@settitle Bash Reference Manual
@c %**end of header
-@ignore
-Last Change: Tue Nov 13 12:48:51 EST 2001
-@end ignore
-
-@set EDITION 2.5a
-@set VERSION 2.05a
-@set UPDATED 13 November 2001
-@set UPDATE-MONTH November 2001
-
-@iftex
-@finalout
-@end iftex
-
@setchapternewpage odd
-@defcodeindex bt
-@defcodeindex rw
-@set BashFeatures
-@ifinfo
-@dircategory Utilities
-@direntry
- * Bash: (bash). The GNU Bourne-Again SHell.
-@end direntry
+@include version.texi
-@format
+@copying
This text is a brief description of the features that are present in
-the Bash shell.
+the Bash shell (version @value{VERSION}, @value{UPDATED}).
This is Edition @value{EDITION}, last updated @value{UPDATED},
of @cite{The GNU Bash Reference Manual},
for @code{Bash}, Version @value{VERSION}.
-Copyright (C) 1991-2001 Free Software Foundation, Inc.
+Copyright @copyright{} 1988-2005 Free Software Foundation, Inc.
Permission is granted to make and distribute verbatim copies of
this manual provided the copyright notice and this permission notice
are preserved on all copies.
-@ignore
-Permission is granted to process this file through TeX and print the
-results, provided the printed document carries copying permission
-notice identical to this one except for the removal of this paragraph
-(this paragraph not being relevant to the printed manual).
-
-@end ignore
-Permission is granted to copy and distribute modified versions of this
-manual under the conditions for verbatim copying, provided that the entire
-resulting derived work is distributed under the terms of a permission
-notice identical to this one.
-
-Permission is granted to copy and distribute translations of this manual
-into another language, under the above conditions for modified versions,
-except that this permission notice may be stated in a translation approved
-by the Free Software Foundation.
-@end format
-@end ifinfo
+@quotation
+Permission is granted to copy, distribute and/or modify this document
+under the terms of the GNU Free Documentation License, Version 1.1 or
+any later version published by the Free Software Foundation; with no
+Invariant Sections, with the Front-Cover texts being ``A GNU Manual,''
+and with the Back-Cover Texts as in (a) below. A copy of the license is
+included in the section entitled ``GNU Free Documentation License.''
+
+(a) The FSF's Back-Cover Text is: ``You have freedom to copy and modify
+this GNU Manual, like GNU software. Copies published by the Free
+Software Foundation raise funds for GNU development.''
+@end quotation
+@end copying
+
+@defcodeindex bt
+@defcodeindex rw
+@set BashFeatures
+
+@dircategory Basics
+@direntry
+* Bash: (bash). The GNU Bourne-Again SHell.
+@end direntry
+
+@finalout
@titlepage
@title Bash Reference Manual
@subtitle Reference Documentation for Bash
@subtitle Edition @value{EDITION}, for @code{Bash} Version @value{VERSION}.
-@subtitle @value{UPDATE-MONTH}
+@subtitle @value{UPDATED-MONTH}
@author Chet Ramey, Case Western Reserve University
@author Brian Fox, Free Software Foundation
+
@page
@vskip 0pt plus 1filll
-Copyright @copyright{} 1991-1999 Free Software Foundation, Inc.
+@insertcopying
-Permission is granted to make and distribute verbatim copies of
-this manual provided the copyright notice and this permission notice
-are preserved on all copies.
-
-Permission is granted to copy and distribute modified versions of this
-manual under the conditions for verbatim copying, provided that the entire
-resulting derived work is distributed under the terms of a permission
-notice identical to this one.
+@sp 1
+Published by the Free Software Foundation @*
+59 Temple Place, Suite 330, @*
+Boston, MA 02111-1307 @*
+USA @*
-Permission is granted to copy and distribute translations of this manual
-into another language, under the above conditions for modified versions,
-except that this permission notice may be stated in a translation approved
-by the Free Software Foundation.
@end titlepage
-@ifinfo
+@contents
+
+@ifnottex
@node Top, Introduction, (dir), (dir)
@top Bash Features
-@end ifinfo
-@ifinfo
This text is a brief description of the features that are present in
-the Bash shell.
+the Bash shell (version @value{VERSION}, @value{UPDATED})..
This is Edition @value{EDITION}, last updated @value{UPDATED},
of @cite{The GNU Bash Reference Manual},
for @code{Bash}, Version @value{VERSION}.
-Copyright (C) 1991, 1993, 1996 Free Software Foundation, Inc.
-
Bash contains features that appear in other popular shells, and some
features that only appear in Bash. Some of the shells that Bash has
borrowed concepts from are the Bourne Shell (@file{sh}), the Korn Shell
@menu
* Introduction:: An introduction to the shell.
-
* Definitions:: Some definitions used in the rest of this
manual.
-
* Basic Shell Features:: The shell "building blocks".
-
* Shell Builtin Commands:: Commands that are a part of the shell.
-
* Shell Variables:: Variables used or set by Bash.
-
* Bash Features:: Features found only in Bash.
-
-* Job Control:: A chapter describing what job control is
- and how Bash allows you to use it.
-
-* Using History Interactively:: Chapter dealing with history expansion
- rules.
-
+* Job Control:: What job control is and how Bash allows you
+ to use it.
+* Using History Interactively:: Command History Expansion
* Command Line Editing:: Chapter describing the command line
editing features.
-
* Installing Bash:: How to build and install Bash on your system.
-
* Reporting Bugs:: How to report bugs in Bash.
-
* Major Differences From The Bourne Shell:: A terse list of the differences
between Bash and historical
versions of /bin/sh.
-
+* Copying This Manual:: Copying this manual.
* Builtin Index:: Index of Bash builtin commands.
-
* Reserved Word Index:: Index of Bash reserved words.
-
* Variable Index:: Quick reference helps you find the
variable you want.
-
* Function Index:: Index of bindable Readline functions.
-
* Concept Index:: General index for concepts described in
this manual.
@end menu
-@end ifinfo
+@end ifnottex
@node Introduction
@chapter Introduction
@menu
* What is Bash?:: A short description of Bash.
-
* What is a shell?:: A brief introduction to shells.
@end menu
for the @sc{gnu} operating system.
The name is an acronym for the @samp{Bourne-Again SHell},
a pun on Stephen Bourne, the author of the direct ancestor of
-the current Unix shell @code{/bin/sh},
+the current Unix shell @code{sh},
which appeared in the Seventh Edition Bell Labs Research version
of Unix.
Like other @sc{gnu} software, Bash is quite portable. It currently runs
on nearly every version of Unix and a few other operating systems @minus{}
independently-supported ports exist for @sc{ms-dos}, @sc{os/2},
-Windows @sc{95/98}, and Windows @sc{nt}.
+and Windows platforms.
@node What is a shell?
@section What is a shell?
At its base, a shell is simply a macro processor that executes
-commands. A Unix shell is both a command interpreter, which
-provides the user interface to the rich set of @sc{gnu} utilities,
-and a programming language, allowing these utilitites to be
-combined. Files containing commands can be created, and become
+commands. The term macro processor means functionality where text
+and symbols are expanded to create larger expressions.
+
+A Unix shell is both a command interpreter and a programming
+language. As a command interpreter, the shell provides the user
+interface to the rich set of @sc{gnu} utilities. The programming
+language features allow these utilitites to be combined.
+Files containing commands can be created, and become
commands themselves. These new commands have the same status as
system commands in directories such as @file{/bin}, allowing users
-or groups to establish custom environments.
+or groups to establish custom environments to automate their common
+tasks.
+
+Shells may be used interactively or non-interactively. In
+interactive mode, they accept input typed from the keyboard.
+When executing non-interactively, shells execute commands read
+from a file.
A shell allows execution of @sc{gnu} commands, both synchronously and
asynchronously.
fine-grained control of the input and output of those commands.
Moreover, the shell allows control over the contents of commands'
environments.
-Shells may be used interactively or non-interactively: they accept
-input typed from the keyboard or from a file.
Shells also provide a small set of built-in
commands (@dfn{builtins}) implementing functionality impossible
Shells offer features geared specifically for
interactive use rather than to augment the programming language.
These interactive features include job control, command line
-editing, history and aliases. Each of these features is
+editing, command history and aliases. Each of these features is
described in this manual.
@node Definitions
The Bourne shell is
the traditional Unix shell originally written by Stephen Bourne.
All of the Bourne shell builtin commands are available in Bash,
-and the rules for evaluation and quoting are taken from the @sc{posix}
-1003.2 specification for the `standard' Unix shell.
+The rules for evaluation and quoting are taken from the @sc{posix}
+specification for the `standard' Unix shell.
This chapter briefly summarizes the shell's `building blocks':
commands, control structures, shell functions, shell @i{parameters},
* Shell Syntax:: What your input means to the shell.
* Shell Commands:: The types of commands you can use.
* Shell Functions:: Grouping commands by name.
-* Shell Parameters:: Special shell variables.
-* Shell Expansions:: How Bash expands variables and the various
+* Shell Parameters:: How the shell stores values.
+* Shell Expansions:: How Bash expands parameters and the various
expansions available.
* Redirections:: A way to control where input and output go.
* Executing Commands:: What happens when you run a command.
@section Shell Syntax
@menu
* Shell Operation:: The basic operation of the shell.
-
* Quoting:: How to remove the special meaning from characters.
-
* Comments:: How to specify comments.
@end menu
* Double Quotes:: How to suppress most of the interpretation of a
sequence of characters.
* ANSI-C Quoting:: How to expand ANSI-C sequences in quoted strings.
-
* Locale Translation:: How to translate strings into different languages.
@end menu
Each of the shell metacharacters (@pxref{Definitions})
has special meaning to the shell and must be quoted if it is to
represent itself.
-When the command history expansion facilities are being used, the
+When the command history expansion facilities are being used
+(@pxref{History Interaction}), the
@var{history expansion} character, usually @samp{!}, must be quoted
to prevent history expansion. @xref{Bash History Facilities}, for
more details concerning history expansion.
+
There are three quoting mechanisms: the
@var{escape character}, single quotes, and double quotes.
Enclosing characters in double quotes (@samp{"}) preserves the literal value
of all characters within the quotes, with the exception of
-@samp{$}, @samp{`}, and @samp{\}.
+@samp{$}, @samp{`}, @samp{\},
+and, when history expansion is enabled, @samp{!}.
The characters @samp{$} and @samp{`}
retain their special meaning within double quotes (@pxref{Shell Expansions}).
The backslash retains its special meaning only when followed by one of
special meaning are left unmodified.
A double quote may be quoted within double quotes by preceding it with
a backslash.
+If enabled, history expansion will be performed unless an @samp{!}
+appearing in double quotes is escaped using a backslash.
+The backslash preceding the @samp{!} is not removed.
The special parameters @samp{*} and @samp{@@} have special meaning
when in double quotes (@pxref{Shell Parameter Expansion}).
@item \x@var{HH}
the eight-bit character whose value is the hexadecimal value @var{HH}
(one or two hex digits)
+@item \c@var{x}
+a control-@var{x} character
@end table
@noindent
* Pipelines:: Connecting the input and output of several
commands.
* Lists:: How to execute commands sequentially.
-* Looping Constructs:: Shell commands for iterative action.
-* Conditional Constructs:: Shell commands for conditional execution.
-* Command Grouping:: Ways to group commands.
+* Compound Commands:: Shell commands for control flow.
@end menu
@node Simple Commands
Each command in a pipeline is executed in its own subshell
(@pxref{Command Execution Environment}). The exit
status of a pipeline is the exit status of the last command in the
-pipeline. If the reserved word @samp{!} precedes the pipeline, the
-exit status is the logical negation of the exit status of the last command.
+pipeline, unless the @code{pipefail} option is enabled
+(@pxref{The Set Builtin}).
+If @code{pipefail} is enabled, the pipeline's return status is the
+value of the last (rightmost) command to exit with a non-zero status,
+or zero if all commands exit successfully.
+If the reserved word @samp{!} precedes the pipeline, the
+exit status is the logical negation of the exit status as described
+above.
+The shell waits for all commands in the pipeline to terminate before
+returning a value.
@node Lists
@subsection Lists of Commands
have equal precedence, followed by @samp{;} and @samp{&},
which have equal precedence.
+A sequence of one or more newlines may appear in a @code{list}
+to delimit commands, equivalent to a semicolon.
+
If a command is terminated by the control operator @samp{&},
the shell executes the command asynchronously in a subshell.
This is known as executing the command in the @var{background}.
@sc{and} and @sc{or} lists is the exit status of the last command
executed in the list.
+@node Compound Commands
+@subsection Compound Commands
+@cindex commands, compound
+
+@menu
+* Looping Constructs:: Shell commands for iterative action.
+* Conditional Constructs:: Shell commands for conditional execution.
+* Command Grouping:: Ways to group commands.
+@end menu
+
+Compound commands are the shell programming constructs.
+Each construct begins with a reserved word or control operator and is
+terminated by a corresponding reserved word or operator.
+Any redirections (@pxref{Redirections}) associated with a compound command
+apply to all commands within that compound command unless explicitly overridden.
+
+Bash provides looping constructs, conditional commands, and mechanisms
+to group commands and execute them as a unit.
+
@node Looping Constructs
-@subsection Looping Constructs
+@subsubsection Looping Constructs
@cindex commands, looping
Bash supports the following looping constructs.
may be used to control loop execution.
@node Conditional Constructs
-@subsection Conditional Constructs
+@subsubsection Conditional Constructs
@cindex commands, conditional
@table @code
@code{case} will selectively execute the @var{command-list} corresponding to
the first @var{pattern} that matches @var{word}.
+If the shell option @code{nocasematch}
+(see the description of @code{shopt} in @ref{Bash Builtins})
+is enabled, the match is performed without regard to the case
+of alphabetic characters.
The @samp{|} is used to separate multiple patterns, and the @samp{)}
operator terminates a pattern list.
A list of patterns and an associated command-list is known
between the @samp{[[} and @samp{]]}; tilde expansion, parameter and
variable expansion, arithmetic expansion, command substitution, process
substitution, and quote removal are performed.
+Conditional operators such as @samp{-f} must be unquoted to be recognized
+as primaries.
When the @samp{==} and @samp{!=} operators are used, the string to the
right of the operator is considered a pattern and matched according
to the rules described below in @ref{Pattern Matching}.
+If the shell option @code{nocasematch}
+(see the description of @code{shopt} in @ref{Bash Builtins})
+is enabled, the match is performed without regard to the case
+of alphabetic characters.
The return value is 0 if the string matches or does not match
the pattern, respectively, and 1 otherwise.
Any part of the pattern may be quoted to force it to be matched as a
string.
+An additional binary operator, @samp{=~}, is available, with the same
+precedence as @samp{==} and @samp{!=}.
+When it is used, the string to the right of the operator is considered
+an extended regular expression and matched accordingly (as in @i{regex}3)).
+The return value is 0 if the string matches
+the pattern, and 1 otherwise.
+If the regular expression is syntactically incorrect, the conditional
+expression's return value is 2.
+If the shell option @code{nocasematch}
+(see the description of @code{shopt} in @ref{Bash Builtins})
+is enabled, the match is performed without regard to the case
+of alphabetic characters.
+Substrings matched by parenthesized subexpressions within the regular
+expression are saved in the array variable @code{BASH_REMATCH}.
+The element of @code{BASH_REMATCH} with index 0 is the portion of the string
+matching the entire regular expression.
+The element of @code{BASH_REMATCH} with index @var{n} is the portion of the
+string matching the @var{n}th parenthesized subexpression.
+
Expressions may be combined using the following operators, listed
in decreasing order of precedence:
True if either @var{expression1} or @var{expression2} is true.
@end table
@noindent
-The @code{&&} and @code{||} commands do not execute @var{expression2} if the
+The @code{&&} and @code{||} operators do not evaluate @var{expression2} if the
value of @var{expression1} is sufficient to determine the return
value of the entire conditional expression.
@end table
@node Command Grouping
-@subsection Grouping Commands
+@subsubsection Grouping Commands
@cindex commands, grouping
Bash provides two ways to group a list of commands to be executed
@end example
Placing a list of commands between parentheses causes a subshell
-to be created, and each of the commands in @var{list} to be executed
-in that subshell. Since the @var{list} is executed in a subshell,
-variable assignments do not remain in effect after the subshell completes.
+environment to be created (@pxref{Command Execution Environment}), and each
+of the commands in @var{list} to be executed in that subshell. Since the
+@var{list} is executed in a subshell, variable assignments do not remain in
+effect after the subshell completes.
@item @{@}
@rwindex @{
Functions are declared using this syntax:
@rwindex function
@example
-[ @code{function} ] @var{name} () @{ @var{command-list}; @}
+[ @code{function} ] @var{name} () @var{compound-command} [ @var{redirections} ]
@end example
This defines a shell function named @var{name}. The reserved
word @code{function} is optional.
If the @code{function} reserved
word is supplied, the parentheses are optional.
-The @var{body} of the function is the @var{command-list} between @{ and @}.
-This list is executed whenever @var{name} is specified as the
-name of a command. The exit status of a function is
-the exit status of the last command executed in the body.
-
-Note that for historical reasons, the curly braces that surround
-the body of the function must be separated from the body by
+The @var{body} of the function is the compound command
+@var{compound-command} (@pxref{Compound Commands}).
+That command is usually a @var{list} enclosed between @{ and @}, but
+may be any compound command listed above.
+@var{compound-command} is executed whenever @var{name} is specified as the
+name of a command.
+Any redirections (@pxref{Redirections}) associated with the shell function
+are performed when the function is executed.
+
+The exit status of a function definition is zero unless a syntax error
+occurs or a readonly function with the same name already exists.
+When executed, the exit status of a function is the exit status of the
+last command executed in the body.
+
+Note that for historical reasons, in the most common usage the curly braces
+that surround the body of the function must be separated from the body by
@code{blank}s or newlines.
This is because the braces are reserved words and are only recognized
as such when they are separated by whitespace.
-Also, the @var{command-list} must be terminated with a semicolon
-or a newline.
+Also, when using the braces, the @var{list} must be terminated by a semicolon,
+a @samp{&}, or a newline.
When a function is executed, the arguments to the
function become the positional parameters
during its execution (@pxref{Positional Parameters}).
The special parameter @samp{#} that expands to the number of
positional parameters is updated to reflect the change.
-Positional parameter @code{0} is unchanged.
-The @env{FUNCNAME} variable is set to the name of the function
-while the function is executing.
+Special parameter @code{0} is unchanged.
+The first element of the @env{FUNCNAME} variable is set to the
+name of the function while the function is executing.
+All other aspects of the shell execution
+environment are identical between a function and its caller
+with the exception that the @env{DEBUG} and @env{RETURN} traps
+are not inherited unless the function has been given the
+@code{trace} attribute using the @code{declare} builtin or
+the @code{-o functrace} option has been enabled with
+the @code{set} builtin,
+(in which case all functions inherit the @env{DEBUG} and @env{RETURN} traps).
+@xref{Bourne Shell Builtins}, for the description of the
+@code{trap} builtin.
If the builtin command @code{return}
is executed in a function, the function completes and
execution resumes with the next command after the function
-call. When a function completes, the values of the
+call.
+Any command associated with the @code{RETURN} trap is executed
+before execution resumes.
+When a function completes, the values of the
positional parameters and the special parameter @samp{#}
are restored to the values they had prior to the function's
execution. If a numeric argument is given to @code{return},
@code{local} builtin. These variables are visible only to
the function and the commands it invokes.
+Function names and definitions may be listed with the
+@option{-f} option to the @code{declare} or @code{typeset}
+builtin commands (@pxref{Bash Builtins}).
+The @option{-F} option to @code{declare} or @code{typeset}
+will list the function names only
+(and optionally the source file and line number, if the @code{extdebug}
+shell option is enabled).
+Functions may be exported so that subshells
+automatically have them defined with the
+@option{-f} option to the @code{export} builtin
+(@pxref{Bourne Shell Builtins}).
+Note that shell functions and variables with the same name may result
+in multiple identically-named entries in the environment passed to the
+shell's children.
+Care should be taken in cases where this may cause a problem.
+
Functions may be recursive. No limit is placed on the number of
recursive calls.
@menu
* Positional Parameters:: The shell's command-line arguments.
-* Special Parameters:: Parameters with special meanings.
+* Special Parameters:: Parameters denoted by special characters.
@end menu
A @var{parameter} is an entity that stores values.
It can be a @code{name}, a number, or one of the special characters
listed below.
-For the shell's purposes, a @var{variable} is a parameter denoted by a
-@code{name}.
+A @var{variable} is a parameter denoted by a @code{name}.
A variable has a @var{value} and zero or more @var{attributes}.
Attributes are assigned using the @code{declare} builtin command
(see the description of the @code{declare} builtin in @ref{Bash Builtins}).
command substitution, arithmetic expansion, and quote
removal (detailed below). If the variable has its @code{integer}
attribute set, then @var{value}
-is subject to arithmetic expansion even if the @code{$((@dots{}))}
+is evaluated as an arithmetic expression even if the @code{$((@dots{}))}
expansion is not used (@pxref{Arithmetic Expansion}).
Word splitting is not performed, with the exception
of @code{"$@@"} as explained below.
Filename expansion is not performed.
Assignment statements may also appear as arguments to the
+@code{alias},
@code{declare}, @code{typeset}, @code{export}, @code{readonly},
and @code{local} builtin commands.
+In the context where an assignment statement is assigning a value
+to a shell variable or array index (@pxref{Arrays}), the @samp{+=}
+operator can be used to
+append to or add to the variable's previous value.
+When @samp{+=} is applied to a variable for which the integer attribute
+has been set, @var{value} is evaluated as an arithmetic expression and
+added to the variable's current value, which is also evaluated.
+When @samp{+=} is applied to an array variable using compound assignment
+(@pxref{Arrays}), the
+variable's value is not unset (as it is when using @samp{=}), and new
+values are appended to the array beginning at one greater than the array's
+maximum index.
+When applied to a string-valued variable, @var{value} is expanded and
+appended to the variable's value.
+
@node Positional Parameters
@subsection Positional Parameters
@cindex parameters, positional
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 _
(An underscore.)
-At shell startup, set to the absolute filename of the shell or shell
-script being executed as passed in the argument list.
+At shell startup, set to the absolute pathname used to invoke the
+shell or shell script being executed as passed in the environment
+or argument list.
Subsequently, expands to the last argument to the previous command,
after expansion.
-Also set to the full pathname of each command executed and placed in
-the environment exported to that command.
+Also set to the full pathname used to invoke each command executed
+and placed in the environment exported to that command.
When checking mail, this parameter holds the name of the mail file.
@end vtable
@var{filename expansion} (@pxref{Filename Expansion}),
but the file names generated need not exist.
Patterns to be brace expanded take the form of an optional @var{preamble},
-followed by a series of comma-separated strings between a pair of braces,
+followed by either a series of comma-separated strings or a sequnce expression
+between a pair of braces,
followed by an optional @var{postscript}.
The preamble is prefixed to each string contained within the braces, and
the postscript is then appended to each resulting string, expanding left
ade ace abe
@end example
+A sequence expression takes the form @code{@{@var{x}..@var{y}@}},
+where @var{x} and @var{y} are either integers or single characters.
+When integers are supplied, the expression expands to each number between
+@var{x} and @var{y}, inclusive.
+When characters are supplied, the expression expands to each character
+lexicographically between @var{x} and @var{y}, inclusive. Note that
+both @var{x} and @var{y} must be of the same type.
+
Brace expansion is performed before any other expansions,
and any characters special to other expansions are preserved
in the result. It is strictly textual. Bash
is not considered eligible for brace expansion.
A correctly-formed brace expansion must contain unquoted opening
-and closing braces, and at least one unquoted comma.
+and closing braces, and at least one unquoted comma or a valid
+sequence expression.
Any incorrectly formed brace expansion is left unchanged.
+A @{ or @samp{,} may be quoted with a backslash to prevent its
+being considered part of a brace expression.
+To avoid conflicts with parameter expansion, the string @samp{$@{}
+is not considered eligible for brace expansion.
+
This construct is typically used as shorthand when the common
prefix of the strings to be generated is longer than in the
above example:
left unchanged.
Each variable assignment is checked for unquoted tilde-prefixes immediately
-following a @samp{:} or @samp{=}.
+following a @samp{:} or the first @samp{=}.
In these cases, tilde expansion is also performed.
Consequently, one may use file names with tildes in assignments to
@env{PATH}, @env{MAILPATH}, and @env{CDPATH},
expanded and that value is used in the rest of the substitution, rather
than the value of @var{parameter} itself.
This is known as @code{indirect expansion}.
-The exception to this is the expansion of $@{!@var{prefix*@}}
+The exceptions to this are the expansions of $@{!@var{prefix*}@}
+and $@{!@var{name}[@@]@}
described below.
+The exclamation point must immediately follow the left brace in order to
+introduce indirection.
In each of the cases below, @var{word} is subject to tilde expansion,
parameter expansion, command substitution, and arithmetic expansion.
If @var{parameter}
is unset or null, the expansion of @var{word}
is assigned to @var{parameter}.
-The value of @var{parameter}
-is then substituted. Positional parameters and special parameters may
-not be assigned to in this way.
+The value of @var{parameter} is then substituted.
+Positional parameters and special parameters may not be assigned to
+in this way.
@item $@{@var{parameter}:?@var{word}@}
If @var{parameter}
If @var{parameter} is an array name indexed by @samp{@@} or @samp{*},
the result is the @var{length}
members of the array beginning with @code{$@{@var{parameter}[@var{offset}]@}}.
+A negative @var{offset} is taken relative to one greater than the maximum
+index of the specified array.
+Note that a negative offset must be separated from the colon by at least
+one space to avoid being confused with the @samp{:-} expansion.
Substring indexing is zero-based unless the positional parameters
are used, in which case the indexing starts at 1.
@item $@{!@var{prefix}*@}
+@itemx $@{!@var{prefix}@@@}
Expands to the names of variables whose names begin with @var{prefix},
separated by the first character of the @env{IFS} special variable.
+@item $@{!@var{name}[@@]@}
+@itemx $@{!@var{name}[*]@}
+If @var{name} is an array variable, expands to the list of array indices
+(keys) assigned in @var{name}.
+If @var{name} is not an array, expands to 0 if @var{name} is set and null
+otherwise.
+When @samp{@@} is used and the expansion appears within double quotes, each
+key expands to a separate word.
+
@item $@{#@var{parameter}@}
The length in characters of the expanded value of @var{parameter} is
substituted.
a double quote inside the parentheses is not treated specially.
All tokens in the expression undergo parameter expansion, command
substitution, and quote removal.
-Arithmetic substitutions may be nested.
+Arithmetic expansions may be nested.
The evaluation is performed according to the rules listed below
(@pxref{Shell Arithmetic}).
unchanged.
If the @code{nullglob} option is set, and no matches are found, the word
is removed.
+If the @code{failglob} shell option is set, and no matches are found,
+an error message is printed and the command is not executed.
If the shell option @code{nocaseglob} is enabled, the match is performed
without regard to the case of alphabetic characters.
See the description of @code{shopt} in @ref{Bash Builtins},
for a description of the @code{nocaseglob}, @code{nullglob},
-and @code{dotglob} options.
+@code{failglob}, and @code{dotglob} options.
The @env{GLOBIGNORE}
shell variable may be used to restrict the set of filenames matching a
is set, each matching filename that also matches one of the patterns in
@env{GLOBIGNORE} is removed from the list of matches. The filenames
@file{.} and @file{..}
-are always ignored, even when @env{GLOBIGNORE}
-is set. However, setting @env{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.
@cindex matching, pattern
Any character that appears in a pattern, other than the special pattern
-characters described below, matches itself. The @sc{nul} character may not
-occur in a pattern. The special pattern characters must be quoted if
-they are to be matched literally.
+characters described below, matches itself.
+The @sc{nul} character may not occur in a pattern.
+A backslash escapes the following character; the
+escaping backslash is discarded when matching.
+The special pattern characters must be quoted if they are to be matched
+literally.
The special pattern characters have the following meanings:
@table @code
following classes defined in the @sc{posix} 1003.2 standard:
@example
alnum alpha ascii blank cntrl digit graph lower
-print punct space upper xdigit
+print punct space upper word xdigit
@end example
@noindent
A character class matches any character belonging to that class.
+The @code{word} character class matches letters, digits, and the character
+@samp{_}.
Within @samp{[} and @samp{]}, an @var{equivalence class} can be
specified using the syntax @code{[=}@var{c}@code{=]}, which
Matches one or more occurrences of the given patterns.
@item @@(@var{pattern-list})
-Matches exactly one of the given patterns.
+Matches one of the given patterns.
@item !(@var{pattern-list})
Matches anything except one of the given patterns.
A failure to open or create a file causes the redirection to fail.
+Redirections using file descriptors greater than 9 should be used with
+care, as they may conflict with file descriptors the shell uses
+internally.
+
@subsection Redirecting Input
Redirection of input causes the file whose name results from
the expansion of @var{word}
The general format for redirecting input is:
@example
-[n]<@var{word}
+[@var{n}]<@var{word}
@end example
@subsection Redirecting Output
Redirection of output causes the file whose name results from
the expansion of @var{word}
-to be opened for writing on file descriptor @code{n},
-or the standard output (file descriptor 1) if @code{n}
+to be opened for writing on file descriptor @var{n},
+or the standard output (file descriptor 1) if @var{n}
is not specified. If the file does not exist it is created;
if it does exist it is truncated to zero size.
The general format for redirecting output is:
@example
-[n]>[|]@var{word}
+[@var{n}]>[|]@var{word}
@end example
If the redirection operator is @samp{>}, and the @code{noclobber}
Redirection of output in this fashion
causes the file whose name results from
the expansion of @var{word}
-to be opened for appending on file descriptor @code{n},
-or the standard output (file descriptor 1) if @code{n}
+to be opened for appending on file descriptor @var{n},
+or the standard output (file descriptor 1) if @var{n}
is not specified. If the file does not exist it is created.
The general format for appending output is:
@example
-[n]>>@var{word}
+[@var{n}]>>@var{word}
@end example
@subsection Redirecting Standard Output and Standard Error
the lines read up to that point are then used as the standard
input for a command.
-The format of here-documents is as follows:
+The format of here-documents is:
@example
<<[@minus{}]@var{word}
@var{here-document}
This allows here-documents within shell scripts to be indented in a
natural fashion.
+@subsection Here Strings
+A variant of here documents, the format is:
+@example
+<<< @var{word}
+@end example
+
+The @var{word} is expanded and supplied to the command on its standard
+input.
+
@subsection Duplicating File Descriptors
The redirection operator
@example
-[n]<&@var{word}
+[@var{n}]<&@var{word}
@end example
@noindent
is used to duplicate input file descriptors.
If @var{word}
-expands to one or more digits, the file descriptor denoted by @code{n}
+expands to one or more digits, the file descriptor denoted by @var{n}
is made to be a copy of that file descriptor.
If the digits in @var{word} do not specify a file descriptor open for
input, a redirection error occurs.
If @var{word}
-evaluates to @samp{-}, file descriptor @code{n} is closed. If
-@code{n} is not specified, the standard input (file descriptor 0) is used.
+evaluates to @samp{-}, file descriptor @var{n} is closed. If
+@var{n} is not specified, the standard input (file descriptor 0) is used.
The operator
@example
-[n]>&@var{word}
+[@var{n}]>&@var{word}
@end example
@noindent
is used similarly to duplicate output file descriptors. If
-@code{n}
-is not specified, the standard output (file descriptor 1) is used.
+@var{n} is not specified, the standard output (file descriptor 1) is used.
If the digits in @var{word} do not specify a file descriptor open for
output, a redirection error occurs.
-As a special case, if @code{n} is omitted, and @var{word} does not
+As a special case, if @var{n} is omitted, and @var{word} does not
expand to one or more digits, the standard output and standard
error are redirected as described previously.
+@subsection Moving File Descriptors
+The redirection operator
+@example
+[@var{n}]<&@var{digit}-
+@end example
+@noindent
+moves the file descriptor @var{digit} to file descriptor @var{n},
+or the standard input (file descriptor 0) if @var{n} is not specified.
+@var{digit} is closed after being duplicated to @var{n}.
+
+Similarly, the redirection operator
+@example
+[@var{n}]>&@var{digit}-
+@end example
+@noindent
+moves the file descriptor @var{digit} to file descriptor @var{n},
+or the standard output (file descriptor 1) if @var{n} is not specified.
+
@subsection Opening File Descriptors for Reading and Writing
The redirection operator
@example
-[n]<>@var{word}
+[@var{n}]<>@var{word}
@end example
@noindent
causes the file whose name is the expansion of @var{word}
to be opened for both reading and writing on file descriptor
-@code{n}, or on file descriptor 0 if @code{n}
+@var{n}, or on file descriptor 0 if @var{n}
is not specified. If the file does not exist, it is created.
@node Executing Commands
@menu
* Simple Command Expansion:: How Bash expands simple commands before
executing them.
-
* Command Search and Execution:: How Bash finds commands and runs them.
-
* Command Execution Environment:: The environment in which Bash
executes commands that are not
shell builtins.
-
* Environment:: The environment given to a command.
-
* Exit Status:: The status returned by commands and how Bash
interprets it.
-
* Signals:: What happens when Bash or a command it runs
receives a signal.
-
@end menu
@node Simple Command Expansion
the file creation mode mask
@item
-shell variables marked for export, along with variables exported for
-the command, passed in the environment (@pxref{Environment})
+shell variables and functions marked for export, along with variables
+exported for the command, passed in the environment (@pxref{Environment})
@item
traps caught by the shell are reset to the values inherited from the
A command invoked in this separate environment cannot affect the
shell's execution environment.
-Command substitution and asynchronous commands are invoked in a
+Command substitution, commands grouped with parentheses,
+and asynchronous commands are invoked in a
subshell environment that is a duplicate of the shell environment,
except that traps caught by the shell are reset to the values
that the shell inherited from its parent at invocation. Builtin
If job control is in effect (@pxref{Job Control}), Bash
ignores @code{SIGTTIN}, @code{SIGTTOU}, and @code{SIGTSTP}.
-Commands started by Bash have signal handlers set to the
+Non-builtin commands started by Bash have signal handlers set to the
values inherited by the shell from its parent.
When job control is not in effect, asynchronous commands
-ignore @code{SIGINT} and @code{SIGQUIT} as well.
+ignore @code{SIGINT} and @code{SIGQUIT} in addition to these inherited
+handlers.
Commands run as a result of
command substitution ignore the keyboard-generated job control signals
@code{SIGTTIN}, @code{SIGTTOU}, and @code{SIGTSTP}.
(@pxref{Bash Builtins}), Bash sends a @code{SIGHUP} to all jobs when
an interactive login shell exits.
-When Bash receives a signal for which a trap has been set while waiting
-for a command to complete, the trap will not be executed until the
-command completes.
+If Bash is waiting for a command to complete and receives a signal
+for which a trap has been set, the trap will not be executed until
+the command completes.
When Bash is waiting for an asynchronous
command via the @code{wait} builtin, the reception of a signal for
which a trap has been set will cause the @code{wait} builtin to return
Many of the builtins have been extended by @sc{posix} or Bash.
+Unless otherwise noted, each builtin command documented as accepting
+options preceded by @samp{-} accepts @samp{--}
+to signify the end of the options.
+For example, the @code{:}, @code{true}, @code{false}, and @code{test}
+builtins do not accept options.
+
@node Bourne Shell Builtins
@section Bourne Shell Builtins
@item cd
@btindex cd
@example
-cd [-LP] [@var{directory}]
+cd [-L|-P] [@var{directory}]
@end example
-Change the current working directory to @var{directory}. If @var{directory}
-is not given, the value of the @env{HOME} shell variable is used. If the
-shell variable @env{CDPATH} exists, it is used as a search path. If
-@var{directory} begins with a slash, @env{CDPATH} is not used.
-The @option{-P} option means
-to not follow symbolic links; symbolic links are followed by default
-or with the @option{-L} option.
+Change the current working directory to @var{directory}.
+If @var{directory} is not given, the value of the @env{HOME} shell
+variable is used.
+If the shell variable @env{CDPATH} exists, it is used as a search path.
+If @var{directory} begins with a slash, @env{CDPATH} is not used.
+
+The @option{-P} option means to not follow symbolic links; symbolic
+links are followed by default or with the @option{-L} option.
If @var{directory} is @samp{-}, it is equivalent to @env{$OLDPWD}.
+
+If a non-empty directory name from @env{CDPATH} is used, or if
+@samp{-} is the first argument, and the directory change is
+successful, the absolute pathname of the new working directory is
+written to the standard output.
+
The return status is zero if the directory is successfully changed,
non-zero otherwise.
If no @var{names} are supplied, or if the @option{-p} option is given, a
list of exported names 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 hash
@btindex hash
@example
-hash [-r] [-p @var{filename}] [-t] [@var{name}]
+hash [-'r] [-p @var{filename}] [-dt] [@var{name}]
@end example
Remember the full pathnames of commands specified as @var{name} arguments,
so they need not be searched for on subsequent invocations.
The @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.
-If no arguments are given, information about remembered commands is printed.
+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 readonly
@btindex readonly
@example
-readonly [-apf] [@var{name}] @dots{}
+readonly [-apf] [@var{name}[=@var{value}]] @dots{}
@end example
Mark each @var{name} as readonly.
The values of these names may not be changed by subsequent assignment.
option is supplied, a list of all readonly names is printed.
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.
with the @code{.} (or @code{source}) builtin, returning either @var{n} or
the exit status of the last command executed within the script as the exit
status of the script.
+Any command associated with the @code{RETURN} trap is executed
+before execution resumes after the function or script.
The return status is non-zero if @code{return} is used outside a function
and not during the execution of a script by @code{.} or @code{source}.
Each operator and operand must be a separate argument.
Expressions are composed of the primaries described below in
@ref{Bash Conditional Expressions}.
+@code{test} does not accept any options, nor does it accept and ignore
+an argument of @option{--} as signifying the end of options.
When the @code{[} form is used, the last argument to the command must
be a @code{]}.
trap [-lp] [@var{arg}] [@var{sigspec} @dots{}]
@end example
The commands in @var{arg} are to be read and executed when the
-shell receives signal @var{sigspec}. If @var{arg} is absent or
-equal to @samp{-}, all specified signals are reset to the values
-they had when the shell was started.
+shell receives signal @var{sigspec}. If @var{arg} is absent (and
+there is a single @var{sigspec}) or
+equal to @samp{-}, each specified signal's disposition is reset
+to the value it had when the shell was started.
If @var{arg} is the null string, then the signal specified by
each @var{sigspec} is ignored by the shell and commands it invokes.
If @var{arg} is not present and @option{-p} has been supplied,
only @option{-p} is given, @code{trap} prints the list of commands
associated with each signal number in a form that may be reused as
shell input.
-Each @var{sigspec} is either a signal name such as @code{SIGINT} (with
-or without the @code{SIG} prefix) or a signal number.
+The @option{-l} option causes the shell to print a list of signal names
+and their corresponding numbers.
+Each @var{sigspec} is either a signal name or a signal number.
+Signal names are case insensitive and the @code{SIG} prefix is optional.
If a @var{sigspec}
is @code{0} or @code{EXIT}, @var{arg} is executed when the shell exits.
If a @var{sigspec} is @code{DEBUG}, the command @var{arg} is executed
-after every simple command.
+before every simple command, @code{for} command, @code{case} command,
+@code{select} command, every arithmetic @code{for} command, and before
+the first command executes in a shell function.
+Refer to the description of the @code{extglob} option to the
+@code{shopt} builtin (@pxref{Bash Builtins}) for details of its
+effect on the @code{DEBUG} trap.
If a @var{sigspec} is @code{ERR}, the command @var{arg}
-is executed whenever a simple command has a non-zero exit status.
-The @code{ERR} trap is not executed if the failed command is part of an
-@code{until} or @code{while} loop, part of an @code{if} statement,
+is executed whenever a simple command has a non-zero exit status,
+subject to the following conditions.
+The @code{ERR} trap is not executed if the failed command is part of the
+command list immediately following an @code{until} or @code{while} keyword,
+part of the test in an @code{if} statement,
part of a @code{&&} or @code{||} list, or if the command's return
status is being inverted using @code{!}.
-The @option{-l} option causes the shell to print a list of signal names
-and their corresponding numbers.
+These are the same conditions obeyed by the @code{errexit} option.
+If a @var{sigspec} is @code{RETURN}, the command @var{arg} is executed
+each time a shell function or a script executed with the @code{.} or
+@code{source} builtins finishes executing.
Signals ignored upon entry to the shell cannot be trapped or reset.
Trapped signals are reset to their original values in a child
If the @option{-f} option is given, the @var{name}s refer to shell
functions, and the function definition is removed.
Readonly variables and functions may not be unset.
-The return status is zero unless a @var{name} does not exist or is
-readonly.
+The return status is zero unless a @var{name} is readonly.
@end table
@node Bash Builtins
bind [-m @var{keymap}] -f @var{filename}
bind [-m @var{keymap}] -x @var{keyseq:shell-command}
bind [-m @var{keymap}] @var{keyseq:function-name}
+bind @var{readline-command}
@end example
Display current Readline (@pxref{Command Line Editing})
-key and function bindings, or
-bind a key sequence to a Readline function or macro. The
-binding syntax accepted is identical to that of
+key and function bindings,
+bind a key sequence to a Readline function or macro,
+or set a Readline variable.
+Each non-option argument is a command as it would appear in a
a Readline initialization file (@pxref{Readline Init File}),
-but each binding must be passed as a separate argument: e.g.,
+but each binding or command must be passed as a separate argument; e.g.,
@samp{"\C-x\C-r":re-read-init-file}.
Options, if supplied, have the following meanings:
The return status is non-zero if @var{shell-builtin} is not a shell
builtin command.
+@item caller
+@btindex caller
+@example
+caller [@var{expr}]
+@end example
+Returns the context of any active subroutine call (a shell function or
+a script executed with the @code{.} or @code{source} builtins).
+
+Without @var{expr}, @code{caller} displays the line number and source
+filename of the current subroutine call.
+If a non-negative integer is supplied as @var{expr}, @code{caller}
+displays the line number, subroutine name, and source file corresponding
+to that position in the current execution call stack. This extra
+information may be used, for example, to print a stack trace. The
+current frame is frame 0.
+
+The return value is 0 unless the shell is not executing a subroutine
+call or @var{expr} does not correspond to a valid position in the
+call stack.
+
@item command
@btindex command
@example
@item declare
@btindex declare
@example
-declare [-afFrxi] [-p] [@var{name}[=@var{value}]]
+declare [-afFirtx] [-p] [@var{name}[=@var{value}] @dots{}]
@end example
Declare variables and give them attributes. If no @var{name}s
are given, then display the values of variables instead.
The @option{-p} option will display the attributes and values of each
-@var{name}. When @option{-p} is used, additional options are ignored.
+@var{name}.
+When @option{-p} is used, additional options are ignored.
The @option{-F} option inhibits the display of function definitions;
-only the function name and attributes are printed. @option{-F} implies
-@option{-f}. The following options can be used to restrict output
-to variables with the specified attributes or to give variables
-attributes:
+only the function name and attributes are printed.
+If the @code{extdebug} shell option is enabled using @code{shopt}
+(@pxref{Bash Builtins}), the source file name and line number where
+the function is defined are displayed as well.
+@option{-F} implies @option{-f}.
+The following options can be used to restrict output to variables with
+the specified attributes or to give variables attributes:
@table @code
@item -a
Make @var{name}s readonly. These names cannot then be assigned values
by subsequent assignment statements or unset.
+@item -t
+Give each @var{name} the @code{trace} attribute.
+Traced functions inherit the @code{DEBUG} and @code{RETURN} traps from
+the calling shell.
+The trace attribute has no special meaning for variables.
+
@item -x
Mark each @var{name} for export to subsequent commands via
the environment.
Using @samp{+} instead of @samp{-} turns off the attribute instead.
When used in a function, @code{declare} makes each @var{name} local,
-as with the @code{local} command.
+as with the @code{local} command. If a variable name is followed by
+=@var{value}, the value of the variable is set to @var{value}.
The return status is zero unless an invalid option is encountered,
an attempt is made to define a function using @samp{-f foo=bar},
The @code{xpg_echo} shell option may be used to
dynamically determine whether or not @code{echo} expands these
escape characters by default.
+@code{echo} does not interpret @option{--} to mean the end of options.
+
@code{echo} interprets the following escape sequences:
@table @code
@item \a
vertical tab
@item \\
backslash
+@item \0@var{nnn}
+the eight-bit character whose value is the octal value @var{nnn}
+(zero to three octal digits)
@item \@var{nnn}
the eight-bit character whose value is the octal value @var{nnn}
-(one to three digits)
+(one to three octal digits)
@item \x@var{HH}
the eight-bit character whose value is the hexadecimal value @var{HH}
(one or two hex digits)
@item local
@btindex local
@example
-local [@var{option}] @var{name}[=@var{value}]
+local [@var{option}] @var{name}[=@var{value}] @dots{}
@end example
For each argument, a local variable named @var{name} is created,
and assigned @var{value}.
@item printf
@btindex printf
@example
-@code{printf} @var{format} [@var{arguments}]
+@code{printf} [-v @var{var}] @var{format} [@var{arguments}]
@end example
Write the formatted @var{arguments} to the standard output under the
control of the @var{format}.
@var{argument}.
In addition to the standard @code{printf(1)} formats, @samp{%b} causes
@code{printf} to expand backslash escape sequences in the corresponding
-@var{argument}, and @samp{%q} causes @code{printf} to output the
+@var{argument},
+(except that @samp{\c} terminates output, backslashes in
+@samp{\'}, @samp{\"}, and @samp{\?} are not removed, and octal escapes
+beginning with @samp{\0} may contain up to four digits),
+and @samp{%q} causes @code{printf} to output the
corresponding @var{argument} in a format that can be reused as shell input.
+The @option{-v} option causes the output to be assigned to the variable
+@var{var} rather than being printed to the standard output.
+
The @var{format} is reused as necessary to consume all of the @var{arguments}.
If the @var{format} requires more @var{arguments} than are supplied, the
extra format specifications behave as if a zero value or null string, as
@item read
@btindex read
@example
-read [-ers] [-a @var{aname}] [-p @var{prompt}] [-t @var{timeout}] [-n @var{nchars}] [-d @var{delim}] [@var{name} @dots{}]
+read [-ers] [-a @var{aname}] [-d @var{delim}] [-n @var{nchars}] [-p @var{prompt}] [-t @var{timeout}] [-u @var{fd}] [@var{name} @dots{}]
@end example
-One line is read from the standard input, and the first word
+One line is read from the standard input, or from the file descriptor
+@var{fd} supplied as an argument to the @option{-u} option, and the first word
is assigned to the first @var{name}, the second word to the second @var{name},
and so on, with leftover words and their intervening separators assigned
to the last @var{name}.
-If there are fewer words read from the standard input than names,
+If there are fewer words read from the input stream than names,
the remaining names are assigned empty values.
The characters in the value of the @env{IFS} variable
are used to split the line into words.
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 or @code{read}
-times out.
+The return code is zero, unless end-of-file is encountered, @code{read}
+times out, or an invalid file descriptor is supplied as the argument to
+@option{-u}.
Options, if supplied, have the following meanings:
@table @code
This option has no effect if @code{read} is not reading input from the
terminal or a pipe.
+@item -u @var{fd}
+Read input from file descriptor @var{fd}.
+
@end table
@item shopt
@ref{Aliases}.
This option is enabled by default for interactive shells.
+@item extdebug
+If set, behavior intended for use by debuggers is enabled:
+
+@enumerate
+@item
+The @option{-F} option to the @code{declare} builtin (@pxref{Bash Builtins})
+displays the source file name and line number corresponding to each function
+name supplied as an argument.
+
+@item
+If the command run by the @code{DEBUG} trap returns a non-zero value, the
+next command is skipped and not executed.
+
+@item
+If the command run by the @code{DEBUG} trap returns a value of 2, and the
+shell is executing in a subroutine (a shell function or a shell script
+executed by the @code{.} or @code{source} builtins), a call to
+@code{return} is simulated.
+
+@item
+@code{BASH_ARGC} and @code{BASH_ARGV} are updated as described in their
+descriptions (@pxref{Bash Variables}).
+
+@item
+Function tracing is enabled: command substitution, shell functions, and
+subshells invoked with @code{( @var{command} )} inherit the
+@code{DEBUG} and @code{RETURN} traps.
+
+@item
+Error tracing is enabled: command substitution, shell functions, and
+subshells invoked with @code{( @var{command} )} inherit the
+@code{ERROR} trap.
+@end enumerate
+
@item extglob
If set, the extended pattern matching features described above
(@pxref{Pattern Matching}) are enabled.
+@item extquote
+If set, @code{$'@var{string}'} and @code{$"@var{string}"} quoting is
+performed within @code{$@{@var{parameter}@}} expansions
+enclosed in double quotes. This option is enabled by default.
+
+@item failglob
+If set, patterns which fail to match filenames during pathname expansion
+result in an expansion error.
+
+@item force_fignore
+If set, the suffixes specified by the @env{FIGNORE} shell variable
+cause words to be ignored when performing word completion even if
+the ignored words are the only possible completions.
+@xref{Bash Variables}, for a description of @env{FIGNORE}.
+This option is enabled by default.
+
+@item gnu_errfmt
+If set, shell error messages are written in the standard @sc{gnu} error
+message format.
+
@item histappend
If set, the history list is appended to the file named by the value
of the @env{HISTFILE}
If set, Bash matches filenames in a case-insensitive fashion when
performing filename expansion.
+@item nocasematch
+If set, Bash matches patterns in a case-insensitive fashion when
+performing matching while executing @code{case} or @code{[[}
+conditional commands.
+
@item nullglob
If set, Bash allows filename patterns which match no
files to expand to a null string, rather than themselves.
This option is enabled by default.
@item promptvars
-If set, prompt strings undergo variable and parameter expansion after
-being expanded (@pxref{Printing a Prompt}).
+If set, prompt strings undergo
+parameter expansion, command substitution, arithmetic
+expansion, and quote removal after being expanded
+as described below (@pxref{Printing a Prompt}).
This option is enabled by default.
@item restricted_shell
@item type
@btindex type
@example
-type [-atp] [@var{name} @dots{}]
+type [-afptP] [@var{name} @dots{}]
@end example
For each @var{name}, indicate how it would be interpreted if used as a
command name.
of the disk file that would be executed, or nothing if @option{-t}
would not return @samp{file}.
+The @option{-P} option forces a path search for each @var{name}, even if
+@option{-t} would not return @samp{file}.
+
+If a command is hashed, @option{-p} and @option{-P} print the hashed value,
+not necessarily the file that appears first in @code{$PATH}.
+
If the @option{-a} option is used, @code{type} returns all of the places
that contain an executable named @var{file}.
This includes aliases and functions, if and only if the @option{-p} option
is not also used.
+If the @option{-f} option is used, @code{type} does not attempt to find
+shell functions, as with the @code{command} builtin.
+
The return status is zero if any of the @var{names} are found, non-zero
if none are found.
@item typeset
@btindex typeset
@example
-typeset [-afFrxi] [-p] [@var{name}[=@var{value}]]
+typeset [-afFrxi] [-p] [@var{name}[=@var{value}] @dots{}]
@end example
The @code{typeset} command is supplied for compatibility with the Korn
shell; however, it has been deprecated in favor of the @code{declare}
If no options or arguments are supplied, @code{set} displays the names
and values of all shell variables and functions, sorted according to the
-current locale, in a format that may be reused as input.
+current locale, in a format that may be reused as input
+for setting or resetting the currently-set variables.
+Read-only variables cannot be reset.
+In @sc{posix} mode, only shell variables are listed.
When options are supplied, they set or unset shell attributes.
Options, if specified, have the following meanings:
@item -e
Exit immediately if a simple command (@pxref{Simple Commands}) exits
-with a non-zero status, unless the command that fails is part of an
-@code{until} or @code{while} loop, part of an @code{if} statement,
+with a non-zero status, unless the command that fails is part of the
+command list immediately following a @code{while} or @code{until}
+keyword, part of the test in an @code{if} statement,
part of a @code{&&} or @code{||} list, or if the command's return
status is being inverted using @code{!}.
A trap on @code{ERR}, if set, is executed before the shell exits.
@item errexit
Same as @code{-e}.
+@item errtrace
+Same as @code{-E}.
+
+@item functrace
+Same as @code{-T}.
+
@item hashall
Same as @code{-h}.
@item physical
Same as @code{-P}.
+@item pipefail
+If set, the return value of a pipeline is the value of the last
+(rightmost) command to exit with a non-zero status, or zero if all
+commands in the pipeline exit successfully.
+This option is disabled by default.
+
@item posix
Change the behavior of Bash where the default operation differs
from the @sc{posix} 1003.2 standard to match the standard
Print shell input lines as they are read.
@item -x
-Print a trace of simple commands and their arguments after they are
-expanded and before they are executed.
+Print a trace of simple commands, \fBfor\fP commands, \fBcase\fP
+commands, \fBselect\fP commands, and arithmetic \fBfor\fP commands
+and their arguments or associated word lists after they are
+expanded and before they are executed. The value of the @env{PS4}
+variable is expanded and the resultant value is printed before
+the command and its expanded arguments.
@item -B
The shell will perform brace expansion (@pxref{Brace Expansion}).
Prevent output redirection using @samp{>}, @samp{>&}, and @samp{<>}
from overwriting existing files.
+@item -E
+If set, any trap on @code{ERR} is inherited by shell functions, command
+substitutions, and commands executed in a subshell environment.
+The @code{ERR} trap is normally not inherited in such cases.
+
@item -H
Enable @samp{!} style history substitution (@pxref{History Interaction}).
This option is on by default for interactive shells.
/usr/local
@end example
+@item -T
+If set, any trap on @code{DEBUG} and @code{RETURN} are inherited by
+shell functions, command substitutions, and commands executed
+in a subshell environment.
+The @code{DEBUG} and @code{RETURN} traps are normally not inherited
+in such cases.
+
@item --
If no arguments follow this option, then the positional parameters are
unset. Otherwise, the positional parameters are set to the
@item PATH
A colon-separated list of directories in which the shell looks for
commands.
+A zero-length (null) directory name in the value of @code{PATH} indicates the
+current directory.
+A null directory name may appear as two adjacent colons, or as an initial
+or trailing colon.
+
@item PS1
The primary prompt string. The default value is @samp{\s-\v\$ }.
@item BASH
The full pathname used to execute the current instance of Bash.
+@item BASH_ARGC
+An array variable whose values are the number of parameters in each
+frame of the current bash execution call stack. The number of
+parameters to the current subroutine (shell function or script executed
+with @code{.} or @code{source}) is at the top of the stack. When a
+subroutine is executed, the number of parameters passed is pushed onto
+@code{BASH_ARGC}.
+The shell sets @code{BASH_ARGC} only when in extended debugging mode
+(see @ref{Bash Builtins}
+for a description of the @code{extdebug} option to the @code{shopt}
+builtin).
+
+@item BASH_ARGV
+An array variable containing all of the parameters in the current bash
+execution call stack. The final parameter of the last subroutine call
+is at the top of the stack; the first parameter of the initial call is
+at the bottom. When a subroutine is executed, the parameters supplied
+are pushed onto @code{BASH_ARGV}.
+The shell sets @code{BASH_ARGV} only when in extended debugging mode
+(see @ref{Bash Builtins}
+for a description of the @code{extdebug} option to the @code{shopt}
+builtin).
+
+@item BASH_COMMAND
+The command currently being executed or about to be executed, unless the
+shell is executing a command as the result of a trap,
+in which case it is the command executing at the time of the trap.
+
@item BASH_ENV
If this variable is set when Bash is invoked to execute a shell
script, its value is expanded and used as the name of a startup file
to read before executing the script. @xref{Bash Startup Files}.
-@item BASH_VERSION
-The version number of the current instance of Bash.
+@item BASH_EXECUTION_STRING
+The command argument to the @option{-c} invocation option.
+
+@item BASH_LINENO
+An array variable whose members are the line numbers in source files
+corresponding to each member of @var{FUNCNAME}.
+@code{$@{BASH_LINENO[$i]@}} is the line number in the source file where
+@code{$@{FUNCNAME[$i]@}} was called.
+The corresponding source file name is @code{$@{BASH_SOURCE[$i]@}}.
+Use @code{LINENO} to obtain the current line number.
+
+@item BASH_REMATCH
+An array variable whose members are assigned by the @samp{=~} binary
+operator to the @code{[[} conditional command
+(@pxref{Conditional Constructs}).
+The element with index 0 is the portion of the string
+matching the entire regular expression.
+The element with index @var{n} is the portion of the
+string matching the @var{n}th parenthesized subexpression.
+This variable is read-only.
+
+@item BASH_SOURCE
+An array variable whose members are the source filenames corresponding
+to the elements in the @code{FUNCNAME} array variable.
+
+@item BASH_SUBSHELL
+Incremented by one each time a subshell or subshell environment is spawned.
+The initial value is 0.
@item BASH_VERSINFO
A readonly array variable (@pxref{Arrays})
@end table
+@item BASH_VERSION
+The version number of the current instance of Bash.
+
@item COLUMNS
Used by the @code{select} builtin command to determine the terminal width
when printing selection lists. Automatically set upon receipt of a
commands invoked by the
programmable completion facilities (@pxref{Programmable Completion}).
+@item COMP_WORDBREAKS
+The set of characters that the Readline library treats as word
+separators when performing word completion.
+If @code{COMP_WORDBREAKS} is unset, it loses its special properties,
+even if it is subsequently reset.
+
@item COMP_WORDS
An array variable consisting of the individual
words in the current command line.
If @env{DIRSTACK} is unset, it loses its special properties, even if
it is subsequently reset.
+@item EMACS
+If Bash finds this variable in the environment when the shell
+starts with value @samp{t}, it assumes that the shell is running in an
+emacs shell buffer and disables line editing.
+
@item EUID
The numeric effective user id of the current user. This variable
is readonly.
value is @samp{.o:~}
@item FUNCNAME
-The name of any currently-executing shell function.
+An array variable containing the names of all shell functions
+currently in the execution call stack.
+The element with index 0 is the name of any currently-executing
+shell function.
+The bottom-most element is "main".
This variable exists only when a shell function is executing.
Assignments to @env{FUNCNAME} have no effect and return an error status.
If @env{FUNCNAME} is unset, it loses its special properties, even if
even if it is subsequently reset.
@item HISTCONTROL
-A value of @samp{ignorespace} means to not enter lines which
-begin with a space or tab into the history list.
-A value of @samp{ignoredups} means to not enter lines which match the last
-entered line.
-A value of @samp{ignoreboth} combines the two options.
-Unset, or set to any other value than those above, means to save
-all lines on the history list.
+A colon-separated list of values controlling how commands are saved on
+the history list.
+If the list of values includes @samp{ignorespace}, lines which begin
+with a space character are not saved in the history list.
+A value of @samp{ignoredups} causes lines which match the previous
+history entry to not be saved.
+A value of @samp{ignoreboth} is shorthand for
+@samp{ignorespace} and @samp{ignoredups}.
+A value of @samp{erasedups} causes all previous lines matching the
+current line to be removed from the history list before that line
+is saved.
+Any value not in the above list is ignored.
+If @env{HISTCONTROL} is unset, or does not include a valid value,
+all lines read by the shell parser are saved on the history list,
+subject to the value of @env{HISTIGNORE}.
The second and subsequent lines of a multi-line compound command are
not tested, and are added to the history regardless of the value of
@env{HISTCONTROL}.
The maximum number of commands to remember on the history list.
The default value is 500.
+@item HISTTIMEFORMAT
+If this variable is set and not null, its value is used as a format string
+for @var{strftime} to print the time stamp associated with each history
+entry displayed by the @code{history} builtin.
+If this variable is set, time stamps are written to the history file so
+they may be preserved across shell sessions.
+
@item HOSTFILE
Contains the name of a file in the same format as @file{/etc/hosts} that
should be read when the shell needs to complete a hostname.
becomes the value assigned plus the number of seconds
since the assignment.
+@item SHELL
+The full pathname to the shell is kept in this environment variable.
+If it is not set when the shell starts,
+Bash assigns to it the full pathname of the current user's login shell.
+
@item SHELLOPTS
A colon-separated list of enabled shell options. Each word in
the list is a valid argument for the @option{-o} option to the
A trailing newline is added when the format string is displayed.
@item TMOUT
-If set to a value greater than zero, the value is interpreted as
+If set to a value greater than zero, @code{TMOUT} is treated as the
+default timeout for the @code{read} builtin (@pxref{Bash Builtins}).
+The @code{select} command (@pxref{Conditional Constructs}) terminates
+if input does not arrive after @code{TMOUT} seconds when input is coming
+from a terminal.
+
+In an interative shell, the value is interpreted as
the number of seconds to wait for input after issuing the primary
prompt when the shell is interactive.
Bash terminates after that number of seconds if input does
not arrive.
+@item TMPDIR
+If set, Bash uses its value as the name of a directory in which
+Bash creates temporary files for the shell's use.
+
@item UID
The numeric real user id of the current user. This variable is readonly.
In addition to the single-character shell command-line options
(@pxref{The Set Builtin}), there are several multi-character
options that you can use. These options must appear on the command
-line before the single-character options in order for them
-to be recognized.
+line before the single-character options to be recognized.
@table @code
+@item --debugger
+Arrange for the debugger profile to be executed before the shell
+starts. Turns on extended debugging mode (see @ref{Bash Builtins}
+for a description of the @code{extdebug} option to the @code{shopt}
+builtin) and shell function tracing
+(see @ref{The Set Builtin} for a description of the @code{-o functrace}
+option).
+
@item --dump-po-strings
A list of all double-quoted strings preceded by @samp{$}
-is printed on the standard ouput
+is printed on the standard output
in the @sc{gnu} @code{gettext} PO (portable object) file format.
Equivalent to @option{-D} except for the output format.
in an interactive shell.
@item --login
-Make this shell act as if it had been directly invoked by login.
-When the shell is interactive, this is equivalent to starting a
-login shell with @samp{exec -l bash}.
-When the shell is not interactive, the login shell startup files will
-be executed.
-@samp{exec bash --login}
-will replace the current shell with a Bash login shell.
-@xref{Bash Startup Files}, for a description of the special behavior
-of a login shell.
+Equivalent to @option{-l}.
@item --noediting
Do not use the @sc{gnu} Readline library (@pxref{Command Line Editing})
Force the shell to run interactively. Interactive shells are
described in @ref{Interactive Shells}.
+@item -l
+Make this shell act as if it had been directly invoked by login.
+When the shell is interactive, this is equivalent to starting a
+login shell with @samp{exec -l bash}.
+When the shell is not interactive, the login shell startup files will
+be executed.
+@samp{exec bash -l} or @samp{exec bash --login}
+will replace the current shell with a Bash login shell.
+@xref{Bash Startup Files}, for a description of the special behavior
+of a login shell.
+
@item -r
Make the shell a restricted shell (@pxref{The Restricted Shell}).
@item -D
A list of all double-quoted strings preceded by @samp{$}
-is printed on the standard ouput.
+is printed on the standard output.
These are the strings that
are subject to language translation when the current locale
is not @code{C} or @code{POSIX} (@pxref{Locale Translation}).
An interactive shell
is one started without non-option arguments, unless @option{-s} is
specified, without specifiying the @option{-c} option, and
-whose input and output are both
+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
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}).
@file{/dev/stdin}, @file{/dev/stdout}, or @file{/dev/stderr}, file
descriptor 0, 1, or 2, respectively, is checked.
+Unless otherwise specified, primaries that operate on files follow symbolic
+links and operate on the target of the link, rather than the link itself.
+
@table @code
@item -a @var{file}
True if @var{file} exists.
True if @var{file} exists and has been modified since it was last read.
@item @var{file1} -nt @var{file2}
-True if @var{file1} is newer (according to
-modification date) than @var{file2}.
+True if @var{file1} is newer (according to modification date)
+than @var{file2}, or if @var{file1} exists and @var{file2} does not.
@item @var{file1} -ot @var{file2}
-True if @var{file1} is older than @var{file2}.
+True if @var{file1} is older than @var{file2},
+or if @var{file2} exists and @var{file1} does not.
@item @var{file1} -ef @var{file2}
-True if @var{file1} and @var{file2} have the same device and
+True if @var{file1} and @var{file2} refer to the same device and
inode numbers.
@item -o @var{optname}
@item @var{string1} == @var{string2}
True if the strings are equal.
-@samp{=} may be used in place of @samp{==}.
+@samp{=} may be used in place of @samp{==} for strict @sc{posix} compliance.
@item @var{string1} != @var{string2}
True if the strings are not equal.
@cindex arithmetic evaluation
The shell allows arithmetic expressions to be evaluated, as one of
-the shell expansions or by the @code{let} builtin.
+the shell expansions or by the @code{let} and the @option{-i} option
+to the @code{declare} builtins.
-Evaluation is done in long integers with no check for overflow,
+Evaluation is done in fixed-width integers with no check for overflow,
though division by 0 is trapped and flagged as an error.
-The operators and their precedence and associativity are the same
-as in the C language.
+The operators and their precedence, associativity, and values
+are the same as in the C language.
The following list of operators is grouped into levels of
equal-precedence operators.
The levels are listed in order of decreasing precedence.
logical OR
@item expr ? expr : expr
-conditional evaluation
+conditional operator
@item = *= /= %= += -= <<= >>= &= ^= |=
assignment
performed before the expression is evaluated.
Within an expression, shell variables may also be referenced by name
without using the parameter expansion syntax.
+A shell variable that is null or unset evaluates to 0 when referenced
+by name without using the parameter expansion syntax.
The value of a variable is evaluated as an arithmetic expression
-when it is referenced.
+when it is referenced, or when a variable which has been given the
+@var{integer} attribute using @samp{declare -i} is assigned a value.
+A null value evaluates to 0.
A shell variable need not have its integer attribute turned on
to be used in an expression.
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
+letters may be used interchangeably to represent numbers between 10
and 35.
Operators are evaluated in order of precedence. Sub-expressions in
The first word of each simple command, if unquoted, is checked to see
if it has an alias.
If so, that word is replaced by the text of the alias.
-The alias name and the replacement text may contain any valid
-shell input, including shell metacharacters, with the exception
-that the alias name may not contain @samp{=}.
+The characters @samp{/}, @samp{$}, @samp{`}, @samp{=} and any of the
+shell metacharacters or quoting characters listed above may not appear
+in an alias name.
+The replacement text may contain any valid
+shell input, including shell metacharacters.
The first word of the replacement text is tested for
aliases, but a word that is identical to an alias being expanded
-is not expanded a second time. This means that one may alias
-@code{ls} to @code{"ls -F"},
+is not expanded a second time.
+This means that one may alias @code{ls} to @code{"ls -F"},
for instance, and Bash does not try to recursively expand the
replacement text. If the last character of the alias value is a
space or tab character, then the next command word following the
conflicts with the shell's filename expansion operators. If the
@var{subscript} is @samp{@@} or @samp{*}, the word expands to all members
of the array @var{name}. These subscripts differ only when the word
-appears within double quotes. If the word is double-quoted,
+appears within double quotes.
+If the word is double-quoted,
@code{$@{name[*]@}} expands to a single word with
the value of each array member separated by the first character of the
@env{IFS} variable, and @code{$@{name[@@]@}} expands each element of
@var{name} to a separate word. When there are no array members,
-@code{$@{name[@@]@}} expands to nothing. This is analogous to the
+@code{$@{name[@@]@}} expands to nothing.
+If the double-quoted expansion occurs within a word, the expansion of
+the first parameter is joined with the beginning part of the original
+word, and the expansion of the last parameter is joined with the last
+part of the original word.
+This is analogous to the
expansion of the special parameters @samp{@@} and @samp{*}.
@code{$@{#name[}@var{subscript}@code{]@}} expands to the length of
@code{$@{name[}@var{subscript}@code{]@}}.
The @code{unset} builtin is used to destroy arrays.
@code{unset} @var{name}[@var{subscript}]
destroys the array element at index @var{subscript}.
+Care must be taken to avoid unwanted side effects caused by filename
+generation.
@code{unset} @var{name}, where @var{name} is an array, removes the
entire array. A subscript of @samp{*} or @samp{@@} also removes the
entire array.
A bell character.
@item \d
The date, in "Weekday Month Date" format (e.g., "Tue May 26").
+@item \D@{@var{format}@}
+The @var{format} is passed to @code{strftime}(3) and the result is inserted
+into the prompt string; an empty @var{format} results in a locale-specific
+time representation. The braces are required.
@item \e
An escape character.
@item \h
@item \V
The release of Bash, version + patchlevel (e.g., 2.00.0)
@item \w
-The current working directory.
+The current working directory, with @env{$HOME} abbreviated with a tilde.
@item \W
-The basename of @env{$PWD}.
+The basename of @env{$PWD}, with @env{$HOME} abbreviated with a tilde.
@item \!
The history number of this command.
@item \#
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:
+with the exception that the following are disallowed or not performed:
+
@itemize @bullet
@item
Changing directories with the @code{cd} builtin.
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
closely to the @sc{posix} 1003.2 standard by changing the behavior to
match that specified by @sc{posix} in areas where the Bash default differs.
+When invoked as @code{sh}, Bash enters @sc{posix} mode after reading the
+startup files.
+
The following list is what's changed when `@sc{posix} mode' is in effect:
@enumerate
example, @code{SIGTSTP}.
@item
-Reserved words may not be aliased.
+The @code{bg} builtin uses the required format to describe each job placed
+in the background, which does not include an indication of whether the job
+is the current or previous job.
+
+@item
+Reserved words appearing in a context where reserved words are recognized
+do not undergo alias expansion.
@item
The @sc{posix} 1003.2 @env{PS1} and @env{PS2} expansions of @samp{!} to
@env{PS2} regardless of the setting of the @code{promptvars} option.
@item
-Interactive comments are enabled by default. (Bash has them on by
-default anyway.)
-
-@item
The @sc{posix} 1003.2 startup files are executed (@env{$ENV}) rather than
the normal Bash files.
@item
The output of @samp{kill -l} prints all the signal names on a single line,
-separated by spaces.
+separated by spaces, without the @samp{SIG} prefix.
+
+@item
+The @code{kill} builtin does not accept signal names with a @samp{SIG}
+prefix.
@item
Non-interactive shells exit if @var{filename} in @code{.} @var{filename}
causes a fatal syntax error in non-interactive shells.
@item
-@sc{posix} 1003.2 `special' builtins are found before shell functions
+@sc{posix} 1003.2 special builtins are found before shell functions
during command lookup.
@item
the command name, and so on.
@item
-If the @code{cd} builtin finds a directory to change to
-using @env{$CDPATH}, the
-value it assigns to the @env{PWD} variable does not contain any
-symbolic links, as if @samp{cd -P} had been executed.
-
-@item
If @env{CDPATH} is set, the @code{cd} builtin will not implicitly
append the current directory to it. This means that @code{cd} will
fail if no valid directory name can be constructed from
@code{SIG}.
@item
+The @code{trap} builtin doesn't check the first argument for a possible
+signal specification and revert the signal handling to the original
+disposition if it is, unless that argument consists solely of digits and
+is a valid signal number. If users want to reset the handler for a given
+signal to the original disposition, they should use @samp{-} as the
+first argument.
+
+@item
The @code{.} and @code{source} builtins do not search the current directory
for the filename argument if it is not found by searching @env{PATH}.
Alias expansion is always enabled, even in non-interactive shells.
@item
+When the @code{alias} builtin displays alias definitions, it does not
+display them with a leading @samp{alias } unless the @option{-p} option
+is supplied.
+
+@item
When the @code{set} builtin is invoked without options, it does not display
shell function names and definitions.
When the @code{set} builtin is invoked without options, it displays
variable values without quotes, unless they contain shell metacharacters,
even if the result contains nonprinting characters.
+
+@item
+When the @code{cd} builtin is invoked in @var{logical} mode, and the pathname
+constructed from @code{$PWD} and the directory name supplied as an argument
+does not refer to an existing directory, @code{cd} will fail instead of
+falling back to @var{physical} mode.
+
+@item
+When the @code{pwd} builtin is supplied the @option{-P} option, it resets
+@code{$PWD} to a pathname containing no symlinks.
+
+@item
+The @code{pwd} builtin verifies that the value it prints is the same as the
+current directory, even if it is not asked to check the file system with the
+@option{-P} option.
+
+@item
+When listing the history, the @code{fc} builtin does not include an
+indication of whether or not a history entry has been modified.
+
+@item
+The default editor used by @code{fc} is @code{ed}.
+
+@item
+The @code{type} and @code{command} builtins will not report a non-executable
+file as having been found, though the shell will attempt to execute such a
+file if it is the only so-named file found in @code{$PATH}.
+
+@item
+The @code{vi} editing mode will invoke the @code{vi} editor directly when
+the @samp{v} command is run, instead of checking @code{$FCEDIT} and
+@code{$EDITOR}.
+
+@item
+When the @code{xpg_echo} option is enabled, Bash does not attempt to interpret
+any arguments to @code{echo} as options. Each argument is displayed, after
+escape characters are converted.
+
@end enumerate
-There is other @sc{posix} 1003.2 behavior that Bash does not implement.
+There is other @sc{posix} 1003.2 behavior that Bash does not implement by
+default even when in @sc{posix} mode.
Specifically:
@enumerate
-@item
-Assignment statements affect the execution environment of all
-builtins, not just special ones.
@item
-When a subshell is created to execute a shell script with execute permission,
-but without a leading @samp{#!}, Bash sets @code{$0} to the full pathname of
-the script as found by searching @code{$PATH}, rather than the command as
-typed by the user.
+The @code{fc} builtin checks @code{$EDITOR} as a program to edit history
+entries if @code{FCEDIT} is unset, rather than defaulting directly to
+@code{ed}. @code{fc} uses @code{ed} if @code{EDITOR} is unset.
@item
-When using @samp{.} to source a shell script found in @code{$PATH}, bash
-checks execute permission bits rather than read permission bits, just as
-if it were searching for a command.
+As noted above, Bash requires the @code{xpg_echo} option to be enabled for
+the @code{echo} builtin to be fully conformant.
@end enumerate
+Bash can be configured to be @sc{posix}-conformant by default, by specifying
+the @option{--enable-strict-posix-default} to @code{configure} when building
+(@pxref{Optional Features}).
+
@node Job Control
@chapter Job Control
character @samp{%} introduces a job name.
Job number @code{n} may be referred to as @samp{%n}.
-The symbols @samp{%%} and
-@samp{%+} refer to the shell's notion of the current job, which
-is the last job stopped while it was in the foreground or started
-in the background. The
-previous job may be referenced using @samp{%-}. In output
+The symbols @samp{%%} and @samp{%+} refer to the shell's notion of the
+current job, which is the last job stopped while it was in the foreground
+or started in the background.
+A single @samp{%} (with no accompanying job specification) also refers
+to the current job.
+The previous job may be referenced using @samp{%-}. In output
pertaining to jobs (e.g., the output of the @code{jobs} command),
the current job is always flagged with a @samp{+}, and the
previous job with a @samp{-}.
Any trap on @code{SIGCHLD} is executed for each child process
that exits.
-If an attempt to exit Bash is while jobs are stopped, the
+If an attempt to exit Bash is made while jobs are stopped, the
shell prints a message warning that there are stopped jobs.
The @code{jobs} command may then be used to inspect their status.
If a second attempt to exit is made without an intervening command,
@item bg
@btindex bg
@example
-bg [@var{jobspec}]
+bg [@var{jobspec} @dots{}]
@end example
-Resume the suspended job @var{jobspec} in the background, as if it
+Resume each suspended job @var{jobspec} in the background, as if it
had been started with @samp{&}.
If @var{jobspec} is not supplied, the current job is used.
The return status is zero unless it is run when job control is not
-enabled, or, when run with job control enabled, if @var{jobspec} was
-not found or @var{jobspec} specifies a job that was started without
-job control.
+enabled, or, when run with job control enabled, any
+@var{jobspec} was not found or specifies a job
+that was started without job control.
@item fg
@btindex fg
@end example
Send a signal specified by @var{sigspec} or @var{signum} to the process
named by job specification @var{jobspec} or process @sc{id} @var{pid}.
-@var{sigspec} is either a signal name such as @code{SIGINT} (with or without
-the @code{SIG} prefix) or a signal number; @var{signum} is a signal number.
+@var{sigspec} is either a case-insensitive signal name such as
+@code{SIGINT} (with or without the @code{SIG} prefix)
+or a signal number; @var{signum} is a signal number.
If @var{sigspec} and @var{signum} are not present, @code{SIGTERM} is used.
The @option{-l} option lists the signal names.
If any arguments are supplied when @option{-l} is given, the names of the
@item wait
@btindex wait
@example
-wait [@var{jobspec} or @var{pid}]
+wait [@var{jobspec} or @var{pid} ...]
@end example
-Wait until the child process specified by process @sc{id} @var{pid} or job
-specification @var{jobspec} exits and return the exit status of the last
-command waited for.
+Wait until the child process specified by each process @sc{id} @var{pid}
+or job specification @var{jobspec} exits and return the exit status of the
+last command waited for.
If a job spec is given, all processes in the job are waited for.
If no arguments are given, all currently active child processes are
waited for, and the return status is zero.
@set readline-appendix
@set history-appendix
@cindex Readline, how to use
-@include rluser.texinfo
+@include rluser.texi
@cindex History, how to use
-@include hsuser.texinfo
+@include hsuser.texi
@clear readline-appendix
@clear history-appendix
@sc{gnu} operating systems, nearly every version of Unix, and several
non-Unix systems such as BeOS and Interix.
Other independent ports exist for
-@sc{ms-dos}, @sc{os/2}, Windows @sc{95/98}, and Windows @sc{nt}.
+@sc{ms-dos}, @sc{os/2}, and Windows platforms.
@menu
* Basic Installation:: Installation instructions.
-
* Compilers and Options:: How to set special options for various
systems.
-
* Compiling For Multiple Architectures:: How to compile Bash for more
than one kind of system from
the same source tree.
-
* Installation Names:: How to set the various paths used by the installation.
-
* Specifying the System Type:: How to configure Bash for a particular system.
-
* Sharing Defaults:: How to share default configuration values among GNU
programs.
-
* Operation Controls:: Options recognized by the configuration program.
-
* Optional Features:: How to enable and disable optional features when
building Bash.
@end menu
@item --with-bash-malloc
Use the Bash version of
-@code{malloc} in @file{lib/malloc/malloc.c}. This is not the same
+@code{malloc} in the directory @file{lib/malloc}. This is not the same
@code{malloc} that appears in @sc{gnu} libc, but an older version
-derived from the 4.2 @sc{bsd} @code{malloc}. This @code{malloc} is
-very fast, but wastes some space on each allocation.
+originally derived from the 4.2 @sc{bsd} @code{malloc}. This @code{malloc}
+is very fast, but wastes some space on each allocation.
This option is enabled by default.
The @file{NOTES} file contains a list of systems for
which this should be turned off, and @code{configure} disables this
@item --with-installed-readline[=@var{PREFIX}]
Define this to make Bash link with a locally-installed version of Readline
rather than the version in @file{lib/readline}. This works only with
-Readline 4.2 and later versions. If @var{PREFIX} is @code{yes} or not
+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
@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.
+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
This allows pipelines as well as shell builtins and functions to be timed.
@item --enable-cond-command
-Include support for the @code{[[} conditional command
+Include support for the @code{[[} conditional command.
+(@pxref{Conditional Constructs}).
+
+@item --enable-cond-regexp
+Include support for matching POSIX regular expressions using the
+@samp{=~} binary operator in the @code{[[} conditional command.
(@pxref{Conditional Constructs}).
+@item --enable-debugger
+Include support for the bash debugger (distributed separately).
+
@item --enable-directory-stack
Include support for a @code{csh}-like directory stack and the
@code{pushd}, @code{popd}, and @code{dirs} builtins
This enables the job control features (@pxref{Job Control}),
if the operating system supports them.
+@item --enable-multibyte
+This enables support for multibyte characters if the operating
+system provides the necessary support.
+
@item --enable-net-redirections
This enables the special handling of filenames of the form
@code{/dev/tcp/@var{host}/@var{port}} and
This enables process substitution (@pxref{Process Substitution}) if
the operating system provides the necessary support.
+@item --enable-progcomp
+Enable the programmable completion facilities
+(@pxref{Programmable Completion}).
+If Readline is not enabled, this option has no effect.
+
@item --enable-prompt-string-decoding
Turn on the interpretation of a number of backslash-escaped characters
in the @env{$PS1}, @env{$PS2}, @env{$PS3}, and @env{$PS4} prompt
strings. See @ref{Printing a Prompt}, for a complete list of prompt
string escape sequences.
-@item --enable-progcomp
-Enable the programmable completion facilities
-(@pxref{Programmable Completion}).
-If Readline is not enabled, this option has no effect.
-
@item --enable-readline
Include support for command-line editing and history with the Bash
version of the Readline library (@pxref{Command Line Editing}).
Include the @code{select} builtin, which allows the generation of simple
menus (@pxref{Conditional Constructs}).
+@item --enable-separate-helpfiles
+Use external files for the documentation displayed by the @code{help} builtin
+instead of storing the text internally.
+
+@item --enable-single-help-strings
+Store the text displayed by the @code{help} builtin as a single string for
+each help topic. This aids in translating the text to different languages.
+You may need to disable this if your compiler cannot handle very long string
+literals.
+
+@item --enable-strict-posix-default
+Make Bash @sc{posix}-conformant by default (@pxref{Bash POSIX Mode}).
+
@item --enable-usg-echo-default
A synonym for @code{--enable-xpg-echo-default}.
without requiring the @option{-e} option.
This sets the default value of the @code{xpg_echo} shell option to @code{on},
which makes the Bash @code{echo} behave more like the version specified in
-the Single Unix Specification, version 2.
+the Single Unix Specification, version 3.
@xref{Bash Builtins}, for a description of the escape sequences that
@code{echo} recognizes.
Please report all bugs you find in Bash.
But first, you should
make sure that it really is a bug, and that it appears in the latest
-version of Bash that you have.
+version of Bash.
+The latest version of Bash is always available for FTP from
+@uref{ftp://ftp.gnu.org/pub/bash/}.
Once you have determined that a bug actually exists, use the
@code{bashbug} command to submit a bug report.
section quickly details the differences of significance. A
number of these differences are explained in greater depth in
previous sections.
-This section uses the version of @code{sh} included in SVR4.2 as
-the baseline reference.
+This section uses the version of @code{sh} included in SVR4.2 (the
+last version of the historical Bourne shell) as the baseline reference.
@itemize @bullet
@item
Bash has command history (@pxref{Bash History Facilities}) and the
@code{history} and @code{fc} builtins to manipulate it.
+The Bash history list maintains timestamp information and uses the
+value of the @code{HISTTIMEFORMAT} variable to display it.
@item
Bash implements @code{csh}-like history expansion
Bash implements the @code{!} keyword to negate the return value of
a pipeline (@pxref{Pipelines}).
Very useful when an @code{if} statement needs to act only if a test fails.
+The Bash @samp{-o pipefail} option to @code{set} will cause a pipeline to
+return a failure status if any command fails.
@item
Bash has the @code{time} reserved word and command timing (@pxref{Pipelines}).
@item
Bash includes the @code{[[} compound command, which makes conditional
-testing part of the shell grammar (@pxref{Conditional Constructs}).
+testing part of the shell grammar (@pxref{Conditional Constructs}), including
+optional regular expression matching.
+
+@item
+Bash provides optional case-insensitive matching for the @code{case} and
+@code{[[} constructs.
@item
Bash includes brace expansion (@pxref{Brace Expansion}) and tilde
command.
@item
+Bash supports the @samp{+=} assignment operator, which appends to the value
+of the variable named on the left hand side.
+
+@item
Bash includes the @sc{posix} pattern removal @samp{%}, @samp{#}, @samp{%%}
and @samp{##} expansions to remove leading or trailing substrings from
variable values (@pxref{Shell Parameter Expansion}).
file (@pxref{Redirections}).
@item
+Bash includes the @samp{<<<} redirection operator, allowing a string to
+be used as the standard input to a command.
+
+@item
+Bash implements the @samp{[n]<&@var{word}} and @samp{[n]>&@var{word}}
+redirection operators, which move one file descriptor to another.
+
+@item
Bash treats a number of filenames specially when they are
used in redirection operators (@pxref{Redirections}).
builtin (@pxref{The Set Builtin}).
@item
+The @samp{-x} (@code{xtrace}) option displays commands other than
+simple commands when performing an execution trace
+(@pxref{The Set Builtin}).
+
+@item
The @code{test} builtin (@pxref{Bourne Shell Builtins})
is slightly different, as it implements the @sc{posix} algorithm,
which specifies the behavior based on the number of arguments.
@item
+Bash includes the @code{caller} builtin, which displays the context of
+any active subroutine call (a shell function or a script executed with
+the @code{.} or @code{source} builtins). This supports the bash
+debugger.
+
+@item
The @code{trap} builtin (@pxref{Bourne Shell Builtins}) allows a
@code{DEBUG} pseudo-signal specification, similar to @code{EXIT}.
-Commands specified with a @code{DEBUG} trap are executed after every
-simple command.
-The @code{DEBUG} trap is not inherited by shell functions.
+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.
+The @code{ERR} trap is not inherited by shell functions unless the
+@code{-o errtrace} option to the @code{set} builtin is enabled.
+
+The @code{trap} builtin (@pxref{Bourne Shell Builtins}) allows a
+@code{RETURN} pseudo-signal specification, similar to
+@code{EXIT} and @code{DEBUG}.
+Commands specified with an @code{RETURN} trap are executed before
+execution resumes after a shell function or a shell script executed with
+@code{.} or @code{source} returns.
+The @code{RETURN} trap is not inherited by shell functions unless the
+function has been given the @code{trace} attribute or the
+@code{functrace} option has been enabled using the @code{shopt} builtin.
@item
The Bash @code{type} builtin is more extensive and gives more information
@code{SIGHUP}.
@item
+Bash includes a number of features to support a separate debugger for
+shell scripts.
+
+@item
The SVR4.2 shell has two privilege-related builtins
(@code{mldmode} and @code{priv}) not present in Bash.
(it turns on job control).
@end itemize
+@node Copying This Manual
+@appendix Copying This Manual
+
+@menu
+* GNU Free Documentation License:: License for copying this manual.
+@end menu
+
+@include fdl.texi
+
@node Builtin Index
@unnumbered Index of Shell Builtin Commands
@printindex bt
@unnumbered Concept Index
@printindex cp
-@contents
@bye
projects / platform / upstream / bash.git / blobdiff