops of the columns. To do this, use the BEGIN pattern (*note -BEGIN/END::.) to cause the header to be printed only 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: - - awk 'BEGIN { printf "%-10s %s\n", "Name", "Number" - printf "%-10s %s\n", "---", "-----" } - { printf "%-10s %s\n", $1, $2 }' BBS-list - -By outputting each column heading with the same format specification -used for the elements of the column, we have made sure that the -headings will be aligned just like the columns. - -The fact that the same format specification is used can be emphasized -by storing it in a variable, like so: - - awk 'BEGIN { format = "%-10s %s\n" - printf format, "Name", "Number" - 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 Print::.). - - - -File: gawk-info, Node: One-liners, Next: Patterns, Prev: Printing, Up: Top - -Useful ``One-liners'' -********************* - -Useful `awk' programs are often 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 manual to become an `awk' expert! - -`awk '{ num_fields = num_fields + NF }' -`` END { print num_fields }''' - This program prints the total number of fields in all input lines. - -`awk 'length($0) > 80'' - This program prints every line 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). - -`awk 'NF > 0'' - 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 '{ if (NF > 0) print }'' - This program also prints every line that has at least one field. - Here we allow the rule to match every line, then decide in the - action whether to print. - -`awk 'BEGIN { for (i = 1; i <= 7; i++)' -`` print int(101 * rand()) }''' - This program prints 7 random numbers from 0 to 100, inclusive. - -`ls -l FILES | awk '{ x += $4 } ; END { print "total bytes: " x }'' - This program prints the total number of bytes used by FILES. - -`expand FILE | awk '{ if (x < length()) x = length() }' -`` END { print "maximum line length is " x }''' - This program prints the maximum line length of FILE. The input - is piped through the `expand' program to change tabs into - spaces, so the widths compared are actually the right--margin - columns. - - |