@c %**start of header
@setfilename bashref.info
@settitle Bash Reference Manual
-@c %**end of header
-
-@ignore
-last change: Mon May 19 12:55:22 EDT 1997
-@end ignore
-
-@set EDITION 2.0
-@set VERSION 2.01
-@set UPDATED 19 May 1997
-@set UPDATE-MONTH May 1997
-
-@iftex
-@finalout
-@end iftex
-
-@setchapternewpage odd
-@defcodeindex bt
-@defcodeindex rw
-@set BashFeatures
-@dircategory Utilities
-@direntry
-* Bash: (bash). GNU Bourne-Again SHell
-@end direntry
+@include version.texi
+@c %**end of header
-@ifinfo
-@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, 1993, 1996 Free Software Foundation, Inc.
+Copyright @copyright{} 1988--2014 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.
+@quotation
+Permission is granted to copy, distribute and/or modify this document
+under the terms of the GNU Free Documentation License, Version 1.3 or
+any later version published by the Free Software Foundation; with no
+Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts.
+A copy of the license is included in the section entitled
+``GNU Free Documentation License''.
+@end quotation
+@end copying
-@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).
+@defcodeindex bt
+@defcodeindex rw
+@set BashFeatures
-@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.
+@dircategory Basics
+@direntry
+* Bash: (bash). The GNU Bourne-Again SHell.
+@end direntry
-Permission is granted to copy and distribute translations of this manual
-into another language, under the above conditions for modified versions,
-except that this permission notice may be stated in a translation approved
-by the Foundation.
-@end format
-@end ifinfo
+@finalout
@titlepage
@title Bash Reference Manual
@subtitle Reference Documentation for Bash
-@subtitle Edition @value{EDITION}, for @code{bash} Version @value{VERSION}.
-@subtitle @value{UPDATED}
+@subtitle Edition @value{EDITION}, for @code{Bash} Version @value{VERSION}.
+@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, 1993, 1996 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.
-
-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}).
+The Bash home page is @url{http://www.gnu.org/software/bash/}.
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
(@file{ksh}), and the C-shell (@file{csh} and its successor,
-@file{tcsh}). The following menu breaks the features up into
-categories based upon which one of these other shells inspired the
-feature.
+@file{tcsh}). The following menu breaks the features up into
+categories, noting which features were inspired by other shells and
+which are specific to Bash.
This manual is meant as a brief introduction to features found in
Bash. The Bash manual page should be used as the definitive
@menu
* Introduction:: An introduction to the shell.
-
* Definitions:: Some definitions used in the rest of this
manual.
-
* Basic Shell Features:: The shell "building blocks".
-
-* Bourne Shell Features:: Features similar to those found in the
- Bourne shell.
-
-* Csh Features:: Features originally found in the
- Berkeley C-Shell.
-
-* Korn Shell Features:: Features originally found in the Korn
- Shell.
-
+* 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.
* Command Line Editing:: Chapter describing the command line
editing features.
-
+* Using History Interactively:: Command History Expansion
* Installing Bash:: How to build and install Bash on your system.
-
* Reporting Bugs:: How to report bugs in Bash.
-
-* 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.
+* Major Differences From The Bourne Shell:: A terse list of the differences
+ between Bash and historical
+ versions of /bin/sh.
+* GNU Free Documentation License:: Copying and sharing this documentation.
+* Indexes:: Various indexes for 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
@section What is Bash?
Bash is the shell, or command language interpreter,
-that will appear in the @sc{GNU} operating system.
+for the @sc{gnu} operating system.
The name is an acronym for the @samp{Bourne-Again SHell},
-a pun on Steve Bourne, the author of the direct ancestor of the current
-Unix shell @code{/bin/sh},
+a pun on Stephen Bourne, the author of the direct ancestor of
+the current Unix shell @code{sh},
which appeared in the Seventh Edition Bell Labs Research version
of Unix.
-Bash is an @code{sh}-compatible shell that incorporates useful
+Bash is largely compatible with @code{sh} and incorporates useful
features from the Korn shell @code{ksh} and the C shell @code{csh}.
-It is ultimately intended to be a
-conformant implementation of the @sc{IEEE} @sc{POSIX} Shell and Tools
-specification (@sc{IEEE} Working Group 1003.2). It offers functional
-improvements over @code{sh} for both interactive and programming use.
-
-While the @sc{GNU} operating system will include a version
-of @code{csh}, Bash will be the default shell.
-Like other @sc{GNU} software, Bash is quite portable. It currently runs
+It is intended to be a conformant implementation of the @sc{ieee}
+@sc{posix} Shell and Tools portion of the @sc{ieee} @sc{posix}
+specification (@sc{ieee} Standard 1003.1).
+It offers functional improvements over @code{sh} for both interactive and
+programming use.
+
+While the @sc{gnu} operating system provides other shells, including
+a version of @code{csh}, Bash is the default shell.
+Like other @sc{gnu} software, Bash is quite portable. It currently runs
on nearly every version of Unix and a few other operating systems @minus{}
-independently-supported ports exist for @sc{OS/2} and Windows @sc{NT}.
+independently-supported ports exist for @sc{ms-dos}, @sc{os/2},
+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 Unix utilities,
-and a programming language, allowing these utilitites to be
-combined. The shell reads commands either from a terminal or a
-file. Files containing commands can be created, and become
+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 utilities 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 like @file{/bin}, allowing users
-or groups to establish custom environments.
-
-A shell allows execution of Unix commands, both synchronously and
-asynchronously. The @dfn{redirection} constructs permit
-fine-grained control of the input and output of those commands,
-and the shell allows control over the contents of their
-environment. Unix shells also provide a small set of built-in
+system commands in directories such as @file{/bin}, allowing users
+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.
+The shell waits for synchronous commands to complete before accepting
+more input; asynchronous commands continue to execute in parallel
+with the shell while it reads and executes additional commands.
+The @dfn{redirection} constructs permit
+fine-grained control of the input and output of those commands.
+Moreover, the shell allows control over the contents of commands'
+environments.
+
+Shells also provide a small set of built-in
commands (@dfn{builtins}) implementing functionality impossible
-(e.g., @code{cd}, @code{break}, @code{continue}, and
-@code{exec}), or inconvenient (@code{history}, @code{getopts},
-@code{kill}, or @code{pwd}, for example) to obtain via separate
-utilities. Shells may be used interactively or
-non-interactively: they accept input typed from the keyboard or
-from a file. All of the shell builtins are described in
+or inconvenient to obtain via separate utilities.
+For example, @code{cd}, @code{break}, @code{continue}, and
+@code{exec} cannot be implemented outside of the shell because
+they directly manipulate the shell itself.
+The @code{history}, @code{getopts}, @code{kill}, or @code{pwd}
+builtins, among others, could be implemented in separate utilities,
+but they are more convenient to use as builtin commands.
+All of the shell builtins are described in
subsequent sections.
While executing commands is essential, most of the power (and
languages. Like any high-level language, the shell provides
variables, flow control constructs, quoting, and functions.
-Shells have begun offering features geared specifically for
+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 POSIX
@cindex POSIX
A family of open system standards based on Unix. Bash
-is concerned with @sc{POSIX} 1003.2, the Shell and Tools Standard.
+is primarily concerned with the Shell and Utilities portion of the
+@sc{posix} 1003.1 standard.
@item blank
A space or tab character.
@item control operator
@cindex control operator
-A @code{word} that performs a control function. It is a @code{newline}
+A @code{token} that performs a control function. It is a @code{newline}
or one of the following:
@samp{||}, @samp{&&}, @samp{&}, @samp{;}, @samp{;;},
-@samp{|}, @samp{(}, or @samp{)}.
+@samp{|}, @samp{|&}, @samp{(}, or @samp{)}.
@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
@cindex operator, shell
A @code{control operator} or a @code{redirection operator}.
@xref{Redirections}, for a list of redirection operators.
+Operators contain at least one unquoted @code{metacharacter}.
@item process group
@cindex process group
A collection of related processes each having the same process
-group @sc{ID}.
+group @sc{id}.
@item process group ID
@cindex process group ID
-A unique identifer that represents a @code{process group}
+A unique identifier that represents a @code{process group}
during its lifetime.
@item reserved word
@item signal
@cindex signal
-A mechanism by which a process may be notified by the kernal
+A mechanism by which a process may be notified by the kernel
of an event occurring in the system.
@item special builtin
@cindex special builtin
A shell builtin command that has been classified as special by the
-@sc{POSIX.2} standard.
+@sc{posix} standard.
@item token
@cindex token
-A sequence of characters considered a single unit by the shell. It is
-either a @code{word} or an @code{operator}.
+A sequence of characters considered a single unit by the shell.
+It is either a @code{word} or an @code{operator}.
@item word
@cindex word
-A @code{token} that is not an @code{operator}.
+A sequence of characters treated as a unit by the shell.
+Words may not include unquoted @code{metacharacters}.
@end table
@node Basic Shell Features
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":
+This chapter briefly summarizes the shell's `building blocks':
commands, control structures, shell functions, shell @i{parameters},
shell expansions,
@i{redirections}, which are a way to direct input and output from
@menu
* Shell Syntax:: What your input means to the shell.
-* Simple Commands:: The most common type of command.
-* Pipelines:: Connecting the input and output of several
- commands.
-* Lists:: How to execute commands sequentially.
-* Looping Constructs:: Shell commands for iterative action.
-* Conditional Constructs:: Shell commands for conditional execution.
-* Command Grouping:: Ways to group commands.
+* Shell Commands:: The types of commands you can use.
* Shell Functions:: Grouping commands by name.
-* Shell Parameters:: Special shell variables.
-* Shell Expansions:: How Bash expands variables and the various
+* 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
+When the shell reads input, it proceeds through a
+sequence of operations. If the input indicates the beginning of a
+comment, the shell ignores the comment symbol (@samp{#}), and the rest
+of that line.
+
+Otherwise, roughly speaking, the shell reads its input and
+divides the input into words and operators, employing the quoting rules
+to select which meanings to assign various words and characters.
+
+The shell then parses these tokens into commands and other constructs,
+removes the special meaning of certain words or characters, expands
+others, redirects input and output as needed, executes the specified
+command, waits for the command's exit status, and makes that exit status
+available for further inspection or processing.
+
@node Shell Operation
@subsection Shell Operation
@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
Breaks the input into words and operators, obeying the quoting rules
-described in @ref{Quoting}. Tokens are separated by
+described in @ref{Quoting}. These tokens are separated by
@code{metacharacters}. Alias expansion is performed by this step
(@pxref{Aliases}).
@item
-Parses the tokens into simple and compound commands.
+Parses the tokens into simple and compound commands
+(@pxref{Shell Commands}).
@item
Performs the various shell expansions (@pxref{Shell Expansions}), breaking
@item
Optionally waits for the command to complete and collects its exit
-status.
+status (@pxref{Exit Status}).
@end enumerate
* 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
reserved words from being recognized as such, and to prevent
parameter expansion.
-Each of the shell @code{metacharacters} (@pxref{Definitions})
-has special meaning to the shell and must be quoted if they are to
-represent themselves. There are three quoting mechanisms: the
+Each of the shell metacharacters (@pxref{Definitions})
+has special meaning to the shell and must be quoted if it is to
+represent itself.
+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
+more details concerning history expansion.
+
+There are three quoting mechanisms: the
@var{escape character}, single quotes, and double quotes.
@node Escape Character
A non-quoted backslash @samp{\} is the Bash escape character.
It preserves the literal value of the next character that follows,
with the exception of @code{newline}. If a @code{\newline} pair
-appears, and the backslash is not quoted, the @code{\newline}
-is treated as a line continuation (that is, it is effectively ignored).
+appears, and the backslash itself is not quoted, the @code{\newline}
+is treated as a line continuation (that is, it is removed from
+the input stream and effectively ignored).
@node Single Quotes
@subsubsection Single Quotes
-Enclosing characters in single quotes preserves the literal value
+Enclosing characters in single quotes (@samp{'}) preserves the literal value
of each character within the quotes. A single quote may not occur
between single quotes, even when preceded by a backslash.
@node Double Quotes
@subsubsection Double Quotes
-Enclosing characters in double quotes preserves the literal value
+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{$} and @samp{`}
-retain their special meaning within double quotes. The backslash
-retains its special meaning only when followed by one of the following
-characters:
+retain their special meaning within double quotes (@pxref{Shell Expansions}).
+The backslash retains its special meaning only when followed by one of
+the following characters:
@samp{$}, @samp{`}, @samp{"}, @samp{\}, or @code{newline}.
+Within double quotes, backslashes that are followed by one of these
+characters are removed. Backslashes preceding characters without a
+special meaning are left unmodified.
A double quote may be quoted within double quotes by preceding it with
a backslash.
+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{$'@var{string}'} are treated specially. The
word expands to @var{string}, with backslash-escaped characters replaced
-as specifed by the ANSI C standard. Backslash escape sequences, if
+as specified by the ANSI C standard. Backslash escape sequences, if
present, are decoded as follows:
@table @code
@item \b
backspace
@item \e
+@itemx \E
an escape character (not ANSI C)
@item \f
form feed
vertical tab
@item \\
backslash
+@item \'
+single quote
+@item \"
+double quote
@item \@var{nnn}
-the character whose @code{ASCII} code is @var{nnn} in octal
+the eight-bit character whose value is the octal value @var{nnn}
+(one to three digits)
+@item \x@var{HH}
+the eight-bit character whose value is the hexadecimal value @var{HH}
+(one or two hex digits)
+@item \u@var{HHHH}
+the Unicode (ISO/IEC 10646) character whose value is the hexadecimal value
+@var{HHHH} (one to four hex digits)
+@item \U@var{HHHHHHHH}
+the Unicode (ISO/IEC 10646) character whose value is the hexadecimal value
+@var{HHHHHHHH} (one to eight hex digits)
+@item \c@var{x}
+a control-@var{x} character
@end table
@noindent
-The result is single-quoted, as if the dollar sign had not been present.
+The expanded result is single-quoted, as if the dollar sign had not
+been present.
@node Locale Translation
@subsubsection Locale-Specific Translation
@cindex localization
+@cindex internationalization
+@cindex native languages
+@cindex translation, native languages
A double-quoted string preceded by a dollar sign (@samp{$}) 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
In a non-interactive shell, or an interactive shell in which the
@code{interactive_comments} option to the @code{shopt}
-builtin is enabled (@pxref{Bash Builtins}),
+builtin is enabled (@pxref{The Shopt Builtin}),
a word beginning with @samp{#}
causes that word and all remaining characters on that line to
be ignored. An interactive shell without the @code{interactive_comments}
option enabled does not allow comments. The @code{interactive_comments}
option is on by default in interactive shells.
+@xref{Interactive Shells}, for a description of what makes
+a shell interactive.
+
+@node Shell Commands
+@section Shell Commands
+@cindex commands, shell
+
+A simple shell command such as @code{echo a b c} consists of the command
+itself followed by arguments, separated by spaces.
+
+More complex shell commands are composed of simple commands arranged together
+in a variety of ways: in a pipeline in which the output of one command
+becomes the input of a second, in a loop or conditional construct, or in
+some other grouping.
+
+@menu
+* Simple Commands:: The most common type of command.
+* Pipelines:: Connecting the input and output of several
+ commands.
+* Lists:: How to execute commands sequentially.
+* Compound Commands:: Shell commands for control flow.
+* Coprocesses:: Two-way communication between commands.
+* GNU Parallel:: Running commands in parallel.
+@end menu
@node Simple Commands
-@section Simple Commands
+@subsection Simple Commands
@cindex commands, simple
-A simple command is the kind of command you'll encounter most often.
+A simple command is the kind of command encountered most often.
It's just a sequence of words separated by @code{blank}s, terminated
-by one of the shell control operators (@pxref{Definitions}). The
-first word generally specifies a command to be executed.
+by one of the shell's control operators (@pxref{Definitions}). The
+first word generally specifies a command to be executed, with the
+rest of the words being that command's arguments.
The return status (@pxref{Exit Status}) of a simple command is
its exit status as provided
-by the @sc{POSIX.1} @code{waitpid} function, or 128+@var{n} if the command
-was terminated by signal @var{n}.
+by the @sc{posix} 1003.1 @code{waitpid} function, or 128+@var{n} if
+the command was terminated by signal @var{n}.
@node Pipelines
-@section Pipelines
+@subsection Pipelines
@cindex pipeline
@cindex commands, pipelines
-A @code{pipeline} is a sequence of simple commands separated by
-@samp{|}.
+A @code{pipeline} is a sequence of simple commands separated by one of
+the control operators @samp{|} or @samp{|&}.
@rwindex time
@rwindex !
@cindex command timing
The format for a pipeline is
@example
-[@code{time} [@code{-p}]] [@code{!}] @var{command1} [@code{|} @var{command2} @dots{}]
+[time [-p]] [!] @var{command1} [ | or |& @var{command2} ] @dots{}
@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. This
+connection is performed before any redirections specified by the
+command.
+
+If @samp{|&} is used, @var{command1}'s standard error, in addition to
+its standard output, is connected to
+@var{command2}'s standard input through the pipe;
+it is shorthand for @code{2>&1 |}.
+This implicit redirection of the standard error to the standard output is
+performed after any redirections specified by the command.
The reserved word @code{time} causes timing statistics
to be printed for the pipeline once it finishes.
-The @samp{-p} option changes the output format to that specified
-by @sc{POSIX}.
-The @code{TIMEFORMAT} variable may be set to a format string that
+The statistics currently consist of elapsed (wall-clock) time and
+user and system time consumed by the command's execution.
+The @option{-p} option changes the output format to that specified
+by @sc{posix}.
+When the shell is in @sc{posix} mode (@pxref{Bash POSIX Mode}),
+it does not recognize @code{time} as a reserved word if the next
+token begins with a @samp{-}.
+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
+shell builtins, shell functions, and pipelines. An external
+@code{time} command cannot time these easily.
+
+When the shell is in @sc{posix} mode (@pxref{Bash POSIX Mode}), @code{time}
+may be followed by a newline. In this case, the shell displays the
+total user and system time consumed by the shell and its children.
+The @env{TIMEFORMAT} variable may be used to specify the format of
+the time information.
-Each command in a pipeline is executed in its own subshell. The exit
+If the pipeline is not executed asynchronously (@pxref{Lists}), the
+shell waits for all commands in the pipeline to complete.
+
+Each command in a pipeline is executed in its own subshell
+(@pxref{Command Execution Environment}). The exit
status of a pipeline is the exit status of the last command in the
-pipeline. If the reserved word @samp{!} precedes the pipeline, the
-exit status is the logical @sc{NOT} of the exit status of the last command.
+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
-@section Lists of Commands
+@subsection Lists of Commands
@cindex commands, lists
A @code{list} is a sequence of one or more pipelines separated by one
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 in the @var{background}
-in a subshell. The shell does not wait for the command to
-finish, and the return status is 0 (true). Commands separated by a
-@samp{;} are executed sequentially; the shell waits for each
-command to terminate in turn. The return status is the
+the shell executes the command asynchronously in a subshell.
+This is known as executing the command in the @var{background}.
+The shell does not wait for the command to finish, and the return
+status is 0 (true).
+When job control is not active (@pxref{Job Control}),
+the standard input for asynchronous commands, in the absence of any
+explicit redirections, is redirected from @code{/dev/null}.
+
+Commands separated by a @samp{;} are executed sequentially; the shell
+waits for each command to terminate in turn. The return status is the
exit status of the last command executed.
-The control operators @samp{&&} and @samp{||}
-denote @sc{AND} lists and @sc{OR} lists, respectively.
-An @sc{AND} list has the form
+@sc{and} and @sc{or} lists are sequences of one or more pipelines
+separated by the control operators @samp{&&} and @samp{||},
+respectively. @sc{and} and @sc{or} lists are executed with left
+associativity.
+
+An @sc{and} list has the form
@example
-@var{command} && @var{command2}
+@var{command1} && @var{command2}
@end example
@noindent
-@var{command2} is executed if, and only if, @var{command}
+@var{command2} is executed if, and only if, @var{command1}
returns an exit status of zero.
-An @sc{OR} list has the form
+An @sc{or} list has the form
@example
-@var{command} || @var{command2}
+@var{command1} || @var{command2}
@end example
@noindent
-@var{command2} is executed if and only if @var{command}
+@var{command2} is executed if, and only if, @var{command1}
returns a non-zero exit status.
The return status of
-@sc{AND} and @sc{OR} lists is the exit status of the last command
+@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.
+
+In most cases a list of commands in a compound command's description may be
+separated from the rest of the command by one or more newlines, and may be
+followed by a newline in place of a semicolon.
+
+Bash provides looping constructs, conditional commands, and mechanisms
+to group commands and execute them as a unit.
+
@node Looping Constructs
-@section Looping Constructs
+@subsubsection Looping Constructs
@cindex commands, looping
-Note that wherever you see a @samp{;} in the description of a
-command's syntax, it may be replaced indiscriminately with
-one or more newlines.
-
Bash supports the following looping constructs.
+Note that wherever a @samp{;} appears in the description of a
+command's syntax, it may be replaced with one or more newlines.
+
@table @code
@item until
@rwindex until
@rwindex do
@rwindex done
The syntax of the @code{until} command is:
+
@example
until @var{test-commands}; do @var{consequent-commands}; done
@end example
-Execute @var{consequent-commands} as long as the final command in
+
+Execute @var{consequent-commands} as long as
@var{test-commands} has an exit status which is not zero.
+The return status is the exit status of the last command executed
+in @var{consequent-commands}, or zero if none was executed.
@item while
@rwindex while
The syntax of the @code{while} command is:
+
@example
while @var{test-commands}; do @var{consequent-commands}; done
@end example
-Execute @var{consequent-commands} as long as the final command in
+Execute @var{consequent-commands} as long as
@var{test-commands} has an exit status of zero.
+The return status is the exit status of the last command executed
+in @var{consequent-commands}, or zero if none was executed.
@item for
@rwindex for
The syntax of the @code{for} command is:
@example
-for @var{name} [in @var{words} @dots{}]; do @var{commands}; done
+for @var{name} [ [in [@var{words} @dots{}] ] ; ] do @var{commands}; done
+@end example
+
+Expand @var{words}, and execute @var{commands} once for each member
+in the resultant list, with @var{name} bound to the current member.
+If @samp{in @var{words}} is not present, the @code{for} command
+executes the @var{commands} once for each positional parameter that is
+set, as if @samp{in "$@@"} had been specified
+(@pxref{Special Parameters}).
+The return status is the exit status of the last command that executes.
+If there are no items in the expansion of @var{words}, no commands are
+executed, and the return status is zero.
+
+An alternate form of the @code{for} command is also supported:
+
+@example
+for (( @var{expr1} ; @var{expr2} ; @var{expr3} )) ; do @var{commands} ; done
@end example
-Execute @var{commands} for each member in @var{words}, with @var{name}
-bound to the current member. If @samp{in @var{words}} is not
-present, @samp{in "$@@"} is assumed.
+First, the arithmetic expression @var{expr1} is evaluated according
+to the rules described below (@pxref{Shell Arithmetic}).
+The arithmetic expression @var{expr2} is then evaluated repeatedly
+until it evaluates to zero.
+Each time @var{expr2} evaluates to a non-zero value, @var{commands} are
+executed and the arithmetic expression @var{expr3} is evaluated.
+If any expression is omitted, it behaves as if it evaluates to 1.
+The return value is the exit status of the last command in @var{commands}
+that is executed, or false if any of the expressions is invalid.
@end table
The @code{break} and @code{continue} builtins (@pxref{Bourne Shell Builtins})
may be used to control loop execution.
@node Conditional Constructs
-@section Conditional Constructs
+@subsubsection Conditional Constructs
@cindex commands, conditional
@table @code
fi
@end example
-Execute @var{consequent-commands} only if the final command in
-@var{test-commands} has an exit status of zero.
-Otherwise, each @code{elif} list is executed in turn,
-and if its exit status is zero,
+The @var{test-commands} list is executed, and if its return status is zero,
+the @var{consequent-commands} list is executed.
+If @var{test-commands} returns a non-zero status, each @code{elif} list
+is executed in turn, and if its exit status is zero,
the corresponding @var{more-consequents} is executed and the
command completes.
If @samp{else @var{alternate-consequents}} is present, and
the final command in the final @code{if} or @code{elif} clause
-has a non-zero exit status, then execute @var{alternate-consequents}.
+has a non-zero exit status, then @var{alternate-consequents} is executed.
+The return status is the exit status of the last command executed, or
+zero if no condition tested true.
@item case
@rwindex case
The syntax of the @code{case} command is:
@example
-@code{case @var{word} in [ ( @var{pattern} [| @var{pattern}]@dots{}) @var{commands} ;;]@dots{} esac}
+case @var{word} in [ [(] @var{pattern} [| @var{pattern}]@dots{}) @var{command-list} ;;]@dots{} esac
@end example
-Selectively execute @var{commands} based upon @var{word} matching
-@var{pattern}. The @samp{|} is used to separate multiple patterns.
+@code{case} will selectively execute the @var{command-list} corresponding to
+the first @var{pattern} that matches @var{word}.
+If the shell option @code{nocasematch}
+(see the description of @code{shopt} in @ref{The Shopt Builtin})
+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
+as a @var{clause}.
+
+Each clause must be terminated with @samp{;;}, @samp{;&}, or @samp{;;&}.
+The @var{word} undergoes tilde expansion, parameter expansion, command
+substitution, arithmetic expansion, and quote removal before matching is
+attempted. Each @var{pattern} undergoes tilde expansion, parameter
+expansion, command substitution, and arithmetic expansion.
+
+There may be an arbitrary number of @code{case} clauses, each terminated
+by a @samp{;;}, @samp{;&}, or @samp{;;&}.
+The first pattern that matches determines the
+command-list that is executed.
+It's a common idiom to use @samp{*} as the final pattern to define the
+default case, since that pattern will always match.
Here is an example using @code{case} in a script that could be used to
describe one interesting feature of an animal:
echo " legs."
@end example
+@noindent
+
+If the @samp{;;} operator is used, no subsequent matches are attempted after
+the first pattern match.
+Using @samp{;&} in place of @samp{;;} causes execution to continue with
+the @var{command-list} associated with the next clause, if any.
+Using @samp{;;&} in place of @samp{;;} causes the shell to test the patterns
+in the next clause, if any, and execute any associated @var{command-list}
+on a successful match.
+
+The return status is zero if no @var{pattern} is matched. Otherwise, the
+return status is the exit status of the @var{command-list} executed.
+
+@item select
+@rwindex select
+
+The @code{select} construct allows the easy generation of menus.
+It has almost the same syntax as the @code{for} command:
+
+@example
+select @var{name} [in @var{words} @dots{}]; do @var{commands}; done
+@end example
+
+The list of words following @code{in} is expanded, generating a list
+of items. The set of expanded words is printed on the standard
+error output stream, each preceded by a number. If the
+@samp{in @var{words}} is omitted, the positional parameters are printed,
+as if @samp{in "$@@"} had been specified.
+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 @env{REPLY}.
+
+The @var{commands} are executed after each selection until a
+@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
+current directory, and displays the name and index of the file
+selected.
+
+@example
+select fname in *;
+do
+ echo you picked $fname \($REPLY\)
+ break;
+done
+@end example
+
@item ((@dots{}))
@example
(( @var{expression} ))
@end example
-The @var{expression} is evaluated according to the rules described
-below (@pxref{Arithmetic Evaluation}).
+The arithmetic @var{expression} is evaluated according to the rules
+described below (@pxref{Shell Arithmetic}).
If the value of the expression is non-zero, the return status is 0;
otherwise the return status is 1. This is exactly equivalent to
@example
let "@var{expression}"
@end example
+@noindent
+@xref{Bash Builtins}, for a full description of the @code{let} builtin.
+
+@item [[@dots{}]]
+@rwindex [[
+@rwindex ]]
+@example
+[[ @var{expression} ]]
+@end example
+
+Return a status of 0 or 1 depending on the evaluation of
+the conditional expression @var{expression}.
+Expressions are composed of the primaries described below in
+@ref{Bash Conditional Expressions}.
+Word splitting and filename expansion are not performed on the words
+between the @code{[[} and @code{]]}; 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 used with @code{[[}, the @samp{<} and @samp{>} operators sort
+lexicographically using the current locale.
+
+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},
+as if the @code{extglob} shell option were enabled.
+The @samp{=} operator is identical to @samp{==}.
+If the shell option @code{nocasematch}
+(see the description of @code{shopt} in @ref{The Shopt Builtin})
+is enabled, the match is performed without regard to the case
+of alphabetic characters.
+The return value is 0 if the string matches (@samp{==}) or does not
+match (@samp{!=})the pattern, and 1 otherwise.
+Any part of the pattern may be quoted to force the quoted portion
+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{The Shopt Builtin})
+is enabled, the match is performed without regard to the case
+of alphabetic characters.
+Any part of the pattern may be quoted to force the quoted portion
+to be matched as a string.
+Bracket expressions in regular expressions must be treated carefully,
+since normal quoting characters lose their meanings between brackets.
+If the pattern is stored in a shell variable, quoting the variable
+expansion forces the entire pattern to be matched as a string.
+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.
+
+For example, the following will match a line
+(stored in the shell variable @var{line})
+if there is a sequence of characters in the value consisting of
+any number, including zero, of
+space characters, zero or one instances of @samp{a}, then a @samp{b}:
+@example
+[[ $line =~ [[:space:]]*(a)?b ]]
+@end example
+
+@noindent
+That means values like @samp{aab} and @samp{ aaaaaab} will match, as
+will a line containing a @samp{b} anywhere in its value.
+
+Storing the regular expression in a shell variable is often a useful
+way to avoid problems with quoting characters that are special to the
+shell.
+It is sometimes difficult to specify a regular expression literally
+without using quotes, or to keep track of the quoting used by regular
+expressions while paying attention to the shell's quote removal.
+Using a shell variable to store the pattern decreases these problems.
+For example, the following is equivalent to the above:
+@example
+pattern='[[:space:]]*(a)?b'
+[[ $line =~ $pattern ]]
+@end example
+
+@noindent
+If you want to match a character that's special to the regular expression
+grammar, it has to be quoted to remove its special meaning.
+This means that in the pattern @samp{xxx.txt}, the @samp{.} matches any
+character in the string (its usual regular expression meaning), but in the
+pattern @samp{"xxx.txt"} it can only match a literal @samp{.}.
+Shell programmers should take special care with backslashes, since backslashes
+are used both by the shell and regular expressions to remove the special
+meaning from the following character.
+The following two sets of commands are @emph{not} equivalent:
+@example
+pattern='\.'
+
+[[ . =~ $pattern ]]
+[[ . =~ \. ]]
+
+[[ . =~ "$pattern" ]]
+[[ . =~ '\.' ]]
+@end example
+@noindent
+The first two matches will succeed, but the second two will not, because
+in the second two the backslash will be part of the pattern to be matched.
+In the first two examples, the backslash removes the special meaning from
+@samp{.}, so the literal @samp{.} matches.
+If the string in the first examples were anything other than @samp{.}, say
+@samp{a}, the pattern would not match, because the quoted @samp{.} in the
+pattern loses its special meaning of matching any single character.
+
+Expressions may be combined using the following operators, listed
+in decreasing order of precedence:
+
+@table @code
+@item ( @var{expression} )
+Returns the value of @var{expression}.
+This may be used to override the normal precedence of operators.
+
+@item ! @var{expression}
+True if @var{expression} is false.
+
+@item @var{expression1} && @var{expression2}
+True if both @var{expression1} and @var{expression2} are true.
+
+@item @var{expression1} || @var{expression2}
+True if either @var{expression1} or @var{expression2} is true.
@end table
-The @code{select} construct, which allows users to choose from a list
-of items presented as a menu, is also available.
-@xref{Korn Shell Constructs}, for a full description of @code{select}.
+@noindent
+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
-@section 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 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 @{
Placing a list of commands between curly braces causes the list to
be executed in the current shell context. No subshell is created.
-The semicolon following @var{list} is required.
+The semicolon (or newline) following @var{list} is required.
@end table
In addition to the creation of a subshell, there is a subtle difference
between these two constructs due to historical reasons. The braces
are @code{reserved words}, so they must be separated from the @var{list}
-by @code{blank}s. The parentheses are @code{operators}, and are
+by @code{blank}s or other shell metacharacters.
+The parentheses are @code{operators}, and are
recognized as separate tokens by the shell even if they are not separated
from the @var{list} by whitespace.
The exit status of both of these constructs is the exit status of
@var{list}.
+@node Coprocesses
+@subsection Coprocesses
+@cindex coprocess
+
+A @code{coprocess} is a shell command preceded by the @code{coproc}
+reserved word.
+A coprocess is executed asynchronously in a subshell, as if the command
+had been terminated with the @samp{&} control operator, with a two-way pipe
+established between the executing shell and the coprocess.
+
+The format for a coprocess is:
+@example
+coproc [@var{NAME}] @var{command} [@var{redirections}]
+@end example
+
+@noindent
+This creates a coprocess named @var{NAME}.
+If @var{NAME} is not supplied, the default name is @var{COPROC}.
+@var{NAME} must not be supplied if @var{command} is a simple
+command (@pxref{Simple Commands}); otherwise, it is interpreted as
+the first word of the simple command.
+
+When the coprocess is executed, the shell creates an array variable
+(@pxref{Arrays})
+named @env{NAME} in the context of the executing shell.
+The standard output of @var{command}
+is connected via a pipe to a file descriptor in the executing shell,
+and that file descriptor is assigned to @env{NAME}[0].
+The standard input of @var{command}
+is connected via a pipe to a file descriptor in the executing shell,
+and that file descriptor is assigned to @env{NAME}[1].
+This pipe is established before any redirections specified by the
+command (@pxref{Redirections}).
+The file descriptors can be utilized as arguments to shell commands
+and redirections using standard word expansions.
+The file descriptors are not available in subshells.
+
+The process ID of the shell spawned to execute the coprocess is
+available as the value of the variable @env{NAME}_PID.
+The @code{wait}
+builtin command may be used to wait for the coprocess to terminate.
+
+Since the coprocess is created as an asynchronous command,
+the @code{coproc} command always returns success.
+The return status of a coprocess is the exit status of @var{command}.
+
+@node GNU Parallel
+@subsection GNU Parallel
+
+There are ways to run commands in parallel that are not built into Bash.
+GNU Parallel is a tool to do just that.
+
+GNU Parallel, as its name suggests, can be used to build and run commands
+in parallel. You may run the same command with different arguments, whether
+they are filenames, usernames, hostnames, or lines read from files. GNU
+Parallel provides shorthand references to many of the most common operations
+(input lines, various portions of the input line, different ways to specify
+the input source, and so on). Parallel can replace @code{xargs} or feed
+commands from its input sources to several different instances of Bash.
+
+For a complete description, refer to the GNU Parallel documentation. A few
+examples should provide a brief introduction to its use.
+
+For example, it is easy to replace @code{xargs} to gzip all html files in the
+current directory and its subdirectories:
+@example
+find . -type f -name '*.html' -print | parallel gzip
+@end example
+@noindent
+If you need to protect special characters such as newlines in file names,
+use find's @option{-print0} option and parallel's @option{-0} option.
+
+You can use Parallel to move files from the current directory when the
+number of files is too large to process with one @code{mv} invocation:
+@example
+ls | parallel mv @{@} destdir
+@end example
+
+As you can see, the @{@} is replaced with each line read from standard input.
+While using @code{ls} will work in most instances, it is not sufficient to
+deal with all filenames.
+If you need to accommodate special characters in filenames, you can use
+
+@example
+find . -depth 1 \! -name '.*' -print0 | parallel -0 mv @{@} destdir
+@end example
+
+@noindent
+as alluded to above.
+
+This will run as many @code{mv} commands as there are files in the current
+directory.
+You can emulate a parallel @code{xargs} by adding the @option{-X} option:
+@example
+find . -depth 1 \! -name '.*' -print0 | parallel -0 -X mv @{@} destdir
+@end example
+
+GNU Parallel can replace certain common idioms that operate on lines read
+from a file (in this case, filenames listed one per line):
+@example
+ while IFS= read -r x; do
+ do-something1 "$x" "config-$x"
+ do-something2 < "$x"
+ done < file | process-output
+@end example
+
+@noindent
+with a more compact syntax reminiscent of lambdas:
+@example
+cat list | parallel "do-something1 @{@} config-@{@} ; do-something2 < @{@}" | process-output
+@end example
+
+Parallel provides a built-in mechanism to remove filename extensions, which
+lends itself to batch file transformations or renaming:
+@example
+ls *.gz | parallel -j+0 "zcat @{@} | bzip2 >@{.@}.bz2 && rm @{@}"
+@end example
+@noindent
+This will recompress all files in the current directory with names ending
+in .gz using bzip2, running one job per CPU (-j+0) in parallel.
+(We use @code{ls} for brevity here; using @code{find} as above is more
+robust in the face of filenames containing unexpected characters.)
+Parallel can take arguments from the command line; the above can also be
+written as
+
+@example
+parallel "zcat @{@} | bzip2 >@{.@}.bz2 && rm @{@}" ::: *.gz
+@end example
+
+If a command generates output, you may want to preserve the input order in
+the output. For instance, the following command
+@example
+@{ echo foss.org.my ; echo debian.org; echo freenetproject.org; @} | parallel traceroute
+@end example
+@noindent
+will display as output the traceroute invocation that finishes first.
+Adding the @option{-k} option
+@example
+@{ echo foss.org.my ; echo debian.org; echo freenetproject.org; @} | parallel -k traceroute
+@end example
+@noindent
+will ensure that the output of @code{traceroute foss.org.my} is displayed first.
+
+Finally, Parallel can be used to run a sequence of shell commands in parallel,
+similar to @samp{cat file | bash}.
+It is not uncommon to take a list of filenames, create a series of shell
+commands to operate on them, and feed that list of commnds to a shell.
+Parallel can speed this up. Assuming that @file{file} contains a list of
+shell commands, one per line,
+
+@example
+parallel -j 10 < file
+@end example
+
+@noindent
+will evaluate the commands using the shell (since no explicit command is
+supplied as an argument), in blocks of ten shell jobs at a time.
+
@node Shell Functions
@section Shell Functions
@cindex shell function
Shell functions are a way to group commands for later execution
using a single name for the group. They are executed just like
-a "regular" command. Shell functions are executed in the current
+a "regular" command.
+When the name of a shell function is used as a simple command name,
+the list of commands associated with that function name is executed.
+Shell functions are executed in the current
shell context; no new process is created to interpret them.
Functions are declared using this syntax:
@rwindex function
@example
-[ @code{function} ] @var{name} () @{ @var{command-list}; @}
+@var{name} () @var{compound-command} [ @var{redirections} ]
+@end example
+
+or
+
+@example
+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. 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.
+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 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.
+When the shell is in @sc{posix} mode (@pxref{Bash POSIX Mode}),
+@var{name} may not be the same as one of the special builtins
+(@pxref{Special Builtins}).
+Any redirections (@pxref{Redirections}) associated with the shell function
+are performed when the function is executed.
+
+A function definition may be deleted using the @option{-f} option to the
+@code{unset} builtin (@pxref{Bourne Shell Builtins}).
+
+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 from the command list
+by whitespace or another shell metacharacter.
+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.
+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 these exceptions:
+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),
+and the @env{ERR} trap is not inherited unless the @code{-o errtrace}
+shell option has been enabled.
+@xref{Bourne Shell Builtins}, for the description of the
+@code{trap} builtin.
+
+The @env{FUNCNEST} variable, if set to a numeric value greater
+than 0, defines a maximum function nesting level. Function
+invocations that exceed the limit cause the entire command to
+abort.
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 function
+are restored to the values they had prior to the function's
execution. If a numeric argument is given to @code{return},
-that is the function return status.
+that is the function's return status; otherwise the function's
+return status is the exit status of the last command executed
+before the @code{return}.
Variables local to the function may be declared with the
@code{local} builtin. These variables are visible only to
the function and the commands it invokes.
-Functions may be recursive. No limit is placed on the number of
-recursive calls.
+Function names and definitions may be listed with the
+@option{-f} option to the @code{declare} (@code{typeset})
+builtin command (@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.
+The @code{FUNCNEST} variable may be used to limit the depth of the
+function call stack and restrict the number of function invocations.
+By default, no limit is placed on the number of recursive calls.
@node Shell Parameters
@section Shell Parameters
@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
is not given, the variable is assigned the null string. All
@var{value}s undergo tilde expansion, parameter and variable expansion,
command substitution, arithmetic expansion, and quote
-removal (detailed below). If the variable has its @samp{-i} attribute
-set (see the description of the @code{declare} builtin in
-@ref{Bash Builtins}), then @var{value}
-is subject to arithmetic expansion even if the @code{$((@dots{}))}
-syntax does not appear (@pxref{Arithmetic Expansion}).
+removal (detailed below). If the variable has its @code{integer}
+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.
+When in @sc{posix} mode (@pxref{Bash POSIX Mode}), these builtins may appear
+in a command after one or more instances of the @code{command} builtin
+and retain these assignment statement properties.
+
+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 @var{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 (for indexed arrays), or added as additional key-value pairs
+in an associative array.
+When applied to a string-valued variable, @var{value} is expanded and
+appended to the variable's value.
+
+A variable can be assigned the @var{nameref} attribute using the
+@option{-n} option to the \fBdeclare\fP or \fBlocal\fP builtin commands
+(@pxref{Bash Builtins})
+to create a @var{nameref}, or a reference to another variable.
+This allows variables to be manipulated indirectly.
+Whenever the nameref variable is referenced or assigned to, the operation
+is actually performed on the variable specified by the nameref variable's
+value.
+A nameref is commonly used within shell functions to refer to a variable
+whose name is passed as an argument to the function.
+For instance, if a variable name is passed to a shell function as its first
+argument, running
+@example
+declare -n ref=$1
+@end example
+@noindent
+inside the function creates a nameref variable @var{ref} whose value is
+the variable name passed as the first argument.
+References and assignments to @var{ref} are treated as references and
+assignments to the variable whose name was passed as @code{$1}.
+
+If the control variable in a @code{for} loop has the nameref attribute,
+the list of words can be a list of shell variables, and a name reference
+will be established for each word in the list, in turn, when the loop is
+executed.
+Array variables cannot be given the @option{-n} attribute.
+However, nameref variables can reference array variables and subscripted
+array variables.
+Namerefs can be unset using the @option{-n} option to the @code{unset} builtin
+(@pxref{Bourne Shell Builtins}).
+Otherwise, if @code{unset} is executed with the name of a nameref variable
+as an argument, the variable referenced by the nameref variable will be unset.
@node Positional Parameters
@subsection Positional Parameters
@cindex parameters, positional
-A @var{positional parameter}
-is a parameter denoted by one or more
+A @var{positional parameter} is a parameter denoted by one or more
digits, other than the single digit @code{0}. Positional parameters are
assigned from the shell's arguments when it is invoked,
-and may be reassigned using the @code{set}
-builtin command. Positional parameters may not be assigned to
-with assignment statements. The positional parameters are
+and may be reassigned using the @code{set} builtin command.
+Positional parameter @code{N} may be referenced as @code{$@{N@}}, or
+as @code{$N} when @code{N} consists of a single digit.
+Positional parameters may not be assigned to with assignment statements.
+The @code{set} and @code{shift} builtins are used to set and
+unset them (@pxref{Shell Builtin Commands}).
+The positional parameters are
temporarily replaced when a shell function is executed
(@pxref{Shell Functions}).
@vtable @code
@item *
-Expands to the positional parameters, starting from one. When the
-expansion occurs within double quotes, it expands to a single word
+@vindex $*
+($*) Expands to the positional parameters, starting from one.
+When the expansion is not within double quotes, each positional parameter
+expands to a separate word.
+In contexts where it is performed, those words
+are subject to further word splitting and pathname expansion.
+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.
-
@item @@
-Expands to the positional parameters, starting from one. When the
-expansion occurs within double quotes, each parameter expands as a
+@vindex $@@
+($@@) Expands to the positional parameters, starting from one. When the
+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).
@item #
-Expands to the number of positional parameters in decimal.
+@vindex $#
+($#) Expands to the number of positional parameters in decimal.
@item ?
-Expands to the exit status of the most recently executed foreground
+@vindex $?
+($?) Expands to the exit status of the most recently executed foreground
pipeline.
@item -
-Expands to the current option flags as specified upon invocation,
-by the @code{set}
+@vindex $-
+($-, 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 process @sc{ID} of the current shell, not the
-subshell.
+@vindex $$
+($$) Expands to the process @sc{id} of the shell. In a @code{()} subshell, it
+expands to the process @sc{id} of the invoking shell, not the subshell.
@item !
-Expands to the process @sc{ID} of the most recently executed background
-(asynchronous) command.
+@vindex $!
+($!) Expands to the process @sc{id} of the job most recently placed into the
+background, whether executed as an asynchronous command or using
+the @code{bg} builtin (@pxref{Job Control Builtins}).
@item 0
-Expands to the name of the shell or shell script. This is set at
-shell initialization. If Bash is invoked with a file of commands,
-@code{$0} is set to the name of that file. If Bash
-is started with the @samp{-c} option, then @code{$0}
-is set to the first argument after the string to be
+@vindex $0
+($0) Expands to the name of the shell or shell script. This is set at
+shell initialization. If Bash is invoked with a file of commands
+(@pxref{Shell Scripts}), @code{$0} is set to the name of that file.
+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 _
-At shell startup, set to the absolute filename of the shell or shell
-script being executed as passed in the argument list.
+@vindex $_
+($_, an underscore.)
+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 filename 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
Expansion is performed on the command line after it has been split into
@code{token}s. There are seven kinds of expansion performed:
+
@itemize @bullet
@item brace expansion
@item tilde expansion
@end itemize
@menu
+* Brace Expansion:: Expansion of expressions within braces.
+* Tilde Expansion:: Expansion of the ~ character.
* Shell Parameter Expansion:: How Bash expands variables to their values.
* Command Substitution:: Using the output of a command as an argument.
+* Arithmetic Expansion:: How to use arithmetic in shell expansions.
* Process Substitution:: A way to write and read to and from a
command.
* Word Splitting:: How the results of expansion are split into separate
words.
@end menu
-Brace expansion, tilde expansion, and arithmetic expansion are described
-in other sections. For brace expansion, see @ref{Brace Expansion}; for
-tilde expansion, see @ref{Tilde Expansion}; and for arithmetic expansion,
-see @ref{Arithmetic Expansion}.
-
-The order of expansions is: brace expansion, tilde expansion,
-parameter, variable, and arithmetic expansion and
-command substitution
-(done in a left-to-right fashion), word splitting, and filename
-expansion.
+The order of expansions is:
+brace expansion;
+tilde expansion, parameter and variable expansion, arithmetic expansion,
+and command substitution (done in a left-to-right fashion);
+word splitting;
+and filename expansion.
On systems that can support it, there is an additional expansion
-available: @var{process substitution}. This is performed at the
-same time as parameter, variable, and arithemtic expansion and
+available: @var{process substitution}.
+This is performed at the
+same time as tilde, parameter, variable, and arithmetic expansion and
command substitution.
Only brace expansion, word splitting, and filename expansion
After all expansions, @code{quote removal} (@pxref{Quote Removal})
is performed.
-@node Shell Parameter Expansion
-@subsection Shell Parameter Expansion
-@cindex parameter expansion
-@cindex expansion, parameter
+@node Brace Expansion
+@subsection Brace Expansion
+@cindex brace expansion
+@cindex expansion, brace
-The @samp{$} character introduces parameter expansion,
-command substitution, or arithmetic expansion. The parameter name
-or symbol to be expanded may be enclosed in braces, which
-are optional but serve to protect the variable to be expanded from
-characters immediately following it which could be
-interpreted as part of the name.
+Brace expansion is a mechanism by which arbitrary strings may be generated.
+This mechanism is similar to
+@var{filename expansion} (@pxref{Filename Expansion}),
+but the filenames generated need not exist.
+Patterns to be brace expanded take the form of an optional @var{preamble},
+followed by either a series of comma-separated strings or a sequence expression
+between a pair of braces,
+followed by an optional @var{postscript}.
+The preamble is prefixed to each string contained within the braces, and
+the postscript is then appended to each resulting string, expanding left
+to right.
+
+Brace expansions may be nested.
+The results of each expanded string are not sorted; left to right order
+is preserved.
+For example,
+@example
+bash$ echo a@{d,c,b@}e
+ade ace abe
+@end example
-The basic form of parameter expansion is $@{@var{parameter}@}.
-The value of @var{parameter} is substituted. The braces are required
-when @var{parameter}
-is a positional parameter with more than one digit,
-or when @var{parameter}
-is followed by a character that is not to be
-interpreted as part of its name.
+A sequence expression takes the form @code{@{@var{x}..@var{y}[..@var{incr}]@}},
+where @var{x} and @var{y} are either integers or single characters,
+and @var{incr}, an optional increment, is an integer.
+When integers are supplied, the expression expands to each number between
+@var{x} and @var{y}, inclusive.
+Supplied integers may be prefixed with @samp{0} to force each term to have the
+same width.
+When either @var{x} or @var{y} begins with a zero, the shell
+attempts to force all generated terms to contain the same number of digits,
+zero-padding where necessary.
+When characters are supplied, the expression expands to each character
+lexicographically between @var{x} and @var{y}, inclusive,
+using the default C locale.
+Note that both @var{x} and @var{y} must be of the same type.
+When the increment is supplied, it is used as the difference between
+each term. The default increment is 1 or -1 as appropriate.
-If the first character of @var{parameter} is an exclamation point,
-a level of variable indirection is introduced.
-Bash uses the value of the variable formed from the rest of
-@var{parameter} as the name of the variable; this variable is then
-expanded and that value is used in the rest of the substitution, rather
-than the value of @var{parameter} itself.
-This is known as @code{indirect expansion}.
+Brace expansion is performed before any other expansions,
+and any characters special to other expansions are preserved
+in the result. It is strictly textual. Bash
+does not apply any syntactic interpretation to the context of the
+expansion or the text between the braces.
+To avoid conflicts with parameter expansion, the string @samp{$@{}
+is not considered eligible for brace expansion.
-In each of the cases below, @var{word} is subject to tilde expansion,
-parameter expansion, command substitution, and arithmetic expansion.
-When not performing substring expansion, Bash tests for a parameter
-that is unset or null; omitting the colon results in a test only for a
-parameter that is unset.
+A correctly-formed brace expansion must contain unquoted opening
+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:
+@example
+mkdir /usr/local/src/bash/@{old,new,dist,bugs@}
+@end example
+or
+@example
+chown root /usr/@{ucb/@{ex,edit@},lib/@{ex?.?*,how_ex@}@}
+@end example
+
+@node Tilde Expansion
+@subsection Tilde Expansion
+@cindex tilde expansion
+@cindex expansion, tilde
+
+If a word begins with an unquoted tilde character (@samp{~}), all of the
+characters up to the first unquoted slash (or all characters,
+if there is no unquoted slash) are considered a @var{tilde-prefix}.
+If none of the characters in the tilde-prefix are quoted, the
+characters in the tilde-prefix following the tilde are treated as a
+possible @var{login name}.
+If this login name is the null string, the tilde is replaced with the
+value of the @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 @env{PWD} replaces the tilde-prefix.
+If the tilde-prefix is @samp{~-}, the value of the shell variable
+@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{-},
+the tilde-prefix is replaced with the
+corresponding element from the directory stack, as it would be displayed
+by the @code{dirs} builtin invoked with the characters following tilde
+in the tilde-prefix as an argument (@pxref{The Directory Stack}).
+If the tilde-prefix, sans the tilde, consists of a number without a
+leading @samp{+} or @samp{-}, @samp{+} is assumed.
+
+If the login name is invalid, or the tilde expansion fails, the word is
+left unchanged.
+
+Each variable assignment is checked for unquoted tilde-prefixes immediately
+following a @samp{:} or the first @samp{=}.
+In these cases, tilde expansion is also performed.
+Consequently, one may use filenames with tildes in assignments to
+@env{PATH}, @env{MAILPATH}, and @env{CDPATH},
+and the shell assigns the expanded value.
+
+The following table shows how Bash treats unquoted tilde-prefixes:
+
+@table @code
+@item ~
+The value of @code{$HOME}
+@item ~/foo
+@file{$HOME/foo}
+
+@item ~fred/foo
+The subdirectory @code{foo} of the home directory of the user
+@code{fred}
+
+@item ~+/foo
+@file{$PWD/foo}
+
+@item ~-/foo
+@file{$@{OLDPWD-'~-'@}/foo}
+
+@item ~@var{N}
+The string that would be displayed by @samp{dirs +@var{N}}
+
+@item ~+@var{N}
+The string that would be displayed by @samp{dirs +@var{N}}
+
+@item ~-@var{N}
+The string that would be displayed by @samp{dirs -@var{N}}
+@end table
+
+@node Shell Parameter Expansion
+@subsection Shell Parameter Expansion
+@cindex parameter expansion
+@cindex expansion, parameter
+
+The @samp{$} character introduces parameter expansion,
+command substitution, or arithmetic expansion. The parameter name
+or symbol to be expanded may be enclosed in braces, which
+are optional but serve to protect the variable to be expanded from
+characters immediately following it which could be
+interpreted as part of the name.
+
+When braces are used, the matching ending brace is the first @samp{@}}
+not escaped by a backslash or within a quoted string, and not within an
+embedded arithmetic expansion, command substitution, or parameter
+expansion.
+
+The basic form of parameter expansion is $@{@var{parameter}@}.
+The value of @var{parameter} is substituted.
+The @var{parameter} is a shell parameter as described above
+(@pxref{Shell Parameters}) or an array reference (@pxref{Arrays}).
+The braces are required when @var{parameter}
+is a positional parameter with more than one digit,
+or when @var{parameter} is followed by a character that is not to be
+interpreted as part of its name.
+
+If the first character of @var{parameter} is an exclamation point (!),
+it introduces a level of variable indirection.
+Bash uses the value of the variable formed from the rest of
+@var{parameter} as the name of the variable; this variable is then
+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 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.
+
+When not performing substring expansion, using the form described
+below (e.g., @samp{:-}), Bash tests for a parameter that is unset or null.
+Omitting the colon results in a test only for a parameter that is unset.
+Put another way, if the colon is included,
+the operator tests for both @var{parameter}'s existence and that its value
+is not null; if the colon is omitted, the operator tests only for existence.
@table @code
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}
@item $@{@var{parameter}:@var{offset}@}
@itemx $@{@var{parameter}:@var{offset}:@var{length}@}
-Expands to up to @var{length} characters of @var{parameter},
-starting at @var{offset}.
-If @var{length} is omitted, expands to the substring of
-@var{parameter}, starting at the character specified by @var{offset}.
-@var{length} and @var{offset} are arithmetic expressions
-(@pxref{Arithmetic Evaluation}).
This is referred to as Substring Expansion.
+It expands to up to @var{length} characters of the value of @var{parameter}
+starting at the character specified by @var{offset}.
+If @var{parameter} is @samp{@@}, an indexed array subscripted by
+@samp{@@} or @samp{*}, or an associative array name, the results differ as
+described below.
+If @var{length} is omitted, it expands to the substring of the value of
+@var{parameter} starting at the character specified by @var{offset}
+and extending to the end of the value.
+@var{length} and @var{offset} are arithmetic expressions
+(@pxref{Shell Arithmetic}).
-@var{length} must evaluate to a number greater than or equal to zero.
If @var{offset} evaluates to a number less than zero, the value
-is used as an offset from the end of the value of @var{parameter}.
+is used as an offset in characters
+from the end of the value of @var{parameter}.
+If @var{length} evaluates to a number less than zero,
+it is interpreted as an offset in characters
+from the end of the value of @var{parameter} rather than
+a number of characters, and the expansion is the characters between
+@var{offset} and that result.
+Note that a negative offset must be separated from the colon by at least
+one space to avoid being confused with the @samp{:-} expansion.
+
+Here are some examples illustrating substring expansion on parameters and
+subscripted arrays:
+
+@verbatim
+$ string=01234567890abcdefgh
+$ echo ${string:7}
+7890abcdefgh
+$ echo ${string:7:0}
+
+$ echo ${string:7:2}
+78
+$ echo ${string:7:-2}
+7890abcdef
+$ echo ${string: -7}
+bcdefgh
+$ echo ${string: -7:0}
+
+$ echo ${string: -7:2}
+bc
+$ echo ${string: -7:-2}
+bcdef
+$ set -- 01234567890abcdefgh
+$ echo ${1:7}
+7890abcdefgh
+$ echo ${1:7:0}
+
+$ echo ${1:7:2}
+78
+$ echo ${1:7:-2}
+7890abcdef
+$ echo ${1: -7}
+bcdefgh
+$ echo ${1: -7:0}
+
+$ echo ${1: -7:2}
+bc
+$ echo ${1: -7:-2}
+bcdef
+$ array[0]=01234567890abcdefgh
+$ echo ${array[0]:7}
+7890abcdefgh
+$ echo ${array[0]:7:0}
+
+$ echo ${array[0]:7:2}
+78
+$ echo ${array[0]:7:-2}
+7890abcdef
+$ echo ${array[0]: -7}
+bcdefgh
+$ echo ${array[0]: -7:0}
+
+$ echo ${array[0]: -7:2}
+bc
+$ echo ${array[0]: -7:-2}
+bcdef
+@end verbatim
+
If @var{parameter} is @samp{@@}, the result is @var{length} positional
parameters beginning at @var{offset}.
-If @var{parameter} is an array name indexed by @samp{@@} or @samp{*},
-the result is the @var{length}
-members of the array beginning with $@{@var{parameter}[@var{offset}]@}.
-Substring indexing is zero-based unless the positional parameters are
-used, in which case the indexing starts at 1.
+A negative @var{offset} is taken relative to one greater than the greatest
+positional parameter, so an offset of -1 evaluates to the last positional
+parameter.
+It is an expansion error if @var{length} evaluates to a number less than zero.
+
+The following examples illustrate substring expansion using positional
+parameters:
+
+@verbatim
+$ set -- 1 2 3 4 5 6 7 8 9 0 a b c d e f g h
+$ echo ${@:7}
+7 8 9 0 a b c d e f g h
+$ echo ${@:7:0}
+
+$ echo ${@:7:2}
+7 8
+$ echo ${@:7:-2}
+bash: -2: substring expression < 0
+$ echo ${@: -7:2}
+b c
+$ echo ${@:0}
+./bash 1 2 3 4 5 6 7 8 9 0 a b c d e f g h
+$ echo ${@:0:2}
+./bash 1
+$ echo ${@: -7:0}
+
+@end verbatim
+
+If @var{parameter} is an indexed array name subscripted
+by @samp{@@} or @samp{*}, the result is the @var{length}
+members of the array beginning with @code{$@{@var{parameter}[@var{offset}]@}}.
+A negative @var{offset} is taken relative to one greater than the maximum
+index of the specified array.
+It is an expansion error if @var{length} evaluates to a number less than zero.
+
+These examples show how you can use substring expansion with indexed
+arrays:
+
+@verbatim
+$ array=(0 1 2 3 4 5 6 7 8 9 0 a b c d e f g h)
+$ echo ${array[@]:7}
+7 8 9 0 a b c d e f g h
+$ echo ${array[@]:7:2}
+7 8
+$ echo ${array[@]: -7:2}
+b c
+$ echo ${array[@]: -7:-2}
+bash: -2: substring expression < 0
+$ echo ${array[@]:0}
+0 1 2 3 4 5 6 7 8 9 0 a b c d e f g h
+$ echo ${array[@]:0:2}
+0 1
+$ echo ${array[@]: -7:0}
+
+@end verbatim
+
+Substring expansion applied to an associative array produces undefined
+results.
+
+Substring indexing is zero-based unless the positional parameters
+are used, in which case the indexing starts at 1 by default.
+If @var{offset} is 0, and the positional parameters are used, @code{$@@} is
+prefixed to the list.
+
+@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 @env{IFS} special variable.
+When @samp{@@} is used and the expansion appears within double quotes, each
+variable name expands to a separate word.
+
+@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 value of @var{parameter} is substituted.
-If @var{parameter}
-is @samp{*} or @samp{@@},
-the length substituted is the number of positional parameters.
+The length in characters of the expanded value of @var{parameter} is
+substituted.
+If @var{parameter} is @samp{*} or @samp{@@}, the value substituted
+is the number of positional parameters.
+If @var{parameter} is an array name subscripted by @samp{*} or @samp{@@},
+the value substituted is the number of elements in the array.
If @var{parameter}
-is an array name subscripted
-by @samp{*} or @samp{@@},
-the length substituted is the number of elements in the array.
+is an indexed array name subscripted by a negative number, that number is
+interpreted as relative to one greater than the maximum index of
+@var{parameter}, so negative indices count back from the end of the
+array, and an index of -1 references the last element.
@item $@{@var{parameter}#@var{word}@}
@itemx $@{@var{parameter}##@var{word}@}
The @var{word}
is expanded to produce a pattern just as in filename
expansion (@pxref{Filename Expansion}). If the pattern matches
-the beginning of the value of @var{parameter},
-then the expansion is the value of @var{parameter}
+the beginning of the expanded value of @var{parameter},
+then the result of the expansion is the expanded value of @var{parameter}
with the shortest matching pattern (the @samp{#} case) or the
longest matching pattern (the @samp{##} case) deleted.
If @var{parameter} is @samp{@@} or @samp{*},
@itemx $@{@var{parameter}%%@var{word}@}
The @var{word} is expanded to produce a pattern just as in
filename expansion.
-If the pattern matches a trailing portion of the value of
-@var{parameter}, then the expansion is the value of @var{parameter}
-with the shortest matching pattern (the @samp{%} case) or the
-longest matching pattern (the @samp{%%} case) deleted.
+If the pattern matches a trailing portion of the expanded value of
+@var{parameter}, then the result of the expansion is the value of
+@var{parameter} with the shortest matching pattern (the @samp{%} case)
+or the longest matching pattern (the @samp{%%} case) deleted.
If @var{parameter} is @samp{@@} or @samp{*},
the pattern removal operation is applied to each positional
parameter in turn, and the expansion is the resultant list.
array in turn, and the expansion is the resultant list.
@item $@{@var{parameter}/@var{pattern}/@var{string}@}
-@itemx $@{@var{parameter}//@var{pattern}/@var{string}@}
The @var{pattern} is expanded to produce a pattern just as in
filename expansion.
@var{Parameter} is expanded and the longest match of @var{pattern}
against its value is replaced with @var{string}.
-In the first form, only the first match is replaced.
-The second form causes all matches of @var{pattern} to be
-replaced with @var{string}.
+If @var{pattern} begins with @samp{/}, all matches of @var{pattern} are
+replaced with @var{string}. Normally only the first match is replaced.
If @var{pattern} begins with @samp{#}, it must match at the beginning
-of @var{string}.
+of the expanded value of @var{parameter}.
If @var{pattern} begins with @samp{%}, it must match at the end
-of @var{string}.
+of the expanded value of @var{parameter}.
If @var{string} is null, matches of @var{pattern} are deleted
and the @code{/} following @var{pattern} may be omitted.
If @var{parameter} is @samp{@@} or @samp{*},
the substitution operation is applied to each member of the
array in turn, and the expansion is the resultant list.
+@item $@{@var{parameter}^@var{pattern}@}
+@itemx $@{@var{parameter}^^@var{pattern}@}
+@itemx $@{@var{parameter},@var{pattern}@}
+@itemx $@{@var{parameter},,@var{pattern}@}
+This expansion modifies the case of alphabetic characters in @var{parameter}.
+The @var{pattern} is expanded to produce a pattern just as in
+filename expansion.
+Each character in the expanded value of @var{parameter} is tested against
+@var{pattern}, and, if it matches the pattern, its case is converted.
+The pattern should not attempt to match more than one character.
+The @samp{^} operator converts lowercase letters matching @var{pattern}
+to uppercase; the @samp{,} operator converts matching uppercase letters
+to lowercase.
+The @samp{^^} and @samp{,,} expansions convert each matched character in the
+expanded value; the @samp{^} and @samp{,} expansions match and convert only
+the first character in the expanded value.
+If @var{pattern} is omitted, it is treated like a @samp{?}, which matches
+every character.
+If @var{parameter} is @samp{@@} or @samp{*},
+the case modification operation is applied to each positional
+parameter in turn, and the expansion is the resultant list.
+If @var{parameter}
+is an array variable subscripted with @samp{@@} or @samp{*},
+the case modification operation is applied to each member of the
+array in turn, and the expansion is the resultant list.
@end table
@node Command Substitution
@cindex command substitution
Command substitution allows the output of a command to replace
-the command name. There are two forms:
+the command itself.
+Command substitution occurs when a command is enclosed as follows:
@example
$(@var{command})
@end example
Bash performs the expansion by executing @var{command} and
replacing the command substitution with the standard output of the
command, with any trailing newlines deleted.
+Embedded newlines are not deleted, but they may be removed during
+word splitting.
+The command substitution @code{$(cat @var{file})} can be
+replaced by the equivalent but faster @code{$(< @var{file})}.
When the old-style backquote form of substitution is used,
backslash retains its literal meaning except when followed by
-@samp{$}, @samp{`}, or @samp{\}.
+@samp{$}, @samp{`}, or @samp{\}.
+The first backquote not preceded by a backslash terminates the
+command substitution.
When using the @code{$(@var{command})} form, all characters between
the parentheses make up the command; none are treated specially.
-Command substitutions may be nested. To nest when using the old form,
-escape the inner backquotes with backslashes.
+Command substitutions may be nested. To nest when using the backquoted
+form, escape the inner backquotes with backslashes.
If the substitution appears within double quotes, word splitting and
filename expansion are not performed on the results.
+@node Arithmetic Expansion
+@subsection Arithmetic Expansion
+@cindex expansion, arithmetic
+@cindex arithmetic expansion
+
+Arithmetic expansion allows the evaluation of an arithmetic expression
+and the substitution of the result. The format for arithmetic expansion is:
+
+@example
+$(( @var{expression} ))
+@end example
+
+The expression is treated as if it were within double quotes, but
+a double quote inside the parentheses is not treated specially.
+All tokens in the expression undergo parameter and variable expansion,
+command substitution, and quote removal.
+The result is treated as the arithmetic expression to be evaluated.
+Arithmetic expansions may be nested.
+
+The evaluation is performed according to the rules listed below
+(@pxref{Shell Arithmetic}).
+If the expression is invalid, Bash prints a message indicating
+failure to the standard error and no substitution occurs.
+
@node Process Substitution
@subsection Process Substitution
@cindex process substitution
Process substitution is supported on systems that support named
-pipes (@sc{FIFO}s) or the @file{/dev/fd} method of naming open files.
+pipes (@sc{fifo}s) or the @file{/dev/fd} method of naming open files.
It takes the form of
@example
<(@var{list})
@end example
@noindent
The process @var{list} is run with its input or output connected to a
-@sc{FIFO} or some file in @file{/dev/fd}. The name of this file is
+@sc{fifo} or some file in @file{/dev/fd}. The name of this file is
passed as an argument to the current command as the result of the
expansion. If the @code{>(@var{list})} form is used, writing to
the file will provide input for @var{list}. If the
@code{<(@var{list})} form is used, the file passed as an
argument should be read to obtain the output of @var{list}.
+Note that no space may appear between the @code{<} or @code{>}
+and the left parenthesis, otherwise the construct would be interpreted
+as a redirection.
-On systems that support it, process substitution is performed
-simultaneously with parameter and variable expansion,
-command substitution, and arithmetic expansion.
+When available, process substitution is performed simultaneously with
+parameter and variable expansion, command substitution, and arithmetic
+expansion.
@node Word Splitting
@subsection Word Splitting
and arithmetic expansion that did not occur within double quotes for
word splitting.
-The shell treats each character of @code{$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}
-has a value other than the default, then sequences of
+The shell treats each character of @env{$IFS} as a delimiter, and splits
+the results of the other expansions into words using these characters
+as field terminators.
+If @env{IFS} is unset, or its value is exactly @code{<space><tab><newline>},
+the default, then sequences of
+@code{ <space>}, @code{<tab>}, and @code{<newline>}
+at the beginning and end of the results of the previous
+expansions are ignored, and any sequence of @env{IFS}
+characters not at the beginning or end 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
-@var{parameter}s
-that have no values, are removed.
+parameters that have no values, are removed.
If a parameter with no value is expanded within double quotes, a
null argument results and is retained.
@node Filename Expansion
@subsection Filename Expansion
+@menu
+* Pattern Matching:: How the shell matches patterns.
+@end menu
@cindex expansion, filename
@cindex expansion, pathname
@cindex filename expansion
@cindex pathname expansion
-After word splitting,
-unless the @samp{-f}
-option has been set (@pxref{The Set Builtin}),
-Bash scans each word for the characters
+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
regarded as a @var{pattern},
and replaced with an alphabetically sorted list of
-file names matching the pattern. If no matching file names are found,
+filenames matching the pattern (@pxref{Pattern Matching}).
+If no matching filenames are found,
and the shell option @code{nullglob} is disabled, the word is left
-unchanged. If the option is set, and no matches are found, the word
-is removed. When a pattern is used for filename generation,
-the character @samp{.}
+unchanged.
+If the @code{nullglob} option is set, and no matches are found, the word
+is removed.
+If the @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.
+
+When a pattern is used for filename expansion, the character @samp{.}
at the start of a filename or immediately following a slash
-must be matched explicitly, unless the shell option @code{dotglob}
-is set. The slash character must always be matched explicitly.
+must be matched explicitly, unless the shell option @code{dotglob} is set.
+When matching a filename, the slash character must always be
+matched explicitly.
In other cases, the @samp{.} character is not treated specially.
-See the description of @code{shopt} in @ref{Bash Builtins},
-for a description of the @code{nullglob} and @code{dotglob} options.
-The @code{GLOBIGNORE}
+See the description of @code{shopt} in @ref{The Shopt Builtin},
+for a description of the @code{nocaseglob}, @code{nullglob},
+@code{failglob}, and @code{dotglob} options.
+
+The @env{GLOBIGNORE}
shell variable may be used to restrict the set of filenames matching a
-@var{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
+@subsubsection Pattern Matching
+@cindex pattern matching
+@cindex matching, pattern
+
+Any character that appears in a pattern, other than the special pattern
+characters described below, matches itself.
+The @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
@item *
Matches any string, including the null string.
+When the @code{globstar} shell option is enabled, and @samp{*} is used in
+a filename expansion context, two adjacent @samp{*}s used as a single
+pattern will match all files and zero or more directories and
+subdirectories.
+If followed by a @samp{/}, two adjacent @samp{*}s will match only
+directories and subdirectories.
@item ?
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 falls 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 values of the
+@env{LC_COLLATE} and @env{LC_ALL} shell variables, 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}, or enable the
+@code{globasciiranges} shell option.
+
+Within @samp{[} and @samp{]}, @var{character classes} can be specified
+using the syntax
+@code{[:}@var{class}@code{:]}, where @var{class} is one of the
+following classes defined in the @sc{posix} standard:
+@example
+alnum alpha ascii blank cntrl digit graph lower
+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 all characters with the same collation weight (as defined
+by the current locale) as the character @var{c}.
+
+Within @samp{[} and @samp{]}, the syntax @code{[.}@var{symbol}@code{.]}
+matches the collating symbol @var{symbol}.
+@end table
+
+If the @code{extglob} shell option is enabled using the @code{shopt}
+builtin, several extended pattern matching operators are recognized.
+In the following description, a @var{pattern-list} is a list of one
+or more patterns separated by a @samp{|}.
+Composite patterns may be formed using one or more of the following
+sub-patterns:
+
+@table @code
+@item ?(@var{pattern-list})
+Matches zero or one occurrence of the given patterns.
+
+@item *(@var{pattern-list})
+Matches zero or more occurrences of the given patterns.
+
+@item +(@var{pattern-list})
+Matches one or more occurrences of the given patterns.
+
+@item @@(@var{pattern-list})
+Matches one of the given patterns.
+
+@item !(@var{pattern-list})
+Matches anything except one of the given patterns.
@end table
@node Quote Removal
Before a command is executed, its input and output
may be @var{redirected}
using a special notation interpreted by the shell.
-Redirection may also be used to open and close files for the
+Redirection allows commands' file handles to be
+duplicated, opened, closed,
+made to refer to different files,
+and can change the files the command reads from and writes to.
+Redirection may also be used to modify file handles in the
current shell execution environment. The following redirection
operators may precede or appear anywhere within a
simple command or may follow a command.
Redirections are processed in the order they appear, from
left to right.
+Each redirection that may be preceded by a file descriptor number
+may instead be preceded by a word of the form @{@var{varname}@}.
+In this case, for each redirection operator except
+>&- and <&-, the shell will allocate a file descriptor greater
+than 10 and assign it to @{@var{varname}@}. If >&- or <&- is preceded
+by @{@var{varname}@}, the value of @var{varname} defines the file
+descriptor to close.
+
In the following descriptions, if the file descriptor number is
omitted, and the first character of the redirection operator is
@samp{<}, the redirection refers to the standard input (file
is @samp{>}, the redirection refers to the standard output (file
descriptor 1).
-The word that follows the redirection operator in the following
-descriptions is subjected to brace expansion, tilde expansion,
-parameter expansion, command substitution, arithmetic expansion,
-quote removal, and filename expansion. If it expands to more
-than one word, Bash reports an error.
+The word following the redirection operator in the following
+descriptions, unless otherwise noted, is subjected to brace expansion,
+tilde expansion, parameter expansion, command substitution, arithmetic
+expansion, quote removal, filename expansion, and word splitting.
+If it expands to more than one word, Bash reports an error.
Note that the order of redirections is significant. For example,
the command
ls > @var{dirlist} 2>&1
@end example
@noindent
-directs both standard output and standard error to the file
-@var{dirlist}, while the command
+directs both standard output (file descriptor 1) and standard error
+(file descriptor 2) to the file @var{dirlist}, while the command
@example
ls 2>&1 > @var{dirlist}
@end example
@noindent
directs only the standard output to file @var{dirlist},
-because the standard error was duplicated as standard output
+because the standard error was made a copy of the standard output
before the standard output was redirected to @var{dirlist}.
+Bash handles several filenames specially when they are used in
+redirections, as described in the following table:
+
+@table @code
+@item /dev/fd/@var{fd}
+If @var{fd} is a valid integer, file descriptor @var{fd} is duplicated.
+
+@item /dev/stdin
+File descriptor 0 is duplicated.
+
+@item /dev/stdout
+File descriptor 1 is duplicated.
+
+@item /dev/stderr
+File descriptor 2 is duplicated.
+
+@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 or service name, Bash attempts to open
+the corresponding TCP 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 or service name, Bash attempts to open
+the corresponding UDP 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 @samp{-C} option to the
-@code{set} builtin has been enabled, the redirection will fail if the
-filename whose name results from the expansion of @var{word} exists.
-If the redirection operator is @samp{>|},
-then the value of the @samp{-C} option to the @code{set}
-builtin command is not tested, and the redirection is attempted even
-if the file named by @var{word} exists.
+If the redirection operator is @samp{>}, and the @code{noclobber}
+option to the @code{set} builtin has been enabled, the redirection
+will fail if the file whose name results from the expansion of
+@var{word} exists and is a regular file.
+If the redirection operator is @samp{>|}, or the redirection operator is
+@samp{>} and the @code{noclobber} option is not enabled, the redirection
+is attempted even if the file named by @var{word} exists.
@subsection Appending Redirected Output
Redirection of output in this fashion
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
-Bash allows both the
+This construct allows both the
standard output (file descriptor 1) and
the standard error output (file descriptor 2)
to be redirected to the file whose name is the
-expansion of @var{word} with this construct.
+expansion of @var{word}.
There are two formats for redirecting standard output and
standard error:
@example
>@var{word} 2>&1
@end example
+When using the second form, @var{word} may not expand to a number or
+@samp{-}. If it does, other redirection operators apply
+(see Duplicating File Descriptors below) for compatibility reasons.
+
+@subsection Appending Standard Output and Standard Error
+This construct allows both the
+standard output (file descriptor 1) and
+the standard error output (file descriptor 2)
+to be appended to the file whose name is the
+expansion of @var{word}.
+
+The format for appending standard output and standard error is:
+@example
+&>>@var{word}
+@end example
+@noindent
+This is semantically equivalent to
+@example
+>>@var{word} 2>&1
+@end example
+(see Duplicating File Descriptors below).
@subsection Here Documents
This type of redirection instructs the shell to read input from the
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}
@var{delimiter}
@end example
-No parameter expansion, command substitution, filename
-expansion, or arithmetic expansion is performed on
+No parameter and variable expansion, command substitution,
+arithmetic expansion, or filename expansion is performed on
@var{word}. If any characters in @var{word} are quoted, the
@var{delimiter} is the result of quote removal on @var{word},
-and the lines in the here-document are not expanded. Otherwise,
-all lines of the here-document are subjected to parameter expansion,
-command substitution, and arithmetic expansion. In the latter
-case, the pair @code{\newline} is ignored, and @samp{\}
+and the lines in the here-document are not expanded.
+If @var{word} is unquoted,
+all lines of the here-document are subjected to
+parameter expansion, command substitution, and arithmetic expansion,
+the character sequence @code{\newline} is ignored, and @samp{\}
must be used to quote the characters
@samp{\}, @samp{$}, and @samp{`}.
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} undergoes
+brace expansion, tilde expansion, parameter and variable expansion,
+command substitution, arithmetic expansion, and quote removal.
+Pathname expansion and word splitting are not performed.
+The result is supplied as a single string 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}
-is made to be a copy of that file descriptor. 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.
+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 @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.
-As a special case, if @code{n} is omitted, and @var{word} does not
-expand to one or more digits, the standard output and standard
+@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.
+If @var{word}
+evaluates to @samp{-}, file descriptor @var{n} is closed.
+As a special case, if @var{n} is omitted, and @var{word} does not
+expand to one or more digits or @samp{-}, 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
@section Executing Commands
@menu
+* Simple Command Expansion:: How Bash expands simple commands before
+ executing them.
* Command Search and Execution:: How Bash finds commands and runs them.
-
+* Command Execution Environment:: The environment in which Bash
+ executes commands that are not
+ shell builtins.
* Environment:: The environment given to a command.
-
* Exit Status:: The status returned by commands and how Bash
interprets it.
-
* Signals:: What happens when Bash or a command it runs
receives a signal.
@end menu
+@node Simple Command Expansion
+@subsection Simple Command Expansion
+@cindex command expansion
+
+When a simple command is executed, the shell performs the following
+expansions, assignments, and redirections, from left to right.
+
+@enumerate
+@item
+The words that the parser has marked as variable assignments (those
+preceding the command name) and redirections are saved for later
+processing.
+
+@item
+The words that are not variable assignments or redirections are
+expanded (@pxref{Shell Expansions}).
+If any words remain after expansion, the first word
+is taken to be the name of the command and the remaining words are
+the arguments.
+
+@item
+Redirections are performed as described above (@pxref{Redirections}).
+
+@item
+The text after the @samp{=} in each variable assignment undergoes tilde
+expansion, parameter expansion, command substitution, arithmetic expansion,
+and quote removal before being assigned to the variable.
+@end enumerate
+
+If no command name results, the variable assignments affect the current
+shell environment. Otherwise, the variables are added to the environment
+of the executed command and do not affect the current shell environment.
+If any of the assignments attempts to assign a value to a readonly variable,
+an error occurs, and the command exits with a non-zero status.
+
+If no command name results, redirections are performed, but do not
+affect the current shell environment. A redirection error causes the
+command to exit with a non-zero status.
+
+If there is a command name left after expansion, execution proceeds as
+described below. Otherwise, the command exits. If one of the expansions
+contained a command substitution, the exit status of the command is
+the exit status of the last command substitution performed. If there
+were no command substitutions, the command exits with a status of zero.
+
@node Command Search and Execution
@subsection Command Search and Execution
@cindex command execution
@item
If the command name contains no slashes, the shell attempts to
locate it. If there exists a shell function by that name, that
-function is invoked as described above in @ref{Shell Functions}.
+function is invoked as described in @ref{Shell Functions}.
@item
If the name does not match a function, the shell searches for
@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
-filenames of executable files (see the description of
-@code{hash} in @ref{Bourne Shell Builtins}) to avoid multiple
-@code{PATH} searches.
-A full search of the directories in @code{$PATH}
+pathnames of executable files to avoid multiple @env{PATH} searches
+(see the description of @code{hash} in @ref{Bourne Shell Builtins}).
+A full search of the directories in @env{$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 a nonzero exit status.
+If the search is unsuccessful, the shell searches for a defined shell
+function named @code{command_not_found_handle}.
+If that function exists, it is invoked with the original command and
+the original command's arguments as its arguments, and the function's
+exit status becomes the exit status of the shell.
+If that function is not defined, the shell prints an error
+message and returns an exit status of 127.
@item
If the search is successful, or if the command name contains
-one or more slashes, the shell executes the named program.
+one or more slashes, the shell executes the named program in
+a separate execution environment.
Argument 0 is set to the name given, and the remaining arguments
to the command are set to the arguments supplied, if any.
@item
If this execution fails because the file is not in executable
-format, and the file is not a directory, it is assumed to be
-@var{shell script} (@pxref{Shell Scripts}).
+format, and the file is not a directory, it is assumed to be a
+@var{shell script} and the shell executes it as described in
+@ref{Shell Scripts}.
+
+@item
+If the command was not begun asynchronously, the shell waits for
+the command to complete and collects its exit status.
+
@end enumerate
+@node Command Execution Environment
+@subsection Command Execution Environment
+@cindex execution environment
+
+The shell has an @var{execution environment}, which consists of the
+following:
+
+@itemize @bullet
+@item
+open files inherited by the shell at invocation, as modified by
+redirections supplied to the @code{exec} builtin
+
+@item
+the current working directory as set by @code{cd}, @code{pushd}, or
+@code{popd}, or inherited by the shell at invocation
+
+@item
+the file creation mode mask as set by @code{umask} or inherited from
+the shell's parent
+
+@item
+current traps set by @code{trap}
+
+@item
+shell parameters that are set by variable assignment or with @code{set}
+or inherited from the shell's parent in the environment
+
+@item
+shell functions defined during execution or inherited from the shell's
+parent in the environment
+
+@item
+options enabled at invocation (either by default or with command-line
+arguments) or by @code{set}
+
+@item
+options enabled by @code{shopt} (@pxref{The Shopt Builtin})
+
+@item
+shell aliases defined with @code{alias} (@pxref{Aliases})
+
+@item
+various process @sc{id}s, including those of background jobs
+(@pxref{Lists}), the value of @code{$$}, and the value of
+@env{$PPID}
+
+@end itemize
+
+When a simple command other than a builtin or shell function
+is to be executed, it
+is invoked in a separate execution environment that consists of
+the following. Unless otherwise noted, the values are inherited
+from the shell.
+
+@itemize @bullet
+@item
+the shell's open files, plus any modifications and additions specified
+by redirections to the command
+
+@item
+the current working directory
+
+@item
+the file creation mode mask
+
+@item
+shell variables 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
+shell's parent, and traps ignored by the shell are ignored
+
+@end itemize
+
+A command invoked in this separate environment cannot affect the
+shell's execution environment.
+
+Command substitution, 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
+commands that are invoked as part of a pipeline are also executed
+in a subshell environment. Changes made to the subshell environment
+cannot affect the shell's execution environment.
+
+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.
+
+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
called the @var{environment}.
This is a list of name-value pairs, of the form @code{name=value}.
-Bash allows you to manipulate the environment in several
-ways. On invocation, the shell scans its own environment and
+Bash provides several ways to manipulate the environment.
+On invocation, the shell scans its own environment and
creates a parameter for each name found, automatically marking
it for @var{export}
to child processes. Executed commands inherit the environment.
of the environment, replacing the old. The environment
inherited by any executed command consists of the shell's
initial environment, whose values may be modified in the shell,
-less any pairs removed by the @code{unset} command, plus any
-additions via the @code{export} and @samp{declare -x} commands.
+less any pairs removed by the @code{unset} and @samp{export -n}
+commands, plus any additions via the @code{export} and
+@samp{declare -x} commands.
The environment for any simple command
or function may be augmented temporarily by prefixing it with
These assignment statements affect only the environment seen
by that command.
-If the @samp{-k} flag is set (@pxref{The Set Builtin}, then all
+If the @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.
When Bash invokes an external command, the variable @samp{$_}
-is set to the full path name of the command and passed to that
+is set to the full pathname of the command and passed to that
command in its environment.
@node Exit Status
@subsection Exit Status
@cindex exit status
-For the purposes of the shell, a command which exits with a
+The exit status of an executed command is the value returned by the
+@var{waitpid} system call or equivalent function. Exit statuses
+fall between 0 and 255, though, as explained below, the shell may
+use values above 125 specially. Exit statuses from shell builtins and
+compound commands are also limited to this range. Under certain
+circumstances, the shell will use special values to indicate specific
+failure modes.
+
+For the shell's purposes, a command which exits with a
zero exit status has succeeded.
A non-zero exit status indicates failure.
This seemingly counter-intuitive scheme is used so there
is one well-defined way to indicate success and a variety of
ways to indicate various failure modes.
-When a command terminates on a fatal signal whose number is @var{n},
-Bash uses the value 128+@var{n} as the exit status.
+When a command terminates on a fatal signal whose number is @var{N},
+Bash uses the value 128+@var{N} as the exit status.
If a command is not found, the child process created to
execute it returns a status of 127. If a command is found
but is not executable, the return status is 126.
+If a command fails because of an error during expansion or redirection,
+the exit status is greater than zero.
+
The exit status is used by the Bash conditional commands
(@pxref{Conditional Constructs}) and some of the list
constructs (@pxref{Lists}).
All of the Bash builtins return an exit status of zero if they succeed
and a non-zero status on failure, so they may be used by the
conditional and list constructs.
+All builtins return an exit status of 2 to indicate incorrect usage.
@node Signals
@subsection Signals
@cindex signal handling
-When Bash is interactive, it ignores
+When Bash is interactive, in the absence of any traps, it ignores
@code{SIGTERM} (so that @samp{kill 0} does not kill an interactive shell),
and @code{SIGINT}
is caught and handled (so that the @code{wait} builtin is interruptible).
If job control is in effect (@pxref{Job Control}), Bash
ignores @code{SIGTTIN}, @code{SIGTTOU}, and @code{SIGTSTP}.
-Synchronous jobs started by Bash have signals set to the
-values inherited by the shell from its parent. When job control
-is not in effect, background jobs (commands terminated with @samp{&})
-ignore @code{SIGINT} and @code{SIGQUIT}.
-Commands run as a result of command substitution ignore the
-keyboard-generated job control signals
+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} 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. To prevent the shell from
-sending the @code{SIGHUP} signal to a particular job, remove it
-from the jobs table with the @code{disown} builtin
-(@pxref{Job Control Builtins})
-or use @code{disown -h} to mark it to not receive @code{SIGHUP}.
+Before exiting, 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
+particular job, it should be removed
+from the jobs table with the @code{disown}
+builtin (@pxref{Job Control Builtins}) or marked
+to not receive @code{SIGHUP} using @code{disown -h}.
+
+If the @code{huponexit} shell option has been set with @code{shopt}
+(@pxref{The Shopt Builtin}), Bash sends a @code{SIGHUP} to all jobs when
+an interactive login shell exits.
+
+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
+immediately with an exit status greater than 128, immediately after
+which the trap is executed.
@node Shell Scripts
@section Shell Scripts
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}
@noindent
if @code{filename} is an executable shell script.
This subshell reinitializes itself, so that the effect is as if a
-new shell had been invoked to interpret the script.
+new shell had been invoked to interpret the script, with the
+exception that the locations of commands remembered by the parent
+(see the description of @code{hash} in @ref{Bourne Shell Builtins})
+are retained by the child.
-Most versions of Unix make this a part of the kernel's command
+Most versions of Unix make this a part of the operating system's command
execution mechanism. If the first line of a script begins with
the two characters @samp{#!}, the remainder of the line specifies
-an interpreter for the program. The arguments to the interpreter
+an interpreter for the program.
+Thus, you can specify Bash, @code{awk}, Perl, or some other
+interpreter and write the rest of the script file in that language.
+
+The arguments to the interpreter
consist of a single optional argument following the interpreter
name on the first line of the script file, followed by the name of
the script file, followed by the rest of the arguments. Bash
themselves. Note that some older versions of Unix limit the interpreter
name and argument to a maximum of 32 characters.
-@node Bourne Shell Features
-@chapter Bourne Shell Style Features
+Bash scripts often begin with @code{#! /bin/bash} (assuming that
+Bash has been installed in @file{/bin}), since this ensures that
+Bash will be used to interpret the script, even if it is executed
+under another shell.
+
+@node Shell Builtin Commands
+@chapter Shell Builtin Commands
@menu
* Bourne Shell Builtins:: Builtin commands inherited from the Bourne
Shell.
-* Bourne Shell Variables:: Variables which Bash uses in the same way
- as the Bourne Shell.
-* Other Bourne Shell Features:: Addtional aspects of Bash which behave in
- the same way as the Bourne Shell.
+* Bash Builtins:: Table of builtins specific to Bash.
+* Modifying Shell Behavior:: Builtins to modify shell attributes and
+ optional behavior.
+* Special Builtins:: Builtin commands classified specially by
+ POSIX.
@end menu
-This section briefly summarizes things which Bash inherits from
-the Bourne Shell: builtins, variables,
-and other features. It also lists the significant differences
-between Bash and the Bourne Shell.
+Builtin commands are contained within the shell itself.
+When the name of a builtin command is used as the first word of
+a simple command (@pxref{Simple Commands}), the shell executes
+the command directly, without invoking another program.
+Builtin commands are necessary to implement functionality impossible
+or inconvenient to obtain with separate utilities.
+
+This section briefly describes the builtins which Bash inherits from
+the Bourne Shell, as well as the builtin commands which are unique
+to or have been extended in Bash.
+
+Several builtin commands are described in other chapters: builtin
+commands which provide the Bash interface to the job control
+facilities (@pxref{Job Control Builtins}), the directory stack
+(@pxref{Directory Stack Builtins}), the command history
+(@pxref{Bash History Builtins}), and the programmable completion
+facilities (@pxref{Programmable Completion Builtins}).
+
+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.
+The @code{:}, @code{true}, @code{false}, and @code{test}
+builtins do not accept options and do not treat @samp{--} specially.
+The @code{exit}, @code{logout}, @code{break}, @code{continue}, @code{let},
+and @code{shift} builtins accept and process arguments beginning
+with @samp{-} without requiring @samp{--}.
+Other builtins that accept arguments but are not specified as accepting
+options interpret arguments beginning with @samp{-} as invalid options and
+require @samp{--} to prevent this interpretation.
@node Bourne Shell Builtins
@section Bourne Shell Builtins
-The following shell builtin commands are inherited from the Bourne
-Shell. These commands are implemented as specified by the @sc{POSIX}
-1003.2 standard.
+The following shell builtin commands are inherited from the Bourne Shell.
+These commands are implemented as specified by the @sc{posix} standard.
@table @code
-@item :
+@item : @r{(a colon)}
@btindex :
@example
: [@var{arguments}]
@end example
+
Do nothing beyond expanding @var{arguments} and performing redirections.
+The return status is zero.
-@item .
+@item . @r{(a period)}
@btindex .
@example
-. @var{filename}
+. @var{filename} [@var{arguments}]
@end example
+
Read and execute commands from the @var{filename} argument in the
-current shell context.
+current shell context. If @var{filename} does not contain a slash,
+the @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.
+The return status is the exit status of the last command executed, or
+zero if no commands are executed. If @var{filename} is not found, or
+cannot be read, the return status is non-zero.
+This builtin is equivalent to @code{source}.
@item break
@btindex break
@example
break [@var{n}]
@end example
+
Exit from a @code{for}, @code{while}, @code{until}, or @code{select} loop.
If @var{n} is supplied, the @var{n}th enclosing loop is exited.
+@var{n} must be greater than or equal to 1.
+The return status is zero unless @var{n} is not greater than or equal to 1.
@item cd
@btindex cd
@example
-cd [-LP] [@var{directory}]
+cd [-L|[-P [-e]] [-@@] [@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; symlinks are followed by default or with the
-@samp{-L} option.
+
+Change the current working directory to @var{directory}.
+If @var{directory} is not supplied, the value of the @env{HOME}
+shell variable is used.
+Any additional arguments following @var{directory} are ignored.
+If the shell variable
+@env{CDPATH} exists, it is used as a search path:
+each directory name in @env{CDPATH} is searched for
+@var{directory}, with alternative directory names in @env{CDPATH}
+separated by a colon (@samp{:}).
+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 resolved while @code{cd} is traversing @var{directory} and before
+processing an instance of @samp{..} in @var{directory}.
+
+By default, or when the @option{-L} option is supplied, symbolic links
+in @var{directory} are resolved after @code{cd} processes an instance
+of @samp{..} in @var{directory}.
+
+If @samp{..} appears in @var{directory}, it is processed by removing the
+immediately preceding pathname component, back to a slash or the beginning
+of @var{directory}.
+
+If the @option{-e} option is supplied with @option{-P}
+and the current working directory cannot be successfully determined
+after a successful directory change, @code{cd} will return an unsuccessful
+status.
+
+On systems that support it, the @option{-@@} option presents the extended
+attributes associated with a file as a directory.
+
+If @var{directory} is @samp{-}, it is converted to @env{$OLDPWD}
+before the directory change is attempted.
+
+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.
@item continue
@btindex continue
@example
continue [@var{n}]
@end example
+
Resume the next iteration of an enclosing @code{for}, @code{while},
@code{until}, or @code{select} loop.
-If @var{n} is supplied, the execution of the
-@var{n}th enclosing loop is resumed.
+If @var{n} is supplied, the execution of the @var{n}th enclosing loop
+is resumed.
+@var{n} must be greater than or equal to 1.
+The return status is zero unless @var{n} is not greater than or equal to 1.
@item eval
@btindex eval
@example
eval [@var{arguments}]
@end example
-The arguments are concatenated together into a single
-command, which is then read and executed.
+
+The arguments are concatenated together into a single command, which is
+then read and executed, and its exit status returned as the exit status
+of @code{eval}.
+If there are no arguments or only empty arguments, the return status is
+zero.
@item exec
@btindex exec
@example
-exec [-cl] [-a @var{name}] [@var{command}] [@var{arguments}]
+exec [-cl] [-a @var{name}] [@var{command} [@var{arguments}]]
@end example
+
If @var{command}
-is supplied, it replaces the shell.
-If the @samp{-l} option is supplied,
-the shell places a dash in the zeroth arg passed to @var{command}.
+is supplied, it replaces the shell without creating a new process.
+If the @option{-l} option is supplied, the shell places a dash at the
+beginning of the zeroth argument passed to @var{command}.
This is what the @code{login} program does.
-The @samp{-c} option causes @var{command}
-to be executed with an empty environment.
-If @samp{-a} is supplied, the shell passes @var{name}
-as the zeroth argument to @var{command}.
+The @option{-c} option causes @var{command} to be executed with an empty
+environment.
+If @option{-a} is supplied, the shell passes @var{name} as the zeroth
+argument to @var{command}.
+If @var{command}
+cannot be executed for some reason, a non-interactive shell exits,
+unless the @code{execfail} shell option
+is enabled. In that case, it returns failure.
+An interactive shell returns failure if the file cannot be executed.
If no @var{command} is specified, redirections may be used to affect
-the current shell environment.
+the current shell environment. If there are no redirection errors, the
+return status is zero; otherwise the return status is non-zero.
@item exit
@btindex exit
@example
exit [@var{n}]
@end example
+
Exit the shell, returning a status of @var{n} to the shell's parent.
+If @var{n} is omitted, the exit status is that of the last command executed.
+Any trap on @code{EXIT} is executed before the shell terminates.
@item export
@btindex export
@example
export [-fn] [-p] [@var{name}[=@var{value}]]
@end example
+
Mark each @var{name} to be passed to child processes
-in the environment. If the @samp{-f} option is supplied, the @var{name}s
-refer to shell functions. The @samp{-n} option means to no longer mark
-each @var{name} for export.
-If no @var{names} are supplied, or if the @samp{-p} option is given, a
-list of exported names is displayed.
+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 @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 names of all exported variables is displayed.
+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 @option{-f} is supplied
+with a name that is not a shell function.
@item getopts
@btindex getopts
@example
getopts @var{optstring} @var{name} [@var{args}]
@end example
+
@code{getopts} is used by shell scripts to parse positional parameters.
-@var{optstring} contains the option letters to be recognized; if a letter
-is followed by a colon, the option is expected to have an
-argument, which should be separated from it by white space.
+@var{optstring} contains the option characters to be recognized; if a
+character is followed by a colon, the option is expected to have an
+argument, which should be separated from it by whitespace.
+The colon (@samp{:}) and question mark (@samp{?}) may not be
+used as option characters.
Each time it is invoked, @code{getopts}
places the next option in the shell variable @var{name}, initializing
@var{name} if it does not exist,
and the index of the next argument to be processed into the
-variable @code{OPTIND}. @code{OPTIND}
-is initialized to 1 each time the shell or a shell script
-is invoked. When an option requires an argument,
-@code{getopts} places that argument into the variable @code{OPTARG}.
-The shell does not reset @code{OPTIND}
-automatically; it must be manually reset between multiple
-calls to @code{getopts}
-within the same shell invocation if a new set of parameters
-is to be used.
+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 @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.
+@env{OPTIND} is set to the index of the first non-option argument,
+and @var{name} is set to @samp{?}.
+
+@code{getopts}
+normally parses the positional parameters, but if more arguments are
+given in @var{args}, @code{getopts} parses those instead.
@code{getopts} can report errors in two ways. If the first character of
@var{optstring} is a colon, @var{silent}
-error reporting is used. In normal operation diagnostic messages
-are printed when illegal options or missing option arguments are
+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}
-is set to 0, no error message will be displayed, even if the first
+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 illegal option is seen,
+If an invalid option is seen,
@code{getopts} places @samp{?} into @var{name} and, if not silent,
-prints an error message and unsets @code{OPTARG}.
+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.
-
-@code{getopts}
-normally parses the positional parameters, but if more arguments are
-given in @var{args}, @code{getopts} parses those instead.
+@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 filenames of commands specified as arguments,
-so they need not be searched for on subsequent invocations. The
-commands are found by searching through the directories listed in
-@code{$PATH}. The @samp{-p} option inhibits the path search, and
-@var{filename} is used as the location of @var{name}.
-The @samp{-r} option causes the shell to forget
-all remembered locations. If no arguments are given, information
-about remembered commands is printed.
+
+Each time @code{hash} is invoked, it remembers the full pathnames of the
+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
+@env{$PATH}.
+Any previously-remembered pathname is discarded.
+The @option{-p} option inhibits the path search, and @var{filename} is
+used as the location of @var{name}.
+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.
@item pwd
@btindex pwd
@example
pwd [-LP]
@end example
-Print the current working directory. If the @samp{-P} option is supplied,
-the path printed will not contain symbolic links. If the @samp{-L} option
-is supplied, the path printed may contain symbolic links.
+
+Print the absolute pathname of the current working directory.
+If the @option{-P} option is supplied, the pathname printed will not
+contain symbolic links.
+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
+is supplied.
@item readonly
@btindex readonly
@example
-readonly [-apf] [@var{name}] @dots{}
+readonly [-aAf] [-p] [@var{name}[=@var{value}]] @dots{}
@end example
-Mark each @var{name} as unchangable. The values of these names may not
-be changed by subsequent assignment. If the @samp{-f} option is supplied,
-each @var{name} refers to a shell function. The @samp{-a} option means
-each @var{name} refers to an array variable.
-If no @var{name} arguments are given, or if the @samp{-p}
+
+Mark each @var{name} as readonly.
+The values of these names may not be changed by subsequent assignment.
+If the @option{-f} option is supplied, each @var{name} refers to a shell
+function.
+The @option{-a} option means each @var{name} refers to an indexed
+array variable; the @option{-A} option means each @var{name} refers
+to an associative array variable.
+If both options are supplied, @option{-A} takes precedence.
+If no @var{name} arguments are given, or if the @option{-p}
option is supplied, a list of all readonly names is printed.
+The other options may be used to restrict the output to a subset of
+the set of readonly names.
+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 @option{-f} option is supplied with a name that is not a shell function.
@item return
@btindex return
@example
return [@var{n}]
@end example
-Cause a shell function to exit with value @var{n}. This may also be used
-to terminate execution of a script being executed with the @code{.}
-builtin.
+
+Cause a shell function to stop executing and return the value @var{n}
+to its caller.
+If @var{n} is not supplied, the return value is the exit status of the
+last command executed in the function.
+@code{return} may also be used to terminate execution of a script
+being executed with the @code{.} (@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.
+If @var{n} is supplied, the return value is its least significant
+8 bits.
+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 supplied a non-numeric
+argument or is used outside a function
+and not during the execution of a script by @code{.} or @code{source}.
@item shift
@btindex shift
@example
shift [@var{n}]
@end example
-Shift positional parameters to the left by @var{n}.
-The positional parameters from @var{n}+1 @dots{}
-are renamed to
-@code{$1} @dots{} .
-Parameters represented by the numbers
-@code{$#} to @var{n}+1 are unset. @var{n}
-must be a non-negative number less than or equal to @code{$#}.
+
+Shift the positional parameters to the left by @var{n}.
+The positional parameters from @var{n}+1 @dots{} @code{$#} are
+renamed to @code{$1} @dots{} @code{$#}-@var{n}.
+Parameters represented by the numbers @code{$#} to @code{$#}-@var{n}+1
+are unset.
+@var{n} must be a non-negative number less than or equal to @code{$#}.
+If @var{n} is zero or greater than @code{$#}, the positional parameters
+are not changed.
+If @var{n} is not supplied, it is assumed to be 1.
+The return status is zero unless @var{n} is greater than @code{$#} or
+less than zero, non-zero otherwise.
@item test
@itemx [
@btindex test
@btindex [
-Evaluate a conditional expression (@pxref{Bash Conditional Expressions}).
-
-@item times
-@btindex times
+@example
+test @var{expr}
+@end example
+
+Evaluate a conditional express
+ion @var{expr} and return a status of 0
+(true) or 1 (false).
+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{]}.
+
+Expressions may be combined using the following operators, listed in
+decreasing order of precedence.
+The evaluation depends on the number of arguments; see below.
+Operator precedence is used when there are five or more arguments.
+
+@table @code
+@item ! @var{expr}
+True if @var{expr} is false.
+
+@item ( @var{expr} )
+Returns the value of @var{expr}.
+This may be used to override the normal precedence of operators.
+
+@item @var{expr1} -a @var{expr2}
+True if both @var{expr1} and @var{expr2} are true.
+
+@item @var{expr1} -o @var{expr2}
+True if either @var{expr1} or @var{expr2} is true.
+@end table
+
+The @code{test} and @code{[} builtins evaluate conditional
+expressions using a set of rules based on the number of arguments.
+
+@table @asis
+@item 0 arguments
+The expression is false.
+
+@item 1 argument
+The expression is true if and only if the argument is not null.
+
+@item 2 arguments
+If the first argument is @samp{!}, the expression is true if and
+only if the second argument is null.
+If the first argument is one of the unary conditional operators
+(@pxref{Bash Conditional Expressions}), the expression
+is true if the unary test is true.
+If the first argument is not a valid unary operator, the expression is
+false.
+
+@item 3 arguments
+The following conditions are applied in the order listed.
+If the second argument is one of the binary conditional
+operators (@pxref{Bash Conditional Expressions}), the
+result of the expression is the result of the binary test using the
+first and third arguments as operands.
+The @samp{-a} and @samp{-o} operators are considered binary operators
+when there are three arguments.
+If the first argument is @samp{!}, the value is the negation of
+the two-argument test using the second and third arguments.
+If the first argument is exactly @samp{(} and the third argument is
+exactly @samp{)}, the result is the one-argument test of the second
+argument.
+Otherwise, the expression is false.
+
+@item 4 arguments
+If the first argument is @samp{!}, the result is the negation of
+the three-argument expression composed of the remaining arguments.
+Otherwise, the expression is parsed and evaluated according to
+precedence using the rules listed above.
+
+@item 5 or more arguments
+The expression is parsed and evaluated according to precedence
+using the rules listed above.
+@end table
+
+When used with @code{test} or @samp{[}, the @samp{<} and @samp{>}
+operators sort lexicographically using ASCII ordering.
+
+@item times
+@btindex times
@example
times
@end example
+
Print out the user and system times used by the shell and its children.
+The return status is zero.
@item trap
@btindex trap
@example
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 @samp{-p}, the shell displays the trap commands
-associated with each @var{sigspec}. If no arguments are supplied, or
-only @samp{-p} is given, @code{trap} prints the list of commands
-associated with each signal number.
-Each @var{sigspec} is either a signal name such as @code{SIGINT} (with
-or without the @code{SIG} prefix) or a signal number.
+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 @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.
+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{extdebug} option to the
+@code{shopt} builtin (@pxref{The Shopt Builtin}) for details of its
+effect on the @code{DEBUG} trap.
+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.
+
+If a @var{sigspec} is @code{ERR}, the command @var{arg}
+is executed whenever
+a pipeline (which may consist of a single simple
+command), a list, or a compound command returns 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 following the @code{if} or @code{elif} reserved words,
+part of a command executed in a @code{&&} or @code{||} list
+except the command following the final @code{&&} or @code{||},
+any command in a pipeline but the last,
+or if the command's return
+status is being inverted using @code{!}.
+These are the same conditions obeyed by the @code{errexit} (@option{-e})
+option.
Signals ignored upon entry to the shell cannot be trapped or reset.
-Trapped signals are reset to their original values in a child
-process when it is created.
+Trapped signals that are not being ignored are reset to their original
+values in a subshell or subshell environment when one is created.
+
+The return status is zero unless a @var{sigspec} does not specify a
+valid signal.
@item umask
@btindex umask
@example
-umask [-S] [@var{mode}]
+umask [-p] [-S] [@var{mode}]
@end example
+
Set the shell process's file creation mask to @var{mode}. If
@var{mode} begins with a digit, it is interpreted as an octal number;
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 @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.
+
+Note that when the mode is interpreted as an octal number, each number
+of the umask is subtracted from @code{7}. Thus, a umask of @code{022}
+results in permissions of @code{755}.
@item unset
@btindex unset
@example
-unset [-fv] [@var{name}]
+unset [-fnv] [@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
-@var{name} refers to a shell variable.
-If the @samp{-f} option is given, the @var{name}s refer to shell
-functions, and the function definition is removed.
-Read-only variables and functions may not be unset.
+Remove each variable or function @var{name}.
+If the @option{-v} option is given, each
+@var{name} refers to a shell variable and that variable is remvoved.
+If the @option{-f} option is given, the @var{name}s refer to shell
+functions, and the function definition is removed.
+If the @option{-n} option is supplied, and @var{name} is a variable with
+the @var{nameref} attribute, @var{name} will be unset rather than the
+variable it references.
+@option{-n} has no effect if the @option{-f} option is supplied.
+If no options are supplied, each @var{name} refers to a variable; if
+there is no variable by that name, any function with that name is
+unset.
+Readonly variables and functions may not be unset.
+The return status is zero unless a @var{name} is readonly.
@end table
-@node Bourne Shell Variables
-@section Bourne Shell Variables
-
-Bash uses certain shell variables in the same way as the Bourne shell.
-In some cases, Bash assigns a default value to the variable.
-
-@vtable @code
+@node Bash Builtins
+@section Bash Builtin Commands
-@item IFS
-A list of characters that separate fields; used when the shell splits
-words as part of expansion.
+This section describes builtin commands which are unique to
+or have been extended in Bash.
+Some of these commands are specified in the @sc{posix} standard.
-@item PATH
-A colon-separated list of directories in which the shell looks for
-commands.
+@table @code
-@item HOME
-The current user's home directory; the default for the @code{cd} builtin
-command.
+@item alias
+@btindex alias
+@example
+alias [-p] [@var{name}[=@var{value}] @dots{}]
+@end example
-@item CDPATH
-A colon-separated list of directories used as a search path for
-the @code{cd} command.
+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}
+whose @var{value} is given. If no @var{value} is given, the name
+and value of the alias is printed.
+Aliases are described in @ref{Aliases}.
-@item MAILPATH
-A colon-separated list of files which the shell periodically checks
-for new mail. You can
-also specify what message is printed by separating the file name from
-the message with a @samp{?}. When used in the text of the message,
-@code{$_} stands for the name of the current mailfile.
+@item bind
+@btindex bind
+@example
+bind [-m @var{keymap}] [-lpsvPSVX]
+bind [-m @var{keymap}] [-q @var{function}] [-u @var{function}] [-r @var{keyseq}]
+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
-@item MAIL
-If this parameter is set to a filename and the @code{MAILPATH} variable
-is not set, Bash informs the user of the arrival of mail in
-the specified file.
+Display current Readline (@pxref{Command Line Editing})
+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
+Readline initialization file (@pxref{Readline Init File}),
+but each binding or command must be passed as a separate argument; e.g.,
+@samp{"\C-x\C-r":re-read-init-file}.
-@item PS1
-The primary prompt string. The default value is @samp{\s-\v\$ }.
+Options, if supplied, have the following meanings:
-@item PS2
-The secondary prompt string. The default value is @samp{> }.
+@table @code
+@item -m @var{keymap}
+Use @var{keymap} as the keymap to be affected by
+the subsequent bindings. Acceptable @var{keymap}
+names are
+@code{emacs},
+@code{emacs-standard},
+@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};
+@code{emacs} is equivalent to @code{emacs-standard}.
-@item OPTIND
-The index of the last option processed by the
-@code{getopts} builtin.
+@item -l
+List the names of all Readline functions.
-@item OPTARG
-The value of the last option argument processed by the
-@code{getopts} builtin.
+@item -p
+Display Readline function names and bindings in such a way that they
+can be used as input or in a Readline initialization file.
-@end vtable
+@item -P
+List current Readline function names and bindings.
-@node Other Bourne Shell Features
-@section Other Bourne Shell Features
+@item -v
+Display Readline variable names and values in such a way that they
+can be used as input or in a Readline initialization file.
-@menu
-* Major Differences From The Bourne Shell:: Major differences between
- Bash and the Bourne shell.
-@end menu
+@item -V
+List current Readline variable names and values.
-Bash implements essentially the same grammar, parameter and variable
-expansion, redirection, and quoting as the Bourne Shell. Bash uses the
-@sc{POSIX} 1003.2 standard as the specification of how these features are to be
-implemented. There are some differences between the traditional Bourne
-shell and the @sc{POSIX} standard; this section quickly details the differences
-of significance. A number of these differences are explained in greater
-depth in subsequent sections.
+@item -s
+Display Readline key sequences bound to macros and the strings they output
+in such a way that they can be used as input or in a Readline
+initialization file.
-@node Major Differences From The Bourne Shell
-@subsection Major Differences From The SVR4.2 Bourne Shell
+@item -S
+Display Readline key sequences bound to macros and the strings they output.
-Bash is @sc{POSIX}-conformant, even where the @sc{POSIX} specification
-differs from traditional @code{sh} behavior.
+@item -f @var{filename}
+Read key bindings from @var{filename}.
-Bash has multi-character invocation options (@pxref{Invoking Bash}).
+@item -q @var{function}
+Query about which keys invoke the named @var{function}.
-Bash has command-line editing (@pxref{Command Line Editing}) and
-the @code{bind} builtin.
+@item -u @var{function}
+Unbind all keys bound to the named @var{function}.
-Bash has command history (@pxref{Bash History Facilities}) and the
-@code{history} and @code{fc} builtins to manipulate it.
+@item -r @var{keyseq}
+Remove any current binding for @var{keyseq}.
+
+@item -x @var{keyseq:shell-command}
+Cause @var{shell-command} to be executed whenever @var{keyseq} is
+entered.
+When @var{shell-command} is executed, the shell sets the
+@code{READLINE_LINE} variable to the contents of the Readline line
+buffer and the @code{READLINE_POINT} variable to the current location
+of the insertion point.
+If the executed command changes the value of @code{READLINE_LINE} or
+@code{READLINE_POINT}, those new values will be reflected in the
+editing state.
+
+@item -X
+List all key sequences bound to shell commands and the associated commands
+in a format that can be reused as input.
+@end table
-Bash implements @code{csh}-like history expansion (@pxref{History Interaction}).
+@noindent
+The return status is zero unless an invalid option is supplied or an
+error occurs.
-Bash has one-dimensional array variables (@pxref{Arrays}), and the
-appropriate variable expansions and assignment syntax to use them.
-Some of the Bash builtins take options to act on arrays. Bash provides
-some built-in array variables.
+@item builtin
+@btindex builtin
+@example
+builtin [@var{shell-builtin} [@var{args}]]
+@end example
-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.
+Run a shell builtin, passing it @var{args}, and return its exit status.
+This is useful when defining a shell function with the same
+name as a shell builtin, retaining the functionality of the builtin within
+the function.
+The return status is non-zero if @var{shell-builtin} is not a shell
+builtin command.
-Bash includes the @code{select} compound command, which allows the
-generation of simple menus (@pxref{Korn Shell Constructs}).
+@item caller
+@btindex caller
+@example
+caller [@var{expr}]
+@end example
-Bash includes brace expansion (@pxref{Brace Expansion}) and tilde
-expansion (@pxref{Tilde Expansion}).
+Returns the context of any active subroutine call (a shell function or
+a script executed with the @code{.} or @code{source} builtins).
-Bash implements command aliases and the @code{alias} and @code{unalias}
-builtins (@pxref{Aliases}).
+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.
-Bash provides shell arithmetic and arithmetic expansion
-(@pxref{Shell Arithmetic}).
+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.
-The @sc{POSIX} and @code{ksh}-style @code{$()} form of command substitution
-is implemented (@pxref{Command Substitution}),
-and preferred to the Bourne shell's @code{``} (which
-is also implemented for backwards compatibility).
+@item command
+@btindex command
+@example
+command [-pVv] @var{command} [@var{arguments} @dots{}]
+@end example
-Variables present in the shell's initial environment are automatically
-exported to child processes. The Bourne shell does not normally do
-this unless the variables are explicitly marked using the @code{export}
-command.
+Runs @var{command} with @var{arguments} ignoring any shell function
+named @var{command}.
+Only shell builtin commands or commands found by searching the
+@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 @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.
-Bash includes the @sc{POSIX} and @code{ksh}-style pattern removal
-@samp{%}, @samp{#}, @samp{%%} and @samp{##} constructs to remove
-leading or trailing substrings from variable values
-(@pxref{Shell Parameter Expansion}).
+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 @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.
-The expansion @code{$@{#xx@}}, which returns the length of @code{$xx},
-is supported (@pxref{Shell Parameter Expansion}).
+@item declare
+@btindex declare
+@example
+declare [-aAfFgilnrtux] [-p] [@var{name}[=@var{value}] @dots{}]
+@end example
-The @code{$'@dots{}'} quoting syntax, which expands ANSI-C
-backslash-escaped characters in the text between the single quotes,
-is supported (@pxref{ANSI-C Quoting}).
+Declare variables and give them attributes. If no @var{name}s
+are given, then display the values of variables instead.
-Bash supports the @code{$"@dots{}"} quoting syntax to do
-locale-specific translation of the characters between the double
-quotes. The @samp{-D} and @samp{--dump-strings} invocation options
-list the translatable strings found in a script
-(@pxref{Locale Translation}).
+The @option{-p} option will display the attributes and values of each
+@var{name}.
+When @option{-p} is used with @var{name} arguments, additional options,
+other than @option{-f} and @option{-F}, are ignored.
-The expansion @code{$@{var:}@var{offset}@code{[:}@var{length}@code{]@}},
-which expands to the substring of @code{var}'s value of length
-@var{length}, optionally beginning at @var{offset}, is present
-(@pxref{Shell Parameter Expansion}).
+When @option{-p} is supplied without @var{name} arguments, @code{declare}
+will display the attributes and values of all variables having the
+attributes specified by the additional options.
+If no other options are supplied with @option{-p}, @code{declare} will
+display the attributes and values of all shell variables. The @option{-f}
+option will restrict the display to shell functions.
-The expansion
-@code{$@{var/[/]}@var{pattern}@code{[/}@var{replacement}@code{]@}},
-which matches @var{pattern} and replaces it with @var{replacement} in
-the value of @code{var}, is available (@pxref{Shell Parameter Expansion}).
+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{The Shopt Builtin}), the source file name and line number where
+the function is defined are displayed as well.
+@option{-F} implies @option{-f}.
-Bash has @var{indirect} variable expansion using @code{$@{!word@}}
-(@pxref{Shell Parameter Expansion}).
+The @option{-g} option forces variables to be created or modified at
+the global scope, even when @code{declare} is executed in a shell function.
+It is ignored in all other cases.
-Bash can expand positional parameters beyond @code{$9} using
-@code{$@{@var{num}@}}.
+The following options can be used to restrict output to variables with
+the specified attributes or to give variables attributes:
-Bash has process substitution (@pxref{Process Substitution}).
+@table @code
+@item -a
+Each @var{name} is an indexed array variable (@pxref{Arrays}).
-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},
-for details.
+@item -A
+Each @var{name} is an associative array variable (@pxref{Arrays}).
-The @code{IFS} variable is used to split only the results of expansion,
-not all words (@pxref{Word Splitting}).
-This closes a longstanding shell security hole.
+@item -f
+Use function names only.
-It is possible to have a variable and a function with the same name;
-@code{sh} does not separate the two name spaces.
+@item -i
+The variable is to be treated as
+an integer; arithmetic evaluation (@pxref{Shell Arithmetic}) is
+performed when the variable is assigned a value.
-Bash functions are permitted to have local variables using the
-@code{local} builtin, and thus useful recursive functions may be written.
+@item -l
+When the variable is assigned a value, all upper-case characters are
+converted to lower-case.
+The upper-case attribute is disabled.
-Variable assignments preceding commands affect only that command, even
-builtins and functions (@pxref{Environment}).
-In @code{sh}, all variable assignments
-preceding commands are global unless the command is executed from the
-file system.
+@item -n
+Give each @var{name} the @var{nameref} attribute, making
+it a name reference to another variable.
+That other variable is defined by the value of @var{name}.
+All references and assignments to @var{name}, except for changing the
+@option{-n} attribute itself, are performed on the variable referenced by
+@var{name}'s value.
+The @option{-n} attribute cannot be applied to array variables.
-Bash performs filename expansion on filenames specified as operands
-to output redirection operators.
+@item -r
+Make @var{name}s readonly. These names cannot then be assigned values
+by subsequent assignment statements or unset.
-Bash contains the @samp{<>} redirection operator, allowing a file to be
-opened for both reading and writing, and the @samp{&>} redirection
-operator, for directing standard output and standard error to the same
-file (@pxref{Redirections}).
+@item -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.
-The @code{noclobber} option is available to avoid overwriting existing
-files with output redirection (@pxref{The Set Builtin}).
-The @samp{>|} redirection operator may be used to override @code{noclobber}.
+@item -u
+When the variable is assigned a value, all lower-case characters are
+converted to upper-case.
+The lower-case attribute is disabled.
-Bash interprets special backslash-escaped characters in the prompt
-strings when interactive (@pxref{Printing a Prompt}).
+@item -x
+Mark each @var{name} for export to subsequent commands via
+the environment.
+@end table
-Bash allows you to write a function to override a builtin, and provides
-access to that builtin's functionality within the function via the
-@code{builtin} and @code{command} builtins (@pxref{Bash Builtins}).
+Using @samp{+} instead of @samp{-} turns off the attribute instead,
+with the exceptions that @samp{+a}
+may not be used to destroy an array variable and @samp{+r} will not
+remove the readonly attribute.
+When used in a function, @code{declare} makes each @var{name} local,
+as with the @code{local} command, unless the @option{-g} option is used.
+If a variable name is followed by =@var{value}, the value of the variable
+is set to @var{value}.
+
+When using @option{-a} or @option{-A} and the compound assignment syntax to
+create array variables, additional attributes do not take effect until
+subsequent assignments.
+
+The return status is zero unless an invalid option is encountered,
+an attempt is made to define a function using @samp{-f foo=bar},
+an attempt is made to assign a value to a readonly variable,
+an attempt is made to assign a value to an array variable without
+using the compound assignment syntax (@pxref{Arrays}),
+one of the @var{names} is not a valid shell variable name,
+an attempt is made to turn off readonly status for a readonly variable,
+an attempt is made to turn off array status for an array variable,
+or an attempt is made to display a non-existent function with @option{-f}.
-The @code{command} builtin allows selective disabling of functions
-when command lookup is performed (@pxref{Bash Builtins}).
+@item echo
+@btindex echo
+@example
+echo [-neE] [@var{arg} @dots{}]
+@end example
-Individual builtins may be enabled or disabled using the @code{enable}
-builtin (@pxref{Bash Builtins}).
+Output the @var{arg}s, separated by spaces, terminated with a
+newline.
+The return status is 0 unless a write error occurs.
+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 @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.
-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}.
+@code{echo} interprets the following escape sequences:
+@table @code
+@item \a
+alert (bell)
+@item \b
+backspace
+@item \c
+suppress further output
+@item \e
+@itemx \E
+escape
+@item \f
+form feed
+@item \n
+new line
+@item \r
+carriage return
+@item \t
+horizontal tab
+@item \v
+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 \x@var{HH}
+the eight-bit character whose value is the hexadecimal value @var{HH}
+(one or two hex digits)
+@item \u@var{HHHH}
+the Unicode (ISO/IEC 10646) character whose value is the hexadecimal value
+@var{HHHH} (one to four hex digits)
+@item \U@var{HHHHHHHH}
+the Unicode (ISO/IEC 10646) character whose value is the hexadecimal value
+@var{HHHHHHHH} (one to eight hex digits)
+@end table
-Shell functions may be exported to children via the environment
-(@pxref{Shell Functions}).
+@item enable
+@btindex enable
+@example
+enable [-a] [-dnps] [-f @var{filename}] [@var{name} @dots{}]
+@end example
-Bash includes a @code{help} builtin for quick reference to shell
-facilities (@pxref{Bash Builtins}).
+Enable and disable builtin shell commands.
+Disabling a builtin allows a disk command which has the same name
+as a shell builtin to be executed without specifying a full pathname,
+even though the shell normally searches for builtins before disk commands.
+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 @env{$PATH} instead of the shell builtin version, type
+@samp{enable -n test}.
-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
-default if no arguments are supplied. The Bash @code{read} builtin
-also accepts a prompt string with the @samp{-p} option and will use
-Readline to obtain the line when given the @samp{-e} option.
+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 @option{-a} option means to list
+each builtin with an indication of whether or not it is enabled.
-Bash includes the @code{shopt} builtin, for finer control of shell
-optional capabilities (@pxref{Bash Builtins}).
+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 @option{-d} option will delete a builtin loaded with @option{-f}.
-Bash has much more optional behavior controllable with the @code{set}
-builtin (@pxref{The Set Builtin}).
+If there are no options, a list of the shell builtins is displayed.
+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 @code{disown} builtin can remove a job from the internal shell
-job table (@pxref{Job Control Builtins}).
+The return status is zero unless a @var{name} is not a shell builtin
+or there is an error loading a new builtin from a shared object.
-The @code{return} builtin may be used to abort execution of scripts
-executed with the @code{.} or @code{source} builtins
-(@pxref{Bourne Shell Builtins}).
+@item help
+@btindex help
+@example
+help [-dms] [@var{pattern}]
+@end example
-The @code{test} builtin (@pxref{Bourne Shell Builtins})
-is slightly different, as it implements the
-@sc{POSIX} 1003.2 algorithm, which specifies the behavior based on the
-number of arguments.
+Display helpful information about builtin commands.
+If @var{pattern} is specified, @code{help} gives detailed help
+on all commands matching @var{pattern}, otherwise a list of
+the builtins is printed.
-The @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.
+Options, if supplied, have the following meanings:
-The Bash @code{export}, @code{readonly}, and @code{declare} builtins can
-take a @samp{-f} option to act on shell functions, a @samp{-p} option to
-display variables with various attributes set in a format that can be
-used as shell input, a @samp{-n} option to remove various variable
-attributes, and @samp{name=value} arguments to set variable attributes
-and values simultaneously.
+@table @code
+@item -d
+Display a short description of each @var{pattern}
+@item -m
+Display the description of each @var{pattern} in a manpage-like format
+@item -s
+Display only a short usage synopsis for each @var{pattern}
+@end table
-The Bash @code{cd} and @code{pwd} builtins (@pxref{Bourne Shell Builtins})
-each take @samp{-L} and @samp{-P} builtins to switch between logical and
-physical modes.
+The return status is zero unless no command matches @var{pattern}.
-The Bash @code{type} builtin is more extensive and gives more information
-about the names it finds (@pxref{Bash Builtins}).
+@item let
+@btindex let
+@example
+let @var{expression} [@var{expression} @dots{}]
+@end example
-Bash implements a @code{csh}-like directory stack, and provides the
-@code{pushd}, @code{popd}, and @code{dirs} builtins to manipulate it
-(@pxref{C Shell Builtins}).
-Bash also makes the directory stack visible as the value of the
-@code{DIRSTACK} shell variable.
+The @code{let} builtin allows arithmetic to be performed on shell
+variables. Each @var{expression} is evaluated according to the
+rules given below in @ref{Shell Arithmetic}. If the
+last @var{expression} evaluates to 0, @code{let} returns 1;
+otherwise 0 is returned.
-The Bash restricted mode is more useful (@pxref{The Restricted Shell});
-the @sc{SVR4.2} shell restricted mode is too limited.
+@item local
+@btindex local
+@example
+local [@var{option}] @var{name}[=@var{value}] @dots{}
+@end example
-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.
+For each argument, a local variable named @var{name} is created,
+and assigned @var{value}.
+The @var{option} can be any of the options accepted by @code{declare}.
+@code{local} can only be used within a function; it makes the variable
+@var{name} have a visible scope restricted to that function and its
+children. The return status is zero unless @code{local} is used outside
+a function, an invalid @var{name} is supplied, or @var{name} is a
+readonly variable.
-The @sc{SVR4.2} shell has two privilege-related builtins
-(@code{mldmode} and @code{priv}) not present in Bash.
+@item logout
+@btindex logout
+@example
+logout [@var{n}]
+@end example
-Bash does not have the @code{stop} or @code{newgrp} builtins.
+Exit a login shell, returning a status of @var{n} to the shell's
+parent.
-Bash does not use the @code{SHACCT} variable or perform shell accounting.
+@item mapfile
+@btindex mapfile
+@example
+mapfile [-n @var{count}] [-O @var{origin}] [-s @var{count}] [-t] [-u @var{fd}]
+ [-C @var{callback}] [-c @var{quantum}] [@var{array}]
+@end example
-The @sc{SVR4.2} @code{sh} uses a @code{TIMEOUT} variable like Bash uses
-@code{TMOUT}.
+Read lines from the standard input into the indexed array variable @var{array},
+or from file descriptor @var{fd}
+if the @option{-u} option is supplied.
+The variable @code{MAPFILE} is the default @var{array}.
+Options, if supplied, have the following meanings:
-More features unique to Bash may be found in
-@ref{Bash Features}.
+@table @code
-@subsection Implementation Differences From The SVR4.2 Shell
+@item -n
+Copy at most @var{count} lines. If @var{count} is 0, all lines are copied.
+@item -O
+Begin assigning to @var{array} at index @var{origin}.
+The default index is 0.
+@item -s
+Discard the first @var{count} lines read.
+@item -t
+Remove a trailing newline from each line read.
+@item -u
+Read lines from file descriptor @var{fd} instead of the standard input.
+@item -C
+Evaluate @var{callback} each time @var{quantum}P lines are read.
+The @option{-c} option specifies @var{quantum}.
+@item -c
+Specify the number of lines read between each call to @var{callback}.
+@end table
-Since Bash is a completely new implementation, it does not suffer from
-many of the limitations of the @sc{SVR4.2} shell. For instance:
+If @option{-C} is specified without @option{-c},
+the default quantum is 5000.
+When @var{callback} is evaluated, it is supplied the index of the next
+array element to be assigned and the line to be assigned to that element
+as additional arguments.
+@var{callback} is evaluated after the line is read but before the
+array element is assigned.
-@itemize @bullet
+If not supplied with an explicit origin, @code{mapfile} will clear @var{array}
+before assigning to it.
-@item
-Bash does not fork a subshell when redirecting into or out of
-a shell control structure such as an @code{if} or @code{while}
-statement.
+@code{mapfile} returns successfully unless an invalid option or option
+argument is supplied, @var{array} is invalid or unassignable, or @var{array}
+is not an indexed array.
-@item
-Bash does not allow unbalanced quotes. The @sc{SVR4.2} shell will silently
-insert a needed closing quote at @code{EOF} under certain circumstances.
-This can be the cause of some hard-to-find errors.
+@item printf
+@btindex printf
+@example
+printf [-v @var{var}] @var{format} [@var{arguments}]
+@end example
-@item
-The @sc{SVR4.2} shell uses a baroque memory management scheme based on
-trapping @code{SIGSEGV}. If the shell is started from a process with
-@code{SIGSEGV} blocked (e.g., by using the @code{system()} C library
-function call), the shell misbehaves badly.
+Write the formatted @var{arguments} to the standard output under the
+control of the @var{format}.
+The @option{-v} option causes the output to be assigned to the variable
+@var{var} rather than being printed to the standard output.
-@item
-In a questionable attempt at security, the @sc{SVR4.2} shell,
-when invoked without the @samp{-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.
+The @var{format} is a character string which contains three types of objects:
+plain characters, which are simply copied to standard output, character
+escape sequences, which are converted and copied to the standard output, and
+format specifications, each of which causes printing of the next successive
+@var{argument}.
+In addition to the standard @code{printf(1)} formats, @code{printf}
+interprets the following extensions:
-@item
-The @sc{SVR4.2} shell does not allow users to trap @code{SIGALRM} or
-@code{SIGCHLD}.
+@table @code
+@item %b
+Causes @code{printf} to expand backslash escape sequences in the
+corresponding @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.
+@item %q
+Causes @code{printf} to output the
+corresponding @var{argument} in a format that can be reused as shell input.
+@item %(@var{datefmt})T
+Causes @code{printf} to output the date-time string resulting from using
+@var{datefmt} as a format string for @code{strftime}(3).
+The corresponding @var{argument} is an integer representing the number of
+seconds since the epoch.
+Two special argument values may be used: -1 represents the current
+time, and -2 represents the time the shell was invoked.
+If no argument is specified, conversion behaves as if -1 had been given.
+This is an exception to the usual @code{printf} behavior.
+@end table
-@item
-For some reason, the @sc{SVR4.2} shell does not allow the @code{MAILCHECK}
-variable to be unset.
+@noindent
+Arguments to non-string format specifiers are treated as C language constants,
+except that a leading plus or minus sign is allowed, and if the leading
+character is a single or double quote, the value is the ASCII value of
+the following character.
-@item
-The @sc{SVR4.2} shell treats @samp{^} as the undocumented equivalent of
-@samp{|}.
+The @var{format} is reused as necessary to consume all of the @var{arguments}.
+If the @var{format} requires more @var{arguments} than are supplied, the
+extra format specifications behave as if a zero value or null string, as
+appropriate, had been supplied. The return value is zero on success,
+non-zero on failure.
-@item
-Bash allows multiple option arguments when it is invoked (@code{-x -v});
-the @sc{SVR4.2} shell allows only one option argument (@code{-xv}). In
-fact, some versions of the shell dump core if the second argument begins
-with a @samp{-}.
+@item read
+@btindex read
+@example
+read [-ers] [-a @var{aname}] [-d @var{delim}] [-i @var{text}] [-n @var{nchars}]
+ [-N @var{nchars}] [-p @var{prompt}] [-t @var{timeout}] [-u @var{fd}] [@var{name} @dots{}]
+@end example
-@item
-The @sc{SVR4.2} shell exits a script if any builtin fails; Bash exits
-a script only if one of the @sc{POSIX.2} special builtins fails, and
-only for certain failures, as enumerated in the @sc{POSIX.2} standard.
+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 input stream than names,
+the remaining names are assigned empty values.
+The characters in the value of the @env{IFS} variable
+are used to split the line into words using the same rules the shell
+uses for expansion (described above in @ref{Word Splitting}).
+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 @env{REPLY}.
+The return code is zero, unless end-of-file is encountered, @code{read}
+times out (in which case the return code is greater than 128),
+a variable assignment error (such as assigning to a readonly variable) occurs,
+or an invalid file descriptor is supplied as the argument to @option{-u}.
-@item
-The @sc{SVR4.2} shell behaves differently when invoked as @code{jsh}
-(it turns on job control).
-@end itemize
+Options, if supplied, have the following meanings:
-@node Csh Features
-@chapter C-Shell Style Features
+@table @code
+@item -a @var{aname}
+The words are assigned to sequential indices of the array variable
+@var{aname}, starting at 0.
+All elements are removed from @var{aname} before the assignment.
+Other @var{name} arguments are ignored.
-The C-Shell (@dfn{@code{csh}}) was created by Bill Joy at The
-University of California at Berkeley. It
-is generally considered to have better features for interactive use than
-the original Bourne shell. Some of the @code{csh} features present in
-Bash include job control, history expansion, `protected' redirection, and
-several variables to control the interactive behaviour of the shell
-(e.g., @code{IGNOREEOF}).
+@item -d @var{delim}
+The first character of @var{delim} is used to terminate the input line,
+rather than newline.
-@xref{Using History Interactively}, for details on history expansion.
+@item -e
+Readline (@pxref{Command Line Editing}) is used to obtain the line.
+Readline uses the current (or default, if line editing was not previously
+active) editing settings.
+
+@item -i @var{text}
+If Readline is being used to read the line, @var{text} is placed into
+the editing buffer before editing begins.
+
+@item -n @var{nchars}
+@code{read} returns after reading @var{nchars} characters rather than
+waiting for a complete line of input, but honor a delimiter if fewer
+than @var{nchars} characters are read before the delimiter.
+
+@item -N @var{nchars}
+@code{read} returns after reading exactly @var{nchars} characters rather
+than waiting for a complete line of input, unless EOF is encountered or
+@code{read} times out.
+Delimiter characters encountered in the input are
+not treated specially and do not cause @code{read} to return until
+@var{nchars} characters are read.
-@menu
-* Brace Expansion:: Expansion of expressions within braces.
-* Tilde Expansion:: Expansion of the ~ character.
-* C Shell Builtins:: Builtin commands adopted from the C Shell.
-* C Shell Variables:: Variables which Bash uses in essentially
- the same way as the C Shell.
-@end menu
+@item -p @var{prompt}
+Display @var{prompt}, without a trailing newline, before attempting
+to read any input.
+The prompt is displayed only if input is coming from a terminal.
-@node Brace Expansion
-@section Brace Expansion
-@cindex brace expansion
-@cindex expansion, brace
+@item -r
+If this option is given, backslash does not act as an escape character.
+The backslash is considered to be part of the line.
+In particular, a backslash-newline pair may not be used as a line
+continuation.
-Brace expansion
-is a mechanism by which arbitrary strings
-may be generated. This mechanism is similar to
-@var{filename expansion} (@pxref{Filename Expansion}),
-but the file names generated
-need not exist. Patterns to be brace expanded take
-the form of an optional @var{preamble},
-followed by a series of comma-separated strings
-between a pair of braces, followed by an optional @var{postamble}.
-The preamble is prepended to each string contained
-within the braces, and the postamble is then appended
-to each resulting string, expanding left to right.
-
-Brace expansions may be nested. The results of each expanded
-string are not sorted; left to right order is preserved.
-For example,
+@item -s
+Silent mode. If input is coming from a terminal, characters are
+not echoed.
+
+@item -t @var{timeout}
+Cause @code{read} to time out and return failure if a complete line of
+input (or a specified number of characters)
+is not read within @var{timeout} seconds.
+@var{timeout} may be a decimal number with a fractional portion following
+the decimal point.
+This option is only effective if @code{read} is reading input from a
+terminal, pipe, or other special file; it has no effect when reading
+from regular files.
+If @code{read} times out, @code{read} saves any partial input read into
+the specified variable @var{name}.
+If @var{timeout} is 0, @code{read} returns immediately, without trying to
+read and data. The exit status is 0 if input is available on
+the specified file descriptor, non-zero otherwise.
+The exit status is greater than 128 if the timeout is exceeded.
+
+@item -u @var{fd}
+Read input from file descriptor @var{fd}.
+@end table
+
+@item readarray
+@btindex readarray
@example
-bash$ echo a@{d,c,b@}e
-ade ace abe
+readarray [-n @var{count}] [-O @var{origin}] [-s @var{count}] [-t] [-u @var{fd}]
+ [-C @var{callback}] [-c @var{quantum}] [@var{array}]
@end example
-Brace expansion is performed before any other expansions,
-and any characters special to other expansions are preserved
-in the result. It is strictly textual. Bash
-does not apply any syntactic interpretation to the context of the
-expansion or the text between the braces.
+Read lines from the standard input into the indexed array variable @var{array},
+or from file descriptor @var{fd}
+if the @option{-u} option is supplied.
-A correctly-formed brace expansion must contain unquoted opening
-and closing braces, and at least one unquoted comma.
-Any incorrectly formed brace expansion is left unchanged.
+A synonym for @code{mapfile}.
-This construct is typically used as shorthand when the common
-prefix of the strings to be generated is longer than in the
-above example:
+@item source
+@btindex source
@example
-mkdir /usr/local/src/bash/@{old,new,dist,bugs@}
+source @var{filename}
@end example
-or
+
+A synonym for @code{.} (@pxref{Bourne Shell Builtins}).
+
+@item type
+@btindex type
@example
-chown root /usr/@{ucb/@{ex,edit@},lib/@{ex?.?*,how_ex@}@}
+type [-afptP] [@var{name} @dots{}]
@end example
-@node Tilde Expansion
-@section Tilde Expansion
-@cindex tilde expansion
-@cindex expansion, tilde
-
-Bash has tilde (~) expansion, similar, but not identical, to that of
-@code{csh}. The following table shows what unquoted words beginning
-with a tilde expand to.
+For each @var{name}, indicate how it would be interpreted if used as a
+command name.
-@table @code
-@item ~
-The current value of @code{$HOME}.
-@item ~/foo
-@file{$HOME/foo}
+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,
+disk file, or shell reserved word, respectively.
+If the @var{name} is not found, then nothing is printed, and
+@code{type} returns a failure status.
-@item ~fred/foo
-The subdirectory @code{foo} of the home directory of the user
-@code{fred}.
+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}.
-@item ~+/foo
-@file{$PWD/foo}
+The @option{-P} option forces a path search for each @var{name}, even if
+@option{-t} would not return @samp{file}.
-@item ~-/foo
-@file{$OLDPWD/foo}
-@end table
+If a command is hashed, @option{-p} and @option{-P} print the hashed value,
+which is not necessarily the file that appears first in @code{$PATH}.
-Bash will also tilde expand words following redirection operators
-and words following @samp{=} in assignment statements.
+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 @option{-p} option
+is not also used.
-@node C Shell Builtins
-@section C Shell Builtins
+If the @option{-f} option is used, @code{type} does not attempt to find
+shell functions, as with the @code{command} builtin.
-Bash has several builtin commands whose definition is very similar
-to @code{csh}.
+The return status is zero if all of the @var{names} are found, non-zero
+if any are not found.
-@table @code
-@btindex pushd
-@item pushd
+@item typeset
+@btindex typeset
@example
-pushd [@var{dir} | @var{+N} | @var{-N}] [-n]
+typeset [-afFgrxilnrtux] [-p] [@var{name}[=@var{value}] @dots{}]
@end example
-Save the current directory on a list and then @code{cd} to
-@var{dir}. With no
-arguments, exchanges the top two directories.
-
-@table @code
-@item +@var{N}
-Brings the @var{N}th directory (counting from the left of the
-list printed by @code{dirs}, starting with zero) to the top of
-the list by rotating the stack.
-@item -@var{N}
-Brings the @var{N}th directory (counting from the right of the
-list printed by @code{dirs}, starting with zero) to the top of
-the list by rotating the stack.
-@item -n
-Suppresses the normal change of directory when adding directories
-to the stack, so that only the stack is manipulated.
-@item @var{dir}
-Makes the current working directory be the top of the stack, and then
-@code{cd}s to @var{dir}. You can see the saved directory list
-with the @code{dirs} command.
-@end table
+The @code{typeset} command is supplied for compatibility with the Korn
+shell.
+It is a synonym for the @code{declare} builtin command.
-@item popd
-@btindex popd
+@item ulimit
+@btindex ulimit
@example
-popd [+@var{N} | -@var{N}] [-n]
+ulimit [-abcdefilmnpqrstuvxHST] [@var{limit}]
@end example
-Pop the directory stack, and @code{cd} to the new top directory. When
-no arguments are given, @code{popd}
-removes the top directory from the stack and
-performs a @code{cd} to the new top directory. The
-elements are numbered from 0 starting at the first directory listed with
-@code{dirs}; i.e., @code{popd} is equivalent to @code{popd +0}.
-@table @code
-@item +@var{N}
-Removes the @var{N}th directory (counting from the left of the
-list printed by @code{dirs}), starting with zero.
-@item -@var{N}
-Removes the @var{N}th directory (counting from the right of the
-list printed by @code{dirs}), starting with zero.
-@item -n
-Suppresses the normal change of directory when removing directories
-from the stack, so that only the stack is manipulated.
-@end table
+@code{ulimit} provides control over the resources available to processes
+started by the shell, on systems that allow such control. If an
+option is given, it is interpreted as follows:
-@item dirs
-@btindex dirs
-@example
-dirs [+@var{N} | -@var{N}] [-clvp]
-@end example
-Display the list of currently remembered directories. Directories
-find their way onto the list with the @code{pushd} command; you can get
-back up through the list with the @code{popd} command.
@table @code
-@item +@var{N}
-Displays the @var{N}th directory (counting from the left of the
-list printed by @code{dirs} when invoked without options), starting
-with zero.
-@item -@var{N}
-Displays the @var{N}th directory (counting from the right of the
-list printed by @code{dirs} when invoked without options), starting
-with zero.
+@item -S
+Change and report the soft limit associated with a resource.
+
+@item -H
+Change and report the hard limit associated with a resource.
+
+@item -a
+All current limits are reported.
+
+@item -b
+The maximum socket buffer size.
+
@item -c
-Clears the directory stack by deleting all of the elements.
-@item -l
-Produces a longer listing; the default listing format uses a
-tilde to denote the home directory.
-@item -p
-Causes @code{dirs} to print the directory stack with one entry per
-line.
-@item -v
-Causes @code{dirs} to print the directory stack with one entry per
-line, prepending each entry with its index in the stack.
-@end table
+The maximum size of core files created.
-@item history
-@btindex history
-@example
-history [-c] [@var{n}]
-history [-anrw] [@var{filename}]
-history -ps @var{arg}
-@end example
+@item -d
+The maximum size of a process's data segment.
-Display the history list with line numbers. Lines prefixed with
-with a @samp{*} have been modified. An argument of @var{n} says
-to list only the last @var{n} lines. Options, if supplied, have
-the following meanings:
+@item -e
+The maximum scheduling priority ("nice").
-@table @code
-@item -w
-Write out the current history to the history file.
+@item -f
+The maximum size of files written by the shell and its children.
-@item -r
-Read the current history file and append its contents to
-the history list.
+@item -i
+The maximum number of pending signals.
-@item -a
-Append the new
-history lines (history lines entered since the beginning of the
-current Bash session) to the history file.
+@item -l
+The maximum size that may be locked into memory.
+
+@item -m
+The maximum resident set size (many systems do not honor this limit).
@item -n
-Append the history lines not already read from the history file
-to the current history list. These are lines appended to the history
-file since the beginning of the current Bash session.
+The maximum number of open file descriptors (most systems do not
+allow this value to be set).
-@item -c
-Clear the history list. This may be combined
-with the other options to replace the history list completely.
+@item -p
+The pipe buffer size.
-@item -s
-The @var{arg}s are added to the end of
-the history list as a single entry.
+@item -q
+The maximum number of bytes in POSIX message queues.
-@item -p
-Perform history substitution on the @var{arg}s and display the result
-on the standard output, without storing the results in the history list.
-@end table
+@item -r
+The maximum real-time scheduling priority.
-When the @samp{-w}, @samp{-r}, @samp{-a}, or @samp{-n} option is
-used, if @var{filename}
-is given, then it is used as the history file. If not, then
-the value of the @code{HISTFILE} variable is used.
+@item -s
+The maximum stack size.
-@item logout
-@btindex logout
-Exit a login shell.
+@item -t
+The maximum amount of cpu time in seconds.
-@item source
-@btindex source
-A synonym for @code{.} (@pxref{Bourne Shell Builtins}).
+@item -u
+The maximum number of processes available to a single user.
-@end table
+@item -v
+The maximum amount of virtual memory available to the shell, and, on
+some systems, to its children.
-@node C Shell Variables
-@section C Shell Variables
+@item -x
+The maximum number of file locks.
-@vtable @code
+@item -T
+The maximum number of threads.
+@end table
-@item IGNOREEOF
-If this variable is set, its value is used the number of consecutive
-@code{EOF}s Bash will read before exiting. By default, Bash will exit
-upon reading a single @code{EOF}. If @code{IGNOREEOF} is not set to
-a numeric value, Bash acts as if its value were 10.
+If @var{limit} is given, and the @option{-a} option is not used,
+@var{limit} 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.
+A hard limit cannot be increased by a non-root user once it is set;
+a soft limit may be increased up to the value of the hard limit.
+Otherwise, the current value of the soft limit for the specified resource
+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 @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{-T}, @option{-b},
+@option{-n} and @option{-u}, which are unscaled values.
-@end vtable
+The return status is zero unless an invalid option or argument is supplied,
+or an error occurs while setting a new limit.
-@node Korn Shell Features
-@chapter Korn Shell Style Features
+@item unalias
+@btindex unalias
+@example
+unalias [-a] [@var{name} @dots{} ]
+@end example
-This section describes features primarily inspired by the
-Korn Shell (@code{ksh}). In some cases, the @sc{POSIX} 1003.2
-standard has adopted these commands and variables from the
-Korn Shell; Bash implements those features using the @sc{POSIX}
-standard as a guide.
+Remove each @var{name} from the list of aliases. If @option{-a} is
+supplied, all aliases are removed.
+Aliases are described in @ref{Aliases}.
+@end table
+@node Modifying Shell Behavior
+@section Modifying Shell Behavior
+
@menu
-* Korn Shell Constructs:: Shell grammar constructs adopted from the
- Korn Shell
-* Korn Shell Builtins:: Builtin commands adopted from the Korn Shell.
-* Korn Shell Variables:: Variables which Bash uses in essentially
- the same way as the Korn Shell.
-* Aliases:: Substituting one command for another.
+* The Set Builtin:: Change the values of shell attributes and
+ positional parameters.
+* The Shopt Builtin:: Modify shell optional behavior.
@end menu
-@node Korn Shell Constructs
-@section Korn Shell Constructs
+@node The Set Builtin
+@subsection The Set Builtin
-Bash includes the Korn Shell @code{select} construct. This construct
-allows the easy generation of menus. It has almost the same syntax as
-the @code{for} command.
+This builtin is so complicated that it deserves its own section. @code{set}
+allows you to change the values of shell options and set the positional
+parameters, or to display the names and values of shell variables.
-The syntax of the @code{select} command is:
-@rwindex select
+@table @code
+@item set
+@btindex set
@example
-select @var{name} [in @var{words} @dots{}]; do @var{commands}; done
+set [--abefhkmnptuvxBCEHPT] [-o @var{option-name}] [@var{argument} @dots{}]
+set [+abefhkmnptuvxBCEHPT] [+o @var{option-name}] [@var{argument} @dots{}]
@end example
-The list of words following @code{in} is expanded, generating a list
-of items. The set of expanded words is printed on the standard
-error, each preceded by a number. If the @samp{in @var{words}}
-is omitted, the positional parameters are printed. The
-@code{PS3} prompt is then displayed and a line is read from the standard
-input. If the line consists of a number corresponding to one of
-the displayed words, then the value of @var{name}
-is set to that word. If the line is empty, the words and prompt
-are displayed again. If @code{EOF} is read, the @code{select}
-command completes. Any other value read causes @var{name}
-to be set to null. The line read is saved in the variable
-@code{REPLY}.
-
-The @var{commands} are executed after each selection until a
-@code{break} or @code{return} command is executed, at which
-point the @code{select} command completes.
+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
+for setting or resetting the currently-set variables.
+Read-only variables cannot be reset.
+In @sc{posix} mode, only shell variables are listed.
-Bash also has adopted command timing from the Korn shell. If the
-@code{time} reserved word precedes a pipeline, which may consist
-of a single command, timing statistics for the pipeline are displayed
-when it completes.
-The statistics currently consist of elapsed (wall-clock) time and
-user and system time consumed by the command's execution.
+When options are supplied, they set or unset shell attributes.
+Options, if specified, have the following meanings:
-The use of @code{time} as a reserved word permits the timing of
-shell builtins, shell functions, and pipelines. An external
-@code{time} command cannot time these easily.
+@table @code
+@item -a
+Mark variables and function which are modified or created for export
+to the environment of subsequent commands.
-@node Korn Shell Builtins
-@section Korn Shell Builtins
+@item -b
+Cause the status of terminated background jobs to be reported
+immediately, rather than before printing the next primary prompt.
-This section describes Bash builtin commands taken from @code{ksh}.
+@item -e
+Exit immediately if
+a pipeline (@pxref{Pipelines}), which may consist of a single simple command
+(@pxref{Simple Commands}),
+a list (@pxref{Lists}),
+or a compound command (@pxref{Compound Commands})
+returns a non-zero status.
+The shell does not exit if 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 any command executed in a @code{&&} or @code{||} list except
+the command following the final @code{&&} or @code{||},
+any command in a pipeline but the last,
+or if the command's return status is being inverted with @code{!}.
+If a compound command other than a subshell
+returns a non-zero status because a command failed
+while @option{-e} was being ignored, the shell does not exit.
+A trap on @code{ERR}, if set, is executed before the shell exits.
+
+This option applies to the shell environment and each subshell environment
+separately (@pxref{Command Execution Environment}), and may cause
+subshells to exit before executing all the commands in the subshell.
+
+If a compound command or shell function executes in a context where
+@option{-e} is being ignored,
+none of the commands executed within the compound command or function body
+will be affected by the @option{-e} setting, even if @option{-e} is set
+and a command returns a failure status.
+If a compound command or shell function sets @option{-e} while executing in
+a context where @option{-e} is ignored, that setting will not have any
+effect until the compound command or the command containing the function
+call completes.
-@table @code
+@item -f
+Disable filename expansion (globbing).
-@item fc
-@btindex fc
-@example
-@code{fc [-e @var{ename}] [-nlr] [@var{first}] [@var{last}]}
-@code{fc -s [@var{pat}=@var{rep}] [@var{command}]}
-@end example
-
-Fix Command. In the first form, a range of commands from @var{first} to
-@var{last} is selected from the history list. Both @var{first} and
-@var{last} may be specified as a string (to locate the most recent
-command beginning with that string) or as a number (an index into the
-history list, where a negative number is used as an offset from the
-current command number). If @var{last} is not specified it is set to
-@var{first}. If @var{first} is not specified it is set to the previous
-command for editing and @minus{}16 for listing. If the @samp{-l} flag is
-given, the commands are listed on standard output. The @samp{-n} flag
-suppresses the command numbers when listing. The @samp{-r} flag
-reverses the order of the listing. Otherwise, the editor given by
-@var{ename} is invoked on a file containing those commands. If
-@var{ename} is not given, the value of the following variable expansion
-is used: @code{$@{FCEDIT:-$@{EDITOR:-vi@}@}}. This says to use the
-value of the @code{FCEDIT} variable if set, or the value of the
-@code{EDITOR} variable if that is set, or @code{vi} if neither is set.
-When editing is complete, the edited commands are echoed and executed.
-
-In the second form, @var{command} is re-executed after each instance
-of @var{pat} in the selected command is replaced by @var{rep}.
-
-A useful alias to use with the @code{fc} command is @code{r='fc -s'}, so
-that typing @samp{r cc} runs the last command beginning with @code{cc}
-and typing @samp{r} re-executes the last command (@pxref{Aliases}).
+@item -h
+Locate and remember (hash) commands as they are looked up for execution.
+This option is enabled by default.
-@item let
-@btindex let
-The @code{let} builtin allows arithmetic to be performed on shell variables.
-For details, refer to @ref{Arithmetic Builtins}.
+@item -k
+All arguments in the form of assignment statements are placed
+in the environment for a command, not just those that precede
+the command name.
-@item typeset
-@btindex typeset
-The @code{typeset} command is supplied for compatibility with the Korn
-shell; however, it has been deprecated in favor of the
-@code{declare} command (@pxref{Bash Builtins}).
+@item -m
+Job control is enabled (@pxref{Job Control}).
+All processes run in a separate process group.
+When a background job completes, the shell prints a line
+containing its exit status.
-@end table
+@item -n
+Read commands but do not execute them; this may be used to check a
+script for syntax errors.
+This option is ignored by interactive shells.
-@node Korn Shell Variables
-@section Korn Shell Variables
+@item -o @var{option-name}
-@vtable @code
+Set the option corresponding to @var{option-name}:
-@item REPLY
-The default variable for the @code{read} builtin.
+@table @code
+@item allexport
+Same as @code{-a}.
-@item RANDOM
-Each time this parameter is referenced, a random integer
-between 0 and 32767 is generated. Assigning a value to this
-variable seeds the random number generator.
+@item braceexpand
+Same as @code{-B}.
-@item SECONDS
-This variable expands to the number of seconds since the
-shell was started. Assignment to this variable resets
-the count to the value assigned, and the expanded value
-becomes the value assigned plus the number of seconds
-since the assignment.
+@item emacs
+Use an @code{emacs}-style line editing interface (@pxref{Command Line Editing}).
+This also affects the editing interface used for @code{read -e}.
-@item PS3
-The value of this variable is used as the prompt for the
-@code{select} command. If this variable is not set, the
-@code{select} command prompts with @samp{#? }
+@item errexit
+Same as @code{-e}.
-@item PS4
-This is the prompt printed before the command line is echoed
-when the @samp{-x} option is set (@pxref{The Set Builtin}).
-The default is @samp{+ }.
+@item errtrace
+Same as @code{-E}.
-@item PWD
-The current working directory as set by the @code{cd} builtin.
+@item functrace
+Same as @code{-T}.
-@item OLDPWD
-The previous working directory as set by the @code{cd} builtin.
+@item hashall
+Same as @code{-h}.
-@item TMOUT
-If set to a value greater than zero, the value is interpreted as
-the number of seconds to wait for input after issuing the primary
-prompt.
-Bash terminates after that number of seconds if input does
-not arrive.
+@item histexpand
+Same as @code{-H}.
-@item LINENO
-The line number in the script or shell function currently executing.
+@item history
+Enable command history, as described in @ref{Bash History Facilities}.
+This option is on by default in interactive shells.
-@item FCEDIT
-The editor used as a default by the @code{fc} builtin command.
+@item ignoreeof
+An interactive shell will not exit upon reading EOF.
-@end vtable
+@item keyword
+Same as @code{-k}.
-@node Aliases
-@section Aliases
-@cindex alias expansion
+@item monitor
+Same as @code{-m}.
-@menu
-* Alias Builtins:: Builtins commands to maniuplate aliases.
-@end menu
+@item noclobber
+Same as @code{-C}.
-The shell maintains a list of @var{aliases}
-that may be set and unset with the @code{alias} and
-@code{unalias} builtin commands.
+@item noexec
+Same as @code{-n}.
-The first word of each command, if unquoted,
-is checked to see if it has an
-alias. If so, that word is replaced by the text of the alias.
-The alias name and the replacement text may contain any valid
-shell input, including shell metacharacters, with the exception
-that the alias name may not contain @key{=}.
-The first word of the replacement text is tested for
-aliases, but a word that is identical to an alias being expanded
-is not expanded a second time. This means that one may alias
-@code{ls} to @code{"ls -F"},
-for instance, and Bash does not try to recursively expand the
-replacement text. If the last character of the alias value is a
-space or tab character, then the next command word following the
-alias is also checked for alias expansion.
+@item noglob
+Same as @code{-f}.
-Aliases are created and listed with the @code{alias}
-command, and removed with the @code{unalias} command.
+@item nolog
+Currently ignored.
-There is no mechanism for using arguments in the replacement text,
-as in @code{csh}.
-If arguments are needed, a shell function should be used
-(@pxref{Shell Functions}).
+@item notify
+Same as @code{-b}.
-Aliases are not expanded when the shell is not interactive,
-unless the @code{expand_aliases} shell option is set using
-@code{shopt} (@pxref{Bash Builtins}).
+@item nounset
+Same as @code{-u}.
-The rules concerning the definition and use of aliases are
-somewhat confusing. Bash
-always reads at least one complete line
-of input before executing any
-of the commands on that line. Aliases are expanded when a
-command is read, not when it is executed. Therefore, an
-alias definition appearing on the same line as another
-command does not take effect until the next line of input is read.
-The commands following the alias definition
-on that line are not affected by the new alias.
-This behavior is also an issue when functions are executed.
-Aliases are expanded when the function definition is read,
-not when the function is executed, because a function definition
-is itself a compound command. As a consequence, aliases
-defined in a function are not available until after that
-function is executed. To be safe, always put
-alias definitions on a separate line, and do not use @code{alias}
-in compound commands.
+@item onecmd
+Same as @code{-t}.
-Note that for almost every purpose, aliases are superseded by
-shell functions.
+@item physical
+Same as @code{-P}.
-@node Alias Builtins
-@subsection Alias Builtins
+@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.
-@table @code
+@item posix
+Change the behavior of Bash where the default operation differs
+from the @sc{posix} standard to match the standard
+(@pxref{Bash POSIX Mode}).
+This is intended to make Bash behave as a strict superset of that
+standard.
-@item alias
-@btindex alias
-@example
-alias [@code{-p}] [@var{name}[=@var{value}] @dots{}]
-@end example
+@item privileged
+Same as @code{-p}.
-Without arguments or with the @samp{-p} option, @code{alias} prints
-the list of aliases on the standard output in a form that allows
-them to be reused as input.
-If arguments are supplied, an alias is defined for each @var{name}
-whose @var{value} is given. If no @var{value} is given, the name
-and value of the alias is printed.
+@item verbose
+Same as @code{-v}.
-@item unalias
-@btindex unalias
-@example
-unalias [-a] [@var{name} @dots{} ]
-@end example
+@item vi
+Use a @code{vi}-style line editing interface.
+This also affects the editing interface used for @code{read -e}.
-Remove each @var{name} from the list of aliases. If @samp{-a} is
-supplied, all aliases are removed.
+@item xtrace
+Same as @code{-x}.
@end table
-@node Bash Features
-@chapter Bash Features
-
-This section describes features unique to Bash.
+@item -p
+Turn on privileged mode.
+In this mode, the @env{$BASH_ENV} and @env{$ENV} files are not
+processed, shell functions are not inherited from the environment,
+and the @env{SHELLOPTS}, @env{BASHOPTS}, @env{CDPATH} and @env{GLOBIGNORE}
+variables, if they appear in the environment, are ignored.
+If the shell is started with the effective user (group) id not equal to the
+real user (group) id, and the @option{-p} option is not supplied, these actions
+are taken and the effective user id is set to the real user id.
+If the @option{-p} option is supplied at startup, the effective user id is
+not reset.
+Turning this option off causes the effective user
+and group ids to be set to the real user and group ids.
-@menu
-* Invoking Bash:: Command line options that you can give
- to Bash.
-* Bash Startup Files:: When and how Bash executes scripts.
-* Is This Shell Interactive?:: Determining the state of a running Bash.
-* Bash Builtins:: Table of builtins specific to Bash.
-* The Set Builtin:: This builtin is so overloaded it
- deserves its own section.
-* Bash Conditional Expressions:: Primitives used in composing expressions for
- the @code{test} builtin.
-* Bash Variables:: List of variables that exist in Bash.
-* Shell Arithmetic:: Arithmetic on shell variables.
-* Arrays:: Array Variables
-* Printing a Prompt:: Controlling the PS1 string.
-* The Restricted Shell:: A more controlled mode of shell execution.
-* Bash POSIX Mode:: Making Bash behave more closely to what
- the POSIX standard specifies.
-@end menu
+@item -t
+Exit after reading and executing one command.
-@node Invoking Bash
-@section Invoking Bash
+@item -u
+Treat unset variables and parameters other than the special parameters
+@samp{@@} or @samp{*} as an error when performing parameter expansion.
+An error message will be written to the standard error, and a non-interactive
+shell will exit.
-@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{}]
-@end example
+@item -v
+Print shell input lines as they are read.
-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.
+@item -x
+Print a trace of simple commands, @code{for} commands, @code{case}
+commands, @code{select} commands, and arithmetic @code{for} 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.
-@table @code
-@item --dump-strings
-Equivalent to @samp{-D}.
+@item -B
+The shell will perform brace expansion (@pxref{Brace Expansion}).
+This option is on by default.
-@item --help
-Display a usage message on standard output and exit sucessfully.
+@item -C
+Prevent output redirection using @samp{>}, @samp{>&}, and @samp{<>}
+from overwriting existing files.
-@item --login
-Make this shell act as if it were directly invoked by login.
-This is equivalent to @samp{exec -l bash} but can be issued from
-another shell, such as @code{csh}. If you wanted to replace your
-current login shell with a Bash login shell, you would say
-@samp{exec bash --login}.
+@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 --noediting
-Do not use the @sc{GNU} Readline library (@pxref{Command Line Editing})
-to read interactive command lines.
+@item -H
+Enable @samp{!} style history substitution (@pxref{History Interaction}).
+This option is on by default for interactive shells.
-@item --noprofile
-Don't load the system-wide startup file @file{/etc/profile}
-or any of the personal initialization files
-@file{~/.bash_profile}, @file{~/.bash_login}, or @file{~/.profile}
-when Bash is invoked as a login shell.
+@item -P
+If set, do not resolve symbolic links when performing commands such as
+@code{cd} which change the current directory. The physical directory
+is used instead. By default, Bash follows
+the logical chain of directories when performing commands
+which change the current directory.
-@item --norc
-Don't read the @file{~/.bashrc} initialization file in an
-interactive shell. This is on by default if the shell is
-invoked as @code{sh}.
+For example, if @file{/usr/sys} is a symbolic link to @file{/usr/local/sys}
+then:
+@example
+$ cd /usr/sys; echo $PWD
+/usr/sys
+$ cd ..; pwd
+/usr
+@end example
-@item --posix
-Change the behavior of Bash where the default operation differs
-from the @sc{POSIX} 1003.2 standard to match the standard. This
-is intended to make Bash behave as a strict superset of that
-standard. @xref{Bash POSIX Mode}, for a description of the Bash
-@sc{POSIX} mode.
+@noindent
+If @code{set -P} is on, then:
+@example
+$ cd /usr/sys; echo $PWD
+/usr/local/sys
+$ cd ..; pwd
+/usr/local
+@end example
-@item --rcfile @var{filename}
-Execute commands from @var{filename} (instead of @file{~/.bashrc})
-in an interactive shell.
+@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 --restricted
-Make the shell a restricted shell (@pxref{The Restricted Shell}).
+@item --
+If no arguments follow this option, then the positional parameters are
+unset. Otherwise, the positional parameters are set to the
+@var{arguments}, even if some of them begin with a @samp{-}.
-@item --verbose
-Equivalent to @samp{-v}.
+@item -
+Signal the end of options, cause all remaining @var{arguments}
+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
-@item --version
-Show version information for this instance of
-Bash on the standard output and exit successfully.
+Using @samp{+} rather than @samp{-} causes these options to be
+turned off. The options can also be used upon invocation of the
+shell. The current set of options may be found in @code{$-}.
+
+The remaining N @var{arguments} are positional parameters and are
+assigned, in order, to @code{$1}, @code{$2}, @dots{} @code{$N}.
+The special parameter @code{#} is set to N.
+The return status is always zero unless an invalid option is supplied.
@end table
-There are several single-character options you can give which are
-not available with the @code{set} builtin.
+@node The Shopt Builtin
+@subsection The Shopt Builtin
+
+This builtin allows you to change additional shell optional behavior.
@table @code
-@item -c @var{string}
-Read and execute commands from @var{string} after processing the
-options, then exit. Any remaining arguments are assigned to the
-positional parameters, starting with @code{$0}.
-@item -i
-Force the shell to run interactively.
+@item shopt
+@btindex shopt
+@example
+shopt [-pqsu] [-o] [@var{optname} @dots{}]
+@end example
-@item -r
-Make the shell restricted.
+Toggle the values of settings controlling optional shell behavior.
+The settings can be either those listed below, or, if the
+@option{-o} option is used, those available with the @option{-o}
+option to the @code{set} builtin command (@pxref{The Set Builtin}).
+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 @option{-p} option causes output to be displayed in a form that
+may be reused as input.
+Other options have the following meanings:
+@table @code
@item -s
-If this flag is present, or if no arguments remain after option
-processing, then commands are read from the standard input.
-This option allows the positional parameters to be set
-when invoking an interactive shell.
+Enable (set) each @var{optname}.
-@item -D
-A list of all double-quoted strings preceded by @samp{$}
-is printed on the standard ouput.
-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.
+@item -u
+Disable (unset) each @var{optname}.
+
+@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 @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 @option{-o} option to the
+@code{set} builtin (@pxref{The Set Builtin}).
@end table
-@cindex interactive shell
-An @emph{interactive} shell is one whose input and output are both
-connected to terminals (as determined by @code{isatty()}), or one
-started with the @samp{-i} option.
+If either @option{-s} or @option{-u}
+is used with no @var{optname} arguments, @code{shopt} shows only
+those options which are set or unset, respectively.
-If arguments remain after option processing, and neither the
-@samp{-c} nor the @samp{-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}
-is set to the name of the file, and the positional parameters
-are set to the remaining arguments.
-Bash reads and executes commands from this file, then exits.
-Bash's exit status is the exit status of the last command executed
-in the script. If no commands are executed, the exit status is 0.
+Unless otherwise noted, the @code{shopt} options are disabled (off)
+by default.
-@node Bash Startup Files
-@section Bash Startup Files
-@cindex startup files
+The return status when listing options is zero if all @var{optnames}
+are enabled, non-zero otherwise. When setting or unsetting options,
+the return status is zero unless an @var{optname} is not a valid shell
+option.
-This section describs how Bash executes its startup files.
-If any of the files exist but cannot be read, Bash reports an error.
-Tildes are expanded in file names as described above under
-Tilde Expansion (@pxref{Tilde Expansion}).
+The list of @code{shopt} options is:
+@table @code
-When Bash is invoked as an interactive login shell, 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
-inhibit this behavior.
+@item autocd
+If set, a command name that is the name of a directory is executed as if
+it were the argument to the @code{cd} command.
+This option is only used by interactive shells.
-When a login shell exits, Bash reads and executes commands from
-the file @file{~/.bash_logout}, if it exists.
+@item cdable_vars
+If this is set, an argument to the @code{cd} builtin command that
+is not a directory is assumed to be the name of a variable whose
+value is the directory to change to.
-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
-execute commands from @var{file} instead of @file{~/.bashrc}.
+@item cdspell
+If set, minor errors in the spelling of a directory component in a
+@code{cd} command will be corrected.
+The errors checked for are transposed characters,
+a missing character, and a character too many.
+If a correction is found, the corrected path is printed,
+and the command proceeds.
+This option is only used by interactive shells.
-So, typically, your @file{~/.bash_profile} contains the line
-@example
-@code{if [ -f @file{~/.bashrc} ]; then . @file{~/.bashrc}; fi}
-@end example
-@noindent
-after (or before) any login-specific initializations.
+@item checkhash
+If this is set, Bash checks that a command found in the hash
+table exists before trying to execute it. If a hashed command no
+longer exists, a normal path search is performed.
-When Bash is started non-interactively, to run a shell script,
-for example, it looks for the variable @code{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:
-@example
-@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
-file name.
+@item checkjobs
+If set, Bash lists the status of any stopped and running jobs before
+exiting an interactive shell. If any jobs are running, this causes
+the exit to be deferred until a second exit is attempted without an
+intervening command (@pxref{Job Control}).
+The shell always postpones exiting if any jobs are stopped.
-If Bash is invoked with the name @code{sh}, it tries to mimic the
-startup behavior of historical versions of @code{sh} as closely as
-possible, while conforming to the @sc{POSIX} standard as well.
-
-When invoked as a login shell, it first attempts to read and execute
-commands from @file{/etc/profile} and @file{~/.profile}, in that order.
-The @samp{--noprofile} option may be used to inhibit this behavior.
-When invoked as an interactive shell with the name @code{sh},
-@code{bash} looks for the variable @code{ENV},
-expands its value if it is defined, and uses the
-expanded value as the name of a file to read and execute.
-Since a shell invoked as @code{sh} does not attempt to read and execute
-commands from any other startup files, the @samp{--rcfile} option has
-no effect.
-A non-interactive shell invoked with the name @code{sh} does not attempt
-to read any startup files.
+@item checkwinsize
+If set, Bash checks the window size after each command
+ and, if necessary, updates the values of
+@env{LINES} and @env{COLUMNS}.
-When invoked as @code{sh}, Bash enters @sc{POSIX} mode after
-the startup files are read.
+@item cmdhist
+If set, Bash
+attempts to save all lines of a multiple-line
+command in the same history entry. This allows
+easy re-editing of multi-line commands.
-When Bash is started in @sc{POSIX} mode, as with the
-@samp{--posix} command line option, it follows the @sc{POSIX} standard
-for startup files.
-In this mode, the @code{ENV} variable is expanded and commands are read
-and executed from the file whose name is the expanded value.
-No other startup files are read.
-This is done by interactive shells only.
+@item compat31
+If set, Bash
+changes its behavior to that of version 3.1 with respect to quoted
+arguments to the conditional command's @samp{=~} operator
+and with respect to locale-specific
+string comparison when using the @code{[[}
+conditional command's @samp{<} and @samp{>} operators.
+Bash versions prior to bash-4.1 use ASCII collation and strcmp(3);
+bash-4.1 and later use the current locale's collation sequence and strcoll(3).
+
+@item compat32
+If set, Bash
+changes its behavior to that of version 3.2 with respect to locale-specific
+string comparison when using the @code{[[}
+conditional command's @samp{<} and @samp{>} operators (see previous item).
-Bash attempts to determine when it is being run by the remote shell
-daemon, usually @code{rshd}. If Bash determines it is being run by
-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
-rshd does not generally invoke the shell with those options or allow
-them to be specified.
+@item compat40
+If set, Bash
+changes its behavior to that of version 4.0 with respect to locale-specific
+string comparison when using the @code{[[}
+conditional command's @samp{<} and @samp{>} operators (see description
+of @code{compat31})
+and the effect of interrupting a command list.
+Bash versions 4.0 and later interrupt the list as if the shell received the
+interrupt; previous versions continue with the next command in the list.
+
+@item compat41
+If set, Bash, when in @sc{posix} mode, treats a single quote in a double-quoted
+parameter expansion as a special character. The single quotes must match
+(an even number) and the characters between the single quotes are considered
+quoted. This is the behavior of @sc{posix} mode through version 4.1.
+The default Bash behavior remains as in previous versions.
+
+@item compat42
+If set, Bash
+does not process the replacement string in the pattern substitution word
+expansion using quote removal.
-@node Is This Shell Interactive?
-@section Is This Shell Interactive?
-@cindex interactive shell
+@item complete_fullquote
+If set, Bash
+quotes all shell metacharacters in filenames and directory names when
+performing completion.
+If not set, Bash
+removes metacharacters such as the dollar sign from the set of
+characters that will be quoted in completed filenames
+when these metacharacters appear in shell variable references in words to be
+completed.
+This means that dollar signs in variable names that expand to directories
+will not be quoted;
+however, any dollar signs appearing in filenames will not be quoted, either.
+This is active only when bash is using backslashes to quote completed
+filenames.
+This variable is set by default, which is the default Bash behavior in
+versions through 4.2.
+
+@item direxpand
+If set, Bash
+replaces directory names with the results of word expansion when performing
+filename completion. This changes the contents of the readline editing
+buffer.
+If not set, Bash attempts to preserve what the user typed.
-As defined in @ref{Invoking Bash}, an interactive shell
-is one whose input and output are both
-connected to terminals (as determined by @code{isatty(3)}),
-or one started with the @samp{-i} option.
+@item dirspell
+If set, Bash
+attempts spelling correction on directory names during word completion
+if the directory name initially supplied does not exist.
-You may wish to determine within a startup script whether Bash is
-running interactively or not. To do this, examine the variable
-@code{$PS1}; it is unset in non-interactive shells, and set in
-interactive shells. Thus:
+@item dotglob
+If set, Bash includes filenames beginning with a `.' in
+the results of filename expansion.
-@example
-if [ -z "$PS1" ]; then
- echo This shell is not interactive
-else
- echo This shell is interactive
-fi
-@end example
+@item execfail
+If this is set, a non-interactive shell will not exit if
+it cannot execute the file specified as an argument to the @code{exec}
+builtin command. An interactive shell does not exit if @code{exec}
+fails.
-Alternatively, you may test the value of the @samp{-} special parameter.
-It contains @code{i} when the shell is interactive. For example:
+@item expand_aliases
+If set, aliases are expanded as described below under Aliases,
+@ref{Aliases}.
+This option is enabled by default for interactive shells.
-@example
-case "$-" in
-*i*) echo This shell is interactive ;;
-*) echo This shell is not interactive ;;
-esac
-@end example
+@item extdebug
+If set, behavior intended for use by debuggers is enabled:
-@node Bash Builtins
-@section Bash Builtin Commands
+@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.
-This section describes builtin commands which are unique to
-or have been extended in Bash.
+@item
+If the command run by the @code{DEBUG} trap returns a non-zero value, the
+next command is skipped and not executed.
-@table @code
+@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 bind
-@btindex bind
-@example
-bind [-m @var{keymap}] [-lpsvPSV] [-q @var{name}] [-r @var{keyseq}]
-bind [-m @var{keymap}] -f @var{filename}
-bind [-m @var{keymap}] @var{keyseq:function-name}
-@end example
+@item
+@code{BASH_ARGC} and @code{BASH_ARGV} are updated as described in their
+descriptions (@pxref{Bash Variables}).
-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
-@file{.inputrc} (@pxref{Readline Init File}),
-but each binding 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:
+@item
+Function tracing is enabled: command substitution, shell functions, and
+subshells invoked with @code{( @var{command} )} inherit the
+@code{DEBUG} and @code{RETURN} traps.
-@table @code
-@item -m @var{keymap}
-Use @var{keymap} as the keymap to be affected by
-the subsequent bindings. Acceptable @var{keymap}
-names are
-@code{emacs},
-@code{emacs-standard},
-@code{emacs-meta},
-@code{emacs-ctlx},
-@code{vi},
-@code{vi-command}, and
-@code{vi-insert}.
-@code{vi} is equivalent to @code{vi-command};
-@code{emacs} is equivalent to @code{emacs-standard}.
+@item
+Error tracing is enabled: command substitution, shell functions, and
+subshells invoked with @code{( @var{command} )} inherit the
+@code{ERR} trap.
+@end enumerate
-@item -l
-List the names of all Readline functions
+@item extglob
+If set, the extended pattern matching features described above
+(@pxref{Pattern Matching}) are enabled.
-@item -p
-Display Readline function names and bindings in such a way that they
-can be re-read
+@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 -P
-List current Readline function names and bindings
+@item failglob
+If set, patterns which fail to match filenames during filename expansion
+result in an expansion error.
-@item -v
-Display Readline variable names and values in such a way that they
-can be re-read
+@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 -V
-List current Readline variable names and values
+@item globasciiranges
+If set, range expressions used in pattern matching bracket expressions
+(@pxref{Pattern Matching})
+behave as if in the traditional C locale when performing
+comparisons. That is, the current locale's collating sequence
+is not taken into account, so
+@samp{b} will not collate between @samp{A} and @samp{B},
+and upper-case and lower-case ASCII characters will collate together.
+
+@item globstar
+If set, the pattern @samp{**} used in a filename expansion context will
+match all files and zero or more directories and subdirectories.
+If the pattern is followed by a @samp{/}, only directories and
+subdirectories match.
+
+@item gnu_errfmt
+If set, shell error messages are written in the standard @sc{gnu} error
+message format.
-@item -s
-Display Readline key sequences bound to macros and the strings they output
-in such a way that they can be re-read
+@item histappend
+If set, the history list is appended to the file named by the value
+of the @env{HISTFILE}
+variable when the shell exits, rather than overwriting the file.
-@item -S
-Display Readline key sequences bound to macros and the strings they output
+@item histreedit
+If set, and Readline
+is being used, a user is given the opportunity to re-edit a
+failed history substitution.
-@item -f @var{filename}
-Read key bindings from @var{filename}
+@item histverify
+If set, and Readline
+is being used, the results of history substitution are not immediately
+passed to the shell parser. Instead, the resulting line is loaded into
+the Readline editing buffer, allowing further modification.
-@item -q
-Query about which keys invoke the named @var{function}
+@item hostcomplete
+If set, and Readline is being used, Bash will attempt to perform
+hostname completion when a word containing a @samp{@@} is being
+completed (@pxref{Commands For Completion}). This option is enabled
+by default.
-@item -r @var{keyseq}
-Remove any current binding for @var{keyseq}
+@item huponexit
+If set, Bash will send @code{SIGHUP} to all jobs when an interactive
+login shell exits (@pxref{Signals}).
-@end table
+@item interactive_comments
+Allow a word beginning with @samp{#}
+to cause that word and all remaining characters on that
+line to be ignored in an interactive shell.
+This option is enabled by default.
-@item builtin
-@btindex builtin
-@example
-builtin [@var{shell-builtin} [@var{args}]]
-@end example
-Run a shell builtin. This is useful when you wish to define a
-shell function with the same name as a shell builtin, but need the
-functionality of the builtin within the function itself.
+@item lastpipe
+If set, and job control is not active, the shell runs the last command of
+a pipeline not executed in the background in the current shell environment.
-@item command
-@btindex command
-@example
-command [-pVv] @var{command} [@var{args} @dots{}]
-@end example
-Runs @var{command} with @var{arg} ignoring shell functions. If
-you have a shell function called @code{ls}, and you wish to call
-the command @code{ls}, you can say @samp{command ls}. The
-@samp{-p} option means to use a default value for @code{$PATH}
-that is guaranteed to find all of the standard utilities.
+@item lithist
+If enabled, and the @code{cmdhist}
+option is enabled, multi-line commands are saved to the history with
+embedded newlines rather than using semicolon separators where possible.
-If either the @samp{-V} or @samp{-v} option is supplied, a
-description of @var{command} is printed. The @samp{-v} option
-causes a single word indicating the command or file name used to
-invoke @var{command} to be printed; the @samp{-V} option produces
-a more verbose description.
+@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 declare
-@btindex declare
-@example
-declare [-afFrxi] [-p] [@var{name}[=@var{value}]]
-@end example
+@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
+@code{"The mail in @var{mailfile} has been read"} is displayed.
-Declare variables and give them attributes. If no @var{name}s
-are given, then display the values of variables instead.
+@item no_empty_cmd_completion
+If set, and Readline is being used, Bash will not attempt to search
+the @env{PATH} for possible completions when completion is attempted
+on an empty line.
-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:
+@item nocaseglob
+If set, Bash matches filenames in a case-insensitive fashion when
+performing filename expansion.
-@table @code
-@item -a
-Each @var{name} is an array variable (@pxref{Arrays}).
+@item nocasematch
+If set, Bash matches patterns in a case-insensitive fashion when
+performing matching while executing @code{case} or @code{[[}
+conditional commands.
-@item -f
-Use function names only.
+@item nullglob
+If set, Bash allows filename patterns which match no
+files to expand to a null string, rather than themselves.
-@item -i
-The variable is to be treated as
-an integer; arithmetic evaluation (@pxref{Shell Arithmetic}) is
-performed when the variable is assigned a value.
+@item progcomp
+If set, the programmable completion facilities
+(@pxref{Programmable Completion}) are enabled.
+This option is enabled by default.
-@item -r
-Make @var{name}s readonly. These names cannot then be assigned values
-by subsequent assignment statements.
+@item promptvars
+If set, prompt strings undergo
+parameter expansion, command substitution, arithmetic
+expansion, and quote removal after being expanded
+as described below (@pxref{Controlling the Prompt}).
+This option is enabled by default.
-@item -x
-Mark each @var{name} for export to subsequent commands via
-the environment.
-@end table
+@item restricted_shell
+The shell sets this option if it is started in restricted mode
+(@pxref{The Restricted Shell}).
+The value may not be changed.
+This is not reset when the startup files are executed, allowing
+the startup files to discover whether or not a shell is restricted.
-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.
+@item shift_verbose
+If this is set, the @code{shift}
+builtin prints an error message when the shift count exceeds the
+number of positional parameters.
-@item echo
-@btindex echo
-@example
-echo [-neE] [arg @dots{}]
-@end example
-Output the @code{arg}s, separated by spaces, terminated with a
-newline. The return status is always 0. If @samp{-n} is
-specified, the trailing newline is suppressed. If the @samp{-e}
-option is given, interpretation of the following backslash-escaped
-characters is enabled. The @samp{-E} option disables the interpretation
-of these escape characters, even on systems where they are interpreted
+@item sourcepath
+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 xpg_echo
+If set, the @code{echo} builtin expands backslash-escape sequences
by default.
-@code{echo} interprets the following escape sequences:
-@table @code
-@item \a
-alert (bell)
-@item \b
-backspace
-@item \c
-suppress trailing newline
-@item \e
-escape
-@item \f
-form feed
-@item \n
-new line
-@item \r
-carriage return
-@item \t
-horizontal tab
-@item \v
-vertical tab
-@item \\
-backslash
-@item \nnn
-the character whose ASCII code is @code{nnn} (octal)
+
@end table
-@item enable
-@btindex enable
-@example
-enable [-n] [-p] [-f @var{filename}] [-ads] [@var{name} @dots{}]
-@end example
-Enable and disable builtin shell commands. This allows you to
-use a disk command which has the same name as a shell builtin.
-If @samp{-n} is used, the @var{name}s become disabled. Otherwise
-@var{name}s are enabled. For example, to use the @code{test} binary
-found via @code{$PATH} instead of the shell builtin version, type
-@samp{enable -n test}.
+@noindent
+The return status when listing options is zero if all @var{optnames}
+are enabled, non-zero otherwise.
+When setting or unsetting options, the return status is zero unless an
+@var{optname} is not a valid shell option.
+@end table
-If the @samp{-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
-each builtin with an indication of whether or not it is enabled.
+@node Special Builtins
+@section Special Builtins
+@cindex special builtin
-The @samp{-f} option means to load the new builtin command @var{name}
-from shared object @var{filename}, on systems that support dynamic loading.
-The @samp{-d} option will delete a builtin loaded with @samp{-f}.
-If there are no options, a list of the shell builtins is displayed.
-The @samp{-s} option restricts @code{enable} to the @sc{POSIX.2} special
-builtins. If @samp{-s} is used with @samp{-f}, the new builtin becomes
-a special builtin.
+For historical reasons, the @sc{posix} standard has classified
+several builtin commands as @emph{special}.
+When Bash is executing in @sc{posix} mode, the special builtins
+differ from other builtin commands in three respects:
-@item help
-@btindex help
-@example
-help [@var{pattern}]
-@end example
-Display helpful information about builtin commands. If
-@var{pattern} is specified, @code{help} gives detailed help
-on all commands matching @var{pattern}, otherwise a list of
-the builtins is printed.
+@enumerate
+@item
+Special builtins are found before shell functions during command lookup.
-@item local
-@btindex local
-@example
-local @var{name}[=@var{value}]
-@end example
-For each argument, create a local variable called @var{name}, and
-give it @var{value}.
-@code{local} can only be used within a function; it makes the variable
-@var{name} have a visible scope restricted to that function and its
-children.
+@item
+If a special builtin returns an error status, a non-interactive shell exits.
-@item logout
-@btindex logout
-@example
-logout [@var{n}]
-@end example
-Exit a login shell, returning a status of @var{n} to the shell's
-parent.
+@item
+Assignment statements preceding the command stay in effect in the shell
+environment after the command completes.
+@end enumerate
-@item read
-@btindex read
+When Bash is not executing in @sc{posix} mode, these builtins behave no
+differently than the rest of the Bash builtin commands.
+The Bash @sc{posix} mode is described in @ref{Bash POSIX Mode}.
+
+These are the @sc{posix} special builtins:
@example
-read [-a @var{aname}] [-p @var{prompt}] [-er] [@var{name} @dots{}]
+@w{break : . continue eval exec exit export readonly return set}
+@w{shift trap unset}
@end example
-One line is read from the standard input, and the first word
-is assigned to the first
-@var{name}, the second word to the second @var{name},
-and so on, with leftover words assigned to the last @var{name}.
-Only the characters in the value of the @code{IFS} variable
-are recognized as word delimiters. If no names
-are supplied, the line read is assigned to the variable @code{REPLY}.
-The return code is zero, unless end-of-file is encountered. Options,
-if supplied, have the following meanings:
-@table @code
-@item -r
-If this option is given, a backslash-newline pair is not ignored, and
-the backslash is considered to be part of the line.
+@node Shell Variables
+@chapter Shell Variables
-@item -p @var{prompt}
-Display @code{prompt}, without a
-trailing newline, before attempting to read any input. The prompt
-is displayed only if input is coming from a terminal.
+@menu
+* Bourne Shell Variables:: Variables which Bash uses in the same way
+ as the Bourne Shell.
+* Bash Variables:: List of variables that exist in Bash.
+@end menu
-@item -a @var{aname}
-The words are assigned to
-sequential indices of the array variable @var{aname}, starting at 0.
+This chapter describes the shell variables that Bash uses.
+Bash automatically assigns default values to a number of variables.
-@item -e
-Readline (@pxref{Command Line Editing})
-is used to obtain the line.
-@end table
+@node Bourne Shell Variables
+@section Bourne Shell Variables
-@item shopt
-@btindex shopt
-@example
-shopt [-pqsu] [-o] [@var{optname} @dots{}]
-@end example
-Toggle the values of variables controlling optional shell behavior.
-With no options, or with the @samp{-p}
-option, a list of all settable options is displayed, with
-an indication of whether or not each is set. Other options have
-the following meanings:
+Bash uses certain shell variables in the same way as the Bourne shell.
+In some cases, Bash assigns a default value to the variable.
-@table @code
-@item -s
-Enable (set) each @var{optname}
+@vtable @code
-@item -u
-Disable (unset) each @var{optname}.
+@item CDPATH
+A colon-separated list of directories used as a search path for
+the @code{cd} builtin command.
-@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},
-the return status is zero if all @var{optnames} are enabled;
-non-zero otherwise.
+@item HOME
+The current user's home directory; the default for the @code{cd} builtin
+command.
+The value of this variable is also used by tilde expansion
+(@pxref{Tilde Expansion}).
-@item -o
-Restricts the values of
-@var{optname} to be those defined for the @samp{-o} option to the
-@code{set} builtin (@pxref{The Set Builtin}).
-@end table
+@item IFS
+A list of characters that separate fields; used when the shell splits
+words as part of expansion.
-If either of
-@samp{-s} or @samp{-u}
-is used with no @var{optname} arguments, the display is limited to
-those options which are set or unset, respectively.
+@item MAIL
+If this parameter is set to a filename or directory name
+and the @env{MAILPATH} variable
+is not set, Bash informs the user of the arrival of mail in
+the specified file or Maildir-format directory.
-Unless otherwise noted, the @code{shopt} options are disabled (off)
-by default.
+@item MAILPATH
+A colon-separated list of filenames which the shell periodically checks
+for new mail.
+Each list entry can specify the message that is printed when new mail
+arrives in the mail file by separating the filename from the message with
+a @samp{?}.
+When used in the text of the message, @code{$_} expands to the name of
+the current mail file.
-The return status when listing options is zero if all @var{optnames}
-are enabled, non-zero otherwise. When setting or unsetting options,
-the return status is zero unless an @var{optname} is not a legal shell
-option.
+@item OPTARG
+The value of the last option argument processed by the @code{getopts} builtin.
-The list of @code{shopt} options is:
-@table @code
-@item cdable_vars
-If this is set, an argument to the @code{cd}
-builtin command that
-is not a directory is assumed to be the name of a variable whose
-value is the directory to change to.
+@item OPTIND
+The index of the last option argument processed by the @code{getopts} builtin.
-@item cdspell
-If set, minor errors in the spelling of a directory component in a
-@code{cd} command will be corrected.
-The errors checked for are transposed characters,
-a missing character, and a character too many.
-If a correction is found, the corrected path is printed,
-and the command proceeds.
-This option is only used by interactive shells.
+@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 checkhash
-If this is set, Bash checks that a command found in the hash
-table exists before trying to execute it. If a hashed command no
-longer exists, a normal path search is performed.
-@item checkwinsize
-If set, Bash checks the window size after each command
-and, if necessary, updates the values of
-@code{LINES} and @code{COLUMNS}.
+@item PS1
+The primary prompt string. The default value is @samp{\s-\v\$ }.
+@xref{Controlling the Prompt}, for the complete list of escape
+sequences that are expanded before @env{PS1} is displayed.
-@item cmdhist
-If set, Bash
-attempts to save all lines of a multiple-line
-command in the same history entry. This allows
-easy re-editing of multi-line commands.
+@item PS2
+The secondary prompt string. The default value is @samp{> }.
-@item dotglob
-If set, Bash includes filenames beginning with a `.' in
-the results of filename expansion.
+@end vtable
-@item execfail
-If this is set, a non-interactive shell will not exit if
-it cannot execute the file specified as an argument to the @code{exec}
-builtin command. An interactive shell does not exit if @code{exec}
-fails.
+@node Bash Variables
+@section Bash Variables
-@item histappend
-If set, the history list is appended to the file named by the value
-of the @code{HISTFILE}
-variable when the shell exits, rather than overwriting the file.
+These variables are set or used by Bash, but other shells
+do not normally treat them specially.
-@item histreedit
-If set, and Readline
-is being used, a user is given the opportunity to re-edit a
-failed history substitution.
+A few variables used by Bash are described in different chapters:
+variables for controlling the job control facilities
+(@pxref{Job Control Variables}).
-@item histverify
-If set, and Readline
-is being used, the results of history substitution are not immediately
-passed to the shell parser. Instead, the resulting line is loaded into
-the Readline editing buffer, allowing further modification.
+@vtable @code
-@item hostcomplete
-If set, and Readline is being used, Bash will attempt to perform
-hostname completion when a word beginning with @samp{@@} is being
-completed (@pxref{Commands For Completion}). This option is enabled
-by default.
+@item BASH
+The full pathname used to execute the current instance of Bash.
-@item interactive_comments
-Allow a word beginning with @samp{#}
-to cause that word and all remaining characters on that
-line to be ignored in an interactive shell.
-This option is enabled by default.
+@item BASHOPTS
+A colon-separated list of enabled shell options. Each word in
+the list is a valid argument for the @option{-s} option to the
+@code{shopt} builtin command (@pxref{The Shopt Builtin}).
+The options appearing in @env{BASHOPTS} are those reported
+as @samp{on} by @samp{shopt}.
+If this variable is in the environment when Bash
+starts up, each shell option in the list will be enabled before
+reading any startup files. This variable is readonly.
-@item lithist
-If enabled, and the @code{cmdhist}
-option is enabled, multi-line commands are saved to the history with
-embedded newlines rather than using semicolon separators where possible.
+@item BASHPID
+Expands to the process ID of the current Bash process.
+This differs from @code{$$} under certain circumstances, such as subshells
+that do not require Bash to be re-initialized.
-@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
-@code{"The mail in @var{mailfile} has been read"} is displayed.
+@item BASH_ALIASES
+An associative array variable whose members correspond to the internal
+list of aliases as maintained by the @code{alias} builtin.
+(@pxref{Bourne Shell Builtins}).
+Elements added to this array appear in the alias list; unsetting array
+elements cause aliases to be removed from the alias list.
+
+@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{The Shopt Builtin}
+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{The Shopt Builtin}
+for a description of the @code{extdebug} option to the @code{shopt}
+builtin).
+
+@item BASH_CMDS
+An associative array variable whose members correspond to the internal
+hash table of commands as maintained by the @code{hash} builtin
+(@pxref{Bourne Shell Builtins}).
+Elements added to this array appear in the hash table; unsetting array
+elements cause commands to be removed from the hash table.
+
+@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_COMPAT
+The value is used to set the shell's compatibility level.
+@xref{The Shopt Builtin}, for a description of the various compatibility
+levels and their effects.
+The value may be a decimal number (e.g., 4.2) or an integer (e.g., 42)
+corresponding to the desired compatibility level.
+If @code{BASH_COMPAT} is unset or set to the empty string, the compatibility
+level is set to the default for the current version.
+If @code{BASH_COMPAT} is set to a value that is not one of the valid
+compatibility levels, the shell prints an error message and sets the
+compatibility level to the default for the current version.
+The valid compatibility levels correspond to the compatibility options
+accepted by the @code{shopt} builtin described above (for example,
+@var{compat42} means that 4.2 and 42 are valid values).
+The current version is also a valid value.
-@item nullglob
-If set, Bash allows filename patterns which match no
-files to expand to a null string, rather than themselves.
+@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 promptvars
-If set, prompt strings undergo variable and parameter expansion after
-being expanded (@pxref{Printing a Prompt}).
-This option is enabled by default.
+@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
+where each corresponding member of @var{FUNCNAME} was invoked.
+@code{$@{BASH_LINENO[$i]@}} is the line number in the source file
+(@code{$@{BASH_SOURCE[$i+1]@}}) where
+@code{$@{FUNCNAME[$i]@}} was called (or @code{$@{BASH_LINENO[$i-1]@}} if
+referenced within another shell function).
+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 where the
+corresponding shell function names in the @code{FUNCNAME} array
+variable are defined.
+The shell function @code{$@{FUNCNAME[$i]@}} is defined in the file
+@code{$@{BASH_SOURCE[$i]@}} and called from @code{$@{BASH_SOURCE[$i+1]@}}
+
+@item BASH_SUBSHELL
+Incremented by one within each subshell or subshell environment when
+the shell begins executing in that environment.
+The initial value is 0.
-@item shift_verbose
-If this is set, the @code{shift}
-builtin prints an error message when the shift count exceeds the
-number of positional parameters.
+@item BASH_VERSINFO
+A readonly array variable (@pxref{Arrays})
+whose members hold version information for this instance of Bash.
+The values assigned to the array members are as follows:
-@item sourcepath
-If set, the @code{source} builtin uses the value of @code{PATH}
-to find the directory containing the file supplied as an argument.
-This is enabled by default.
-@end table
+@table @code
-@item type
-@btindex type
-@example
-type [-all] [-type | -path] [@var{name} @dots{}]
-@end example
-For each @var{name}, indicate how it would be interpreted if used as a
-command name.
+@item BASH_VERSINFO[0]
+The major version number (the @var{release}).
-If the @samp{-type} flag is used, @code{type} returns 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,
-disk file, or shell reserved word, respectively.
-If the @var{name} is not found, then nothing is printed, and
-@code{type} returns a failure status.
+@item BASH_VERSINFO[1]
+The minor version number (the @var{version}).
-If the @samp{-path} flag is used, @code{type} either returns the name
-of the disk file that would be executed, or nothing if @samp{-type}
-would not return @samp{file}.
+@item BASH_VERSINFO[2]
+The patch level.
-If the @samp{-all} flag is used, returns all of the places that contain
-an executable named @var{file}. This includes aliases and functions,
-if and only if the @samp{-path} flag is not also used.
+@item BASH_VERSINFO[3]
+The build version.
-@code{type} accepts @samp{-a}, @samp{-t}, and @samp{-p} as equivalent to
-@samp{-all}, @samp{-type}, and @samp{-path}, respectively.
+@item BASH_VERSINFO[4]
+The release status (e.g., @var{beta1}).
-@item ulimit
-@btindex ulimit
-@example
-ulimit [-acdflmnpstuvSH] [@var{limit}]
-@end example
-@code{ulimit} provides control over the resources available to processes
-started by the shell, on systems that allow such control. If an
-option is given, it is interpreted as follows:
-@table @code
-@item -S
-change and report the soft limit associated with a resource.
+@item BASH_VERSINFO[5]
+The value of @env{MACHTYPE}.
+@end table
-@item -H
-change and report the hard limit associated with a resource.
+@item BASH_VERSION
+The version number of the current instance of Bash.
-@item -a
-all current limits are reported.
+@item BASH_XTRACEFD
+If set to an integer corresponding to a valid file descriptor, Bash
+will write the trace output generated when @samp{set -x}
+is enabled to that file descriptor.
+This allows tracing output to be separated from diagnostic and error
+messages.
+The file descriptor is closed when @code{BASH_XTRACEFD} is unset or assigned
+a new value.
+Unsetting @code{BASH_XTRACEFD} or assigning it the empty string causes the
+trace output to be sent to the standard error.
+Note that setting @code{BASH_XTRACEFD} to 2 (the standard error file
+descriptor) and then unsetting it will result in the standard error
+being closed.
+
+@item CHILD_MAX
+Set the number of exited child status values for the shell to remember.
+Bash will not allow this value to be decreased below a @sc{posix}-mandated
+minimum, and there is a maximum value (currently 8192) that this may
+not exceed.
+The minimum value is system-dependent.
+
+@item COLUMNS
+Used by the @code{select} command to determine the terminal width
+when printing selection lists.
+Automatically set if the @code{checkwinsize} option is enabled
+(@pxref{The Shopt Builtin}), or in an interactive shell upon receipt of a
+@code{SIGWINCH}.
+
+@item COMP_CWORD
+An index into @env{$@{COMP_WORDS@}} of the word containing the current
+cursor position.
+This variable is available only in shell functions invoked by the
+programmable completion facilities (@pxref{Programmable Completion}).
+
+@item COMP_LINE
+The current command line.
+This variable is available only in shell functions and external
+commands invoked by the
+programmable completion facilities (@pxref{Programmable Completion}).
+
+@item COMP_POINT
+The index of the current cursor position relative to the beginning of
+the current command.
+If the current cursor position is at the end of the current command,
+the value of this variable is equal to @code{$@{#COMP_LINE@}}.
+This variable is available only in shell functions and external
+commands invoked by the
+programmable completion facilities (@pxref{Programmable Completion}).
+
+@item COMP_TYPE
+Set to an integer value corresponding to the type of completion attempted
+that caused a completion function to be called:
+@var{TAB}, for normal completion,
+@samp{?}, for listing completions after successive tabs,
+@samp{!}, for listing alternatives on partial word completion,
+@samp{@@}, to list completions if the word is not unmodified,
+or
+@samp{%}, for menu completion.
+This variable is available only in shell functions and external
+commands invoked by the
+programmable completion facilities (@pxref{Programmable Completion}).
+
+@item COMP_KEY
+The key (or final key of a key sequence) used to invoke the current
+completion function.
+
+@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 -c
-the maximum size of core files created.
+@item COMP_WORDS
+An array variable consisting of the individual
+words in the current command line.
+The line is split into words as Readline would split it, using
+@code{COMP_WORDBREAKS} as described above.
+This variable is available only in shell functions invoked by the
+programmable completion facilities (@pxref{Programmable Completion}).
-@item -d
-the maximum size of a process's data segment.
+@item COMPREPLY
+An array variable from which Bash reads the possible completions
+generated by a shell function invoked by the programmable completion
+facility (@pxref{Programmable Completion}).
+Each array element contains one possible completion.
-@item -f
-the maximum size of files created by the shell.
+@item COPROC
+An array variable created to hold the file descriptors
+for output from and input to an unnamed coprocess (@pxref{Coprocesses}).
-@item -l
-The maximum size that may be locked into memory.
+@item DIRSTACK
+An array variable containing the current contents of the directory stack.
+Directories appear in the stack in the order they are displayed by the
+@code{dirs} builtin.
+Assigning to members of this array variable may be used to modify
+directories already in the stack, but the @code{pushd} and @code{popd}
+builtins must be used to add and remove directories.
+Assignment to this variable will not change the current directory.
+If @env{DIRSTACK} is unset, it loses its special properties, even if
+it is subsequently reset.
-@item -m
-the maximum resident set size.
+@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 -n
-the maximum number of open file descriptors.
+@item ENV
+Similar to @code{BASH_ENV}; used when the shell is invoked in
+@sc{posix} Mode (@pxref{Bash POSIX Mode}).
-@item -p
-the pipe buffer size.
+@item EUID
+The numeric effective user id of the current user. This variable
+is readonly.
-@item -s
-the maximum stack size.
+@item FCEDIT
+The editor used as a default by the @option{-e} option to the @code{fc}
+builtin command.
-@item -t
-the maximum amount of cpu time in seconds.
+@item FIGNORE
+A colon-separated list of suffixes to ignore when performing
+filename completion.
+A filename whose suffix matches one of the entries in
+@env{FIGNORE}
+is excluded from the list of matched filenames. A sample
+value is @samp{.o:~}
-@item -u
-the maximum number of processes available to a single user.
+@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 (the one with the highest index)
+is @code{"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 -v
-the maximum amount of virtual memory available to the process.
+This variable can be used with @code{BASH_LINENO} and @code{BASH_SOURCE}.
+Each element of @code{FUNCNAME} has corresponding elements in
+@code{BASH_LINENO} and @code{BASH_SOURCE} to describe the call stack.
+For instance, @code{$@{FUNCNAME[$i]@}} was called from the file
+@code{$@{BASH_SOURCE[$i+1]@}} at line number @code{$@{BASH_LINENO[$i]@}}.
+The @code{caller} builtin displays the current call stack using this
+information.
-@end table
+@item FUNCNEST
+If set to a numeric value greater than 0, defines a maximum function
+nesting level. Function invocations that exceed this nesting level
+will cause the current command to abort.
-If @var{limit} is given, it is the new value of the specified resource.
-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,
-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
-are unscaled values.
+@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 @env{GLOBIGNORE}, it is removed from the list
+of matches.
-@end table
+@item GROUPS
+An array variable containing the list of groups of which the current
+user is a member.
+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.
-@node The Set Builtin
-@section The Set Builtin
+@item histchars
+Up to three characters which control history expansion, quick
+substitution, and tokenization (@pxref{History Interaction}).
+The first character is the
+@var{history expansion} character, that is, the character which signifies the
+start of a history expansion, normally @samp{!}. The second character is the
+character which signifies `quick substitution' when seen as the first
+character on a line, normally @samp{^}. The optional third character is the
+character which indicates that the remainder of the line is a comment when
+found as the first character of a word, usually @samp{#}. The history
+comment character causes history substitution to be skipped for the
+remaining words on the line. It does not necessarily cause the shell
+parser to treat the rest of the line as a comment.
-This builtin is so overloaded that it deserves its own section.
+@item HISTCMD
+The history number, or index in the history list, of the current
+command. If @env{HISTCMD} is unset, it loses its special properties,
+even if it is subsequently reset.
-@table @code
-@item set
-@btindex set
-@example
-set [-abefhkmnptuvxdBCHP] [-o @var{option}] [@var{argument} @dots{}]
-@end example
+@item HISTCONTROL
+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
+@env{HISTCONTROL}.
-@table @code
-@item -a
-Mark variables which are modified or created for export.
+@item HISTFILE
+The name of the file to which the command history is saved. The
+default value is @file{~/.bash_history}.
-@item -b
-Cause the status of terminated background jobs to be reported
-immediately, rather than before printing the next primary prompt.
+@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
+by removing the oldest entries.
+The history file is also truncated to this size after
+writing it when a shell exits.
+If the value is 0, the history file is truncated to zero size.
+Non-numeric values and numeric values less than zero inhibit truncation.
+The shell sets the default value to the value of @env{HISTSIZE}
+after reading any startup files.
-@item -e
-Exit immediately if a simple command exits with a non-zero status.
+@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 @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
+@env{HISTIGNORE}.
-@item -f
-Disable file name generation (globbing).
+@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 -h
-Locate and remember (hash) commands as they are looked up for execution.
+@item HISTSIZE
+The maximum number of commands to remember on the history list.
+If the value is 0, commands are not saved in the history list.
+Numeric values less than zero result in every command being saved
+on the history list (there is no limit).
+The shell sets the default value to 500 after reading any startup files.
+
+@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.
+This uses the history comment character to distinguish timestamps from
+other history lines.
-@item -k
-All arguments in the form of assignment statements are placed
-in the environment for a command, not just those that precede
-the command name.
+@item HOSTFILE
+Contains the name of a file in the same format as @file{/etc/hosts} that
+should be read when the shell needs to complete a hostname.
+The list of possible hostname completions may be changed while the shell
+is running;
+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 @env{HOSTFILE} is set, but has no value, or does not name a readable file,
+Bash attempts to read
+@file{/etc/hosts} to obtain the list of possible hostname completions.
+When @env{HOSTFILE} is unset, the hostname list is cleared.
-@item -m
-Job control is enabled (@pxref{Job Control}).
+@item HOSTNAME
+The name of the current host.
-@item -n
-Read commands but do not execute them.
+@item HOSTTYPE
+A string describing the machine Bash is running on.
-@item -o @var{option-name}
+@item IGNOREEOF
+Controls the action of the shell on receipt of an @code{EOF} character
+as the sole input. If set, the value denotes the number
+of consecutive @code{EOF} characters that can be read as the
+first character on an input line
+before the shell will exit. If the variable exists but does not
+have a numeric value (or has no value) then the default is 10.
+If the variable does not exist, then @code{EOF} signifies the end of
+input to the shell. This is only in effect for interactive shells.
-Set the flag corresponding to @var{option-name}:
+@item INPUTRC
+The name of the Readline initialization file, overriding the default
+of @file{~/.inputrc}.
-@table @code
-@item allexport
-same as @code{-a}.
+@item LANG
+Used to determine the locale category for any category not specifically
+selected with a variable starting with @code{LC_}.
-@item braceexpand
-same as @code{-B}.
+@item LC_ALL
+This variable overrides the value of @env{LANG} and any other
+@code{LC_} variable specifying a locale category.
-@item emacs
-use an @code{emacs}-style line editing interface (@pxref{Command Line Editing}).
+@item LC_COLLATE
+This variable determines the collation order used when sorting the
+results of filename expansion, and
+determines the behavior of range expressions, equivalence classes,
+and collating sequences within filename expansion and pattern matching
+(@pxref{Filename Expansion}).
-@item errexit
-same as @code{-e}.
+@item LC_CTYPE
+This variable determines the interpretation of characters and the
+behavior of character classes within filename expansion and pattern
+matching (@pxref{Filename Expansion}).
-@item hashall
-same as @code{-h}.
+@item LC_MESSAGES
+This variable determines the locale used to translate double-quoted
+strings preceded by a @samp{$} (@pxref{Locale Translation}).
-@item histexpand
-same as @code{-H}.
+@item LC_NUMERIC
+This variable determines the locale category used for number formatting.
-@item history
-Enable command history, as described in @ref{Bash History Facilities}.
-This option is on by default in interactive shells.
+@item LINENO
+The line number in the script or shell function currently executing.
-@item ignoreeof
-the shell will not exit upon reading EOF.
+@item LINES
+Used by the @code{select} command to determine the column length
+for printing selection lists.
+Automatically set if the @code{checkwinsize} option is enabled
+(@pxref{The Shopt Builtin}), or in an interactive shell upon receipt of a
+@code{SIGWINCH}.
-@item keyword
-same as @code{-k}.
+@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 monitor
-same as @code{-m}.
+@item MAILCHECK
+How often (in seconds) that the shell should check for mail in the
+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 noclobber
-same as @code{-C}.
+@item MAPFILE
+An array variable created to hold the text read by the
+@code{mapfile} builtin when no variable name is supplied.
-@item noexec
-same as @code{-n}.
+@item OLDPWD
+The previous working directory as set by the @code{cd} builtin.
-@item noglob
-same as @code{-f}.
+@item OPTERR
+If set to the value 1, Bash displays error messages
+generated by the @code{getopts} builtin command.
-@item notify
-same as @code{-b}.
+@item OSTYPE
+A string describing the operating system Bash is running on.
-@item nounset
-same as @code{-u}.
+@item PIPESTATUS
+An array variable (@pxref{Arrays})
+containing a list of exit status values from the processes
+in the most-recently-executed foreground pipeline (which may
+contain only a single command).
-@item onecmd
-same as @code{-t}.
+@item POSIXLY_CORRECT
+If this variable is in the environment when 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, Bash enables @sc{posix} mode,
+as if the command
+@example
+@code{set -o posix}
+@end example
+@noindent
+had been executed.
-@item physical
-same as @code{-P}.
+@item PPID
+The process @sc{id} of the shell's parent process. This variable
+is readonly.
-@item posix
-change the behavior of Bash where the default operation differs
-from the @sc{POSIX} 1003.2 standard to match the standard. This
-is intended to make Bash behave as a strict superset of that
-standard.
+@item PROMPT_COMMAND
+If set, the value is interpreted as a command to execute
+before the printing of each primary prompt (@env{$PS1}).
-@item privileged
-same as @code{-p}.
+@item PROMPT_DIRTRIM
+If set to a number greater than zero, the value is used as the number of
+trailing directory components to retain when expanding the @code{\w} and
+@code{\W} prompt string escapes (@pxref{Controlling the Prompt}).
+Characters removed are replaced with an ellipsis.
-@item verbose
-same as @code{-v}.
+@item PS3
+The value of this variable is used as the prompt for the
+@code{select} command. If this variable is not set, the
+@code{select} command prompts with @samp{#? }
-@item vi
-use a @code{vi}-style line editing interface.
+@item PS4
+The value is the prompt printed before the command line is echoed
+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{+ }.
-@item xtrace
-same as @code{-x}.
-@end table
+@item PWD
+The current working directory as set by the @code{cd} builtin.
-@item -p
-Turn on privileged mode.
-In this mode, the @code{$BASH_ENV}
-file is not processed, and shell functions
-are not inherited from the environment. This is enabled automatically
-on startup if the effective user (group) id is not equal to the real
-user (group) id. Turning this option off causes the effective user
-and group ids to be set to the real user and group ids.
+@item RANDOM
+Each time this parameter is referenced, a random integer
+between 0 and 32767 is generated. Assigning a value to this
+variable seeds the random number generator.
-@item -t
-Exit after reading and executing one command.
+@item READLINE_LINE
+The contents of the Readline line buffer, for use
+with @samp{bind -x} (@pxref{Bash Builtins}).
-@item -u
-Treat unset variables as an error when substituting.
+@item READLINE_POINT
+The position of the insertion point in the Readline line buffer, for use
+with @samp{bind -x} (@pxref{Bash Builtins}).
-@item -v
-Print shell input lines as they are read.
+@item REPLY
+The default variable for the @code{read} builtin.
-@item -x
-Print commands and their arguments as they are executed.
-
-@item -B
-The shell will perform brace expansion (@pxref{Brace Expansion}).
-This option is on by default.
-
-@item -C
-Disallow output redirection to existing files.
-
-@item -H
-Enable @samp{!} style history substitution (@pxref{History Interaction}).
-This flag is on by default for interactive shells.
-
-@item -P
-If set, do not follow symbolic links when performing commands such as
-@code{cd} which change the current directory. The physical directory
-is used instead. By default, Bash follows
-the logical chain of directories when performing commands
-which change the current directory.
-
-For example, if @file{/usr/sys} is a link to @file{/usr/local/sys} then:
-@example
-$ cd /usr/sys; echo $PWD
-/usr/sys
-$ cd ..; pwd
-/usr
-@end example
-
-@noindent
-If @code{set -P} is on, then:
-@example
-$ cd /usr/sys; echo $PWD
-/usr/local/sys
-$ cd ..; pwd
-/usr/local
-@end example
-
-@item --
-If no arguments follow this flag, then the positional parameters are
-unset. Otherwise, the positional parameters are set to the
-@var{arguments}, even if some of them begin with a @samp{-}.
-
-@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.
-If there are no arguments, the positional parameters remain unchanged.
-@end table
-
-Using @samp{+} rather than @samp{-} causes these flags to be
-turned off. The flags can also be used upon invocation of the
-shell. The current set of flags may be found in @code{$-}.
-
-The remaining N @var{arguments} are positional parameters and are
-assigned, in order, to @code{$1}, @code{$2}, @dots{} @code{$N}. If
-no arguments are given, all shell variables are printed.
-@end table
-
-@node Bash Conditional Expressions
-@section Bash Conditional Expressions
-@cindex expressions, conditional
-
-Conditional expressions are used by the @code{test} and @code{[} builtins.
-
-Expressions may be unary or binary. Unary
-expressions are often used to examine the status of a file. There
-are string operators and numeric comparison operators as well. Each
-operator and operand must be a separate argument. If @var{file}
-is of the form @file{/dev/fd/@var{N}}, then file descriptor @var{N} is
-checked. Expressions are composed of the following primaries:
-
-@table @code
-@item -b @var{file}
-True if @var{file} exists and is a block special file.
-
-@item -c @var{file}
-True if @var{file} exists and is a character special file.
-
-@item -d @var{file}
-True if @var{file} exists and is a directory.
-
-@item -e @var{file}
-True if @var{file} exists.
-
-@item -f @var{file}
-True if @var{file} exists and is a regular file.
-
-@item -g @var{file}
-True if @var{file} exists and is set-group-id.
-
-@item -k @var{file}
-True if @var{file} has its "sticky" bit set.
-
-@item -L @var{file}
-True if @var{file} exists and is a symbolic link.
-
-@item -p @var{file}
-True if @var{file} exists and is a named pipe.
-
-@item -r @var{file}
-True if @var{file} exists and is readable.
-
-@item -s @var{file}
-True if @var{file} exists and has a size greater than zero.
-
-@item -S @var{file}
-True if @var{file} exists and is a socket.
-
-@item -t @var{fd}
-True if @var{fd} is opened on a terminal.
-
-@item -u @var{file}
-True if @var{file} exists and its set-user-id bit is set.
-
-@item -w @var{file}
-True if @var{file} exists and is writable.
-
-@item -x @var{file}
-True if @var{file} exists and is executable.
-
-@item -O @var{file}
-True if @var{file} exists and is owned by the effective user id.
-
-@item -G @var{file}
-True if @var{file} exists and is owned by the effective group id.
-
-@item @var{file1} -nt @var{file2}
-True if @var{file1} is newer (according to
-modification date) than @var{file2}.
-
-@item @var{file1} -ot @var{file2}
-True if @var{file1} is older than @var{file2}.
-
-@item @var{file1} -ef @var{file2}
-True if @var{file1} and @var{file2} have 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}
-option to the @code{set} builtin (@pxref{The Set Builtin}).
-
-@item -z @var{string}
-True if the length of @var{string} is zero.
-
-@item -n @var{string}
-@itemx @var{string}
-True if the length of @var{string} is non-zero.
-
-@item @var{string1} = @var{string2}
-True if the strings are equal. @samp{==} may be used in place of
-@samp{=}.
-
-@item @var{string1} != @var{string2}
-True if the strings are not equal.
-
-@item @var{string1} < @var{string2}
-True if @var{string1} sorts before @var{string2} lexicographically.
-
-@item @var{string1} > @var{string2}
-True if @var{string1} sorts after @var{string2} lexicographically.
-
-@item ! @var{expr}
-True if @var{expr} is false.
-
-@item @var{expr1} -a @var{expr2}
-True if both @var{expr1} and @var{expr2} are true.
-
-@item @var{expr1} -o @var{expr2}
-True if either @var{expr1} and @var{expr2} is true.
-
-@item @var{arg1} OP @var{arg2}
-@code{OP} is one of
-@samp{-eq}, @samp{-ne}, @samp{-lt}, @samp{-le}, @samp{-gt}, or @samp{-ge}.
-These arithmetic binary operators return true if @var{arg1}
-is equal to, not equal to, less than, less than or equal to,
-greater than, or greater than or equal to @var{arg2},
-respectively. @var{Arg1} and @var{arg2}
-may be positive or negative integers.
-
-@end table
-
-The Bash @code{test} and @code{[} builtins evaluate conditional
-expressions using a set of rules based on the number of arguments.
-These are the rules:
-
-@table @asis
-@item 0 arguments
-The expression is false.
-@item 1 argument
-The expression is true if and only if the argument is not null.
-@item 2 arguments
-If the first argument is @samp{!}, the expression is true if and
-only if the second argument is null. If the first argument is
-one of the listed unary operators, the expression is true if the
-unary test is true. If the first argument is not a legal unary
-operator, the expression is false.
-@item 3 arguments
-If the first argument is @samp{!}, the value is the negation of
-the two-argument test using the second and third arguments.
-If the second argument is one of the binary operators, the result
-of the expression is the result of the binary test using the first
-and third arguments as operands.
-If the first argument is exactly @samp{(} and the third argument is
-exactly @samp{)}, the result is the one-argument test of the second
-argument.
-Otherwise, the expression is false.
-The @samp{-a} and @samp{-o} operators are considered binary operators
-in this case.
-@item 4 arguments
-If the first argument is @samp{!}, the result is the negation of
-the three-argument expression composed of the remaining arguments.
-Otherwise, the expression is parsed and evaluated according to
-precedence. @samp{-a} has a higher precedence than @samp{-o}.
-@item 5 or more arguments
-The expression is parsed and evaluated according to precedence,
-with @samp{-a} having a higher precedence than @samp{-o}.
-@end table
-
-@node Bash Variables
-@section Bash Variables
+@item SECONDS
+This variable expands to the number of seconds since the
+shell was started. Assignment to this variable resets
+the count to the value assigned, and the expanded value
+becomes the value assigned plus the number of seconds
+since the assignment.
-These variables are set or used by Bash, but other shells
-do not normally treat them specially.
+@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.
-@vtable @code
+@item SHELLOPTS
+A colon-separated list of enabled shell options. Each word in
+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 @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
+reading any startup files. This variable is readonly.
-@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 SHLVL
+Incremented by one each time a new instance of Bash is started. This is
+intended to be a count of how deeply your Bash shells are nested.
@item TIMEFORMAT
The value of this parameter is used as a format string specifying
the form @var{MM}m@var{SS}.@var{FF}s.
The value of @var{p} determines whether or not the fraction is included.
-If this variable is not set, bash acts as if it had the value
+If this variable is not set, Bash acts as if it had the value
@example
-@code{$'\nreal\t%3lR\nuser\t%3lU\nsys\t%3lS'}.
+@code{$'\nreal\t%3lR\nuser\t%3lU\nsys\t%3lS'}
@end example
If the value is null, no timing information is displayed.
A trailing newline is added when the format string is displayed.
-@item HISTCONTROL
-Set to a value of @samp{ignorespace}, it means don't enter lines which
-begin with a space or tab into the history list. Set to a value
-of @samp{ignoredups}, it means don't enter lines which match the last
-entered line. A value of @samp{ignoreboth} combines the two options.
-Unset, or set to any other value than those above, means to save
-all lines on the history list.
+@item TMOUT
+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 interactive shell, the value is interpreted as
+the number of seconds to wait for a line of input after issuing
+the primary prompt.
+Bash
+terminates after waiting for that number of seconds if a complete
+line of 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 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 fully specify the
-line (no implicit @samp{*} is appended). Each pattern is tested
-against the line after the checks specified by @code{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.
+@item UID
+The numeric real user id of the current user. This variable is readonly.
-@code{HISTIGNORE} subsumes the function of @code{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}.
+@end vtable
-@item HISTFILE
-The name of the file to which the command history is saved. The
-default is @file{~/.bash_history}.
+@node Bash Features
+@chapter Bash Features
-@item HISTSIZE
-If set, this is the maximum number of commands to remember in the
-history.
+This chapter describes features unique to Bash.
-@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 default
-value is 500. The history file is also truncated to this size after
-writing it when an interactive shell exits.
+@menu
+* Invoking Bash:: Command line options that you can give
+ to Bash.
+* Bash Startup Files:: When and how Bash executes scripts.
+* Interactive Shells:: What an interactive shell is.
+* Bash Conditional Expressions:: Primitives used in composing expressions for
+ the @code{test} builtin.
+* Shell Arithmetic:: Arithmetic on shell variables.
+* Aliases:: Substituting one command for another.
+* Arrays:: Array Variables.
+* The Directory Stack:: History of visited directories.
+* Controlling the Prompt:: Customizing the various prompt strings.
+* The Restricted Shell:: A more controlled mode of shell execution.
+* Bash POSIX Mode:: Making Bash behave more closely to what
+ the POSIX standard specifies.
+@end menu
-@item histchars
-Up to three characters which control history expansion, quick
-substitution, and tokenization (@pxref{History Interaction}).
-The first character is the
-@dfn{history-expansion-char}, that is, the character which signifies the
-start of a history expansion, normally @samp{!}. The second character is the
-character which signifies `quick substitution' when seen as the first
-character on a line, normally @samp{^}. The optional third character is the
-character which signifies the remainder of the line is a comment, when
-found as the first character of a word, usually @samp{#}. The history
-comment character causes history substitution to be skipped for the
-remaining words on the line. It does not necessarily cause the shell
-parser to treat the rest of the line as a comment.
+@node Invoking Bash
+@section Invoking Bash
-@item HISTCMD
-The history number, or index in the history list, of the current
-command. If @code{HISTCMD} is unset, it loses its special properties,
-even if it is subsequently reset.
+@example
+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
-@item HOSTFILE
-Contains the name of a file in the same format as @file{/etc/hosts} that
-should be read when the shell needs to complete a hostname. You can
-change the file interactively; the next time you attempt to complete a
-hostname, Bash will add the contents of the new file to the already
-existing database.
+All of the single-character options used with the @code{set} builtin
+(@pxref{The Set Builtin}) can be used as options when the shell is invoked.
+In addition, there are several multi-character
+options that you can use. These options must appear on the command
+line before the single-character options to be recognized.
-@item MAILCHECK
-How often (in seconds) that the shell should check for mail
-in the files specified in @code{MAILPATH}.
+@table @code
+@item --debugger
+Arrange for the debugger profile to be executed before the shell
+starts. Turns on extended debugging mode (see @ref{The Shopt Builtin}
+for a description of the @code{extdebug} option to the @code{shopt}
+builtin).
-@item PROMPT_COMMAND
-If present, this contains a string which is a command to execute
-before the printing of each primary prompt (@code{$PS1}).
+@item --dump-po-strings
+A list of all double-quoted strings preceded by @samp{$}
+is printed on the standard output
+in the @sc{gnu} @code{gettext} PO (portable object) file format.
+Equivalent to @option{-D} except for the output format.
-@item UID
-The numeric real user id of the current user.
+@item --dump-strings
+Equivalent to @option{-D}.
-@item EUID
-The numeric effective user id of the current user.
+@item --help
+Display a usage message on standard output and exit successfully.
-@item GROUPS
-An array variable containing the list of groups of which the current
-user is a member.
+@item --init-file @var{filename}
+@itemx --rcfile @var{filename}
+Execute commands from @var{filename} (instead of @file{~/.bashrc})
+in an interactive shell.
-@item PPID
-The process id of the shell's parent process.
+@item --login
+Equivalent to @option{-l}.
-@item HOSTNAME
-The name of the current host.
+@item --noediting
+Do not use the @sc{gnu} Readline library (@pxref{Command Line Editing})
+to read command lines when the shell is interactive.
-@item HOSTTYPE
-A string describing the machine Bash is running on.
+@item --noprofile
+Don't load the system-wide startup file @file{/etc/profile}
+or any of the personal initialization files
+@file{~/.bash_profile}, @file{~/.bash_login}, or @file{~/.profile}
+when Bash is invoked as a login shell.
-@item OSTYPE
-A string describing the operating system Bash is running on.
+@item --norc
+Don't read the @file{~/.bashrc} initialization file in an
+interactive shell. This is on by default if the shell is
+invoked as @code{sh}.
-@item MACHTYPE
-A string that fully describes the system type on which Bash
-is executing, in the standard GNU @var{cpu-company-system} format.
+@item --posix
+Change the behavior of Bash where the default operation differs
+from the @sc{posix} standard to match the standard. This
+is intended to make Bash behave as a strict superset of that
+standard. @xref{Bash POSIX Mode}, for a description of the Bash
+@sc{posix} mode.
-@item SHELLOPTS
-A colon-separated list of enabled shell options. Each word in
-the list is a valid argument for the @samp{-o} option to the
-@code{set} builtin command (@pxref{The Set Builtin}).
-The options appearing in @code{SHELLOPTS} are those reported
-as @samp{on} by @samp{set -o}.
-If this variable is in the environment when Bash
-starts up, each shell option in the list will be enabled before
-reading any startup files. This variable is readonly.
+@item --restricted
+Make the shell a restricted shell (@pxref{The Restricted Shell}).
-@item FIGNORE
-A colon-separated list of suffixes to ignore when performing
-filename completion.
-A file name whose suffix matches one of the entries in
-@code{FIGNORE}
-is excluded from the list of matched file names. A sample
-value is @samp{.o:~}
+@item --verbose
+Equivalent to @option{-v}. Print shell input lines as they're read.
-@item GLOBIGNORE
-A colon-separated list of patterns defining the set of filenames to
-be ignored by filename expansion.
-If a filename matched by a filename expansion pattern also matches one
-of the patterns in @code{GLOBIGNORE}, it is removed from the list
-of matches.
+@item --version
+Show version information for this instance of
+Bash on the standard output and exit successfully.
+@end table
-@item DIRSTACK
-An array variable (@pxref{Arrays})
-containing the current contents of the directory stack.
-Directories appear in the stack in the order they are displayed by the
-@code{dirs} builtin.
-Assigning to members of this array variable may be used to modify
-directories already in the stack, but the @code{pushd} and @code{popd}
-builtins must be used to add and remove directories.
-Assignment to this variable will not change the current directory.
-If @code{DIRSTACK} is unset, it loses its special properties, even if
-it is subsequently reset.
+There are several single-character options that may be supplied at
+invocation which are not available with the @code{set} builtin.
-@item PIPESTATUS
-An array variable (@pxref{Arrays})
-containing a list of exit status values from the processes
-in the most-recently-executed foreground pipeline (which may
-contain only a single command).
+@table @code
+@item -c
+Read and execute commands from the first non-option @var{argument}
+after processing the options, then exit.
+Any remaining arguments are assigned to the
+positional parameters, starting with @code{$0}.
-@item INPUTRC
-The name of the Readline startup file, overriding the default
-of @file{~/.inputrc}.
+@item -i
+Force the shell to run interactively. Interactive shells are
+described in @ref{Interactive Shells}.
-@item BASH
-The full filename used to execute the current instance of Bash.
+@item -l
+Make this shell act as if it had been directly invoked by login.
+When the shell is interactive, this is equivalent to starting a
+login shell with @samp{exec -l bash}.
+When the shell is not interactive, the login shell startup files will
+be executed.
+@samp{exec bash -l} or @samp{exec bash --login}
+will replace the current shell with a Bash login shell.
+@xref{Bash Startup Files}, for a description of the special behavior
+of a login shell.
-@item BASH_VERSION
-The version number of the current instance of Bash.
+@item -r
+Make the shell a restricted shell (@pxref{The Restricted Shell}).
-@item BASH_VERSINFO
-An array variable whose members hold version information for this
-instance of Bash.
-The values assigned to the array members are as follows:
+@item -s
+If this option is present, or if no arguments remain after option
+processing, then commands are read from the standard input.
+This option allows the positional parameters to be set
+when invoking an interactive shell.
-@table @code
+@item -D
+A list of all double-quoted strings preceded by @samp{$}
+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 @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{The Shopt Builtin}).
+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 BASH_VERSINFO[0]
-The major version number (the @var{release}).
+@item --
+A @code{--} signals the end of options and disables further option
+processing.
+Any arguments after the @code{--} are treated as filenames and arguments.
+@end table
-@item BASH_VERSINFO[1]
-The minor version number (the @var{version}).
+@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.
-@item BASH_VERSINFO[2]
-The patch level.
+@cindex interactive shell
+An @emph{interactive} shell is one started without non-option arguments,
+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 @option{-i} option. @xref{Interactive Shells}, for more
+information.
-@item BASH_VERSINFO[3]
-The build version.
+If arguments remain after option processing, and neither the
+@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}
+is set to the name of the file, and the positional parameters
+are set to the remaining arguments.
+Bash reads and executes commands from this file, then exits.
+Bash's exit status is the exit status of the last command executed
+in the script. If no commands are executed, the exit status is 0.
-@item BASH_VERSINFO[4]
-The release status (e.g., @var{beta1}).
+@node Bash Startup Files
+@section Bash Startup Files
+@cindex startup files
-@item BASH_VERSINFO[5]
-The value of @code{MACHTYPE}.
+This section describes how Bash executes its startup files.
+If any of the files exist but cannot be read, Bash reports an error.
+Tildes are expanded in filenames as described above under
+Tilde Expansion (@pxref{Tilde Expansion}).
-@end table
+Interactive shells are described in @ref{Interactive Shells}.
-@item SHLVL
-Incremented by one each time a new instance of Bash is started. This is
-intended to be a count of how deeply your Bash shells are nested.
+@subsubheading Invoked as an interactive login shell, or with @option{--login}
-@item OPTERR
-If set to the value 1, Bash displays error messages
-generated by the @code{getopts} builtin command.
+When Bash is invoked as an interactive login shell, or as a
+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 @option{--noprofile} option may be used when the shell is started to
+inhibit this behavior.
-@item LANG
-Used to determine the locale category for any category not specifically
-selected with a variable starting with @code{LC_}.
+When a login shell exits, Bash reads and executes commands from
+the file @file{~/.bash_logout}, if it exists.
-@item LC_ALL
-This variable overrides the value of @code{LANG} and any other
-@code{LC_} variable specifying a locale category.
+@subsubheading Invoked as an interactive non-login shell
-@item LC_COLLATE
-This variable determines the collation order used when sorting the
-results of filename expansion (@pxref{Filename Expansion}).
+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 @option{--norc} option.
+The @option{--rcfile @var{file}} option will force Bash to read and
+execute commands from @var{file} instead of @file{~/.bashrc}.
-@item LC_MESSAGES
-This variable determines the locale used to translate double-quoted
-strings preceded by a @samp{$} (@pxref{Locale Translation}).
+So, typically, your @file{~/.bash_profile} contains the line
+@example
+@code{if [ -f ~/.bashrc ]; then . ~/.bashrc; fi}
+@end example
+@noindent
+after (or before) any login-specific initializations.
-@item IGNOREEOF
-Controls the action of the shell on receipt of an @code{EOF} character
-as the sole input. If set, then the value of it is the number
-of consecutive @code{EOF} characters that can be read as the
-first character on an input line
-before the shell will exit. If the variable exists but does not
-have a numeric value (or has no value) then the default is 10.
-If the variable does not exist, then @code{EOF} signifies the end of
-input to the shell. This is only in effect for interactive shells.
+@subsubheading Invoked non-interactively
-@end vtable
+When Bash is started non-interactively, to run a shell script,
+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:
+@example
+@code{if [ -n "$BASH_ENV" ]; then . "$BASH_ENV"; fi}
+@end example
+@noindent
+but the value of the @env{PATH} variable is not used to search for the
+filename.
-@node Shell Arithmetic
-@section Shell Arithmetic
-@cindex arithmetic, shell
+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.
-@menu
-* Arithmetic Evaluation:: How shell arithmetic works.
-* Arithmetic Expansion:: How to use arithmetic in shell expansions.
-* Arithmetic Builtins:: Builtin commands that use shell arithmetic.
-@end menu
+@subsubheading Invoked with name @code{sh}
-Bash includes several mechanisms to evaluate arithmetic expressions
-and display the result or use it as part of a command.
+If Bash is invoked with the name @code{sh}, it tries to mimic the
+startup behavior of historical versions of @code{sh} as closely as
+possible, while conforming to the @sc{posix} standard as well.
+
+When invoked as an interactive login shell, or as a non-interactive
+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 @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 @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 @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.
-@node Arithmetic Evaluation
-@subsection Arithmetic Evaluation
-@cindex expressions, arithmetic
-@cindex evaluation, arithmetic
-@cindex arithmetic evaluation
+When invoked as @code{sh}, Bash enters @sc{posix} mode after
+the startup files are read.
-The shell allows arithmetic expressions to be evaluated, as one of
-the shell expansions or by the @code{let} builtin.
+@subsubheading Invoked in @sc{posix} mode
-Evaluation is done in long integers with no check for overflow,
-though division by 0 is trapped and flagged as an error. The
-following list of operators is grouped into levels of
-equal-precedence operators. The levels are listed in order of
-decreasing precedence.
+When Bash is started in @sc{posix} mode, as with the
+@option{--posix} command line option, it follows the @sc{posix} standard
+for startup files.
+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.
-@table @code
-@item - +
-unary minus and plus
+@subsubheading Invoked by remote shell daemon
-@item ! ~
-logical and bitwise negation
+Bash attempts to determine when it is being run with its standard input
+connected to a network connection, as when executed by the remote shell
+daemon, usually @code{rshd}, or the secure shell daemon @code{sshd}.
+If Bash determines it is being run in
+this fashion, 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 @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
+neither @code{rshd} nor @code{sshd} generally invoke the shell with those
+options or allow them to be specified.
+
+@subsubheading Invoked with unequal effective and real @sc{uid/gid}s
+
+If Bash is started with the effective user (group) id not equal to the
+real user (group) id, and the @option{-p} option is not supplied, no startup
+files are read, shell functions are not inherited from the environment,
+the @env{SHELLOPTS}, @env{BASHOPTS}, @env{CDPATH}, and @env{GLOBIGNORE}
+variables, if they appear in the environment, are ignored, and the effective
+user id is set to the real user id.
+If the @option{-p} option is supplied at invocation, the startup behavior is
+the same, but the effective user id is not reset.
+
+@node Interactive Shells
+@section Interactive Shells
+@cindex interactive shell
+@cindex shell, interactive
-@item * / %
-multiplication, division, remainder
+@menu
+* What is an Interactive Shell?:: What determines whether a shell is Interactive.
+* Is this Shell Interactive?:: How to tell if a shell is interactive.
+* Interactive Shell Behavior:: What changes in a interactive shell?
+@end menu
-@item + -
-addition, subtraction
+@node What is an Interactive Shell?
+@subsection What is an Interactive Shell?
-@item << >>
-left and right bitwise shifts
+An interactive shell
+is one started without non-option arguments, unless @option{-s} is
+specified, without specifying 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 @option{-i} option.
-@item <= >= < >
-comparison
+An interactive shell generally reads from and writes to a user's
+terminal.
-@item == !=
-equality and inequality
+The @option{-s} invocation option may be used to set the positional parameters
+when an interactive shell is started.
-@item &
-bitwise AND
+@node Is this Shell Interactive?
+@subsection Is this Shell Interactive?
-@item ^
-bitwise exclusive OR
+To determine within a startup script whether or not Bash is
+running interactively,
+test the value of the @samp{-} special parameter.
+It contains @code{i} when the shell is interactive. For example:
-@item |
-bitwise OR
+@example
+case "$-" in
+*i*) echo This shell is interactive ;;
+*) echo This shell is not interactive ;;
+esac
+@end example
-@item &&
-logical AND
+Alternatively, startup scripts may examine the variable
+@env{PS1}; it is unset in non-interactive shells, and set in
+interactive shells. Thus:
-@item ||
-logical OR
+@example
+if [ -z "$PS1" ]; then
+ echo This shell is not interactive
+else
+ echo This shell is interactive
+fi
+@end example
-@item expr ? expr : expr
-conditional evaluation
+@node Interactive Shell Behavior
+@subsection Interactive Shell Behavior
-@item = *= /= %= += -= <<= >>= &= ^= |=
-assignment
-@end table
+When the shell is running interactively, it changes its behavior in
+several ways.
-Shell variables are allowed as operands; parameter expansion is
-performed before the expression is evaluated.
-The value of a parameter is coerced to a long integer within
-an expression. A shell variable need not have its integer attribute
-turned on to be used in an expression.
+@enumerate
+@item
+Startup files are read and executed as described in @ref{Bash Startup Files}.
-Constants with a leading 0 are interpreted as octal numbers.
-A leading @samp{0x} or @samp{0X} denotes hexadecimal. Otherwise,
-numbers take the form [@var{base}@code{#}]@var{n}, where @var{base}
-is a decimal number between 2 and 64 representing the arithmetic
-base, and @var{n} is a number in that base. If @var{base} 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.
-If @var{base} is less than or equal to 36, lowercase and uppercase
-letters may be used interchangably to represent numbers between 10
-and 35.
+@item
+Job Control (@pxref{Job Control}) is enabled by default. When job
+control is in effect, Bash ignores the keyboard-generated job control
+signals @code{SIGTTIN}, @code{SIGTTOU}, and @code{SIGTSTP}.
-Operators are evaluated in order of precedence. Sub-expressions in
-parentheses are evaluated first and may override the precedence
-rules above.
+@item
+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.
-@node Arithmetic Expansion
-@subsection Arithmetic Expansion
-@cindex expansion, arithmetic
-@cindex arithmetic expansion
+@item
+Bash executes the value of the @env{PROMPT_COMMAND} variable as a command
+before printing the primary prompt, @env{$PS1}
+(@pxref{Bash Variables}).
-Arithmetic expansion allows the evaluation of an arithmetic expression
-and the substitution of the result. The format for arithmetic expansion is:
+@item
+Readline (@pxref{Command Line Editing}) is used to read commands from
+the user's terminal.
+
+@item
+Bash inspects the value of the @code{ignoreeof} option to @code{set -o}
+instead of exiting immediately when it receives an @code{EOF} on its
+standard input when reading a command (@pxref{The Set Builtin}).
+
+@item
+Command history (@pxref{Bash History Facilities})
+and history expansion (@pxref{History Interaction})
+are enabled by default.
+Bash will save the command history to the file named by @env{$HISTFILE}
+when a shell with history enabled exits.
+
+@item
+Alias expansion (@pxref{Aliases}) is performed by default.
+
+@item
+In the absence of any traps, Bash ignores @code{SIGTERM}
+(@pxref{Signals}).
+
+@item
+In the absence of any traps, @code{SIGINT} is caught and handled
+((@pxref{Signals}).
+@code{SIGINT} will interrupt some shell builtins.
+
+@item
+An interactive login shell sends a @code{SIGHUP} to all jobs on exit
+if the @code{huponexit} shell option has been enabled (@pxref{Signals}).
+
+@item
+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
+@env{MAIL}, @env{MAILPATH}, and @env{MAILCHECK} shell variables
+(@pxref{Bash Variables}).
+
+@item
+Expansion errors due to references to unbound shell variables after
+@samp{set -u} has been enabled will not cause the shell to exit
+(@pxref{The Set Builtin}).
+
+@item
+The shell will not exit on expansion errors caused by @var{var} being unset
+or null in @code{$@{@var{var}:?@var{word}@}} expansions
+(@pxref{Shell Parameter Expansion}).
+
+@item
+Redirection errors encountered by shell builtins will not cause the
+shell to exit.
+
+@item
+When running in @sc{posix} mode, a special builtin returning an error
+status will not cause the shell to exit (@pxref{Bash POSIX Mode}).
+
+@item
+A failed @code{exec} will not cause the shell to exit
+(@pxref{Bourne Shell Builtins}).
+
+@item
+Parser syntax errors will not cause the shell to exit.
+
+@item
+Simple spelling correction for directory arguments to the @code{cd}
+builtin is enabled by default (see the description of the @code{cdspell}
+option to the @code{shopt} builtin in @ref{The Shopt Builtin}).
+
+@item
+The shell will check the value of the @env{TMOUT} variable and exit
+if a command is not read within the specified number of seconds after
+printing @env{$PS1} (@pxref{Bash Variables}).
+
+@end enumerate
+
+@node Bash Conditional Expressions
+@section Bash Conditional Expressions
+@cindex expressions, conditional
+
+Conditional expressions are used by the @code{[[} compound command
+and the @code{test} and @code{[} builtin commands.
+
+Expressions may be unary or binary.
+Unary expressions are often used to examine the status of a file.
+There are string operators and numeric comparison operators as well.
+If the @var{file} argument to one of the primaries is of the form
+@file{/dev/fd/@var{N}}, then file descriptor @var{N} is checked.
+If the @var{file} argument to one of the primaries is one of
+@file{/dev/stdin}, @file{/dev/stdout}, or @file{/dev/stderr}, file
+descriptor 0, 1, or 2, respectively, is checked.
+
+When used with @code{[[}, the @samp{<} and @samp{>} operators sort
+lexicographically using the current locale.
+The @code{test} command uses ASCII ordering.
+
+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.
+
+@item -b @var{file}
+True if @var{file} exists and is a block special file.
+
+@item -c @var{file}
+True if @var{file} exists and is a character special file.
+
+@item -d @var{file}
+True if @var{file} exists and is a directory.
+
+@item -e @var{file}
+True if @var{file} exists.
+
+@item -f @var{file}
+True if @var{file} exists and is a regular file.
+
+@item -g @var{file}
+True if @var{file} exists and its set-group-id bit is set.
+
+@item -h @var{file}
+True if @var{file} exists and is a symbolic link.
+
+@item -k @var{file}
+True if @var{file} exists and its "sticky" bit is set.
+
+@item -p @var{file}
+True if @var{file} exists and is a named pipe (FIFO).
+
+@item -r @var{file}
+True if @var{file} exists and is readable.
+
+@item -s @var{file}
+True if @var{file} exists and has a size greater than zero.
+
+@item -t @var{fd}
+True if file descriptor @var{fd} is open and refers to a terminal.
+
+@item -u @var{file}
+True if @var{file} exists and its set-user-id bit is set.
+
+@item -w @var{file}
+True if @var{file} exists and is writable.
+
+@item -x @var{file}
+True if @var{file} exists and is executable.
+
+@item -G @var{file}
+True if @var{file} exists and is owned by the effective group id.
+
+@item -L @var{file}
+True if @var{file} exists and is a symbolic link.
+
+@item -N @var{file}
+True if @var{file} exists and has been modified since it was last read.
+
+@item -O @var{file}
+True if @var{file} exists and is owned by the effective user id.
+
+@item -S @var{file}
+True if @var{file} exists and is a socket.
+
+@item @var{file1} -ef @var{file2}
+True if @var{file1} and @var{file2} refer to the same device and
+inode numbers.
+
+@item @var{file1} -nt @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},
+or if @var{file2} exists and @var{file1} does not.
+
+@item -o @var{optname}
+True if the shell option @var{optname} is enabled.
+The list of options appears in the description of the @option{-o}
+option to the @code{set} builtin (@pxref{The Set Builtin}).
+
+@item -v @var{varname}
+True if the shell variable @var{varname} is set (has been assigned a value).
+
+@item -R @var{varname}
+True if the shell variable @var{varname} is set and is a name reference.
+
+@item -z @var{string}
+True if the length of @var{string} is zero.
+
+@item -n @var{string}
+@itemx @var{string}
+True if the length of @var{string} is non-zero.
+
+@item @var{string1} == @var{string2}
+@itemx @var{string1} = @var{string2}
+True if the strings are equal.
+When used with the @code{[[} command, this performs pattern matching as
+described above (@pxref{Conditional Constructs}).
+
+@samp{=} should be used with the @code{test} command for @sc{posix} conformance.
+
+@item @var{string1} != @var{string2}
+True if the strings are not equal.
+
+@item @var{string1} < @var{string2}
+True if @var{string1} sorts before @var{string2} lexicographically.
+
+@item @var{string1} > @var{string2}
+True if @var{string1} sorts after @var{string2} lexicographically.
+
+@item @var{arg1} OP @var{arg2}
+@code{OP} is one of
+@samp{-eq}, @samp{-ne}, @samp{-lt}, @samp{-le}, @samp{-gt}, or @samp{-ge}.
+These arithmetic binary operators return true if @var{arg1}
+is equal to, not equal to, less than, less than or equal to,
+greater than, or greater than or equal to @var{arg2},
+respectively. @var{Arg1} and @var{arg2}
+may be positive or negative integers.
+@end table
+
+@node Shell Arithmetic
+@section Shell Arithmetic
+@cindex arithmetic, shell
+@cindex shell arithmetic
+@cindex expressions, arithmetic
+@cindex evaluation, arithmetic
+@cindex arithmetic evaluation
+
+The shell allows arithmetic expressions to be evaluated, as one of
+the shell expansions or by the @code{let} and the @option{-i} option
+to the @code{declare} builtins.
+
+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, 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.
+
+@table @code
+
+@item @var{id}++ @var{id}--
+variable post-increment and post-decrement
+
+@item ++@var{id} --@var{id}
+variable pre-increment and pre-decrement
+
+@item - +
+unary minus and plus
+
+@item ! ~
+logical and bitwise negation
+
+@item **
+exponentiation
+
+@item * / %
+multiplication, division, remainder
+
+@item + -
+addition, subtraction
+
+@item << >>
+left and right bitwise shifts
+
+@item <= >= < >
+comparison
+
+@item == !=
+equality and inequality
+
+@item &
+bitwise AND
+
+@item ^
+bitwise exclusive OR
+
+@item |
+bitwise OR
+
+@item &&
+logical AND
+
+@item ||
+logical OR
+
+@item expr ? expr : expr
+conditional operator
+
+@item = *= /= %= += -= <<= >>= &= ^= |=
+assignment
+
+@item expr1 , expr2
+comma
+@end table
+
+Shell variables are allowed as operands; parameter expansion is
+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, 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 @var{integer} attribute turned on
+to be used in an expression.
+
+Constants with a leading 0 are interpreted as octal numbers.
+A leading @samp{0x} or @samp{0X} denotes hexadecimal. Otherwise,
+numbers take the form [@var{base}@code{#}]@var{n}, where the optional @var{base}
+is a decimal number between 2 and 64 representing the arithmetic
+base, and @var{n} is a number in that base.
+If @var{base}@code{#} is omitted, then base 10 is used.
+When specifying @var{n},
+he digits greater than 9 are represented by the lowercase letters,
+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 interchangeably to represent numbers between 10
+and 35.
+
+Operators are evaluated in order of precedence. Sub-expressions in
+parentheses are evaluated first and may override the precedence
+rules above.
+
+@node Aliases
+@section Aliases
+@cindex alias expansion
+
+@var{Aliases} allow a string to be substituted for a word when it is used
+as the first word of a simple command.
+The shell maintains a list of aliases that may be set and unset with
+the @code{alias} and @code{unalias} builtin commands.
+
+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 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"},
+for instance, and Bash does not try to recursively expand the
+replacement text.
+If the last character of the alias value is a
+@var{blank}, then the next command word following the
+alias is also checked for alias expansion.
+
+Aliases are created and listed with the @code{alias}
+command, and removed with the @code{unalias} command.
+
+There is no mechanism for using arguments in the replacement text,
+as in @code{csh}.
+If arguments are needed, a shell function should be used
+(@pxref{Shell Functions}).
+
+Aliases are not expanded when the shell is not interactive,
+unless the @code{expand_aliases} shell option is set using
+@code{shopt} (@pxref{The Shopt Builtin}).
+
+The rules concerning the definition and use of aliases are
+somewhat confusing. Bash
+always reads at least one complete line
+of input before executing any
+of the commands on that line. Aliases are expanded when a
+command is read, not when it is executed. Therefore, an
+alias definition appearing on the same line as another
+command does not take effect until the next line of input is read.
+The commands following the alias definition
+on that line are not affected by the new alias.
+This behavior is also an issue when functions are executed.
+Aliases are expanded when a function definition is read,
+not when the function is executed, because a function definition
+is itself a compound command. As a consequence, aliases
+defined in a function are not available until after that
+function is executed. To be safe, always put
+alias definitions on a separate line, and do not use @code{alias}
+in compound commands.
+
+For almost every purpose, shell functions are preferred over aliases.
+
+@node Arrays
+@section Arrays
+@cindex arrays
+
+Bash provides one-dimensional indexed and associative array variables.
+Any variable may be used as an indexed array;
+the @code{declare} builtin will explicitly declare an array.
+There is no maximum
+limit on the size of an array, nor any requirement that members
+be indexed or assigned contiguously.
+Indexed arrays are referenced using integers (including arithmetic
+expressions (@pxref{Shell Arithmetic})) and are zero-based;
+associative arrays use arbitrary strings.
+Unless otherwise noted, indexed array indices must be non-negative integers.
+
+An indexed array is created automatically if any variable is assigned to
+using the syntax
+@example
+@var{name}[@var{subscript}]=@var{value}
+@end example
+
+@noindent
+The @var{subscript}
+is treated as an arithmetic expression that must evaluate to a number.
+To explicitly declare an array, use
+@example
+declare -a @var{name}
+@end example
+@noindent
+The syntax
+@example
+declare -a @var{name}[@var{subscript}]
+@end example
+@noindent
+is also accepted; the @var{subscript} is ignored.
+
+@noindent
+Associative arrays are created using
+@example
+declare -A @var{name}.
+@end example
+
+Attributes may be
+specified for an array variable using the @code{declare} and
+@code{readonly} builtins. Each attribute applies to all members of
+an array.
+
+Arrays are assigned to using compound assignments of the form
+@example
+@var{name}=(@var{value1} @var{value2} @dots{} )
+@end example
+@noindent
+where each
+@var{value} is of the form @code{[@var{subscript}]=}@var{string}.
+Indexed array assignments do not require anything but @var{string}.
+When assigning to indexed arrays, if
+the optional subscript is supplied, that index is assigned to;
+otherwise the index of the element assigned is the last index assigned
+to by the statement plus one. Indexing starts at zero.
+
+When assigning to an associative array, the subscript is required.
+
+This syntax is also accepted by the @code{declare}
+builtin. Individual array elements may be assigned to using the
+@code{@var{name}[@var{subscript}]=@var{value}} syntax introduced above.
+
+When assigning to an indexed array, if @var{name}
+is subscripted by a negative number, that number is
+interpreted as relative to one greater than the maximum index of
+@var{name}, so negative indices count back from the end of the
+array, and an index of -1 references the last element.
+
+Any element of an array may be referenced using
+@code{$@{@var{name}[@var{subscript}]@}}.
+The braces are required to avoid
+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,
+@code{$@{@var{name}[*]@}} expands to a single word with
+the value of each array member separated by the first character of the
+@env{IFS} variable, and @code{$@{@var{name}[@@]@}} expands each element of
+@var{name} to a separate word. When there are no array members,
+@code{$@{@var{name}[@@]@}} expands to nothing.
+If the double-quoted expansion occurs within a word, the expansion of
+the first parameter is joined with the beginning part of the original
+word, and the expansion of the last parameter is joined with the last
+part of the original word.
+This is analogous to the
+expansion of the special parameters @samp{@@} and @samp{*}.
+@code{$@{#@var{name}[@var{subscript}]@}} expands to the length of
+@code{$@{@var{name}[@var{subscript}]@}}.
+If @var{subscript} is @samp{@@} or
+@samp{*}, the expansion is the number of elements in the array.
+Referencing an array variable without a subscript is equivalent to
+referencing with a subscript of 0.
+If the @var{subscript}
+used to reference an element of an indexed array
+evaluates to a number less than zero, it is
+interpreted as relative to one greater than the maximum index of the array,
+so negative indices count back from the end of the array,
+and an index of -1 refers to the last element.
+
+An array variable is considered set if a subscript has been assigned a
+value. The null string is a valid value.
+
+It is possible to obtain the keys (indices) of an array as well as the values.
+$@{!@var{name}[@@]@} and $@{!@var{name}[*]@} expand to the indices
+assigned in array variable @var{name}.
+The treatment when in double quotes is similar to the expansion of the
+special parameters @samp{@@} and @samp{*} within double quotes.
+
+The @code{unset} builtin is used to destroy arrays.
+@code{unset @var{name}[@var{subscript}]}
+destroys the array element at index @var{subscript}.
+Negative subscripts to indexed arrays are interpreted as described above.
+Care must be taken to avoid unwanted side effects caused by filename
+expansion.
+@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 @option{-a} option to specify an indexed
+array and a @option{-A} option to specify an associative array.
+If both options are supplied, @option{-A} takes precedence.
+The @code{read} 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}
+builtins display array values in a way that allows them to be
+reused as input.
+
+@node The Directory Stack
+@section The Directory Stack
+@cindex directory stack
+
+@menu
+* Directory Stack Builtins:: Bash builtin commands to manipulate
+ the directory stack.
+@end menu
+
+The directory stack is a list of recently-visited directories. The
+@code{pushd} builtin adds directories to the stack as it changes
+the current directory, and the @code{popd} builtin removes specified
+directories from the stack and changes the current directory to
+the directory removed. The @code{dirs} builtin displays the contents
+of the directory stack.
+
+The contents of the directory stack are also visible
+as the value of the @env{DIRSTACK} shell variable.
+
+@node Directory Stack Builtins
+@subsection Directory Stack Builtins
+
+@table @code
+
+@item dirs
+@btindex dirs
+@example
+dirs [-clpv] [+@var{N} | -@var{N}]
+@end example
+
+Display the list of currently remembered directories. Directories
+are added to the list with the @code{pushd} command; the
+@code{popd} command removes directories from the list.
+
+@table @code
+@item -c
+Clears the directory stack by deleting all of the elements.
+@item -l
+Produces a listing using full pathnames;
+the default listing format uses a tilde to denote the home directory.
+@item -p
+Causes @code{dirs} to print the directory stack with one entry per
+line.
+@item -v
+Causes @code{dirs} to print the directory stack with one entry per
+line, prefixing each entry with its index in the stack.
+@item +@var{N}
+Displays the @var{N}th directory (counting from the left of the
+list printed by @code{dirs} when invoked without options), starting
+with zero.
+@item -@var{N}
+Displays the @var{N}th directory (counting from the right of the
+list printed by @code{dirs} when invoked without options), starting
+with zero.
+@end table
+
+@item popd
+@btindex popd
+@example
+popd [-n] [+@var{N} | -@var{N}]
+@end example
+
+Remove the top entry from the directory stack, and @code{cd}
+to the new top directory.
+When no arguments are given, @code{popd}
+removes the top directory from the stack and
+performs a @code{cd} to the new top directory. The
+elements are numbered from 0 starting at the first directory listed with
+@code{dirs}; that is, @code{popd} is equivalent to @code{popd +0}.
+
+@table @code
+@item -n
+Suppresses the normal change of directory when removing directories
+from the stack, so that only the stack is manipulated.
+@item +@var{N}
+Removes the @var{N}th directory (counting from the left of the
+list printed by @code{dirs}), starting with zero.
+@item -@var{N}
+Removes the @var{N}th directory (counting from the right of the
+list printed by @code{dirs}), starting with zero.
+@end table
+
+@btindex pushd
+@item pushd
+@example
+pushd [-n] [@var{+N} | @var{-N} | @var{dir}]
+@end example
+
+Save the current directory on the top of the directory stack
+and then @code{cd} to @var{dir}.
+With no arguments, @code{pushd} exchanges the top two directories.
+
+@table @code
+@item -n
+Suppresses the normal change of directory when adding directories
+to the stack, so that only the stack is manipulated.
+@item +@var{N}
+Brings the @var{N}th directory (counting from the left of the
+list printed by @code{dirs}, starting with zero) to the top of
+the list by rotating the stack.
+@item -@var{N}
+Brings the @var{N}th directory (counting from the right of the
+list printed by @code{dirs}, starting with zero) to the top of
+the list by rotating the stack.
+@item @var{dir}
+Makes the current working directory be the top of the stack, making
+it the new current directory as if it had been supplied as an argument
+to the @code{cd} builtin.
+@end table
+@end table
+
+@node Controlling the Prompt
+@section Controlling the Prompt
+@cindex prompting
+
+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.
+
+In addition, the following table describes the special characters which
+can appear in the prompt variables @env{PS1} to @env{PS4}:
+
+@table @code
+@item \a
+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 hostname, up to the first `.'.
+@item \H
+The hostname.
+@item \j
+The number of jobs currently managed by the shell.
+@item \l
+The basename of the shell's terminal device name.
+@item \n
+A newline.
+@item \r
+A carriage return.
+@item \s
+The name of the shell, the basename of @code{$0} (the portion
+following the final slash).
+@item \t
+The time, in 24-hour HH:MM:SS format.
+@item \T
+The time, in 12-hour HH:MM:SS format.
+@item \@@
+The time, in 12-hour am/pm format.
+@item \A
+The time, in 24-hour HH:MM format.
+@item \u
+The username of the current user.
+@item \v
+The version of Bash (e.g., 2.00)
+@item \V
+The release of Bash, version + patchlevel (e.g., 2.00.0)
+@item \w
+The current working directory, with @env{$HOME} abbreviated with a tilde
+(uses the @env{$PROMPT_DIRTRIM} variable).
+@item \W
+The basename of @env{$PWD}, with @env{$HOME} abbreviated with a tilde.
+@item \!
+The history number of this command.
+@item \#
+The command number of this command.
+@item \$
+If the effective uid is 0, @code{#}, otherwise @code{$}.
+@item \@var{nnn}
+The character whose ASCII code is the octal value @var{nnn}.
+@item \\
+A backslash.
+@item \[
+Begin a sequence of non-printing characters. This could be used to
+embed a terminal control sequence into the prompt.
+@item \]
+End a sequence of non-printing characters.
+@end table
+
+The command number and the history number are usually different:
+the history number of a command is its position in the history
+list, which may include commands restored from the history file
+(@pxref{Bash History Facilities}), while the command number is
+the position in the sequence of commands executed during the current
+shell session.
+
+After the string is decoded, it is expanded via
+parameter expansion, command substitution, arithmetic
+expansion, and quote removal, subject to the value of the
+@code{promptvars} shell option (@pxref{Bash Builtins}).
+
+@node The Restricted Shell
+@section The Restricted Shell
+@cindex restricted shell
+
+If Bash is started with the name @code{rbash}, or the
+@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 or not performed:
+
+@itemize @bullet
+@item
+Changing directories with the @code{cd} builtin.
+@item
+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 @option{-p}
+option to the @code{hash} builtin command.
+@item
+Importing function definitions from the shell environment at startup.
+@item
+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.
+@item
+Using the @code{exec} builtin to replace the shell with another command.
+@item
+Adding or deleting builtin commands with the
+@option{-f} and @option{-d} options to the @code{enable} builtin.
+@item
+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 @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} 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
+@env{$PATH} to find the new location. This is also available with
+@samp{shopt -s checkhash}.
+
+@item
+The message printed by the job control code and builtins when a job
+exits with a non-zero status is `Done(status)'.
+
+@item
+The message printed by the job control code and builtins when a job
+is stopped is `Stopped(@var{signame})', where @var{signame} is, for
+example, @code{SIGTSTP}.
+
+@item
+The @code{bg} builtin uses the required format to describe each job placed
+in the background, which does not include an indication of whether the job
+is the current or previous job.
+
+@item
+Reserved words appearing in a context where reserved words are recognized
+do not undergo alias expansion.
+
+@item
+The @sc{posix} @env{PS1} and @env{PS2} expansions of @samp{!} to
+the history number and @samp{!!} to @samp{!} are enabled,
+and parameter expansion is performed on the values of @env{PS1} and
+@env{PS2} regardless of the setting of the @code{promptvars} option.
+
+@item
+The @sc{posix} startup files are executed (@env{$ENV}) rather than
+the normal Bash files.
+
+@item
+Tilde expansion is only performed on assignments preceding a command
+name, rather than on all assignment statements on the line.
+
+@item
+The @code{command} builtin does not prevent builtins that take assignment
+statements as arguments from expanding them as assignment statements;
+when not in @sc{posix} mode, assignment builtins lose their assignment
+statement expansion properties when preceded by @code{command}.
+
+@item
+The default history file is @file{~/.sh_history} (this is the
+default value of @env{$HISTFILE}).
+
+@item
+The output of @samp{kill -l} prints all the signal names on a single line,
+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}
+is not found.
+
+@item
+Non-interactive shells exit if a syntax error in an arithmetic expansion
+results in an invalid expression.
+
+@item
+Non-interactive shells exit if there is a syntax error in a script read
+with the @code{.} or @code{source} builtins, or in a string processed by
+the @code{eval} builtin.
+
+@item
+Redirection operators do not perform filename expansion on the word
+in the redirection unless the shell is interactive.
+
+@item
+Redirection operators do not perform word splitting on the word in the
+redirection.
+
+@item
+Function names must be valid shell @code{name}s. That is, they may not
+contain characters other than letters, digits, and underscores, and
+may not start with a digit. Declaring a function with an invalid name
+causes a fatal syntax error in non-interactive shells.
+
+@item
+Function names may not be the same as one of the @sc{posix} special
+builtins.
+
+@item
+@sc{posix} special builtins are found before shell functions
+during command lookup.
+
+@item
+The @code{time} reserved word may be used by itself as a command. When
+used in this way, it displays timing statistics for the shell and its
+completed children. The @env{TIMEFORMAT} variable controls the format
+of the timing information.
+
+@item
+When parsing and expanding a $@{@dots{}@} expansion that appears within
+double quotes, single quotes are no longer special and cannot be used to
+quote a closing brace or other special character, unless the operator is
+one of those defined to perform pattern removal. In this case, they do
+not have to appear as matched pairs.
+
+@item
+The parser does not recognize @code{time} as a reserved word if the next
+token begins with a @samp{-}.
+
+@item
+If a @sc{posix} special builtin returns an error status, a
+non-interactive shell exits. The fatal errors are those listed in
+the @sc{posix} standard, and include things like passing incorrect options,
+redirection errors, variable assignment errors for assignments preceding
+the command name, and so on.
+
+@item
+A non-interactive shell exits with an error status if a variable
+assignment error occurs when no command name follows the assignment
+statements.
+A variable assignment error occurs, for example, when trying to assign
+a value to a readonly variable.
+
+@item
+A non-interactive shell exits with an error status if a variable
+assignment error occurs in an assignment statement preceding a special
+builtin, but not with any other simple command.
+
+@item
+A non-interactive shell exits with an error status if the iteration
+variable in a @code{for} statement or the selection variable in a
+@code{select} statement is a readonly variable.
+
+@item
+Process substitution is not available.
+
+@item
+While variable indirection is available, it may not be applied to the
+@samp{#} and @samp{?} special parameters.
+
+@item
+Assignment statements preceding @sc{posix} special builtins
+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}.
+
+@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
+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{$PATH}.
+
+@item
+The @code{vi} editing mode will invoke the @code{vi} editor directly when
+the @samp{v} command is run, instead of checking @code{$VISUAL} and
+@code{$EDITOR}.
+
+@item
+When the @code{xpg_echo} option is enabled, Bash does not attempt to interpret
+any arguments to @code{echo} as options. Each argument is displayed, after
+escape characters are converted.
+
+@item
+The @code{ulimit} builtin uses a block size of 512 bytes for the @option{-c}
+and @option{-f} options.
+
+@item
+The arrival of @code{SIGCHLD} when a trap is set on @code{SIGCHLD} does
+not interrupt the @code{wait} builtin and cause it to return immediately.
+The trap command is run once for each child that exits.
+
+@item
+The @code{read} builtin may be interrupted by a signal for which a trap
+has been set.
+If Bash receives a trapped signal while executing @code{read}, the trap
+handler executes and @code{read} returns an exit status greater than 128.
+
+@end enumerate
+
+There is other @sc{posix} behavior that Bash does not implement by
+default even when in @sc{posix} mode.
+Specifically:
+
+@enumerate
+
+@item
+The @code{fc} builtin checks @code{$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
+
+This chapter discusses what job control is, how it works, and how
+Bash allows you to access its facilities.
+
+@menu
+* Job Control Basics:: How job control works.
+* Job Control Builtins:: Bash builtin commands used to interact
+ with job control.
+* Job Control Variables:: Variables Bash uses to customize job
+ control.
+@end menu
+
+@node Job Control Basics
+@section Job Control Basics
+@cindex job control
+@cindex foreground
+@cindex background
+@cindex suspending jobs
+
+Job control
+refers to the ability to selectively stop (suspend)
+the execution of processes and continue (resume)
+their execution at a later point. A user typically employs
+this facility via an interactive interface supplied jointly
+by the operating system kernel's terminal driver and Bash.
+
+The shell associates a @var{job} with each pipeline. It keeps a
+table of currently executing jobs, which may be listed with the
+@code{jobs} command. When Bash starts a job
+asynchronously, it prints a line that looks
+like:
+@example
+[1] 25647
+@end example
+@noindent
+indicating that this job is job number 1 and that the process @sc{id}
+of the last process in the pipeline associated with this job is
+25647. All of the processes in a single pipeline are members of
+the same job. Bash uses the @var{job} abstraction as the
+basis for job control.
+
+To facilitate the implementation of the user interface to job
+control, the operating system maintains the notion of a current terminal
+process group @sc{id}. Members of this process group (processes whose
+process group @sc{id} is equal to the current terminal process group
+@sc{id}) receive keyboard-generated signals such as @code{SIGINT}.
+These processes are said to be in the foreground. Background
+processes are those whose process group @sc{id} differs from the
+terminal's; such processes are immune to keyboard-generated
+signals. Only foreground processes are allowed to read from or, if
+the user so specifies with @code{stty tostop}, write to the terminal.
+Background processes which attempt to
+read from (write to when @code{stty tostop} is in effect) the
+terminal are sent a @code{SIGTTIN} (@code{SIGTTOU})
+signal by the kernel's terminal driver,
+which, unless caught, suspends the process.
+
+If the operating system on which Bash is running supports
+job control, Bash contains facilities to use it. Typing the
+@var{suspend} character (typically @samp{^Z}, Control-Z) while a
+process is running causes that process to be stopped and returns
+control to Bash. Typing the @var{delayed suspend} character
+(typically @samp{^Y}, Control-Y) causes the process to be stopped
+when it attempts to read input from the terminal, and control to
+be returned to Bash. The user then manipulates the state of
+this job, using the @code{bg} command to continue it in the
+background, the @code{fg} command to continue it in the
+foreground, or the @code{kill} command to kill it. A @samp{^Z}
+takes effect immediately, and has the additional side effect of
+causing pending output and typeahead to be discarded.
+
+There are a number of ways to refer to a job in the shell. The
+character @samp{%} introduces a job specification (@var{jobspec}).
+
+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.
+A single @samp{%} (with no accompanying job specification) also refers
+to the current job.
+The previous job may be referenced using @samp{%-}.
+If there is only a single job, @samp{%+} and @samp{%-} can both be used
+to refer to that job.
+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{-}.
+
+A job may also be referred to
+using a prefix of the name used to start it, or using a substring
+that appears in its command line. For example, @samp{%ce} refers
+to a stopped @code{ce} job. Using @samp{%?ce}, on the
+other hand, refers to any job containing the string @samp{ce} in
+its command line. If the prefix or substring matches more than one job,
+Bash reports an error.
+
+Simply naming a job can be used to bring it into the foreground:
+@samp{%1} is a synonym for @samp{fg %1}, bringing job 1 from the
+background into the foreground. Similarly, @samp{%1 &} resumes
+job 1 in the background, equivalent to @samp{bg %1}
+
+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 @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 made while jobs are stopped, (or running, if
+the @code{checkjobs} option is enabled -- see @ref{The Shopt Builtin}), the
+shell prints a warning message, and if the @code{checkjobs} option is
+enabled, lists the jobs and their statuses.
+The @code{jobs} command may then be used to inspect their status.
+If a second attempt to exit is made without an intervening command,
+Bash does not print another warning, and any stopped jobs are terminated.
+
+@node Job Control Builtins
+@section Job Control Builtins
+
+@table @code
+
+@item bg
+@btindex bg
+@example
+bg [@var{jobspec} @dots{}]
+@end example
+
+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, any
+@var{jobspec} was not found or specifies a job
+that was started without job control.
+
+@item fg
+@btindex fg
+@example
+fg [@var{jobspec}]
+@end example
+
+Resume the job @var{jobspec} in the foreground and make it the current job.
+If @var{jobspec} is not supplied, the current job is used.
+The return status is that of the command placed into the foreground,
+or non-zero if run when job control is disabled or, when run with
+job control enabled, @var{jobspec} does not specify a valid job or
+@var{jobspec} specifies a job that was started without job control.
+
+@item jobs
+@btindex jobs
+@example
+jobs [-lnprs] [@var{jobspec}]
+jobs -x @var{command} [@var{arguments}]
+@end example
+
+The first form lists the active jobs. The options have the
+following meanings:
+
+@table @code
+@item -l
+List process @sc{id}s in addition to the normal information.
+
+@item -n
+Display information only about jobs that have changed status since
+the user was last notified of their status.
+
+@item -p
+List only the process @sc{id} of the job's process group leader.
+
+@item -r
+Display only running jobs.
+
+@item -s
+Display only stopped jobs.
+@end table
+
+If @var{jobspec} is given,
+output is restricted to information about that job.
+If @var{jobspec} is not supplied, the status of all jobs is
+listed.
+
+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.
+
+@item kill
+@btindex kill
+@example
+kill [-s @var{sigspec}] [-n @var{signum}] [-@var{sigspec}] @var{jobspec} or @var{pid}
+kill -l [@var{exit_status}]
+@end example
+
+Send a signal specified by @var{sigspec} or @var{signum} to the process
+named by job specification @var{jobspec} or process @sc{id} @var{pid}.
+@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 @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
+status of a process terminated by a signal.
+The return status is zero if at least one signal was successfully sent,
+or non-zero if an error occurs or an invalid option is encountered.
+
+@item wait
+@btindex wait
+@example
+wait [-n] [@var{jobspec} or @var{pid} @dots{}]
+@end example
+
+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.
+If the @option{-n} option is supplied, @code{wait} waits for any job to
+terminate and returns its exit status.
+If neither @var{jobspec} nor @var{pid} specifies an active child process
+of the shell, the return status is 127.
+
+@item disown
+@btindex disown
+@example
+disown [-ar] [-h] [@var{jobspec} @dots{}]
+@end example
+
+Without options, remove each @var{jobspec} from the table of
+active jobs.
+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 @option{-a} nor the
+@option{-r} option is supplied, the current job is used.
+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
+@btindex suspend
+@example
+suspend [-f]
+@end example
+
+Suspend the execution of this shell until it receives a
+@code{SIGCONT} signal.
+A login shell cannot be suspended; the @option{-f}
+option can be used to override this and force the suspension.
+@end table
+
+When job control is not active, the @code{kill} and @code{wait}
+builtins do not accept @var{jobspec} arguments. They must be
+supplied process @sc{id}s.
+
+@node Job Control Variables
+@section Job Control Variables
+
+@vtable @code
+
+@item auto_resume
+This variable controls how the shell interacts with the user and
+job control. If this variable exists then single word simple
+commands without redirections are treated as candidates for resumption
+of an existing job. There is no ambiguity allowed; if there is
+more than one job beginning with the string typed, then
+the most recently accessed job will be selected.
+The name of a stopped job, in this context, is the command line
+used to start it. If this variable is set to the value @samp{exact},
+the string supplied must match the name of a stopped job exactly;
+if set to @samp{substring},
+the string supplied needs to match a substring of the name of a
+stopped job. The @samp{substring} value provides functionality
+analogous to the @samp{%?} job @sc{id} (@pxref{Job Control Basics}).
+If set to any other value, the supplied string must
+be a prefix of a stopped job's name; this provides functionality
+analogous to the @samp{%} job @sc{id}.
+
+@end vtable
+
+@set readline-appendix
+@set history-appendix
+@cindex Readline, how to use
+@include rluser.texi
+@cindex History, how to use
+@include hsuser.texi
+@clear readline-appendix
+@clear history-appendix
+
+@node Installing Bash
+@chapter Installing Bash
+
+This chapter provides basic instructions for installing Bash on
+the various supported platforms. The distribution supports the
+@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}, 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
-@example
-$(( @var{expression} ))
-@end example
+@node Basic Installation
+@section Basic Installation
+@cindex installation
+@cindex configuration
+@cindex Bash installation
+@cindex Bash configuration
-The expression is treated as if it were within double quotes, but
-a double quote inside the braces or parentheses is not treated
-specially. All tokens in the expression undergo parameter
-expansion, command substitution, and quote removal. Arithmetic
-substitutions may be nested.
+These are installation instructions for Bash.
-The evaluation is performed according to the rules listed above.
-If the expression is invalid, Bash
-prints a message indicating failure and no substitution occurs.
+The simplest way to compile Bash is:
-@node Arithmetic Builtins
-@subsection Arithmetic Builtins
+@enumerate
+@item
+@code{cd} to the directory containing the source code and type
+@samp{./configure} to configure Bash for your system. If you're
+using @code{csh} on an old version of System V, you might need to
+type @samp{sh ./configure} instead to prevent @code{csh} from trying
+to execute @code{configure} itself.
-@table @code
+Running @code{configure} takes some time.
+While running, it prints messages telling which features it is
+checking for.
-@item let
-@btindex let
-@example
-let @var{expression} [@var{expression}]
-@end example
-The @code{let} builtin allows arithmetic to be performed on shell
-variables. Each @var{expression} is evaluated according to the
-rules given previously (@pxref{Arithmetic Evaluation}). If the
-last @var{expression} evaluates to 0, @code{let} returns 1;
-otherwise 0 is returned.
-@end table
+@item
+Type @samp{make} to compile Bash and build the @code{bashbug} bug
+reporting script.
-@node Arrays
-@section Arrays
-@cindex arrays
+@item
+Optionally, type @samp{make tests} to run the Bash test suite.
-Bash provides one-dimensional array variables. Any variable may be used as
-an array; the @code{declare} builtin will explicitly declare an array.
-There is no maximum
-limit on the size of an array, nor any requirement that members
-be indexed or assigned contiguously. Arrays are zero-based.
+@item
+Type @samp{make install} to install @code{bash} and @code{bashbug}.
+This will also install the manual pages and Info file.
+
+@end enumerate
+
+The @code{configure} shell script attempts to guess correct
+values for various system-dependent variables used during
+compilation. It uses those values to create a @file{Makefile} in
+each directory of the package (the top directory, the
+@file{builtins}, @file{doc}, and @file{support} directories,
+each directory under @file{lib}, and several others). It also creates a
+@file{config.h} file containing system-dependent definitions.
+Finally, it creates a shell script named @code{config.status} that you
+can run in the future to recreate the current configuration, a
+file @file{config.cache} that saves the results of its tests to
+speed up reconfiguring, and a file @file{config.log} containing
+compiler output (useful mainly for debugging @code{configure}).
+If at some point
+@file{config.cache} contains results you don't want to keep, you
+may remove or edit it.
+
+To find out more about the options and arguments that the
+@code{configure} script understands, type
-An array is created automatically if any variable is assigned to using
-the syntax
@example
-name[@var{subscript}]=@var{value}
+bash-2.04$ ./configure --help
@end example
@noindent
-The @var{subscript}
-is treated as an arithmetic expression that must evaluate to a number
-greater than or equal to zero. To explicitly declare an array, use
+at the Bash prompt in your Bash source directory.
+
+If you need to do unusual things to compile Bash, please
+try to figure out how @code{configure} could check whether or not
+to do them, and mail diffs or instructions to
+@email{bash-maintainers@@gnu.org} so they can be
+considered for the next release.
+
+The file @file{configure.ac} is used to create @code{configure}
+by a program called Autoconf. You only need
+@file{configure.ac} 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 2.50 or
+newer.
+
+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
+a different kind of computer), type @samp{make distclean}.
+
+@node Compilers and Options
+@section Compilers and Options
+
+Some systems require unusual options for compilation or linking
+that the @code{configure} script does not know about. You can
+give @code{configure} initial values for variables by setting
+them in the environment. Using a Bourne-compatible shell, you
+can do that on the command line like this:
+
@example
-declare -a @var{name}
+CC=c89 CFLAGS=-O2 LIBS=-lposix ./configure
@end example
-@noindent
-The syntax
+
+On systems that have the @code{env} program, you can do it like this:
+
@example
-declare -a @var{name}[@var{subscript}]
+env CPPFLAGS=-I/usr/local/include LDFLAGS=-s ./configure
@end example
-@noindent
-is also accepted; the @var{subscript} is ignored. Attributes may be
-specified for an array variable using the @code{declare} and
-@code{readonly} builtins. Each attribute applies to all members of
-an array.
-Arrays are assigned to using compound assignments of the form
+The configuration process uses GCC to build Bash if it
+is available.
+
+@node Compiling For Multiple Architectures
+@section Compiling For Multiple Architectures
+
+You can compile Bash for more than one kind of computer at the
+same time, by placing the object files for each architecture in their
+own directory. To do this, you must use a version of @code{make} that
+supports the @code{VPATH} variable, such as GNU @code{make}.
+@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 @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 `..'.
+
+If you have to use a @code{make} that does not supports the @code{VPATH}
+variable, you can compile Bash for one architecture at a
+time in the source code directory. After you have installed
+Bash for one architecture, use @samp{make distclean} before
+reconfiguring for another architecture.
+
+Alternatively, if your system supports symbolic links, you can use the
+@file{support/mkclone} script to create a build tree which has
+symbolic links back to each file in the source directory. Here's an
+example that creates a build directory in the current directory from a
+source directory @file{/usr/gnu/src/bash-2.0}:
+
@example
-name=(value@var{1} @dots{} value@var{n})
+bash /usr/gnu/src/bash-2.0/support/mkclone -s /usr/gnu/src/bash-2.0 .
@end example
-@noindent
-where each
-@var{value} is of the form @code{[[@var{subscript}]=]}@var{string}. If
-the optional subscript is supplied, that index is assigned to;
-otherwise the index of the element assigned is the last index assigned
-to by the statement plus one. Indexing starts at zero.
-This syntax is also accepted by the @code{declare}
-builtin. Individual array elements may be assigned to using the
-@code{name[}@var{subscript}@code{]=}@var{value} syntax introduced above.
-Any element of an array may be referenced using
-@code{$@{name[}@var{subscript}@code{]@}}.
-The braces are required to avoid
-conflicts with the shell's filename expansion operators. If the
-@var{subscript} is @samp{@@} or @samp{*}, the word expands to all members
-of the array @var{name}. These subscripts differ only when the word
-appears within double quotes. If the word is double-quoted,
-@code{$@{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{$@{name[@@]@}} expands each element of
-@var{name} to a separate word. When there are no array members,
-@code{$@{name[@@]@}} expands to nothing. 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{]@}}.
-If @var{subscript} is @samp{@@} or
-@samp{*}, the expansion is the number of elements in the array.
-Referencing an array variable without a subscript is equivalent to
-referencing element zero.
+@noindent
+The @code{mkclone} script requires Bash, so you must have already built
+Bash for at least one architecture before you can create build
+directories for other architectures.
-The @code{unset} builtin is used to destroy arrays.
-@code{unset} @var{name[subscript]}
-destroys the array element at index @var{subscript}.
-@code{unset} @var{name}, where @var{name} is an array, removes the
-entire array. A subscript of @samp{*} or @samp{@@} also removes the
-entire array.
+@node Installation Names
+@section Installation Names
-The @code{declare}, @code{local}, and @code{readonly}
-builtins each accept a @samp{-a}
-option to specify an array. The @code{read}
-builtin accepts a @samp{-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}
-builtins display array values in a way that allows them to be
-reused as input.
+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 @option{--prefix=@var{PATH}},
+or by specifying a value for the @code{DESTDIR} @samp{make}
+variable when running @samp{make install}.
-@node Printing a Prompt
-@section Controlling the Prompt
-@cindex prompting
+You can specify separate installation prefixes for
+architecture-specific files and architecture-independent files.
+If you give @code{configure} the option
+@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.
-The value of the variable @code{PROMPT_COMMAND} is examined just before
-Bash prints each primary prompt. If it is set and non-null, then the
-value is executed just as if you had typed it on the command line.
+@node Specifying the System Type
+@section Specifying the System Type
-In addition, the following table describes the special characters which
-can appear in the prompt variables:
+There may be some features @code{configure} can not figure out
+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 @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{i386-unknown-freebsd4.2}).
-@table @code
-@item \a
-a bell character.
-@item \d
-the date, in "Weekday Month Date" format (e.g., "Tue May 26").
-@item \e
-an escape character.
-@item \h
-the hostname, up to the first `.'.
-@item \H
-the hostname.
-@item \n
-newline.
-@item \s
-the name of the shell, the basename of @code{$0} (the portion
-following the final slash).
-@item \t
-the time, in 24-hour HH:MM:SS format.
-@item \T
-the time, in 12-hour HH:MM:SS format.
-@item \@@
-the time, in 12-hour am/pm format.
-@item \v
-the version of Bash (e.g., 2.00)
-@item \V
-the release of Bash, version + patchlevel (e.g., 2.00.0)
-@item \w
-the current working directory.
-@item \W
-the basename of @code{$PWD}.
-@item \u
-your username.
-@item \!
-the history number of this command.
-@item \#
-the command number of this command.
-@item \$
-if the effective uid is 0, @code{#}, otherwise @code{$}.
-@item \nnn
-the character corresponding to the octal number @code{nnn}.
-@item \\
-a backslash.
-@item \[
-begin a sequence of non-printing characters. This could be used to
-embed a terminal control sequence into the prompt.
-@item \]
-end a sequence of non-printing characters.
-@end table
+See the file @file{support/config.sub} for the possible
+values of each field.
-@node The Restricted Shell
-@section The Restricted Shell
-@cindex restricted shell
+@node Sharing Defaults
+@section Sharing Defaults
-If Bash is started with the name @code{rbash}, or the
-@samp{--restricted}
-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:
-@itemize @bullet
-@item
-Changing directories with the @code{cd} builtin.
-@item
-Setting or unsetting the values of the @code{SHELL} or @code{PATH}
-variables.
-@item
-Specifying command names containing slashes.
-@item
-Specifying a filename containing a slash as an argument to the @code{.}
-builtin command.
-@item
-Importing function definitions from the shell environment at startup.
-@item
-Redirecting output using the @samp{>}, @samp{>|}, @samp{<>}, @samp{>&},
-@samp{&>}, and @samp{>>} redirection operators.
-@item
-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.
-@item
-Specifying the @samp{-p} option to the @code{command} builtin.
-@item
-Turning off restricted mode with @samp{set +r}.
-@end itemize
+If you want to set default values for @code{configure} scripts to
+share, you can create a site shell script called
+@code{config.site} that gives default values for variables like
+@code{CC}, @code{cache_file}, and @code{prefix}. @code{configure}
+looks for @file{PREFIX/share/config.site} if it exists, then
+@file{PREFIX/etc/config.site} if it exists. Or, you can set the
+@code{CONFIG_SITE} environment variable to the location of the site
+script. A warning: the Bash @code{configure} looks for a site script,
+but not all @code{configure} scripts do.
-@node Bash POSIX Mode
-@section Bash POSIX Mode
-@cindex POSIX Mode
+@node Operation Controls
+@section Operation Controls
-Starting Bash with the @samp{--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.2} standard by changing the behavior to match that
-specified by @sc{POSIX.2} in areas where the Bash default differs.
+@code{configure} recognizes the following options to control how it
+operates.
-The following list is what's changed when `@sc{POSIX} mode' is in effect:
+@table @code
-@enumerate
-@item
-When a command in the hash table no longer exists, Bash will re-search
-@code{$PATH} to find the new location. This is also available with
-@samp{shopt -s checkhash}.
+@item --cache-file=@var{file}
+Use and save the results of the tests in
+@var{file} instead of @file{./config.cache}. Set @var{file} to
+@file{/dev/null} to disable caching, for debugging
+@code{configure}.
-@item
-The @samp{>&} redirection does not redirect stdout and stderr.
+@item --help
+Print a summary of the options to @code{configure}, and exit.
-@item
-The message printed by the job control code and builtins when a job
-exits with a non-zero status is `Done(status)'.
+@item --quiet
+@itemx --silent
+@itemx -q
+Do not print messages saying which checks are being made.
-@item
-Reserved words may not be aliased.
+@item --srcdir=@var{dir}
+Look for the Bash source code in directory @var{dir}. Usually
+@code{configure} can determine that directory automatically.
-@item
-The @sc{POSIX.2} @code{PS1} and @code{PS2} expansions of @samp{!} to
-the history number and @samp{!!} to @samp{!} are enabled,
-and parameter expansion is performed on
-the value regardless of the setting of the @code{promptvars} option.
+@item --version
+Print the version of Autoconf used to generate the @code{configure}
+script, and exit.
+@end table
-@item
-Interactive comments are enabled by default. (Note that Bash has
-them on by default anyway.)
+@code{configure} also accepts some other, not widely used, boilerplate
+options. @samp{configure --help} prints the complete list.
-@item
-The @sc{POSIX.2} startup files are executed (@code{$ENV}) rather than
-the normal Bash files.
+@node Optional Features
+@section Optional Features
-@item
-Tilde expansion is only performed on assignments preceding a command
-name, rather than on all assignment statements on the line.
+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 @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
+@option{--without-@var{package}}. To configure Bash without a feature
+that is enabled by default, use @option{--disable-@var{feature}}.
-@item
-The default history file is @file{~/.sh_history} (this is the
-default value of @code{$HISTFILE}).
+Here is a complete list of the @option{--enable-} and
+@option{--with-} options that the Bash @code{configure} recognizes.
-@item
-The output of @samp{kill -l} prints all the signal names on a single line,
-separated by spaces.
+@table @code
+@item --with-afs
+Define if you are using the Andrew File System from Transarc.
-@item
-Non-interactive shells exit if @var{filename} in @code{.} @var{filename}
-is not found.
+@item --with-bash-malloc
+Use the Bash version of
+@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
+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
+option automatically for a number of systems.
-@item
-Redirection operators do not perform filename expansion on the word
-in the redirection unless the shell is interactive.
+@item --with-curses
+Use the curses library instead of the termcap library. This should
+be supplied if your system has an inadequate or incomplete termcap
+database.
-@item
-Function names must be valid shell @code{name}s. That is, they may not
-contain characters other than letters, digits, and underscores, and
-may not start with a digit. Declaring a function with an illegal name
-causes a fatal syntax error in non-interactive shells.
+@item --with-gnu-malloc
+A synonym for @code{--with-bash-malloc}.
+
+@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 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
-@sc{POSIX.2} `special' builtins are found before shell functions
-during command lookup.
+@item --with-purify
+Define this to use the Purify memory allocation checker from Rational
+Software.
-@item
-If a @sc{POSIX.2} special builtin returns an error status, a
-non-interactive shell exits. The fatal errors are those listed in
-the POSIX.2 standard, and include things like passing incorrect options,
-redirection errors, variable assignment errors for assignments preceding
-the command name, and so on.
+@item --enable-minimal-config
+This produces a shell with minimal features, close to the historical
+Bourne shell.
+@end table
-@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.
+There are several @option{--enable-} options that alter how Bash is
+compiled and linked, rather than changing run-time features.
-@item
-A non-interactive shell exits with an error status if a variable
-assignment error occurs when no command name follows the assignment
-statements.
-A variable assignment error occurs, for example, when trying to assign
-a value to a read-only variable.
+@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.
+
+@item --enable-static-link
+This causes Bash to be linked statically, if @code{gcc} is being used.
+This could be used to build a version to use as root's shell.
+@end table
-@item
-A non-interactive shell exits with an error status if the iteration
-variable in a @code{for} statement or the selection variable in a
-@code{select} statement is a read-only variable.
+The @samp{minimal-config} option can be used to disable all of
+the following options, but it is processed first, so individual
+options may be enabled using @samp{enable-@var{feature}}.
-@item
-Process substitution is not available.
+All of the following options except for @samp{disabled-builtins},
+@samp{directpand-default}, and
+@samp{xpg-echo-default} are
+enabled by default, unless the operating system does not provide the
+necessary support.
-@item
-Assignment statements preceding @sc{POSIX.2} @code{special} builtins
-persist in the shell environment after the builtin completes.
+@table @code
+@item --enable-alias
+Allow alias expansion and include the @code{alias} and @code{unalias}
+builtins (@pxref{Aliases}).
-@item
-The @code{export} and @code{readonly} builtin commands display their
-output in the format required by @sc{POSIX.2}.
+@item --enable-arith-for-command
+Include support for the alternate form of the @code{for} command
+that behaves like the C language @code{for} statement
+(@pxref{Looping Constructs}).
-@end enumerate
+@item --enable-array-variables
+Include support for one-dimensional array shell variables
+(@pxref{Arrays}).
-There is other @sc{POSIX.2} behavior that Bash does not implement.
-Specifically:
+@item --enable-bang-history
+Include support for @code{csh}-like history substitution
+(@pxref{History Interaction}).
-@enumerate
-@item
-Assignment statements affect the execution environment of all
-builtins, not just special ones.
-@end enumerate
+@item --enable-brace-expansion
+Include @code{csh}-like brace expansion
+( @code{b@{a,b@}c} @expansion{} @code{bac bbc} ).
+See @ref{Brace Expansion}, for a complete description.
-@node Job Control
-@chapter Job Control
+@item --enable-casemod-attributes
+Include support for case-modifying attributes in the @code{declare} builtin
+and assignment statements. Variables with the @var{uppercase} attribute,
+for example, will have their values converted to uppercase upon assignment.
-This chapter disusses what job control is, how it works, and how
-Bash allows you to access its facilities.
+@item --enable-casemod-expansion
+Include support for case-modifying word expansions.
-@menu
-* Job Control Basics:: How job control works.
-* Job Control Builtins:: Bash builtin commands used to interact
- with job control.
-* Job Control Variables:: Variables Bash uses to customize job
- control.
-@end menu
+@item --enable-command-timing
+Include support for recognizing @code{time} as a reserved word and for
+displaying timing statistics for the pipeline following @code{time}
+(@pxref{Pipelines}).
+This allows pipelines as well as shell builtins and functions to be timed.
-@node Job Control Basics
-@section Job Control Basics
-@cindex job control
-@cindex foreground
-@cindex background
-@cindex suspending jobs
+@item --enable-cond-command
+Include support for the @code{[[} conditional command.
+(@pxref{Conditional Constructs}).
-Job control
-refers to the ability to selectively stop (suspend)
-the execution of processes and continue (resume)
-their execution at a later point. A user typically employs
-this facility via an interactive interface supplied jointly
-by the system's terminal driver and Bash.
+@item --enable-cond-regexp
+Include support for matching @sc{posix} regular expressions using the
+@samp{=~} binary operator in the @code{[[} conditional command.
+(@pxref{Conditional Constructs}).
-The shell associates a @var{job} with each pipeline. It keeps a
-table of currently executing jobs, which may be listed with the
-@code{jobs} command. When Bash starts a job
-asynchronously (in the background), it prints a line that looks
-like:
-@example
-[1] 25647
-@end example
-@noindent
-indicating that this job is job number 1 and that the process @sc{ID}
-of the last process in the pipeline associated with this job is
-25647. All of the processes in a single pipeline are members of
-the same job. Bash uses the @var{job} abstraction as the
-basis for job control.
+@item --enable-coprocesses
+Include support for coprocesses and the @code{coproc} reserved word
+(@pxref{Pipelines}).
-To facilitate the implementation of the user interface to job
-control, the system maintains the notion of a current terminal
-process group @sc{ID}. Members of this process group (processes whose
-process group @sc{ID} is equal to the current terminal process group
-@sc{ID}) receive keyboard-generated signals such as @code{SIGINT}.
-These processes are said to be in the foreground. Background
-processes are those whose process group @sc{ID} differs from the
-terminal's; such processes are immune to keyboard-generated
-signals. Only foreground processes are allowed to read from or
-write to the terminal. Background processes which attempt to
-read from (write to) the terminal are sent a @code{SIGTTIN}
-(@code{SIGTTOU}) signal by the terminal driver, which, unless
-caught, suspends the process.
+@item --enable-debugger
+Include support for the bash debugger (distributed separately).
-If the operating system on which Bash is running supports
-job control, Bash allows you to use it. Typing the
-@var{suspend} character (typically @samp{^Z}, Control-Z) while a
-process is running causes that process to be stopped and returns
-you to Bash. Typing the @var{delayed suspend} character
-(typically @samp{^Y}, Control-Y) causes the process to be stopped
-when it attempts to read input from the terminal, and control to
-be returned to Bash. You may then manipulate the state of
-this job, using the @code{bg} command to continue it in the
-background, the @code{fg} command to continue it in the
-foreground, or the @code{kill} command to kill it. A @samp{^Z}
-takes effect immediately, and has the additional side effect of
-causing pending output and typeahead to be discarded.
+@item --enable-direxpand-default
+Cause the @code{direxpand} shell option (@pxref{The Shopt Builtin})
+to be enabled by default when the shell starts.
+It is normally disabled by default.
-There are a number of ways to refer to a job in the shell. The
-character @samp{%} introduces a job name. Job number @code{n}
-may be referred to as @samp{%n}. A job may also be referred to
-using a prefix of the name used to start it, or using a substring
-that appears in its command line. For example, @samp{%ce} refers
-to a stopped @code{ce} job. Using @samp{%?ce}, on the
-other hand, refers to any job containing the string @samp{ce} in
-its command line. If the prefix or substring matches more than one job,
-Bash reports an error. The symbols @samp{%%} and
-@samp{%+} refer to the shell's notion of the current job, which
-is the last job stopped while it was in the foreground. The
-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{-}.
+@item --enable-directory-stack
+Include support for a @code{csh}-like directory stack and the
+@code{pushd}, @code{popd}, and @code{dirs} builtins
+(@pxref{The Directory Stack}).
-Simply naming a job can be used to bring it into the foreground:
-@samp{%1} is a synonym for @samp{fg %1}, bringing job 1 from the
-background into the foreground. Similarly, @samp{%1 &} resumes
-job 1 in the background, equivalent to @samp{bg %1}
+@item --enable-disabled-builtins
+Allow builtin commands to be invoked via @samp{builtin xxx}
+even after @code{xxx} has been disabled using @samp{enable -n xxx}.
+See @ref{Bash Builtins}, for details of the @code{builtin} and
+@code{enable} builtin commands.
-The shell learns immediately whenever a job changes state.
-Normally, Bash waits until it is about to print a prompt
-before reporting changes in a job's status so as to not interrupt
-any other output. If the
-the @samp{-b} option to the @code{set} builtin is set,
-Bash reports such changes immediately (@pxref{The Set Builtin}).
+@item --enable-dparen-arithmetic
+Include support for the @code{((@dots{}))} command
+(@pxref{Conditional Constructs}).
-If you attempt to exit Bash while jobs are stopped, the
-shell prints a message warning you that you have stopped jobs.
-You may then use the
-@code{jobs} command to inspect their status. If you do this, or
-try to exit again immediately, you are not warned again, and the
-stopped jobs are terminated.
+@item --enable-extended-glob
+Include support for the extended pattern matching features described
+above under @ref{Pattern Matching}.
-@node Job Control Builtins
-@section Job Control Builtins
+@item --enable-extended-glob-default
+Set the default value of the @var{extglob} shell option described
+above under @ref{The Shopt Builtin} to be enabled.
-@table @code
+@item --enable-glob-asciirange-default
+Set the default value of the @var{globasciiranges} shell option described
+above under @ref{The Shopt Builtin} to be enabled.
+This controls the behavior of character ranges when used in pattern matching
+bracket expressions.
-@item bg
-@btindex bg
-@example
-bg [@var{jobspec}]
-@end example
-Place @var{jobspec} into the background, as if it had been started
-with @samp{&}. If @var{jobspec} is not supplied, the current job
-is used.
+@item --enable-help-builtin
+Include the @code{help} builtin, which displays help on shell builtins and
+variables (@pxref{Bash Builtins}).
-@item fg
-@btindex fg
-@example
-fg [@var{jobspec}]
-@end example
-Bring @var{jobspec} into the foreground and make it the current job.
-If @var{jobspec} is not supplied, the current job is used.
+@item --enable-history
+Include command history and the @code{fc} and @code{history}
+builtin commands (@pxref{Bash History Facilities}).
-@item jobs
-@btindex jobs
-@example
-jobs [-lpnrs] [@var{jobspec}]
-jobs -x @var{command} [@var{jobspec}]
-@end example
+@item --enable-job-control
+This enables the job control features (@pxref{Job Control}),
+if the operating system supports them.
-The first form lists the active jobs. The options have the
-following meanings:
+@item --enable-multibyte
+This enables support for multibyte characters if the operating
+system provides the necessary support.
-@table @code
-@item -l
-List process @sc{ID}s in addition to the normal information
+@item --enable-net-redirections
+This enables the special handling of filenames of the form
+@code{/dev/tcp/@var{host}/@var{port}} and
+@code{/dev/udp/@var{host}/@var{port}}
+when used in redirections (@pxref{Redirections}).
-@item -n
-Display information only about jobs that have changed status since
-you were last notified of their status.
+@item --enable-process-substitution
+This enables process substitution (@pxref{Process Substitution}) if
+the operating system provides the necessary support.
-@item -p
-List only the process @sc{ID} of the job's process group
-leader.
+@item --enable-progcomp
+Enable the programmable completion facilities
+(@pxref{Programmable Completion}).
+If Readline is not enabled, this option has no effect.
-@item -r
-Restrict output to running jobs.
+@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{Controlling the Prompt}, for a complete list of prompt
+string escape sequences.
-@item -s
-Restrict output to stopped jobs.
-@end table
+@item --enable-readline
+Include support for command-line editing and history with the Bash
+version of the Readline library (@pxref{Command Line Editing}).
-If @var{jobspec} is given,
-output is restricted to information about that job.
-If @var{jobspec} is not supplied, the status of all jobs is
-listed.
+@item --enable-restricted
+Include support for a @dfn{restricted shell}. If this is enabled, Bash,
+when called as @code{rbash}, enters a restricted mode. See
+@ref{The Restricted Shell}, for a description of restricted mode.
-If the @samp{-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.
+@item --enable-select
+Include the @code{select} compound command, which allows the generation of
+simple menus (@pxref{Conditional Constructs}).
-@item kill
-@btindex kill
-@example
-kill [-s @var{sigspec}] [-n @var{signum}] [-@var{sigspec}] @var{jobspec}
-kill -l [@var{sigspec}]
-@end example
-Send a signal specified by @var{sigspec} or @var{signum} to the process
-named by @var{jobspec}.
-@var{sigspec} is either a signal name such as @code{SIGINT} (with or without
-the @code{SIG} prefix) or a signal number; @var{signum} is a signal number.
-If @var{sigspec} and @var{signum} are not present, @code{SIGTERM} is used.
-The @samp{-l} option lists the signal names, or the signal name
-corresponding to @var{sigspec}.
+@item --enable-separate-helpfiles
+Use external files for the documentation displayed by the @code{help} builtin
+instead of storing the text internally.
-@item wait
-@btindex wait
-@example
-wait [@var{jobspec}|@var{pid}]
-@end example
-Wait until the child process specified by process @sc{ID} @var{pid} or job
-specification @var{jobspec} exits and report its exit status. If a job
-spec is given, all processes in the job are waited for. If no arguments
-are given, all currently active child processes are waited for.
+@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 disown
-@btindex disown
-@example
-disown [-h] [@var{jobspec} @dots{}]
-@end example
-Without options, each @var{jobspec} is removed from the table of
-active jobs.
-If the @samp{-h} option is given, the job is not removed from the table,
-but is marked so that @code{SIGHUP} is not sent to the job if the shell
-receives a @code{SIGHUP}.
-If @var{jobspec} is not present, the current job is used.
+@item --enable-strict-posix-default
+Make Bash @sc{posix}-conformant by default (@pxref{Bash POSIX Mode}).
-@item suspend
-@btindex suspend
-@example
-suspend [-f]
-@end example
-Suspend the execution of this shell until it receives a
-@code{SIGCONT} signal. The @samp{-f} option means to suspend
-even if the shell is a login shell.
+@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 @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 3.
+@xref{Bash Builtins}, for a description of the escape sequences that
+@code{echo} recognizes.
@end table
-When job control is not active, the @code{kill} and @code{wait}
-builtins do not accept @var{jobspec} arguments. They must be
-supplied process @sc{ID}s.
+The file @file{config-top.h} contains C Preprocessor
+@samp{#define} statements for options which are not settable from
+@code{configure}.
+Some of these are not meant to be changed; beware of the consequences if
+you do.
+Read the comments associated with each definition for more
+information about its effect.
-@node Job Control Variables
-@section Job Control Variables
+@node Reporting Bugs
+@appendix Reporting Bugs
-@vtable @code
+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.
+The latest version of Bash is always available for FTP from
+@uref{ftp://ftp.gnu.org/pub/gnu/bash/}.
-@item auto_resume
-This variable controls how the shell interacts with the user and
-job control. If this variable exists then single word simple
-commands without redirects are treated as candidates for resumption
-of an existing job. There is no ambiguity allowed; if there is
-more than one job beginning with the string typed, then
-the most recently accessed job will be selected.
-The name of a stopped job, in this context, is the command line
-used to start it. If this variable is set to the value @samp{exact},
-the string supplied must match the name of a stopped job exactly;
-if set to @samp{substring},
-the string supplied needs to match a substring of the name of a
-stopped job. The @samp{substring} value provides functionality
-analogous to the @samp{%?} job @sc{ID} (@pxref{Job Control Basics}).
-If set to any other value, the supplied string must
-be a prefix of a stopped job's name; this provides functionality
-analogous to the @samp{%} job @sc{ID}.
+Once you have determined that a bug actually exists, use the
+@code{bashbug} command to submit a bug report.
+If you have a fix, you are encouraged to mail that as well!
+Suggestions and `philosophical' bug reports may be mailed
+to @email{bug-bash@@gnu.org} or posted to the Usenet
+newsgroup @code{gnu.bash.bug}.
-@end vtable
+All bug reports should include:
+@itemize @bullet
+@item
+The version number of Bash.
+@item
+The hardware and operating system.
+@item
+The compiler used to compile Bash.
+@item
+A description of the bug behaviour.
+@item
+A short script or `recipe' which exercises the bug and may be used
+to reproduce it.
+@end itemize
-@set readline-appendix
-@set history-appendix
-@cindex History, how to use
-@include hsuser.texinfo
-@cindex Readline, how to use
-@include rluser.texinfo
-@clear readline-appendix
-@clear history-appendix
+@noindent
+@code{bashbug} inserts the first three items automatically into
+the template it provides for filing a bug report.
-@node Installing Bash
-@chapter Installing Bash
+Please send all reports concerning this manual to
+@email{bug-bash@@gnu.org}.
-This chapter provides basic instructions for installing Bash on
-the various supported platforms. The distribution supports nearly every
-version of Unix (and, someday, @sc{GNU}). Other independent ports exist for
-@sc{OS/2}, Windows 95, and Windows @sc{NT}.
+@node Major Differences From The Bourne Shell
+@appendix Major Differences From The Bourne Shell
+
+Bash implements essentially the same grammar, parameter and
+variable expansion, redirection, and quoting as the Bourne Shell.
+Bash uses the @sc{posix} standard as the specification of
+how these features are to be implemented. There are some
+differences between the traditional Bourne shell and Bash; this
+section quickly details the differences of significance. A
+number of these differences are explained in greater depth in
+previous sections.
+This section uses the version of @code{sh} included in SVR4.2 (the
+last version of the historical Bourne shell) as the baseline reference.
-@menu
-* Basic Installation:: Installation instructions.
+@itemize @bullet
-* Compilers and Options:: How to set special options for various
- systems.
+@item
+Bash is @sc{posix}-conformant, even where the @sc{posix} specification
+differs from traditional @code{sh} behavior (@pxref{Bash POSIX Mode}).
-* Compiling For Multiple Architectures:: How to compile Bash for more
- than one kind of system from
- the same source tree.
+@item
+Bash has multi-character invocation options (@pxref{Invoking Bash}).
-* Installation Names:: How to set the various paths used by the installation.
+@item
+Bash has command-line editing (@pxref{Command Line Editing}) and
+the @code{bind} builtin.
-* Specifying the System Type:: How to configure Bash for a particular system.
+@item
+Bash provides a programmable word completion mechanism
+(@pxref{Programmable Completion}), and builtin commands
+@code{complete}, @code{compgen}, and @code{compopt}, to
+manipulate it.
-* Sharing Defaults:: How to share default configuration values among GNU
- programs.
+@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.
-* Operation Controls:: Options recognized by the configuration program.
+@item
+Bash implements @code{csh}-like history expansion
+(@pxref{History Interaction}).
-* Optional Features:: How to enable and disable optional features when
- building Bash.
-@end menu
+@item
+Bash has one-dimensional array variables (@pxref{Arrays}), and the
+appropriate variable expansions and assignment syntax to use them.
+Several of the Bash builtins take options to act on arrays.
+Bash provides a number of built-in array variables.
-@node Basic Installation
-@section Basic Installation
-@cindex installation
-@cindex configuration
-@cindex Bash installation
-@cindex Bash configuration
+@item
+The @code{$'@dots{}'} quoting syntax, which expands ANSI-C
+backslash-escaped characters in the text between the single quotes,
+is supported (@pxref{ANSI-C Quoting}).
-These are installation instructions for Bash.
+@item
+Bash supports the @code{$"@dots{}"} quoting syntax to do
+locale-specific translation of the characters between the double
+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}).
-The @code{configure} shell script attempts to guess correct
-values for various system-dependent variables used during
-compilation. It uses those values to create a @file{Makefile} in
-each directory of the package (the top directory, the
-@file{builtins} and @file{doc} directories, and the
-each directory under @file{lib}). It also creates a
-@file{config.h} file containing system-dependent definitions.
-Finally, it creates a shell script named @code{config.status} that you
-can run in the future to recreate the current configuration, a
-file @file{config.cache} that saves the results of its tests to
-speed up reconfiguring, and a file @file{config.log} containing
-compiler output (useful mainly for debugging @code{configure}).
-If at some point
-@file{config.cache} contains results you don't want to keep, you
-may remove or edit it.
+@item
+Bash implements the @code{!} keyword to negate the return value of
+a pipeline (@pxref{Pipelines}).
+Very useful when an @code{if} statement needs to act only if a test fails.
+The Bash @samp{-o pipefail} option to @code{set} will cause a pipeline to
+return a failure status if any command fails.
-If you need to do unusual things to compile the package, please
-try to figure out how @code{configure} could check whether or not
-to do them, and mail diffs or instructions to
-@code{bash-maintainers@@prep.ai.mit.edu} so they can be
-considered for the next release.
+@item
+Bash has the @code{time} reserved word and command timing (@pxref{Pipelines}).
+The display of the timing statistics may be controlled with the
+@env{TIMEFORMAT} variable.
-The file @file{configure.in} is used to create @code{configure}
-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
-newer.
+@item
+Bash implements the @code{for (( @var{expr1} ; @var{expr2} ; @var{expr3} ))}
+arithmetic for command, similar to the C language (@pxref{Looping Constructs}).
-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.
+@item
+Bash includes the @code{select} compound command, which allows the
+generation of simple menus (@pxref{Conditional Constructs}).
-The simplest way to compile Bash is:
+@item
+Bash includes the @code{[[} compound command, which makes conditional
+testing part of the shell grammar (@pxref{Conditional Constructs}), including
+optional regular expression matching.
-@enumerate
@item
-@code{cd} to the directory containing the source code and type
-@samp{./configure} to configure Bash for your system. If you're
-using @code{csh} on an old version of System V, you might need to
-type @samp{sh ./configure} instead to prevent @code{csh} from trying
-to execute @code{configure} itself.
+Bash provides optional case-insensitive matching for the @code{case} and
+@code{[[} constructs.
-Running @code{configure} takes awhile. While running, it prints some
-messages telling which features it is checking for.
+@item
+Bash includes brace expansion (@pxref{Brace Expansion}) and tilde
+expansion (@pxref{Tilde Expansion}).
@item
-Type @samp{make} to compile Bash and build the @code{bashbug} bug
-reporting script.
+Bash implements command aliases and the @code{alias} and @code{unalias}
+builtins (@pxref{Aliases}).
@item
-Optionally, type @samp{make tests} to run the Bash test suite.
+Bash provides shell arithmetic, the @code{((} compound command
+(@pxref{Conditional Constructs}),
+and arithmetic expansion (@pxref{Shell Arithmetic}).
@item
-Type @samp{make install} to install @code{bash} and @code{bashbug}.
-This will also install the manual pages and Info file.
+Variables present in the shell's initial environment are automatically
+exported to child processes. The Bourne shell does not normally do
+this unless the variables are explicitly marked using the @code{export}
+command.
-@end enumerate
+@item
+Bash supports the @samp{+=} assignment operator, which appends to the value
+of the variable named on the left hand side.
-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
-a different kind of computer), type @samp{make distclean}.
+@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}).
-@node Compilers and Options
-@section Compilers and Options
+@item
+The expansion @code{$@{#xx@}}, which returns the length of @code{$@{xx@}},
+is supported (@pxref{Shell Parameter Expansion}).
-Some systems require unusual options for compilation or linking
-that the @code{configure} script does not know about. You can
-give @code{configure} initial values for variables by setting
-them in the environment. Using a Bourne-compatible shell, you
-can do that on the command line like this:
+@item
+The expansion @code{$@{var:}@var{offset}@code{[:}@var{length}@code{]@}},
+which expands to the substring of @code{var}'s value of length
+@var{length}, beginning at @var{offset}, is present
+(@pxref{Shell Parameter Expansion}).
-@example
-CC=c89 CFLAGS=-O2 LIBS=-lposix ./configure
-@end example
+@item
+The expansion
+@code{$@{var/[/]}@var{pattern}@code{[/}@var{replacement}@code{]@}},
+which matches @var{pattern} and replaces it with @var{replacement} in
+the value of @code{var}, is available (@pxref{Shell Parameter Expansion}).
-On systems that have the @code{env} program, you can do it like this:
+@item
+The expansion @code{$@{!@var{prefix}*@}} expansion, which expands to
+the names of all shell variables whose names begin with @var{prefix},
+is available (@pxref{Shell Parameter Expansion}).
-@example
-env CPPFLAGS=-I/usr/local/include LDFLAGS=-s ./configure
-@end example
+@item
+Bash has @var{indirect} variable expansion using @code{$@{!word@}}
+(@pxref{Shell Parameter Expansion}).
-The configuration process uses GCC to build Bash if it
-is available.
+@item
+Bash can expand positional parameters beyond @code{$9} using
+@code{$@{@var{num}@}}.
-@node Compiling For Multiple Architectures
-@section Compiling For Multiple Architectures
+@item
+The @sc{posix} @code{$()} form of command substitution
+is implemented (@pxref{Command Substitution}),
+and preferred to the Bourne shell's @code{``} (which
+is also implemented for backwards compatibility).
-You can compile Bash for more than one kind of computer at the
-same time, by placing the object files for each architecture in their
-own directory. To do this, you must use a version of @code{make} that
-supports the @code{VPATH} variable, such as GNU @code{make}.
-@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
-source files are. @code{configure} automatically checks for the
-source code in the directory that @code{configure} is in and in `..'.
+@item
+Bash has process substitution (@pxref{Process Substitution}).
-If you have to use a @code{make} that does not supports the @code{VPATH}
-variable, you can compile Bash for one architecture at a
-time in the source code directory. After you have installed
-Bash for one architecture, use @samp{make distclean} before
-reconfiguring for another architecture.
+@item
+Bash automatically assigns variables that provide information about the
+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.
-Alternatively, if your system supports symbolic links, you can use the
-@file{support/mkclone} script to create a build tree which has
-symbolic links back to each file in the source directory. Here's an
-example that creates a build directory in the current directory from a
-source directory @file{/usr/gnu/src/bash-2.0}:
+@item
+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.
-@example
-bash /usr/gnu/src/bash-2.0/support/mkclone -s /usr/gnu/src/bash-2.0 .
-@end example
+@item
+The filename expansion bracket expression code uses @samp{!} and @samp{^}
+to negate the set of characters between the brackets.
+The Bourne shell uses only @samp{!}.
-@noindent
-The @code{mkclone} script requires Bash, so you must have already built
-Bash for at least one architecture before you can create build
-directories for other architectures.
+@item
+Bash implements the full set of @sc{posix} filename expansion operators,
+including @var{character classes}, @var{equivalence classes}, and
+@var{collating symbols} (@pxref{Filename Expansion}).
-@node Installation Names
-@section Installation Names
+@item
+Bash implements extended pattern matching features when the @code{extglob}
+shell option is enabled (@pxref{Pattern Matching}).
-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=PATH}.
+@item
+It is possible to have a variable and a function with the same name;
+@code{sh} does not separate the two name spaces.
-You can specify separate installation prefixes for
-architecture-specific files and architecture-independent files.
-If you give @code{configure} the option
-@samp{--exec-prefix=PATH}, the package will use @samp{PATH} as the
-prefix for installing programs and libraries. Documentation and
-other data files will still use the regular prefix.
+@item
+Bash functions are permitted to have local variables using the
+@code{local} builtin, and thus useful recursive functions may be written
+(@pxref{Bash Builtins}).
-@node Specifying the System Type
-@section Specifying the System Type
+@item
+Variable assignments preceding commands affect only that command, even
+builtins and functions (@pxref{Environment}).
+In @code{sh}, all variable assignments
+preceding commands are global unless the command is executed from the
+file system.
-There may be some features @code{configure} can not figure out
-automatically, but needs to determine by the type of host the
-package will run on. Usually @code{configure} can figure that
-out, but if it prints a message saying it can not guess the host
-type, give it the @samp{--host=TYPE} option. @samp{TYPE} can
-either be a short name for the system type, such as @samp{sun4},
-or a canonical name with three fields: @samp{CPU-COMPANY-SYSTEM}
-(e.g., @samp{sparc-sun-sunos4.1.2}).
+@item
+Bash performs filename expansion on filenames specified as operands
+to input and output redirection operators (@pxref{Redirections}).
-@noindent See the file @file{support/config.sub} for the possible
-values of each field.
+@item
+Bash contains the @samp{<>} redirection operator, allowing a file to be
+opened for both reading and writing, and the @samp{&>} redirection
+operator, for directing standard output and standard error to the same
+file (@pxref{Redirections}).
-@node Sharing Defaults
-@section Sharing Defaults
+@item
+Bash includes the @samp{<<<} redirection operator, allowing a string to
+be used as the standard input to a command.
-If you want to set default values for @code{configure} scripts to
-share, you can create a site shell script called
-@code{config.site} that gives default values for variables like
-@code{CC}, @code{cache_file}, and @code{prefix}. @code{configure}
-looks for @file{PREFIX/share/config.site} if it exists, then
-@file{PREFIX/etc/config.site} if it exists. Or, you can set the
-@code{CONFIG_SITE} environment variable to the location of the site
-script. A warning: the Bash @code{configure} looks for a site script,
-but not all @code{configure} scripts do.
+@item
+Bash implements the @samp{[n]<&@var{word}} and @samp{[n]>&@var{word}}
+redirection operators, which move one file descriptor to another.
-@node Operation Controls
-@section Operation Controls
+@item
+Bash treats a number of filenames specially when they are
+used in redirection operators (@pxref{Redirections}).
-@code{configure} recognizes the following options to control how it
-operates.
+@item
+Bash can open network connections to arbitrary machines and services
+with the redirection operators (@pxref{Redirections}).
-@table @code
+@item
+The @code{noclobber} option is available to avoid overwriting existing
+files with output redirection (@pxref{The Set Builtin}).
+The @samp{>|} redirection operator may be used to override @code{noclobber}.
-@item --cache-file=@var{FILE}
-Use and save the results of the tests in
-@var{FILE} instead of @file{./config.cache}. Set @var{FILE} to
-@file{/dev/null} to disable caching, for debugging
-@code{configure}.
+@item
+The Bash @code{cd} and @code{pwd} builtins (@pxref{Bourne Shell Builtins})
+each take @option{-L} and @option{-P} options to switch between logical and
+physical modes.
-@item --help
-Print a summary of the options to @code{configure}, and exit.
+@item
+Bash allows a function to override a builtin with the same name, and provides
+access to that builtin's functionality within the function via the
+@code{builtin} and @code{command} builtins (@pxref{Bash Builtins}).
-@item --quiet
-@itemx --silent
-@itemx -q
-Do not print messages saying which checks are being made.
+@item
+The @code{command} builtin allows selective disabling of functions
+when command lookup is performed (@pxref{Bash Builtins}).
-@item --srcdir=@var{DIR}
-Look for the Bash source code in directory @var{DIR}. Usually
-@code{configure} can determine that directory automatically.
+@item
+Individual builtins may be enabled or disabled using the @code{enable}
+builtin (@pxref{Bash Builtins}).
-@item --version
-Print the version of Autoconf used to generate the @code{configure}
-script, and exit.
-@end table
+@item
+The Bash @code{exec} builtin takes additional options that allow users
+to control the contents of the environment passed to the executed
+command, and what the zeroth argument to the command is to be
+(@pxref{Bourne Shell Builtins}).
-@code{configure} also accepts some other, not widely used, boilerplate
-options.
+@item
+Shell functions may be exported to children via the environment
+using @code{export -f} (@pxref{Shell Functions}).
-@node Optional Features
-@section Optional Features
+@item
+The Bash @code{export}, @code{readonly}, and @code{declare} builtins can
+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 @option{-n} option to remove various variable
+attributes, and @samp{name=value} arguments to set variable attributes
+and values simultaneously.
-The Bash @code{configure} has a number of @samp{--enable-@var{FEATURE}}
-options, where @var{FEATURE} indicates an optional part of the
-package. There are also several @samp{--with-@var{PACKAGE}} options,
-where @var{PACKAGE} is something like @samp{gnu-malloc} or
-@samp{purify} (for the Purify memory allocation checker). To
-turn off the default use of a package, use
-@samp{--without-@var{PACKAGE}}. To configure Bash without a feature
-that is enabled by default, use @samp{--disable-@var{FEATURE}}.
+@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 @env{$PATH}, using @samp{hash -p}
+(@pxref{Bourne Shell Builtins}).
-Here is a complete list of the @samp{--enable-} and
-@samp{--with-} options that the Bash @code{configure} recognizes.
+@item
+Bash includes a @code{help} builtin for quick reference to shell
+facilities (@pxref{Bash Builtins}).
-@table @code
-@item --with-afs
-Define if you are using the Andrew File System from Transarc.
+@item
+The @code{printf} builtin is available to display formatted output
+(@pxref{Bash Builtins}).
-@item --with-curses
-Use the curses library instead of the termcap library. This should
-be supplied if your system has an inadequate or incomplete termcap
-database.
+@item
+The Bash @code{read} builtin (@pxref{Bash Builtins})
+will read a line ending in @samp{\} with
+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 @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 @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
+@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 --with-glibc-malloc
-Use the @sc{GNU} libc version of @code{malloc} in
-@file{lib/malloc/gmalloc.c}. This is somewhat slower than the
-default @code{malloc}, but wastes considerably less space.
+@item
+The @code{return} builtin may be used to abort execution of scripts
+executed with the @code{.} or @code{source} builtins
+(@pxref{Bourne Shell Builtins}).
-@item --with-gnu-malloc
-Use the @sc{GNU} version of
-@code{malloc} in @file{lib/malloc/malloc.c}. This is not the same
-@code{malloc} that appears in @sc{GNU} libc, but an older version
-derived from the 4.2 @sc{BSD} @code{malloc}. This @code{malloc} is
-very fast, but wastes a lot of space. This option is enabled by
-default. The @file{NOTES} file contains a list of systems for
-which this should be turned off, and @code{configure} disables this
-option automatically for a number of systems.
+@item
+Bash includes the @code{shopt} builtin, for finer control of shell
+optional capabilities (@pxref{The Shopt Builtin}), and allows these options
+to be set and unset at shell invocation (@pxref{Invoking Bash}).
-@item --with-purify
-Define this to use the Purify memory allocation checker from Pure
-Software.
+@item
+Bash has much more optional behavior controllable with the @code{set}
+builtin (@pxref{The Set Builtin}).
-@item --enable-minimal-config
-This produces a shell with minimal features, close to the historical
-Bourne shell.
-@end table
+@item
+The @samp{-x} (@option{xtrace}) option displays commands other than
+simple commands when performing an execution trace
+(@pxref{The Set Builtin}).
-@noindent
-The @samp{minimal-config} option can be used to disable all of
-the following options, but it is processed first, so individual
-options may be enabled using @samp{enable-@var{FEATURE}}.
+@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.
-All of the following options except for @samp{disabled-builtins} and
-@samp{usg-echo-default} are
-enabled by default, unless the operating system does not provide the
-necessary support.
+@item
+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.
-@table @code
-@item --enable-alias
-Allow alias expansion and include the @code{alias} and @code{unalias}
-builtins.
+@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 --enable-array-variables
-Include support for one-dimensional array shell variables.
+@item
+The Bash @code{type} builtin is more extensive and gives more information
+about the names it finds (@pxref{Bash Builtins}).
-@item --enable-bang-history
-Include support for @code{csh}-like history substitution.
+@item
+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}).
-@item --enable-brace-expansion
-Include @code{csh}-like brace expansion
-( @code{b@{a,b@}c} @expansion{} @code{bac bbc} ).
+@item
+Bash implements a @code{csh}-like directory stack, and provides the
+@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
+@env{DIRSTACK} shell variable.
-@item --enable-command-timing
-Include support for recognizing @code{time} as a reserved word and for
-displaying timing statistics for the pipeline following @code{time}. This
-allows pipelines as well as shell builtins and functions to be timed.
+@item
+Bash interprets special backslash-escaped characters in the prompt
+strings when interactive (@pxref{Controlling the Prompt}).
-@item --enable-directory-stack
-Include support for a @code{csh}-like directory stack and the
-@code{pushd}, @code{popd}, and @code{dirs} builtins.
+@item
+The Bash restricted mode is more useful (@pxref{The Restricted Shell});
+the SVR4.2 shell restricted mode is too limited.
-@item --enable-disabled-builtins
-Allow builtin commands to be invoked via @samp{builtin xxx}
-even after @code{xxx} has been disabled using @samp{enable -n xxx}.
-See @ref{Bash Builtins}, for details of the @code{builtin} and
-@code{enable} builtin commands.
+@item
+The @code{disown} builtin can remove a job from the internal shell
+job table (@pxref{Job Control Builtins}) or suppress the sending
+of @code{SIGHUP} to a job when the shell exits as the result of a
+@code{SIGHUP}.
-@item --enable-dparen-arithmetic
-Include support for the @code{ksh} @code{((@dots{}))} command.
+@item
+Bash includes a number of features to support a separate debugger for
+shell scripts.
-@item --enable-help-builtin
-Include the @code{help} builtin, which displays help on shell builtins and
-variables.
+@item
+The SVR4.2 shell has two privilege-related builtins
+(@code{mldmode} and @code{priv}) not present in Bash.
-@item --enable-history
-Include command history and the @code{fc} and @code{history}
-builtin commands.
+@item
+Bash does not have the @code{stop} or @code{newgrp} builtins.
-@item --enable-job-control
-This enables job control features, if the @sc{OS} supports them.
+@item
+Bash does not use the @env{SHACCT} variable or perform shell accounting.
-@item --enable-process-substitution
-This enables process substitution (@pxref{Process Substitution}) if
-the @sc{OS} provides the necessary support.
+@item
+The SVR4.2 @code{sh} uses a @env{TIMEOUT} variable like Bash uses
+@env{TMOUT}.
-@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.
+@end itemize
-@item --enable-readline
-Include support for command-line editing and history with the Bash
-version of the Readline library.
+@noindent
+More features unique to Bash may be found in @ref{Bash Features}.
-@item --enable-restricted
-Include support for a @dfn{restricted shell}. If this is enabled, Bash,
-when called as @code{rbash}, enters a restricted mode. See
-@ref{The Restricted Shell}, for a description of restricted mode.
-@item --enable-select
-Include the @code{ksh} @code{select} builtin, which allows the
-generation of simple menus.
+@appendixsec Implementation Differences From The SVR4.2 Shell
-@item --enable-usg-echo-default
-Make the @code{echo} builtin expand backslash-escaped characters by default,
-without requiring the @samp{-e} option. This makes the Bash @code{echo}
-behave more like the System V version.
+Since Bash is a completely new implementation, it does not suffer from
+many of the limitations of the SVR4.2 shell. For instance:
-@end table
+@itemize @bullet
-The file @file{config.h.top} contains C Preprocessor
-@samp{#define} statements for options which are not settable from
-@code{configure}.
-Some of these are not meant to be changed; beware of the consequences if
-you do.
-Read the comments associated with each definition for more
-information about its effect.
+@item
+Bash does not fork a subshell when redirecting into or out of
+a shell control structure such as an @code{if} or @code{while}
+statement.
-@node Reporting Bugs
-@appendix Reporting Bugs
+@item
+Bash does not allow unbalanced quotes. The SVR4.2 shell will silently
+insert a needed closing quote at @code{EOF} under certain circumstances.
+This can be the cause of some hard-to-find errors.
-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.
+@item
+The SVR4.2 shell uses a baroque memory management scheme based on
+trapping @code{SIGSEGV}. If the shell is started from a process with
+@code{SIGSEGV} blocked (e.g., by using the @code{system()} C library
+function call), it misbehaves badly.
-Once you have determined that a bug actually exists, use the
-@code{bashbug} command to submit a bug report.
-If you have a fix, you are encouraged to mail that as well!
-Suggestions and `philosophical' bug reports may be mailed
-to @code{bug-bash@@prep.ai.MIT.Edu} or posted to the Usenet
-newsgroup @code{gnu.bash.bug}.
+@item
+In a questionable attempt at security, the SVR4.2 shell,
+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.
-All bug reports should include:
-@itemize @bullet
@item
-The version number of Bash.
+The SVR4.2 shell does not allow users to trap @code{SIGSEGV},
+@code{SIGALRM}, or @code{SIGCHLD}.
+
@item
-The hardware and operating system.
+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 compiler used to compile Bash.
+The SVR4.2 shell treats @samp{^} as the undocumented equivalent of
+@samp{|}.
+
@item
-A description of the bug behaviour.
+Bash allows multiple option arguments when it is invoked (@code{-x -v});
+the SVR4.2 shell allows only one option argument (@code{-xv}). In
+fact, some versions of the shell dump core if the second argument begins
+with a @samp{-}.
+
@item
-A short script or `recipe' which exercises the bug and may be used
-to reproduce it.
+The SVR4.2 shell exits a script if any builtin fails; Bash exits
+a script only if one of the @sc{posix} special builtins fails, and
+only for certain failures, as enumerated in the @sc{posix} standard.
+
+@item
+The SVR4.2 shell behaves differently when invoked as @code{jsh}
+(it turns on job control).
@end itemize
-@noindent
-@code{bashbug} inserts the first three items automatically into
-the template it provides for filing a bug report.
+@node GNU Free Documentation License
+@appendix GNU Free Documentation License
-Please send all reports concerning this manual to
-@code{chet@@ins.CWRU.Edu}.
+@include fdl.texi
+
+@node Indexes
+@appendix Indexes
+
+@menu
+* 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
@node Builtin Index
-@appendix Index of Shell Builtin Commands
+@appendixsec Index of Shell Builtin Commands
@printindex bt
@node Reserved Word Index
-@appendix Shell Reserved Words
+@appendixsec Index of Shell Reserved Words
@printindex rw
@node Variable Index
-@appendix Parameter and Variable Index
+@appendixsec Parameter and Variable Index
@printindex vr
@node Function Index
-@appendix Function Index
+@appendixsec Function Index
@printindex fn
@node Concept Index
-@appendix Concept Index
+@appendixsec Concept Index
@printindex cp
-@contents
@bye
projects / platform / upstream / bash.git / blobdiff