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diff --git a/doc/bashref.texi b/doc/bashref.texi index 2d1717d1..854090ec 100644 --- a/doc/bashref.texi +++ b/doc/bashref.texi @@ -5,13 +5,13 @@ @c %**end of header @ignore -last change: Mon May 19 12:55:22 EDT 1997 +last change: Wed Mar 25 11:36:48 EST 1998 @end ignore -@set EDITION 2.0 -@set VERSION 2.01 -@set UPDATED 19 May 1997 -@set UPDATE-MONTH May 1997 +@set EDITION 2.2 +@set VERSION 2.02 +@set UPDATED 1 April 1998 +@set UPDATE-MONTH April 1998 @iftex @finalout @@ -22,12 +22,12 @@ last change: Mon May 19 12:55:22 EDT 1997 @defcodeindex rw @set BashFeatures +@ifinfo @dircategory Utilities @direntry -* Bash: (bash). GNU Bourne-Again SHell + * Bash: (bash). The GNU Bourne-Again SHell. @end direntry -@ifinfo @format This text is a brief description of the features that are present in the Bash shell. @@ -36,7 +36,7 @@ This is Edition @value{EDITION}, last updated @value{UPDATED}, of @cite{The GNU Bash Reference Manual}, for @code{Bash}, Version @value{VERSION}. -Copyright (C) 1991, 1993, 1996 Free Software Foundation, Inc. +Copyright (C) 1991, 1993, 1996, 1997 Free Software Foundation, Inc. Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice @@ -57,7 +57,7 @@ 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. +by the Free Software Foundation. @end format @end ifinfo @@ -125,12 +125,6 @@ reference on shell behavior. * Bourne Shell Features:: Features similar to those found in the Bourne shell. -* Csh Features:: Features originally found in the - Berkeley C-Shell. - -* Korn Shell Features:: Features originally found in the Korn - Shell. - * Bash Features:: Features found only in Bash. * Job Control:: A chapter describing what job control is @@ -181,16 +175,17 @@ of Unix. Bash is an @code{sh}-compatible shell that incorporates useful features from the Korn shell @code{ksh} and the C shell @code{csh}. -It is ultimately intended to be a -conformant implementation of the @sc{IEEE} @sc{POSIX} Shell and Tools -specification (@sc{IEEE} Working Group 1003.2). It offers functional -improvements over @code{sh} for both interactive and programming use. +It is intended to be a conformant implementation of the @sc{IEEE} +@sc{POSIX} Shell and Tools specification (@sc{IEEE} Working Group 1003.2). +It offers functional improvements over @code{sh} for both interactive and +programming use. While the @sc{GNU} operating system will include a version of @code{csh}, Bash will be the default shell. Like other @sc{GNU} software, Bash is quite portable. It currently runs on nearly every version of Unix and a few other operating systems @minus{} -independently-supported ports exist for @sc{OS/2} and Windows @sc{NT}. +independently-supported ports exist for @sc{MS-DOS}, @sc{OS/2}, +Windows @sc{95}, and Windows @sc{NT}. @node What is a shell? @section What is a shell? @@ -199,14 +194,17 @@ At its base, a shell is simply a macro processor that executes commands. A Unix shell is both a command interpreter, which provides the user interface to the rich set of Unix utilities, and a programming language, allowing these utilitites to be -combined. The shell reads commands either from a terminal or a -file. Files containing commands can be created, and become +combined. Files containing commands can be created, and become commands themselves. These new commands have the same status as system commands in directories like @file{/bin}, allowing users or groups to establish custom environments. A shell allows execution of Unix commands, both synchronously and -asynchronously. The @dfn{redirection} constructs permit +asynchronously. +The shell waits for synchronous commands to complete before accepting +more input; asynchronous commands continue to execute in parallel +with the shell while it reads and executes additional commands. +The @dfn{redirection} constructs permit fine-grained control of the input and output of those commands, and the shell allows control over the contents of their environment. Unix shells also provide a small set of built-in @@ -351,7 +349,7 @@ All of the Bourne shell builtin commands are available in Bash, and the rules for evaluation and quoting are taken from the @sc{POSIX} 1003.2 specification for the `standard' Unix shell. -This chapter briefly summarizes the shell's "building blocks": +This chapter briefly summarizes the shell's `building blocks': commands, control structures, shell functions, shell @i{parameters}, shell expansions, @i{redirections}, which are a way to direct input and output from @@ -359,13 +357,7 @@ and to named files, and how the shell executes commands. @menu * Shell Syntax:: What your input means to the shell. -* Simple Commands:: The most common type of command. -* Pipelines:: Connecting the input and output of several - commands. -* Lists:: How to execute commands sequentially. -* Looping Constructs:: Shell commands for iterative action. -* Conditional Constructs:: Shell commands for conditional execution. -* Command Grouping:: Ways to group commands. +* Shell Commands:: The types of commands you can use. * Shell Functions:: Grouping commands by name. * Shell Parameters:: Special shell variables. * Shell Expansions:: How Bash expands variables and the various @@ -400,12 +392,13 @@ supplied as an argument to the @samp{-c} invocation option @item Breaks the input into words and operators, obeying the quoting rules -described in @ref{Quoting}. Tokens are separated by +described in @ref{Quoting}. These tokens are separated by @code{metacharacters}. Alias expansion is performed by this step (@pxref{Aliases}). @item -Parses the tokens into simple and compound commands. +Parses the tokens into simple and compound commands +(@pxref{Shell Commands}). @item Performs the various shell expansions (@pxref{Shell Expansions}), breaking @@ -421,7 +414,7 @@ Executes the command (@pxref{Executing Commands}). @item Optionally waits for the command to complete and collects its exit -status. +status (@pxref{Exit Status}). @end enumerate @@ -446,9 +439,9 @@ disable special treatment for special characters, to prevent reserved words from being recognized as such, and to prevent parameter expansion. -Each of the shell @code{metacharacters} (@pxref{Definitions}) -has special meaning to the shell and must be quoted if they are to -represent themselves. There are three quoting mechanisms: the +Each of the shell metacharacters (@pxref{Definitions}) +has special meaning to the shell and must be quoted if it is to +represent itself. There are three quoting mechanisms: the @var{escape character}, single quotes, and double quotes. @node Escape Character @@ -456,8 +449,9 @@ represent themselves. There are three quoting mechanisms: the A non-quoted backslash @samp{\} is the Bash escape character. It preserves the literal value of the next character that follows, with the exception of @code{newline}. If a @code{\newline} pair -appears, and the backslash is not quoted, the @code{\newline} -is treated as a line continuation (that is, it is effectively ignored). +appears, and the backslash itself is not quoted, the @code{\newline} +is treated as a line continuation (that is, it is removed from +the input stream and effectively ignored). @node Single Quotes @subsubsection Single Quotes @@ -473,10 +467,13 @@ Enclosing characters in double quotes preserves the literal value of all characters within the quotes, with the exception of @samp{$}, @samp{`}, and @samp{\}. The characters @samp{$} and @samp{`} -retain their special meaning within double quotes. The backslash -retains its special meaning only when followed by one of the following -characters: +retain their special meaning within double quotes (@pxref{Shell Expansions}). +The backslash retains its special meaning only when followed by one of +the following characters: @samp{$}, @samp{`}, @samp{"}, @samp{\}, or @code{newline}. +Within double quotes, backslashes that are followed by one of these +characters are removed. Backslashes preceding characters without a +special meaning are left unmodified. A double quote may be quoted within double quotes by preceding it with a backslash. @@ -512,7 +509,11 @@ vertical tab @item \\ backslash @item \@var{nnn} -the character whose @code{ASCII} code is @var{nnn} in octal +the character whose @code{ASCII} code is the octal value @var{nnn} +(one to three digits) +@item \x@var{nnn} +the character whose @code{ASCII} code is the hexadecimal value @var{nnn} +(one to three digits) @end table @noindent @@ -541,14 +542,29 @@ causes that word and all remaining characters on that line to be ignored. An interactive shell without the @code{interactive_comments} option enabled does not allow comments. The @code{interactive_comments} option is on by default in interactive shells. +@xref{Is This Shell Interactive?}, for a description of what makes +a shell interactive. + +@node Shell Commands +@section Shell Commands +@cindex commands, shell +@menu +* Simple Commands:: The most common type of command. +* Pipelines:: Connecting the input and output of several + commands. +* Lists:: How to execute commands sequentially. +* Looping Constructs:: Shell commands for iterative action. +* Conditional Constructs:: Shell commands for conditional execution. +* Command Grouping:: Ways to group commands. +@end menu @node Simple Commands -@section Simple Commands +@subsection Simple Commands @cindex commands, simple -A simple command is the kind of command you'll encounter most often. +A simple command is the kind of command encountered most often. It's just a sequence of words separated by @code{blank}s, terminated -by one of the shell control operators (@pxref{Definitions}). The +by one of the shell's control operators (@pxref{Definitions}). The first word generally specifies a command to be executed. The return status (@pxref{Exit Status}) of a simple command is @@ -557,7 +573,7 @@ by the @sc{POSIX.1} @code{waitpid} function, or 128+@var{n} if the command was terminated by signal @var{n}. @node Pipelines -@section Pipelines +@subsection Pipelines @cindex pipeline @cindex commands, pipelines @@ -579,19 +595,28 @@ output. The reserved word @code{time} causes timing statistics to be printed for the pipeline once it finishes. +The statistics currently consist of elapsed (wall-clock) time and +user and system time consumed by the command's execution. The @samp{-p} option changes the output format to that specified by @sc{POSIX}. The @code{TIMEFORMAT} variable may be set to a format string that specifies how the timing information should be displayed. @xref{Bash Variables}, for a description of the available formats. +The use of @code{time} as a reserved word permits the timing of +shell builtins, shell functions, and pipelines. An external +@code{time} command cannot time these easily. + +If the pipeline is not executed asynchronously (@pxref{Lists}), the +shell waits for all commands in the pipeline to complete. -Each command in a pipeline is executed in its own subshell. The exit +Each command in a pipeline is executed in its own subshell +(@pxref{Command Execution Environment}). The exit status of a pipeline is the exit status of the last command in the pipeline. If the reserved word @samp{!} precedes the pipeline, the -exit status is the logical @sc{NOT} of the exit status of the last command. +exit status is the logical negation of the exit status of the last command. @node Lists -@section Lists of Commands +@subsection Lists of Commands @cindex commands, lists A @code{list} is a sequence of one or more pipelines separated by one @@ -604,11 +629,15 @@ have equal precedence, followed by @samp{;} and @samp{&}, which have equal precedence. If a command is terminated by the control operator @samp{&}, -the shell executes the command in the @var{background} -in a subshell. The shell does not wait for the command to -finish, and the return status is 0 (true). Commands separated by a -@samp{;} are executed sequentially; the shell waits for each -command to terminate in turn. The return status is the +the shell executes the command asynchronously in a subshell. +This is known as executing the command in the @var{background}. +The shell does not wait for the command to finish, and the return +status is 0 (true). +The standard input for asynchronous commands, in the absence of any +explicit redirections, is redirected from @code{/dev/null}. + +Commands separated by a @samp{;} are executed sequentially; the shell +waits for each command to terminate in turn. The return status is the exit status of the last command executed. The control operators @samp{&&} and @samp{||} @@ -628,7 +657,7 @@ An @sc{OR} list has the form @end example @noindent -@var{command2} is executed if and only if @var{command} +@var{command2} is executed if, and only if, @var{command} returns a non-zero exit status. The return status of @@ -636,15 +665,14 @@ The return status of executed in the list. @node Looping Constructs -@section Looping Constructs +@subsection Looping Constructs @cindex commands, looping -Note that wherever you see a @samp{;} in the description of a -command's syntax, it may be replaced indiscriminately with -one or more newlines. - Bash supports the following looping constructs. +Note that wherever you see a @samp{;} in the description of a +command's syntax, it may be replaced with one or more newlines. + @table @code @item until @rwindex until @@ -654,8 +682,10 @@ The syntax of the @code{until} command is: @example until @var{test-commands}; do @var{consequent-commands}; done @end example -Execute @var{consequent-commands} as long as the final command in +Execute @var{consequent-commands} as long as @var{test-commands} has an exit status which is not zero. +The return status is the exit status of the last command executed +in @var{consequent-commands}, or zero if none was executed. @item while @rwindex while @@ -664,8 +694,10 @@ The syntax of the @code{while} command is: while @var{test-commands}; do @var{consequent-commands}; done @end example -Execute @var{consequent-commands} as long as the final command in +Execute @var{consequent-commands} as long as @var{test-commands} has an exit status of zero. +The return status is the exit status of the last command executed +in @var{consequent-commands}, or zero if none was executed. @item for @rwindex for @@ -674,17 +706,19 @@ The syntax of the @code{for} command is: @example for @var{name} [in @var{words} @dots{}]; do @var{commands}; done @end example -Execute @var{commands} for each member in @var{words}, with @var{name} -bound to the current member. If @samp{in @var{words}} is not -present, @samp{in "$@@"} is assumed. - +Expand @var{words}, and execute @var{commands} once for each member +in the resultant list, with @var{name} bound to the current member. +If @samp{in @var{words}} is not present, @samp{in "$@@"} is assumed. +The return status is the exit status of the last command that executes. +If there are no items in the expansion of @var{words}, no commands are +executed, and the return status is zero. @end table The @code{break} and @code{continue} builtins (@pxref{Bourne Shell Builtins}) may be used to control loop execution. @node Conditional Constructs -@section Conditional Constructs +@subsection Conditional Constructs @cindex commands, conditional @table @code @@ -705,15 +739,17 @@ if @var{test-commands}; then fi @end example -Execute @var{consequent-commands} only if the final command in -@var{test-commands} has an exit status of zero. -Otherwise, each @code{elif} list is executed in turn, -and if its exit status is zero, +The @var{test-commands} list is executed, and if its return status is zero, +the @var{consequent-commands} list is executed. +If @var{test-commands} returns a non-zero status, each @code{elif} list +is executed in turn, and if its exit status is zero, the corresponding @var{more-consequents} is executed and the command completes. If @samp{else @var{alternate-consequents}} is present, and the final command in the final @code{if} or @code{elif} clause -has a non-zero exit status, then execute @var{alternate-consequents}. +has a non-zero exit status, then @var{alternate-consequents} is executed. +The return status is the exit status of the last command executed, or +zero if no condition tested true. @item case @rwindex case @@ -722,11 +758,23 @@ has a non-zero exit status, then execute @var{alternate-consequents}. The syntax of the @code{case} command is: @example -@code{case @var{word} in [ ( @var{pattern} [| @var{pattern}]@dots{}) @var{commands} ;;]@dots{} esac} +@code{case @var{word} in [ [(] @var{pattern} [| @var{pattern}]@dots{}) @var{command-list} ;;]@dots{} esac} @end example -Selectively execute @var{commands} based upon @var{word} matching -@var{pattern}. The @samp{|} is used to separate multiple patterns. +@code{case} will selectively execute the @var{command-list} corresponding to +the first @var{pattern} that matches @var{word}. +The @samp{|} is used to separate multiple patterns, and the @samp{)} +operator terminates a pattern list. +A list of patterns and an associated command-list is known +as a @var{clause}. Each clause must be terminated with @samp{;;}. +The @var{word} undergoes tilde expansion, parameter expansion, command +substitution, arithmetic expansion, and quote removal before matching is +attempted. Each @var{pattern} undergoes tilde expansion, parameter +expansion, command substitution, and arithmetic expansion. + +There may be an arbitrary number of @code{case} clauses, each terminated +by a @samp{;;}. The first pattern that matches determines the +command-list that is executed. Here is an example using @code{case} in a script that could be used to describe one interesting feature of an animal: @@ -743,27 +791,115 @@ esac echo " legs." @end example +@noindent +The return status is zero if no @var{pattern} is matched. Otherwise, the +return status is the exit status of the @var{command-list} executed. + +@item select +@rwindex select + +The @code{select} construct allows the easy generation of menus. +It has almost the same syntax as the @code{for} command: + +@example +select @var{name} [in @var{words} @dots{}]; do @var{commands}; done +@end example + +The list of words following @code{in} is expanded, generating a list +of items. The set of expanded words is printed on the standard +error output stream, each preceded by a number. If the +@samp{in @var{words}} is omitted, the positional parameters are printed, +as if @samp{in "$@@"} had been specifed. +The @code{PS3} prompt is then displayed and a line is read from the +standard input. +If the line consists of a number corresponding to one of the displayed +words, then the value of @var{name} is set to that word. +If the line is empty, the words and prompt are displayed again. +If @code{EOF} is read, the @code{select} command completes. +Any other value read causes @var{name} to be set to null. +The line read is saved in the variable @code{REPLY}. + +The @var{commands} are executed after each selection until a +@code{break} or @code{return} command is executed, at which +point the @code{select} command completes. + +Here is an example that allows the user to pick a filename from the +current directory, and displays the name and index of the file +selected. + +@example +select fname in *; +do + echo you picked $fname \($REPLY\) + break; +done +@end example + @item ((@dots{})) @example (( @var{expression} )) @end example -The @var{expression} is evaluated according to the rules described -below (@pxref{Arithmetic Evaluation}). +The arithmetic @var{expression} is evaluated according to the rules +described below (@pxref{Shell Arithmetic}). If the value of the expression is non-zero, the return status is 0; otherwise the return status is 1. This is exactly equivalent to @example let "@var{expression}" @end example +@noindent +@xref{Bash Builtins}, for a full description of the @code{let} builtin. +@item [[@dots{}]] +@rwindex [[ +@rwindex ]] +@example +[[ @var{expression} ]] +@end example + +Return a status of 0 or 1 depending on the evaluation of +the conditional expression @var{expression}. +Expressions are composed of the primaries described below in +@ref{Bash Conditional Expressions}. +Word splitting and filename expansion are not performed on the words +between the @samp{[[} and @samp{]]}; tilde expansion, parameter and +variable expansion, arithmetic expansion, command substitution, process +substitution, and quote removal are performed. + +When the @samp{==} and @samp{!=} operators are used, the string to the +right of the operator is considered a pattern and matched according +to the rules described below in @ref{Pattern Matching}. +The return value is 0 if the string matches or does not match +the pattern, respectively, and 1 otherwise. +Any part of the pattern may be quoted to force it to be matched as a +string. + +Expressions may be combined using the following operators, listed +in decreasing order of precedence: + +@table @code +@item ( @var{expression} ) +Returns the value of @var{expression}. +This may be used to override the normal precedence of operators. + +@item ! @var{expression} +True if @var{expression} is false. + +@item @var{expression1} && @var{expression2} +True if both @var{expression1} and @var{expression2} are true. + +@item @var{expression1} || @var{expression2} +True if either @var{expression1} or @var{expression2} is true. @end table +@noindent +The && and || commands do not execute @var{expression2} if the +value of @var{expression1} is sufficient to determine the return +value of the entire conditional expression. -The @code{select} construct, which allows users to choose from a list -of items presented as a menu, is also available. -@xref{Korn Shell Constructs}, for a full description of @code{select}. +@end table @node Command Grouping -@section Grouping Commands +@subsection Grouping Commands @cindex commands, grouping Bash provides two ways to group a list of commands to be executed @@ -778,9 +914,9 @@ commands in the list may be redirected to a single stream. @end example Placing a list of commands between parentheses causes a subshell -to be created, and each of the commands to be executed in that -subshell. Since the @var{list} is executed in a subshell, variable -assignments do not remain in effect after the subshell completes. +to be created, and each of the commands in @var{list} to be executed +in that subshell. Since the @var{list} is executed in a subshell, +variable assignments do not remain in effect after the subshell completes. @item @{@} @rwindex @{ @@ -791,7 +927,7 @@ assignments do not remain in effect after the subshell completes. Placing a list of commands between curly braces causes the list to be executed in the current shell context. No subshell is created. -The semicolon following @var{list} is required. +The semicolon (or newline) following @var{list} is required. @end table In addition to the creation of a subshell, there is a subtle difference @@ -821,9 +957,11 @@ Functions are declared using this syntax: @end example This defines a shell function named @var{name}. The reserved -word @code{function} is optional. The @var{body} of the -function is the @var{command-list} between @{ and @}. This list -is executed whenever @var{name} is specified as the +word @code{function} is optional. +If the @code{function} reserved +word is supplied, the parentheses are optional. +The @var{body} of the function is the @var{command-list} between @{ and @}. +This list is executed whenever @var{name} is specified as the name of a command. The exit status of a function is the exit status of the last command executed in the body. @@ -839,9 +977,11 @@ is executed in a function, the function completes and execution resumes with the next command after the function call. When a function completes, the values of the positional parameters and the special parameter @samp{#} -are restored to the values they had prior to function +are restored to the values they had prior to the function's execution. If a numeric argument is given to @code{return}, -that is the function return status. +that is the function's return status; otherwise the functions's +return status is the exit status of the last command executed +before the @code{return}. Variables local to the function may be declared with the @code{local} builtin. These variables are visible only to @@ -880,11 +1020,11 @@ If @var{value} is not given, the variable is assigned the null string. All @var{value}s undergo tilde expansion, parameter and variable expansion, command substitution, arithmetic expansion, and quote -removal (detailed below). If the variable has its @samp{-i} attribute -set (see the description of the @code{declare} builtin in +removal (detailed below). If the variable has its @code{integer} +attribute set (see the description of the @code{declare} builtin in @ref{Bash Builtins}), then @var{value} is subject to arithmetic expansion even if the @code{$((@dots{}))} -syntax does not appear (@pxref{Arithmetic Expansion}). +expansion is not used (@pxref{Arithmetic Expansion}). Word splitting is not performed, with the exception of @code{"$@@"} as explained below. Filename expansion is not performed. @@ -893,12 +1033,12 @@ Filename expansion is not performed. @subsection Positional Parameters @cindex parameters, positional -A @var{positional parameter} -is a parameter denoted by one or more +A @var{positional parameter} is a parameter denoted by one or more digits, other than the single digit @code{0}. Positional parameters are assigned from the shell's arguments when it is invoked, -and may be reassigned using the @code{set} -builtin command. Positional parameters may not be assigned to +and may be reassigned using the @code{set} builtin command. +Positional parameter @code{N} may be referenced as @code{$@{N@}}. +Positional parameters may not be assigned to with assignment statements. The positional parameters are temporarily replaced when a shell function is executed (@pxref{Shell Functions}). @@ -931,7 +1071,7 @@ separators. @item @@ Expands to the positional parameters, starting from one. When the -expansion occurs within double quotes, each parameter expands as a +expansion occurs within double quotes, each parameter expands to a separate word. That is, @code{"$@@"} is equivalent to @code{"$1" "$2" @dots{}}. When there are no positional parameters, @code{"$@@"} and @@ -953,8 +1093,7 @@ builtin command, or those set by the shell itself @item $ Expands to the process @sc{ID} of the shell. In a @code{()} subshell, it -expands to the process @sc{ID} of the current shell, not the -subshell. +expands to the process @sc{ID} of the invoking shell, not the subshell. @item ! Expands to the process @sc{ID} of the most recently executed background @@ -962,10 +1101,10 @@ Expands to the process @sc{ID} of the most recently executed background @item 0 Expands to the name of the shell or shell script. This is set at -shell initialization. If Bash is invoked with a file of commands, -@code{$0} is set to the name of that file. If Bash -is started with the @samp{-c} option, then @code{$0} -is set to the first argument after the string to be +shell initialization. If Bash is invoked with a file of commands +(@pxref{Shell Scripts}), @code{$0} is set to the name of that file. +If Bash is started with the @samp{-c} option (@pxref{Invoking Bash}), +then @code{$0} is set to the first argument after the string to be executed, if one is present. Otherwise, it is set to the filename used to invoke Bash, as given by argument zero. @@ -974,7 +1113,7 @@ At shell startup, set to the absolute filename of the shell or shell script being executed as passed in the argument list. Subsequently, expands to the last argument to the previous command, after expansion. -Also set to the full filename of each command executed and placed in +Also set to the full pathname of each command executed and placed in the environment exported to that command. When checking mail, this parameter holds the name of the mail file. @end vtable @@ -996,8 +1135,11 @@ Expansion is performed on the command line after it has been split into @end itemize @menu +* Brace Expansion:: Expansion of expressions within braces. +* Tilde Expansion:: Expansion of the ~ character. * Shell Parameter Expansion:: How Bash expands variables to their values. * Command Substitution:: Using the output of a command as an argument. +* Arithmetic Expansion:: How to use arithmetic in shell expansions. * Process Substitution:: A way to write and read to and from a command. * Word Splitting:: How the results of expansion are split into separate @@ -1007,11 +1149,6 @@ Expansion is performed on the command line after it has been split into words. @end menu -Brace expansion, tilde expansion, and arithmetic expansion are described -in other sections. For brace expansion, see @ref{Brace Expansion}; for -tilde expansion, see @ref{Tilde Expansion}; and for arithmetic expansion, -see @ref{Arithmetic Expansion}. - The order of expansions is: brace expansion, tilde expansion, parameter, variable, and arithmetic expansion and command substitution @@ -1020,7 +1157,7 @@ expansion. On systems that can support it, there is an additional expansion available: @var{process substitution}. This is performed at the -same time as parameter, variable, and arithemtic expansion and +same time as parameter, variable, and arithmetic expansion and command substitution. Only brace expansion, word splitting, and filename expansion @@ -1033,6 +1170,124 @@ The only exceptions to this are the expansions of After all expansions, @code{quote removal} (@pxref{Quote Removal}) is performed. +@node Brace Expansion +@subsection Brace Expansion +@cindex brace expansion +@cindex expansion, brace + +Brace expansion +is a mechanism by which arbitrary strings +may be generated. This mechanism is similar to +@var{filename expansion} (@pxref{Filename Expansion}), +but the file names generated +need not exist. Patterns to be brace expanded take +the form of an optional @var{preamble}, +followed by a series of comma-separated strings +between a pair of braces, followed by an optional @var{postscript}. +The preamble is prepended to each string contained +within the braces, and the postscript is then appended +to each resulting string, expanding left to right. + +Brace expansions may be nested. The results of each expanded +string are not sorted; left to right order is preserved. +For example, +@example +bash$ echo a@{d,c,b@}e +ade ace abe +@end example + +Brace expansion is performed before any other expansions, +and any characters special to other expansions are preserved +in the result. It is strictly textual. Bash +does not apply any syntactic interpretation to the context of the +expansion or the text between the braces. + +A correctly-formed brace expansion must contain unquoted opening +and closing braces, and at least one unquoted comma. +Any incorrectly formed brace expansion is left unchanged. + +This construct is typically used as shorthand when the common +prefix of the strings to be generated is longer than in the +above example: +@example +mkdir /usr/local/src/bash/@{old,new,dist,bugs@} +@end example +or +@example +chown root /usr/@{ucb/@{ex,edit@},lib/@{ex?.?*,how_ex@}@} +@end example + +@node Tilde Expansion +@subsection Tilde Expansion +@cindex tilde expansion +@cindex expansion, tilde + +If a word begins with an unquoted tilde character (@samp{~}), all of the +characters up to the first unquoted slash (or all characters, +if there is no unquoted slash) are considered a @var{tilde-prefix}. +If none of the characters in the tilde-prefix are quoted, the +characters in the tilde-prefix following the tilde are treated as a +possible @var{login name}. +If this login name is the null string, the tilde is replaced with the +value of the @code{HOME} shell variable. +If @code{HOME} is unset, the home directory of the user executing the +shell is substituted instead. +Otherwise, the tilde-prefix is replaced with the home directory +associated with the specified login name. + +If the tilde-prefix is @samp{~+}, the value of +the shell variable @code{PWD} replaces the tilde-prefix. +If the tilde-prefix is @samp{~-}, the value of the shell variable +@code{OLDPWD}, if it is set, is substituted. + +If the characters following the tilde in the tilde-prefix consist of a +number @var{N}, optionally prefixed by a @samp{+} or a @samp{-}, +the tilde-prefix is replaced with the +corresponding element from the directory stack, as it would be displayed +by the @code{dirs} builtin invoked with the characters following tilde +in the tilde-prefix as an argument (@pxref{The Directory Stack}). +If the tilde-prefix, sans the tilde, consists of a number without a +leading @samp{+} or @samp{-}, @samp{+} is assumed. + +If the login name is invalid, or the tilde expansion fails, the word is +left unchanged. + +Each variable assignment is checked for unquoted tilde-prefixes immediately +following a @samp{:} or @samp{=}. +In these cases, tilde expansion is also performed. +Consequently, one may use file names with tildes in assignments to +@code{PATH}, @code{MAILPATH}, and @code{CDPATH}, +and the shell assigns the expanded value. + +The following table shows how Bash treats unquoted tilde-prefixes: + +@table @code +@item ~ +The value of @code{$HOME} +@item ~/foo +@file{$HOME/foo} + +@item ~fred/foo +The subdirectory @code{foo} of the home directory of the user +@code{fred} + +@item ~+/foo +@file{$PWD/foo} + +@item ~-/foo +@file{$@{OLDPWD-'~-'@}/foo} + +@item ~@var{N} +The string that would be displayed by @samp{dirs +@var{N}} + +@item ~+@var{N} +The string that would be displayed by @samp{dirs +@var{N}} + +@item ~-@var{N} +The string that would be displayed by @samp{dirs -@var{N}} + +@end table + @node Shell Parameter Expansion @subsection Shell Parameter Expansion @cindex parameter expansion @@ -1045,6 +1300,11 @@ are optional but serve to protect the variable to be expanded from characters immediately following it which could be interpreted as part of the name. +When braces are used, the matching ending brace is the first @samp{@}} +not escaped by a backslash or within a quoted string, and not within an +embedded arithmetic expansion, command substitution, or parameter +expansion. + The basic form of parameter expansion is $@{@var{parameter}@}. The value of @var{parameter} is substituted. The braces are required when @var{parameter} @@ -1098,11 +1358,11 @@ is null or unset, nothing is substituted, otherwise the expansion of @item $@{@var{parameter}:@var{offset}@} @itemx $@{@var{parameter}:@var{offset}:@var{length}@} Expands to up to @var{length} characters of @var{parameter}, -starting at @var{offset}. +starting at the character specified by @var{offset}. If @var{length} is omitted, expands to the substring of @var{parameter}, starting at the character specified by @var{offset}. @var{length} and @var{offset} are arithmetic expressions -(@pxref{Arithmetic Evaluation}). +(@pxref{Shell Arithmetic}). This is referred to as Substring Expansion. @var{length} must evaluate to a number greater than or equal to zero. @@ -1112,27 +1372,25 @@ If @var{parameter} is @samp{@@}, the result is @var{length} positional parameters beginning at @var{offset}. If @var{parameter} is an array name indexed by @samp{@@} or @samp{*}, the result is the @var{length} -members of the array beginning with $@{@var{parameter}[@var{offset}]@}. -Substring indexing is zero-based unless the positional parameters are -used, in which case the indexing starts at 1. +members of the array beginning with @code{$@{@var{parameter}[@var{offset}]@}}. +Substring indexing is zero-based unless the positional parameters +are used, in which case the indexing starts at 1. @item $@{#@var{parameter}@} -The length in characters of the value of @var{parameter} is substituted. -If @var{parameter} -is @samp{*} or @samp{@@}, -the length substituted is the number of positional parameters. -If @var{parameter} -is an array name subscripted -by @samp{*} or @samp{@@}, -the length substituted is the number of elements in the array. +The length in characters of the expanded value of @var{parameter} is +substituted. +If @var{parameter} is @samp{*} or @samp{@@}, the value substituted +is the number of positional parameters. +If @var{parameter} is an array name subscripted by @samp{*} or @samp{@@}, +the value substituted is the number of elements in the array. @item $@{@var{parameter}#@var{word}@} @itemx $@{@var{parameter}##@var{word}@} The @var{word} is expanded to produce a pattern just as in filename expansion (@pxref{Filename Expansion}). If the pattern matches -the beginning of the value of @var{parameter}, -then the expansion is the value of @var{parameter} +the beginning of the expanded value of @var{parameter}, +then the result of the expansion is the expanded value of @var{parameter} with the shortest matching pattern (the @samp{#} case) or the longest matching pattern (the @samp{##} case) deleted. If @var{parameter} is @samp{@@} or @samp{*}, @@ -1147,10 +1405,10 @@ array in turn, and the expansion is the resultant list. @itemx $@{@var{parameter}%%@var{word}@} The @var{word} is expanded to produce a pattern just as in filename expansion. -If the pattern matches a trailing portion of the value of -@var{parameter}, then the expansion is the value of @var{parameter} -with the shortest matching pattern (the @samp{%} case) or the -longest matching pattern (the @samp{%%} case) deleted. +If the pattern matches a trailing portion of the expanded value of +@var{parameter}, then the result of the expansion is the value of +@var{parameter} with the shortest matching pattern (the @samp{%} case) +or the longest matching pattern (the @samp{%%} case) deleted. If @var{parameter} is @samp{@@} or @samp{*}, the pattern removal operation is applied to each positional parameter in turn, and the expansion is the resultant list. @@ -1204,19 +1462,48 @@ or Bash performs the expansion by executing @var{command} and replacing the command substitution with the standard output of the command, with any trailing newlines deleted. +Embedded newlines are not deleted, but they may be removed during +word splitting. +The command substitution @code{$(cat @var{file})} can be +replaced by the equivalent but faster @code{$(< @var{file})}. When the old-style backquote form of substitution is used, backslash retains its literal meaning except when followed by -@samp{$}, @samp{`}, or @samp{\}. +@samp{$}, @samp{`}, or @samp{\}. +The first backquote not preceded by a backslash terminates the +command substitution. When using the @code{$(@var{command})} form, all characters between the parentheses make up the command; none are treated specially. -Command substitutions may be nested. To nest when using the old form, -escape the inner backquotes with backslashes. +Command substitutions may be nested. To nest when using the backquoted +form, escape the inner backquotes with backslashes. If the substitution appears within double quotes, word splitting and filename expansion are not performed on the results. +@node Arithmetic Expansion +@subsection Arithmetic Expansion +@cindex expansion, arithmetic +@cindex arithmetic expansion + +Arithmetic expansion allows the evaluation of an arithmetic expression +and the substitution of the result. The format for arithmetic expansion is: + +@example +$(( @var{expression} )) +@end example + +The expression is treated as if it were within double quotes, but +a double quote inside the parentheses is not treated specially. +All tokens in the expression undergo parameter expansion, command +substitution, and quote removal. +Arithmetic substitutions may be nested. + +The evaluation is performed according to the rules listed below +(@pxref{Shell Arithmetic}). +If the expression is invalid, Bash prints a message indicating +failure to the standard error and no substitution occurs. + @node Process Substitution @subsection Process Substitution @cindex process substitution @@ -1241,9 +1528,9 @@ the file will provide input for @var{list}. If the @code{<(@var{list})} form is used, the file passed as an argument should be read to obtain the output of @var{list}. -On systems that support it, process substitution is performed -simultaneously with parameter and variable expansion, -command substitution, and arithmetic expansion. +When available, process substitution is performed simultaneously with +parameter and variable expansion, command substitution, and arithmetic +expansion. @node Word Splitting @subsection Word Splitting @@ -1282,38 +1569,46 @@ is performed. @node Filename Expansion @subsection Filename Expansion +@menu +* Pattern Matching:: How the shell matches patterns. +@end menu @cindex expansion, filename @cindex expansion, pathname @cindex filename expansion @cindex pathname expansion -After word splitting, -unless the @samp{-f} -option has been set (@pxref{The Set Builtin}), -Bash scans each word for the characters -@samp{*}, @samp{?}, and @samp{[}. +After word splitting, unless the @samp{-f} option has been set +(@pxref{The Set Builtin}), Bash scans each word for the characters +@samp{*}, @samp{?}, @samp{(}, and @samp{[}. If one of these characters appears, then the word is regarded as a @var{pattern}, and replaced with an alphabetically sorted list of file names matching the pattern. If no matching file names are found, and the shell option @code{nullglob} is disabled, the word is left -unchanged. If the option is set, and no matches are found, the word -is removed. When a pattern is used for filename generation, -the character @samp{.} +unchanged. +If the @code{nullglob} option is set, and no matches are found, the word +is removed. +If the shell option @code{nocaseglob} is enabled, the match is performed +without regard to the case of alphabetic characters. + +When a pattern is used for filename generation, the character @samp{.} at the start of a filename or immediately following a slash -must be matched explicitly, unless the shell option @code{dotglob} -is set. The slash character must always be matched explicitly. +must be matched explicitly, unless the shell option @code{dotglob} is set. +When matching a file name, the slash character must always be +matched explicitly. In other cases, the @samp{.} character is not treated specially. + See the description of @code{shopt} in @ref{Bash Builtins}, -for a description of the @code{nullglob} and @code{dotglob} options. +for a description of the @code{nocaseglob}, @code{nullglob}, +and @code{dotglob} options. The @code{GLOBIGNORE} shell variable may be used to restrict the set of filenames matching a -@var{pattern}. If @code{GLOBIGNORE} +pattern. If @code{GLOBIGNORE} is set, each matching filename that also matches one of the patterns in @code{GLOBIGNORE} is removed from the list of matches. The filenames @file{.} and @file{..} -are always ignored, even when @code{GLOBIGNORE}. +are always ignored, even when @code{GLOBIGNORE} is set. However, setting @code{GLOBIGNORE} has the effect of enabling the @code{dotglob} shell option, so all other filenames beginning with a @@ -1323,6 +1618,16 @@ To get the old behavior of ignoring filenames beginning with a The @code{dotglob} option is disabled when @code{GLOBIGNORE} is unset. +@node Pattern Matching +@subsubsection Pattern Matching +@cindex pattern matching +@cindex matching, pattern + +Any character that appears in a pattern, other than the special pattern +characters described below, matches itself. The NUL character may not +occur in a pattern. The special pattern characters must be quoted if +they are to be matched literally. + The special pattern characters have the following meanings: @table @code @item * @@ -1339,6 +1644,49 @@ then any character not enclosed is matched. A @samp{@minus{}} may be matched by including it as the first or last character in the set. A @samp{]} may be matched by including it as the first character in the set. + +Within @samp{[} and @samp{]}, @var{character classes} can be specified +using the syntax +@code{[:}@var{class}@code{:]}, where @var{class} is one of the +following classes defined in the @sc{POSIX.2} standard: +@example +alnum alpha ascii blank cntrl digit graph lower +print punct space upper xdigit +@end example +@noindent +A character class matches any character belonging to that class. + +Within @samp{[} and @samp{]}, an @var{equivalence class} can be +specified using the syntax @code{[=}@var{c}@code{=]}, which +matches all characters with the same collation weight (as defined +by the current locale) as the character @var{c}. + +Within @samp{[} and @samp{]}, the syntax @code{[.}@var{symbol}@code{.]} +matches the collating symbol @var{symbol}. +@end table + +If the @code{extglob} shell option is enabled using the @code{shopt} +builtin, several extended pattern matching operators are recognized. +In the following description, a @var{pattern-list} is a list of one +or more patterns separated by a @samp{|}. +Composite patterns may be formed using one or more of the following +sub-patterns: + +@table @code +@item ?(@var{pattern-list}) +Matches zero or one occurrence of the given patterns. + +@item *(@var{pattern-list}) +Matches zero or more occurrences of the given patterns. + +@item +(@var{pattern-list}) +Matches one or more occurrences of the given patterns. + +@item @@(@var{pattern-list}) +Matches exactly one of the given patterns. + +@item !(@var{pattern-list}) +Matches anything except one of the given patterns. @end table @node Quote Removal @@ -1369,11 +1717,11 @@ descriptor 0). If the first character of the redirection operator is @samp{>}, the redirection refers to the standard output (file descriptor 1). -The word that follows the redirection operator in the following -descriptions is subjected to brace expansion, tilde expansion, -parameter expansion, command substitution, arithmetic expansion, -quote removal, and filename expansion. If it expands to more -than one word, Bash reports an error. +The word following the redirection operator in the following +descriptions, unless otherwise noted, is subjected to brace expansion, +tilde expansion, parameter expansion, command substitution, arithmetic +expansion, quote removal, and filename expansion. +If it expands to more than one word, Bash reports an error. Note that the order of redirections is significant. For example, the command @@ -1391,6 +1739,8 @@ directs only the standard output to file @var{dirlist}, because the standard error was duplicated as standard output before the standard output was redirected to @var{dirlist}. +A failure to open or create a file causes the redirection to fail. + @subsection Redirecting Input Redirection of input causes the file whose name results from the expansion of @var{word} @@ -1416,13 +1766,13 @@ The general format for redirecting output is: [n]>[|]@var{word} @end example -If the redirection operator is @samp{>}, and the @samp{-C} option to the -@code{set} builtin has been enabled, the redirection will fail if the -filename whose name results from the expansion of @var{word} exists. -If the redirection operator is @samp{>|}, -then the value of the @samp{-C} option to the @code{set} -builtin command is not tested, and the redirection is attempted even -if the file named by @var{word} exists. +If the redirection operator is @samp{>}, and the @code{noclobber} +option to the @code{set} builtin has been enabled, the redirection +will fail if the filename whose name results from the expansion of +@var{word} exists and is a regular file. +If the redirection operator is @samp{>|}, or the redirection operator is +@samp{>} and the @code{noclobber} option is not enabled, the redirection +is attempted even if the file named by @var{word} exists. @subsection Appending Redirected Output Redirection of output in this fashion @@ -1479,7 +1829,8 @@ No parameter expansion, command substitution, filename expansion, or arithmetic expansion is performed on @var{word}. If any characters in @var{word} are quoted, the @var{delimiter} is the result of quote removal on @var{word}, -and the lines in the here-document are not expanded. Otherwise, +and the lines in the here-document are not expanded. +If @var{word} is unquoted, all lines of the here-document are subjected to parameter expansion, command substitution, and arithmetic expansion. In the latter case, the pair @code{\newline} is ignored, and @samp{\} @@ -1501,7 +1852,10 @@ The redirection operator is used to duplicate input file descriptors. If @var{word} expands to one or more digits, the file descriptor denoted by @code{n} -is made to be a copy of that file descriptor. If @var{word} +is made to be a copy of that file descriptor. +If the digits in @var{word} do not specify a file descriptor open for +input, a redirection error occurs. +If @var{word} evaluates to @samp{-}, file descriptor @code{n} is closed. If @code{n} is not specified, the standard input (file descriptor 0) is used. @@ -1513,6 +1867,8 @@ The operator is used similarly to duplicate output file descriptors. If @code{n} is not specified, the standard output (file descriptor 1) is used. +If the digits in @var{word} do not specify a file descriptor open for +output, a redirection error occurs. As a special case, if @code{n} is omitted, and @var{word} does not expand to one or more digits, the standard output and standard error are redirected as described previously. @@ -1532,8 +1888,15 @@ is not specified. If the file does not exist, it is created. @section Executing Commands @menu +* Simple Command Expansion:: How Bash expands simple commands before + executing them. + * Command Search and Execution:: How Bash finds commands and runs them. +* Command Execution Environment:: The environment in which Bash + executes commands that are not + shell builtins. + * Environment:: The environment given to a command. * Exit Status:: The status returned by commands and how Bash @@ -1541,8 +1904,54 @@ is not specified. If the file does not exist, it is created. * Signals:: What happens when Bash or a command it runs receives a signal. + @end menu +@node Simple Command Expansion +@subsection Simple Command Expansion +@cindex command expansion + +When a simple command is executed, the shell performs the following +expansions, assignments, and redirections, from left to right. + +@enumerate +@item +The words that the parser has marked as variable assignments (those +preceding the command name) and redirections are saved for later +processing. + +@item +The words that are not variable assignments or redirections are +expanded (@pxref{Shell Expansions}). +If any words remain after expansion, the first word +is taken to be the name of the command and the remaining words are +the arguments. + +@item +Redirections are performed as described above (@pxref{Redirections}). + +@item +The text after the @samp{=} in each variable assignment undergoes tilde +expansion, parameter expansion, command substitution, arithmetic expansion, +and quote removal before being assigned to the variable. +@end enumerate + +If no command name results, the variable assignments affect the current +shell environment. Otherwise, the variables are added to the environment +of the executed command and do not affect the current shell environment. +If any of the assignments attempts to assign a value to a readonly variable, +an error occurs, and the command exits with a non-zero status. + +If no command name results, redirections are performed, but do not +affect the current shell environment. A redirection error causes the +command to exit with a non-zero status. + +If there is a command name left after expansion, execution proceeds as +described below. Otherwise, the command exits. If one of the expansions +contained a command substitution, the exit status of the command is +the exit status of the last command substitution performed. If there +were no command substitutions, the command exits with a status of zero. + @node Command Search and Execution @subsection Command Search and Execution @cindex command execution @@ -1568,26 +1977,118 @@ If the name is neither a shell function nor a builtin, and contains no slashes, Bash searches each element of @code{$PATH} for a directory containing an executable file by that name. Bash uses a hash table to remember the full -filenames of executable files (see the description of -@code{hash} in @ref{Bourne Shell Builtins}) to avoid multiple -@code{PATH} searches. +pathnames of executable files to avoid multiple @code{PATH} searches +(see the description of @code{hash} in @ref{Bourne Shell Builtins}). A full search of the directories in @code{$PATH} is performed only if the command is not found in the hash table. If the search is unsuccessful, the shell prints an error -message and returns a nonzero exit status. +message and returns an exit status of 127. @item If the search is successful, or if the command name contains -one or more slashes, the shell executes the named program. +one or more slashes, the shell executes the named program in +a separate execution environment. Argument 0 is set to the name given, and the remaining arguments to the command are set to the arguments supplied, if any. @item If this execution fails because the file is not in executable -format, and the file is not a directory, it is assumed to be -@var{shell script} (@pxref{Shell Scripts}). +format, and the file is not a directory, it is assumed to be a +@var{shell script} and the shell executes it as described in +@ref{Shell Scripts}. + +@item +If the command was not begun asynchronously, the shell waits for +the command to complete and collects its exit status. + @end enumerate +@node Command Execution Environment +@subsection Command Execution Environment +@cindex execution environment + +The shell has an @var{execution environment}, which consists of the +following: + +@itemize @bullet +@item +open files inherited by the shell at invocation, as modified by +redirections supplied to the @code{exec} builtin + +@item +the current working directory as set by @code{cd}, @code{pushd}, or +@code{popd}, or inherited by the shell at invocation + +@item +the file creation mode mask as set by @code{umask} or inherited from +the shell's parent + +@item +current traps set by @code{trap} + +@item +shell parameters that are set by variable assignment or with @code{set} +or inherited from the shell's parent in the environment + +@item +shell functions defined during execution or inherited from the shell's +parent in the environment + +@item +options enabled at invocation (either by default or with command-line +arguments) or by @code{set} + +@item +options enabled by @code{shopt} + +@item +shell aliases defined with @code{alias} (@pxref{Aliases}) + +@item +various process IDs, including those of background jobs +(@pxref{Lists}), the value of @code{$$}, and the value of +@code{$PPID} + +@end itemize + +When a simple command other than a builtin or shell function +is to be executed, it +is invoked in a separate execution environment that consists of +the following. Unless otherwise noted, the values are inherited +from the shell. + +@itemize @bullet +@item +the shell's open files, plus any modifications and additions specified +by redirections to the command + +@item +the current working directory + +@item +the file creation mode mask + +@item +shell variables marked for export, along with variables exported for +the command, passed in the environment (@pxref{Environment}) + +@item +traps caught by the shell are reset to the values inherited from the +shell's parent, and traps ignored by the shell are ignored + +@end itemize + +A command invoked in this separate environment cannot affect the +shell's execution environment. + +Command substitution and asynchronous commands are invoked in a +subshell environment that is a duplicate of the shell environment, +except that traps caught by the shell are reset to the values +that the shell inherited from its parent at invocation. Builtin +commands that are invoked as part of a pipeline are also executed +in a subshell environment. Changes made to the subshell environment +cannot affect the shell's execution environment. + @node Environment @subsection Environment @cindex environment @@ -1608,8 +2109,9 @@ in the environment is modified, the new value becomes part of the environment, replacing the old. The environment inherited by any executed command consists of the shell's initial environment, whose values may be modified in the shell, -less any pairs removed by the @code{unset} command, plus any -additions via the @code{export} and @samp{declare -x} commands. +less any pairs removed by the @code{unset} and @samp{export -n} +commands, plus any additions via the @code{export} and +@samp{declare -x} commands. The environment for any simple command or function may be augmented temporarily by prefixing it with @@ -1617,7 +2119,7 @@ parameter assignments, as described in @ref{Shell Parameters}. These assignment statements affect only the environment seen by that command. -If the @samp{-k} flag is set (@pxref{The Set Builtin}, then all +If the @samp{-k} option is set (@pxref{The Set Builtin}), then all parameter assignments are placed in the environment for a command, not just those that precede the command name. @@ -1629,7 +2131,7 @@ command in its environment. @subsection Exit Status @cindex exit status -For the purposes of the shell, a command which exits with a +For the shell's purposes, a command which exits with a zero exit status has succeeded. A non-zero exit status indicates failure. This seemingly counter-intuitive scheme is used so there @@ -1642,6 +2144,9 @@ If a command is not found, the child process created to execute it returns a status of 127. If a command is found but is not executable, the return status is 126. +If a command fails because of an error during expansion or redirection, +the exit status is greater than zero. + The exit status is used by the Bash conditional commands (@pxref{Conditional Constructs}) and some of the list constructs (@pxref{Lists}). @@ -1649,12 +2154,13 @@ constructs (@pxref{Lists}). All of the Bash builtins return an exit status of zero if they succeed and a non-zero status on failure, so they may be used by the conditional and list constructs. +All builtins return an exit status of 2 to indicate incorrect usage. @node Signals @subsection Signals @cindex signal handling -When Bash is interactive, it ignores +When Bash is interactive, in the absence of any traps, it ignores @code{SIGTERM} (so that @samp{kill 0} does not kill an interactive shell), and @code{SIGINT} is caught and handled (so that the @code{wait} builtin is interruptible). @@ -1663,21 +2169,37 @@ In all cases, Bash ignores @code{SIGQUIT}. If job control is in effect (@pxref{Job Control}), Bash ignores @code{SIGTTIN}, @code{SIGTTOU}, and @code{SIGTSTP}. -Synchronous jobs started by Bash have signals set to the -values inherited by the shell from its parent. When job control -is not in effect, background jobs (commands terminated with @samp{&}) -ignore @code{SIGINT} and @code{SIGQUIT}. -Commands run as a result of command substitution ignore the -keyboard-generated job control signals +Commands started by Bash have signal handlers set to the +values inherited by the shell from its parent. +When job control is not in effect, asynchronous commands +ignore @code{SIGINT} and @code{SIGQUIT} as well. +Commands run as a result of +command substitution ignore the keyboard-generated job control signals @code{SIGTTIN}, @code{SIGTTOU}, and @code{SIGTSTP}. The shell exits by default upon receipt of a @code{SIGHUP}. -Before exiting, it resends the @code{SIGHUP} -to all jobs, running or stopped. To prevent the shell from -sending the @code{SIGHUP} signal to a particular job, remove it -from the jobs table with the @code{disown} builtin -(@pxref{Job Control Builtins}) -or use @code{disown -h} to mark it to not receive @code{SIGHUP}. +Before exiting, it resends the @code{SIGHUP} to all jobs, running +or stopped. +Stopped jobs are sent @code{SIGCONT} to ensure that they receive +the @code{SIGHUP}. +To prevent the shell from sending the @code{SIGHUP} signal to a +particular job, it should be removed +from the jobs table with the @code{disown} +builtin (@pxref{Job Control Builtins}) or marked +to not receive @code{SIGHUP} using @code{disown -h}. + +If the @code{huponexit} shell option has been set with @code{shopt} +(@pxref{Bash Builtins}), Bash sends a @code{SIGHUP} to all jobs when +an interactive login shell exits. + +When Bash receives a signal for which a trap has been set while waiting +for a command to complete, the trap will not be executed until the +command completes. +When Bash is waiting for an asynchronous +command via the @code{wait} builtin, the reception of a signal for +which a trap has been set will cause the @code{wait} builtin to return +immediately with an exit status greater than 128, immediately after +which the trap is executed. @node Shell Scripts @section Shell Scripts @@ -1711,7 +2233,10 @@ bash filename @var{arguments} @noindent if @code{filename} is an executable shell script. This subshell reinitializes itself, so that the effect is as if a -new shell had been invoked to interpret the script. +new shell had been invoked to interpret the script, with the +exception that the locations of commands remembered by the parent +(see the description of @code{hash} in @ref{Bourne Shell Builtins}) +are retained by the child. Most versions of Unix make this a part of the kernel's command execution mechanism. If the first line of a script begins with @@ -1737,9 +2262,9 @@ name and argument to a maximum of 32 characters. @end menu This section briefly summarizes things which Bash inherits from -the Bourne Shell: builtins, variables, -and other features. It also lists the significant differences -between Bash and the Bourne Shell. +the Bourne Shell: builtins, variables, and other features. +It also lists the significant differences between Bash and the Bourne Shell. +Many of the builtins have been extended by @sc{POSIX} or Bash. @node Bourne Shell Builtins @section Bourne Shell Builtins @@ -1755,6 +2280,7 @@ Shell. These commands are implemented as specified by the @sc{POSIX} : [@var{arguments}] @end example Do nothing beyond expanding @var{arguments} and performing redirections. +The return status is zero. @item . @btindex . @@ -1762,7 +2288,13 @@ Do nothing beyond expanding @var{arguments} and performing redirections. . @var{filename} @end example Read and execute commands from the @var{filename} argument in the -current shell context. +current shell context. If @var{filename} does not contain a slash, +the @code{$PATH} variable is used to find +@var{filename}. The current directory is searched if @var{filename} +is not found in @code{$PATH}. +The return status is the exit status of the last command executed, or +zero if no commands are executed. If @var{filename} is not found, or +cannot be read, the return status is non-zero. @item break @btindex break @@ -1771,6 +2303,8 @@ break [@var{n}] @end example Exit from a @code{for}, @code{while}, @code{until}, or @code{select} loop. If @var{n} is supplied, the @var{n}th enclosing loop is exited. +@var{n} must be greater than or equal to 1. +The return status is zero unless @var{n} is not greater than or equal to 1. @item cd @btindex cd @@ -1782,8 +2316,11 @@ is not given, the value of the @code{HOME} shell variable is used. If the shell variable @code{CDPATH} exists, it is used as a search path. If @var{directory} begins with a slash, @code{CDPATH} is not used. The @samp{-P} option means -to not follow symbolic links; symlinks are followed by default or with the -@samp{-L} option. +to not follow symbolic links; symbolic links are followed by default +or with the @samp{-L} option. +If @var{directory} is @samp{-}, it is equivalent to @code{$OLDPWD}. +The return status is zero if the directory is successfully changed, +non-zero otherwise. @item continue @btindex continue @@ -1792,33 +2329,39 @@ continue [@var{n}] @end example Resume the next iteration of an enclosing @code{for}, @code{while}, @code{until}, or @code{select} loop. -If @var{n} is supplied, the execution of the -@var{n}th enclosing loop is resumed. +If @var{n} is supplied, the execution of the @var{n}th enclosing loop +is resumed. +@var{n} must be greater than or equal to 1. +The return status is zero unless @var{n} is not greater than or equal to 1. @item eval @btindex eval @example eval [@var{arguments}] @end example -The arguments are concatenated together into a single -command, which is then read and executed. +The arguments are concatenated together into a single command, which is +then read and executed, and its exit status returned as the exit status +of @code{eval}. +If there are no arguments or only empty arguments, the return status is +zero. @item exec @btindex exec @example -exec [-cl] [-a @var{name}] [@var{command}] [@var{arguments}] +exec [-cl] [-a @var{name}] [@var{command} [@var{arguments}]] @end example If @var{command} -is supplied, it replaces the shell. -If the @samp{-l} option is supplied, -the shell places a dash in the zeroth arg passed to @var{command}. +is supplied, it replaces the shell without creating a new process. +If the @samp{-l} option is supplied, the shell places a dash in the +zeroth arg passed to @var{command}. This is what the @code{login} program does. -The @samp{-c} option causes @var{command} -to be executed with an empty environment. -If @samp{-a} is supplied, the shell passes @var{name} -as the zeroth argument to @var{command}. +The @samp{-c} option causes @var{command} to be executed with an empty +environment. +If @samp{-a} is supplied, the shell passes @var{name} as the zeroth +argument to @var{command}. If no @var{command} is specified, redirections may be used to affect -the current shell environment. +the current shell environment. If there are no redirection errors, the +return status is zero; otherwise the return status is non-zero. @item exit @btindex exit @@ -1826,6 +2369,7 @@ the current shell environment. exit [@var{n}] @end example Exit the shell, returning a status of @var{n} to the shell's parent. +Any trap on @code{EXIT} is executed before the shell terminates. @item export @btindex export @@ -1834,10 +2378,14 @@ export [-fn] [-p] [@var{name}[=@var{value}]] @end example Mark each @var{name} to be passed to child processes in the environment. If the @samp{-f} option is supplied, the @var{name}s -refer to shell functions. The @samp{-n} option means to no longer mark -each @var{name} for export. +refer to shell functions; otherwise the names refer to shell variables. +The @samp{-n} option means to no longer mark each @var{name} for export. If no @var{names} are supplied, or if the @samp{-p} option is given, a list of exported names is displayed. +The @samp{-p} option displays output in a form that may be reused as input. +The return status is zero unless an invalid option is supplied, one of +the names is not a valid shell variable name, or @samp{-f} is supplied +with a name that is not a shell function. @item getopts @btindex getopts @@ -1852,26 +2400,34 @@ Each time it is invoked, @code{getopts} places the next option in the shell variable @var{name}, initializing @var{name} if it does not exist, and the index of the next argument to be processed into the -variable @code{OPTIND}. @code{OPTIND} -is initialized to 1 each time the shell or a shell script -is invoked. When an option requires an argument, +variable @code{OPTIND}. +@code{OPTIND} is initialized to 1 each time the shell or a shell script +is invoked. +When an option requires an argument, @code{getopts} places that argument into the variable @code{OPTARG}. -The shell does not reset @code{OPTIND} -automatically; it must be manually reset between multiple -calls to @code{getopts} -within the same shell invocation if a new set of parameters -is to be used. +The shell does not reset @code{OPTIND} automatically; it must be manually +reset between multiple calls to @code{getopts} within the same shell +invocation if a new set of parameters is to be used. + +When the end of options is encountered, @code{getopts} exits with a +return value greater than zero. +@code{OPTIND} is set to the index of the first non-option argument, +and @code{name} is set to @samp{?}. + +@code{getopts} +normally parses the positional parameters, but if more arguments are +given in @var{args}, @code{getopts} parses those instead. @code{getopts} can report errors in two ways. If the first character of @var{optstring} is a colon, @var{silent} error reporting is used. In normal operation diagnostic messages -are printed when illegal options or missing option arguments are +are printed when invalid options or missing option arguments are encountered. If the variable @code{OPTERR} -is set to 0, no error message will be displayed, even if the first +is set to 0, no error messages will be displayed, even if the first character of @code{optstring} is not a colon. -If an illegal option is seen, +If an invalid option is seen, @code{getopts} places @samp{?} into @var{name} and, if not silent, prints an error message and unsets @code{OPTARG}. If @code{getopts} is silent, the option character found is placed in @@ -1883,72 +2439,152 @@ is not silent, a question mark (@samp{?}) is placed in @var{name}, If @code{getopts} is silent, then a colon (@samp{:}) is placed in @var{name} and @code{OPTARG} is set to the option character found. -@code{getopts} -normally parses the positional parameters, but if more arguments are -given in @var{args}, @code{getopts} parses those instead. - @item hash @btindex hash @example hash [-r] [-p @var{filename}] [@var{name}] @end example -Remember the full filenames of commands specified as arguments, -so they need not be searched for on subsequent invocations. The -commands are found by searching through the directories listed in -@code{$PATH}. The @samp{-p} option inhibits the path search, and -@var{filename} is used as the location of @var{name}. -The @samp{-r} option causes the shell to forget -all remembered locations. If no arguments are given, information -about remembered commands is printed. +Remember the full pathnames of commands specified as @var{name} arguments, +so they need not be searched for on subsequent invocations. +The commands are found by searching through the directories listed in +@code{$PATH}. +The @samp{-p} option inhibits the path search, and @var{filename} is +used as the location of @var{name}. +The @samp{-r} option causes the shell to forget all remembered locations. +If no arguments are given, information about remembered commands is printed. +The return status is zero unless a @var{name} is not found or an invalid +option is supplied. @item pwd @btindex pwd @example pwd [-LP] @end example -Print the current working directory. If the @samp{-P} option is supplied, -the path printed will not contain symbolic links. If the @samp{-L} option -is supplied, the path printed may contain symbolic links. +Print the current working directory. +If the @samp{-P} option is supplied, the path printed will not +contain symbolic links. +If the @samp{-L} option is supplied, the path printed may contain +symbolic links. +The return status is zero unless an error is encountered while +determining the name of the current directory or an invalid option +is supplied. @item readonly @btindex readonly @example readonly [-apf] [@var{name}] @dots{} @end example -Mark each @var{name} as unchangable. The values of these names may not -be changed by subsequent assignment. If the @samp{-f} option is supplied, -each @var{name} refers to a shell function. The @samp{-a} option means -each @var{name} refers to an array variable. +Mark each @var{name} as readonly. +The values of these names may not be changed by subsequent assignment. +If the @samp{-f} option is supplied, each @var{name} refers to a shell +function. +The @samp{-a} option means each @var{name} refers to an array variable. If no @var{name} arguments are given, or if the @samp{-p} option is supplied, a list of all readonly names is printed. +The @samp{-p} option causes output to be displayed in a format that +may be reused as input. +The return status is zero unless an invalid option is supplied, one of +the @var{name} arguments is not a valid shell variable or function name, +or the @samp{-f} option is supplied with a name that is not a shell function. @item return @btindex return @example return [@var{n}] @end example -Cause a shell function to exit with value @var{n}. This may also be used -to terminate execution of a script being executed with the @code{.} -builtin. +Cause a shell function to exit with the return value @var{n}. +This may also be used to terminate execution of a script being executed +with the @code{.} builtin, returning either @var{n} or the exit status +of the last command executed within the script as the exit status of the +script. +The return status is false if @code{return} is used outside a function +and not during the execution of a script by @samp{.}. @item shift @btindex shift @example shift [@var{n}] @end example -Shift positional parameters to the left by @var{n}. -The positional parameters from @var{n}+1 @dots{} -are renamed to -@code{$1} @dots{} . -Parameters represented by the numbers -@code{$#} to @var{n}+1 are unset. @var{n} -must be a non-negative number less than or equal to @code{$#}. +Shift the positional parameters to the left by @var{n}. +The positional parameters from @var{n}+1 @dots{} @code{$#} are +renamed to @code{$1} @dots{} @code{$#}-@var{n}+1. +Parameters represented by the numbers @code{$#} to @var{n}+1 are unset. +@var{n} must be a non-negative number less than or equal to @code{$#}. +If @var{n} is zero or greater than @code{$#}, the positional parameters +are not changed. +The return status is zero unless @var{n} is greater than @code{$#} or +less than zero, non-zero otherwise. @item test @itemx [ @btindex test @btindex [ -Evaluate a conditional expression (@pxref{Bash Conditional Expressions}). +Evaluate a conditional expression @var{expr}. +Each operator and operand must be a separate argument. +Expressions are composed of the primaries described below in +@ref{Bash Conditional Expressions}. + +Expressions may be combined using the following operators, listed in +decreasing order of precedence. + +@table @code +@item ! @var{expr} +True if @var{expr} is false. + +@item ( @var{expr} ) +Returns the value of @var{expr}. +This may be used to override the normal precedence of operators. + +@item @var{expr1} -a @var{expr2} +True if both @var{expr1} and @var{expr2} are true. + +@item @var{expr1} -o @var{expr2} +True if either @var{expr1} or @var{expr2} is true. +@end table + +The @code{test} and @code{[} builtins evaluate conditional +expressions using a set of rules based on the number of arguments. + +@table @asis +@item 0 arguments +The expression is false. + +@item 1 argument +The expression is true if and only if the argument is not null. + +@item 2 arguments +If the first argument is @samp{!}, the expression is true if and +only if the second argument is null. +If the first argument is one of the unary conditional operators +(@pxref{Bash Conditional Expressions}), the expression +is true if the unary test is true. +If the first argument is not a valid unary operator, the expression is +false. + +@item 3 arguments +If the second argument is one of the binary conditional +operators (@pxref{Bash Conditional Expressions}), the +result of the expression is the result of the binary test using the +first and third arguments as operands. +If the first argument is @samp{!}, the value is the negation of +the two-argument test using the second and third arguments. +If the first argument is exactly @samp{(} and the third argument is +exactly @samp{)}, the result is the one-argument test of the second +argument. +Otherwise, the expression is false. +The @samp{-a} and @samp{-o} operators are considered binary operators +in this case. + +@item 4 arguments +If the first argument is @samp{!}, the result is the negation of +the three-argument expression composed of the remaining arguments. +Otherwise, the expression is parsed and evaluated according to +precedence using the rules listed above. + +@item 5 or more arguments +The expression is parsed and evaluated according to precedence +using the rules listed above. +@end table @item times @btindex times @@ -1956,6 +2592,7 @@ Evaluate a conditional expression (@pxref{Bash Conditional Expressions}). times @end example Print out the user and system times used by the shell and its children. +The return status is zero. @item trap @btindex trap @@ -1971,7 +2608,8 @@ each @var{sigspec} is ignored by the shell and commands it invokes. If @var{arg} is @samp{-p}, the shell displays the trap commands associated with each @var{sigspec}. If no arguments are supplied, or only @samp{-p} is given, @code{trap} prints the list of commands -associated with each signal number. +associated with each signal number in a form that may be reused as +shell input. Each @var{sigspec} is either a signal name such as @code{SIGINT} (with or without the @code{SIG} prefix) or a signal number. If a @var{sigspec} @@ -1985,10 +2623,13 @@ Signals ignored upon entry to the shell cannot be trapped or reset. Trapped signals are reset to their original values in a child process when it is created. +The return status is zero unless a @var{sigspec} does not specify a +valid signal. + @item umask @btindex umask @example -umask [-S] [@var{mode}] +umask [-p] [-S] [@var{mode}] @end example Set the shell process's file creation mask to @var{mode}. If @var{mode} begins with a digit, it is interpreted as an octal number; @@ -1997,6 +2638,10 @@ to that accepted by the @code{chmod} command. If @var{mode} is omitted, the current value of the mask is printed. If the @samp{-S} option is supplied without a @var{mode} argument, the mask is printed in a symbolic format. +If the @samp{-p} option is supplied, and @var{mode} +is omitted, the output is in a form that may be reused as input. +The return status is zero if the mode is successfully changed or if +no @var{mode} argument is supplied, and non-zero otherwise. @item unset @btindex unset @@ -2008,8 +2653,9 @@ If no options are supplied, or the @samp{-v} option is given, each @var{name} refers to a shell variable. If the @samp{-f} option is given, the @var{name}s refer to shell functions, and the function definition is removed. -Read-only variables and functions may not be unset. - +Readonly variables and functions may not be unset. +The return status is zero unless a @var{name} does not exist or is +readonly. @end table @node Bourne Shell Variables @@ -2020,48 +2666,50 @@ In some cases, Bash assigns a default value to the variable. @vtable @code -@item IFS -A list of characters that separate fields; used when the shell splits -words as part of expansion. - -@item PATH -A colon-separated list of directories in which the shell looks for -commands. +@item CDPATH +A colon-separated list of directories used as a search path for +the @code{cd} builtin command. @item HOME The current user's home directory; the default for the @code{cd} builtin command. +The value of this variable is also used by tilde expansion +(@pxref{Tilde Expansion}). -@item CDPATH -A colon-separated list of directories used as a search path for -the @code{cd} command. - -@item MAILPATH -A colon-separated list of files which the shell periodically checks -for new mail. You can -also specify what message is printed by separating the file name from -the message with a @samp{?}. When used in the text of the message, -@code{$_} stands for the name of the current mailfile. +@item IFS +A list of characters that separate fields; used when the shell splits +words as part of expansion. @item MAIL If this parameter is set to a filename and the @code{MAILPATH} variable is not set, Bash informs the user of the arrival of mail in the specified file. +@item MAILPATH +A colon-separated list of filenames which the shell periodically checks +for new mail. +Each list entry can specify the message that is printed when new mail +arrives in the mail file by separating the file name from the message with +a @samp{?}. +When used in the text of the message, @code{$_} expands to the name of +the current mail file. + +@item OPTARG +The value of the last option argument processed by the @code{getopts} builtin. + +@item OPTIND +The index of the last option argument processed by the @code{getopts} builtin. + +@item PATH +A colon-separated list of directories in which the shell looks for +commands. + @item PS1 The primary prompt string. The default value is @samp{\s-\v\$ }. @item PS2 The secondary prompt string. The default value is @samp{> }. -@item OPTIND -The index of the last option processed by the -@code{getopts} builtin. - -@item OPTARG -The value of the last option argument processed by the -@code{getopts} builtin. - @end vtable @node Other Bourne Shell Features @@ -2072,155 +2720,235 @@ The value of the last option argument processed by the Bash and the Bourne shell. @end menu -Bash implements essentially the same grammar, parameter and variable -expansion, redirection, and quoting as the Bourne Shell. Bash uses the -@sc{POSIX} 1003.2 standard as the specification of how these features are to be -implemented. There are some differences between the traditional Bourne -shell and the @sc{POSIX} standard; this section quickly details the differences -of significance. A number of these differences are explained in greater -depth in subsequent sections. +Bash implements essentially the same grammar, parameter and +variable expansion, redirection, and quoting as the Bourne Shell. +Bash uses the @sc{POSIX} 1003.2 standard as the specification of +how these features are to be implemented. There are some +differences between the traditional Bourne shell and Bash; this +section quickly details the differences of significance. A +number of these differences are explained in greater depth in +subsequent sections. @node Major Differences From The Bourne Shell @subsection Major Differences From The SVR4.2 Bourne Shell +@itemize @bullet + +@item Bash is @sc{POSIX}-conformant, even where the @sc{POSIX} specification differs from traditional @code{sh} behavior. +@item Bash has multi-character invocation options (@pxref{Invoking Bash}). +@item Bash has command-line editing (@pxref{Command Line Editing}) and the @code{bind} builtin. +@item Bash has command history (@pxref{Bash History Facilities}) and the @code{history} and @code{fc} builtins to manipulate it. -Bash implements @code{csh}-like history expansion (@pxref{History Interaction}). +@item +Bash implements @code{csh}-like history expansion +(@pxref{History Interaction}). +@item Bash has one-dimensional array variables (@pxref{Arrays}), and the appropriate variable expansions and assignment syntax to use them. -Some of the Bash builtins take options to act on arrays. Bash provides -some built-in array variables. +Several of the Bash builtins take options to act on arrays. +Bash provides a number of built-in array variables. + +@item +The @code{$'@dots{}'} quoting syntax, which expands ANSI-C +backslash-escaped characters in the text between the single quotes, +is supported (@pxref{ANSI-C Quoting}). +@item +Bash supports the @code{$"@dots{}"} quoting syntax to do +locale-specific translation of the characters between the double +quotes. The @samp{-D}, @samp{--dump-strings}, and @samp{--dump-po-strings} +invocation options list the translatable strings found in a script +(@pxref{Locale Translation}). + +@item Bash implements the @code{!} keyword to negate the return value of a pipeline (@pxref{Pipelines}). Very useful when an @code{if} statement needs to act only if a test fails. +@item +Bash has the @code{time} reserved word and command timing (@pxref{Pipelines}). +The display of the timing statistics may be controlled with the +@code{TIMEFORMAT} variable. + +@item Bash includes the @code{select} compound command, which allows the -generation of simple menus (@pxref{Korn Shell Constructs}). +generation of simple menus (@pxref{Conditional Constructs}). +@item +Bash includes the @code{[[} compound command, which makes conditional +testing part of the shell grammar (@pxref{Conditional Constructs}). + +@item Bash includes brace expansion (@pxref{Brace Expansion}) and tilde expansion (@pxref{Tilde Expansion}). +@item Bash implements command aliases and the @code{alias} and @code{unalias} builtins (@pxref{Aliases}). -Bash provides shell arithmetic and arithmetic expansion -(@pxref{Shell Arithmetic}). - -The @sc{POSIX} and @code{ksh}-style @code{$()} form of command substitution -is implemented (@pxref{Command Substitution}), -and preferred to the Bourne shell's @code{``} (which -is also implemented for backwards compatibility). +@item +Bash provides shell arithmetic, the @code{((} compound command +(@pxref{Conditional Constructs}), +and arithmetic expansion (@pxref{Shell Arithmetic}). +@item Variables present in the shell's initial environment are automatically exported to child processes. The Bourne shell does not normally do this unless the variables are explicitly marked using the @code{export} command. -Bash includes the @sc{POSIX} and @code{ksh}-style pattern removal -@samp{%}, @samp{#}, @samp{%%} and @samp{##} constructs to remove -leading or trailing substrings from variable values -(@pxref{Shell Parameter Expansion}). +@item +Bash includes the @sc{POSIX} pattern removal @samp{%}, @samp{#}, @samp{%%} +and @samp{##} expansions to remove leading or trailing substrings from +variable values (@pxref{Shell Parameter Expansion}). -The expansion @code{$@{#xx@}}, which returns the length of @code{$xx}, +@item +The expansion @code{$@{#xx@}}, which returns the length of @code{$@{xx@}}, is supported (@pxref{Shell Parameter Expansion}). -The @code{$'@dots{}'} quoting syntax, which expands ANSI-C -backslash-escaped characters in the text between the single quotes, -is supported (@pxref{ANSI-C Quoting}). - -Bash supports the @code{$"@dots{}"} quoting syntax to do -locale-specific translation of the characters between the double -quotes. The @samp{-D} and @samp{--dump-strings} invocation options -list the translatable strings found in a script -(@pxref{Locale Translation}). - +@item The expansion @code{$@{var:}@var{offset}@code{[:}@var{length}@code{]@}}, which expands to the substring of @code{var}'s value of length -@var{length}, optionally beginning at @var{offset}, is present +@var{length}, beginning at @var{offset}, is present (@pxref{Shell Parameter Expansion}). +@item The expansion @code{$@{var/[/]}@var{pattern}@code{[/}@var{replacement}@code{]@}}, which matches @var{pattern} and replaces it with @var{replacement} in the value of @code{var}, is available (@pxref{Shell Parameter Expansion}). +@item Bash has @var{indirect} variable expansion using @code{$@{!word@}} (@pxref{Shell Parameter Expansion}). +@item Bash can expand positional parameters beyond @code{$9} using @code{$@{@var{num}@}}. +@item +The @sc{POSIX} @code{$()} form of command substitution +is implemented (@pxref{Command Substitution}), +and preferred to the Bourne shell's @code{``} (which +is also implemented for backwards compatibility). + +@item Bash has process substitution (@pxref{Process Substitution}). +@item Bash automatically assigns variables that provide information about the current user (@code{UID}, @code{EUID}, and @code{GROUPS}), the current host (@code{HOSTTYPE}, @code{OSTYPE}, @code{MACHTYPE}, and @code{HOSTNAME}), and the instance of Bash that is running (@code{BASH}, -@code{BASH_VERSION}, and @code{BASH_VERSINFO}. @xref{Bash Variables}, +@code{BASH_VERSION}, and @code{BASH_VERSINFO}). @xref{Bash Variables}, for details. +@item The @code{IFS} variable is used to split only the results of expansion, not all words (@pxref{Word Splitting}). This closes a longstanding shell security hole. +@item +Bash implements the full set of @sc{POSIX.2} filename expansion operators, +including @var{character classes}, @var{equivalence classes}, and +@var{collating symbols} (@pxref{Filename Expansion}). + +@item +Bash implements extended pattern matching features when the @code{extglob} +shell option is enabled (@pxref{Pattern Matching}). + +@item It is possible to have a variable and a function with the same name; @code{sh} does not separate the two name spaces. +@item Bash functions are permitted to have local variables using the @code{local} builtin, and thus useful recursive functions may be written. +@item Variable assignments preceding commands affect only that command, even builtins and functions (@pxref{Environment}). In @code{sh}, all variable assignments preceding commands are global unless the command is executed from the file system. +@item Bash performs filename expansion on filenames specified as operands -to output redirection operators. +to input and output redirection operators. +@item Bash contains the @samp{<>} redirection operator, allowing a file to be opened for both reading and writing, and the @samp{&>} redirection operator, for directing standard output and standard error to the same file (@pxref{Redirections}). +@item The @code{noclobber} option is available to avoid overwriting existing files with output redirection (@pxref{The Set Builtin}). The @samp{>|} redirection operator may be used to override @code{noclobber}. -Bash interprets special backslash-escaped characters in the prompt -strings when interactive (@pxref{Printing a Prompt}). +@item +The Bash @code{cd} and @code{pwd} builtins (@pxref{Bourne Shell Builtins}) +each take @samp{-L} and @samp{-P} builtins to switch between logical and +physical modes. -Bash allows you to write a function to override a builtin, and provides +@item +Bash allows a function to override a builtin with the same name, and provides access to that builtin's functionality within the function via the @code{builtin} and @code{command} builtins (@pxref{Bash Builtins}). +@item The @code{command} builtin allows selective disabling of functions when command lookup is performed (@pxref{Bash Builtins}). +@item Individual builtins may be enabled or disabled using the @code{enable} builtin (@pxref{Bash Builtins}). -The Bash @code{hash} builtin allows a name to be associated with -an arbitrary filename, even when that filename cannot be found by -searching the @code{$PATH}, using @samp{hash -p}. +@item +The Bash @code{exec} builtin takes additional options that allow users +to control the contents of the environment passed to the executed +command, and what the zeroth argument to the command is to be +(@pxref{Bourne Shell Builtins}). +@item Shell functions may be exported to children via the environment -(@pxref{Shell Functions}). +using @code{export -f} (@pxref{Shell Functions}). + +@item +The Bash @code{export}, @code{readonly}, and @code{declare} builtins can +take a @samp{-f} option to act on shell functions, a @samp{-p} option to +display variables with various attributes set in a format that can be +used as shell input, a @samp{-n} option to remove various variable +attributes, and @samp{name=value} arguments to set variable attributes +and values simultaneously. +@item +The Bash @code{hash} builtin allows a name to be associated with +an arbitrary filename, even when that filename cannot be found by +searching the @code{$PATH}, using @samp{hash -p} +(@pxref{Bourne Shell Builtins}). + +@item Bash includes a @code{help} builtin for quick reference to shell facilities (@pxref{Bash Builtins}). +@item +The @code{printf} builtin is available to display formatted output +(@pxref{Bash Builtins}). + +@item The Bash @code{read} builtin (@pxref{Bash Builtins}) will read a line ending in @samp{\} with the @samp{-r} option, and will use the @code{REPLY} variable as a @@ -2228,69 +2956,79 @@ default if no arguments are supplied. The Bash @code{read} builtin also accepts a prompt string with the @samp{-p} option and will use Readline to obtain the line when given the @samp{-e} option. +@item +The @code{return} builtin may be used to abort execution of scripts +executed with the @code{.} or @code{source} builtins +(@pxref{Bourne Shell Builtins}). + +@item Bash includes the @code{shopt} builtin, for finer control of shell optional capabilities (@pxref{Bash Builtins}). +@item Bash has much more optional behavior controllable with the @code{set} builtin (@pxref{The Set Builtin}). -The @code{disown} builtin can remove a job from the internal shell -job table (@pxref{Job Control Builtins}). - -The @code{return} builtin may be used to abort execution of scripts -executed with the @code{.} or @code{source} builtins -(@pxref{Bourne Shell Builtins}). - +@item The @code{test} builtin (@pxref{Bourne Shell Builtins}) -is slightly different, as it implements the -@sc{POSIX} 1003.2 algorithm, which specifies the behavior based on the -number of arguments. +is slightly different, as it implements the @sc{POSIX} algorithm, +which specifies the behavior based on the number of arguments. +@item The @code{trap} builtin (@pxref{Bourne Shell Builtins}) allows a @code{DEBUG} pseudo-signal specification, similar to @code{EXIT}. Commands specified with a @code{DEBUG} trap are executed after every simple command. The @code{DEBUG} trap is not inherited by shell functions. -The Bash @code{export}, @code{readonly}, and @code{declare} builtins can -take a @samp{-f} option to act on shell functions, a @samp{-p} option to -display variables with various attributes set in a format that can be -used as shell input, a @samp{-n} option to remove various variable -attributes, and @samp{name=value} arguments to set variable attributes -and values simultaneously. - -The Bash @code{cd} and @code{pwd} builtins (@pxref{Bourne Shell Builtins}) -each take @samp{-L} and @samp{-P} builtins to switch between logical and -physical modes. - +@item The Bash @code{type} builtin is more extensive and gives more information about the names it finds (@pxref{Bash Builtins}). +@item +The Bash @code{umask} builtin permits a @samp{-p} option to cause +the output to be displayed in the form of a @code{umask} command +that may be reused as input (@pxref{Bourne Shell Builtins}). + +@item Bash implements a @code{csh}-like directory stack, and provides the @code{pushd}, @code{popd}, and @code{dirs} builtins to manipulate it -(@pxref{C Shell Builtins}). +(@pxref{The Directory Stack}). Bash also makes the directory stack visible as the value of the @code{DIRSTACK} shell variable. +@item +Bash interprets special backslash-escaped characters in the prompt +strings when interactive (@pxref{Printing a Prompt}). + +@item The Bash restricted mode is more useful (@pxref{The Restricted Shell}); the @sc{SVR4.2} shell restricted mode is too limited. -Bash has the @code{time} reserved word and command timing (@pxref{Pipelines}). -The display of the timing statistics may be controlled with the -@code{TIMEFORMAT} variable. +@item +The @code{disown} builtin can remove a job from the internal shell +job table (@pxref{Job Control Builtins}) or suppress the sending +of @code{SIGHUP} to a job when the shell exits as the result of a +@code{SIGHUP}. +@item The @sc{SVR4.2} shell has two privilege-related builtins (@code{mldmode} and @code{priv}) not present in Bash. +@item Bash does not have the @code{stop} or @code{newgrp} builtins. +@item Bash does not use the @code{SHACCT} variable or perform shell accounting. +@item The @sc{SVR4.2} @code{sh} uses a @code{TIMEOUT} variable like Bash uses @code{TMOUT}. -More features unique to Bash may be found in -@ref{Bash Features}. +@end itemize + +@noindent +More features unique to Bash may be found in @ref{Bash Features}. @subsection Implementation Differences From The SVR4.2 Shell @@ -2313,7 +3051,7 @@ This can be the cause of some hard-to-find errors. The @sc{SVR4.2} shell uses a baroque memory management scheme based on trapping @code{SIGSEGV}. If the shell is started from a process with @code{SIGSEGV} blocked (e.g., by using the @code{system()} C library -function call), the shell misbehaves badly. +function call), it misbehaves badly. @item In a questionable attempt at security, the @sc{SVR4.2} shell, @@ -2323,12 +3061,12 @@ magic threshold value, commonly 100. This can lead to unexpected results. @item -The @sc{SVR4.2} shell does not allow users to trap @code{SIGALRM} or -@code{SIGCHLD}. +The @sc{SVR4.2} shell does not allow users to trap @code{SIGSEGV}, +@code{SIGALRM}, or @code{SIGCHLD}. @item -For some reason, the @sc{SVR4.2} shell does not allow the @code{MAILCHECK} -variable to be unset. +The @sc{SVR4.2} shell does not allow the @code{IFS}, @code{MAILCHECK}, +@code{PATH}, @code{PS1}, or @code{PS2} variables to be unset. @item The @sc{SVR4.2} shell treats @samp{^} as the undocumented equivalent of @@ -2350,515 +3088,6 @@ The @sc{SVR4.2} shell behaves differently when invoked as @code{jsh} (it turns on job control). @end itemize -@node Csh Features -@chapter C-Shell Style Features - -The C-Shell (@dfn{@code{csh}}) was created by Bill Joy at The -University of California at Berkeley. It -is generally considered to have better features for interactive use than -the original Bourne shell. Some of the @code{csh} features present in -Bash include job control, history expansion, `protected' redirection, and -several variables to control the interactive behaviour of the shell -(e.g., @code{IGNOREEOF}). - -@xref{Using History Interactively}, for details on history expansion. - -@menu -* Brace Expansion:: Expansion of expressions within braces. -* Tilde Expansion:: Expansion of the ~ character. -* C Shell Builtins:: Builtin commands adopted from the C Shell. -* C Shell Variables:: Variables which Bash uses in essentially - the same way as the C Shell. -@end menu - -@node Brace Expansion -@section Brace Expansion -@cindex brace expansion -@cindex expansion, brace - -Brace expansion -is a mechanism by which arbitrary strings -may be generated. This mechanism is similar to -@var{filename expansion} (@pxref{Filename Expansion}), -but the file names generated -need not exist. Patterns to be brace expanded take -the form of an optional @var{preamble}, -followed by a series of comma-separated strings -between a pair of braces, followed by an optional @var{postamble}. -The preamble is prepended to each string contained -within the braces, and the postamble is then appended -to each resulting string, expanding left to right. - -Brace expansions may be nested. The results of each expanded -string are not sorted; left to right order is preserved. -For example, -@example -bash$ echo a@{d,c,b@}e -ade ace abe -@end example - -Brace expansion is performed before any other expansions, -and any characters special to other expansions are preserved -in the result. It is strictly textual. Bash -does not apply any syntactic interpretation to the context of the -expansion or the text between the braces. - -A correctly-formed brace expansion must contain unquoted opening -and closing braces, and at least one unquoted comma. -Any incorrectly formed brace expansion is left unchanged. - -This construct is typically used as shorthand when the common -prefix of the strings to be generated is longer than in the -above example: -@example -mkdir /usr/local/src/bash/@{old,new,dist,bugs@} -@end example -or -@example -chown root /usr/@{ucb/@{ex,edit@},lib/@{ex?.?*,how_ex@}@} -@end example - -@node Tilde Expansion -@section Tilde Expansion -@cindex tilde expansion -@cindex expansion, tilde - -Bash has tilde (~) expansion, similar, but not identical, to that of -@code{csh}. The following table shows what unquoted words beginning -with a tilde expand to. - -@table @code -@item ~ -The current value of @code{$HOME}. -@item ~/foo -@file{$HOME/foo} - -@item ~fred/foo -The subdirectory @code{foo} of the home directory of the user -@code{fred}. - -@item ~+/foo -@file{$PWD/foo} - -@item ~-/foo -@file{$OLDPWD/foo} -@end table - -Bash will also tilde expand words following redirection operators -and words following @samp{=} in assignment statements. - -@node C Shell Builtins -@section C Shell Builtins - -Bash has several builtin commands whose definition is very similar -to @code{csh}. - -@table @code -@btindex pushd -@item pushd -@example -pushd [@var{dir} | @var{+N} | @var{-N}] [-n] -@end example - -Save the current directory on a list and then @code{cd} to -@var{dir}. With no -arguments, exchanges the top two directories. - -@table @code -@item +@var{N} -Brings the @var{N}th directory (counting from the left of the -list printed by @code{dirs}, starting with zero) to the top of -the list by rotating the stack. -@item -@var{N} -Brings the @var{N}th directory (counting from the right of the -list printed by @code{dirs}, starting with zero) to the top of -the list by rotating the stack. -@item -n -Suppresses the normal change of directory when adding directories -to the stack, so that only the stack is manipulated. -@item @var{dir} -Makes the current working directory be the top of the stack, and then -@code{cd}s to @var{dir}. You can see the saved directory list -with the @code{dirs} command. -@end table - -@item popd -@btindex popd -@example -popd [+@var{N} | -@var{N}] [-n] -@end example - -Pop the directory stack, and @code{cd} to the new top directory. When -no arguments are given, @code{popd} -removes the top directory from the stack and -performs a @code{cd} to the new top directory. The -elements are numbered from 0 starting at the first directory listed with -@code{dirs}; i.e., @code{popd} is equivalent to @code{popd +0}. -@table @code -@item +@var{N} -Removes the @var{N}th directory (counting from the left of the -list printed by @code{dirs}), starting with zero. -@item -@var{N} -Removes the @var{N}th directory (counting from the right of the -list printed by @code{dirs}), starting with zero. -@item -n -Suppresses the normal change of directory when removing directories -from the stack, so that only the stack is manipulated. -@end table - -@item dirs -@btindex dirs -@example -dirs [+@var{N} | -@var{N}] [-clvp] -@end example -Display the list of currently remembered directories. Directories -find their way onto the list with the @code{pushd} command; you can get -back up through the list with the @code{popd} command. -@table @code -@item +@var{N} -Displays the @var{N}th directory (counting from the left of the -list printed by @code{dirs} when invoked without options), starting -with zero. -@item -@var{N} -Displays the @var{N}th directory (counting from the right of the -list printed by @code{dirs} when invoked without options), starting -with zero. -@item -c -Clears the directory stack by deleting all of the elements. -@item -l -Produces a longer listing; the default listing format uses a -tilde to denote the home directory. -@item -p -Causes @code{dirs} to print the directory stack with one entry per -line. -@item -v -Causes @code{dirs} to print the directory stack with one entry per -line, prepending each entry with its index in the stack. -@end table - -@item history -@btindex history -@example -history [-c] [@var{n}] -history [-anrw] [@var{filename}] -history -ps @var{arg} -@end example - -Display the history list with line numbers. Lines prefixed with -with a @samp{*} have been modified. An argument of @var{n} says -to list only the last @var{n} lines. Options, if supplied, have -the following meanings: - -@table @code -@item -w -Write out the current history to the history file. - -@item -r -Read the current history file and append its contents to -the history list. - -@item -a -Append the new -history lines (history lines entered since the beginning of the -current Bash session) to the history file. - -@item -n -Append the history lines not already read from the history file -to the current history list. These are lines appended to the history -file since the beginning of the current Bash session. - -@item -c -Clear the history list. This may be combined -with the other options to replace the history list completely. - -@item -s -The @var{arg}s are added to the end of -the history list as a single entry. - -@item -p -Perform history substitution on the @var{arg}s and display the result -on the standard output, without storing the results in the history list. -@end table - -When the @samp{-w}, @samp{-r}, @samp{-a}, or @samp{-n} option is -used, if @var{filename} -is given, then it is used as the history file. If not, then -the value of the @code{HISTFILE} variable is used. - -@item logout -@btindex logout -Exit a login shell. - -@item source -@btindex source -A synonym for @code{.} (@pxref{Bourne Shell Builtins}). - -@end table - -@node C Shell Variables -@section C Shell Variables - -@vtable @code - -@item IGNOREEOF -If this variable is set, its value is used the number of consecutive -@code{EOF}s Bash will read before exiting. By default, Bash will exit -upon reading a single @code{EOF}. If @code{IGNOREEOF} is not set to -a numeric value, Bash acts as if its value were 10. - -@end vtable - -@node Korn Shell Features -@chapter Korn Shell Style Features - -This section describes features primarily inspired by the -Korn Shell (@code{ksh}). In some cases, the @sc{POSIX} 1003.2 -standard has adopted these commands and variables from the -Korn Shell; Bash implements those features using the @sc{POSIX} -standard as a guide. - -@menu -* Korn Shell Constructs:: Shell grammar constructs adopted from the - Korn Shell -* Korn Shell Builtins:: Builtin commands adopted from the Korn Shell. -* Korn Shell Variables:: Variables which Bash uses in essentially - the same way as the Korn Shell. -* Aliases:: Substituting one command for another. -@end menu - -@node Korn Shell Constructs -@section Korn Shell Constructs - -Bash includes the Korn Shell @code{select} construct. This construct -allows the easy generation of menus. It has almost the same syntax as -the @code{for} command. - -The syntax of the @code{select} command is: -@rwindex select -@example -select @var{name} [in @var{words} @dots{}]; do @var{commands}; done -@end example - -The list of words following @code{in} is expanded, generating a list -of items. The set of expanded words is printed on the standard -error, each preceded by a number. If the @samp{in @var{words}} -is omitted, the positional parameters are printed. The -@code{PS3} prompt is then displayed and a line is read from the standard -input. If the line consists of a number corresponding to one of -the displayed words, then the value of @var{name} -is set to that word. If the line is empty, the words and prompt -are displayed again. If @code{EOF} is read, the @code{select} -command completes. Any other value read causes @var{name} -to be set to null. The line read is saved in the variable -@code{REPLY}. - -The @var{commands} are executed after each selection until a -@code{break} or @code{return} command is executed, at which -point the @code{select} command completes. - -Bash also has adopted command timing from the Korn shell. If the -@code{time} reserved word precedes a pipeline, which may consist -of a single command, timing statistics for the pipeline are displayed -when it completes. -The statistics currently consist of elapsed (wall-clock) time and -user and system time consumed by the command's execution. - -The use of @code{time} as a reserved word permits the timing of -shell builtins, shell functions, and pipelines. An external -@code{time} command cannot time these easily. - -@node Korn Shell Builtins -@section Korn Shell Builtins - -This section describes Bash builtin commands taken from @code{ksh}. - -@table @code - -@item fc -@btindex fc -@example -@code{fc [-e @var{ename}] [-nlr] [@var{first}] [@var{last}]} -@code{fc -s [@var{pat}=@var{rep}] [@var{command}]} -@end example - -Fix Command. In the first form, a range of commands from @var{first} to -@var{last} is selected from the history list. Both @var{first} and -@var{last} may be specified as a string (to locate the most recent -command beginning with that string) or as a number (an index into the -history list, where a negative number is used as an offset from the -current command number). If @var{last} is not specified it is set to -@var{first}. If @var{first} is not specified it is set to the previous -command for editing and @minus{}16 for listing. If the @samp{-l} flag is -given, the commands are listed on standard output. The @samp{-n} flag -suppresses the command numbers when listing. The @samp{-r} flag -reverses the order of the listing. Otherwise, the editor given by -@var{ename} is invoked on a file containing those commands. If -@var{ename} is not given, the value of the following variable expansion -is used: @code{$@{FCEDIT:-$@{EDITOR:-vi@}@}}. This says to use the -value of the @code{FCEDIT} variable if set, or the value of the -@code{EDITOR} variable if that is set, or @code{vi} if neither is set. -When editing is complete, the edited commands are echoed and executed. - -In the second form, @var{command} is re-executed after each instance -of @var{pat} in the selected command is replaced by @var{rep}. - -A useful alias to use with the @code{fc} command is @code{r='fc -s'}, so -that typing @samp{r cc} runs the last command beginning with @code{cc} -and typing @samp{r} re-executes the last command (@pxref{Aliases}). - -@item let -@btindex let -The @code{let} builtin allows arithmetic to be performed on shell variables. -For details, refer to @ref{Arithmetic Builtins}. - -@item typeset -@btindex typeset -The @code{typeset} command is supplied for compatibility with the Korn -shell; however, it has been deprecated in favor of the -@code{declare} command (@pxref{Bash Builtins}). - -@end table - -@node Korn Shell Variables -@section Korn Shell Variables - -@vtable @code - -@item REPLY -The default variable for the @code{read} builtin. - -@item RANDOM -Each time this parameter is referenced, a random integer -between 0 and 32767 is generated. Assigning a value to this -variable seeds the random number generator. - -@item SECONDS -This variable expands to the number of seconds since the -shell was started. Assignment to this variable resets -the count to the value assigned, and the expanded value -becomes the value assigned plus the number of seconds -since the assignment. - -@item PS3 -The value of this variable is used as the prompt for the -@code{select} command. If this variable is not set, the -@code{select} command prompts with @samp{#? } - -@item PS4 -This is the prompt printed before the command line is echoed -when the @samp{-x} option is set (@pxref{The Set Builtin}). -The default is @samp{+ }. - -@item PWD -The current working directory as set by the @code{cd} builtin. - -@item OLDPWD -The previous working directory as set by the @code{cd} builtin. - -@item TMOUT -If set to a value greater than zero, the value is interpreted as -the number of seconds to wait for input after issuing the primary -prompt. -Bash terminates after that number of seconds if input does -not arrive. - -@item LINENO -The line number in the script or shell function currently executing. - -@item FCEDIT -The editor used as a default by the @code{fc} builtin command. - -@end vtable - -@node Aliases -@section Aliases -@cindex alias expansion - -@menu -* Alias Builtins:: Builtins commands to maniuplate aliases. -@end menu - -The shell maintains a list of @var{aliases} -that may be set and unset with the @code{alias} and -@code{unalias} builtin commands. - -The first word of each command, if unquoted, -is checked to see if it has an -alias. If so, that word is replaced by the text of the alias. -The alias name and the replacement text may contain any valid -shell input, including shell metacharacters, with the exception -that the alias name may not contain @key{=}. -The first word of the replacement text is tested for -aliases, but a word that is identical to an alias being expanded -is not expanded a second time. This means that one may alias -@code{ls} to @code{"ls -F"}, -for instance, and Bash does not try to recursively expand the -replacement text. If the last character of the alias value is a -space or tab character, then the next command word following the -alias is also checked for alias expansion. - -Aliases are created and listed with the @code{alias} -command, and removed with the @code{unalias} command. - -There is no mechanism for using arguments in the replacement text, -as in @code{csh}. -If arguments are needed, a shell function should be used -(@pxref{Shell Functions}). - -Aliases are not expanded when the shell is not interactive, -unless the @code{expand_aliases} shell option is set using -@code{shopt} (@pxref{Bash Builtins}). - -The rules concerning the definition and use of aliases are -somewhat confusing. Bash -always reads at least one complete line -of input before executing any -of the commands on that line. Aliases are expanded when a -command is read, not when it is executed. Therefore, an -alias definition appearing on the same line as another -command does not take effect until the next line of input is read. -The commands following the alias definition -on that line are not affected by the new alias. -This behavior is also an issue when functions are executed. -Aliases are expanded when the function definition is read, -not when the function is executed, because a function definition -is itself a compound command. As a consequence, aliases -defined in a function are not available until after that -function is executed. To be safe, always put -alias definitions on a separate line, and do not use @code{alias} -in compound commands. - -Note that for almost every purpose, aliases are superseded by -shell functions. - -@node Alias Builtins -@subsection Alias Builtins - -@table @code - -@item alias -@btindex alias -@example -alias [@code{-p}] [@var{name}[=@var{value}] @dots{}] -@end example - -Without arguments or with the @samp{-p} option, @code{alias} prints -the list of aliases on the standard output in a form that allows -them to be reused as input. -If arguments are supplied, an alias is defined for each @var{name} -whose @var{value} is given. If no @var{value} is given, the name -and value of the alias is printed. - -@item unalias -@btindex unalias -@example -unalias [-a] [@var{name} @dots{} ] -@end example - -Remove each @var{name} from the list of aliases. If @samp{-a} is -supplied, all aliases are removed. -@end table - @node Bash Features @chapter Bash Features @@ -2876,7 +3105,9 @@ This section describes features unique to Bash. the @code{test} builtin. * Bash Variables:: List of variables that exist in Bash. * Shell Arithmetic:: Arithmetic on shell variables. -* Arrays:: Array Variables +* Aliases:: Substituting one command for another. +* Arrays:: Array Variables. +* The Directory Stack:: History of visited directories. * Printing a Prompt:: Controlling the PS1 string. * The Restricted Shell:: A more controlled mode of shell execution. * Bash POSIX Mode:: Making Bash behave more closely to what @@ -2899,6 +3130,10 @@ line before the single-character options in order for them to be recognized. @table @code +@item --dump-po-strings +Equivalent to @samp{-D}, but the output is in the GNU @code{gettext} +PO (portable object) file format. + @item --dump-strings Equivalent to @samp{-D}. @@ -2908,9 +3143,8 @@ Display a usage message on standard output and exit sucessfully. @item --login Make this shell act as if it were directly invoked by login. This is equivalent to @samp{exec -l bash} but can be issued from -another shell, such as @code{csh}. If you wanted to replace your -current login shell with a Bash login shell, you would say -@samp{exec bash --login}. +another shell, such as @code{csh}. @samp{exec bash --login} +will replace the current shell with a Bash login shell. @item --noediting Do not use the @sc{GNU} Readline library (@pxref{Command Line Editing}) @@ -2950,8 +3184,8 @@ Bash on the standard output and exit successfully. @end table -There are several single-character options you can give which are -not available with the @code{set} builtin. +There are several single-character options that may be supplied at +invocation which are not available with the @code{set} builtin. @table @code @item -c @var{string} @@ -2963,10 +3197,10 @@ positional parameters, starting with @code{$0}. Force the shell to run interactively. @item -r -Make the shell restricted. +Make the shell a restricted shell (@pxref{The Restricted Shell}). @item -s -If this flag is present, or if no arguments remain after option +If this option is present, or if no arguments remain after option processing, then commands are read from the standard input. This option allows the positional parameters to be set when invoking an interactive shell. @@ -2979,11 +3213,16 @@ are subject to language translation when the current locale is not @code{C} or @code{POSIX} (@pxref{Locale Translation}). This implies the @samp{-n} option; no commands will be executed. +@item -- +A @code{--} signals the end of options and disables further option +processing. +Any arguments after the @code{--} are treated as filenames and arguments. + @end table @cindex interactive shell An @emph{interactive} shell is one whose input and output are both -connected to terminals (as determined by @code{isatty()}), or one +connected to terminals (as determined by @code{isatty(3)}), or one started with the @samp{-i} option. If arguments remain after option processing, and neither the @@ -3046,13 +3285,13 @@ If Bash is invoked with the name @code{sh}, it tries to mimic the startup behavior of historical versions of @code{sh} as closely as possible, while conforming to the @sc{POSIX} standard as well. -When invoked as a login shell, it first attempts to read and execute -commands from @file{/etc/profile} and @file{~/.profile}, in that order. +When invoked as an interactive login shell, it first attempts to read +and execute commands from @file{/etc/profile} and @file{~/.profile}, in +that order. The @samp{--noprofile} option may be used to inhibit this behavior. -When invoked as an interactive shell with the name @code{sh}, -@code{bash} looks for the variable @code{ENV}, -expands its value if it is defined, and uses the -expanded value as the name of a file to read and execute. +When invoked as an interactive shell with the name @code{sh}, Bash +looks for the variable @code{ENV}, expands its value if it is defined, +and uses the expanded value as the name of a file to read and execute. Since a shell invoked as @code{sh} does not attempt to read and execute commands from any other startup files, the @samp{--rcfile} option has no effect. @@ -3065,10 +3304,10 @@ the startup files are read. When Bash is started in @sc{POSIX} mode, as with the @samp{--posix} command line option, it follows the @sc{POSIX} standard for startup files. -In this mode, the @code{ENV} variable is expanded and commands are read -and executed from the file whose name is the expanded value. +In this mode, interactive shells expand the @code{ENV} variable +and commands are read and executed from the file whose name is the +expanded value. No other startup files are read. -This is done by interactive shells only. Bash attempts to determine when it is being run by the remote shell daemon, usually @code{rshd}. If Bash determines it is being run by @@ -3077,8 +3316,8 @@ file exists and is readable. It will not do this if invoked as @code{sh}. The @samp{--norc} option may be used to inhibit this behavior, and the @samp{--rcfile} option may be used to force another file to be read, but -rshd does not generally invoke the shell with those options or allow -them to be specified. +@code{rshd} does not generally invoke the shell with those options or +allow them to be specified. @node Is This Shell Interactive? @section Is This Shell Interactive? @@ -3089,8 +3328,8 @@ is one whose input and output are both connected to terminals (as determined by @code{isatty(3)}), or one started with the @samp{-i} option. -You may wish to determine within a startup script whether Bash is -running interactively or not. To do this, examine the variable +To determine within a startup script whether Bash is +running interactively or not, examine the variable @code{$PS1}; it is unset in non-interactive shells, and set in interactive shells. Thus: @@ -3102,7 +3341,8 @@ else fi @end example -Alternatively, you may test the value of the @samp{-} special parameter. +Alternatively, startup scripts may test the value of the @samp{-} +special parameter. It contains @code{i} when the shell is interactive. For example: @example @@ -3123,7 +3363,8 @@ or have been extended in Bash. @item bind @btindex bind @example -bind [-m @var{keymap}] [-lpsvPSV] [-q @var{name}] [-r @var{keyseq}] +bind [-m @var{keymap}] [-lpsvPSV] +bind [-m @var{keymap}] [-q @var{function}] [-u @var{function}] [-r @var{keyseq}] bind [-m @var{keymap}] -f @var{filename} bind [-m @var{keymap}] @var{keyseq:function-name} @end example @@ -3153,65 +3394,83 @@ names are @code{emacs} is equivalent to @code{emacs-standard}. @item -l -List the names of all Readline functions +List the names of all Readline functions. @item -p Display Readline function names and bindings in such a way that they -can be re-read +can be re-read. @item -P -List current Readline function names and bindings +List current Readline function names and bindings. @item -v Display Readline variable names and values in such a way that they -can be re-read +can be re-read. @item -V -List current Readline variable names and values +List current Readline variable names and values. @item -s Display Readline key sequences bound to macros and the strings they output -in such a way that they can be re-read +in such a way that they can be re-read. @item -S -Display Readline key sequences bound to macros and the strings they output +Display Readline key sequences bound to macros and the strings they output. @item -f @var{filename} -Read key bindings from @var{filename} +Read key bindings from @var{filename}. -@item -q -Query about which keys invoke the named @var{function} +@item -q @var{function} +Query about which keys invoke the named @var{function}. + +@item -u @var{function} +Unbind all keys bound to the named @var{function}. @item -r @var{keyseq} -Remove any current binding for @var{keyseq} +Remove any current binding for @var{keyseq}. @end table +@noindent +The return status is zero unless an invalid option is supplied or an +error occurs. + @item builtin @btindex builtin @example builtin [@var{shell-builtin} [@var{args}]] @end example -Run a shell builtin. This is useful when you wish to define a -shell function with the same name as a shell builtin, but need the -functionality of the builtin within the function itself. +Run a shell builtin, passing it @var{args}, and return its exit status. +This is useful when defining a shell function with the same +name as a shell builtin, retaining the functionality of the builtin within +the function. +The return status is non-zero if @var{shell-builtin} is not a shell +builtin command. @item command @btindex command @example -command [-pVv] @var{command} [@var{args} @dots{}] +command [-pVv] @var{command} [@var{arguments} @dots{}] @end example -Runs @var{command} with @var{arg} ignoring shell functions. If -you have a shell function called @code{ls}, and you wish to call -the command @code{ls}, you can say @samp{command ls}. The -@samp{-p} option means to use a default value for @code{$PATH} +Runs @var{command} with @var{arguments} ignoring any shell function +named @var{command}. +Only shell builtin commands or commands found by searching the +@code{PATH} are executed. +If there is a shell function named @code{ls}, running @samp{command ls} +within the function will execute the external command @code{ls} +instead of calling the function recursively. +The @samp{-p} option means to use a default value for @code{$PATH} that is guaranteed to find all of the standard utilities. +The return status in this case is 127 if @var{command} cannot be +found or an error occurred, and the exit status of @var{command} +otherwise. If either the @samp{-V} or @samp{-v} option is supplied, a description of @var{command} is printed. The @samp{-v} option causes a single word indicating the command or file name used to -invoke @var{command} to be printed; the @samp{-V} option produces -a more verbose description. +invoke @var{command} to be displayed; the @samp{-V} option produces +a more verbose description. In this case, the return status is +zero if @var{command} is found, and non-zero if not. @item declare @btindex declare @@ -3244,30 +3503,40 @@ performed when the variable is assigned a value. @item -r Make @var{name}s readonly. These names cannot then be assigned values -by subsequent assignment statements. +by subsequent assignment statements or unset. @item -x Mark each @var{name} for export to subsequent commands via the environment. @end table -Using @samp{+} -instead of @samp{-} turns off the attribute instead. When used in -a function, @code{declare} makes each @var{name} local, as with the -@code{local} command. +Using @samp{+} instead of @samp{-} turns off the attribute instead. +When used in a function, @code{declare} makes each @var{name} local, +as with the @code{local} command. + +The return status is zero unless an invalid option is encountered, +an attempt is made to define a function using @code{-f foo=bar}, +an attempt is made to assign a value to a readonly variable, +an attempt is made to assign a value to an array variable without +using the compound assignment syntax (@pxref{Arrays}), +one of the @var{names} is not a valid shell variable name, +an attempt is made to turn off readonly status for a readonly variable, +an attempt is made to turn off array status for an array variable, +or an attempt is made to display a non-existent function with @samp{-f}. @item echo @btindex echo @example -echo [-neE] [arg @dots{}] +echo [-neE] [@var{arg} @dots{}] @end example -Output the @code{arg}s, separated by spaces, terminated with a -newline. The return status is always 0. If @samp{-n} is -specified, the trailing newline is suppressed. If the @samp{-e} -option is given, interpretation of the following backslash-escaped -characters is enabled. The @samp{-E} option disables the interpretation -of these escape characters, even on systems where they are interpreted -by default. +Output the @var{arg}s, separated by spaces, terminated with a +newline. +The return status is always 0. +If @samp{-n} is specified, the trailing newline is suppressed. +If the @samp{-e} option is given, interpretation of the following +backslash-escaped characters is enabled. +The @samp{-E} option disables the interpretation of these escape characters, +even on systems where they are interpreted by default. @code{echo} interprets the following escape sequences: @table @code @item \a @@ -3290,8 +3559,12 @@ horizontal tab vertical tab @item \\ backslash -@item \nnn -the character whose ASCII code is @code{nnn} (octal) +@item \@var{nnn} +the character whose @code{ASCII} code is the octal value @var{nnn} +(one to three digits) +@item \x@var{nnn} +the character whose @code{ASCII} code is the hexadecimal value @var{nnn} +(one to three digits) @end table @item enable @@ -3299,8 +3572,10 @@ the character whose ASCII code is @code{nnn} (octal) @example enable [-n] [-p] [-f @var{filename}] [-ads] [@var{name} @dots{}] @end example -Enable and disable builtin shell commands. This allows you to -use a disk command which has the same name as a shell builtin. +Enable and disable builtin shell commands. +Disabling a builtin allows a disk command which has the same name +as a shell builtin to be executed with specifying a full pathname, +even though the shell normally searches for builtins before disk commands. If @samp{-n} is used, the @var{name}s become disabled. Otherwise @var{name}s are enabled. For example, to use the @code{test} binary found via @code{$PATH} instead of the shell builtin version, type @@ -3315,31 +3590,48 @@ each builtin with an indication of whether or not it is enabled. The @samp{-f} option means to load the new builtin command @var{name} from shared object @var{filename}, on systems that support dynamic loading. The @samp{-d} option will delete a builtin loaded with @samp{-f}. + If there are no options, a list of the shell builtins is displayed. -The @samp{-s} option restricts @code{enable} to the @sc{POSIX.2} special +The @samp{-s} option restricts @code{enable} to the @sc{POSIX} special builtins. If @samp{-s} is used with @samp{-f}, the new builtin becomes a special builtin. +The return status is zero unless a @var{name} is not a shell builtin +or there is an error loading a new builtin from a shared object. + @item help @btindex help @example help [@var{pattern}] @end example -Display helpful information about builtin commands. If -@var{pattern} is specified, @code{help} gives detailed help +Display helpful information about builtin commands. +If @var{pattern} is specified, @code{help} gives detailed help on all commands matching @var{pattern}, otherwise a list of -the builtins is printed. +the builtins is printed. The return status is zero unless no +command matches @var{pattern}. + +@item let +@btindex let +@example +let @var{expression} [@var{expression}] +@end example +The @code{let} builtin allows arithmetic to be performed on shell +variables. Each @var{expression} is evaluated according to the +rules given below in @ref{Shell Arithmetic}. If the +last @var{expression} evaluates to 0, @code{let} returns 1; +otherwise 0 is returned. @item local @btindex local @example local @var{name}[=@var{value}] @end example -For each argument, create a local variable called @var{name}, and -give it @var{value}. +For each argument, a local variable named @var{name} is created, +and assigned @var{value}. @code{local} can only be used within a function; it makes the variable @var{name} have a visible scope restricted to that function and its -children. +children. The return status is zero unless @code{local} is used outside +a function or an invalid @var{name} is supplied. @item logout @btindex logout @@ -3349,20 +3641,45 @@ logout [@var{n}] Exit a login shell, returning a status of @var{n} to the shell's parent. +@item printf +@btindex printf +@example +@code{printf} @var{format} [@var{arguments}] +@end example +Write the formatted @var{arguments} to the standard output under the +control of the @var{format}. +The @var{format} is a character string which contains three types of objects: +plain characters, which are simply copied to standard output, character +escape sequences, which are converted and copied to the standard output, and +format specifications, each of which causes printing of the next successive +@var{argument}. +In addition to the standard @code{printf(1)} formats, @samp{%b} causes +@code{printf} to expand backslash escape sequences in the corresponding +@var{argument}, and @samp{%q} causes @code{printf} to output the +corresponding @var{argument} in a format that can be reused as shell input. + +The @var{format} is reused as necessary to consume all of the @var{arguments}. +If the @var{format} requires more @var{arguments} than are supplied, the +extra format specifications behave as if a zero value or null string, as +appropriate, had been supplied. + @item read @btindex read @example read [-a @var{aname}] [-p @var{prompt}] [-er] [@var{name} @dots{}] @end example One line is read from the standard input, and the first word -is assigned to the first -@var{name}, the second word to the second @var{name}, -and so on, with leftover words assigned to the last @var{name}. -Only the characters in the value of the @code{IFS} variable -are recognized as word delimiters. If no names -are supplied, the line read is assigned to the variable @code{REPLY}. -The return code is zero, unless end-of-file is encountered. Options, -if supplied, have the following meanings: +is assigned to the first @var{name}, the second word to the second @var{name}, +and so on, with leftover words and their intervening separators assigned +to the last @var{name}. +If there are fewer words read from the standard input than names, +the remaining names are assigned empty values. +The characters in the value of the @code{IFS} variable +are used to split the line into words. +If no names are supplied, the line read is assigned to the +variable @code{REPLY}. +The return code is zero, unless end-of-file is encountered. +Options, if supplied, have the following meanings: @table @code @item -r @@ -3370,13 +3687,15 @@ If this option is given, a backslash-newline pair is not ignored, and the backslash is considered to be part of the line. @item -p @var{prompt} -Display @code{prompt}, without a +Display @var{prompt}, without a trailing newline, before attempting to read any input. The prompt is displayed only if input is coming from a terminal. @item -a @var{aname} -The words are assigned to -sequential indices of the array variable @var{aname}, starting at 0. +The words are assigned to sequential indices of the array variable +@var{aname}, starting at 0. +All elements are removed from @var{aname} before the assignment. +Other @var{name} arguments are ignored. @item -e Readline (@pxref{Command Line Editing}) @@ -3389,14 +3708,15 @@ is used to obtain the line. shopt [-pqsu] [-o] [@var{optname} @dots{}] @end example Toggle the values of variables controlling optional shell behavior. -With no options, or with the @samp{-p} -option, a list of all settable options is displayed, with -an indication of whether or not each is set. Other options have -the following meanings: +With no options, or with the @samp{-p} option, a list of all settable +options is displayed, with an indication of whether or not each is set. +The @samp{-p} option causes output to be displayed in a form that +may be reused as input. +Other options have the following meanings: @table @code @item -s -Enable (set) each @var{optname} +Enable (set) each @var{optname}. @item -u Disable (unset) each @var{optname}. @@ -3414,8 +3734,7 @@ Restricts the values of @code{set} builtin (@pxref{The Set Builtin}). @end table -If either of -@samp{-s} or @samp{-u} +If either @samp{-s} or @samp{-u} is used with no @var{optname} arguments, the display is limited to those options which are set or unset, respectively. @@ -3424,7 +3743,7 @@ by default. The return status when listing options is zero if all @var{optnames} are enabled, non-zero otherwise. When setting or unsetting options, -the return status is zero unless an @var{optname} is not a legal shell +the return status is zero unless an @var{optname} is not a valid shell option. The list of @code{shopt} options is: @@ -3470,6 +3789,15 @@ it cannot execute the file specified as an argument to the @code{exec} builtin command. An interactive shell does not exit if @code{exec} fails. +@item expand_aliases +If set, aliases are expanded as described below< under Aliases +(@pxref{Aliases}). +This option is enabled by default for interactive shells. + +@item extglob +If set, the extended pattern matching features described above +(@pxref{Pattern Matching}) are enabled. + @item histappend If set, the history list is appended to the file named by the value of the @code{HISTFILE} @@ -3488,10 +3816,14 @@ the Readline editing buffer, allowing further modification. @item hostcomplete If set, and Readline is being used, Bash will attempt to perform -hostname completion when a word beginning with @samp{@@} is being +hostname completion when a word containing a @samp{@@} is being completed (@pxref{Commands For Completion}). This option is enabled by default. +@item huponexit +If set, Bash will send @code{SIGHUP} to all jobs when an interactive +login shell exits (@pxref{Signals}). + @item interactive_comments Allow a word beginning with @samp{#} to cause that word and all remaining characters on that @@ -3508,6 +3840,10 @@ If set, and a file that Bash is checking for mail has been accessed since the last time it was checked, the message @code{"The mail in @var{mailfile} has been read"} is displayed. +@item nocaseglob +If set, Bash matches filenames in a case-insensitive fashion when +performing filename expansion. + @item nullglob If set, Bash allows filename patterns which match no files to expand to a null string, rather than themselves. @@ -3525,18 +3861,31 @@ number of positional parameters. @item sourcepath If set, the @code{source} builtin uses the value of @code{PATH} to find the directory containing the file supplied as an argument. -This is enabled by default. +This option is enabled by default. @end table +@noindent +The return status when listing options is zero if all @var{optnames} +are enabled, non-zero otherwise. +When setting or unsetting options, the return status is zero unless an +@var{optname} is not a valid shell option. + +@item source +@btindex source +@example +source @var{filename} +@end example +A synonym for @code{.} (@pxref{Bourne Shell Builtins}). + @item type @btindex type @example -type [-all] [-type | -path] [@var{name} @dots{}] +type [-atp] [@var{name} @dots{}] @end example For each @var{name}, indicate how it would be interpreted if used as a command name. -If the @samp{-type} flag is used, @code{type} returns a single word +If the @samp{-t} option is used, @code{type} prints a single word which is one of @samp{alias}, @samp{function}, @samp{builtin}, @samp{file} or @samp{keyword}, if @var{name} is an alias, shell function, shell builtin, @@ -3544,16 +3893,26 @@ disk file, or shell reserved word, respectively. If the @var{name} is not found, then nothing is printed, and @code{type} returns a failure status. -If the @samp{-path} flag is used, @code{type} either returns the name -of the disk file that would be executed, or nothing if @samp{-type} +If the @samp{-p} option is used, @code{type} either returns the name +of the disk file that would be executed, or nothing if @samp{-t} would not return @samp{file}. -If the @samp{-all} flag is used, returns all of the places that contain -an executable named @var{file}. This includes aliases and functions, -if and only if the @samp{-path} flag is not also used. +If the @samp{-a} option is used, @code{type} returns all of the places +that contain an executable named @var{file}. +This includes aliases and functions, if and only if the @samp{-p} option +is not also used. -@code{type} accepts @samp{-a}, @samp{-t}, and @samp{-p} as equivalent to -@samp{-all}, @samp{-type}, and @samp{-path}, respectively. +The return status is zero if any of the @var{names} are found, non-zero +if none are found. + +@item typeset +@btindex typeset +@example +typeset [-afFrxi] [-p] [@var{name}[=@var{value}]] +@end example +The @code{typeset} command is supplied for compatibility with the Korn +shell; however, it has been deprecated in favor of the @code{declare} +builtin command. @item ulimit @btindex ulimit @@ -3565,46 +3924,46 @@ started by the shell, on systems that allow such control. If an option is given, it is interpreted as follows: @table @code @item -S -change and report the soft limit associated with a resource. +Change and report the soft limit associated with a resource. @item -H -change and report the hard limit associated with a resource. +Change and report the hard limit associated with a resource. @item -a -all current limits are reported. +All current limits are reported. @item -c -the maximum size of core files created. +The maximum size of core files created. @item -d -the maximum size of a process's data segment. +The maximum size of a process's data segment. @item -f -the maximum size of files created by the shell. +The maximum size of files created by the shell. @item -l The maximum size that may be locked into memory. @item -m -the maximum resident set size. +The maximum resident set size. @item -n -the maximum number of open file descriptors. +The maximum number of open file descriptors. @item -p -the pipe buffer size. +The pipe buffer size. @item -s -the maximum stack size. +The maximum stack size. @item -t -the maximum amount of cpu time in seconds. +The maximum amount of cpu time in seconds. @item -u -the maximum number of processes available to a single user. +The maximum number of processes available to a single user. @item -v -the maximum amount of virtual memory available to the process. +The maximum amount of virtual memory available to the process. @end table @@ -3618,20 +3977,31 @@ increments, except for @samp{-t}, which is in seconds, @samp{-p}, which is in units of 512-byte blocks, and @samp{-n} and @samp{-u}, which are unscaled values. +The return status is zero unless an invalid option is supplied, a +non-numeric argument other than @code{unlimited} is supplied as a +@var{limit}, or an error occurs while setting a new limit. + @end table @node The Set Builtin @section The Set Builtin -This builtin is so overloaded that it deserves its own section. +This builtin is so complicated that it deserves its own section. @table @code @item set @btindex set @example -set [-abefhkmnptuvxdBCHP] [-o @var{option}] [@var{argument} @dots{}] +set [--abefhkmnptuvxBCHP] [-o @var{option}] [@var{argument} @dots{}] @end example +If no options or arguments are supplied, @code{set} displays the names +and values of all shell variables and functions, sorted according to the +current locale, in a format that may be reused as input. + +When options are supplied, they set or unset shell attributes. +Options, if specified, have the following meanings: + @table @code @item -a Mark variables which are modified or created for export. @@ -3641,13 +4011,18 @@ Cause the status of terminated background jobs to be reported immediately, rather than before printing the next primary prompt. @item -e -Exit immediately if a simple command exits with a non-zero status. +Exit immediately if a simple command (@pxref{Simple Commands}) exits +with a non-zero status, unless the command that fails is part of an +@code{until} or @code{while} loop, part of an @code{if} statement, +part of a @code{&&} or @code{||} list, or if the command's return +status is being inverted using @code{!}. @item -f Disable file name generation (globbing). @item -h Locate and remember (hash) commands as they are looked up for execution. +This option is enabled by default. @item -k All arguments in the form of assignment statements are placed @@ -3658,89 +4033,94 @@ the command name. Job control is enabled (@pxref{Job Control}). @item -n -Read commands but do not execute them. +Read commands but do not execute them; this may be used to check a +script for syntax errors. +This option is ignored by interactive shells. @item -o @var{option-name} -Set the flag corresponding to @var{option-name}: +Set the option corresponding to @var{option-name}: @table @code @item allexport -same as @code{-a}. +Same as @code{-a}. @item braceexpand -same as @code{-B}. +Same as @code{-B}. @item emacs -use an @code{emacs}-style line editing interface (@pxref{Command Line Editing}). +Use an @code{emacs}-style line editing interface (@pxref{Command Line Editing}). @item errexit -same as @code{-e}. +Same as @code{-e}. @item hashall -same as @code{-h}. +Same as @code{-h}. @item histexpand -same as @code{-H}. +Same as @code{-H}. @item history Enable command history, as described in @ref{Bash History Facilities}. This option is on by default in interactive shells. @item ignoreeof -the shell will not exit upon reading EOF. +An interactive shell will not exit upon reading EOF. @item keyword -same as @code{-k}. +Same as @code{-k}. @item monitor -same as @code{-m}. +Same as @code{-m}. @item noclobber -same as @code{-C}. +Same as @code{-C}. @item noexec -same as @code{-n}. +Same as @code{-n}. @item noglob -same as @code{-f}. +Same as @code{-f}. @item notify -same as @code{-b}. +Same as @code{-b}. @item nounset -same as @code{-u}. +Same as @code{-u}. @item onecmd -same as @code{-t}. +Same as @code{-t}. @item physical -same as @code{-P}. +Same as @code{-P}. @item posix -change the behavior of Bash where the default operation differs -from the @sc{POSIX} 1003.2 standard to match the standard. This -is intended to make Bash behave as a strict superset of that +Change the behavior of Bash where the default operation differs +from the @sc{POSIX} 1003.2 standard to match the standard +(@pxref{Bash POSIX Mode}). +This is intended to make Bash behave as a strict superset of that standard. @item privileged -same as @code{-p}. +Same as @code{-p}. @item verbose -same as @code{-v}. +Same as @code{-v}. @item vi -use a @code{vi}-style line editing interface. +Use a @code{vi}-style line editing interface. @item xtrace -same as @code{-x}. +Same as @code{-x}. @end table @item -p Turn on privileged mode. -In this mode, the @code{$BASH_ENV} -file is not processed, and shell functions -are not inherited from the environment. This is enabled automatically +In this mode, the @code{$BASH_ENV} and @code{$ENV} files are not +processed, shell functions are not inherited from the environment, +and the @code{SHELLOPTS} variable, if it appears in the environment, +is ignored. +This is enabled automatically on startup if the effective user (group) id is not equal to the real user (group) id. Turning this option off causes the effective user and group ids to be set to the real user and group ids. @@ -3749,24 +4129,28 @@ and group ids to be set to the real user and group ids. Exit after reading and executing one command. @item -u -Treat unset variables as an error when substituting. +Treat unset variables as an error when performing parameter expansion. +An error message will be written to the standard error, and a non-interactive +shell will exit. @item -v Print shell input lines as they are read. @item -x -Print commands and their arguments as they are executed. +Print a trace of simple commands and their arguments after they are +expanded and before they are executed. @item -B The shell will perform brace expansion (@pxref{Brace Expansion}). This option is on by default. @item -C -Disallow output redirection to existing files. +Prevent output redirection using @samp{>}, @samp{>&}, and @samp{<>} +from overwriting existing files. @item -H Enable @samp{!} style history substitution (@pxref{History Interaction}). -This flag is on by default for interactive shells. +This option is on by default for interactive shells. @item -P If set, do not follow symbolic links when performing commands such as @@ -3775,7 +4159,8 @@ is used instead. By default, Bash follows the logical chain of directories when performing commands which change the current directory. -For example, if @file{/usr/sys} is a link to @file{/usr/local/sys} then: +For example, if @file{/usr/sys} is a symbolic link to @file{/usr/local/sys} +then: @example $ cd /usr/sys; echo $PWD /usr/sys @@ -3793,7 +4178,7 @@ $ cd ..; pwd @end example @item -- -If no arguments follow this flag, then the positional parameters are +If no arguments follow this option, then the positional parameters are unset. Otherwise, the positional parameters are set to the @var{arguments}, even if some of them begin with a @samp{-}. @@ -3804,29 +4189,34 @@ and @samp{-v} options are turned off. If there are no arguments, the positional parameters remain unchanged. @end table -Using @samp{+} rather than @samp{-} causes these flags to be -turned off. The flags can also be used upon invocation of the -shell. The current set of flags may be found in @code{$-}. +Using @samp{+} rather than @samp{-} causes these options to be +turned off. The options can also be used upon invocation of the +shell. The current set of options may be found in @code{$-}. The remaining N @var{arguments} are positional parameters and are -assigned, in order, to @code{$1}, @code{$2}, @dots{} @code{$N}. If -no arguments are given, all shell variables are printed. +assigned, in order, to @code{$1}, @code{$2}, @dots{} @code{$N}. +The special parameter @code{#} is set to N. + +The return status is always zero unless an invalid option is supplied. @end table @node Bash Conditional Expressions @section Bash Conditional Expressions @cindex expressions, conditional -Conditional expressions are used by the @code{test} and @code{[} builtins. +Conditional expressions are used by the @code{[[} compound command +and the @code{test} and @code{[} builtin commands. -Expressions may be unary or binary. Unary -expressions are often used to examine the status of a file. There -are string operators and numeric comparison operators as well. Each -operator and operand must be a separate argument. If @var{file} -is of the form @file{/dev/fd/@var{N}}, then file descriptor @var{N} is -checked. Expressions are composed of the following primaries: +Expressions may be unary or binary. +Unary expressions are often used to examine the status of a file. +There are string operators and numeric comparison operators as well. +If any @var{file} argument to one of the primaries is of the form +@file{/dev/fd/@var{N}}, then file descriptor @var{N} is checked. @table @code +@item -a @var{file} +True if @var{file} exists. + @item -b @var{file} True if @var{file} exists and is a block special file. @@ -3843,16 +4233,13 @@ True if @var{file} exists. True if @var{file} exists and is a regular file. @item -g @var{file} -True if @var{file} exists and is set-group-id. +True if @var{file} exists and its set-group-id bit is set. @item -k @var{file} -True if @var{file} has its "sticky" bit set. - -@item -L @var{file} -True if @var{file} exists and is a symbolic link. +True if @var{file} exists and its "sticky" bit is set. @item -p @var{file} -True if @var{file} exists and is a named pipe. +True if @var{file} exists and is a named pipe (FIFO). @item -r @var{file} True if @var{file} exists and is readable. @@ -3860,11 +4247,8 @@ True if @var{file} exists and is readable. @item -s @var{file} True if @var{file} exists and has a size greater than zero. -@item -S @var{file} -True if @var{file} exists and is a socket. - @item -t @var{fd} -True if @var{fd} is opened on a terminal. +True if file descriptor @var{fd} is open and refers to a terminal. @item -u @var{file} True if @var{file} exists and its set-user-id bit is set. @@ -3881,6 +4265,15 @@ True if @var{file} exists and is owned by the effective user id. @item -G @var{file} True if @var{file} exists and is owned by the effective group id. +@item -L @var{file} +True if @var{file} exists and is a symbolic link. + +@item -S @var{file} +True if @var{file} exists and is a socket. + +@item -N @var{file} +True if @var{file} exists and has been modified since it was last read. + @item @var{file1} -nt @var{file2} True if @var{file1} is newer (according to modification date) than @var{file2}. @@ -3904,27 +4297,20 @@ True if the length of @var{string} is zero. @itemx @var{string} True if the length of @var{string} is non-zero. -@item @var{string1} = @var{string2} -True if the strings are equal. @samp{==} may be used in place of -@samp{=}. +@item @var{string1} == @var{string2} +True if the strings are equal. +@samp{=} may be used in place of @samp{==}. @item @var{string1} != @var{string2} True if the strings are not equal. @item @var{string1} < @var{string2} -True if @var{string1} sorts before @var{string2} lexicographically. +True if @var{string1} sorts before @var{string2} lexicographically +in the current locale. @item @var{string1} > @var{string2} -True if @var{string1} sorts after @var{string2} lexicographically. - -@item ! @var{expr} -True if @var{expr} is false. - -@item @var{expr1} -a @var{expr2} -True if both @var{expr1} and @var{expr2} are true. - -@item @var{expr1} -o @var{expr2} -True if either @var{expr1} and @var{expr2} is true. +True if @var{string1} sorts after @var{string2} lexicographically +in the current locale. @item @var{arg1} OP @var{arg2} @code{OP} is one of @@ -3937,43 +4323,6 @@ may be positive or negative integers. @end table -The Bash @code{test} and @code{[} builtins evaluate conditional -expressions using a set of rules based on the number of arguments. -These are the rules: - -@table @asis -@item 0 arguments -The expression is false. -@item 1 argument -The expression is true if and only if the argument is not null. -@item 2 arguments -If the first argument is @samp{!}, the expression is true if and -only if the second argument is null. If the first argument is -one of the listed unary operators, the expression is true if the -unary test is true. If the first argument is not a legal unary -operator, the expression is false. -@item 3 arguments -If the first argument is @samp{!}, the value is the negation of -the two-argument test using the second and third arguments. -If the second argument is one of the binary operators, the result -of the expression is the result of the binary test using the first -and third arguments as operands. -If the first argument is exactly @samp{(} and the third argument is -exactly @samp{)}, the result is the one-argument test of the second -argument. -Otherwise, the expression is false. -The @samp{-a} and @samp{-o} operators are considered binary operators -in this case. -@item 4 arguments -If the first argument is @samp{!}, the result is the negation of -the three-argument expression composed of the remaining arguments. -Otherwise, the expression is parsed and evaluated according to -precedence. @samp{-a} has a higher precedence than @samp{-o}. -@item 5 or more arguments -The expression is parsed and evaluated according to precedence, -with @samp{-a} having a higher precedence than @samp{-o}. -@end table - @node Bash Variables @section Bash Variables @@ -3982,56 +4331,101 @@ do not normally treat them specially. @vtable @code +@item BASH +The full pathname used to execute the current instance of Bash. + @item BASH_ENV If this variable is set when Bash is invoked to execute a shell script, its value is expanded and used as the name of a startup file to read before executing the script. @xref{Bash Startup Files}. -@item TIMEFORMAT -The value of this parameter is used as a format string specifying -how the timing information for pipelines prefixed with the @code{time} -reserved word should be displayed. -The @samp{%} character introduces an -escape sequence that is expanded to a time value or other -information. -The escape sequences and their meanings are as -follows; the braces denote optional portions. +@item BASH_VERSION +The version number of the current instance of Bash. + +@item BASH_VERSINFO +A readonly array variable whose members hold version information for +this instance of Bash. +The values assigned to the array members are as follows: @table @code -@item %% -A literal @samp{%}. +@item BASH_VERSINFO[0] +The major version number (the @var{release}). -@item %[@var{p}][l]R -The elapsed time in seconds. +@item BASH_VERSINFO[1] +The minor version number (the @var{version}). -@item %[@var{p}][l]U -The number of CPU seconds spent in user mode. +@item BASH_VERSINFO[2] +The patch level. -@item %[@var{p}][l]S -The number of CPU seconds spent in system mode. +@item BASH_VERSINFO[3] +The build version. + +@item BASH_VERSINFO[4] +The release status (e.g., @var{beta1}). + +@item BASH_VERSINFO[5] +The value of @code{MACHTYPE}. -@item %P -The CPU percentage, computed as (%U + %S) / %R. @end table -The optional @var{p} is a digit specifying the precision, the number of -fractional digits after a decimal point. -A value of 0 causes no decimal point or fraction to be output. -At most three places after the decimal point may be specified; values -of @var{p} greater than 3 are changed to 3. -If @var{p} is not specified, the value 3 is used. +@item DIRSTACK +An array variable (@pxref{Arrays}) +containing the current contents of the directory stack. +Directories appear in the stack in the order they are displayed by the +@code{dirs} builtin. +Assigning to members of this array variable may be used to modify +directories already in the stack, but the @code{pushd} and @code{popd} +builtins must be used to add and remove directories. +Assignment to this variable will not change the current directory. +If @code{DIRSTACK} is unset, it loses its special properties, even if +it is subsequently reset. -The optional @code{l} specifies a longer format, including minutes, of -the form @var{MM}m@var{SS}.@var{FF}s. -The value of @var{p} determines whether or not the fraction is included. +@item EUID +The numeric effective user id of the current user. This variable +is readonly. -If this variable is not set, bash acts as if it had the value -@example -@code{$'\nreal\t%3lR\nuser\t%3lU\nsys\t%3lS'}. -@end example -If the value is null, no timing information is displayed. -A trailing newline is added when the format string is displayed. +@item FCEDIT +The editor used as a default by the @samp{-e} option to the @code{fc} +builtin command. + +@item FIGNORE +A colon-separated list of suffixes to ignore when performing +filename completion. +A file name whose suffix matches one of the entries in +@code{FIGNORE} +is excluded from the list of matched file names. A sample +value is @samp{.o:~} + +@item GLOBIGNORE +A colon-separated list of patterns defining the set of filenames to +be ignored by filename expansion. +If a filename matched by a filename expansion pattern also matches one +of the patterns in @code{GLOBIGNORE}, it is removed from the list +of matches. + +@item GROUPS +An array variable containing the list of groups of which the current +user is a member. This variable is readonly. + +@item histchars +Up to three characters which control history expansion, quick +substitution, and tokenization (@pxref{History Interaction}). +The first character is the +@dfn{history-expansion-char}, that is, the character which signifies the +start of a history expansion, normally @samp{!}. The second character is the +character which signifies `quick substitution' when seen as the first +character on a line, normally @samp{^}. The optional third character is the +character which indicates that the remainder of the line is a comment when +found as the first character of a word, usually @samp{#}. The history +comment character causes history substitution to be skipped for the +remaining words on the line. It does not necessarily cause the shell +parser to treat the rest of the line as a comment. + +@item HISTCMD +The history number, or index in the history list, of the current +command. If @code{HISTCMD} is unset, it loses its special properties, +even if it is subsequently reset. @item HISTCONTROL Set to a value of @samp{ignorespace}, it means don't enter lines which @@ -4040,6 +4434,9 @@ of @samp{ignoredups}, it means don't enter lines which match the last entered line. A value of @samp{ignoreboth} combines the two options. Unset, or set to any other value than those above, means to save all lines on the history list. +The second and subsequent lines of a multi-line compound command are +not tested, and are added to the history regardless of the value of +@code{HISTCONTROL}. @item HISTIGNORE A colon-separated list of patterns used to decide which command @@ -4051,6 +4448,9 @@ are applied. In addition to the normal shell pattern matching characters, @samp{&} matches the previous history line. @samp{&} may be escaped using a backslash. The backslash is removed before attempting a match. +The second and subsequent lines of a multi-line compound command are +not tested, and are added to the history regardless of the value of +@code{HISTIGNORE}. @code{HISTIGNORE} subsumes the function of @code{HISTCONTROL}. A pattern of @samp{&} is identical to @code{ignoredups}, and a @@ -4063,8 +4463,8 @@ The name of the file to which the command history is saved. The default is @file{~/.bash_history}. @item HISTSIZE -If set, this is the maximum number of commands to remember in the -history. +The maximum number of commands to remember on the history list. +The default value is 500. @item HISTFILESIZE The maximum number of lines contained in the history file. When this @@ -4073,25 +4473,6 @@ necessary, to contain no more than that number of lines. The default value is 500. The history file is also truncated to this size after writing it when an interactive shell exits. -@item histchars -Up to three characters which control history expansion, quick -substitution, and tokenization (@pxref{History Interaction}). -The first character is the -@dfn{history-expansion-char}, that is, the character which signifies the -start of a history expansion, normally @samp{!}. The second character is the -character which signifies `quick substitution' when seen as the first -character on a line, normally @samp{^}. The optional third character is the -character which signifies the remainder of the line is a comment, when -found as the first character of a word, usually @samp{#}. The history -comment character causes history substitution to be skipped for the -remaining words on the line. It does not necessarily cause the shell -parser to treat the rest of the line as a comment. - -@item HISTCMD -The history number, or index in the history list, of the current -command. If @code{HISTCMD} is unset, it loses its special properties, -even if it is subsequently reset. - @item HOSTFILE Contains the name of a file in the same format as @file{/etc/hosts} that should be read when the shell needs to complete a hostname. You can @@ -4099,76 +4480,70 @@ change the file interactively; the next time you attempt to complete a hostname, Bash will add the contents of the new file to the already existing database. -@item MAILCHECK -How often (in seconds) that the shell should check for mail -in the files specified in @code{MAILPATH}. +@item HOSTNAME +The name of the current host. -@item PROMPT_COMMAND -If present, this contains a string which is a command to execute -before the printing of each primary prompt (@code{$PS1}). +@item HOSTTYPE +A string describing the machine Bash is running on. -@item UID -The numeric real user id of the current user. +@item IGNOREEOF +Controls the action of the shell on receipt of an @code{EOF} character +as the sole input. If set, the value denotes the number +of consecutive @code{EOF} characters that can be read as the +first character on an input line +before the shell will exit. If the variable exists but does not +have a numeric value (or has no value) then the default is 10. +If the variable does not exist, then @code{EOF} signifies the end of +input to the shell. This is only in effect for interactive shells. -@item EUID -The numeric effective user id of the current user. +@item INPUTRC +The name of the Readline startup file, overriding the default +of @file{~/.inputrc}. -@item GROUPS -An array variable containing the list of groups of which the current -user is a member. +@item LANG +Used to determine the locale category for any category not specifically +selected with a variable starting with @code{LC_}. -@item PPID -The process id of the shell's parent process. +@item LC_ALL +This variable overrides the value of @code{LANG} and any other +@code{LC_} variable specifying a locale category. -@item HOSTNAME -The name of the current host. +@item LC_COLLATE +This variable determines the collation order used when sorting the +results of filename expansion, and +determines the behavior of range expressions, equivalence classes, +and collating sequences within filename expansion and pattern matching +(@pxref{Filename Expansion}). -@item HOSTTYPE -A string describing the machine Bash is running on. +@item LC_CTYPE +This variable determines the interpretation of characters and the +behavior of character classes within filename expansion and pattern +matching (@pxref{Filename Expansion}). -@item OSTYPE -A string describing the operating system Bash is running on. +@item LC_MESSAGES +This variable determines the locale used to translate double-quoted +strings preceded by a @samp{$} (@pxref{Locale Translation}). + +@item LINENO +The line number in the script or shell function currently executing. @item MACHTYPE A string that fully describes the system type on which Bash is executing, in the standard GNU @var{cpu-company-system} format. -@item SHELLOPTS -A colon-separated list of enabled shell options. Each word in -the list is a valid argument for the @samp{-o} option to the -@code{set} builtin command (@pxref{The Set Builtin}). -The options appearing in @code{SHELLOPTS} are those reported -as @samp{on} by @samp{set -o}. -If this variable is in the environment when Bash -starts up, each shell option in the list will be enabled before -reading any startup files. This variable is readonly. +@item MAILCHECK +How often (in seconds) that the shell should check for mail in the +files specified in the @code{MAILPATH} or @code{MAIL} variables. -@item FIGNORE -A colon-separated list of suffixes to ignore when performing -filename completion. -A file name whose suffix matches one of the entries in -@code{FIGNORE} -is excluded from the list of matched file names. A sample -value is @samp{.o:~} +@item OLDPWD +The previous working directory as set by the @code{cd} builtin. -@item GLOBIGNORE -A colon-separated list of patterns defining the set of filenames to -be ignored by filename expansion. -If a filename matched by a filename expansion pattern also matches one -of the patterns in @code{GLOBIGNORE}, it is removed from the list -of matches. +@item OPTERR +If set to the value 1, Bash displays error messages +generated by the @code{getopts} builtin command. -@item DIRSTACK -An array variable (@pxref{Arrays}) -containing the current contents of the directory stack. -Directories appear in the stack in the order they are displayed by the -@code{dirs} builtin. -Assigning to members of this array variable may be used to modify -directories already in the stack, but the @code{pushd} and @code{popd} -builtins must be used to add and remove directories. -Assignment to this variable will not change the current directory. -If @code{DIRSTACK} is unset, it loses its special properties, even if -it is subsequently reset. +@item OSTYPE +A string describing the operating system Bash is running on. @item PIPESTATUS An array variable (@pxref{Arrays}) @@ -4176,94 +4551,120 @@ containing a list of exit status values from the processes in the most-recently-executed foreground pipeline (which may contain only a single command). -@item INPUTRC -The name of the Readline startup file, overriding the default -of @file{~/.inputrc}. - -@item BASH -The full filename used to execute the current instance of Bash. - -@item BASH_VERSION -The version number of the current instance of Bash. - -@item BASH_VERSINFO -An array variable whose members hold version information for this -instance of Bash. -The values assigned to the array members are as follows: +@item PPID +The process id of the shell's parent process. This variable +is readonly. -@table @code +@item PROMPT_COMMAND +If present, this contains a string which is a command to execute +before the printing of each primary prompt (@code{$PS1}). -@item BASH_VERSINFO[0] -The major version number (the @var{release}). +@item PS3 +The value of this variable is used as the prompt for the +@code{select} command. If this variable is not set, the +@code{select} command prompts with @samp{#? } -@item BASH_VERSINFO[1] -The minor version number (the @var{version}). +@item PS4 +This is the prompt printed before the command line is echoed +when the @samp{-x} option is set (@pxref{The Set Builtin}). +The first character of @code{PS4} is replicated multiple times, as +necessary, to indicate multiple levels of indirection. +The default is @samp{+ }. -@item BASH_VERSINFO[2] -The patch level. +@item PWD +The current working directory as set by the @code{cd} builtin. -@item BASH_VERSINFO[3] -The build version. +@item RANDOM +Each time this parameter is referenced, a random integer +between 0 and 32767 is generated. Assigning a value to this +variable seeds the random number generator. -@item BASH_VERSINFO[4] -The release status (e.g., @var{beta1}). +@item REPLY +The default variable for the @code{read} builtin. -@item BASH_VERSINFO[5] -The value of @code{MACHTYPE}. +@item SECONDS +This variable expands to the number of seconds since the +shell was started. Assignment to this variable resets +the count to the value assigned, and the expanded value +becomes the value assigned plus the number of seconds +since the assignment. -@end table +@item SHELLOPTS +A colon-separated list of enabled shell options. Each word in +the list is a valid argument for the @samp{-o} option to the +@code{set} builtin command (@pxref{The Set Builtin}). +The options appearing in @code{SHELLOPTS} are those reported +as @samp{on} by @samp{set -o}. +If this variable is in the environment when Bash +starts up, each shell option in the list will be enabled before +reading any startup files. This variable is readonly. @item SHLVL Incremented by one each time a new instance of Bash is started. This is intended to be a count of how deeply your Bash shells are nested. -@item OPTERR -If set to the value 1, Bash displays error messages -generated by the @code{getopts} builtin command. +@item TIMEFORMAT +The value of this parameter is used as a format string specifying +how the timing information for pipelines prefixed with the @code{time} +reserved word should be displayed. +The @samp{%} character introduces an +escape sequence that is expanded to a time value or other +information. +The escape sequences and their meanings are as +follows; the braces denote optional portions. -@item LANG -Used to determine the locale category for any category not specifically -selected with a variable starting with @code{LC_}. +@table @code -@item LC_ALL -This variable overrides the value of @code{LANG} and any other -@code{LC_} variable specifying a locale category. +@item %% +A literal @samp{%}. -@item LC_COLLATE -This variable determines the collation order used when sorting the -results of filename expansion (@pxref{Filename Expansion}). +@item %[@var{p}][l]R +The elapsed time in seconds. -@item LC_MESSAGES -This variable determines the locale used to translate double-quoted -strings preceded by a @samp{$} (@pxref{Locale Translation}). +@item %[@var{p}][l]U +The number of CPU seconds spent in user mode. -@item IGNOREEOF -Controls the action of the shell on receipt of an @code{EOF} character -as the sole input. If set, then the value of it is the number -of consecutive @code{EOF} characters that can be read as the -first character on an input line -before the shell will exit. If the variable exists but does not -have a numeric value (or has no value) then the default is 10. -If the variable does not exist, then @code{EOF} signifies the end of -input to the shell. This is only in effect for interactive shells. +@item %[@var{p}][l]S +The number of CPU seconds spent in system mode. + +@item %P +The CPU percentage, computed as (%U + %S) / %R. +@end table + +The optional @var{p} is a digit specifying the precision, the number of +fractional digits after a decimal point. +A value of 0 causes no decimal point or fraction to be output. +At most three places after the decimal point may be specified; values +of @var{p} greater than 3 are changed to 3. +If @var{p} is not specified, the value 3 is used. + +The optional @code{l} specifies a longer format, including minutes, of +the form @var{MM}m@var{SS}.@var{FF}s. +The value of @var{p} determines whether or not the fraction is included. + +If this variable is not set, Bash acts as if it had the value +@example +@code{$'\nreal\t%3lR\nuser\t%3lU\nsys\t%3lS'} +@end example +If the value is null, no timing information is displayed. +A trailing newline is added when the format string is displayed. + +@item TMOUT +If set to a value greater than zero, the value is interpreted as +the number of seconds to wait for input after issuing the primary +prompt. +Bash terminates after that number of seconds if input does +not arrive. + +@item UID +The numeric real user id of the current user. This variable is readonly. @end vtable @node Shell Arithmetic @section Shell Arithmetic @cindex arithmetic, shell - -@menu -* Arithmetic Evaluation:: How shell arithmetic works. -* Arithmetic Expansion:: How to use arithmetic in shell expansions. -* Arithmetic Builtins:: Builtin commands that use shell arithmetic. -@end menu - -Bash includes several mechanisms to evaluate arithmetic expressions -and display the result or use it as part of a command. - -@node Arithmetic Evaluation -@subsection Arithmetic Evaluation +@cindex shell arithmetic @cindex expressions, arithmetic @cindex evaluation, arithmetic @cindex arithmetic evaluation @@ -4284,6 +4685,9 @@ unary minus and plus @item ! ~ logical and bitwise negation +@item ** +exponentiation + @item * / % multiplication, division, remainder @@ -4343,43 +4747,95 @@ Operators are evaluated in order of precedence. Sub-expressions in parentheses are evaluated first and may override the precedence rules above. -@node Arithmetic Expansion -@subsection Arithmetic Expansion -@cindex expansion, arithmetic -@cindex arithmetic expansion +@node Aliases +@section Aliases +@cindex alias expansion -Arithmetic expansion allows the evaluation of an arithmetic expression -and the substitution of the result. The format for arithmetic expansion is: +@menu +* Alias Builtins:: Builtins commands to maniuplate aliases. +@end menu -@example -$(( @var{expression} )) -@end example +Aliases allow a string to be substituted for a word when it is used +as the first word of a simple command. +The shell maintains a list of @var{aliases} +that may be set and unset with the @code{alias} and +@code{unalias} builtin commands. -The expression is treated as if it were within double quotes, but -a double quote inside the braces or parentheses is not treated -specially. All tokens in the expression undergo parameter -expansion, command substitution, and quote removal. Arithmetic -substitutions may be nested. +The first word of each simple command, if unquoted, is checked to see +if it has an alias. +If so, that word is replaced by the text of the alias. +The alias name and the replacement text may contain any valid +shell input, including shell metacharacters, with the exception +that the alias name may not contain @samp{=}. +The first word of the replacement text is tested for +aliases, but a word that is identical to an alias being expanded +is not expanded a second time. This means that one may alias +@code{ls} to @code{"ls -F"}, +for instance, and Bash does not try to recursively expand the +replacement text. If the last character of the alias value is a +space or tab character, then the next command word following the +alias is also checked for alias expansion. + +Aliases are created and listed with the @code{alias} +command, and removed with the @code{unalias} command. + +There is no mechanism for using arguments in the replacement text, +as in @code{csh}. +If arguments are needed, a shell function should be used +(@pxref{Shell Functions}). + +Aliases are not expanded when the shell is not interactive, +unless the @code{expand_aliases} shell option is set using +@code{shopt} (@pxref{Bash Builtins}). + +The rules concerning the definition and use of aliases are +somewhat confusing. Bash +always reads at least one complete line +of input before executing any +of the commands on that line. Aliases are expanded when a +command is read, not when it is executed. Therefore, an +alias definition appearing on the same line as another +command does not take effect until the next line of input is read. +The commands following the alias definition +on that line are not affected by the new alias. +This behavior is also an issue when functions are executed. +Aliases are expanded when a function definition is read, +not when the function is executed, because a function definition +is itself a compound command. As a consequence, aliases +defined in a function are not available until after that +function is executed. To be safe, always put +alias definitions on a separate line, and do not use @code{alias} +in compound commands. -The evaluation is performed according to the rules listed above. -If the expression is invalid, Bash -prints a message indicating failure and no substitution occurs. +For almost every purpose, aliases are superseded by +shell functions. -@node Arithmetic Builtins -@subsection Arithmetic Builtins +@node Alias Builtins +@subsection Alias Builtins @table @code -@item let -@btindex let +@item alias +@btindex alias @example -let @var{expression} [@var{expression}] +alias [@code{-p}] [@var{name}[=@var{value}] @dots{}] @end example -The @code{let} builtin allows arithmetic to be performed on shell -variables. Each @var{expression} is evaluated according to the -rules given previously (@pxref{Arithmetic Evaluation}). If the -last @var{expression} evaluates to 0, @code{let} returns 1; -otherwise 0 is returned. + +Without arguments or with the @samp{-p} option, @code{alias} prints +the list of aliases on the standard output in a form that allows +them to be reused as input. +If arguments are supplied, an alias is defined for each @var{name} +whose @var{value} is given. If no @var{value} is given, the name +and value of the alias is printed. + +@item unalias +@btindex unalias +@example +unalias [-a] [@var{name} @dots{} ] +@end example + +Remove each @var{name} from the list of aliases. If @samp{-a} is +supplied, all aliases are removed. @end table @node Arrays @@ -4451,7 +4907,7 @@ Referencing an array variable without a subscript is equivalent to referencing element zero. The @code{unset} builtin is used to destroy arrays. -@code{unset} @var{name[subscript]} +@code{unset} @code{name[@var{subscript}]} destroys the array element at index @var{subscript}. @code{unset} @var{name}, where @var{name} is an array, removes the entire array. A subscript of @samp{*} or @samp{@@} also removes the @@ -4467,64 +4923,167 @@ individual array elements. The @code{set} and @code{declare} builtins display array values in a way that allows them to be reused as input. +@node The Directory Stack +@section The Directory Stack +@cindex directory stack + +The directory stack is a list of recently-visited directories. The +@code{pushd} builtin adds directories to the stack as it changes +the current directory, and the @code{popd} builtin removes specified +directories from the stack and changes the current directory to +the directory removed. The @code{dirs} builtin displays the contents +of the directory stack. + +The contents of the directory stack are also visible +as the value of the @code{DIRSTACK} shell variable. + +@table @code + +@item dirs +@btindex dirs +@example +dirs [+@var{N} | -@var{N}] [-clvp] +@end example +Display the list of currently remembered directories. Directories +are added to the list with the @code{pushd} command; the +@code{popd} command removes directories from the list. +@table @code +@item +@var{N} +Displays the @var{N}th directory (counting from the left of the +list printed by @code{dirs} when invoked without options), starting +with zero. +@item -@var{N} +Displays the @var{N}th directory (counting from the right of the +list printed by @code{dirs} when invoked without options), starting +with zero. +@item -c +Clears the directory stack by deleting all of the elements. +@item -l +Produces a longer listing; the default listing format uses a +tilde to denote the home directory. +@item -p +Causes @code{dirs} to print the directory stack with one entry per +line. +@item -v +Causes @code{dirs} to print the directory stack with one entry per +line, prefixing each entry with its index in the stack. +@end table + +@item popd +@btindex popd +@example +popd [+@var{N} | -@var{N}] [-n] +@end example + +Remove the top entry from the directory stack, and @code{cd} +to the new top directory. +When no arguments are given, @code{popd} +removes the top directory from the stack and +performs a @code{cd} to the new top directory. The +elements are numbered from 0 starting at the first directory listed with +@code{dirs}; i.e., @code{popd} is equivalent to @code{popd +0}. +@table @code +@item +@var{N} +Removes the @var{N}th directory (counting from the left of the +list printed by @code{dirs}), starting with zero. +@item -@var{N} +Removes the @var{N}th directory (counting from the right of the +list printed by @code{dirs}), starting with zero. +@item -n +Suppresses the normal change of directory when removing directories +from the stack, so that only the stack is manipulated. +@end table + +@btindex pushd +@item pushd +@example +pushd [@var{dir} | @var{+N} | @var{-N}] [-n] +@end example + +Save the current directory on the top of the directory stack +and then @code{cd} to @var{dir}. +With no arguments, @code{pushd} exchanges the top two directories. + +@table @code +@item +@var{N} +Brings the @var{N}th directory (counting from the left of the +list printed by @code{dirs}, starting with zero) to the top of +the list by rotating the stack. +@item -@var{N} +Brings the @var{N}th directory (counting from the right of the +list printed by @code{dirs}, starting with zero) to the top of +the list by rotating the stack. +@item -n +Suppresses the normal change of directory when adding directories +to the stack, so that only the stack is manipulated. +@item @var{dir} +Makes the current working directory be the top of the stack, and then +executes the equivalent of `@code{cd} @var{dir}'. +@code{cd}s to @var{dir}. +@end table + +@end table + @node Printing a Prompt @section Controlling the Prompt @cindex prompting The value of the variable @code{PROMPT_COMMAND} is examined just before Bash prints each primary prompt. If it is set and non-null, then the -value is executed just as if you had typed it on the command line. +value is executed just as if it had been typed on the command line. In addition, the following table describes the special characters which can appear in the prompt variables: @table @code @item \a -a bell character. +A bell character. @item \d -the date, in "Weekday Month Date" format (e.g., "Tue May 26"). +The date, in "Weekday Month Date" format (e.g., "Tue May 26"). @item \e -an escape character. +An escape character. @item \h -the hostname, up to the first `.'. +The hostname, up to the first `.'. @item \H -the hostname. +The hostname. @item \n -newline. +A newline. +@item \r +A carriage return. @item \s -the name of the shell, the basename of @code{$0} (the portion +The name of the shell, the basename of @code{$0} (the portion following the final slash). @item \t -the time, in 24-hour HH:MM:SS format. +The time, in 24-hour HH:MM:SS format. @item \T -the time, in 12-hour HH:MM:SS format. +The time, in 12-hour HH:MM:SS format. @item \@@ -the time, in 12-hour am/pm format. +The time, in 12-hour am/pm format. +@item \u +The username of the current user. @item \v -the version of Bash (e.g., 2.00) +The version of Bash (e.g., 2.00) @item \V -the release of Bash, version + patchlevel (e.g., 2.00.0) +The release of Bash, version + patchlevel (e.g., 2.00.0) @item \w -the current working directory. +The current working directory. @item \W -the basename of @code{$PWD}. -@item \u -your username. +The basename of @code{$PWD}. @item \! -the history number of this command. +The history number of this command. @item \# -the command number of this command. +The command number of this command. @item \$ -if the effective uid is 0, @code{#}, otherwise @code{$}. -@item \nnn -the character corresponding to the octal number @code{nnn}. +If the effective uid is 0, @code{#}, otherwise @code{$}. +@item \@var{nnn} +The character whose ASCII code is the octal value @var{nnn}. @item \\ -a backslash. +A backslash. @item \[ -begin a sequence of non-printing characters. This could be used to +Begin a sequence of non-printing characters. This could be used to embed a terminal control sequence into the prompt. @item \] -end a sequence of non-printing characters. +End a sequence of non-printing characters. @end table @node The Restricted Shell @@ -4552,6 +5111,8 @@ builtin command. @item Importing function definitions from the shell environment at startup. @item +Parsing the value of @code{SHELLOPTS} from the shell environment at startup. +@item Redirecting output using the @samp{>}, @samp{>|}, @samp{<>}, @samp{>&}, @samp{&>}, and @samp{>>} redirection operators. @item @@ -4562,7 +5123,7 @@ Adding or deleting builtin commands with the @item Specifying the @samp{-p} option to the @code{command} builtin. @item -Turning off restricted mode with @samp{set +r}. +Turning off restricted mode with @samp{set +r} or @samp{set +o restricted}. @end itemize @node Bash POSIX Mode @@ -4595,12 +5156,12 @@ Reserved words may not be aliased. @item The @sc{POSIX.2} @code{PS1} and @code{PS2} expansions of @samp{!} to the history number and @samp{!!} to @samp{!} are enabled, -and parameter expansion is performed on -the value regardless of the setting of the @code{promptvars} option. +and parameter expansion is performed on the values of @code{PS1} and +@code{PS2} regardless of the setting of the @code{promptvars} option. @item -Interactive comments are enabled by default. (Note that Bash has -them on by default anyway.) +Interactive comments are enabled by default. (Bash has them on by +default anyway.) @item The @sc{POSIX.2} startup files are executed (@code{$ENV}) rather than @@ -4623,13 +5184,17 @@ Non-interactive shells exit if @var{filename} in @code{.} @var{filename} is not found. @item +Non-interactive shells exit if a syntax error in an arithmetic expansion +results in an invalid expression. + +@item Redirection operators do not perform filename expansion on the word in the redirection unless the shell is interactive. @item Function names must be valid shell @code{name}s. That is, they may not contain characters other than letters, digits, and underscores, and -may not start with a digit. Declaring a function with an illegal name +may not start with a digit. Declaring a function with an invalid name causes a fatal syntax error in non-interactive shells. @item @@ -4650,22 +5215,30 @@ value it assigns to the @code{PWD} variable does not contain any symbolic links, as if @samp{cd -P} had been executed. @item +If @code{$CDPATH} is set, the @code{cd} builtin will not implicitly +append the current directory to it. This means that @code{cd} will +fail if no valid directory name can be constructed from +any of the entries in @code{$CDPATH}, even if the a directory with +the same name as the name given as an argument to @code{cd} exists +in the current directory. + +@item A non-interactive shell exits with an error status if a variable assignment error occurs when no command name follows the assignment statements. A variable assignment error occurs, for example, when trying to assign -a value to a read-only variable. +a value to a readonly variable. @item A non-interactive shell exits with an error status if the iteration variable in a @code{for} statement or the selection variable in a -@code{select} statement is a read-only variable. +@code{select} statement is a readonly variable. @item Process substitution is not available. @item -Assignment statements preceding @sc{POSIX.2} @code{special} builtins +Assignment statements preceding @sc{POSIX.2} special builtins persist in the shell environment after the builtin completes. @item @@ -4686,7 +5259,7 @@ builtins, not just special ones. @node Job Control @chapter Job Control -This chapter disusses what job control is, how it works, and how +This chapter discusses what job control is, how it works, and how Bash allows you to access its facilities. @menu @@ -4714,7 +5287,7 @@ by the system's terminal driver and Bash. The shell associates a @var{job} with each pipeline. It keeps a table of currently executing jobs, which may be listed with the @code{jobs} command. When Bash starts a job -asynchronously (in the background), it prints a line that looks +asynchronously, it prints a line that looks like: @example [1] 25647 @@ -4741,13 +5314,13 @@ read from (write to) the terminal are sent a @code{SIGTTIN} caught, suspends the process. If the operating system on which Bash is running supports -job control, Bash allows you to use it. Typing the +job control, Bash contains facilities to use it. Typing the @var{suspend} character (typically @samp{^Z}, Control-Z) while a process is running causes that process to be stopped and returns -you to Bash. Typing the @var{delayed suspend} character +control to Bash. Typing the @var{delayed suspend} character (typically @samp{^Y}, Control-Y) causes the process to be stopped when it attempts to read input from the terminal, and control to -be returned to Bash. You may then manipulate the state of +be returned to Bash. The user then manipulates the state of this job, using the @code{bg} command to continue it in the background, the @code{fg} command to continue it in the foreground, or the @code{kill} command to kill it. A @samp{^Z} @@ -4764,7 +5337,8 @@ other hand, refers to any job containing the string @samp{ce} in its command line. If the prefix or substring matches more than one job, Bash reports an error. The symbols @samp{%%} and @samp{%+} refer to the shell's notion of the current job, which -is the last job stopped while it was in the foreground. The +is the last job stopped while it was in the foreground or started +in the background. The previous job may be referenced using @samp{%-}. In output pertaining to jobs (e.g., the output of the @code{jobs} command), the current job is always flagged with a @samp{+}, and the @@ -4779,15 +5353,14 @@ The shell learns immediately whenever a job changes state. Normally, Bash waits until it is about to print a prompt before reporting changes in a job's status so as to not interrupt any other output. If the -the @samp{-b} option to the @code{set} builtin is set, +the @samp{-b} option to the @code{set} builtin is enabled, Bash reports such changes immediately (@pxref{The Set Builtin}). -If you attempt to exit Bash while jobs are stopped, the -shell prints a message warning you that you have stopped jobs. -You may then use the -@code{jobs} command to inspect their status. If you do this, or -try to exit again immediately, you are not warned again, and the -stopped jobs are terminated. +If an attempt to exit Bash is while jobs are stopped, the +shell prints a message warning that there are stopped jobs. +The @code{jobs} command may then be used to inspect their status. +If a second attempt to exit is made without an intervening command, +Bash does not print another warning, and the stopped jobs are terminated. @node Job Control Builtins @section Job Control Builtins @@ -4799,23 +5372,31 @@ stopped jobs are terminated. @example bg [@var{jobspec}] @end example -Place @var{jobspec} into the background, as if it had been started -with @samp{&}. If @var{jobspec} is not supplied, the current job -is used. +Resume the suspended job @var{jobspec} in the background, as if it +had been started with @samp{&}. +If @var{jobspec} is not supplied, the current job is used. +The return status is zero unless it is run when job control is not +enabled, or, when run with job control enabled, if @var{jobspec} was +not found or @var{jobspec} specifies a job that was started without +job control. @item fg @btindex fg @example fg [@var{jobspec}] @end example -Bring @var{jobspec} into the foreground and make it the current job. +Resume the job @var{jobspec} in the foreground and make it the current job. If @var{jobspec} is not supplied, the current job is used. +The return status is that of the command placed into the foreground, +or non-zero if run when job control is disabled or, when run with +job control enabled, @var{jobspec} does not specify a valid job or +@var{jobspec} specifies a job that was started without job control. @item jobs @btindex jobs @example jobs [-lpnrs] [@var{jobspec}] -jobs -x @var{command} [@var{jobspec}] +jobs -x @var{command} [@var{arguments}] @end example The first form lists the active jobs. The options have the @@ -4823,15 +5404,14 @@ following meanings: @table @code @item -l -List process @sc{ID}s in addition to the normal information +List process @sc{ID}s in addition to the normal information. @item -n Display information only about jobs that have changed status since -you were last notified of their status. +the user was last notified of their status. @item -p -List only the process @sc{ID} of the job's process group -leader. +List only the process @sc{ID} of the job's process group leader. @item -r Restrict output to running jobs. @@ -4853,16 +5433,22 @@ passing it @var{argument}s, returning its exit status. @item kill @btindex kill @example -kill [-s @var{sigspec}] [-n @var{signum}] [-@var{sigspec}] @var{jobspec} -kill -l [@var{sigspec}] +kill [-s @var{sigspec}] [-n @var{signum}] [-@var{sigspec}] @var{jobspec} or @var{pid} +kill -l [@var{exit_status}] @end example Send a signal specified by @var{sigspec} or @var{signum} to the process -named by @var{jobspec}. +named by job specification @var{jobspec} or process ID @var{pid}. @var{sigspec} is either a signal name such as @code{SIGINT} (with or without the @code{SIG} prefix) or a signal number; @var{signum} is a signal number. If @var{sigspec} and @var{signum} are not present, @code{SIGTERM} is used. -The @samp{-l} option lists the signal names, or the signal name -corresponding to @var{sigspec}. +The @samp{-l} option lists the signal names. +If any arguments are supplied when @samp{-l} is given, the names of the +signals corresponding to the arguments are listed, and the return status +is zero. +@var{exit_status} is a number specifying a signal number or the exit +status of a process terminated by a signal. +The return status is zero if at least one signal was successfully sent, +or non-zero if an error occurs or an invalid option is encountered. @item wait @btindex wait @@ -4870,21 +5456,29 @@ corresponding to @var{sigspec}. wait [@var{jobspec}|@var{pid}] @end example Wait until the child process specified by process @sc{ID} @var{pid} or job -specification @var{jobspec} exits and report its exit status. If a job -spec is given, all processes in the job are waited for. If no arguments -are given, all currently active child processes are waited for. +specification @var{jobspec} exits and return the exit status of the last +command waited for. +If a job spec is given, all processes in the job are waited for. +If no arguments are given, all currently active child processes are +waited for, and the return status is zero. +If neither @var{jobspec} nor @var{pid} specifies an active child process +of the shell, the return status is 127. @item disown @btindex disown @example -disown [-h] [@var{jobspec} @dots{}] +disown [-ar] [-h] [@var{jobspec} @dots{}] @end example Without options, each @var{jobspec} is removed from the table of active jobs. If the @samp{-h} option is given, the job is not removed from the table, but is marked so that @code{SIGHUP} is not sent to the job if the shell receives a @code{SIGHUP}. -If @var{jobspec} is not present, the current job is used. +If @var{jobspec} is not present, and neither the @samp{-a} nor @samp{-r} +option is supplied, the current job is used. +If no @var{jobspec} is supplied, the @samp{-a} option means to remove or +mark all jobs; the @samp{-r} option without a @var{jobspec} +argument restricts operation to running jobs. @item suspend @btindex suspend @@ -4909,7 +5503,7 @@ supplied process @sc{ID}s. @item auto_resume This variable controls how the shell interacts with the user and job control. If this variable exists then single word simple -commands without redirects are treated as candidates for resumption +commands without redirections are treated as candidates for resumption of an existing job. There is no ambiguity allowed; if there is more than one job beginning with the string typed, then the most recently accessed job will be selected. @@ -4941,7 +5535,7 @@ analogous to the @samp{%} job @sc{ID}. This chapter provides basic instructions for installing Bash on the various supported platforms. The distribution supports nearly every version of Unix (and, someday, @sc{GNU}). Other independent ports exist for -@sc{OS/2}, Windows 95, and Windows @sc{NT}. +@sc{MS-DOS}, @sc{OS/2}, Windows @sc{95}, and Windows @sc{NT}. @menu * Basic Installation:: Installation instructions. @@ -4991,10 +5585,10 @@ If at some point @file{config.cache} contains results you don't want to keep, you may remove or edit it. -If you need to do unusual things to compile the package, please +If you need to do unusual things to compile Bash, please try to figure out how @code{configure} could check whether or not to do them, and mail diffs or instructions to -@code{bash-maintainers@@prep.ai.mit.edu} so they can be +@email{bash-maintainers@@gnu.org} so they can be considered for the next release. The file @file{configure.in} is used to create @code{configure} @@ -5112,7 +5706,7 @@ giving @code{configure} the option @samp{--prefix=PATH}. You can specify separate installation prefixes for architecture-specific files and architecture-independent files. If you give @code{configure} the option -@samp{--exec-prefix=PATH}, the package will use @samp{PATH} as the +@samp{--exec-prefix=PATH}, @samp{make install} will use @samp{PATH} as the prefix for installing programs and libraries. Documentation and other data files will still use the regular prefix. @@ -5120,8 +5714,8 @@ other data files will still use the regular prefix. @section Specifying the System Type There may be some features @code{configure} can not figure out -automatically, but needs to determine by the type of host the -package will run on. Usually @code{configure} can figure that +automatically, but needs to determine by the type of host Bash +will run on. Usually @code{configure} can figure that out, but if it prints a message saying it can not guess the host type, give it the @samp{--host=TYPE} option. @samp{TYPE} can either be a short name for the system type, such as @samp{sun4}, @@ -5182,11 +5776,10 @@ options. @section Optional Features The Bash @code{configure} has a number of @samp{--enable-@var{FEATURE}} -options, where @var{FEATURE} indicates an optional part of the -package. There are also several @samp{--with-@var{PACKAGE}} options, -where @var{PACKAGE} is something like @samp{gnu-malloc} or -@samp{purify} (for the Purify memory allocation checker). To -turn off the default use of a package, use +options, where @var{FEATURE} indicates an optional part of Bash. +There are also several @samp{--with-@var{PACKAGE}} options, +where @var{PACKAGE} is something like @samp{gnu-malloc} or @samp{purify}. +To turn off the default use of a package, use @samp{--without-@var{PACKAGE}}. To configure Bash without a feature that is enabled by default, use @samp{--disable-@var{FEATURE}}. @@ -5204,16 +5797,21 @@ database. @item --with-glibc-malloc Use the @sc{GNU} libc version of @code{malloc} in -@file{lib/malloc/gmalloc.c}. This is somewhat slower than the -default @code{malloc}, but wastes considerably less space. +@file{lib/malloc/gmalloc.c}. This is not the version of @code{malloc} +that appears in glibc version 2, but a modified version of the +@code{malloc} from glibc version 1. This is somewhat slower than the +default @code{malloc}, but wastes less space on a per-allocation +basis, and will return memory to the operating system under +some circumstances. @item --with-gnu-malloc Use the @sc{GNU} version of @code{malloc} in @file{lib/malloc/malloc.c}. This is not the same @code{malloc} that appears in @sc{GNU} libc, but an older version derived from the 4.2 @sc{BSD} @code{malloc}. This @code{malloc} is -very fast, but wastes a lot of space. This option is enabled by -default. The @file{NOTES} file contains a list of systems for +very fast, but wastes some space on each allocation. +This option is enabled by default. +The @file{NOTES} file contains a list of systems for which this should be turned off, and @code{configure} disables this option automatically for a number of systems. @@ -5226,7 +5824,19 @@ This produces a shell with minimal features, close to the historical Bourne shell. @end table -@noindent +There are several @samp{--enable-} options that alter how Bash is +compiled and linked, rather than changing run-time features. + +@table @code +@item --enable-profiling +This builds a Bash binary that produces profiling information to be +processed by @code{gprof} each time it is executed. + +@item --enable-static-link +This causes Bash to be linked statically, if @code{gcc} is being used. +This could be used to build a version to use as root's shell. +@end table + The @samp{minimal-config} option can be used to disable all of the following options, but it is processed first, so individual options may be enabled using @samp{enable-@var{FEATURE}}. @@ -5239,26 +5849,34 @@ necessary support. @table @code @item --enable-alias Allow alias expansion and include the @code{alias} and @code{unalias} -builtins. +builtins (@pxref{Aliases}). @item --enable-array-variables -Include support for one-dimensional array shell variables. +Include support for one-dimensional array shell variables +(@pxref{Arrays}). @item --enable-bang-history -Include support for @code{csh}-like history substitution. +Include support for @code{csh}-like history substitution +(@pxref{History Interaction}). @item --enable-brace-expansion Include @code{csh}-like brace expansion ( @code{b@{a,b@}c} @expansion{} @code{bac bbc} ). +See @ref{Brace Expansion}, for a complete description. @item --enable-command-timing Include support for recognizing @code{time} as a reserved word and for displaying timing statistics for the pipeline following @code{time}. This allows pipelines as well as shell builtins and functions to be timed. +@item --enable-cond-command +Include support for the @code{[[} conditional command +(@pxref{Conditional Constructs}). + @item --enable-directory-stack Include support for a @code{csh}-like directory stack and the -@code{pushd}, @code{popd}, and @code{dirs} builtins. +@code{pushd}, @code{popd}, and @code{dirs} builtins +(@pxref{The Directory Stack}). @item --enable-disabled-builtins Allow builtin commands to be invoked via @samp{builtin xxx} @@ -5267,7 +5885,12 @@ See @ref{Bash Builtins}, for details of the @code{builtin} and @code{enable} builtin commands. @item --enable-dparen-arithmetic -Include support for the @code{ksh} @code{((@dots{}))} command. +Include support for the @code{((@dots{}))} command +(@pxref{Conditional Constructs}). + +@item --enable-extended-glob +Include support for the extended pattern matching features described +above under @ref{Pattern Matching}. @item --enable-help-builtin Include the @code{help} builtin, which displays help on shell builtins and @@ -5278,20 +5901,22 @@ Include command history and the @code{fc} and @code{history} builtin commands. @item --enable-job-control -This enables job control features, if the @sc{OS} supports them. +This enables the job control features (@pxref{Job Control}), +if the operating system supports them. @item --enable-process-substitution This enables process substitution (@pxref{Process Substitution}) if -the @sc{OS} provides the necessary support. +the operating system provides the necessary support. @item --enable-prompt-string-decoding Turn on the interpretation of a number of backslash-escaped characters in the @code{$PS1}, @code{$PS2}, @code{$PS3}, and @code{$PS4} prompt -strings. +strings. See @ref{Printing a Prompt}, for a complete list of prompt +string escape sequences. @item --enable-readline Include support for command-line editing and history with the Bash -version of the Readline library. +version of the Readline library (@pxref{Command Line Editing}). @item --enable-restricted Include support for a @dfn{restricted shell}. If this is enabled, Bash, @@ -5299,8 +5924,8 @@ when called as @code{rbash}, enters a restricted mode. See @ref{The Restricted Shell}, for a description of restricted mode. @item --enable-select -Include the @code{ksh} @code{select} builtin, which allows the -generation of simple menus. +Include the @code{select} builtin, which allows the generation of simple +menus (@pxref{Conditional Constructs}). @item --enable-usg-echo-default Make the @code{echo} builtin expand backslash-escaped characters by default, @@ -5329,7 +5954,7 @@ Once you have determined that a bug actually exists, use the @code{bashbug} command to submit a bug report. If you have a fix, you are encouraged to mail that as well! Suggestions and `philosophical' bug reports may be mailed -to @code{bug-bash@@prep.ai.MIT.Edu} or posted to the Usenet +to @email{bug-bash@@gnu.org} or posted to the Usenet newsgroup @code{gnu.bash.bug}. All bug reports should include: @@ -5352,7 +5977,7 @@ to reproduce it. the template it provides for filing a bug report. Please send all reports concerning this manual to -@code{chet@@ins.CWRU.Edu}. +@email{chet@@po.CWRU.Edu}. @node Builtin Index @appendix Index of Shell Builtin Commands |