@settitle Bash Reference Manual
@c %**end of header
-@ignore
-Last Change: Tue Mar 14 11:38:10 EST 2000
-@end ignore
-
-@set EDITION 2.4
-@set VERSION 2.04
-@set UPDATED 14 March 2000
-@set UPDATE-MONTH March 2000
-
-@iftex
-@finalout
-@end iftex
-
@setchapternewpage odd
-@defcodeindex bt
-@defcodeindex rw
-@set BashFeatures
-@ifinfo
-@dircategory Utilities
-@direntry
- * Bash: (bash). The GNU Bourne-Again SHell.
-@end direntry
+@include version.texi
-@format
+@copying
This text is a brief description of the features that are present in
-the Bash shell.
+the Bash shell (version @value{VERSION}, @value{UPDATED}).
This is Edition @value{EDITION}, last updated @value{UPDATED},
of @cite{The GNU Bash Reference Manual},
for @code{Bash}, Version @value{VERSION}.
-Copyright (C) 1991-1999 Free Software Foundation, Inc.
+Copyright @copyright{} 1988-2005 Free Software Foundation, Inc.
Permission is granted to make and distribute verbatim copies of
this manual provided the copyright notice and this permission notice
are preserved on all copies.
-@ignore
-Permission is granted to process this file through TeX and print the
-results, provided the printed document carries copying permission
-notice identical to this one except for the removal of this paragraph
-(this paragraph not being relevant to the printed manual).
-
-@end ignore
-Permission is granted to copy and distribute modified versions of this
-manual under the conditions for verbatim copying, provided that the entire
-resulting derived work is distributed under the terms of a permission
-notice identical to this one.
-
-Permission is granted to copy and distribute translations of this manual
-into another language, under the above conditions for modified versions,
-except that this permission notice may be stated in a translation approved
-by the Free Software Foundation.
-@end format
-@end ifinfo
+@quotation
+Permission is granted to copy, distribute and/or modify this document
+under the terms of the GNU Free Documentation License, Version 1.1 or
+any later version published by the Free Software Foundation; with no
+Invariant Sections, with the Front-Cover texts being ``A GNU Manual,''
+and with the Back-Cover Texts as in (a) below. A copy of the license is
+included in the section entitled ``GNU Free Documentation License.''
+
+(a) The FSF's Back-Cover Text is: ``You have freedom to copy and modify
+this GNU Manual, like GNU software. Copies published by the Free
+Software Foundation raise funds for GNU development.''
+@end quotation
+@end copying
+
+@defcodeindex bt
+@defcodeindex rw
+@set BashFeatures
+
+@dircategory Basics
+@direntry
+* Bash: (bash). The GNU Bourne-Again SHell.
+@end direntry
+
+@finalout
@titlepage
@title Bash Reference Manual
@subtitle Reference Documentation for Bash
@subtitle Edition @value{EDITION}, for @code{Bash} Version @value{VERSION}.
-@subtitle @value{UPDATE-MONTH}
+@subtitle @value{UPDATED-MONTH}
@author Chet Ramey, Case Western Reserve University
@author Brian Fox, Free Software Foundation
+
@page
@vskip 0pt plus 1filll
-Copyright @copyright{} 1991-1999 Free Software Foundation, Inc.
-
-Permission is granted to make and distribute verbatim copies of
-this manual provided the copyright notice and this permission notice
-are preserved on all copies.
+@insertcopying
-Permission is granted to copy and distribute modified versions of this
-manual under the conditions for verbatim copying, provided that the entire
-resulting derived work is distributed under the terms of a permission
-notice identical to this one.
+@sp 1
+Published by the Free Software Foundation @*
+59 Temple Place, Suite 330, @*
+Boston, MA 02111-1307 @*
+USA @*
-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 Free Software Foundation.
@end titlepage
-@ifinfo
+@contents
+
+@ifnottex
@node Top, Introduction, (dir), (dir)
@top Bash Features
-@end ifinfo
-@ifinfo
This text is a brief description of the features that are present in
-the Bash shell.
+the Bash shell (version @value{VERSION}, @value{UPDATED})..
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.
-
Bash contains features that appear in other popular shells, and some
features that only appear in Bash. Some of the shells that Bash has
borrowed concepts from are the Bourne Shell (@file{sh}), the Korn Shell
@menu
* Introduction:: An introduction to the shell.
-
* Definitions:: Some definitions used in the rest of this
manual.
-
* Basic Shell Features:: The shell "building blocks".
-
* Shell Builtin Commands:: Commands that are a part of the shell.
-
* Shell Variables:: Variables used or set by Bash.
-
* Bash Features:: Features found only in Bash.
-
-* Job Control:: A chapter describing what job control is
- and how Bash allows you to use it.
-
-* Using History Interactively:: Chapter dealing with history expansion
- rules.
-
+* Job Control:: What job control is and how Bash allows you
+ to use it.
+* Using History Interactively:: Command History Expansion
* Command Line Editing:: Chapter describing the command line
editing features.
-
* Installing Bash:: How to build and install Bash on your system.
-
* Reporting Bugs:: How to report bugs in Bash.
-
* Major Differences From The Bourne Shell:: A terse list of the differences
between Bash and historical
versions of /bin/sh.
-
+* Copying This Manual:: Copying this manual.
* Builtin Index:: Index of Bash builtin commands.
-
* Reserved Word Index:: Index of Bash reserved words.
-
* Variable Index:: Quick reference helps you find the
variable you want.
-
* Function Index:: Index of bindable Readline functions.
-
* Concept Index:: General index for concepts described in
this manual.
@end menu
-@end ifinfo
+@end ifnottex
@node Introduction
@chapter Introduction
@menu
* What is Bash?:: A short description of Bash.
-
* What is a shell?:: A brief introduction to shells.
@end menu
for the @sc{gnu} operating system.
The name is an acronym for the @samp{Bourne-Again SHell},
a pun on Stephen Bourne, the author of the direct ancestor of
-the current Unix shell @code{/bin/sh},
+the current Unix shell @code{sh},
which appeared in the Seventh Edition Bell Labs Research version
of Unix.
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{ms-dos}, @sc{os/2},
-Windows @sc{95/98}, and Windows @sc{nt}.
+and Windows platforms.
@node What is a shell?
@section What is a shell?
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 @sc{gnu} utilities,
-and a programming language, allowing these utilitites to be
-combined. Files containing commands can be created, and become
+commands. The term macro processor means functionality where text
+and symbols are expanded to create larger expressions.
+
+A Unix shell is both a command interpreter and a programming
+language. As a command interpreter, the shell provides the user
+interface to the rich set of @sc{gnu} utilities. The programming
+language features allow these utilitites to be combined.
+Files containing commands can be created, and become
commands themselves. These new commands have the same status as
system commands in directories such as @file{/bin}, allowing users
-or groups to establish custom environments.
+or groups to establish custom environments to automate their common
+tasks.
+
+Shells may be used interactively or non-interactively. In
+interactive mode, they accept input typed from the keyboard.
+When executing non-interactively, shells execute commands read
+from a file.
A shell allows execution of @sc{gnu} commands, both synchronously and
asynchronously.
fine-grained control of the input and output of those commands.
Moreover, the shell allows control over the contents of commands'
environments.
-Shells may be used interactively or non-interactively: they accept
-input typed from the keyboard or from a file.
Shells also provide a small set of built-in
commands (@dfn{builtins}) implementing functionality impossible
Shells offer features geared specifically for
interactive use rather than to augment the programming language.
These interactive features include job control, command line
-editing, history and aliases. Each of these features is
+editing, command history and aliases. Each of these features is
described in this manual.
@node Definitions
@item exit status
@cindex exit status
-The value returned by a command to its caller.
+The value returned by a command to its caller. The value is restricted
+to eight bits, so the maximum value is 255.
@item field
@cindex field
The Bourne shell is
the traditional Unix shell originally written by Stephen Bourne.
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.
+The rules for evaluation and quoting are taken from the @sc{posix}
+specification for the `standard' Unix shell.
This chapter briefly summarizes the shell's `building blocks':
commands, control structures, shell functions, shell @i{parameters},
* Shell Syntax:: What your input means to the shell.
* 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
+* Shell Parameters:: How the shell stores values.
+* Shell Expansions:: How Bash expands parameters and the various
expansions available.
* Redirections:: A way to control where input and output go.
* Executing Commands:: What happens when you run a command.
@section Shell Syntax
@menu
* Shell Operation:: The basic operation of the shell.
-
* Quoting:: How to remove the special meaning from characters.
-
* Comments:: How to specify comments.
@end menu
@enumerate
@item
Reads its input from a file (@pxref{Shell Scripts}), from a string
-supplied as an argument to the @samp{-c} invocation option
+supplied as an argument to the @option{-c} invocation option
(@pxref{Invoking Bash}), or from the user's terminal.
@item
* Double Quotes:: How to suppress most of the interpretation of a
sequence of characters.
* ANSI-C Quoting:: How to expand ANSI-C sequences in quoted strings.
-
* Locale Translation:: How to translate strings into different languages.
@end menu
Each of the shell metacharacters (@pxref{Definitions})
has special meaning to the shell and must be quoted if it is to
represent itself.
-When the command history expansion facilities are being used, the
+When the command history expansion facilities are being used
+(@pxref{History Interaction}), the
@var{history expansion} character, usually @samp{!}, must be quoted
-to prevent history expansion. @xref{Bash History Facilities} for
+to prevent history expansion. @xref{Bash History Facilities}, for
more details concerning history expansion.
+
There are three quoting mechanisms: the
@var{escape character}, single quotes, and double quotes.
Enclosing characters in double quotes (@samp{"}) preserves the literal value
of all characters within the quotes, with the exception of
-@samp{$}, @samp{`}, and @samp{\}.
+@samp{$}, @samp{`}, @samp{\},
+and, when history expansion is enabled, @samp{!}.
The characters @samp{$} and @samp{`}
retain their special meaning within double quotes (@pxref{Shell Expansions}).
The backslash retains its special meaning only when followed by one of
special meaning are left unmodified.
A double quote may be quoted within double quotes by preceding it with
a backslash.
+If enabled, history expansion will be performed unless an @samp{!}
+appearing in double quotes is escaped using a backslash.
+The backslash preceding the @samp{!} is not removed.
The special parameters @samp{*} and @samp{@@} have special meaning
when in double quotes (@pxref{Shell Parameter Expansion}).
Words of the form @code{$'@var{string}'} are treated specially. The
word expands to @var{string}, with backslash-escaped characters replaced
-as specifed by the ANSI C standard. Backslash escape sequences, if
+as specified by the ANSI C standard. Backslash escape sequences, if
present, are decoded as follows:
@table @code
@item \'
single quote
@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}
+the eight-bit character whose value is the octal value @var{nnn}
(one to three digits)
+@item \x@var{HH}
+the eight-bit character whose value is the hexadecimal value @var{HH}
+(one or two hex digits)
+@item \c@var{x}
+a control-@var{x} character
@end table
@noindent
@node Locale Translation
@subsubsection Locale-Specific Translation
@cindex localization
+@cindex internationalization
+@cindex native languages
+@cindex translation, native languages
A double-quoted string preceded by a dollar sign (@samp{$}) will cause
the string to be translated according to the current locale.
If the string is translated and replaced, the replacement is
double-quoted.
+@vindex LC_MESSAGES
+@vindex TEXTDOMAIN
+@vindex TEXTDOMAINDIR
+Some systems use the message catalog selected by the @env{LC_MESSAGES}
+shell variable. Others create the name of the message catalog from the
+value of the @env{TEXTDOMAIN} shell variable, possibly adding a
+suffix of @samp{.mo}. If you use the @env{TEXTDOMAIN} variable, you
+may need to set the @env{TEXTDOMAINDIR} variable to the location of
+the message catalog files. Still others use both variables in this
+fashion:
+@env{TEXTDOMAINDIR}/@env{LC_MESSAGES}/LC_MESSAGES/@env{TEXTDOMAIN}.mo.
+
@node Comments
@subsection Comments
@cindex comments, shell
* 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.
+* Compound Commands:: Shell commands for control flow.
@end menu
@node Simple Commands
@end example
@noindent
-The output of each command in the pipeline is connected to the input of
-the next command. That is, each command reads the previous command's
-output.
+The output of each command in the pipeline is connected via a pipe
+to the input of the next command.
+That is, each command reads the previous command's 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
+The @option{-p} option changes the output format to that specified
by @sc{posix}.
-The @code{TIMEFORMAT} variable may be set to a format string that
+The @env{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
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 negation of the exit status of the last command.
+pipeline, unless the @code{pipefail} option is enabled
+(@pxref{The Set Builtin}).
+If @code{pipefail} is enabled, the pipeline's return status is the
+value of the last (rightmost) command to exit with a non-zero status,
+or zero if all commands exit successfully.
+If the reserved word @samp{!} precedes the pipeline, the
+exit status is the logical negation of the exit status as described
+above.
+The shell waits for all commands in the pipeline to terminate before
+returning a value.
@node Lists
@subsection Lists of Commands
have equal precedence, followed by @samp{;} and @samp{&},
which have equal precedence.
+A sequence of one or more newlines may appear in a @code{list}
+to delimit commands, equivalent to a semicolon.
+
If a command is terminated by the control operator @samp{&},
the shell executes the command asynchronously in a subshell.
This is known as executing the command in the @var{background}.
@sc{and} and @sc{or} lists is the exit status of the last command
executed in the list.
+@node Compound Commands
+@subsection Compound Commands
+@cindex commands, compound
+
+@menu
+* Looping Constructs:: Shell commands for iterative action.
+* Conditional Constructs:: Shell commands for conditional execution.
+* Command Grouping:: Ways to group commands.
+@end menu
+
+Compound commands are the shell programming constructs.
+Each construct begins with a reserved word or control operator and is
+terminated by a corresponding reserved word or operator.
+Any redirections (@pxref{Redirections}) associated with a compound command
+apply to all commands within that compound command unless explicitly overridden.
+
+Bash provides looping constructs, conditional commands, and mechanisms
+to group commands and execute them as a unit.
+
@node Looping Constructs
-@subsection Looping Constructs
+@subsubsection Looping Constructs
@cindex commands, looping
Bash supports the following looping constructs.
may be used to control loop execution.
@node Conditional Constructs
-@subsection Conditional Constructs
+@subsubsection Conditional Constructs
@cindex commands, conditional
@table @code
@code{case} will selectively execute the @var{command-list} corresponding to
the first @var{pattern} that matches @var{word}.
+If the shell option @code{nocasematch}
+(see the description of @code{shopt} in @ref{Bash Builtins})
+is enabled, the match is performed without regard to the case
+of alphabetic characters.
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
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
+The @env{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 line read is saved in the variable @env{REPLY}.
The @var{commands} are executed after each selection until a
-@code{break} or @code{return} command is executed, at which
+@code{break} 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
between the @samp{[[} and @samp{]]}; tilde expansion, parameter and
variable expansion, arithmetic expansion, command substitution, process
substitution, and quote removal are performed.
+Conditional operators such as @samp{-f} must be unquoted to be recognized
+as primaries.
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}.
+If the shell option @code{nocasematch}
+(see the description of @code{shopt} in @ref{Bash Builtins})
+is enabled, the match is performed without regard to the case
+of alphabetic characters.
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.
+An additional binary operator, @samp{=~}, is available, with the same
+precedence as @samp{==} and @samp{!=}.
+When it is used, the string to the right of the operator is considered
+an extended regular expression and matched accordingly (as in @i{regex}3)).
+The return value is 0 if the string matches
+the pattern, and 1 otherwise.
+If the regular expression is syntactically incorrect, the conditional
+expression's return value is 2.
+If the shell option @code{nocasematch}
+(see the description of @code{shopt} in @ref{Bash Builtins})
+is enabled, the match is performed without regard to the case
+of alphabetic characters.
+Substrings matched by parenthesized subexpressions within the regular
+expression are saved in the array variable @code{BASH_REMATCH}.
+The element of @code{BASH_REMATCH} with index 0 is the portion of the string
+matching the entire regular expression.
+The element of @code{BASH_REMATCH} with index @var{n} is the portion of the
+string matching the @var{n}th parenthesized subexpression.
+
Expressions may be combined using the following operators, listed
in decreasing order of precedence:
True if either @var{expression1} or @var{expression2} is true.
@end table
@noindent
-The @code{&&} and @code{||} commands do not execute @var{expression2} if the
+The @code{&&} and @code{||} operators do not evaluate @var{expression2} if the
value of @var{expression1} is sufficient to determine the return
value of the entire conditional expression.
@end table
@node Command Grouping
-@subsection Grouping Commands
+@subsubsection Grouping Commands
@cindex commands, grouping
Bash provides two ways to group a list of commands to be executed
@end example
Placing a list of commands between parentheses causes a subshell
-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.
+environment to be created (@pxref{Command Execution Environment}), 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 @{
Functions are declared using this syntax:
@rwindex function
@example
-[ @code{function} ] @var{name} () @{ @var{command-list}; @}
+[ @code{function} ] @var{name} () @var{compound-command} [ @var{redirections} ]
@end example
This defines a shell function named @var{name}. The reserved
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.
-
-Note that for historical reasons, the curly braces that surround
-the body of the function must be separated from the body by
+The @var{body} of the function is the compound command
+@var{compound-command} (@pxref{Compound Commands}).
+That command is usually a @var{list} enclosed between @{ and @}, but
+may be any compound command listed above.
+@var{compound-command} is executed whenever @var{name} is specified as the
+name of a command.
+Any redirections (@pxref{Redirections}) associated with the shell function
+are performed when the function is executed.
+
+The exit status of a function definition is zero unless a syntax error
+occurs or a readonly function with the same name already exists.
+When executed, the exit status of a function is the exit status of the
+last command executed in the body.
+
+Note that for historical reasons, in the most common usage the curly braces
+that surround the body of the function must be separated from the body by
@code{blank}s or newlines.
This is because the braces are reserved words and are only recognized
as such when they are separated by whitespace.
-Also, the @var{command-list} must be terminated with a semicolon
-or a newline.
+Also, when using the braces, the @var{list} must be terminated by a semicolon,
+a @samp{&}, or a newline.
When a function is executed, the arguments to the
function become the positional parameters
during its execution (@pxref{Positional Parameters}).
The special parameter @samp{#} that expands to the number of
positional parameters is updated to reflect the change.
-Positional parameter @code{0} is unchanged.
-The @code{FUNCNAME} variable is set to the name of the function
-while the function is executing.
+Special parameter @code{0} is unchanged.
+The first element of the @env{FUNCNAME} variable is set to the
+name of the function while the function is executing.
+All other aspects of the shell execution
+environment are identical between a function and its caller
+with the exception that the @env{DEBUG} and @env{RETURN} traps
+are not inherited unless the function has been given the
+@code{trace} attribute using the @code{declare} builtin or
+the @code{-o functrace} option has been enabled with
+the @code{set} builtin,
+(in which case all functions inherit the @env{DEBUG} and @env{RETURN} traps).
+@xref{Bourne Shell Builtins}, for the description of the
+@code{trap} builtin.
If the builtin command @code{return}
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
+call.
+Any command associated with the @code{RETURN} trap is executed
+before execution resumes.
+When a function completes, the values of the
positional parameters and the special parameter @samp{#}
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's return status; otherwise the functions's
+that is the function's return status; otherwise the function's
return status is the exit status of the last command executed
before the @code{return}.
@code{local} builtin. These variables are visible only to
the function and the commands it invokes.
+Function names and definitions may be listed with the
+@option{-f} option to the @code{declare} or @code{typeset}
+builtin commands (@pxref{Bash Builtins}).
+The @option{-F} option to @code{declare} or @code{typeset}
+will list the function names only
+(and optionally the source file and line number, if the @code{extdebug}
+shell option is enabled).
+Functions may be exported so that subshells
+automatically have them defined with the
+@option{-f} option to the @code{export} builtin
+(@pxref{Bourne Shell Builtins}).
+Note that shell functions and variables with the same name may result
+in multiple identically-named entries in the environment passed to the
+shell's children.
+Care should be taken in cases where this may cause a problem.
+
Functions may be recursive. No limit is placed on the number of
recursive calls.
@menu
* Positional Parameters:: The shell's command-line arguments.
-* Special Parameters:: Parameters with special meanings.
+* Special Parameters:: Parameters denoted by special characters.
@end menu
A @var{parameter} is an entity that stores values.
It can be a @code{name}, a number, or one of the special characters
listed below.
-For the shell's purposes, a @var{variable} is a parameter denoted by a
-@code{name}.
+A @var{variable} is a parameter denoted by a @code{name}.
+A variable has a @var{value} and zero or more @var{attributes}.
+Attributes are assigned using the @code{declare} builtin command
+(see the description of the @code{declare} builtin in @ref{Bash Builtins}).
A parameter is set if it has been assigned a value. The null string is
a valid value. Once a variable is set, it may be unset only by using
@var{value}s undergo tilde expansion, parameter and variable expansion,
command substitution, arithmetic expansion, and quote
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{$((@dots{}))}
+attribute set, then @var{value}
+is evaluated as an arithmetic expression even if the @code{$((@dots{}))}
expansion is not used (@pxref{Arithmetic Expansion}).
Word splitting is not performed, with the exception
of @code{"$@@"} as explained below.
Filename expansion is not performed.
+Assignment statements may also appear as arguments to the
+@code{alias},
+@code{declare}, @code{typeset}, @code{export}, @code{readonly},
+and @code{local} builtin commands.
+
+In the context where an assignment statement is assigning a value
+to a shell variable or array index (@pxref{Arrays}), the @samp{+=}
+operator can be used to
+append to or add to the variable's previous value.
+When @samp{+=} is applied to a variable for which the integer attribute
+has been set, @var{value} is evaluated as an arithmetic expression and
+added to the variable's current value, which is also evaluated.
+When @samp{+=} is applied to an array variable using compound assignment
+(@pxref{Arrays}), the
+variable's value is not unset (as it is when using @samp{=}), and new
+values are appended to the array beginning at one greater than the array's
+maximum index.
+When applied to a string-valued variable, @var{value} is expanded and
+appended to the variable's value.
@node Positional Parameters
@subsection Positional Parameters
Expands to the positional parameters, starting from one. When the
expansion occurs within double quotes, it expands to a single word
with the value of each parameter separated by the first character
-of the @code{IFS}
+of the @env{IFS}
special variable. That is, @code{"$*"} is equivalent
to @code{"$1@var{c}$2@var{c}@dots{}"}, where @var{c}
is the first character of the value of the @code{IFS}
variable.
-If @code{IFS} is unset, the parameters are separated by spaces.
-If @code{IFS} is null, the parameters are joined without intervening
+If @env{IFS} is unset, the parameters are separated by spaces.
+If @env{IFS} is null, the parameters are joined without intervening
separators.
expansion occurs within double quotes, each parameter expands to a
separate word. That is, @code{"$@@"} is equivalent to
@code{"$1" "$2" @dots{}}.
+If the double-quoted expansion occurs within a word, the expansion of
+the first parameter is joined with the beginning part of the original
+word, and the expansion of the last parameter is joined with the last
+part of the original word.
When there are no positional parameters, @code{"$@@"} and
@code{$@@}
expand to nothing (i.e., they are removed).
(A hyphen.) Expands to the current option flags as specified upon
invocation, by the @code{set}
builtin command, or those set by the shell itself
-(such as the @samp{-i} option).
+(such as the @option{-i} option).
@item $
Expands to the process @sc{id} of the shell. In a @code{()} subshell, it
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
(@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}),
+If Bash is started with the @option{-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.
@item _
(An underscore.)
-At shell startup, set to the absolute filename of the shell or shell
-script being executed as passed in the argument list.
+At shell startup, set to the absolute pathname used to invoke the
+shell or shell script being executed as passed in the environment
+or argument list.
Subsequently, expands to the last argument to the previous command,
after expansion.
-Also set to the full pathname of each command executed and placed in
-the environment exported to that command.
+Also set to the full pathname used to invoke 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
@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 either a series of comma-separated strings or a sequnce expression
+between a pair of braces,
followed by an optional @var{postscript}.
The preamble is prefixed to each string contained within the braces, and
the postscript is then appended to each resulting string, expanding left
ade ace abe
@end example
+A sequence expression takes the form @code{@{@var{x}..@var{y}@}},
+where @var{x} and @var{y} are either integers or single characters.
+When integers are supplied, the expression expands to each number between
+@var{x} and @var{y}, inclusive.
+When characters are supplied, the expression expands to each character
+lexicographically between @var{x} and @var{y}, inclusive. Note that
+both @var{x} and @var{y} must be of the same type.
+
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
is not considered eligible for brace expansion.
A correctly-formed brace expansion must contain unquoted opening
-and closing braces, and at least one unquoted comma.
+and closing braces, and at least one unquoted comma or a valid
+sequence expression.
Any incorrectly formed brace expansion is left unchanged.
+A @{ or @samp{,} may be quoted with a backslash to prevent its
+being considered part of a brace expression.
+To avoid conflicts with parameter expansion, the string @samp{$@{}
+is not considered eligible for brace expansion.
+
This construct is typically used as shorthand when the common
prefix of the strings to be generated is longer than in the
above example:
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
+value of the @env{HOME} shell variable.
+If @env{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.
+the shell variable @env{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.
+@env{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{-},
left unchanged.
Each variable assignment is checked for unquoted tilde-prefixes immediately
-following a @samp{:} or @samp{=}.
+following a @samp{:} or the first @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},
+@env{PATH}, @env{MAILPATH}, and @env{CDPATH},
and the shell assigns the expanded value.
The following table shows how Bash treats unquoted tilde-prefixes:
expanded and that value is used in the rest of the substitution, rather
than the value of @var{parameter} itself.
This is known as @code{indirect expansion}.
-The exception to this is the expansion of $@{!@var{prefix*@}}
+The exceptions to this are the expansions of $@{!@var{prefix*}@}
+and $@{!@var{name}[@@]@}
described below.
+The exclamation point must immediately follow the left brace in order to
+introduce indirection.
In each of the cases below, @var{word} is subject to tilde expansion,
parameter expansion, command substitution, and arithmetic expansion.
If @var{parameter}
is unset or null, the expansion of @var{word}
is assigned to @var{parameter}.
-The value of @var{parameter}
-is then substituted. Positional parameters and special parameters may
-not be assigned to in this way.
+The value of @var{parameter} is then substituted.
+Positional parameters and special parameters may not be assigned to
+in this way.
@item $@{@var{parameter}:?@var{word}@}
If @var{parameter}
If @var{parameter} is an array name indexed by @samp{@@} or @samp{*},
the result is the @var{length}
members of the array beginning with @code{$@{@var{parameter}[@var{offset}]@}}.
+A negative @var{offset} is taken relative to one greater than the maximum
+index of the specified array.
+Note that a negative offset must be separated from the colon by at least
+one space to avoid being confused with the @samp{:-} expansion.
Substring indexing is zero-based unless the positional parameters
are used, in which case the indexing starts at 1.
@item $@{!@var{prefix}*@}
+@itemx $@{!@var{prefix}@@@}
Expands to the names of variables whose names begin with @var{prefix},
-separated by the first character of the @code{IFS} special variable.
+separated by the first character of the @env{IFS} special variable.
+
+@item $@{!@var{name}[@@]@}
+@itemx $@{!@var{name}[*]@}
+If @var{name} is an array variable, expands to the list of array indices
+(keys) assigned in @var{name}.
+If @var{name} is not an array, expands to 0 if @var{name} is set and null
+otherwise.
+When @samp{@@} is used and the expansion appears within double quotes, each
+key expands to a separate word.
@item $@{#@var{parameter}@}
The length in characters of the expanded value of @var{parameter} is
a double quote inside the parentheses is not treated specially.
All tokens in the expression undergo parameter expansion, command
substitution, and quote removal.
-Arithmetic substitutions may be nested.
+Arithmetic expansions may be nested.
The evaluation is performed according to the rules listed below
(@pxref{Shell Arithmetic}).
and arithmetic expansion that did not occur within double quotes for
word splitting.
-The shell treats each character of @code{$IFS}
+The shell treats each character of @env{$IFS}
as a delimiter, and splits the results of the other
expansions into words on these characters. If
-@code{IFS} is unset, or its value is exactly @code{<space><tab><newline>},
-the default, then any sequence of @code{IFS}
-characters serves to delimit words. If @code{IFS}
+@env{IFS} is unset, or its value is exactly @code{<space><tab><newline>},
+the default, then any sequence of @env{IFS}
+characters serves to delimit words. If @env{IFS}
has a value other than the default, then sequences of
the whitespace characters @code{space} and @code{tab}
are ignored at the beginning and end of the
word, as long as the whitespace character is in the
-value of @code{IFS} (an @code{IFS} whitespace character).
-Any character in @code{IFS} that is not @code{IFS}
-whitespace, along with any adjacent @code{IFS}
-whitespace characters, delimits a field. A sequence of @code{IFS}
+value of @env{IFS} (an @env{IFS} whitespace character).
+Any character in @env{IFS} that is not @env{IFS}
+whitespace, along with any adjacent @env{IFS}
+whitespace characters, delimits a field. A sequence of @env{IFS}
whitespace characters is also treated as a delimiter.
-If the value of @code{IFS} is null, no word splitting occurs.
+If the value of @env{IFS} is null, no word splitting occurs.
Explicit null arguments (@code{""} or @code{''}) are retained.
Unquoted implicit null arguments, resulting from the expansion of
@cindex filename expansion
@cindex pathname expansion
-After word splitting, unless the @samp{-f} option has been set
+After word splitting, unless the @option{-f} option has been set
(@pxref{The Set Builtin}), Bash scans each word for the characters
@samp{*}, @samp{?}, and @samp{[}.
If one of these characters appears, then the word is
unchanged.
If the @code{nullglob} option is set, and no matches are found, the word
is removed.
+If the @code{failglob} shell option is set, and no matches are found,
+an error message is printed and the command is not executed.
If the shell option @code{nocaseglob} is enabled, the match is performed
without regard to the case of alphabetic characters.
See the description of @code{shopt} in @ref{Bash Builtins},
for a description of the @code{nocaseglob}, @code{nullglob},
-and @code{dotglob} options.
+@code{failglob}, and @code{dotglob} options.
-The @code{GLOBIGNORE}
+The @env{GLOBIGNORE}
shell variable may be used to restrict the set of filenames matching a
-pattern. If @code{GLOBIGNORE}
+pattern. If @env{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
+@env{GLOBIGNORE} is removed from the list of matches. The filenames
@file{.} and @file{..}
-are always ignored, even when @code{GLOBIGNORE}
-is set. However, setting @code{GLOBIGNORE} has the effect of
+are always ignored when @env{GLOBIGNORE}
+is set and not null.
+However, setting @env{GLOBIGNORE} to a non-null value has the effect of
enabling the @code{dotglob}
shell option, so all other filenames beginning with a
@samp{.} will match.
To get the old behavior of ignoring filenames beginning with a
-@samp{.}, make @samp{.*} one of the patterns in @code{GLOBIGNORE}.
-The @code{dotglob} option is disabled when @code{GLOBIGNORE}
+@samp{.}, make @samp{.*} one of the patterns in @env{GLOBIGNORE}.
+The @code{dotglob} option is disabled when @env{GLOBIGNORE}
is unset.
@node Pattern Matching
@cindex matching, pattern
Any character that appears in a pattern, other than the special pattern
-characters described below, matches itself. The @sc{nul} character may not
-occur in a pattern. The special pattern characters must be quoted if
-they are to be matched literally.
+characters described below, matches itself.
+The @sc{nul} character may not occur in a pattern.
+A backslash escapes the following character; the
+escaping backslash is discarded when matching.
+The special pattern characters must be quoted if they are to be matched
+literally.
The special pattern characters have the following meanings:
@table @code
Matches any single character.
@item [@dots{}]
Matches any one of the enclosed characters. A pair of characters
-separated by a minus sign denotes a @var{range};
-any character lexically between those two characters, inclusive,
+separated by a hyphen denotes a @var{range expression};
+any character that sorts between those two characters, inclusive,
+using the current locale's collating sequence and character set,
is matched. If the first character following the
@samp{[} is a @samp{!} or a @samp{^}
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.
+The sorting order of characters in range expressions is determined by
+the current locale and the value of the @env{LC_COLLATE} shell variable,
+if set.
+
+For example, in the default C locale, @samp{[a-dx-z]} is equivalent to
+@samp{[abcdxyz]}. Many locales sort characters in dictionary order, and in
+these locales @samp{[a-dx-z]} is typically not equivalent to @samp{[abcdxyz]};
+it might be equivalent to @samp{[aBbCcDdxXyYz]}, for example. To obtain
+the traditional interpretation of ranges in bracket expressions, you can
+force the use of the C locale by setting the @env{LC_COLLATE} or
+@env{LC_ALL} environment variable to the value @samp{C}.
Within @samp{[} and @samp{]}, @var{character classes} can be specified
using the syntax
following classes defined in the @sc{posix} 1003.2 standard:
@example
alnum alpha ascii blank cntrl digit graph lower
-print punct space upper xdigit
+print punct space upper word xdigit
@end example
@noindent
A character class matches any character belonging to that class.
+The @code{word} character class matches letters, digits, and the character
+@samp{_}.
Within @samp{[} and @samp{]}, an @var{equivalence class} can be
specified using the syntax @code{[=}@var{c}@code{=]}, which
Matches one or more occurrences of the given patterns.
@item @@(@var{pattern-list})
-Matches exactly one of the given patterns.
+Matches one of the given patterns.
@item !(@var{pattern-list})
Matches anything except one of the given patterns.
@item /dev/tcp/@var{host}/@var{port}
If @var{host} is a valid hostname or Internet address, and @var{port}
-is an integer port number, Bash attempts to open a TCP connection
-to the corresponding socket.
+is an integer port number or service name, Bash attempts to open a TCP
+connection to the corresponding socket.
@item /dev/udp/@var{host}/@var{port}
If @var{host} is a valid hostname or Internet address, and @var{port}
-is an integer port number, Bash attempts to open a UDP connection
-to the corresponding socket.
+is an integer port number or service name, Bash attempts to open a UDP
+connection to the corresponding socket.
@end table
A failure to open or create a file causes the redirection to fail.
+Redirections using file descriptors greater than 9 should be used with
+care, as they may conflict with file descriptors the shell uses
+internally.
+
@subsection Redirecting Input
Redirection of input causes the file whose name results from
the expansion of @var{word}
The general format for redirecting input is:
@example
-[n]<@var{word}
+[@var{n}]<@var{word}
@end example
@subsection Redirecting Output
Redirection of output causes the file whose name results from
the expansion of @var{word}
-to be opened for writing on file descriptor @code{n},
-or the standard output (file descriptor 1) if @code{n}
+to be opened for writing on file descriptor @var{n},
+or the standard output (file descriptor 1) if @var{n}
is not specified. If the file does not exist it is created;
if it does exist it is truncated to zero size.
The general format for redirecting output is:
@example
-[n]>[|]@var{word}
+[@var{n}]>[|]@var{word}
@end example
If the redirection operator is @samp{>}, and the @code{noclobber}
Redirection of output in this fashion
causes the file whose name results from
the expansion of @var{word}
-to be opened for appending on file descriptor @code{n},
-or the standard output (file descriptor 1) if @code{n}
+to be opened for appending on file descriptor @var{n},
+or the standard output (file descriptor 1) if @var{n}
is not specified. If the file does not exist it is created.
The general format for appending output is:
@example
-[n]>>@var{word}
+[@var{n}]>>@var{word}
@end example
@subsection Redirecting Standard Output and Standard Error
the lines read up to that point are then used as the standard
input for a command.
-The format of here-documents is as follows:
+The format of here-documents is:
@example
<<[@minus{}]@var{word}
@var{here-document}
This allows here-documents within shell scripts to be indented in a
natural fashion.
+@subsection Here Strings
+A variant of here documents, the format is:
+@example
+<<< @var{word}
+@end example
+
+The @var{word} is expanded and supplied to the command on its standard
+input.
+
@subsection Duplicating File Descriptors
The redirection operator
@example
-[n]<&@var{word}
+[@var{n}]<&@var{word}
@end example
@noindent
is used to duplicate input file descriptors.
If @var{word}
-expands to one or more digits, the file descriptor denoted by @code{n}
+expands to one or more digits, the file descriptor denoted by @var{n}
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.
+evaluates to @samp{-}, file descriptor @var{n} is closed. If
+@var{n} is not specified, the standard input (file descriptor 0) is used.
The operator
@example
-[n]>&@var{word}
+[@var{n}]>&@var{word}
@end example
@noindent
is used similarly to duplicate output file descriptors. If
-@code{n}
-is not specified, the standard output (file descriptor 1) is used.
+@var{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
+As a special case, if @var{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.
+@subsection Moving File Descriptors
+The redirection operator
+@example
+[@var{n}]<&@var{digit}-
+@end example
+@noindent
+moves the file descriptor @var{digit} to file descriptor @var{n},
+or the standard input (file descriptor 0) if @var{n} is not specified.
+@var{digit} is closed after being duplicated to @var{n}.
+
+Similarly, the redirection operator
+@example
+[@var{n}]>&@var{digit}-
+@end example
+@noindent
+moves the file descriptor @var{digit} to file descriptor @var{n},
+or the standard output (file descriptor 1) if @var{n} is not specified.
+
@subsection Opening File Descriptors for Reading and Writing
The redirection operator
@example
-[n]<>@var{word}
+[@var{n}]<>@var{word}
@end example
@noindent
causes the file whose name is the expansion of @var{word}
to be opened for both reading and writing on file descriptor
-@code{n}, or on file descriptor 0 if @code{n}
+@var{n}, or on file descriptor 0 if @var{n}
is not specified. If the file does not exist, it is created.
@node 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
interprets it.
-
* Signals:: What happens when Bash or a command it runs
receives a signal.
-
@end menu
@node Simple Command Expansion
@item
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
+@env{$PATH} for a directory containing an executable file
by that name. Bash uses a hash table to remember the full
-pathnames of executable files to avoid multiple @code{PATH} searches
+pathnames of executable files to avoid multiple @env{PATH} searches
(see the description of @code{hash} in @ref{Bourne Shell Builtins}).
-A full search of the directories in @code{$PATH}
+A full search of the directories in @env{$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 an exit status of 127.
@item
various process @sc{id}s, including those of background jobs
(@pxref{Lists}), the value of @code{$$}, and the value of
-@code{$PPID}
+@env{$PPID}
@end itemize
the file creation mode mask
@item
-shell variables marked for export, along with variables exported for
-the command, passed in the environment (@pxref{Environment})
+shell variables and functions 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
A command invoked in this separate environment cannot affect the
shell's execution environment.
-Command substitution and asynchronous commands are invoked in a
+Command substitution, commands grouped with parentheses,
+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
in a subshell environment. Changes made to the subshell environment
cannot affect the shell's execution environment.
+If a command is followed by a @samp{&} and job control is not active, the
+default standard input for the command is the empty file @file{/dev/null}.
+Otherwise, the invoked command inherits the file descriptors of the calling
+shell as modified by redirections.
+
@node Environment
@subsection Environment
@cindex environment
These assignment statements affect only the environment seen
by that command.
-If the @samp{-k} option is set (@pxref{The Set Builtin}), then all
+If the @option{-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.
If job control is in effect (@pxref{Job Control}), Bash
ignores @code{SIGTTIN}, @code{SIGTTOU}, and @code{SIGTSTP}.
-Commands started by Bash have signal handlers set to the
+Non-builtin 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.
+ignore @code{SIGINT} and @code{SIGQUIT} in addition to these inherited
+handlers.
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.
+Before exiting, an interactive shell 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
(@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.
+If Bash is waiting for a command to complete and receives a signal
+for which a trap has been set, 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
A shell script is a text file containing shell commands. When such
a file is used as the first non-option argument when invoking Bash,
-and neither the @samp{-c} nor @samp{-s} option is supplied
+and neither the @option{-c} nor @option{-s} option is supplied
(@pxref{Invoking Bash}),
Bash reads and executes commands from the file, then exits. This
-mode of operation creates a non-interactive shell. When Bash runs
+mode of operation creates a non-interactive shell. The shell first
+searches for the file in the current directory, and looks in the
+directories in @env{$PATH} if not found there.
+
+When Bash runs
a shell script, it sets the special parameter @code{0} to the name
of the file, rather than the name of the shell, and the positional
parameters are set to the remaining arguments, if any are given.
A shell script may be made executable by using the @code{chmod} command
to turn on the execute bit. When Bash finds such a file while
-searching the @code{$PATH} for a command, it spawns a subshell to
+searching the @env{$PATH} for a command, it spawns a subshell to
execute it. In other words, executing
@example
filename @var{arguments}
Many of the builtins have been extended by @sc{posix} or Bash.
+Unless otherwise noted, each builtin command documented as accepting
+options preceded by @samp{-} accepts @samp{--}
+to signify the end of the options.
+For example, the @code{:}, @code{true}, @code{false}, and @code{test}
+builtins do not accept options.
+
@node Bourne Shell Builtins
@section Bourne Shell Builtins
@end example
Read and execute commands from the @var{filename} argument in the
current shell context. If @var{filename} does not contain a slash,
-the @code{PATH} variable is used to find
-@var{filename}. The current directory is searched if @var{filename}
-is not found in @code{$PATH}.
+the @env{PATH} variable is used to find @var{filename}.
+When Bash is not in @sc{posix} mode, the current directory is searched
+if @var{filename} is not found in @env{$PATH}.
If any @var{arguments} are supplied, they become the positional
parameters when @var{filename} is executed. Otherwise the positional
parameters are unchanged.
@item cd
@btindex cd
@example
-cd [-LP] [@var{directory}]
+cd [-L|-P] [@var{directory}]
@end example
-Change the current working directory to @var{directory}. If @var{directory}
-is not given, the value of the @code{HOME} shell variable is used. If the
-shell variable @code{CDPATH} exists, it is used as a search path. If
-@var{directory} begins with a slash, @code{CDPATH} is not used.
-The @samp{-P} option means
-to not follow symbolic links; symbolic links are followed by default
-or with the @samp{-L} option.
-If @var{directory} is @samp{-}, it is equivalent to @code{$OLDPWD}.
+Change the current working directory to @var{directory}.
+If @var{directory} is not given, the value of the @env{HOME} shell
+variable is used.
+If the shell variable @env{CDPATH} exists, it is used as a search path.
+If @var{directory} begins with a slash, @env{CDPATH} is not used.
+
+The @option{-P} option means to not follow symbolic links; symbolic
+links are followed by default or with the @option{-L} option.
+If @var{directory} is @samp{-}, it is equivalent to @env{$OLDPWD}.
+
+If a non-empty directory name from @env{CDPATH} is used, or if
+@samp{-} is the first argument, and the directory change is
+successful, the absolute pathname of the new working directory is
+written to the standard output.
+
The return status is zero if the directory is successfully changed,
non-zero otherwise.
@end example
If @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 at the
+If the @option{-l} option is supplied, the shell places a dash at the
beginning of 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
+The @option{-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
+If @option{-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. If there are no redirection errors, the
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
+in the environment. If the @option{-f} option is supplied, the @var{name}s
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
+The @option{-n} option means to no longer mark each @var{name} for export.
+If no @var{names} are supplied, or if the @option{-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 @option{-p} option displays output in a form that may be reused as input.
+If a variable name is followed by =@var{value}, the value of
+the variable is set to @var{value}.
+
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
+the names is not a valid shell variable name, or @option{-f} is supplied
with a name that is not a shell function.
@item 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
+variable @env{OPTIND}.
+@env{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
+@code{getopts} places that argument into the variable @env{OPTARG}.
+The shell does not reset @env{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,
+@env{OPTIND} is set to the index of the first non-option argument,
and @code{name} is set to @samp{?}.
@code{getopts}
error reporting is used. In normal operation diagnostic messages
are printed when invalid options or missing option arguments are
encountered.
-If the variable @code{OPTERR}
+If the variable @env{OPTERR}
is set to 0, no error messages will be displayed, even if the first
character of @code{optstring} is not a colon.
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}.
+prints an error message and unsets @env{OPTARG}.
If @code{getopts} is silent, the option character found is placed in
-@code{OPTARG} and no diagnostic message is printed.
+@env{OPTARG} and no diagnostic message is printed.
If a required argument is not found, and @code{getopts}
is not silent, a question mark (@samp{?}) is placed in @var{name},
@code{OPTARG} is unset, and a diagnostic message is printed.
If @code{getopts} is silent, then a colon (@samp{:}) is placed in
-@var{name} and @code{OPTARG} is set to the option character found.
+@var{name} and @env{OPTARG} is set to the option character found.
@item hash
@btindex hash
@example
-hash [-r] [-p @var{filename}] [@var{name}]
+hash [-'r] [-p @var{filename}] [-dt] [@var{name}]
@end example
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
+@env{$PATH}.
+The @option{-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 @option{-r} option causes the shell to forget all remembered locations.
+The @option{-d} option causes the shell to forget the remembered location
+of each @var{name}.
+If the @option{-t} option is supplied, the full pathname to which each
+@var{name} corresponds is printed. If multiple @var{name} arguments are
+supplied with @option{-t} the @var{name} is printed before the hashed
+full pathname.
+The @option{-l} option causes output to be displayed in a format
+that may be reused as input.
+If no arguments are given, or if only @option{-l} is supplied,
+information about remembered commands is printed.
The return status is zero unless a @var{name} is not found or an invalid
option is supplied.
pwd [-LP]
@end example
Print the absolute pathname of the current working directory.
-If the @samp{-P} option is supplied, the pathname printed will not
+If the @option{-P} option is supplied, the pathname printed will not
contain symbolic links.
-If the @samp{-L} option is supplied, the pathname printed may contain
+If the @option{-L} option is supplied, the pathname 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
@item readonly
@btindex readonly
@example
-readonly [-apf] [@var{name}] @dots{}
+readonly [-apf] [@var{name}[=@var{value}]] @dots{}
@end example
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
+If the @option{-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}
+The @option{-a} option means each @var{name} refers to an array variable.
+If no @var{name} arguments are given, or if the @option{-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
+The @option{-p} option causes output to be displayed in a format that
may be reused as input.
+If a variable name is followed by =@var{value}, the value of
+the variable is set to @var{value}.
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.
+or the @option{-f} option is supplied with a name that is not a shell function.
@item return
@btindex return
with the @code{.} (or @code{source}) 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
+Any command associated with the @code{RETURN} trap is executed
+before execution resumes after the function or script.
+The return status is non-zero if @code{return} is used outside a function
and not during the execution of a script by @code{.} or @code{source}.
@item shift
Each operator and operand must be a separate argument.
Expressions are composed of the primaries described below in
@ref{Bash Conditional Expressions}.
+@code{test} does not accept any options, nor does it accept and ignore
+an argument of @option{--} as signifying the end of options.
When the @code{[} form is used, the last argument to the command must
be a @code{]}.
trap [-lp] [@var{arg}] [@var{sigspec} @dots{}]
@end example
The commands in @var{arg} are to be read and executed when the
-shell receives signal @var{sigspec}. If @var{arg} is absent or
-equal to @samp{-}, all specified signals are reset to the values
-they had when the shell was started.
+shell receives signal @var{sigspec}. If @var{arg} is absent (and
+there is a single @var{sigspec}) or
+equal to @samp{-}, each specified signal's disposition is reset
+to the value it had when the shell was started.
If @var{arg} is the null string, then the signal specified by
each @var{sigspec} is ignored by the shell and commands it invokes.
-If @var{arg} is not present and @samp{-p} has been supplied,
+If @var{arg} is not present and @option{-p} has been supplied,
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
+only @option{-p} is given, @code{trap} prints the list of commands
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.
+The @option{-l} option causes the shell to print a list of signal names
+and their corresponding numbers.
+Each @var{sigspec} is either a signal name or a signal number.
+Signal names are case insensitive and the @code{SIG} prefix is optional.
If a @var{sigspec}
is @code{0} or @code{EXIT}, @var{arg} is executed when the shell exits.
If a @var{sigspec} is @code{DEBUG}, the command @var{arg} is executed
-after every simple command.
-The @samp{-l} option causes the shell to print a list of signal names
-and their corresponding numbers.
+before every simple command, @code{for} command, @code{case} command,
+@code{select} command, every arithmetic @code{for} command, and before
+the first command executes in a shell function.
+Refer to the description of the @code{extglob} option to the
+@code{shopt} builtin (@pxref{Bash Builtins}) for details of its
+effect on the @code{DEBUG} trap.
+If a @var{sigspec} is @code{ERR}, the command @var{arg}
+is executed whenever a simple command has a non-zero exit status,
+subject to the following conditions.
+The @code{ERR} trap is not executed if the failed command is part of the
+command list immediately following an @code{until} or @code{while} keyword,
+part of the test in an @code{if} statement,
+part of a @code{&&} or @code{||} list, or if the command's return
+status is being inverted using @code{!}.
+These are the same conditions obeyed by the @code{errexit} option.
+If a @var{sigspec} is @code{RETURN}, the command @var{arg} is executed
+each time a shell function or a script executed with the @code{.} or
+@code{source} builtins finishes executing.
Signals ignored upon entry to the shell cannot be trapped or reset.
Trapped signals are reset to their original values in a child
@var{mode} begins with a digit, it is interpreted as an octal number;
if not, it is interpreted as a symbolic mode mask similar
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}
+omitted, the current value of the mask is printed. If the @option{-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}
+If the @option{-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.
unset [-fv] [@var{name}]
@end example
Each variable or function @var{name} is removed.
-If no options are supplied, or the @samp{-v} option is given, each
+If no options are supplied, or the @option{-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
+If the @option{-f} option is given, the @var{name}s refer to shell
functions, and the function definition is removed.
Readonly variables and functions may not be unset.
-The return status is zero unless a @var{name} does not exist or is
-readonly.
+The return status is zero unless a @var{name} is readonly.
@end table
@node Bash Builtins
alias [@code{-p}] [@var{name}[=@var{value}] @dots{}]
@end example
-Without arguments or with the @samp{-p} option, @code{alias} prints
+Without arguments or with the @option{-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}
bind [-m @var{keymap}] -f @var{filename}
bind [-m @var{keymap}] -x @var{keyseq:shell-command}
bind [-m @var{keymap}] @var{keyseq:function-name}
+bind @var{readline-command}
@end example
Display current Readline (@pxref{Command Line Editing})
-key and function bindings, or
-bind a key sequence to a Readline function or macro. The
-binding syntax accepted is identical to that of
+key and function bindings,
+bind a key sequence to a Readline function or macro,
+or set a Readline variable.
+Each non-option argument is a command as it would appear in a
a Readline initialization file (@pxref{Readline Init File}),
-but each binding must be passed as a separate argument: e.g.,
+but each binding or command must be passed as a separate argument; e.g.,
@samp{"\C-x\C-r":re-read-init-file}.
Options, if supplied, have the following meanings:
@code{emacs-meta},
@code{emacs-ctlx},
@code{vi},
+@code{vi-move},
@code{vi-command}, and
@code{vi-insert}.
@code{vi} is equivalent to @code{vi-command};
The return status is non-zero if @var{shell-builtin} is not a shell
builtin command.
+@item caller
+@btindex caller
+@example
+caller [@var{expr}]
+@end example
+Returns the context of any active subroutine call (a shell function or
+a script executed with the @code{.} or @code{source} builtins).
+
+Without @var{expr}, @code{caller} displays the line number and source
+filename of the current subroutine call.
+If a non-negative integer is supplied as @var{expr}, @code{caller}
+displays the line number, subroutine name, and source file corresponding
+to that position in the current execution call stack. This extra
+information may be used, for example, to print a stack trace. The
+current frame is frame 0.
+
+The return value is 0 unless the shell is not executing a subroutine
+call or @var{expr} does not correspond to a valid position in the
+call stack.
+
@item command
@btindex command
@example
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.
+@env{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}
+The @option{-p} option means to use a default value for @env{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
+If either the @option{-V} or @option{-v} option is supplied, a
+description of @var{command} is printed. The @option{-v} option
causes a single word indicating the command or file name used to
-invoke @var{command} to be displayed; the @samp{-V} option produces
+invoke @var{command} to be displayed; the @option{-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
@example
-declare [-afFrxi] [-p] [@var{name}[=@var{value}]]
+declare [-afFirtx] [-p] [@var{name}[=@var{value}] @dots{}]
@end example
Declare variables and give them attributes. If no @var{name}s
are given, then display the values of variables instead.
-The @samp{-p} option will display the attributes and values of each
-@var{name}. When @samp{-p} is used, additional options are ignored.
-The @samp{-F} option inhibits the display of function definitions;
-only the function name and attributes are printed. @samp{-F} implies
-@samp{-f}. The following options can be used to restrict output
-to variables with the specified attributes or to give variables
-attributes:
+The @option{-p} option will display the attributes and values of each
+@var{name}.
+When @option{-p} is used, additional options are ignored.
+The @option{-F} option inhibits the display of function definitions;
+only the function name and attributes are printed.
+If the @code{extdebug} shell option is enabled using @code{shopt}
+(@pxref{Bash Builtins}), the source file name and line number where
+the function is defined are displayed as well.
+@option{-F} implies @option{-f}.
+The following options can be used to restrict output to variables with
+the specified attributes or to give variables attributes:
@table @code
@item -a
Make @var{name}s readonly. These names cannot then be assigned values
by subsequent assignment statements or unset.
+@item -t
+Give each @var{name} the @code{trace} attribute.
+Traced functions inherit the @code{DEBUG} and @code{RETURN} traps from
+the calling shell.
+The trace attribute has no special meaning for variables.
+
@item -x
Mark each @var{name} for export to subsequent commands via
the environment.
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.
+as with the @code{local} command. If a variable name is followed by
+=@var{value}, the value of the variable is set to @var{value}.
The return status is zero unless an invalid option is encountered,
an attempt is made to define a function using @samp{-f foo=bar},
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}.
+or an attempt is made to display a non-existent function with @option{-f}.
@item echo
@btindex echo
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
+If @option{-n} is specified, the trailing newline is suppressed.
+If the @option{-e} option is given, interpretation of the following
backslash-escaped characters is enabled.
-The @samp{-E} option disables the interpretation of these escape characters,
+The @option{-E} option disables the interpretation of these escape characters,
even on systems where they are interpreted by default.
The @code{xpg_echo} shell option may be used to
dynamically determine whether or not @code{echo} expands these
escape characters by default.
+@code{echo} does not interpret @option{--} to mean the end of options.
+
@code{echo} interprets the following escape sequences:
@table @code
@item \a
vertical tab
@item \\
backslash
+@item \0@var{nnn}
+the eight-bit character whose value is the octal value @var{nnn}
+(zero to three octal digits)
@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)
+the eight-bit character whose value is the octal value @var{nnn}
+(one to three octal digits)
+@item \x@var{HH}
+the eight-bit character whose value is the hexadecimal value @var{HH}
+(one or two hex digits)
@end table
@item enable
Disabling a builtin allows a disk command which has the same name
as a shell builtin to be executed without 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
+If @option{-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{$PATH} instead of the shell builtin version, type
+found via @env{$PATH} instead of the shell builtin version, type
@samp{enable -n test}.
-If the @samp{-p} option is supplied, or no @var{name} arguments appear,
+If the @option{-p} option is supplied, or no @var{name} arguments appear,
a list of shell builtins is printed. With no other arguments, the list
consists of all enabled shell builtins.
-The @samp{-a} option means to list
+The @option{-a} option means to list
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}
+The @option{-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}.
+The @option{-d} option will delete a builtin loaded with @option{-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} special
-builtins. If @samp{-s} is used with @samp{-f}, the new builtin becomes
+The @option{-s} option restricts @code{enable} to the @sc{posix} special
+builtins. If @option{-s} is used with @option{-f}, the new builtin becomes
a special builtin (@pxref{Special Builtins}).
The return status is zero unless a @var{name} is not a shell builtin
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 @samp{-s} option restricts the information displayed to a short
+The @option{-s} option restricts the information displayed to a short
usage synopsis.
The return status is zero unless no command matches @var{pattern}.
@item local
@btindex local
@example
-local [@var{option}] @var{name}[=@var{value}]
+local [@var{option}] @var{name}[=@var{value}] @dots{}
@end example
For each argument, a local variable named @var{name} is created,
and assigned @var{value}.
@item printf
@btindex printf
@example
-@code{printf} @var{format} [@var{arguments}]
+@code{printf} [-v @var{var}] @var{format} [@var{arguments}]
@end example
Write the formatted @var{arguments} to the standard output under the
control of the @var{format}.
@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
+@var{argument},
+(except that @samp{\c} terminates output, backslashes in
+@samp{\'}, @samp{\"}, and @samp{\?} are not removed, and octal escapes
+beginning with @samp{\0} may contain up to four digits),
+and @samp{%q} causes @code{printf} to output the
corresponding @var{argument} in a format that can be reused as shell input.
+The @option{-v} option causes the output to be assigned to the variable
+@var{var} rather than being printed to the standard output.
+
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
@item read
@btindex read
@example
-read [-ers] [-a @var{aname}] [-p @var{prompt}] [-t @var{timeout}] [-n @var{nchars}] [-d @var{delim}] [@var{name} @dots{}]
+read [-ers] [-a @var{aname}] [-d @var{delim}] [-n @var{nchars}] [-p @var{prompt}] [-t @var{timeout}] [-u @var{fd}] [@var{name} @dots{}]
@end example
-One line is read from the standard input, and the first word
+One line is read from the standard input, or from the file descriptor
+@var{fd} supplied as an argument to the @option{-u} option, 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 and their intervening separators assigned
to the last @var{name}.
-If there are fewer words read from the standard input than names,
+If there are fewer words read from the input stream than names,
the remaining names are assigned empty values.
-The characters in the value of the @code{IFS} variable
+The characters in the value of the @env{IFS} variable
are used to split the line into words.
The backslash character @samp{\} may be used to remove any special
meaning for the next character read and for line continuation.
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 or @code{read}
-times out.
+variable @env{REPLY}.
+The return code is zero, unless end-of-file is encountered, @code{read}
+times out, or an invalid file descriptor is supplied as the argument to
+@option{-u}.
Options, if supplied, have the following meanings:
@table @code
This option has no effect if @code{read} is not reading input from the
terminal or a pipe.
+@item -u @var{fd}
+Read input from file descriptor @var{fd}.
+
@end table
@item shopt
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
+With no options, or with the @option{-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
+The @option{-p} option causes output to be displayed in a form that
may be reused as input.
Other options have the following meanings:
@item -q
Suppresses normal output; the return status
indicates whether the @var{optname} is set or unset.
-If multiple @var{optname} arguments are given with @samp{-q},
+If multiple @var{optname} arguments are given with @option{-q},
the return status is zero if all @var{optnames} are enabled;
non-zero otherwise.
@item -o
Restricts the values of
-@var{optname} to be those defined for the @samp{-o} option to the
+@var{optname} to be those defined for the @option{-o} option to the
@code{set} builtin (@pxref{The Set Builtin}).
@end table
-If either @samp{-s} or @samp{-u}
+If either @option{-s} or @option{-u}
is used with no @var{optname} arguments, the display is limited to
those options which are set or unset, respectively.
@item checkwinsize
If set, Bash checks the window size after each command
and, if necessary, updates the values of
-@code{LINES} and @code{COLUMNS}.
+@env{LINES} and @env{COLUMNS}.
@item cmdhist
If set, Bash
@ref{Aliases}.
This option is enabled by default for interactive shells.
+@item extdebug
+If set, behavior intended for use by debuggers is enabled:
+
+@enumerate
+@item
+The @option{-F} option to the @code{declare} builtin (@pxref{Bash Builtins})
+displays the source file name and line number corresponding to each function
+name supplied as an argument.
+
+@item
+If the command run by the @code{DEBUG} trap returns a non-zero value, the
+next command is skipped and not executed.
+
+@item
+If the command run by the @code{DEBUG} trap returns a value of 2, and the
+shell is executing in a subroutine (a shell function or a shell script
+executed by the @code{.} or @code{source} builtins), a call to
+@code{return} is simulated.
+
+@item
+@code{BASH_ARGC} and @code{BASH_ARGV} are updated as described in their
+descriptions (@pxref{Bash Variables}).
+
+@item
+Function tracing is enabled: command substitution, shell functions, and
+subshells invoked with @code{( @var{command} )} inherit the
+@code{DEBUG} and @code{RETURN} traps.
+
+@item
+Error tracing is enabled: command substitution, shell functions, and
+subshells invoked with @code{( @var{command} )} inherit the
+@code{ERROR} trap.
+@end enumerate
+
@item extglob
If set, the extended pattern matching features described above
(@pxref{Pattern Matching}) are enabled.
+@item extquote
+If set, @code{$'@var{string}'} and @code{$"@var{string}"} quoting is
+performed within @code{$@{@var{parameter}@}} expansions
+enclosed in double quotes. This option is enabled by default.
+
+@item failglob
+If set, patterns which fail to match filenames during pathname expansion
+result in an expansion error.
+
+@item force_fignore
+If set, the suffixes specified by the @env{FIGNORE} shell variable
+cause words to be ignored when performing word completion even if
+the ignored words are the only possible completions.
+@xref{Bash Variables}, for a description of @env{FIGNORE}.
+This option is enabled by default.
+
+@item gnu_errfmt
+If set, shell error messages are written in the standard @sc{gnu} error
+message format.
+
@item histappend
If set, the history list is appended to the file named by the value
-of the @code{HISTFILE}
+of the @env{HISTFILE}
variable when the shell exits, rather than overwriting the file.
@item histreedit
option is enabled, multi-line commands are saved to the history with
embedded newlines rather than using semicolon separators where possible.
+@item login_shell
+The shell sets this option if it is started as a login shell
+(@pxref{Invoking Bash}).
+The value may not be changed.
+
@item mailwarn
If set, and a file that Bash is checking for mail has been
accessed since the last time it was checked, the message
@item no_empty_cmd_completion
If set, and Readline is being used, Bash will not attempt to search
-the @code{PATH} for possible completions when completion is attempted
+the @env{PATH} for possible completions when completion is attempted
on an empty line.
@item nocaseglob
If set, Bash matches filenames in a case-insensitive fashion when
performing filename expansion.
+@item nocasematch
+If set, Bash matches patterns in a case-insensitive fashion when
+performing matching while executing @code{case} or @code{[[}
+conditional commands.
+
@item nullglob
If set, Bash allows filename patterns which match no
files to expand to a null string, rather than themselves.
This option is enabled by default.
@item promptvars
-If set, prompt strings undergo variable and parameter expansion after
-being expanded (@pxref{Printing a Prompt}).
+If set, prompt strings undergo
+parameter expansion, command substitution, arithmetic
+expansion, and quote removal after being expanded
+as described below (@pxref{Printing a Prompt}).
This option is enabled by default.
@item restricted_shell
number of positional parameters.
@item sourcepath
-If set, the @code{source} builtin uses the value of @code{PATH}
+If set, the @code{source} builtin uses the value of @env{PATH}
to find the directory containing the file supplied as an argument.
This option is enabled by default.
@item type
@btindex type
@example
-type [-atp] [@var{name} @dots{}]
+type [-afptP] [@var{name} @dots{}]
@end example
For each @var{name}, indicate how it would be interpreted if used as a
command name.
-If the @samp{-t} option is used, @code{type} prints a single word
+If the @option{-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,
If the @var{name} is not found, then nothing is printed, and
@code{type} returns a failure status.
-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}
+If the @option{-p} option is used, @code{type} either returns the name
+of the disk file that would be executed, or nothing if @option{-t}
would not return @samp{file}.
-If the @samp{-a} option is used, @code{type} returns all of the places
+The @option{-P} option forces a path search for each @var{name}, even if
+@option{-t} would not return @samp{file}.
+
+If a command is hashed, @option{-p} and @option{-P} print the hashed value,
+not necessarily the file that appears first in @code{$PATH}.
+
+If the @option{-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
+This includes aliases and functions, if and only if the @option{-p} option
is not also used.
+If the @option{-f} option is used, @code{type} does not attempt to find
+shell functions, as with the @code{command} builtin.
+
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}]]
+typeset [-afFrxi] [-p] [@var{name}[=@var{value}] @dots{}]
@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}
@end table
-If @var{limit} is given, it is the new value of the specified resource.
+If @var{limit} is given, it is the new value of the specified resource;
+the special @var{limit} values @code{hard}, @code{soft}, and
+@code{unlimited} stand for the current hard limit, the current soft limit,
+and no limit, respectively.
Otherwise, the current value of the soft limit for the specified resource
-is printed, unless the @samp{-H} option is supplied.
-When setting new limits, if neither @samp{-H} nor @samp{-S} is supplied,
+is printed, unless the @option{-H} option is supplied.
+When setting new limits, if neither @option{-H} nor @option{-S} is supplied,
both the hard and soft limits are set.
-If no option is given, then @samp{-f} is assumed. Values are in 1024-byte
-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
+If no option is given, then @option{-f} is assumed. Values are in 1024-byte
+increments, except for @option{-t}, which is in seconds, @option{-p},
+which is in units of 512-byte blocks, and @option{-n} and @option{-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.
+The return status is zero unless an invalid option or argument is supplied,
+or an error occurs while setting a new limit.
@item unalias
@btindex unalias
unalias [-a] [@var{name} @dots{} ]
@end example
-Remove each @var{name} from the list of aliases. If @samp{-a} is
+Remove each @var{name} from the list of aliases. If @option{-a} is
supplied, all aliases are removed.
Aliases are described in @ref{Aliases}.
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.
+current locale, in a format that may be reused as input
+for setting or resetting the currently-set variables.
+Read-only variables cannot be reset.
+In @sc{posix} mode, only shell variables are listed.
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.
+Mark variables and function which are modified or created for export
+to the environment of subsequent commands.
@item -b
Cause the status of terminated background jobs to be reported
@item -e
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,
+with a non-zero status, unless the command that fails is part of the
+command list immediately following a @code{while} or @code{until}
+keyword, part of the test in an @code{if} statement,
part of a @code{&&} or @code{||} list, or if the command's return
status is being inverted using @code{!}.
+A trap on @code{ERR}, if set, is executed before the shell exits.
@item -f
Disable file name generation (globbing).
@item errexit
Same as @code{-e}.
+@item errtrace
+Same as @code{-E}.
+
+@item functrace
+Same as @code{-T}.
+
@item hashall
Same as @code{-h}.
@item noglob
Same as @code{-f}.
+@item nolog
+Currently ignored.
+
@item notify
Same as @code{-b}.
@item physical
Same as @code{-P}.
+@item pipefail
+If set, the return value of a pipeline is the value of the last
+(rightmost) command to exit with a non-zero status, or zero if all
+commands in the pipeline exit successfully.
+This option is disabled by default.
+
@item posix
Change the behavior of Bash where the default operation differs
from the @sc{posix} 1003.2 standard to match the standard
@item -p
Turn on privileged mode.
-In this mode, the @code{$BASH_ENV} and @code{$ENV} files are not
+In this mode, the @env{$BASH_ENV} and @env{$ENV} files are not
processed, shell functions are not inherited from the environment,
-and the @code{SHELLOPTS} variable, if it appears in the environment,
+and the @env{SHELLOPTS} variable, if it appears in the environment,
is ignored.
If the shell is started with the effective user (group) id not equal to the
real user (group) id, and the @code{-p} option is not supplied, these actions
Print shell input lines as they are read.
@item -x
-Print a trace of simple commands and their arguments after they are
-expanded and before they are executed.
+Print a trace of simple commands, \fBfor\fP commands, \fBcase\fP
+commands, \fBselect\fP commands, and arithmetic \fBfor\fP commands
+and their arguments or associated word lists after they are
+expanded and before they are executed. The value of the @env{PS4}
+variable is expanded and the resultant value is printed before
+the command and its expanded arguments.
@item -B
The shell will perform brace expansion (@pxref{Brace Expansion}).
Prevent output redirection using @samp{>}, @samp{>&}, and @samp{<>}
from overwriting existing files.
+@item -E
+If set, any trap on @code{ERR} is inherited by shell functions, command
+substitutions, and commands executed in a subshell environment.
+The @code{ERR} trap is normally not inherited in such cases.
+
@item -H
Enable @samp{!} style history substitution (@pxref{History Interaction}).
This option is on by default for interactive shells.
/usr/local
@end example
+@item -T
+If set, any trap on @code{DEBUG} and @code{RETURN} are inherited by
+shell functions, command substitutions, and commands executed
+in a subshell environment.
+The @code{DEBUG} and @code{RETURN} traps are normally not inherited
+in such cases.
+
@item --
If no arguments follow this option, then the positional parameters are
unset. Otherwise, the positional parameters are set to the
@item -
Signal the end of options, cause all remaining @var{arguments}
-to be assigned to the positional parameters. The @samp{-x}
-and @samp{-v} options are turned off.
+to be assigned to the positional parameters. The @option{-x}
+and @option{-v} options are turned off.
If there are no arguments, the positional parameters remain unchanged.
@end table
words as part of expansion.
@item MAIL
-If this parameter is set to a filename and the @code{MAILPATH} variable
+If this parameter is set to a filename and the @env{MAILPATH} variable
is not set, Bash informs the user of the arrival of mail in
the specified file.
@item PATH
A colon-separated list of directories in which the shell looks for
commands.
+A zero-length (null) directory name in the value of @code{PATH} indicates the
+current directory.
+A null directory name may appear as two adjacent colons, or as an initial
+or trailing colon.
+
@item PS1
The primary prompt string. The default value is @samp{\s-\v\$ }.
@xref{Printing a Prompt}, for the complete list of escape
-sequences that are expanded before @code{PS1} is displayed.
+sequences that are expanded before @env{PS1} is displayed.
@item PS2
The secondary prompt string. The default value is @samp{> }.
@item BASH
The full pathname used to execute the current instance of Bash.
+@item BASH_ARGC
+An array variable whose values are the number of parameters in each
+frame of the current bash execution call stack. The number of
+parameters to the current subroutine (shell function or script executed
+with @code{.} or @code{source}) is at the top of the stack. When a
+subroutine is executed, the number of parameters passed is pushed onto
+@code{BASH_ARGC}.
+The shell sets @code{BASH_ARGC} only when in extended debugging mode
+(see @ref{Bash Builtins}
+for a description of the @code{extdebug} option to the @code{shopt}
+builtin).
+
+@item BASH_ARGV
+An array variable containing all of the parameters in the current bash
+execution call stack. The final parameter of the last subroutine call
+is at the top of the stack; the first parameter of the initial call is
+at the bottom. When a subroutine is executed, the parameters supplied
+are pushed onto @code{BASH_ARGV}.
+The shell sets @code{BASH_ARGV} only when in extended debugging mode
+(see @ref{Bash Builtins}
+for a description of the @code{extdebug} option to the @code{shopt}
+builtin).
+
+@item BASH_COMMAND
+The command currently being executed or about to be executed, unless the
+shell is executing a command as the result of a trap,
+in which case it is the command executing at the time of the trap.
+
@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 BASH_VERSION
-The version number of the current instance of Bash.
+@item BASH_EXECUTION_STRING
+The command argument to the @option{-c} invocation option.
+
+@item BASH_LINENO
+An array variable whose members are the line numbers in source files
+corresponding to each member of @var{FUNCNAME}.
+@code{$@{BASH_LINENO[$i]@}} is the line number in the source file where
+@code{$@{FUNCNAME[$i]@}} was called.
+The corresponding source file name is @code{$@{BASH_SOURCE[$i]@}}.
+Use @code{LINENO} to obtain the current line number.
+
+@item BASH_REMATCH
+An array variable whose members are assigned by the @samp{=~} binary
+operator to the @code{[[} conditional command
+(@pxref{Conditional Constructs}).
+The element with index 0 is the portion of the string
+matching the entire regular expression.
+The element with index @var{n} is the portion of the
+string matching the @var{n}th parenthesized subexpression.
+This variable is read-only.
+
+@item BASH_SOURCE
+An array variable whose members are the source filenames corresponding
+to the elements in the @code{FUNCNAME} array variable.
+
+@item BASH_SUBSHELL
+Incremented by one each time a subshell or subshell environment is spawned.
+The initial value is 0.
@item BASH_VERSINFO
A readonly array variable (@pxref{Arrays})
The release status (e.g., @var{beta1}).
@item BASH_VERSINFO[5]
-The value of @code{MACHTYPE}.
+The value of @env{MACHTYPE}.
@end table
-@item COMP_WORDS
-An array variable consisting of the individual
-words in the current command line.
-This variable is available only in shell functions invoked by the
-programmable completion facilities (@pxref{Programmable Completion}).
+@item BASH_VERSION
+The version number of the current instance of Bash.
+
+@item COLUMNS
+Used by the @code{select} builtin command to determine the terminal width
+when printing selection lists. Automatically set upon receipt of a
+@code{SIGWINCH}.
@item COMP_CWORD
-An index into @code{$@{COMP_WORDS@}} of the word containing the current
+An index into @env{$@{COMP_WORDS@}} of the word containing the current
cursor position.
This variable is available only in shell functions invoked by the
programmable completion facilities (@pxref{Programmable Completion}).
commands invoked by the
programmable completion facilities (@pxref{Programmable Completion}).
+@item COMP_WORDBREAKS
+The set of characters that the Readline library treats as word
+separators when performing word completion.
+If @code{COMP_WORDBREAKS} is unset, it loses its special properties,
+even if it is subsequently reset.
+
+@item COMP_WORDS
+An array variable consisting of the individual
+words in the current command line.
+This variable is available only in shell functions invoked by the
+programmable completion facilities (@pxref{Programmable Completion}).
+
@item COMPREPLY
An array variable from which Bash reads the possible completions
generated by a shell function invoked by the programmable completion
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
+If @env{DIRSTACK} is unset, it loses its special properties, even if
it is subsequently reset.
+@item EMACS
+If Bash finds this variable in the environment when the shell
+starts with value @samp{t}, it assumes that the shell is running in an
+emacs shell buffer and disables line editing.
+
@item EUID
The numeric effective user id of the current user. This variable
is readonly.
@item FCEDIT
-The editor used as a default by the @samp{-e} option to the @code{fc}
+The editor used as a default by the @option{-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}
+@env{FIGNORE}
is excluded from the list of matched file names. A sample
value is @samp{.o:~}
+@item FUNCNAME
+An array variable containing the names of all shell functions
+currently in the execution call stack.
+The element with index 0 is the name of any currently-executing
+shell function.
+The bottom-most element is "main".
+This variable exists only when a shell function is executing.
+Assignments to @env{FUNCNAME} have no effect and return an error status.
+If @env{FUNCNAME} is unset, it loses its special properties, even if
+it is subsequently reset.
+
@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 the patterns in @env{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.
-Assignments to @code{GROUPS} have no effect and are silently discarded.
-If @code{GROUPS} is unset, it loses its special properties, even if it is
+Assignments to @env{GROUPS} have no effect and return an error status.
+If @env{GROUPS} is unset, it loses its special properties, even if it is
subsequently reset.
@item histchars
@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,
+command. If @env{HISTCMD} is unset, it loses its special properties,
even if it is subsequently reset.
-@item FUNCNAME
-The name of any currently-executing shell function.
-This variable exists only when a shell function is executing.
-Assignments to @code{FUNCNAME} have no effect and are silently discarded.
-If @code{FUNCNAME} is unset, it loses its special properties, even if
-it is subsequently reset.
-
@item HISTCONTROL
-A value of @samp{ignorespace} means to not enter lines which
-begin with a space or tab into the history list.
-A value of @samp{ignoredups} means to not 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.
+A colon-separated list of values controlling how commands are saved on
+the history list.
+If the list of values includes @samp{ignorespace}, lines which begin
+with a space character are not saved in the history list.
+A value of @samp{ignoredups} causes lines which match the previous
+history entry to not be saved.
+A value of @samp{ignoreboth} is shorthand for
+@samp{ignorespace} and @samp{ignoredups}.
+A value of @samp{erasedups} causes all previous lines matching the
+current line to be removed from the history list before that line
+is saved.
+Any value not in the above list is ignored.
+If @env{HISTCONTROL} is unset, or does not include a valid value,
+all lines read by the shell parser are saved on the history list,
+subject to the value of @env{HISTIGNORE}.
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}.
+@env{HISTCONTROL}.
+
+@item HISTFILE
+The name of the file to which the command history is saved. The
+default value is @file{~/.bash_history}.
+
+@item HISTFILESIZE
+The maximum number of lines contained in the history file. When this
+variable is assigned a value, the history file is truncated, if
+necessary, to contain no more than that number of lines.
+The history file is also truncated to this size after
+writing it when an interactive shell exits.
+The default value is 500.
@item HISTIGNORE
A colon-separated list of patterns used to decide which command
lines should be saved on the history list. Each pattern is
anchored at the beginning of the line and must match the complete
line (no implicit @samp{*} is appended). Each pattern is tested
-against the line after the checks specified by @code{HISTCONTROL}
+against the line after the checks specified by @env{HISTCONTROL}
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}.
+@env{HISTIGNORE}.
-@code{HISTIGNORE} subsumes the function of @code{HISTCONTROL}. A
+@env{HISTIGNORE} subsumes the function of @env{HISTCONTROL}. A
pattern of @samp{&} is identical to @code{ignoredups}, and a
pattern of @samp{[ ]*} is identical to @code{ignorespace}.
Combining these two patterns, separating them with a colon,
provides the functionality of @code{ignoreboth}.
-@item HISTFILE
-The name of the file to which the command history is saved. The
-default value is @file{~/.bash_history}.
-
@item HISTSIZE
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
-variable is assigned a value, the history file is truncated, if
-necessary, to contain no more than that number of lines.
-The history file is also truncated to this size after
-writing it when an interactive shell exits.
-The default value is 500.
+@item HISTTIMEFORMAT
+If this variable is set and not null, its value is used as a format string
+for @var{strftime} to print the time stamp associated with each history
+entry displayed by the @code{history} builtin.
+If this variable is set, time stamps are written to the history file so
+they may be preserved across shell sessions.
@item HOSTFILE
Contains the name of a file in the same format as @file{/etc/hosts} that
the next time hostname completion is attempted after the
value is changed, Bash adds the contents of the new file to the
existing list.
-If @code{HOSTFILE} is set, but has no value, Bash attempts to read
+If @env{HOSTFILE} is set, but has no value, Bash attempts to read
@file{/etc/hosts} to obtain the list of possible hostname completions.
-When @code{HOSTFILE} is unset, the hostname list is cleared.
+When @env{HOSTFILE} is unset, the hostname list is cleared.
@item HOSTNAME
The name of the current host.
selected with a variable starting with @code{LC_}.
@item LC_ALL
-This variable overrides the value of @code{LANG} and any other
+This variable overrides the value of @env{LANG} and any other
@code{LC_} variable specifying a locale category.
@item LC_COLLATE
@item LINENO
The line number in the script or shell function currently executing.
+@item LINES
+Used by the @code{select} builtin command to determine the column length
+for printing selection lists. Automatically set upon receipt of a
+@code{SIGWINCH}.
+
@item MACHTYPE
A string that fully describes the system type on which Bash
is executing, in the standard @sc{gnu} @var{cpu-company-system} format.
@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.
+files specified in the @env{MAILPATH} or @env{MAIL} variables.
+The default is 60 seconds. When it is time to check
+for mail, the shell does so before displaying the primary prompt.
+If this variable is unset, or set to a value that is not a number
+greater than or equal to zero, the shell disables mail checking.
@item OLDPWD
The previous working directory as set by the @code{cd} builtin.
in the most-recently-executed foreground pipeline (which may
contain only a single command).
+@item POSIXLY_CORRECT
+If this variable is in the environment when @code{bash} starts, the shell
+enters @sc{posix} mode (@pxref{Bash POSIX Mode}) before reading the
+startup files, as if the @option{--posix} invocation option had been supplied.
+If it is set while the shell is running, @code{bash} enables @sc{posix} mode,
+as if the command
+@example
+@code{set -o posix}
+@end example
+@noindent
+had been executed.
+
@item PPID
The process @sc{id} of the shell's parent process. This variable
is readonly.
@item PROMPT_COMMAND
If set, the value is interpreted as a command to execute
-before the printing of each primary prompt (@code{$PS1}).
+before the printing of each primary prompt (@env{$PS1}).
@item PS3
The value of this variable is used as the prompt for the
@item PS4
The value 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
+when the @option{-x} option is set (@pxref{The Set Builtin}).
+The first character of @env{PS4} is replicated multiple times, as
necessary, to indicate multiple levels of indirection.
The default is @samp{+ }.
becomes the value assigned plus the number of seconds
since the assignment.
+@item SHELL
+The full pathname to the shell is kept in this environment variable.
+If it is not set when the shell starts,
+Bash assigns to it the full pathname of the current user's login shell.
+
@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
+the list is a valid argument for the @option{-o} option to the
@code{set} builtin command (@pxref{The Set Builtin}).
-The options appearing in @code{SHELLOPTS} are those reported
+The options appearing in @env{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
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
+If set to a value greater than zero, @code{TMOUT} is treated as the
+default timeout for the @code{read} builtin (@pxref{Bash Builtins}).
+The @code{select} command (@pxref{Conditional Constructs}) terminates
+if input does not arrive after @code{TMOUT} seconds when input is coming
+from a terminal.
+
+In an interative shell, the value is interpreted as
the number of seconds to wait for input after issuing the primary
prompt when the shell is interactive.
Bash terminates after that number of seconds if input does
not arrive.
+@item TMPDIR
+If set, Bash uses its value as the name of a directory in which
+Bash creates temporary files for the shell's use.
+
@item UID
The numeric real user id of the current user. This variable is readonly.
@section Invoking Bash
@example
-bash [long-opt] [-ir] [-abefhkmnptuvxdBCDHP] [-o @var{option}] [@var{argument} @dots{}]
-bash [long-opt] [-abefhkmnptuvxdBCDHP] [-o @var{option}] -c @var{string} [@var{argument} @dots{}]
-bash [long-opt] -s [-abefhkmnptuvxdBCDHP] [-o @var{option}] [@var{argument} @dots{}]
+bash [long-opt] [-ir] [-abefhkmnptuvxdBCDHP] [-o @var{option}] [-O @var{shopt_option}] [@var{argument} @dots{}]
+bash [long-opt] [-abefhkmnptuvxdBCDHP] [-o @var{option}] [-O @var{shopt_option}] -c @var{string} [@var{argument} @dots{}]
+bash [long-opt] -s [-abefhkmnptuvxdBCDHP] [-o @var{option}] [-O @var{shopt_option}] [@var{argument} @dots{}]
@end example
In addition to the single-character shell command-line options
(@pxref{The Set Builtin}), there are several multi-character
options that you can use. These options must appear on the command
-line before the single-character options in order for them
-to be recognized.
+line before the single-character options to be recognized.
@table @code
+@item --debugger
+Arrange for the debugger profile to be executed before the shell
+starts. Turns on extended debugging mode (see @ref{Bash Builtins}
+for a description of the @code{extdebug} option to the @code{shopt}
+builtin) and shell function tracing
+(see @ref{The Set Builtin} for a description of the @code{-o functrace}
+option).
+
@item --dump-po-strings
A list of all double-quoted strings preceded by @samp{$}
-is printed on the standard ouput
+is printed on the standard output
in the @sc{gnu} @code{gettext} PO (portable object) file format.
-Equivalent to @samp{-D} except for the output format.
+Equivalent to @option{-D} except for the output format.
@item --dump-strings
-Equivalent to @samp{-D}.
+Equivalent to @option{-D}.
@item --help
Display a usage message on standard output and exit sucessfully.
+@item --init-file @var{filename}
+@itemx --rcfile @var{filename}
+Execute commands from @var{filename} (instead of @file{~/.bashrc})
+in an interactive shell.
+
@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}. @samp{exec bash --login}
-will replace the current shell with a Bash login shell.
-@xref{Bash Startup Files}, for a description of the special behavior
-of a login shell.
+Equivalent to @option{-l}.
@item --noediting
Do not use the @sc{gnu} Readline library (@pxref{Command Line Editing})
standard. @xref{Bash POSIX Mode}, for a description of the Bash
@sc{posix} mode.
-@item --rcfile @var{filename}
-Execute commands from @var{filename} (instead of @file{~/.bashrc})
-in an interactive shell.
-
@item --restricted
Make the shell a restricted shell (@pxref{The Restricted Shell}).
@item --verbose
-Equivalent to @samp{-v}. Print shell input lines as they're read.
+Equivalent to @option{-v}. Print shell input lines as they're read.
@item --version
Show version information for this instance of
Force the shell to run interactively. Interactive shells are
described in @ref{Interactive Shells}.
+@item -l
+Make this shell act as if it had been directly invoked by login.
+When the shell is interactive, this is equivalent to starting a
+login shell with @samp{exec -l bash}.
+When the shell is not interactive, the login shell startup files will
+be executed.
+@samp{exec bash -l} or @samp{exec bash --login}
+will replace the current shell with a Bash login shell.
+@xref{Bash Startup Files}, for a description of the special behavior
+of a login shell.
+
@item -r
Make the shell a restricted shell (@pxref{The Restricted Shell}).
@item -D
A list of all double-quoted strings preceded by @samp{$}
-is printed on the standard ouput.
+is printed on the standard output.
These are the strings that
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.
+This implies the @option{-n} option; no commands will be executed.
+
+@item [-+]O [@var{shopt_option}]
+@var{shopt_option} is one of the shell options accepted by the
+@code{shopt} builtin (@pxref{Shell Builtin Commands}).
+If @var{shopt_option} is present, @option{-O} sets the value of that option;
+@option{+O} unsets it.
+If @var{shopt_option} is not supplied, the names and values of the shell
+options accepted by @code{shopt} are printed on the standard output.
+If the invocation option is @option{+O}, the output is displayed in a format
+that may be reused as input.
@item --
A @code{--} signals the end of options and disables further option
@end table
+@cindex login shell
+A @emph{login} shell is one whose first character of argument zero is
+@samp{-}, or one invoked with the @option{--login} option.
+
@cindex interactive shell
An @emph{interactive} shell is one started without non-option arguments,
-unless @samp{-s} is specified,
-without specifying the @samp{-c} option, and whose input and output are both
+unless @option{-s} is specified,
+without specifying the @option{-c} option, and whose input and output are both
connected to terminals (as determined by @code{isatty(3)}), or one
-started with the @samp{-i} option. @xref{Interactive Shells} for more
+started with the @option{-i} option. @xref{Interactive Shells}, for more
information.
If arguments remain after option processing, and neither the
-@samp{-c} nor the @samp{-s}
+@option{-c} nor the @option{-s}
option has been supplied, the first argument is assumed to
be the name of a file containing shell commands (@pxref{Shell Scripts}).
When Bash is invoked in this fashion, @code{$0}
Interactive shells are described in @ref{Interactive Shells}.
-@subsubheading Invoked as an interactive login shell, or with @samp{--login}
+@subsubheading Invoked as an interactive login shell, or with @option{--login}
When Bash is invoked as an interactive login shell, or as a
-non-interactive shell with the @samp{--login} option, it first reads and
+non-interactive shell with the @option{--login} option, it first reads and
executes commands from the file @file{/etc/profile}, if that file exists.
After reading that file, it looks for @file{~/.bash_profile},
@file{~/.bash_login}, and @file{~/.profile}, in that order, and reads
and executes commands from the first one that exists and is readable.
-The @samp{--noprofile} option may be used when the shell is started to
+The @option{--noprofile} option may be used when the shell is started to
inhibit this behavior.
When a login shell exits, Bash reads and executes commands from
When an interactive shell that is not a login shell is started, Bash
reads and executes commands from @file{~/.bashrc}, if that file exists.
-This may be inhibited by using the @samp{--norc} option.
-The @samp{--rcfile @var{file}} option will force Bash to read and
+This may be inhibited by using the @option{--norc} option.
+The @option{--rcfile @var{file}} option will force Bash to read and
execute commands from @var{file} instead of @file{~/.bashrc}.
So, typically, your @file{~/.bash_profile} contains the line
@subsubheading Invoked non-interactively
When Bash is started non-interactively, to run a shell script,
-for example, it looks for the variable @code{BASH_ENV} in the environment,
+for example, it looks for the variable @env{BASH_ENV} in the environment,
expands its value if it appears there, and uses the expanded value as
the name of a file to read and execute. Bash behaves as if the
following command were executed:
@code{if [ -n "$BASH_ENV" ]; then . "$BASH_ENV"; fi}
@end example
@noindent
-but the value of the @code{PATH} variable is not used to search for the
+but the value of the @env{PATH} variable is not used to search for the
file name.
+As noted above, if a non-interactive shell is invoked with the
+@option{--login} option, Bash attempts to read and execute commands from the
+login shell startup files.
+
@subsubheading Invoked with name @code{sh}
If Bash is invoked with the name @code{sh}, it tries to mimic the
possible, while conforming to the @sc{posix} standard as well.
When invoked as an interactive login shell, or as a non-interactive
-shell with the @samp{--login} option, it first attempts to read
+shell with the @option{--login} option, 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.
+The @option{--noprofile} option may be used to inhibit this behavior.
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,
+looks for the variable @env{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
+commands from any other startup files, the @option{--rcfile} option has
no effect.
A non-interactive shell invoked with the name @code{sh} does not attempt
to read any other startup files.
@subsubheading Invoked in @sc{posix} mode
When Bash is started in @sc{posix} mode, as with the
-@samp{--posix} command line option, it follows the @sc{posix} standard
+@option{--posix} command line option, it follows the @sc{posix} standard
for startup files.
-In this mode, interactive shells expand the @code{ENV} variable
+In this mode, interactive shells expand the @env{ENV} variable
and commands are read and executed from the file whose name is the
expanded value.
No other startup files are read.
rshd, it reads and executes commands from @file{~/.bashrc}, if that
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
+The @option{--norc} option may be used to inhibit this behavior, and the
+@option{--rcfile} option may be used to force another file to be read, but
@code{rshd} does not generally invoke the shell with those options or
allow them to be specified.
If Bash is started with the effective user (group) id not equal to the
real user (group) id, and the @code{-p} option is not supplied, no startup
files are read, shell functions are not inherited from the environment,
-the @code{SHELLOPTS} variable, if it appears in the environment, is ignored,
+the @env{SHELLOPTS} variable, if it appears in the environment, is ignored,
and the effective user id is set to the real user id.
If the @code{-p} option is supplied at invocation, the startup behavior is
the same, but the effective user id is not reset.
@subsection What is an Interactive Shell?
An interactive shell
-is one started without non-option arguments, unless @samp{-s} is
-specified, without specifiying the @samp{-c} option, and
-whose input and output are both
+is one started without non-option arguments, unless @option{-s} is
+specified, without specifiying the @option{-c} option, and
+whose input and error output are both
connected to terminals (as determined by @code{isatty(3)}),
-or one started with the @samp{-i} option.
+or one started with the @option{-i} option.
An interactive shell generally reads from and writes to a user's
terminal.
-The @samp{-s} invocation option may be used to set the positional parameters
+The @option{-s} invocation option may be used to set the positional parameters
when an interactive shell is started.
@node Is this Shell Interactive?
@end example
Alternatively, startup scripts may examine the variable
-@code{$PS1}; it is unset in non-interactive shells, and set in
+@env{PS1}; it is unset in non-interactive shells, and set in
interactive shells. Thus:
@example
signals @code{SIGTTIN}, @code{SIGTTOU}, and @code{SIGTSTP}.
@item
-Bash expands and displays @code{$PS1} before reading the first line
-of a command, and expands and displays @code{$PS2} before reading the
+Bash expands and displays @env{PS1} before reading the first line
+of a command, and expands and displays @env{PS2} before reading the
second and subsequent lines of a multi-line command.
@item
-Bash executes the value of the @code{PROMPT_COMMAND} variable as a command
-before printing the primary prompt, @code{$PS1}
+Bash executes the value of the @env{PROMPT_COMMAND} variable as a command
+before printing the primary prompt, @env{$PS1}
(@pxref{Bash Variables}).
@item
Command history (@pxref{Bash History Facilities})
and history expansion (@pxref{History Interaction})
are enabled by default.
-Bash will save the command history to the file named by @code{$HISTFILE}
+Bash will save the command history to the file named by @env{$HISTFILE}
when an interactive shell exits.
@item
if the @code{hupoxexit} shell option has been enabled (@pxref{Signals}).
@item
-The @samp{-n} invocation option is ignored, and @samp{set -n} has
+The @option{-n} invocation option is ignored, and @samp{set -n} has
no effect (@pxref{The Set Builtin}).
@item
Bash will check for mail periodically, depending on the values of the
-@code{MAIL}, @code{MAILPATH}, and @code{MAILCHECK} shell variables
+@env{MAIL}, @env{MAILPATH}, and @env{MAILCHECK} shell variables
(@pxref{Bash Variables}).
@item
@item
When running in @sc{posix} mode, a special builtin returning an error
status will not cause the shell to exit (@pxref{Bash POSIX Mode}).
+
@item
A failed @code{exec} will not cause the shell to exit
(@pxref{Bourne Shell Builtins}).
option to the @code{shopt} builtin in @ref{Bash Builtins}).
@item
-The shell will check the value of the @code{TMOUT} variable and exit
+The shell will check the value of the @env{TMOUT} variable and exit
if a command is not read within the specified number of seconds after
-printing @code{$PS1} (@pxref{Bash Variables}).
+printing @env{$PS1} (@pxref{Bash Variables}).
@end enumerate
@file{/dev/stdin}, @file{/dev/stdout}, or @file{/dev/stderr}, file
descriptor 0, 1, or 2, respectively, is checked.
+Unless otherwise specified, primaries that operate on files follow symbolic
+links and operate on the target of the link, rather than the link itself.
+
@table @code
@item -a @var{file}
True if @var{file} exists.
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}.
+True if @var{file1} is newer (according to modification date)
+than @var{file2}, or if @var{file1} exists and @var{file2} does not.
@item @var{file1} -ot @var{file2}
-True if @var{file1} is older than @var{file2}.
+True if @var{file1} is older than @var{file2},
+or if @var{file2} exists and @var{file1} does not.
@item @var{file1} -ef @var{file2}
-True if @var{file1} and @var{file2} have the same device and
+True if @var{file1} and @var{file2} refer to the same device and
inode numbers.
@item -o @var{optname}
True if shell option @var{optname} is enabled.
-The list of options appears in the description of the @samp{-o}
+The list of options appears in the description of the @option{-o}
option to the @code{set} builtin (@pxref{The Set Builtin}).
@item -z @var{string}
@item @var{string1} == @var{string2}
True if the strings are equal.
-@samp{=} may be used in place of @samp{==}.
+@samp{=} may be used in place of @samp{==} for strict @sc{posix} compliance.
@item @var{string1} != @var{string2}
True if the strings are not equal.
@cindex arithmetic evaluation
The shell allows arithmetic expressions to be evaluated, as one of
-the shell expansions or by the @code{let} builtin.
+the shell expansions or by the @code{let} and the @option{-i} option
+to the @code{declare} builtins.
-Evaluation is done in long integers with no check for overflow,
+Evaluation is done in fixed-width integers with no check for overflow,
though division by 0 is trapped and flagged as an error.
-The operators and their precedence and associativity are the same
-as in the C language.
+The operators and their precedence, associativity, and values
+are the same as in the C language.
The following list of operators is grouped into levels of
equal-precedence operators.
The levels are listed in order of decreasing precedence.
logical OR
@item expr ? expr : expr
-conditional evaluation
+conditional operator
@item = *= /= %= += -= <<= >>= &= ^= |=
assignment
performed before the expression is evaluated.
Within an expression, shell variables may also be referenced by name
without using the parameter expansion syntax.
+A shell variable that is null or unset evaluates to 0 when referenced
+by name without using the parameter expansion syntax.
The value of a variable is evaluated as an arithmetic expression
-when it is referenced.
+when it is referenced, or when a variable which has been given the
+@var{integer} attribute using @samp{declare -i} is assigned a value.
+A null value evaluates to 0.
A shell variable need not have its integer attribute turned on
to be used in an expression.
base, and @var{n} is a number in that base. If @var{base}@code{#} is
omitted, then base 10 is used.
The digits greater than 9 are represented by the lowercase letters,
-the uppercase letters, @samp{_}, and @samp{@@}, in that order.
+the uppercase letters, @samp{@@}, and @samp{_}, in that order.
If @var{base} is less than or equal to 36, lowercase and uppercase
-letters may be used interchangably to represent numbers between 10
+letters may be used interchangeably to represent numbers between 10
and 35.
Operators are evaluated in order of precedence. Sub-expressions in
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 characters @samp{/}, @samp{$}, @samp{`}, @samp{=} and any of the
+shell metacharacters or quoting characters listed above may not appear
+in an alias name.
+The replacement text may contain any valid
+shell input, including shell metacharacters.
The first word of the replacement text is tested for
aliases, but a word that is identical to an alias being expanded
-is not expanded a second time. This means that one may alias
-@code{ls} to @code{"ls -F"},
+is not expanded a second time.
+This means that one may alias @code{ls} to @code{"ls -F"},
for instance, and Bash does not try to recursively expand the
replacement text. If the last character of the alias value is a
space or tab character, then the next command word following the
conflicts with the shell's filename expansion operators. If the
@var{subscript} is @samp{@@} or @samp{*}, the word expands to all members
of the array @var{name}. These subscripts differ only when the word
-appears within double quotes. If the word is double-quoted,
+appears within double quotes.
+If the word is double-quoted,
@code{$@{name[*]@}} expands to a single word with
the value of each array member separated by the first character of the
-@code{IFS} variable, and @code{$@{name[@@]@}} expands each element of
+@env{IFS} variable, and @code{$@{name[@@]@}} expands each element of
@var{name} to a separate word. When there are no array members,
-@code{$@{name[@@]@}} expands to nothing. This is analogous to the
+@code{$@{name[@@]@}} expands to nothing.
+If the double-quoted expansion occurs within a word, the expansion of
+the first parameter is joined with the beginning part of the original
+word, and the expansion of the last parameter is joined with the last
+part of the original word.
+This is analogous to the
expansion of the special parameters @samp{@@} and @samp{*}.
@code{$@{#name[}@var{subscript}@code{]@}} expands to the length of
@code{$@{name[}@var{subscript}@code{]@}}.
referencing element zero.
The @code{unset} builtin is used to destroy arrays.
-@code{unset} @var{name[subscript]}
+@code{unset} @var{name}[@var{subscript}]
destroys the array element at index @var{subscript}.
+Care must be taken to avoid unwanted side effects caused by filename
+generation.
@code{unset} @var{name}, where @var{name} is an array, removes the
entire array. A subscript of @samp{*} or @samp{@@} also removes the
entire array.
The @code{declare}, @code{local}, and @code{readonly}
-builtins each accept a @samp{-a}
+builtins each accept a @option{-a}
option to specify an array. The @code{read}
-builtin accepts a @samp{-a}
+builtin accepts a @option{-a}
option to assign a list of words read from the standard input
to an array, and can read values from the standard input into
individual array elements. The @code{set} and @code{declare}
of the directory stack.
The contents of the directory stack are also visible
-as the value of the @code{DIRSTACK} shell variable.
+as the value of the @env{DIRSTACK} shell variable.
@node Directory Stack Builtins
@subsection Directory Stack Builtins
@section Controlling the Prompt
@cindex prompting
-The value of the variable @code{PROMPT_COMMAND} is examined just before
-Bash prints each primary prompt. If @code{PROMPT_COMMAND} is set and
+The value of the variable @env{PROMPT_COMMAND} is examined just before
+Bash prints each primary prompt. If @env{PROMPT_COMMAND} is set and
has a non-null value, then the
value is executed just as if it had been typed on the command line.
A bell character.
@item \d
The date, in "Weekday Month Date" format (e.g., "Tue May 26").
+@item \D@{@var{format}@}
+The @var{format} is passed to @code{strftime}(3) and the result is inserted
+into the prompt string; an empty @var{format} results in a locale-specific
+time representation. The braces are required.
@item \e
An escape character.
@item \h
The time, in 12-hour HH:MM:SS format.
@item \@@
The time, in 12-hour am/pm format.
+@item \A
+The time, in 24-hour HH:MM format.
@item \u
The username of the current user.
@item \v
@item \V
The release of Bash, version + patchlevel (e.g., 2.00.0)
@item \w
-The current working directory.
+The current working directory, with @env{$HOME} abbreviated with a tilde.
@item \W
-The basename of @code{$PWD}.
+The basename of @env{$PWD}, with @env{$HOME} abbreviated with a tilde.
@item \!
The history number of this command.
@item \#
@cindex restricted shell
If Bash is started with the name @code{rbash}, or the
-@samp{--restricted}
+@option{--restricted}
+or
+@option{-r}
option is supplied at invocation, the shell becomes restricted.
A restricted shell is used to
set up an environment more controlled than the standard shell.
A restricted shell behaves identically to @code{bash}
-with the exception that the following are disallowed:
+with the exception that the following are disallowed or not performed:
+
@itemize @bullet
@item
Changing directories with the @code{cd} builtin.
@item
-Setting or unsetting the values of the @code{SHELL}, @code{PATH},
-@code{ENV}, or @code{BASH_ENV} variables.
+Setting or unsetting the values of the @env{SHELL}, @env{PATH},
+@env{ENV}, or @env{BASH_ENV} variables.
@item
Specifying command names containing slashes.
@item
Specifying a filename containing a slash as an argument to the @code{.}
builtin command.
@item
-Specifying a filename containing a slash as an argument to the @samp{-p}
+Specifying a filename containing a slash as an argument to the @option{-p}
option to the @code{hash} 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.
+Parsing the value of @env{SHELLOPTS} from the shell environment at startup.
@item
Redirecting output using the @samp{>}, @samp{>|}, @samp{<>}, @samp{>&},
@samp{&>}, and @samp{>>} redirection operators.
Using the @code{exec} builtin to replace the shell with another command.
@item
Adding or deleting builtin commands with the
-@samp{-f} and @samp{-d} options to the @code{enable} builtin.
+@option{-f} and @option{-d} options to the @code{enable} builtin.
@item
-Specifying the @samp{-p} option to the @code{command} builtin.
+Using the @code{enable} builtin command to enable disabled shell builtins.
+@item
+Specifying the @option{-p} option to the @code{command} builtin.
@item
Turning off restricted mode with @samp{set +r} or @samp{set +o restricted}.
@end itemize
+These restrictions are enforced after any startup files are read.
+
+When a command that is found to be a shell script is executed
+(@pxref{Shell Scripts}), @code{rbash} turns off any restrictions in
+the shell spawned to execute the script.
+
@node Bash POSIX Mode
@section Bash POSIX Mode
@cindex POSIX Mode
-Starting Bash with the @samp{--posix} command-line option or executing
+Starting Bash with the @option{--posix} command-line option or executing
@samp{set -o posix} while Bash is running will cause Bash to conform more
closely to the @sc{posix} 1003.2 standard by changing the behavior to
match that specified by @sc{posix} in areas where the Bash default differs.
+When invoked as @code{sh}, Bash enters @sc{posix} mode after reading the
+startup files.
+
The following list is what's changed when `@sc{posix} mode' is in effect:
@enumerate
@item
When a command in the hash table no longer exists, Bash will re-search
-@code{$PATH} to find the new location. This is also available with
+@env{$PATH} to find the new location. This is also available with
@samp{shopt -s checkhash}.
@item
-The @samp{>&} redirection does not redirect stdout and stderr.
+The message printed by the job control code and builtins when a job
+exits with a non-zero status is `Done(status)'.
@item
The message printed by the job control code and builtins when a job
-exits with a non-zero status is `Done(status)'.
+is stopped is `Stopped(@var{signame})', where @var{signame} is, for
+example, @code{SIGTSTP}.
@item
-Reserved words may not be aliased.
+The @code{bg} builtin uses the required format to describe each job placed
+in the background, which does not include an indication of whether the job
+is the current or previous job.
@item
-The @sc{posix} 1003.2 @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 values of @code{PS1} and
-@code{PS2} regardless of the setting of the @code{promptvars} option.
+Reserved words appearing in a context where reserved words are recognized
+do not undergo alias expansion.
@item
-Interactive comments are enabled by default. (Bash has them on by
-default anyway.)
+The @sc{posix} 1003.2 @env{PS1} and @env{PS2} expansions of @samp{!} to
+the history number and @samp{!!} to @samp{!} are enabled,
+and parameter expansion is performed on the values of @env{PS1} and
+@env{PS2} regardless of the setting of the @code{promptvars} option.
@item
-The @sc{posix} 1003.2 startup files are executed (@code{$ENV}) rather than
+The @sc{posix} 1003.2 startup files are executed (@env{$ENV}) rather than
the normal Bash files.
@item
@item
The default history file is @file{~/.sh_history} (this is the
-default value of @code{$HISTFILE}).
+default value of @env{$HISTFILE}).
@item
The output of @samp{kill -l} prints all the signal names on a single line,
-separated by spaces.
+separated by spaces, without the @samp{SIG} prefix.
+
+@item
+The @code{kill} builtin does not accept signal names with a @samp{SIG}
+prefix.
@item
Non-interactive shells exit if @var{filename} in @code{.} @var{filename}
causes a fatal syntax error in non-interactive shells.
@item
-@sc{posix} 1003.2 `special' builtins are found before shell functions
+@sc{posix} 1003.2 special builtins are found before shell functions
during command lookup.
@item
the command name, and so on.
@item
-If the @code{cd} builtin finds a directory to change to
-using @code{$CDPATH}, the
-value it assigns to the @code{PWD} variable does not contain any
-symbolic links, as if @samp{cd -P} had been executed.
-
-@item
-If @code{$CDPATH} is set, the @code{cd} builtin will not implicitly
+If @env{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{$CDPATH}, even if the a directory with
+any of the entries in @env{$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.
persist in the shell environment after the builtin completes.
@item
+Assignment statements preceding shell function calls persist in the
+shell environment after the function returns, as if a @sc{posix}
+special builtin command had been executed.
+
+@item
The @code{export} and @code{readonly} builtin commands display their
output in the format required by @sc{posix} 1003.2.
+@item
+The @code{trap} builtin displays signal names without the leading
+@code{SIG}.
+
+@item
+The @code{trap} builtin doesn't check the first argument for a possible
+signal specification and revert the signal handling to the original
+disposition if it is, unless that argument consists solely of digits and
+is a valid signal number. If users want to reset the handler for a given
+signal to the original disposition, they should use @samp{-} as the
+first argument.
+
+@item
+The @code{.} and @code{source} builtins do not search the current directory
+for the filename argument if it is not found by searching @env{PATH}.
+
+@item
+Subshells spawned to execute command substitutions inherit the value of
+the @option{-e} option from the parent shell. When not in @sc{posix} mode,
+Bash clears the @option{-e} option in such subshells.
+
+@item
+Alias expansion is always enabled, even in non-interactive shells.
+
+@item
+When the @code{alias} builtin displays alias definitions, it does not
+display them with a leading @samp{alias } unless the @option{-p} option
+is supplied.
+
+@item
+When the @code{set} builtin is invoked without options, it does not display
+shell function names and definitions.
+
+@item
+When the @code{set} builtin is invoked without options, it displays
+variable values without quotes, unless they contain shell metacharacters,
+even if the result contains nonprinting characters.
+
+@item
+When the @code{cd} builtin is invoked in @var{logical} mode, and the pathname
+constructed from @code{$PWD} and the directory name supplied as an argument
+does not refer to an existing directory, @code{cd} will fail instead of
+falling back to @var{physical} mode.
+
+@item
+When the @code{pwd} builtin is supplied the @option{-P} option, it resets
+@code{$PWD} to a pathname containing no symlinks.
+
+@item
+The @code{pwd} builtin verifies that the value it prints is the same as the
+current directory, even if it is not asked to check the file system with the
+@option{-P} option.
+
+@item
+When listing the history, the @code{fc} builtin does not include an
+indication of whether or not a history entry has been modified.
+
+@item
+The default editor used by @code{fc} is @code{ed}.
+
+@item
+The @code{type} and @code{command} builtins will not report a non-executable
+file as having been found, though the shell will attempt to execute such a
+file if it is the only so-named file found in @code{$PATH}.
+
+@item
+The @code{vi} editing mode will invoke the @code{vi} editor directly when
+the @samp{v} command is run, instead of checking @code{$FCEDIT} and
+@code{$EDITOR}.
+
+@item
+When the @code{xpg_echo} option is enabled, Bash does not attempt to interpret
+any arguments to @code{echo} as options. Each argument is displayed, after
+escape characters are converted.
+
@end enumerate
-There is other @sc{posix} 1003.2 behavior that Bash does not implement.
+There is other @sc{posix} 1003.2 behavior that Bash does not implement by
+default even when in @sc{posix} mode.
Specifically:
@enumerate
+
@item
-Assignment statements affect the execution environment of all
-builtins, not just special ones.
+The @code{fc} builtin checks @code{$EDITOR} as a program to edit history
+entries if @code{FCEDIT} is unset, rather than defaulting directly to
+@code{ed}. @code{fc} uses @code{ed} if @code{EDITOR} is unset.
+
+@item
+As noted above, Bash requires the @code{xpg_echo} option to be enabled for
+the @code{echo} builtin to be fully conformant.
+
@end enumerate
+Bash can be configured to be @sc{posix}-conformant by default, by specifying
+the @option{--enable-strict-posix-default} to @code{configure} when building
+(@pxref{Optional Features}).
+
@node Job Control
@chapter Job Control
character @samp{%} introduces a job name.
Job number @code{n} may be referred to as @samp{%n}.
-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 or started
-in the background. The
-previous job may be referenced using @samp{%-}. In output
+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
+or started in the background.
+A single @samp{%} (with no accompanying job specification) also refers
+to the current job.
+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
previous job with a @samp{-}.
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 enabled,
+any other output.
+If the @option{-b} option to the @code{set} builtin is enabled,
Bash reports such changes immediately (@pxref{The Set Builtin}).
+Any trap on @code{SIGCHLD} is executed for each child process
+that exits.
-If an attempt to exit Bash is while jobs are stopped, the
+If an attempt to exit Bash is made 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,
@item bg
@btindex bg
@example
-bg [@var{jobspec}]
+bg [@var{jobspec} @dots{}]
@end example
-Resume the suspended job @var{jobspec} in the background, as if it
+Resume each 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.
+enabled, or, when run with job control enabled, any
+@var{jobspec} was not found or specifies a job
+that was started without job control.
@item fg
@btindex fg
If @var{jobspec} is not supplied, the status of all jobs is
listed.
-If the @samp{-x} option is supplied, @code{jobs} replaces any
+If the @option{-x} option is supplied, @code{jobs} replaces any
@var{jobspec} found in @var{command} or @var{arguments} with the
corresponding process group @sc{id}, and executes @var{command},
passing it @var{argument}s, returning its exit status.
@end example
Send a signal specified by @var{sigspec} or @var{signum} to the process
named by job specification @var{jobspec} or process @sc{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.
+@var{sigspec} is either a case-insensitive 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.
-If any arguments are supplied when @samp{-l} is given, the names of the
+The @option{-l} option lists the signal names.
+If any arguments are supplied when @option{-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
@item wait
@btindex wait
@example
-wait [@var{jobspec} or @var{pid}]
+wait [@var{jobspec} or @var{pid} ...]
@end example
-Wait until the child process specified by process @sc{id} @var{pid} or job
-specification @var{jobspec} exits and return the exit status of the last
-command waited for.
+Wait until the child process specified by each process @sc{id} @var{pid}
+or job 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.
@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,
+If the @option{-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, and neither the @samp{-a} nor @samp{-r}
+If @var{jobspec} is not present, and neither the @option{-a} nor @option{-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}
+If no @var{jobspec} is supplied, the @option{-a} option means to remove or
+mark all jobs; the @option{-r} option without a @var{jobspec}
argument restricts operation to running jobs.
@item suspend
suspend [-f]
@end example
Suspend the execution of this shell until it receives a
-@code{SIGCONT} signal. The @samp{-f} option means to suspend
+@code{SIGCONT} signal. The @option{-f} option means to suspend
even if the shell is a login shell.
@end table
@set readline-appendix
@set history-appendix
@cindex Readline, how to use
-@include rluser.texinfo
+@include rluser.texi
@cindex History, how to use
-@include hsuser.texinfo
+@include hsuser.texi
@clear readline-appendix
@clear history-appendix
@sc{gnu} operating systems, nearly every version of Unix, and several
non-Unix systems such as BeOS and Interix.
Other independent ports exist for
-@sc{ms-dos}, @sc{os/2}, Windows @sc{95/98}, and Windows @sc{nt}.
+@sc{ms-dos}, @sc{os/2}, and Windows platforms.
@menu
* Basic Installation:: Installation instructions.
-
* Compilers and Options:: How to set special options for various
systems.
-
* Compiling For Multiple Architectures:: How to compile Bash for more
than one kind of system from
the same source tree.
-
* Installation Names:: How to set the various paths used by the installation.
-
* Specifying the System Type:: How to configure Bash for a particular system.
-
* Sharing Defaults:: How to share default configuration values among GNU
programs.
-
* Operation Controls:: Options recognized by the configuration program.
-
* Optional Features:: How to enable and disable optional features when
building Bash.
@end menu
by a program called Autoconf. You only need
@file{configure.in} if you want to change it or regenerate
@code{configure} using a newer version of Autoconf. If
-you do this, make sure you are using Autoconf version 2.10 or
+you do this, make sure you are using Autoconf version 2.50 or
newer.
-If you need to change @file{configure.in} or regenerate
-@code{configure}, you will need to create two files:
-@file{_distribution} and @file{_patchlevel}. @file{_distribution}
-should contain the major and minor version numbers of the Bash
-distribution, for example @samp{2.01}. @file{_patchlevel} should
-contain the patch level of the Bash distribution, @samp{0} for
-example. The script @file{support/mkconffiles} has been provided
-to automate the creation of these files.
-
You can remove the program binaries and object files from the
source code directory by typing @samp{make clean}. To also remove the
files that @code{configure} created (so you can compile Bash for
@code{cd} to the
directory where you want the object files and executables to go and run
the @code{configure} script from the source directory. You may need to
-supply the @samp{--srcdir=PATH} argument to tell @code{configure} where the
+supply the @option{--srcdir=PATH} argument to tell @code{configure} where the
source files are. @code{configure} automatically checks for the
source code in the directory that @code{configure} is in and in `..'.
By default, @samp{make install} will install into
@file{/usr/local/bin}, @file{/usr/local/man}, etc. You can
specify an installation prefix other than @file{/usr/local} by
-giving @code{configure} the option @samp{--prefix=@var{PATH}}.
+giving @code{configure} the option @option{--prefix=@var{PATH}},
+or by specifying a value for the @code{DESTDIR} @samp{make}
+variable when running @samp{make install}.
You can specify separate installation prefixes for
architecture-specific files and architecture-independent files.
If you give @code{configure} the option
-@samp{--exec-prefix=@var{PATH}}, @samp{make install} will use
+@option{--exec-prefix=@var{PATH}}, @samp{make install} will use
@var{PATH} as the prefix for installing programs and libraries.
Documentation and 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 Bash
+automatically, but need 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
+type, give it the @option{--host=TYPE} option. @samp{TYPE} can
either be a short name for the system type, such as @samp{sun4},
or a canonical name with three fields: @samp{CPU-COMPANY-SYSTEM}
-(e.g., @samp{sparc-sun-sunos4.1.2}).
+(e.g., @samp{i386-unknown-freebsd4.2}).
See the file @file{support/config.sub} for the possible
values of each field.
@node Optional Features
@section Optional Features
-The Bash @code{configure} has a number of @samp{--enable-@var{feature}}
+The Bash @code{configure} has a number of @option{--enable-@var{feature}}
options, where @var{feature} indicates an optional part of Bash.
-There are also several @samp{--with-@var{package}} options,
+There are also several @option{--with-@var{package}} options,
where @var{package} is something like @samp{bash-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}}.
+@option{--without-@var{package}}. To configure Bash without a feature
+that is enabled by default, use @option{--disable-@var{feature}}.
-Here is a complete list of the @samp{--enable-} and
-@samp{--with-} options that the Bash @code{configure} recognizes.
+Here is a complete list of the @option{--enable-} and
+@option{--with-} options that the Bash @code{configure} recognizes.
@table @code
@item --with-afs
@item --with-bash-malloc
Use the Bash version of
-@code{malloc} in @file{lib/malloc/malloc.c}. This is not the same
+@code{malloc} in the directory @file{lib/malloc}. 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 some space on each allocation.
+originally derived from the 4.2 @sc{bsd} @code{malloc}. This @code{malloc}
+is 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
be supplied if your system has an inadequate or incomplete termcap
database.
-@item --with-glibc-malloc
-Use the @sc{gnu} libc version of @code{malloc} in
-@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
-certain circumstances.
-
@item --with-gnu-malloc
A synonym for @code{--with-bash-malloc}.
-@item --with-installed-readline
+@item --with-installed-readline[=@var{PREFIX}]
Define this to make Bash link with a locally-installed version of Readline
rather than the version in @file{lib/readline}. This works only with
-Readline 4.1 and later versions.
+Readline 5.0 and later versions. If @var{PREFIX} is @code{yes} or not
+supplied, @code{configure} uses the values of the make variables
+@code{includedir} and @code{libdir}, which are subdirectories of @code{prefix}
+by default, to find the installed version of Readline if it is not in
+the standard system include and library directories.
+If @var{PREFIX} is @code{no}, Bash links with the version in
+@file{lib/readline}.
+If @var{PREFIX} is set to any other value, @code{configure} treats it as
+a directory pathname and looks for
+the installed version of Readline in subdirectories of that directory
+(include files in @var{PREFIX}/@code{include} and the library in
+@var{PREFIX}/@code{lib}).
@item --with-purify
Define this to use the Purify memory allocation checker from Rational
Bourne shell.
@end table
-There are several @samp{--enable-} options that alter how Bash is
+There are several @option{--enable-} options that alter how Bash is
compiled and linked, rather than changing run-time features.
@table @code
+@item --enable-largefile
+Enable support for @uref{http://www.sas.com/standards/large_file/x_open.20Mar96.html,
+large files} if the operating system requires special compiler options
+to build programs which can access large files. This is enabled by
+default, if the operating system provides large file support.
+
@item --enable-profiling
This builds a Bash binary that produces profiling information to be
processed by @code{gprof} each time it is executed.
This allows pipelines as well as shell builtins and functions to be timed.
@item --enable-cond-command
-Include support for the @code{[[} conditional command
+Include support for the @code{[[} conditional command.
(@pxref{Conditional Constructs}).
+@item --enable-cond-regexp
+Include support for matching POSIX regular expressions using the
+@samp{=~} binary operator in the @code{[[} conditional command.
+(@pxref{Conditional Constructs}).
+
+@item --enable-debugger
+Include support for the bash debugger (distributed separately).
+
@item --enable-directory-stack
Include support for a @code{csh}-like directory stack and the
@code{pushd}, @code{popd}, and @code{dirs} builtins
This enables the job control features (@pxref{Job Control}),
if the operating system supports them.
+@item --enable-multibyte
+This enables support for multibyte characters if the operating
+system provides the necessary support.
+
@item --enable-net-redirections
This enables the special handling of filenames of the form
@code{/dev/tcp/@var{host}/@var{port}} and
This enables process substitution (@pxref{Process Substitution}) if
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. See @ref{Printing a Prompt}, for a complete list of prompt
-string escape sequences.
-
@item --enable-progcomp
Enable the programmable completion facilities
(@pxref{Programmable Completion}).
If Readline is not enabled, this option has no effect.
+@item --enable-prompt-string-decoding
+Turn on the interpretation of a number of backslash-escaped characters
+in the @env{$PS1}, @env{$PS2}, @env{$PS3}, and @env{$PS4} prompt
+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 (@pxref{Command Line Editing}).
Include the @code{select} builtin, which allows the generation of simple
menus (@pxref{Conditional Constructs}).
+@item --enable-separate-helpfiles
+Use external files for the documentation displayed by the @code{help} builtin
+instead of storing the text internally.
+
+@item --enable-single-help-strings
+Store the text displayed by the @code{help} builtin as a single string for
+each help topic. This aids in translating the text to different languages.
+You may need to disable this if your compiler cannot handle very long string
+literals.
+
+@item --enable-strict-posix-default
+Make Bash @sc{posix}-conformant by default (@pxref{Bash POSIX Mode}).
+
@item --enable-usg-echo-default
A synonym for @code{--enable-xpg-echo-default}.
@item --enable-xpg-echo-default
Make the @code{echo} builtin expand backslash-escaped characters by default,
-without requiring the @samp{-e} option.
+without requiring the @option{-e} option.
This sets the default value of the @code{xpg_echo} shell option to @code{on},
which makes the Bash @code{echo} behave more like the version specified in
-the Single Unix Specification, version 2.
+the Single Unix Specification, version 3.
@xref{Bash Builtins}, for a description of the escape sequences that
@code{echo} recognizes.
Please report all bugs you find in Bash.
But first, you should
make sure that it really is a bug, and that it appears in the latest
-version of Bash that you have.
+version of Bash.
+The latest version of Bash is always available for FTP from
+@uref{ftp://ftp.gnu.org/pub/bash/}.
Once you have determined that a bug actually exists, use the
@code{bashbug} command to submit a bug report.
section quickly details the differences of significance. A
number of these differences are explained in greater depth in
previous sections.
-This section uses the version of @code{sh} included SVR4.2 as
-the baseline reference.
+This section uses the version of @code{sh} included in SVR4.2 (the
+last version of the historical Bourne shell) as the baseline reference.
@itemize @bullet
@item
Bash is @sc{posix}-conformant, even where the @sc{posix} specification
-differs from traditional @code{sh} behavior.
+differs from traditional @code{sh} behavior (@pxref{Bash POSIX Mode}).
@item
Bash has multi-character invocation options (@pxref{Invoking Bash}).
@item
Bash has command history (@pxref{Bash History Facilities}) and the
@code{history} and @code{fc} builtins to manipulate it.
+The Bash history list maintains timestamp information and uses the
+value of the @code{HISTTIMEFORMAT} variable to display it.
@item
Bash implements @code{csh}-like history expansion
@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}
+quotes. The @option{-D}, @option{--dump-strings}, and @option{--dump-po-strings}
invocation options list the translatable strings found in a script
(@pxref{Locale Translation}).
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.
+The Bash @samp{-o pipefail} option to @code{set} will cause a pipeline to
+return a failure status if any command 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.
+@env{TIMEFORMAT} variable.
@item
Bash implements the @code{for (( @var{expr1} ; @var{expr2} ; @var{expr3} ))}
@item
Bash includes the @code{[[} compound command, which makes conditional
-testing part of the shell grammar (@pxref{Conditional Constructs}).
+testing part of the shell grammar (@pxref{Conditional Constructs}), including
+optional regular expression matching.
+
+@item
+Bash provides optional case-insensitive matching for the @code{case} and
+@code{[[} constructs.
@item
Bash includes brace expansion (@pxref{Brace Expansion}) and tilde
command.
@item
+Bash supports the @samp{+=} assignment operator, which appends to the value
+of the variable named on the left hand side.
+
+@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}).
@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},
+current user (@env{UID}, @env{EUID}, and @env{GROUPS}), the current host
+(@env{HOSTTYPE}, @env{OSTYPE}, @env{MACHTYPE}, and @env{HOSTNAME}),
+and the instance of Bash that is running (@env{BASH},
+@env{BASH_VERSION}, and @env{BASH_VERSINFO}). @xref{Bash Variables},
for details.
@item
-The @code{IFS} variable is used to split only the results of expansion,
+The @env{IFS} variable is used to split only the results of expansion,
not all words (@pxref{Word Splitting}).
This closes a longstanding shell security hole.
file (@pxref{Redirections}).
@item
+Bash includes the @samp{<<<} redirection operator, allowing a string to
+be used as the standard input to a command.
+
+@item
+Bash implements the @samp{[n]<&@var{word}} and @samp{[n]>&@var{word}}
+redirection operators, which move one file descriptor to another.
+
+@item
Bash treats a number of filenames specially when they are
used in redirection operators (@pxref{Redirections}).
@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
+each take @option{-L} and @option{-P} options to switch between logical and
physical modes.
@item
@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
+take a @option{-f} option to act on shell functions, a @option{-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
+used as shell input, a @option{-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}
+searching the @env{$PATH}, using @samp{hash -p}
(@pxref{Bourne Shell Builtins}).
@item
@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
+the @option{-r} option, and will use the @env{REPLY} variable as a
default if no non-option 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.
+also accepts a prompt string with the @option{-p} option and will use
+Readline to obtain the line when given the @option{-e} option.
The @code{read} builtin also has additional options to control input:
-the @samp{-s} option will turn off echoing of input characters as
-they are read, the @samp{-t} option will allow @code{read} to time out
+the @option{-s} option will turn off echoing of input characters as
+they are read, the @option{-t} option will allow @code{read} to time out
if input does not arrive within a specified number of seconds, the
-@samp{-n} option will allow reading only a specified number of
-characters rather than a full line, and the @samp{-d} option will read
+@option{-n} option will allow reading only a specified number of
+characters rather than a full line, and the @option{-d} option will read
until a particular character rather than newline.
@item
@item
Bash includes the @code{shopt} builtin, for finer control of shell
-optional capabilities (@pxref{Bash Builtins}).
+optional capabilities (@pxref{Bash Builtins}), and allows these options
+to be set and unset at shell invocation (@pxref{Invoking Bash}).
@item
Bash has much more optional behavior controllable with the @code{set}
builtin (@pxref{The Set Builtin}).
@item
+The @samp{-x} (@code{xtrace}) option displays commands other than
+simple commands when performing an execution trace
+(@pxref{The Set Builtin}).
+
+@item
The @code{test} builtin (@pxref{Bourne Shell Builtins})
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.
+Bash includes the @code{caller} builtin, which displays the context of
+any active subroutine call (a shell function or a script executed with
+the @code{.} or @code{source} builtins). This supports the bash
+debugger.
+
+@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 before every
+simple command, @code{for} command, @code{case} command,
+@code{select} command, every arithmetic @code{for} command, and before
+the first command executes in a shell function.
+The @code{DEBUG} trap is not inherited by shell functions unless the
+function has been given the @code{trace} attribute or the
+@code{functrace} option has been enabled using the @code{shopt} builtin.
+The @code{extdebug} shell option has additional effects on the
+@code{DEBUG} trap.
+
+The @code{trap} builtin (@pxref{Bourne Shell Builtins}) allows an
+@code{ERR} pseudo-signal specification, similar to @code{EXIT} and @code{DEBUG}.
+Commands specified with an @code{ERR} trap are executed after a simple
+command fails, with a few exceptions.
+The @code{ERR} trap is not inherited by shell functions unless the
+@code{-o errtrace} option to the @code{set} builtin is enabled.
+
+The @code{trap} builtin (@pxref{Bourne Shell Builtins}) allows a
+@code{RETURN} pseudo-signal specification, similar to
+@code{EXIT} and @code{DEBUG}.
+Commands specified with an @code{RETURN} trap are executed before
+execution resumes after a shell function or a shell script executed with
+@code{.} or @code{source} returns.
+The @code{RETURN} trap is not inherited by shell functions unless the
+function has been given the @code{trace} attribute or the
+@code{functrace} option has been enabled using the @code{shopt} builtin.
@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 Bash @code{umask} builtin permits a @option{-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}).
@code{pushd}, @code{popd}, and @code{dirs} builtins to manipulate it
(@pxref{The Directory Stack}).
Bash also makes the directory stack visible as the value of the
-@code{DIRSTACK} shell variable.
+@env{DIRSTACK} shell variable.
@item
Bash interprets special backslash-escaped characters in the prompt
@code{SIGHUP}.
@item
+Bash includes a number of features to support a separate debugger for
+shell scripts.
+
+@item
The SVR4.2 shell has two privilege-related builtins
(@code{mldmode} and @code{priv}) not present in Bash.
Bash does not have the @code{stop} or @code{newgrp} builtins.
@item
-Bash does not use the @code{SHACCT} variable or perform shell accounting.
+Bash does not use the @env{SHACCT} variable or perform shell accounting.
@item
-The SVR4.2 @code{sh} uses a @code{TIMEOUT} variable like Bash uses
-@code{TMOUT}.
+The SVR4.2 @code{sh} uses a @env{TIMEOUT} variable like Bash uses
+@env{TMOUT}.
@end itemize
@item
In a questionable attempt at security, the SVR4.2 shell,
-when invoked without the @samp{-p} option, will alter its real
+when invoked without the @option{-p} option, will alter its real
and effective @sc{uid} and @sc{gid} if they are less than some
magic threshold value, commonly 100.
This can lead to unexpected results.
@code{SIGALRM}, or @code{SIGCHLD}.
@item
-The SVR4.2 shell does not allow the @code{IFS}, @code{MAILCHECK},
-@code{PATH}, @code{PS1}, or @code{PS2} variables to be unset.
+The SVR4.2 shell does not allow the @env{IFS}, @env{MAILCHECK},
+@env{PATH}, @env{PS1}, or @env{PS2} variables to be unset.
@item
The SVR4.2 shell treats @samp{^} as the undocumented equivalent of
(it turns on job control).
@end itemize
+@node Copying This Manual
+@appendix Copying This Manual
+
+@menu
+* GNU Free Documentation License:: License for copying this manual.
+@end menu
+
+@include fdl.texi
+
@node Builtin Index
@unnumbered Index of Shell Builtin Commands
@printindex bt
@unnumbered Concept Index
@printindex cp
-@contents
@bye
projects / platform / upstream / bash.git / blobdiff