File: bash.1

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bash 5.0-4
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file content (11024 lines) | stat: -rw-r--r-- 326,294 bytes parent folder | download | duplicates (3)
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.\"
.\" MAN PAGE COMMENTS to
.\"
.\"	Chet Ramey
.\"	Case Western Reserve University
.\"	chet.ramey@case.edu
.\"
.\"	Last Change: Fri Dec  7 09:48:47 EST 2018
.\"
.\" bash_builtins, strip all but Built-Ins section
.de zZ
..
.de zY
..
.\"
.\" File Name macro.  This used to be `.PN', for Path Name,
.\" but Sun doesn't seem to like that very much.
.\"
.de FN
\fI\|\\$1\|\fP
..
.\" Number register zZ is defined in bash-builtins(7)
.\" Number register zY is defined in rbash(1)
.\" This man-page is included in them
.if !rzZ .nr zZ 0 \" avoid a warning about an undefined register
.if !rzY .nr zY 0 \" avoid a warning about an undefined register
.if \n(zZ=1 .ig zZ
.if \n(zY=1 .ig zY
.TH BASH 1 "2018 December 7" "GNU Bash 5.0"
.\"
.\" There's some problem with having a `@'
.\" in a tagged paragraph with the BSD man macros.
.\" It has to do with `@' appearing in the }1 macro.
.\" This is a problem on 4.3 BSD and Ultrix, but Sun
.\" appears to have fixed it.
.\" If you're seeing the characters
.\" `@u-3p' appearing before the lines reading
.\" `possible-hostname-completions
.\" and `complete-hostname' down in READLINE,
.\" then uncomment this redefinition.
.\"
.\" .de }1
.\" .ds ]X \&\\*(]B\\
.\" .nr )E 0
.\" .if !"\\$1"" .nr )I \\$1n
.\" .}f
.\" .ll \\n(LLu
.\" .in \\n()Ru+\\n(INu+\\n()Iu
.\" .ti \\n(INu
.\" .ie !\\n()Iu+\\n()Ru-\w\\*(]Xu-3p \{\\*(]X
.\" .br\}
.\" .el \\*(]X\h|\\n()Iu+\\n()Ru\c
.\" .}f
.\" ..
.SH NAME
bash \- GNU Bourne-Again SHell
.SH SYNOPSIS
.B bash
[options]
[command_string | file]
.SH COPYRIGHT
.if n Bash is Copyright (C) 1989-2018 by the Free Software Foundation, Inc.
.if t Bash is Copyright \(co 1989-2018 by the Free Software Foundation, Inc.
.SH DESCRIPTION
.B Bash
is an \fBsh\fR-compatible command language interpreter that
executes commands read from the standard input or from a file.
.B Bash
also incorporates useful features from the \fIKorn\fP and \fIC\fP
shells (\fBksh\fP and \fBcsh\fP).
.PP
.B Bash
is intended to be a conformant implementation of the
Shell and Utilities portion of the IEEE POSIX specification
(IEEE Standard 1003.1).
.B Bash
can be configured to be POSIX-conformant by default.
.SH OPTIONS
All of the single-character shell options documented in the
description of the \fBset\fR builtin command, including \fB\-o\fP,
can be used as options when the shell is invoked.
In addition, \fBbash\fR
interprets the following options when it is invoked:
.PP
.PD 0
.TP 10
.B \-c
If the
.B \-c
option is present, then commands are read from the first non-option argument
.IR command_string .
If there are arguments after the
.IR command_string ,
the first argument is assigned to
.B $0
and any remaining arguments are assigned to the positional parameters.
The assignment to
.B $0
sets the name of the shell, which is used in warning and error messages.
.TP
.B \-i
If the
.B \-i
option is present, the shell is
.IR interactive .
.TP
.B \-l
Make
.B bash
act as if it had been invoked as a login shell (see
.SM
.B INVOCATION
below).
.TP
.B \-r
If the
.B \-r
option is present, the shell becomes
.I restricted
(see
.SM
.B "RESTRICTED SHELL"
below).
.TP
.B \-s
If the
.B \-s
option is present, or if no arguments remain after option
processing, then commands are read from the standard input.
This option allows the positional parameters to be set
when invoking an interactive shell or when reading input
through a pipe.
.TP
.B \-v
Print shell input lines as they are read.
.TP
.B \-x
Print commands and their arguments as they are executed.
.TP
.B \-D
A list of all double-quoted strings preceded by \fB$\fP
is printed on the standard output.
These are the strings that
are subject to language translation when the current locale
is not \fBC\fP or \fBPOSIX\fP.
This implies the \fB\-n\fP option; no commands will be executed.
.TP
.B [\-+]O [\fIshopt_option\fP]
\fIshopt_option\fP is one of the shell options accepted by the
\fBshopt\fP builtin (see
.SM
.B SHELL BUILTIN COMMANDS
below).
If \fIshopt_option\fP is present, \fB\-O\fP sets the value of that option;
\fB+O\fP unsets it.
If \fIshopt_option\fP is not supplied, the names and values of the shell
options accepted by \fBshopt\fP are printed on the standard output.
If the invocation option is \fB+O\fP, the output is displayed in a format
that may be reused as input.
.TP
.B \-\-
A
.B \-\-
signals the end of options and disables further option processing.
Any arguments after the
.B \-\-
are treated as filenames and arguments.  An argument of
.B \-
is equivalent to \fB\-\-\fP.
.PD
.PP
.B Bash
also interprets a number of multi-character options.
These options must appear on the command line before the
single-character options to be recognized.
.PP
.PD 0
.TP
.B \-\-debugger
Arrange for the debugger profile to be executed before the shell
starts.
Turns on extended debugging mode (see the description of the
.B extdebug
option to the
.B shopt
builtin below).
.TP
.B \-\-dump\-po\-strings
Equivalent to \fB\-D\fP, but the output is in the GNU \fIgettext\fP
\fBpo\fP (portable object) file format.
.TP
.B \-\-dump\-strings
Equivalent to \fB\-D\fP.
.TP
.B \-\-help
Display a usage message on standard output and exit successfully.
.TP
\fB\-\-init\-file\fP \fIfile\fP
.PD 0
.TP
\fB\-\-rcfile\fP \fIfile\fP
.PD
Execute commands from
.I file
instead of the system wide initialization file
.I /etc/bash.bashrc
and the standard personal initialization file
.I ~/.bashrc
if the shell is interactive (see
.SM
.B INVOCATION
below).
.TP
.B \-\-login
Equivalent to \fB\-l\fP.
.TP
.B \-\-noediting
Do not use the GNU
.B readline
library to read command lines when the shell is interactive.
.TP
.B \-\-noprofile
Do not read either the system-wide startup file
.FN /etc/profile
or any of the personal initialization files
.IR ~/.bash_profile ,
.IR ~/.bash_login ,
or
.IR ~/.profile .
By default,
.B bash
reads these files when it is invoked as a login shell (see
.SM
.B INVOCATION
below).
.TP
.B \-\-norc
Do not read and execute the system wide initialization file
.I /etc/bash.bashrc
and the personal initialization file
.I ~/.bashrc
if the shell is interactive.
This option is on by default if the shell is invoked as
.BR sh .
.TP
.B \-\-posix
Change the behavior of \fBbash\fP where the default operation differs
from the POSIX standard to match the standard (\fIposix mode\fP).
See
.SM
.B "SEE ALSO"
below for a reference to a document that details how posix mode affects
bash's behavior.
.TP
.B \-\-restricted
The shell becomes restricted (see
.SM
.B "RESTRICTED SHELL"
below).
.TP
.B \-\-verbose
Equivalent to \fB\-v\fP.
.TP
.B \-\-version
Show version information for this instance of
.B bash
on the standard output and exit successfully.
.PD
.SH ARGUMENTS
If arguments remain after option processing, and neither the
.B \-c
nor the
.B \-s
option has been supplied, the first argument is assumed to
be the name of a file containing shell commands.
If
.B bash
is invoked in this fashion,
.B $0
is set to the name of the file, and the positional parameters
are set to the remaining arguments.
.B Bash
reads and executes commands from this file, then exits.
\fBBash\fP's exit status is the exit status of the last command
executed in the script.
If no commands are executed, the exit status is 0.
An attempt is first made to open the file in the current directory, and,
if no file is found, then the shell searches the directories in
.SM
.B PATH
for the script.
.SH INVOCATION
A \fIlogin shell\fP is one whose first character of argument zero is a
.BR \- ,
or one started with the
.B \-\-login
option.
.PP
An \fIinteractive\fP shell is one started without non-option arguments
(unless \fB\-s\fP is specified)
and without the
.B \-c
option
whose standard input and error are
both connected to terminals (as determined by
.IR isatty (3)),
or one started with the
.B \-i
option.
.SM
.B PS1
is set and
.B $\-
includes
.B i
if
.B bash
is interactive,
allowing a shell script or a startup file to test this state.
.PP
The following paragraphs describe how
.B bash
executes its startup files.
If any of the files exist but cannot be read,
.B bash
reports an error.
Tildes are expanded in filenames as described below under
.B "Tilde Expansion"
in the
.SM
.B EXPANSION
section.
.PP
When
.B bash
is invoked as an interactive login shell, or as a non-interactive shell
with the \fB\-\-login\fP option, it first reads and
executes commands from the file \fI/etc/profile\fP, if that
file exists.
After reading that file, it looks for \fI~/.bash_profile\fP,
\fI~/.bash_login\fP, and \fI~/.profile\fP, in that order, and reads
and executes commands from the first one that exists and is readable.
The
.B \-\-noprofile
option may be used when the shell is started to inhibit this behavior.
.PP
When an interactive login shell exits,
or a non-interactive login shell executes the \fBexit\fP builtin command,
.B bash
reads and executes commands from the file \fI~/.bash_logout\fP, if it
exists.
.PP
When an interactive shell that is not a login shell is started,
.B bash
reads and executes commands from \fI/etc/bash.bashrc\fP and \fI~/.bashrc\fP,
if these files exist.
This may be inhibited by using the
.B \-\-norc
option.
The \fB\-\-rcfile\fP \fIfile\fP option will force
.B bash
to read and execute commands from \fIfile\fP instead of
\fI/etc/bash.bashrc\fP and \fI~/.bashrc\fP.
.PP
When
.B bash
is started non-interactively, to run a shell script, for example, it
looks for the variable
.SM
.B BASH_ENV
in the environment, expands its value if it appears there, and uses the
expanded value as the name of a file to read and execute.
.B Bash
behaves as if the following command were executed:
.sp .5
.RS
.if t \f(CWif [ \-n "$BASH_ENV" ]; then . "$BASH_ENV"; fi\fP
.if n if [ \-n "$BASH_ENV" ]; then . "$BASH_ENV"; fi
.RE
.sp .5
but the value of the
.SM
.B PATH
variable is not used to search for the filename.
.PP
If
.B bash
is invoked with the name
.BR sh ,
it tries to mimic the startup behavior of historical versions of
.B sh
as closely as possible,
while conforming to the POSIX standard as well.
When invoked as an interactive login shell, or a non-interactive
shell with the \fB\-\-login\fP option, it first attempts to
read and execute commands from
.I /etc/profile
and
.IR ~/.profile ,
in that order.
The
.B \-\-noprofile
option may be used to inhibit this behavior.
When invoked as an interactive shell with the name
.BR sh ,
.B bash
looks for the variable
.SM
.BR ENV ,
expands its value if it is defined, and uses the
expanded value as the name of a file to read and execute.
Since a shell invoked as
.B sh
does not attempt to read and execute commands from any other startup
files, the
.B \-\-rcfile
option has no effect.
A non-interactive shell invoked with the name
.B sh
does not attempt to read any other startup files. 
When invoked as
.BR sh ,
.B bash
enters
.I posix
mode after the startup files are read.
.PP
When
.B bash
is started in
.I posix
mode, as with the
.B \-\-posix
command line option, it follows the POSIX standard for startup files.
In this mode, interactive shells expand the
.SM
.B ENV
variable and commands are read and executed from the file
whose name is the expanded value.
No other startup files are read.
.PP
.B Bash
attempts to determine when it is being run with its standard input
connected to a network connection, as when executed by the remote shell
daemon, usually \fIrshd\fP, or the secure shell daemon \fIsshd\fP.
If
.B bash
determines it is being run in this fashion, it reads and executes
commands from \fI~/.bashrc\fP and \fI~/.bashrc\fP, if these files
exist and are readable.
It will not do this if invoked as \fBsh\fP.
The
.B \-\-norc
option may be used to inhibit this behavior, and the
.B \-\-rcfile
option may be used to force another file to be read, but neither
\fIrshd\fP nor \fIsshd\fP generally invoke the shell with those options
or allow them to be specified.
.PP
If the shell is started with the effective user (group) id not equal to the
real user (group) id, and the \fB\-p\fP option is not supplied, no startup
files are read, shell functions are not inherited from the environment, the
.SM
.BR SHELLOPTS ,
.SM
.BR BASHOPTS ,
.SM
.BR CDPATH ,
and
.SM
.B GLOBIGNORE
variables, if they appear in the environment, are ignored,
and the effective user id is set to the real user id.
If the \fB\-p\fP option is supplied at invocation, the startup behavior is
the same, but the effective user id is not reset.
.SH DEFINITIONS
.PP
The following definitions are used throughout the rest of this
document.
.PD 0
.TP
.B blank
A space or tab.
.TP
.B word
A sequence of characters considered as a single unit by the shell.
Also known as a
.BR token .
.TP
.B name
A
.I word
consisting only of alphanumeric characters and underscores, and
beginning with an alphabetic character or an underscore.  Also
referred to as an
.BR identifier .
.TP
.B metacharacter
A character that, when unquoted, separates words.  One of the following:
.br
.RS
.PP
.if t \fB|  &  ;  (  )  <  >  space  tab  newline\fP
.if n \fB|  & ; ( ) < > space tab newline\fP
.RE
.PP
.TP
.B control operator
A \fItoken\fP that performs a control function.  It is one of the following
symbols:
.RS
.PP
.if t \fB||  &  &&  ;  ;;  ;&  ;;&  (  )  |  |&    <newline>\fP
.if n \fB|| & && ; ;; ;& ;;& ( ) | |& <newline>\fP
.RE
.PD
.SH "RESERVED WORDS"
\fIReserved words\fP are words that have a special meaning to the shell.
The following words are recognized as reserved when unquoted and either
the first word of a simple command (see
.SM
.B SHELL GRAMMAR
below) or the third word of a
.B case
or
.B for
command:
.if t .RS
.PP
.B
.if n ! case  coproc  do done elif else esac fi for function if in select then until while { } time [[ ]]
.if t !    case    coproc    do    done    elif    else    esac    fi    for    function    if    in    select    then    until    while    {    }    time    [[    ]]
.if t .RE
.SH "SHELL GRAMMAR"
.SS Simple Commands
.PP
A \fIsimple command\fP is a sequence of optional variable assignments
followed by \fBblank\fP-separated words and redirections, and
terminated by a \fIcontrol operator\fP.  The first word
specifies the command to be executed, and is passed as argument zero.
The remaining words are passed as arguments to the invoked command.
.PP
The return value of a \fIsimple command\fP is its exit status, or
128+\fIn\^\fP if the command is terminated by signal
.IR n .
.SS Pipelines
.PP
A \fIpipeline\fP is a sequence of one or more commands separated by
one of the control operators
.B |
or \fB|&\fP.
The format for a pipeline is:
.RS
.PP
[\fBtime\fP [\fB\-p\fP]] [ ! ] \fIcommand\fP [ [\fB|\fP\(bv\fB|&\fP] \fIcommand2\fP ... ]
.RE
.PP
The standard output of
.I command
is connected via a pipe to the standard input of
.IR command2 .
This connection is performed before any redirections specified by the
command (see
.SM
.B REDIRECTION
below).
If \fB|&\fP is used, \fIcommand\fP's standard error, in addition to its
standard output, is connected to
\fIcommand2\fP's standard input through the pipe;
it is shorthand for \fB2>&1 |\fP.
This implicit redirection of the standard error to the standard output is
performed after any redirections specified by the command.
.PP
The return status of a pipeline is the exit status of the last
command, unless the \fBpipefail\fP option is enabled.
If \fBpipefail\fP 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
.B !
precedes a pipeline, the exit status of that pipeline 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.
.PP
If the
.B time
reserved word precedes a pipeline, the elapsed as well as user and
system time consumed by its execution are reported when the pipeline
terminates.
The \fB\-p\fP option changes the output format to that specified by POSIX.
When the shell is in \fIposix mode\fP, it does not recognize
\fBtime\fP as a reserved word if the next token begins with a `-'.
The
.SM
.B TIMEFORMAT
variable may be set to a format string that specifies how the timing
information should be displayed; see the description of
.SM
.B TIMEFORMAT
under
.B "Shell Variables"
below.
.PP
When the shell is in \fIposix mode\fP, \fBtime\fP
may be followed by a newline.  In this case, the shell displays the
total user and system time consumed by the shell and its children.
The
.SM
.B TIMEFORMAT
variable may be used to specify the format of
the time information.
.PP
Each command in a pipeline is executed as a separate process (i.e., in a
subshell).
See
.SM
\fBCOMMAND EXECUTION ENVIRONMENT\fP
for a description of a subshell environment.
If the \fBlastpipe\fP option is enabled using the \fBshopt\fP builtin
(see the description of \fBshopt\fP below),
the last element of a pipeline may be run by the shell process.
.SS Lists
.PP
A \fIlist\fP is a sequence of one or more pipelines separated by one
of the operators
.BR ; ,
.BR & ,
.BR && ,
or
.BR || ,
and optionally terminated by one of
.BR ; ,
.BR & ,
or
.BR <newline> .
.PP
Of these list operators,
.B &&
and
.B ||
have equal precedence, followed by
.B ;
and
.BR & ,
which have equal precedence.
.PP
A sequence of one or more newlines may appear in a \fIlist\fP instead
of a semicolon to delimit commands.
.PP
If a command is terminated by the control operator
.BR & ,
the shell executes the command in the \fIbackground\fP
in a subshell.
The shell does not wait for the command to
finish, and the return status is 0.
These are referred to as \fIasynchronous\fP commands.
Commands separated by a
.B ;
are executed sequentially; the shell waits for each
command to terminate in turn.  The return status is the
exit status of the last command executed.
.PP
AND and OR lists are sequences of one or more pipelines separated by the
\fB&&\fP and \fB||\fP control operators, respectively.
AND and OR lists are executed with left associativity.
An AND list has the form
.RS
.PP
\fIcommand1\fP \fB&&\fP \fIcommand2\fP
.RE
.PP
.I command2
is executed if, and only if,
.I command1
returns an exit status of zero (success).
.PP
An OR list has the form
.RS
.PP
\fIcommand1\fP \fB||\fP \fIcommand2\fP
.PP
.RE
.PP
.I command2
is executed if, and only if,
.I command1
returns a non-zero exit status.
The return status of
AND and OR lists is the exit status of the last command
executed in the list.
.SS Compound Commands
.PP
A \fIcompound command\fP is one of the following.
In most cases a \fIlist\fP in a command's description may be separated from
the rest of the command by one or more newlines, and may be followed by a
newline in place of a semicolon.
.TP
(\fIlist\fP)
\fIlist\fP is executed in a subshell environment (see
.SM
\fBCOMMAND EXECUTION ENVIRONMENT\fP
below).
Variable assignments and builtin
commands that affect the shell's environment do not remain in effect
after the command completes.  The return status is the exit status of
\fIlist\fP.
.TP
{ \fIlist\fP; }
\fIlist\fP is simply executed in the current shell environment.
\fIlist\fP must be terminated with a newline or semicolon.
This is known as a \fIgroup command\fP.
The return status is the exit status of
\fIlist\fP.
Note that unlike the metacharacters \fB(\fP and \fB)\fP, \fB{\fP and
\fB}\fP are \fIreserved words\fP and must occur where a reserved
word is permitted to be recognized.  Since they do not cause a word
break, they must be separated from \fIlist\fP by whitespace or another
shell metacharacter.
.TP
((\fIexpression\fP))
The \fIexpression\fP is evaluated according to the rules described
below under
.SM
.BR "ARITHMETIC EVALUATION" .
If the value of the expression is non-zero, the return status is 0;
otherwise the return status is 1.  This is exactly equivalent to
\fBlet "\fIexpression\fP"\fR.
.TP
\fB[[\fP \fIexpression\fP \fB]]\fP
Return a status of 0 or 1 depending on the evaluation of
the conditional expression \fIexpression\fP.
Expressions are composed of the primaries described below under
.SM
.BR "CONDITIONAL EXPRESSIONS" .
Word splitting and pathname expansion are not performed on the words
between the \fB[[\fP and \fB]]\fP; tilde expansion,
parameter and variable expansion,
arithmetic expansion, command substitution, process
substitution, and quote removal are performed.
Conditional operators such as \fB\-f\fP must be unquoted to be recognized
as primaries.
.if t .sp 0.5
.if n .sp 1
When used with \fB[[\fP, the \fB<\fP and \fB>\fP operators sort
lexicographically using the current locale.
.PP
See the description of the \fItest\fP builtin command (section SHELL
BUILTIN COMMANDS below) for the handling of parameters (i.e.
missing parameters).
.if t .sp 0.5
.if n .sp 1
When the \fB==\fP and \fB!=\fP operators are used, the string to the
right of the operator is considered a pattern and matched according
to the rules described below under \fBPattern Matching\fP,
as if the \fBextglob\fP shell option were enabled.
The \fB=\fP operator is equivalent to \fB==\fP.
If the
.B nocasematch
shell option is enabled, the match is performed without regard to the case
of alphabetic characters.
The return value is 0 if the string matches (\fB==\fP) or does not match
(\fB!=\fP) the pattern, and 1 otherwise.
Any part of the pattern may be quoted to force the quoted portion
to be matched as a string.
.if t .sp 0.5
.if n .sp 1
An additional binary operator, \fB=~\fP, is available, with the same
precedence as \fB==\fP and \fB!=\fP.
When it is used, the string to the right of the operator is considered
a POSIX extended regular expression and matched accordingly (as in \fIregex\fP(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
.B nocasematch
shell option is enabled, the match is performed without regard to the case
of alphabetic characters.
Any part of the pattern may be quoted to force the quoted portion
to be matched as a string.
Bracket expressions in regular expressions must be treated carefully,
since normal quoting characters lose their meanings between brackets.
If the pattern is stored in a shell variable, quoting the variable
expansion forces the entire pattern to be matched as a string.
Substrings matched by parenthesized subexpressions within the regular
expression are saved in the array variable
.SM
.BR BASH_REMATCH .
The element of
.SM
.B BASH_REMATCH
with index 0 is the portion of the string
matching the entire regular expression.
The element of
.SM
.B BASH_REMATCH
with index \fIn\fP is the portion of the
string matching the \fIn\fPth parenthesized subexpression.
.if t .sp 0.5
.if n .sp 1
Expressions may be combined using the following operators, listed
in decreasing order of precedence:
.if t .sp 0.5
.if n .sp 1
.RS
.PD 0
.TP
.B ( \fIexpression\fP )
Returns the value of \fIexpression\fP.
This may be used to override the normal precedence of operators.
.TP
.B ! \fIexpression\fP
True if
.I expression
is false.
.TP
\fIexpression1\fP \fB&&\fP \fIexpression2\fP
True if both
.I expression1
and
.I expression2
are true.
.TP
\fIexpression1\fP \fB||\fP \fIexpression2\fP
True if either
.I expression1
or
.I expression2
is true.
.PD
.LP
The \fB&&\fP and \fB||\fP
operators do not evaluate \fIexpression2\fP if the value of
\fIexpression1\fP is sufficient to determine the return value of
the entire conditional expression.
.RE
.TP
\fBfor\fP \fIname\fP [ [ \fBin\fP [ \fIword ...\fP ] ] ; ] \fBdo\fP \fIlist\fP ; \fBdone\fP
The list of words following \fBin\fP is expanded, generating a list
of items.
The variable \fIname\fP is set to each element of this list
in turn, and \fIlist\fP is executed each time.
If the \fBin\fP \fIword\fP is omitted, the \fBfor\fP command executes
\fIlist\fP once for each positional parameter that is set (see
.SM
.B PARAMETERS
below).
The return status is the exit status of the last command that executes.
If the expansion of the items following \fBin\fP results in an empty
list, no commands are executed, and the return status is 0.
.TP
\fBfor\fP (( \fIexpr1\fP ; \fIexpr2\fP ; \fIexpr3\fP )) ; \fBdo\fP \fIlist\fP ; \fBdone\fP
First, the arithmetic expression \fIexpr1\fP is evaluated according
to the rules described below under
.SM
.BR "ARITHMETIC EVALUATION" .
The arithmetic expression \fIexpr2\fP is then evaluated repeatedly
until it evaluates to zero.
Each time \fIexpr2\fP evaluates to a non-zero value, \fIlist\fP is
executed and the arithmetic expression \fIexpr3\fP is evaluated.
If any expression is omitted, it behaves as if it evaluates to 1.
The return value is the exit status of the last command in \fIlist\fP
that is executed, or false if any of the expressions is invalid.
.TP
\fBselect\fP \fIname\fP [ \fBin\fP \fIword\fP ] ; \fBdo\fP \fIlist\fP ; \fBdone\fP
The list of words following \fBin\fP is expanded, generating a list
of items.  The set of expanded words is printed on the standard
error, each preceded by a number.  If the \fBin\fP
\fIword\fP is omitted, the positional parameters are printed (see
.SM
.B PARAMETERS
below).  The
.SM
.B PS3
prompt is then displayed and a line read from the standard input.
If the line consists of a number corresponding to one of
the displayed words, then the value of
.I name
is set to that word.  If the line is empty, the words and prompt
are displayed again.  If EOF is read, the command completes.  Any
other value read causes
.I name
to be set to null.  The line read is saved in the variable
.SM
.BR REPLY .
The
.I list
is executed after each selection until a
.B break
command is executed.
The exit status of
.B select
is the exit status of the last command executed in
.IR list ,
or zero if no commands were executed.
.TP
\fBcase\fP \fIword\fP \fBin\fP [ [(] \fIpattern\fP [ \fB|\fP \fIpattern\fP ] \
... ) \fIlist\fP ;; ] ... \fBesac\fP
A \fBcase\fP command first expands \fIword\fP, and tries to match
it against each \fIpattern\fP in turn, using the matching rules
described under
.B Pattern Matching
below.
The \fIword\fP is expanded using tilde
expansion, parameter and variable expansion, arithmetic expansion,
command substitution, process substitution and quote removal.
Each \fIpattern\fP examined is expanded using tilde
expansion, parameter and variable expansion, arithmetic expansion,
command substitution, and process substitution.
If the
.B nocasematch
shell option is enabled, the match is performed without regard to the case
of alphabetic characters.
When a match is found, the corresponding \fIlist\fP is executed.
If the \fB;;\fP operator is used, no subsequent matches are attempted after
the first pattern match.
Using \fB;&\fP in place of \fB;;\fP causes execution to continue with
the \fIlist\fP associated with the next set of patterns.
Using \fB;;&\fP in place of \fB;;\fP causes the shell to test the next
pattern list in the statement, if any, and execute any associated \fIlist\fP
on a successful match.
The exit status is zero if no
pattern matches.  Otherwise, it is the exit status of the
last command executed in \fIlist\fP.
.TP
\fBif\fP \fIlist\fP; \fBthen\fP \fIlist\fP; \
[ \fBelif\fP \fIlist\fP; \fBthen\fP \fIlist\fP; ] ... \
[ \fBelse\fP \fIlist\fP; ] \fBfi\fP
The
.B if
.I list
is executed.  If its exit status is zero, the
\fBthen\fP \fIlist\fP is executed.  Otherwise, each \fBelif\fP
\fIlist\fP is executed in turn, and if its exit status is zero,
the corresponding \fBthen\fP \fIlist\fP is executed and the
command completes.  Otherwise, the \fBelse\fP \fIlist\fP is
executed, if present.  The exit status is the exit status of the
last command executed, or zero if no condition tested true.
.TP
\fBwhile\fP \fIlist-1\fP; \fBdo\fP \fIlist-2\fP; \fBdone\fP
.PD 0
.TP
\fBuntil\fP \fIlist-1\fP; \fBdo\fP \fIlist-2\fP; \fBdone\fP
.PD
The \fBwhile\fP command continuously executes the list
\fIlist-2\fP as long as the last command in the list \fIlist-1\fP returns
an exit status of zero.  The \fBuntil\fP command is identical
to the \fBwhile\fP command, except that the test is negated:
.I list-2
is executed as long as the last command in
.I list-1
returns a non-zero exit status.
The exit status of the \fBwhile\fP and \fBuntil\fP commands
is the exit status
of the last command executed in \fIlist-2\fP, or zero if
none was executed.
.SS Coprocesses
.PP
A \fIcoprocess\fP is a shell command preceded by the \fBcoproc\fP reserved
word.
A coprocess is executed asynchronously in a subshell, as if the command
had been terminated with the \fB&\fP control operator, with a two-way pipe
established between the executing shell and the coprocess.
.PP
The format for a coprocess is:
.RS
.PP
\fBcoproc\fP [\fINAME\fP] \fIcommand\fP [\fIredirections\fP]
.RE
.PP
This creates a coprocess named \fINAME\fP.
If \fINAME\fP is not supplied, the default name is \fBCOPROC\fP.
\fINAME\fP must not be supplied if \fIcommand\fP is a \fIsimple
command\fP (see above); otherwise, it is interpreted as the first word
of the simple command.
When the coprocess is executed, the shell creates an array variable (see
.B Arrays
below) named \fINAME\fP in the context of the executing shell.
The standard output of
.I command
is connected via a pipe to a file descriptor in the executing shell,
and that file descriptor is assigned to \fINAME\fP[0].
The standard input of
.I command
is connected via a pipe to a file descriptor in the executing shell,
and that file descriptor is assigned to \fINAME\fP[1].
This pipe is established before any redirections specified by the
command (see
.SM
.B REDIRECTION
below).
The file descriptors can be utilized as arguments to shell commands
and redirections using standard word expansions.
Other than those created to execute command and process substitutions,
the file descriptors are not available in subshells.
The process ID of the shell spawned to execute the coprocess is
available as the value of the variable \fINAME\fP_PID.
The \fBwait\fP
builtin command may be used to wait for the coprocess to terminate.
.PP
Since the coprocess is created as an asynchronous command,
the \fBcoproc\fP command always returns success.
The return status of a coprocess is the exit status of \fIcommand\fP.
.SS Shell Function Definitions
.PP
A shell function is an object that is called like a simple command and
executes a compound command with a new set of positional parameters.
Shell functions are declared as follows:
.TP
\fIname\fP () \fIcompound\-command\fP [\fIredirection\fP]
.PD 0
.TP
\fBfunction\fP \fIname\fP [()] \fIcompound\-command\fP [\fIredirection\fP]
.PD
This defines a function named \fIname\fP.
The reserved word \fBfunction\fP is optional.
If the \fBfunction\fP reserved word is supplied, the parentheses are optional.
The \fIbody\fP of the function is the compound command
.I compound\-command
(see \fBCompound Commands\fP above).
That command is usually a \fIlist\fP of commands between { and }, but
may be any command listed under \fBCompound Commands\fP above,
with one exception: If the \fBfunction\fP reserved word is used, but the
parentheses are not supplied, the braces are required.
\fIcompound\-command\fP is executed whenever \fIname\fP is specified as the
name of a simple command.
When in \fIposix mode\fP, \fIname\fP may not be the name of one of the
POSIX \fIspecial builtins\fP.
Any redirections (see
.SM
.B REDIRECTION
below) specified when a function is defined 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.  (See
.SM
.B FUNCTIONS
below.)
.SH COMMENTS
In a non-interactive shell, or an interactive shell in which the
.B interactive_comments
option to the
.B shopt
builtin is enabled (see
.SM
.B "SHELL BUILTIN COMMANDS"
below), a word beginning with
.B #
causes that word and all remaining characters on that line to
be ignored.  An interactive shell without the
.B interactive_comments
option enabled does not allow comments.  The
.B interactive_comments
option is on by default in interactive shells.
.SH QUOTING
\fIQuoting\fP is used to remove the special meaning of certain
characters or words to the shell.  Quoting can be used to
disable special treatment for special characters, to prevent
reserved words from being recognized as such, and to prevent
parameter expansion.
.PP
Each of the \fImetacharacters\fP listed above under
.SM
.B DEFINITIONS
has special meaning to the shell and must be quoted if it is to
represent itself.
.PP
When the command history expansion facilities are being used
(see
.SM
.B HISTORY EXPANSION
below), the
\fIhistory expansion\fP character, usually \fB!\fP, must be quoted
to prevent history expansion.
.PP
There are three quoting mechanisms: the
.IR "escape character" ,
single quotes, and double quotes.
.PP
A non-quoted backslash (\fB\e\fP) is the
.IR "escape character" .
It preserves the literal value of the next character that follows,
with the exception of <newline>.  If a \fB\e\fP<newline> pair
appears, and the backslash is not itself quoted, the \fB\e\fP<newline>
is treated as a line continuation (that is, it is removed from the
input stream and effectively ignored).
.PP
Enclosing characters in single quotes preserves the literal value
of each character within the quotes.  A single quote may not occur
between single quotes, even when preceded by a backslash.
.PP
Enclosing characters in double quotes preserves the literal value
of all characters within the quotes, with the exception of
.BR $ ,
.BR \` ,
.BR \e ,
and, when history expansion is enabled,
.BR ! .
When the shell is in \fIposix mode\fP, the \fB!\fP has no special meaning
within double quotes, even when history expansion is enabled.
The characters
.B $
and
.B \`
retain their special meaning within double quotes.  The backslash
retains its special meaning only when followed by one of the following
characters:
.BR $ ,
.BR \` ,
\^\fB"\fP\^,
.BR \e ,
or
.BR <newline> .
A double quote may be quoted within double quotes by preceding it with
a backslash.
If enabled, history expansion will be performed unless an
.B !
appearing in double quotes is escaped using a backslash.
The backslash preceding the
.B !
is not removed.
.PP
The special parameters
.B *
and
.B @
have special meaning when in double
quotes (see
.SM
.B PARAMETERS
below).
.PP
Words of the form \fB$\fP\(aq\fIstring\fP\(aq are treated specially.  The
word expands to \fIstring\fP, with backslash-escaped characters replaced
as specified by the ANSI C standard.  Backslash escape sequences, if
present, are decoded as follows:
.RS
.PD 0
.TP
.B \ea
alert (bell)
.TP
.B \eb
backspace
.TP
.B \ee
.TP
.B \eE
an escape character
.TP
.B \ef
form feed
.TP
.B \en
new line
.TP
.B \er
carriage return
.TP
.B \et
horizontal tab
.TP
.B \ev
vertical tab
.TP
.B \e\e
backslash
.TP
.B \e\(aq
single quote
.TP
.B \e\(dq
double quote
.TP
.B \e?
question mark
.TP
.B \e\fInnn\fP
the eight-bit character whose value is the octal value \fInnn\fP
(one to three octal digits)
.TP
.B \ex\fIHH\fP
the eight-bit character whose value is the hexadecimal value \fIHH\fP
(one or two hex digits)
.TP
.B \eu\fIHHHH\fP
the Unicode (ISO/IEC 10646) character whose value is the hexadecimal value
\fIHHHH\fP (one to four hex digits)
.TP
.B \eU\fIHHHHHHHH\fP
the Unicode (ISO/IEC 10646) character whose value is the hexadecimal value
\fIHHHHHHHH\fP (one to eight hex digits)
.TP
.B \ec\fIx\fP
a control-\fIx\fP character
.PD
.RE
.LP
The expanded result is single-quoted, as if the dollar sign had
not been present.
.PP
A double-quoted string preceded by a dollar sign (\fB$\fP\(dq\fIstring\fP\(dq)
will cause the string to be translated according to the current locale.
If the current locale is \fBC\fP or \fBPOSIX\fP, the dollar sign
is ignored.
If the string is translated and replaced, the replacement is
double-quoted.
.SH PARAMETERS
A
.I parameter
is an entity that stores values.
It can be a
.IR name ,
a number, or one of the special characters listed below under
.BR "Special Parameters" .
A
.I variable
is a parameter denoted by a
.IR name .
A variable has a \fIvalue\fP and zero or more \fIattributes\fP.
Attributes are assigned using the
.B declare
builtin command (see
.B declare
below in
.SM
.BR "SHELL BUILTIN COMMANDS" ).
.PP
A parameter is set if it has been assigned a value.  The null string is
a valid value.  Once a variable is set, it may be unset only by using
the
.B unset
builtin command (see
.SM
.B SHELL BUILTIN COMMANDS
below).
.PP
A
.I variable
may be assigned to by a statement of the form
.RS
.PP
\fIname\fP=[\fIvalue\fP]
.RE
.PP
If
.I value
is not given, the variable is assigned the null string.  All
.I values
undergo tilde expansion, parameter and variable expansion,
command substitution, arithmetic expansion, and quote
removal (see
.SM
.B EXPANSION
below).  If the variable has its
.B integer
attribute set, then
.I value
is evaluated as an arithmetic expression even if the $((...)) expansion is
not used (see
.B "Arithmetic Expansion"
below).
Word splitting is not performed, with the exception
of \fB"$@"\fP as explained below under
.BR "Special Parameters" .
Pathname expansion is not performed.
Assignment statements may also appear as arguments to the
.BR alias ,
.BR declare ,
.BR typeset ,
.BR export ,
.BR readonly ,
and
.B local
builtin commands (\fIdeclaration\fP commands).
When in \fIposix mode\fP, these builtins may appear in a command after
one or more instances of the \fBcommand\fP builtin and retain these
assignment statement properties.
.PP
In the context where an assignment statement is assigning a value
to a shell variable or array index, the += operator can be used to
append to or add to the variable's previous value.
This includes arguments to builtin commands such as \fBdeclare\fP that
accept assignment statements (\fIdeclaration\fP commands).
When += is applied to a variable for which the \fIinteger\fP attribute has been
set, \fIvalue\fP is evaluated as an arithmetic expression and added to the
variable's current value, which is also evaluated.
When += is applied to an array variable using compound assignment (see
.B Arrays
below), the
variable's value is not unset (as it is when using =), and new values are
appended to the array beginning at one greater than the array's maximum index
(for indexed arrays) or added as additional key\-value pairs in an
associative array.
When applied to a string-valued variable, \fIvalue\fP is expanded and
appended to the variable's value.
.PP
A variable can be assigned the \fInameref\fP attribute using the
\fB\-n\fP option to the \fBdeclare\fP or \fBlocal\fP builtin commands
(see the descriptions of \fBdeclare\fP and \fBlocal\fP below)
to create a \fInameref\fP, or a reference to another variable.
This allows variables to be manipulated indirectly.
Whenever the nameref variable is referenced, assigned to, unset, or has
its attributes modified (other than using or changing the \fInameref\fP
attribute itself), the
operation is actually performed on the variable specified by the nameref
variable's value.
A nameref is commonly used within shell functions to refer to a variable
whose name is passed as an argument to the function.
For instance, if a variable name is passed to a shell function as its first
argument, running
.sp .5
.RS
.if t \f(CWdeclare -n ref=$1\fP
.if n declare -n ref=$1
.RE
.sp .5
inside the function creates a nameref variable \fBref\fP whose value is
the variable name passed as the first argument.
References and assignments to \fBref\fP, and changes to its attributes,
are treated as references, assignments, and attribute modifications
to the variable whose name was passed as \fB$1\fP.
If the control variable in a \fBfor\fP loop has the nameref attribute,
the list of words can be a list of shell variables, and a name reference
will be established for each word in the list, in turn, when the loop is
executed.
Array variables cannot be given the \fBnameref\fP attribute.
However, nameref variables can reference array variables and subscripted
array variables.
Namerefs can be unset using the \fB\-n\fP option to the \fBunset\fP builtin.
Otherwise, if \fBunset\fP is executed with the name of a nameref variable
as an argument, the variable referenced by the nameref variable will be unset.
.SS Positional Parameters
.PP
A
.I positional parameter
is a parameter denoted by one or more
digits, other than the single digit 0.  Positional parameters are
assigned from the shell's arguments when it is invoked,
and may be reassigned using the
.B set
builtin command.  Positional parameters may not be assigned to
with assignment statements.  The positional parameters are
temporarily replaced when a shell function is executed (see
.SM
.B FUNCTIONS
below).
.PP
When a positional parameter consisting of more than a single
digit is expanded, it must be enclosed in braces (see
.SM
.B EXPANSION
below).
.SS Special Parameters
.PP
The shell treats several parameters specially.  These parameters may
only be referenced; assignment to them is not allowed.
.PD 0
.TP
.B *
Expands to the positional parameters, starting from one.
When the expansion is not within double quotes, each positional parameter
expands to a separate word.
In contexts where it is performed, those words
are subject to further word splitting and pathname expansion.
When the expansion occurs within double quotes, it expands to a single word
with the value of each parameter separated by the first character of the
.SM
.B IFS
special variable.  That is, "\fB$*\fP" is equivalent
to "\fB$1\fP\fIc\fP\fB$2\fP\fIc\fP\fB...\fP", where
.I c
is the first character of the value of the
.SM
.B IFS
variable.  If
.SM
.B IFS
is unset, the parameters are separated by spaces.
If
.SM
.B IFS
is null, the parameters are joined without intervening separators.
.TP
.B @
Expands to the positional parameters, starting from one.
In contexts where word splitting is performed, this expands each
positional parameter to a separate word; if not within double
quotes, these words are subject to word splitting.
In contexts where word splitting is not performed,
this expands to a single word
with each positional parameter separated by a space.
When the
expansion occurs within double quotes, each parameter expands to a
separate word.  That is, "\fB$@\fP" is equivalent to
"\fB$1\fP" "\fB$2\fP" ...
If the double-quoted expansion occurs within a word, the expansion of
the first parameter is joined with the beginning part of the original
word, and the expansion of the last parameter is joined with the last
part of the original word.
When there are no positional parameters, "\fB$@\fP" and
.B $@
expand to nothing (i.e., they are removed).
.TP
.B #
Expands to the number of positional parameters in decimal.
.TP
.B ?
Expands to the exit status of the most recently executed foreground
pipeline.
.TP
.B \-
Expands to the current option flags as specified upon invocation, 
by the
.B set
builtin command, or those set by the shell itself
(such as the
.B \-i
option).
.TP
.B $
Expands to the process ID of the shell.  In a () subshell, it
expands to the process ID of the current shell, not the
subshell.
.TP
.B !
Expands to the process ID of the job most recently placed into the
background, whether executed as an asynchronous command or using
the \fBbg\fP builtin (see
.SM
.B "JOB CONTROL"
below).
.TP
.B 0
Expands to the name of the shell or shell script.  This is set at
shell initialization.  If
.B bash
is invoked with a file of commands,
.B $0
is set to the name of that file.  If
.B bash
is started with the
.B \-c
option, then
.B $0
is set to the first argument after the string to be
executed, if one is present.  Otherwise, it is set
to the filename used to invoke
.BR bash ,
as given by argument zero.
.TP
.B _
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 simple
command executed in the foreground, after expansion.
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
currently being checked.
.PD
.SS Shell Variables
.PP
The following variables are set by the shell:
.PP
.PD 0
.TP
.B BASH
Expands to the full filename used to invoke this instance of
.BR bash .
.TP
.B BASHOPTS
A colon-separated list of enabled shell options.  Each word in
the list is a valid argument for the
.B \-s
option to the
.B shopt
builtin command (see
.SM
.B "SHELL BUILTIN COMMANDS"
below).  The options appearing in
.SM
.B BASHOPTS
are those reported as
.I on
by \fBshopt\fP.
If this variable is in the environment when
.B bash
starts up, each shell option in the list will be enabled before
reading any startup files.
This variable is read-only.
.TP
.B BASHPID
Expands to the process ID of the current \fBbash\fP process.
This differs from \fB$$\fP under certain circumstances, such as subshells
that do not require \fBbash\fP to be re-initialized.
Assignments to
.SM
.B BASHPID
have no effect.
If
.B BASHPID
is unset, it loses its special properties, even if it is
subsequently reset.
.TP
.B BASH_ALIASES
An associative array variable whose members correspond to the internal
list of aliases as maintained by the \fBalias\fP builtin.
Elements added to this array appear in the alias list; however,
unsetting array elements currently does not cause aliases to be removed
from the alias list.
If
.B BASH_ALIASES
is unset, it loses its special properties, even if it is
subsequently reset.
.TP
.B BASH_ARGC
An array variable whose values are the number of parameters in each
frame of the current \fBbash\fP execution call stack.
The number of
parameters to the current subroutine (shell function or script executed
with \fB.\fP or \fBsource\fP) is at the top of the stack.
When a subroutine is executed, the number of parameters passed is pushed onto
.SM
.BR BASH_ARGC .
The shell sets
.SM
.B BASH_ARGC
only when in extended debugging mode (see the description of the
.B extdebug
option to the
.B shopt
builtin below).
Setting \fBextdebug\fP after the shell has started to execute a script,
or referencing this variable when \fBextdebug\fP is not set,
may result in inconsistent values.
.TP
.B BASH_ARGV
An array variable containing all of the parameters in the current \fBbash\fP
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
.SM
.BR BASH_ARGV .
The shell sets
.SM
.B BASH_ARGV
only when in extended debugging mode
(see the description of the
.B extdebug
option to the
.B shopt
builtin below).
Setting \fBextdebug\fP after the shell has started to execute a script,
or referencing this variable when \fBextdebug\fP is not set,
may result in inconsistent values.
.TP
.B BASH_ARGV0
When referenced, this variable expands to the name of the shell or shell
script (identical to
.BR $0 ;
see the description of special parameter 0 above).
Assignment to
.B BASH_ARGV0
causes the value assigned to also be assigned to \fB$0\fP.
If
.B BASH_ARGV0
is unset, it loses its special properties, even if it is
subsequently reset.
.TP
.B BASH_CMDS
An associative array variable whose members correspond to the internal
hash table of commands as maintained by the \fBhash\fP builtin.
Elements added to this array appear in the hash table; however,
unsetting array elements currently does not cause command names to be removed
from the hash table.
If
.B BASH_CMDS
is unset, it loses its special properties, even if it is
subsequently reset.
.TP
.B BASH_COMMAND
The command currently being executed or about to be executed, unless the
shell is executing a command as the result of a trap,
in which case it is the command executing at the time of the trap.
.TP
.B BASH_EXECUTION_STRING
The command argument to the \fB\-c\fP invocation option.
.TP
.B BASH_LINENO
An array variable whose members are the line numbers in source files
where each corresponding member of
.SM
.B FUNCNAME
was invoked.
\fB${BASH_LINENO[\fP\fI$i\fP\fB]}\fP is the line number in the source
file (\fB${BASH_SOURCE[\fP\fI$i+1\fP\fB]}\fP) where
\fB${FUNCNAME[\fP\fI$i\fP\fB]}\fP was called
(or \fB${BASH_LINENO[\fP\fI$i-1\fP\fB]}\fP if referenced within another
shell function).
Use
.SM
.B LINENO
to obtain the current line number.
.TP
.B BASH_LOADABLES_PATH
A colon-separated list of directories in which the shell looks for
dynamically loadable builtins specified by the
.B enable
command.
.TP
.B BASH_REMATCH
An array variable whose members are assigned by the \fB=~\fP binary
operator to the \fB[[\fP conditional command.
The element with index 0 is the portion of the string
matching the entire regular expression.
The element with index \fIn\fP is the portion of the
string matching the \fIn\fPth parenthesized subexpression.
This variable is read-only.
.TP
.B BASH_SOURCE
An array variable whose members are the source filenames
where the corresponding shell function names in the
.SM
.B FUNCNAME
array variable are defined.
The shell function
\fB${FUNCNAME[\fP\fI$i\fP\fB]}\fP is defined in the file
\fB${BASH_SOURCE[\fP\fI$i\fP\fB]}\fP and called from
\fB${BASH_SOURCE[\fP\fI$i+1\fP\fB]}\fP.
.TP
.B BASH_SUBSHELL
Incremented by one within each subshell or subshell environment when
the shell begins executing in that environment.
The initial value is 0.
.TP
.B BASH_VERSINFO
A readonly array variable whose members hold version information for
this instance of
.BR bash .
The values assigned to the array members are as follows:
.sp .5
.RS
.TP 24
.B BASH_VERSINFO[\fR0\fP]
The major version number (the \fIrelease\fP).
.TP
.B BASH_VERSINFO[\fR1\fP]
The minor version number (the \fIversion\fP).
.TP
.B BASH_VERSINFO[\fR2\fP]
The patch level.
.TP
.B BASH_VERSINFO[\fR3\fP]
The build version.
.TP
.B BASH_VERSINFO[\fR4\fP]
The release status (e.g., \fIbeta1\fP).
.TP
.B BASH_VERSINFO[\fR5\fP]
The value of
.SM
.BR MACHTYPE .
.RE
.TP
.B BASH_VERSION
Expands to a string describing the version of this instance of
.BR bash .
.TP
.B COMP_CWORD
An index into \fB${COMP_WORDS}\fP of the word containing the current
cursor position.
This variable is available only in shell functions invoked by the
programmable completion facilities (see \fBProgrammable Completion\fP
below).
.TP
.B COMP_KEY
The key (or final key of a key sequence) used to invoke the current
completion function.
.TP
.B COMP_LINE
The current command line.
This variable is available only in shell functions and external
commands invoked by the
programmable completion facilities (see \fBProgrammable Completion\fP
below).
.TP
.B COMP_POINT
The index of the current cursor position relative to the beginning of
the current command.
If the current cursor position is at the end of the current command,
the value of this variable is equal to \fB${#COMP_LINE}\fP.
This variable is available only in shell functions and external
commands invoked by the
programmable completion facilities (see \fBProgrammable Completion\fP
below).
.TP
.B COMP_TYPE
Set to an integer value corresponding to the type of completion attempted
that caused a completion function to be called:
\fITAB\fP, for normal completion,
\fI?\fP, for listing completions after successive tabs,
\fI!\fP, for listing alternatives on partial word completion,
\fI@\fP, to list completions if the word is not unmodified,
or
\fI%\fP, for menu completion.
This variable is available only in shell functions and external
commands invoked by the
programmable completion facilities (see \fBProgrammable Completion\fP
below).
.TP
.B COMP_WORDBREAKS
The set of characters that the \fBreadline\fP library treats as word
separators when performing word completion.
If
.SM
.B COMP_WORDBREAKS
is unset, it loses its special properties, even if it is
subsequently reset.
.TP
.B COMP_WORDS
An array variable (see \fBArrays\fP below) consisting of the individual
words in the current command line.
The line is split into words as \fBreadline\fP would split it, using
.SM
.B COMP_WORDBREAKS
as described above.
This variable is available only in shell functions invoked by the
programmable completion facilities (see \fBProgrammable Completion\fP
below).
.TP
.B COPROC
An array variable (see \fBArrays\fP below) created to hold the file descriptors
for output from and input to an unnamed coprocess (see \fBCoprocesses\fP
above).
.TP
.B DIRSTACK
An array variable (see
.B Arrays
below) containing the current contents of the directory stack.
Directories appear in the stack in the order they are displayed by the
.B dirs
builtin.
Assigning to members of this array variable may be used to modify
directories already in the stack, but the
.B pushd
and
.B popd
builtins must be used to add and remove directories.
Assignment to this variable will not change the current directory.
If
.SM
.B DIRSTACK
is unset, it loses its special properties, even if it is
subsequently reset.
.TP
.B EPOCHREALTIME
Each time this parameter is referenced, it expands to the number of seconds
since the Unix Epoch (see \fItime\fP\fR(3)\fP) as a floating point value
with micro-second granularity.
Assignments to
.SM
.B EPOCHREALTIME
are ignored.
If
.SM
.B EPOCHREALTIME
is unset, it loses its special properties, even if it is
subsequently reset.
.TP
.B EPOCHSECONDS
Each time this parameter is referenced, it expands to the number of seconds
since the Unix Epoch (see \fItime\fP\fR(3)\fP).
Assignments to
.SM
.B EPOCHSECONDS
are ignored.
If
.SM
.B EPOCHSECONDS
is unset, it loses its special properties, even if it is
subsequently reset.
.TP
.B EUID
Expands to the effective user ID of the current user, initialized at
shell startup.  This variable is readonly.
.TP
.B FUNCNAME
An array variable containing the names of all shell functions
currently in the execution call stack.
The element with index 0 is the name of any currently-executing
shell function.
The bottom-most element (the one with the highest index) is
.if t \f(CW"main"\fP.
.if n "main".
This variable exists only when a shell function is executing.
Assignments to
.SM
.B FUNCNAME
have no effect.
If
.SM
.B FUNCNAME
is unset, it loses its special properties, even if it is
subsequently reset.
.if t .sp 0.5
.if n .sp 1
This variable can be used with \fBBASH_LINENO\fP and \fBBASH_SOURCE\fP.
Each element of \fBFUNCNAME\fP has corresponding elements in
\fBBASH_LINENO\fP and \fBBASH_SOURCE\fP to describe the call stack.
For instance, \fB${FUNCNAME[\fP\fI$i\fP\fB]}\fP was called from the file
\fB${BASH_SOURCE[\fP\fI$i+1\fP\fB]}\fP at line number
\fB${BASH_LINENO[\fP\fI$i\fP\fB]}\fP.
The \fBcaller\fP builtin displays the current call stack using this
information.
.TP
.B GROUPS
An array variable containing the list of groups of which the current
user is a member.
Assignments to
.SM
.B GROUPS
have no effect.
If
.SM
.B GROUPS
is unset, it loses its special properties, even if it is
subsequently reset.
.TP
.B HISTCMD
The history number, or index in the history list, of the current
command.
If
.SM
.B HISTCMD
is unset, it loses its special properties, even if it is
subsequently reset.
.TP
.B HOSTNAME
Automatically set to the name of the current host.
.TP
.B HOSTTYPE
Automatically set to a string that uniquely
describes the type of machine on which
.B bash
is executing.
The default is system-dependent.
.TP
.B LINENO
Each time this parameter is referenced, the shell substitutes
a decimal number representing the current sequential line number
(starting with 1) within a script or function.  When not in a
script or function, the value substituted is not guaranteed to
be meaningful.
If
.SM
.B LINENO
is unset, it loses its special properties, even if it is
subsequently reset.
.TP
.B MACHTYPE
Automatically set to a string that fully describes the system
type on which
.B bash
is executing, in the standard GNU \fIcpu-company-system\fP format.
The default is system-dependent.
.TP
.B MAPFILE
An array variable (see \fBArrays\fP below) created to hold the text
read by the \fBmapfile\fP builtin when no variable name is supplied.
.TP
.B OLDPWD
The previous working directory as set by the
.B cd
command.
.TP
.B OPTARG
The value of the last option argument processed by the
.B getopts
builtin command (see
.SM
.B SHELL BUILTIN COMMANDS
below).
.TP
.B OPTIND
The index of the next argument to be processed by the
.B getopts
builtin command (see
.SM
.B SHELL BUILTIN COMMANDS
below).
.TP
.B OSTYPE
Automatically set to a string that
describes the operating system on which
.B bash
is executing.
The default is system-dependent.
.TP
.B PIPESTATUS
An array variable (see
.B Arrays
below) containing a list of exit status values from the processes
in the most-recently-executed foreground pipeline (which may
contain only a single command).
.TP
.B PPID
The process ID of the shell's parent.  This variable is readonly.
.TP
.B PWD
The current working directory as set by the
.B cd
command.
.TP
.B RANDOM
Each time this parameter is referenced, a random integer between
0 and 32767 is
generated.  The sequence of random numbers may be initialized by assigning
a value to
.SM
.BR RANDOM .
If
.SM
.B RANDOM
is unset, it loses its special properties, even if it is
subsequently reset.
.TP
.B READLINE_LINE
The contents of the
.B readline
line buffer, for use with
.if t \f(CWbind -x\fP
.if n "bind -x"
(see
.SM
.B "SHELL BUILTIN COMMANDS"
below).
.TP
.B READLINE_POINT
The position of the insertion point in the
.B readline
line buffer, for use with
.if t \f(CWbind -x\fP
.if n "bind -x"
(see
.SM
.B "SHELL BUILTIN COMMANDS"
below).
.TP
.B REPLY
Set to the line of input read by the
.B read
builtin command when no arguments are supplied.
.TP
.B SECONDS
Each time this parameter is
referenced, the number of seconds since shell invocation is returned.  If a
value is assigned to
.SM
.BR SECONDS ,
the value returned upon subsequent
references is
the number of seconds since the assignment plus the value assigned.
If
.SM
.B SECONDS
is unset, it loses its special properties, even if it is
subsequently reset.
.TP
.B SHELLOPTS
A colon-separated list of enabled shell options.  Each word in
the list is a valid argument for the
.B \-o
option to the
.B set
builtin command (see
.SM
.B "SHELL BUILTIN COMMANDS"
below).  The options appearing in
.SM
.B SHELLOPTS
are those reported as
.I on
by \fBset \-o\fP.
If this variable is in the environment when
.B bash
starts up, each shell option in the list will be enabled before
reading any startup files.
This variable is read-only.
.TP
.B SHLVL
Incremented by one each time an instance of
.B bash
is started.
.TP
.B UID
Expands to the user ID of the current user, initialized at shell startup.
This variable is readonly.
.PD
.PP
The following variables are used by the shell.  In some cases,
.B bash
assigns a default value to a variable; these cases are noted
below.
.PP
.PD 0
.TP
.B BASH_COMPAT
The value is used to set the shell's compatibility level.
See the description of the \fBshopt\fP builtin below under
\fBSHELL BUILTIN COMMANDS\fP
for a description of the various compatibility
levels and their effects.
The value may be a decimal number (e.g., 4.2) or an integer (e.g., 42)
corresponding to the desired compatibility level.
If \fBBASH_COMPAT\fP is unset or set to the empty string, the compatibility
level is set to the default for the current version.
If \fBBASH_COMPAT\fP is set to a value that is not one of the valid
compatibility levels, the shell prints an error message and sets the
compatibility level to the default for the current version.
The valid compatibility levels correspond to the compatibility options
accepted by the \fBshopt\fP builtin described below (for example,
\fBcompat42\fP means that 4.2 and 42 are valid values).
The current version is also a valid value.
.TP
.B BASH_ENV
If this parameter is set when \fBbash\fP is executing a shell script,
its value is interpreted as a filename containing commands to
initialize the shell, as in
.IR ~/.bashrc .
The value of
.SM
.B BASH_ENV
is subjected to parameter expansion, command substitution, and arithmetic
expansion before being interpreted as a filename.
.SM
.B PATH
is not used to search for the resultant filename.
.TP
.B BASH_XTRACEFD
If set to an integer corresponding to a valid file descriptor, \fBbash\fP
will write the trace output generated when
.if t \f(CWset -x\fP
.if n \fIset -x\fP
is enabled to that file descriptor.
The file descriptor is closed when
.SM
.B BASH_XTRACEFD
is unset or assigned a new value.
Unsetting
.SM
.B BASH_XTRACEFD
or assigning it the empty string causes the
trace output to be sent to the standard error.
Note that setting
.SM
.B BASH_XTRACEFD
to 2 (the standard error file
descriptor) and then unsetting it will result in the standard error
being closed.
.TP
.B CDPATH
The search path for the
.B cd
command.
This is a colon-separated list of directories in which the shell looks
for destination directories specified by the
.B cd
command.
A sample value is
.if t \f(CW".:~:/usr"\fP.
.if n ".:~:/usr".
.TP
.B CHILD_MAX
Set the number of exited child status values for the shell to remember.
Bash will not allow this value to be decreased below a POSIX-mandated
minimum, and there is a maximum value (currently 8192) that this may
not exceed.
The minimum value is system-dependent.
.TP
.B COLUMNS
Used by the \fBselect\fP compound command to determine the terminal width
when printing selection lists.
Automatically set if the
.B checkwinsize
option is enabled or in an interactive shell upon receipt of a
.SM
.BR SIGWINCH .
.TP
.B COMPREPLY
An array variable from which \fBbash\fP reads the possible completions
generated by a shell function invoked by the programmable completion
facility (see \fBProgrammable Completion\fP below).
Each array element contains one possible completion.
.TP
.B EMACS
If \fBbash\fP finds this variable in the environment when the shell starts
with value
.if t \f(CWt\fP,
.if n "t",
it assumes that the shell is running in an Emacs shell buffer and disables
line editing.
.TP
.B ENV
Similar to
.SM
.BR BASH_ENV ;
used when the shell is invoked in \fIposix mode\fP.
.TP
.B EXECIGNORE
A colon-separated list of shell patterns (see \fBPattern Matching\fP)
defining the list of filenames to be ignored by command search using
\fBPATH\fP.
Files whose full pathnames match one of these patterns are not considered
executable files for the purposes of completion and command execution
via \fBPATH\fP lookup.
This does not affect the behavior of the \fB[\fP, \fBtest\fP, and \fB[[\fP
commands.
Full pathnames in the command hash table are not subject to \fBEXECIGNORE\fP.
Use this variable to ignore shared library files that have the executable
bit set, but are not executable files.
The pattern matching honors the setting of the \fBextglob\fP shell
option.
.TP
.B FCEDIT
The default editor for the
.B fc
builtin command.
.TP
.B FIGNORE
A colon-separated list of suffixes to ignore when performing
filename completion (see
.SM
.B READLINE
below).
A filename whose suffix matches one of the entries in 
.SM
.B FIGNORE
is excluded from the list of matched filenames.
A sample value is
.if t \f(CW".o:~"\fP.
.if n ".o:~"
(Quoting is needed when assigning a value to this variable,
which contains tildes).
.TP
.B FUNCNEST
If set to a numeric value greater than 0, defines a maximum function
nesting level.  Function invocations that exceed this nesting level
will cause the current command to abort.
.TP
.B GLOBIGNORE
A colon-separated list of patterns defining the set of file names to
be ignored by pathname expansion.
If a file name matched by a pathname expansion pattern also matches one
of the patterns in
.SM
.BR GLOBIGNORE ,
it is removed from the list of matches.
.TP
.B HISTCONTROL
A colon-separated list of values controlling how commands are saved on
the history list.
If the list of values includes
.IR ignorespace ,
lines which begin with a
.B space
character are not saved in the history list.
A value of
.I ignoredups
causes lines matching the previous history entry to not be saved.
A value of
.I ignoreboth
is shorthand for \fIignorespace\fP and \fIignoredups\fP.
A value of
.I 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
.SM
.B 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
.SM
.BR 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
.SM
.BR HISTCONTROL .
.TP
.B HISTFILE
The name of the file in which command history is saved (see
.SM
.B HISTORY
below).  The default value is \fI~/.bash_history\fP.  If unset, the
command history is not saved when a shell exits.
.TP
.B HISTFILESIZE
The maximum number of lines contained in the history file.  When this
variable is assigned a value, the history file is truncated, if
necessary,
to contain no more than that number of lines by removing the oldest entries.
The history file is also truncated to this size after
writing it when a shell exits.
If the value is 0, the history file is truncated to zero size.
Non-numeric values and numeric values less than zero inhibit truncation.
The shell sets the default value to the value of \fBHISTSIZE\fP
after reading any startup files.
.TP
.B HISTIGNORE
A colon-separated list of patterns used to decide which command lines
should be saved on the history list.  Each pattern is anchored at the
beginning of the line and must match the complete line (no implicit
`\fB*\fP' is appended).  Each pattern is tested against the line
after the checks specified by
.SM
.B HISTCONTROL
are applied.
In addition to the normal shell pattern matching characters, `\fB&\fP'
matches the previous history line.  `\fB&\fP' may be escaped using a
backslash; the backslash is removed before attempting a match.
The second and subsequent lines of a multi-line compound command are
not tested, and are added to the history regardless of the value of
.SM
.BR HISTIGNORE .
The pattern matching honors the setting of the \fBextglob\fP shell
option.
.TP
.B HISTSIZE
The number of commands to remember in the command history (see
.SM
.B HISTORY
below).
If the value is 0, commands are not saved in the history list.
Numeric values less than zero result in every command being saved
on the history list (there is no limit).
The shell sets the default value to 500 after reading any startup files.
.TP
.B HISTTIMEFORMAT
If this variable is set and not null, its value is used as a format string
for \fIstrftime\fP(3) to print the time stamp associated with each history
entry displayed by the \fBhistory\fP builtin.
If this variable is set, time stamps are written to the history file so
they may be preserved across shell sessions.
This uses the history comment character to distinguish timestamps from
other history lines.
.TP
.B HOME
The home directory of the current user; the default argument for the
\fBcd\fP builtin command.
The value of this variable is also used when performing tilde expansion.
.TP
.B HOSTFILE
Contains the name of a file in the same format as
.FN /etc/hosts
that should be read when the shell needs to complete a
hostname.
The list of possible hostname completions may be changed while the
shell is running;
the next time hostname completion is attempted after the
value is changed,
.B bash
adds the contents of the new file to the existing list.
If
.SM
.B HOSTFILE
is set, but has no value, or does not name a readable file,
\fBbash\fP attempts to read
.FN /etc/hosts
to obtain the list of possible hostname completions.
When
.SM
.B HOSTFILE
is unset, the hostname list is cleared.
.TP
.B IFS
The
.I Internal Field Separator
that is used
for word splitting after expansion and to
split lines into words with the
.B read
builtin command.  The default value is
``<space><tab><newline>''.
.TP
.B IGNOREEOF
Controls the
action of an interactive shell on receipt of an
.SM
.B EOF
character as the sole input.  If set, the value is the number of
consecutive
.SM
.B EOF
characters which must be
typed as the first characters on an input line before
.B bash
exits.  If the variable exists but does not have a numeric value, or
has no value, the default value is 10.  If it does not exist,
.SM
.B EOF
signifies the end of input to the shell.
.TP
.B INPUTRC
The filename for the
.B readline
startup file, overriding the default of
.FN ~/.inputrc
(see
.SM
.B READLINE
below).
.TP
.B INSIDE_EMACS
If this variable appears in the environment when the shell starts,
\fBbash\fP assumes that it is running inside an Emacs shell buffer
and may disable line editing, depending on the value of \fBTERM\fP.
.TP
.B LANG
Used to determine the locale category for any category not specifically
selected with a variable starting with \fBLC_\fP.
.TP
.B LC_ALL
This variable overrides the value of
.SM
.B LANG
and any other
\fBLC_\fP variable specifying a locale category.
.TP
.B LC_COLLATE
This variable determines the collation order used when sorting the
results of pathname expansion, and determines the behavior of range
expressions, equivalence classes, and collating sequences within
pathname expansion and pattern matching.
.TP
.B LC_CTYPE
This variable determines the interpretation of characters and the
behavior of character classes within pathname expansion and pattern
matching.
.TP
.B LC_MESSAGES
This variable determines the locale used to translate double-quoted
strings preceded by a \fB$\fP.
.TP
.B LC_NUMERIC
This variable determines the locale category used for number formatting.
.TP
.B LC_TIME
This variable determines the locale category used for data and time
formatting.
.TP
.B LINES
Used by the \fBselect\fP compound command to determine the column length
for printing selection lists.
Automatically set if the
.B checkwinsize
option is enabled or in an interactive shell upon receipt of a
.SM
.BR SIGWINCH .
.TP
.B MAIL
If this parameter is set to a file or directory name and the
.SM
.B MAILPATH
variable is not set,
.B bash
informs the user of the arrival of mail in the specified file or
Maildir-format directory.
.TP
.B MAILCHECK
Specifies how
often (in seconds)
.B bash
checks for mail.  The default is 60 seconds.  When it is time to check
for mail, the shell does so before displaying the primary prompt.
If this variable is unset, or set to a value that is not a number
greater than or equal to zero, the shell disables mail checking.
.TP
.B MAILPATH
A colon-separated list of filenames to be checked for mail.
The message to be printed when mail arrives in a particular file
may be specified by separating the filename from the message with a `?'.
When used in the text of the message, \fB$_\fP expands to the name of
the current mailfile.
Example:
.RS
.PP
\fBMAILPATH\fP=\(aq/var/mail/bfox?"You have mail":~/shell\-mail?"$_ has mail!"\(aq
.PP
.B Bash
can be configured to supply
a default value for this variable (there is no value by default),
but the location of the user
mail files that it uses is system dependent (e.g., /var/mail/\fB$USER\fP).
.RE
.TP
.B OPTERR
If set to the value 1,
.B bash
displays error messages generated by the
.B getopts
builtin command (see
.SM
.B SHELL BUILTIN COMMANDS
below).
.SM
.B OPTERR
is initialized to 1 each time the shell is invoked or a shell
script is executed.
.TP
.B PATH
The search path for commands.  It
is a colon-separated list of directories in which
the shell looks for commands (see
.SM
.B COMMAND EXECUTION
below).
A zero-length (null) directory name in the value of
.SM
.B PATH
indicates the current directory.
A null directory name may appear as two adjacent colons, or as an initial
or trailing colon.
The default path is system-dependent,
and is set by the administrator who installs
.BR bash .
A common value is
.na
.if t \f(CW/usr/local/bin:\:/usr/local/sbin:\:/usr/bin:\:/usr/sbin:\:/bin:\:/sbin\fP.
.if n ``/usr/local/bin:\:/usr/local/sbin:\:/usr/bin:\:/usr/sbin:\:/bin:\:/sbin''.
.ad
.TP
.B POSIXLY_CORRECT
If this variable is in the environment when \fBbash\fP starts, the shell
enters \fIposix mode\fP before reading the startup files, as if the
.B \-\-posix
invocation option had been supplied.  If it is set while the shell is
running, \fBbash\fP enables \fIposix mode\fP, as if the command
.if t \f(CWset -o posix\fP
.if n \fIset -o posix\fP
had been executed.
When the shell enters \fIposix mode\fP, it sets this variable if it was
not already set.
.TP
.B PROMPT_COMMAND
If set, the value is executed as a command prior to issuing each primary
prompt.
.TP
.B PROMPT_DIRTRIM
If set to a number greater than zero, the value is used as the number of
trailing directory components to retain when expanding the \fB\ew\fP and
\fB\eW\fP prompt string escapes (see
.SM
.B PROMPTING
below).  Characters removed are replaced with an ellipsis.
.TP
.B PS0
The value of this parameter is expanded (see
.SM
.B PROMPTING
below) and displayed by interactive shells after reading a command
and before the command is executed.
.TP
.B PS1
The value of this parameter is expanded (see
.SM
.B PROMPTING
below) and used as the primary prompt string.  The default value is
``\fB\es\-\ev\e$ \fP''.
.TP
.B PS2
The value of this parameter is expanded as with
.SM
.B PS1
and used as the secondary prompt string.  The default is
``\fB> \fP''.
.TP
.B PS3
The value of this parameter is used as the prompt for the
.B select
command (see
.SM
.B SHELL GRAMMAR
above).
.TP
.B PS4
The value of this parameter is expanded as with
.SM
.B PS1
and the value is printed before each command
.B bash
displays during an execution trace.  The first character of
the expanded value of
.SM
.B PS4
is replicated multiple times, as necessary, to indicate multiple
levels of indirection.  The default is ``\fB+ \fP''.
.TP
.B SHELL
The full pathname to the shell is kept in this environment variable.
If it is not set when the shell starts,
.B bash
assigns to it the full pathname of the current user's login shell.
.TP
.B TIMEFORMAT
The value of this parameter is used as a format string specifying
how the timing information for pipelines prefixed with the
.B time
reserved word should be displayed.
The \fB%\fP character introduces an escape sequence that is
expanded to a time value or other information.
The escape sequences and their meanings are as follows; the
braces denote optional portions.
.sp .5
.RS
.PD 0
.TP 10
.B %%
A literal \fB%\fP.
.TP
.B %[\fIp\fP][l]R
The elapsed time in seconds.
.TP
.B %[\fIp\fP][l]U
The number of CPU seconds spent in user mode.
.TP
.B %[\fIp\fP][l]S
The number of CPU seconds spent in system mode.
.TP
.B %P
The CPU percentage, computed as (%U + %S) / %R.
.PD
.RE
.IP
The optional \fIp\fP is a digit specifying the \fIprecision\fP,
the number of fractional digits after a decimal point.
A value of 0 causes no decimal point or fraction to be output.
At most three places after the decimal point may be specified;
values of \fIp\fP greater than 3 are changed to 3.
If \fIp\fP is not specified, the value 3 is used.
.IP
The optional \fBl\fP specifies a longer format, including
minutes, of the form \fIMM\fPm\fISS\fP.\fIFF\fPs.
The value of \fIp\fP determines whether or not the fraction is
included.
.IP
If this variable is not set, \fBbash\fP acts as if it had the
value \fB$\(aq\enreal\et%3lR\enuser\et%3lU\ensys\et%3lS\(aq\fP.
If the value is null, no timing information is displayed.
A trailing newline is added when the format string is displayed.
.PD 0
.TP
.B TMOUT
If set to a value greater than zero,
.SM
.B TMOUT
is treated as the
default timeout for the \fBread\fP builtin.
The \fBselect\fP command terminates if input does not arrive
after
.SM
.B TMOUT
seconds when input is coming from a terminal.
In an interactive shell, the value is interpreted as the
number of seconds to wait for a line of input after issuing the
primary prompt.
.B Bash
terminates after waiting for that number of seconds if a complete
line of input does not arrive.
.TP
.B TMPDIR
If set, \fBbash\fP uses its value as the name of a directory in which
\fBbash\fP creates temporary files for the shell's use.
.TP
.B auto_resume
This variable controls how the shell interacts with the user and
job control.  If this variable is set, single word simple
commands without redirections are treated as candidates for resumption
of an existing stopped job.  There is no ambiguity allowed; if there is
more than one job beginning with the string typed, the job most recently
accessed is selected.  The
.I name
of a stopped job, in this context, is the command line used to
start it.
If set to the value
.IR exact ,
the string supplied must match the name of a stopped job exactly;
if set to
.IR substring ,
the string supplied needs to match a substring of the name of a
stopped job.  The
.I substring
value provides functionality analogous to the
.B %?
job identifier (see
.SM
.B JOB CONTROL
below).  If set to any other value, the supplied string must
be a prefix of a stopped job's name; this provides functionality
analogous to the \fB%\fP\fIstring\fP job identifier.
.TP
.B histchars
The two or three characters which control history expansion
and tokenization (see
.SM
.B HISTORY EXPANSION
below).  The first character is the \fIhistory expansion\fP character,
the character which signals the start of a history
expansion, normally `\fB!\fP'.
The second character is the \fIquick substitution\fP
character, which is used as shorthand for re-running the previous
command entered, substituting one string for another in the command.
The default is `\fB^\fP'.
The optional third character is the character
which indicates that the remainder of the line is a comment when found
as the first character of a word, normally `\fB#\fP'.  The history
comment character causes history substitution to be skipped for the
remaining words on the line.  It does not necessarily cause the shell
parser to treat the rest of the line as a comment.
.PD
.SS Arrays
.B Bash
provides one-dimensional indexed and associative array variables.
Any variable may be used as an indexed array; the
.B declare
builtin will explicitly declare an array.
There is no maximum
limit on the size of an array, nor any requirement that members
be indexed or assigned contiguously.
Indexed arrays are referenced using integers (including arithmetic
expressions) and are zero-based; associative arrays are referenced
using arbitrary strings.
Unless otherwise noted, indexed array indices must be non-negative integers.
.PP
An indexed array is created automatically if any variable is assigned to
using the syntax \fIname\fP[\fIsubscript\fP]=\fIvalue\fP.  The
.I subscript
is treated as an arithmetic expression that must evaluate to a number.
To explicitly declare an indexed array, use
.B declare \-a \fIname\fP
(see
.SM
.B SHELL BUILTIN COMMANDS
below).
.B declare \-a \fIname\fP[\fIsubscript\fP]
is also accepted; the \fIsubscript\fP is ignored.
.PP
Associative arrays are created using
.BR "declare \-A \fIname\fP" .
.PP
Attributes may be
specified for an array variable using the
.B declare
and
.B readonly
builtins.  Each attribute applies to all members of an array.
.PP
Arrays are assigned to using compound assignments of the form
\fIname\fP=\fB(\fPvalue\fI1\fP ... value\fIn\fP\fB)\fP, where each
\fIvalue\fP is of the form [\fIsubscript\fP]=\fIstring\fP.
Indexed array assignments do not require anything but \fIstring\fP.
When assigning to indexed arrays, if the optional brackets and subscript
are supplied, that index is assigned to;
otherwise the index of the element assigned is the last index assigned
to by the statement plus one.  Indexing starts at zero.
.PP
When assigning to an associative array, the subscript is required.
.PP
This syntax is also accepted by the
.B declare
builtin.  Individual array elements may be assigned to using the
\fIname\fP[\fIsubscript\fP]=\fIvalue\fP syntax introduced above.
When assigning to an indexed array, if
.I name
is subscripted by a negative number, that number is
interpreted as relative to one greater than the maximum index of
\fIname\fP, so negative indices count back from the end of the
array, and an index of \-1 references the last element.
.PP
Any element of an array may be referenced using
${\fIname\fP[\fIsubscript\fP]}.  The braces are required to avoid
conflicts with pathname expansion.  If
\fIsubscript\fP is \fB@\fP or \fB*\fP, the word expands to
all members of \fIname\fP.  These subscripts differ only when the
word appears within double quotes.  If the word is double-quoted,
${\fIname\fP[*]} expands to a single
word with the value of each array member separated by the first
character of the
.SM
.B IFS
special variable, and ${\fIname\fP[@]} expands each element of
\fIname\fP to a separate word.  When there are no array members,
${\fIname\fP[@]} 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 \fB*\fP and \fB@\fP (see
.B Special Parameters
above).  ${#\fIname\fP[\fIsubscript\fP]} expands to the length of
${\fIname\fP[\fIsubscript\fP]}.  If \fIsubscript\fP is \fB*\fP or
\fB@\fP, the expansion is the number of elements in the array.
If the
.I subscript
used to reference an element of an indexed array
evaluates to a number less than zero, it is
interpreted as relative to one greater than the maximum index of the array,
so negative indices count back from the end of the
array, and an index of \-1 references the last element.
.PP
Referencing an array variable without a subscript is equivalent to
referencing the array with a subscript of 0.
Any reference to a variable using a valid subscript is legal, and
.B bash
will create an array if necessary.
.PP
An array variable is considered set if a subscript has been assigned a
value.  The null string is a valid value.
.PP
It is possible to obtain the keys (indices) of an array as well as the values.
${\fB!\fP\fIname\fP[\fI@\fP]} and ${\fB!\fP\fIname\fP[\fI*\fP]}
expand to the indices assigned in array variable \fIname\fP.
The treatment when in double quotes is similar to the expansion of the
special parameters \fI@\fP and \fI*\fP within double quotes.
.PP
The
.B unset
builtin is used to destroy arrays.  \fBunset\fP \fIname\fP[\fIsubscript\fP]
destroys the array element at index \fIsubscript\fP,
for both indexed and associative arrays.
Negative subscripts to indexed arrays are interpreted as described above.
Unsetting the last element of an array variable does not unset the variable.
\fBunset\fP \fIname\fP, where \fIname\fP is an array, or
\fBunset\fP \fIname\fP[\fIsubscript\fP], where
\fIsubscript\fP is \fB*\fP or \fB@\fP, removes the entire array.
.PP
When using a variable name with a subscript as an argument to a command,
such as with \fBunset\fP, without using the word expansion syntax
described above, the argument is subject to pathname expansion.
If pathname expansion is not desired, the argument should be quoted.
.PP
The
.BR declare ,
.BR local ,
and
.B readonly
builtins each accept a
.B \-a
option to specify an indexed array and a
.B \-A
option to specify an associative array.
If both options are supplied,
.B \-A
takes precedence.
The
.B read
builtin accepts a
.B \-a
option to assign a list of words read from the standard input
to an array.  The
.B set
and
.B declare
builtins display array values in a way that allows them to be
reused as assignments.
.SH EXPANSION
Expansion is performed on the command line after it has been split into
words.  There are seven kinds of expansion performed:
.IR "brace expansion" ,
.IR "tilde expansion" ,
.IR "parameter and variable expansion" ,
.IR "command substitution" ,
.IR "arithmetic expansion" ,
.IR "word splitting" ,
and
.IR "pathname expansion" .
.PP
The order of expansions is:
brace expansion;
tilde expansion, parameter and variable expansion, arithmetic expansion,
and command substitution (done in a left-to-right fashion);
word splitting;
and pathname expansion.
.PP
On systems that can support it, there is an additional expansion
available: \fIprocess substitution\fP.
This is performed at the
same time as tilde, parameter, variable, and arithmetic expansion and
command substitution.
.PP
After these expansions are performed, quote characters present in the
original word are removed unless they have been quoted themselves
(\fIquote removal\fP).
.PP
Only brace expansion, word splitting, and pathname expansion
can increase the number of words of the expansion; other expansions
expand a single word to a single word.
The only exceptions to this are the expansions of
"\fB$@\fP" and "\fB${\fP\fIname\fP\fB[@]}\fP",
and, in most cases, \fB$*\fP and \fB${\fP\fIname\fP\fB[*]}\fP
as explained above (see
.SM
.BR PARAMETERS ).
.SS Brace Expansion
.PP
.I "Brace expansion"
is a mechanism by which arbitrary strings
may be generated.  This mechanism is similar to
\fIpathname expansion\fP, but the filenames generated
need not exist.  Patterns to be brace expanded take
the form of an optional
.IR preamble ,
followed by either a series of comma-separated strings or
a sequence expression between a pair of braces, followed by
an optional
.IR postscript .
The preamble is prefixed to each string contained
within the braces, and the postscript is then appended
to each resulting string, expanding left to right.
.PP
Brace expansions may be nested.  The results of each expanded
string are not sorted; left to right order is preserved.
For example, a\fB{\fPd,c,b\fB}\fPe expands into `ade ace abe'.
.PP
A sequence expression takes the form
\fB{\fP\fIx\fP\fB..\fP\fIy\fP\fB[..\fP\fIincr\fP\fB]}\fP,
where \fIx\fP and \fIy\fP are either integers or single characters,
and \fIincr\fP, an optional increment, is an integer.
When integers are supplied, the expression expands to each number between
\fIx\fP and \fIy\fP, inclusive.
Supplied integers may be prefixed with \fI0\fP to force each term to have the
same width.
When either \fIx\fP or \fPy\fP begins with a zero, the shell
attempts to force all generated terms to contain the same number of digits,
zero-padding where necessary.
When characters are supplied, the expression expands to each character
lexicographically between \fIx\fP and \fIy\fP, inclusive,
using the default C locale.
Note that both \fIx\fP and \fIy\fP must be of the same type.
When the increment is supplied, it is used as the difference between
each term.  The default increment is 1 or \-1 as appropriate.
.PP
Brace expansion is performed before any other expansions,
and any characters special to other expansions are preserved
in the result.  It is strictly textual.
.B Bash
does not apply any syntactic interpretation to the context of the
expansion or the text between the braces.
.PP
A correctly-formed brace expansion must contain unquoted opening
and closing braces, and at least one unquoted comma or a valid
sequence expression.
Any incorrectly formed brace expansion is left unchanged.
A \fB{\fP or \fB,\fP may be quoted with a backslash to prevent its
being considered part of a brace expression.
To avoid conflicts with parameter expansion, the string \fB${\fP
is not considered eligible for brace expansion, and inhibits brace
expansion until the closing \fB}\fP.
.PP
This construct is typically used as shorthand when the common
prefix of the strings to be generated is longer than in the
above example:
.RS
.PP
mkdir /usr/local/src/bash/{old,new,dist,bugs}
.RE
or
.RS
chown root /usr/{ucb/{ex,edit},lib/{ex?.?*,how_ex}}
.RE
.PP
Brace expansion introduces a slight incompatibility with
historical versions of
.BR sh .
.B sh
does not treat opening or closing braces specially when they
appear as part of a word, and preserves them in the output.
.B Bash
removes braces from words as a consequence of brace
expansion.  For example, a word entered to
.B sh
as \fIfile{1,2}\fP
appears identically in the output.  The same word is
output as
.I file1 file2
after expansion by
.BR bash .
If strict compatibility with
.B sh
is desired, start
.B bash
with the
.B +B
option or disable brace expansion with the
.B +B
option to the
.B set
command (see
.SM
.B SHELL BUILTIN COMMANDS
below).
.SS Tilde Expansion
.PP
If a word begins with an unquoted tilde character (`\fB~\fP'), all of
the characters preceding the first unquoted slash (or all characters,
if there is no unquoted slash) are considered a \fItilde-prefix\fP.
If none of the characters in the tilde-prefix are quoted, the
characters in the tilde-prefix following the tilde are treated as a
possible \fIlogin name\fP.
If this login name is the null string, the tilde is replaced with the
value of the shell parameter
.SM
.BR HOME .
If
.SM
.B HOME
is unset, the home directory of the user executing the shell is
substituted instead.
Otherwise, the tilde-prefix is replaced with the home directory
associated with the specified login name.
.PP
If the tilde-prefix is a `~+', the value of the shell variable
.SM
.B PWD
replaces the tilde-prefix.
If the tilde-prefix is a `~\-', the value of the shell variable
.SM
.BR OLDPWD ,
if it is set, is substituted.
If the characters following the tilde in the tilde-prefix consist
of a number \fIN\fP, optionally prefixed
by a `+' or a `\-', the tilde-prefix is replaced with the corresponding
element from the directory stack, as it would be displayed by the
.B dirs
builtin invoked with the tilde-prefix as an argument.
If the characters following the tilde in the tilde-prefix consist of a
number without a leading `+' or `\-', `+' is assumed.
.PP
If the login name is invalid, or the tilde expansion fails, the word
is unchanged.
.PP
Each variable assignment is checked for unquoted tilde-prefixes immediately
following a
.B :
or the first
.BR = .
In these cases, tilde expansion is also performed.
Consequently, one may use filenames with tildes in assignments to
.SM
.BR PATH ,
.SM
.BR MAILPATH ,
and
.SM
.BR CDPATH ,
and the shell assigns the expanded value.
.PP
Bash also performs tilde expansion on words satisfying the conditions of
variable assignments (as described above under
.SM
.BR PARAMETERS )
when they appear as arguments to simple commands.
Bash does not do this, except for the \fIdeclaration\fP commands listed
above, when in \fIposix mode\fP.
.SS Parameter Expansion
.PP
The `\fB$\fP' character introduces parameter expansion,
command substitution, or arithmetic expansion.  The parameter name
or symbol to be expanded may be enclosed in braces, which
are optional but serve to protect the variable to be expanded from
characters immediately following it which could be
interpreted as part of the name.
.PP
When braces are used, the matching ending brace is the first `\fB}\fP'
not escaped by a backslash or within a quoted string, and not within an
embedded arithmetic expansion, command substitution, or parameter
expansion.
.PP
.PD 0
.TP
${\fIparameter\fP}
The value of \fIparameter\fP is substituted.  The braces are required
when
.I parameter
is a positional parameter with more than one digit,
or when
.I parameter
is followed by a character which is not to be
interpreted as part of its name.
The \fIparameter\fP is a shell parameter as described above
\fBPARAMETERS\fP) or an array reference (\fBArrays\fP).
.PD
.PP
If the first character of \fIparameter\fP is an exclamation point (\fB!\fP),
and \fIparameter\fP is not a \fInameref\fP,
it introduces a level of indirection.
\fBBash\fP uses the value formed by expanding the rest of
\fIparameter\fP as the new \fIparameter\fP; this is then
expanded and that value is used in the rest of the expansion, rather
than the expansion of the original \fIparameter\fP.
This is known as \fIindirect expansion\fP.
The value is subject to tilde expansion,
parameter expansion, command substitution, and arithmetic expansion.
If \fIparameter\fP is a nameref, this expands to the name of the
parameter referenced by \fIparameter\fP instead of performing the
complete indirect expansion.
The exceptions to this are the expansions of ${\fB!\fP\fIprefix\fP\fB*\fP} and
${\fB!\fP\fIname\fP[\fI@\fP]} described below.
The exclamation point must immediately follow the left brace in order to
introduce indirection.
.PP
In each of the cases below, \fIword\fP is subject to tilde expansion,
parameter expansion, command substitution, and arithmetic expansion.
.PP
When not performing substring expansion, using the forms documented below
(e.g., \fB:-\fP),
\fBbash\fP tests for a parameter that is unset or null.  Omitting the colon
results in a test only for a parameter that is unset.
.PP
.PD 0
.TP
${\fIparameter\fP\fB:\-\fP\fIword\fP}
\fBUse Default Values\fP.  If
.I parameter
is unset or null, the expansion of
.I word
is substituted.  Otherwise, the value of
.I parameter
is substituted.
.TP
${\fIparameter\fP\fB:=\fP\fIword\fP}
\fBAssign Default Values\fP.
If
.I parameter
is unset or null, the expansion of
.I word
is assigned to
.IR parameter .
The value of
.I parameter
is then substituted.  Positional parameters and special parameters may
not be assigned to in this way.
.TP
${\fIparameter\fP\fB:?\fP\fIword\fP}
\fBDisplay Error if Null or Unset\fP.
If
.I parameter
is null or unset, the expansion of \fIword\fP (or a message to that effect
if
.I word
is not present) is written to the standard error and the shell, if it
is not interactive, exits.  Otherwise, the value of \fIparameter\fP is
substituted.
.TP
${\fIparameter\fP\fB:+\fP\fIword\fP}
\fBUse Alternate Value\fP.
If
.I parameter
is null or unset, nothing is substituted, otherwise the expansion of
.I word
is substituted.
.TP
${\fIparameter\fP\fB:\fP\fIoffset\fP}
.PD 0
.TP
${\fIparameter\fP\fB:\fP\fIoffset\fP\fB:\fP\fIlength\fP}
.PD
\fBSubstring Expansion\fP.
Expands to up to \fIlength\fP characters of the value of \fIparameter\fP
starting at the character specified by \fIoffset\fP.
If \fIparameter\fP is \fB@\fP, an indexed array subscripted by
\fB@\fP or \fB*\fP, or an associative array name, the results differ as
described below.
If \fIlength\fP is omitted, expands to the substring of the value of
\fIparameter\fP starting at the character specified by \fIoffset\fP
and extending to the end of the value.
\fIlength\fP and \fIoffset\fP are arithmetic expressions (see
.SM
.B
ARITHMETIC EVALUATION
below).
.sp 1
If \fIoffset\fP evaluates to a number less than zero, the value
is used as an offset in characters
from the end of the value of \fIparameter\fP.
If \fIlength\fP evaluates to a number less than zero,
it is interpreted as an offset in characters
from the end of the value of \fIparameter\fP rather than
a number of characters, and the expansion is the characters between
\fIoffset\fP and that result.
Note that a negative offset must be separated from the colon by at least
one space to avoid being confused with the \fB:-\fP expansion.
.sp 1
If \fIparameter\fP is \fB@\fP, the result is \fIlength\fP positional
parameters beginning at \fIoffset\fP.
A negative \fIoffset\fP is taken relative to one greater than the greatest
positional parameter, so an offset of \-1 evaluates to the last positional
parameter.
It is an expansion error if \fIlength\fP evaluates to a number less than
zero.
.sp 1
If \fIparameter\fP is an indexed array name subscripted by @ or *,
the result is the \fIlength\fP
members of the array beginning with ${\fIparameter\fP[\fIoffset\fP]}.
A negative \fIoffset\fP is taken relative to one greater than the maximum
index of the specified array.
It is an expansion error if \fIlength\fP evaluates to a number less than
zero.
.sp 1
Substring expansion applied to an associative array produces undefined
results.
.sp 1
Substring indexing is zero-based unless the positional parameters
are used, in which case the indexing starts at 1 by default.
If \fIoffset\fP is 0, and the positional parameters are used, \fB$0\fP is
prefixed to the list.
.TP
${\fB!\fP\fIprefix\fP\fB*\fP}
.PD 0
.TP
${\fB!\fP\fIprefix\fP\fB@\fP}
.PD
\fBNames matching prefix\fP.
Expands to the names of variables whose names begin with \fIprefix\fP,
separated by the first character of the
.SM
.B IFS
special variable.
When \fI@\fP is used and the expansion appears within double quotes, each
variable name expands to a separate word.
.TP
${\fB!\fP\fIname\fP[\fI@\fP]}
.PD 0
.TP
${\fB!\fP\fIname\fP[\fI*\fP]}
.PD
\fBList of array keys\fP.
If \fIname\fP is an array variable, expands to the list of array indices
(keys) assigned in \fIname\fP.
If \fIname\fP is not an array, expands to 0 if \fIname\fP is set and null
otherwise.
When \fI@\fP is used and the expansion appears within double quotes, each
key expands to a separate word.
.TP
${\fB#\fP\fIparameter\fP}
\fBParameter length\fP.
The length in characters of the value of \fIparameter\fP is substituted.
If
.I parameter
is
.B *
or
.BR @ ,
the value substituted is the number of positional parameters.
If
.I parameter
is an array name subscripted by
.B *
or
.BR @ ,
the value substituted is the number of elements in the array.
If
.I parameter
is an indexed array name subscripted by a negative number, that number is
interpreted as relative to one greater than the maximum index of
\fIparameter\fP, so negative indices count back from the end of the
array, and an index of \-1 references the last element.
.TP
${\fIparameter\fP\fB#\fP\fIword\fP}
.PD 0
.TP
${\fIparameter\fP\fB##\fP\fIword\fP}
.PD
\fBRemove matching prefix pattern\fP.
The
.I word
is expanded to produce a pattern just as in pathname
expansion, and matched against the expanded value of
.I parameter
using the rules described under
.B Pattern Matching
below.
If the pattern matches the beginning of
the value of
.IR parameter ,
then the result of the expansion is the expanded value of
.I parameter
with the shortest matching pattern (the ``\fB#\fP'' case) or the
longest matching pattern (the ``\fB##\fP'' case) deleted.
If
.I parameter
is
.B @
or
.BR * ,
the pattern removal operation is applied to each positional
parameter in turn, and the expansion is the resultant list.
If
.I parameter
is an array variable subscripted with
.B @
or
.BR * ,
the pattern removal operation is applied to each member of the
array in turn, and the expansion is the resultant list.
.TP
${\fIparameter\fP\fB%\fP\fIword\fP}
.PD 0
.TP
${\fIparameter\fP\fB%%\fP\fIword\fP}
.PD
\fBRemove matching suffix pattern\fP.
The \fIword\fP is expanded to produce a pattern just as in
pathname expansion, and matched against the expanded value of
.I parameter
using the rules described under
.B Pattern Matching
below.
If the pattern matches a trailing portion of the expanded value of
.IR parameter ,
then the result of the expansion is the expanded value of
.I parameter
with the shortest matching pattern (the ``\fB%\fP'' case) or the
longest matching pattern (the ``\fB%%\fP'' case) deleted.
If
.I parameter
is
.B @
or
.BR * ,
the pattern removal operation is applied to each positional
parameter in turn, and the expansion is the resultant list.
If
.I parameter
is an array variable subscripted with
.B @
or
.BR * ,
the pattern removal operation is applied to each member of the
array in turn, and the expansion is the resultant list.
.TP
${\fIparameter\fP\fB/\fP\fIpattern\fP\fB/\fP\fIstring\fP}
\fBPattern substitution\fP.
The \fIpattern\fP is expanded to produce a pattern just as in
pathname expansion,
\fIParameter\fP is expanded and the longest match of \fIpattern\fP
against its value is replaced with \fIstring\fP.
The match is performed using the rules described under
.B Pattern Matching
below.
If \fIpattern\fP begins with \fB/\fP, all matches of \fIpattern\fP are
replaced with \fIstring\fP.  Normally only the first match is replaced.
If \fIpattern\fP begins with \fB#\fP, it must match at the beginning
of the expanded value of \fIparameter\fP.
If \fIpattern\fP begins with \fB%\fP, it must match at the end
of the expanded value of \fIparameter\fP.
If \fIstring\fP is null, matches of \fIpattern\fP are deleted
and the \fB/\fP following \fIpattern\fP may be omitted.
If the
.B nocasematch
shell option is enabled, the match is performed without regard to the case
of alphabetic characters.
If
.I parameter
is
.B @
or
.BR * ,
the substitution operation is applied to each positional
parameter in turn, and the expansion is the resultant list.
If
.I parameter
is an array variable subscripted with
.B @
or
.BR * ,
the substitution operation is applied to each member of the
array in turn, and the expansion is the resultant list.
.TP
${\fIparameter\fP\fB^\fP\fIpattern\fP}
.PD 0
.TP
${\fIparameter\fP\fB^^\fP\fIpattern\fP}
.TP
${\fIparameter\fP\fB,\fP\fIpattern\fP}
.TP
${\fIparameter\fP\fB,,\fP\fIpattern\fP}
.PD
\fBCase modification\fP.
This expansion modifies the case of alphabetic characters in \fIparameter\fP.
The \fIpattern\fP is expanded to produce a pattern just as in
pathname expansion.
Each character in the expanded value of \fIparameter\fP is tested against
\fIpattern\fP, and, if it matches the pattern, its case is converted.
The pattern should not attempt to match more than one character.
The \fB^\fP operator converts lowercase letters matching \fIpattern\fP
to uppercase; the \fB,\fP operator converts matching uppercase letters
to lowercase.
The \fB^^\fP and \fB,,\fP expansions convert each matched character in the
expanded value; the \fB^\fP and \fB,\fP expansions match and convert only
the first character in the expanded value.
If \fIpattern\fP is omitted, it is treated like a \fB?\fP, which matches
every character.
If
.I parameter
is
.B @
or
.BR * ,
the case modification operation is applied to each positional
parameter in turn, and the expansion is the resultant list.
If
.I parameter
is an array variable subscripted with
.B @
or
.BR * ,
the case modification operation is applied to each member of the
array in turn, and the expansion is the resultant list.
.TP
${\fIparameter\fP\fB@\fP\fIoperator\fP}
\fBParameter transformation\fP.
The expansion is either a transformation of the value of \fIparameter\fP
or information about \fIparameter\fP itself, depending on the value of
\fIoperator\fP.  Each \fIoperator\fP is a single letter:
.sp 1
.RS
.PD 0
.TP
.B Q
The expansion is a string that is the value of \fIparameter\fP quoted in a
format that can be reused as input.
.TP
.B E
The expansion is a string that is the value of \fIparameter\fP with backslash
escape sequences expanded as with the \fB$'...'\fP quoting mechanism.
.TP
.B P
The expansion is a string that is the result of expanding the value of
\fIparameter\fP as if it were a prompt string (see \fBPROMPTING\fP below).
.TP
.B A
The expansion is a string in the form of
an assignment statement or \fBdeclare\fP command that, if
evaluated, will recreate \fIparameter\fP with its attributes and value.
.TP
.B a
The expansion is a string consisting of flag values representing
\fIparameter\fP's attributes.
.PD
.PP
If
.I parameter
is
.B @
or
.BR * ,
the operation is applied to each positional
parameter in turn, and the expansion is the resultant list.
If
.I parameter
is an array variable subscripted with
.B @
or
.BR * ,
the operation is applied to each member of the
array in turn, and the expansion is the resultant list.
.sp 1
The result of the expansion is subject to word splitting and pathname
expansion as described below.
.RE
.SS Command Substitution
.PP
\fICommand substitution\fP allows the output of a command to replace
the command name.  There are two forms:
.RS
.PP
\fB$(\fP\fIcommand\fP\|\fB)\fP
.RE
or
.RS
\fB\`\fP\fIcommand\fP\fB\`\fP
.RE
.PP
.B Bash
performs the expansion by executing \fIcommand\fP in a subshell environment
and replacing the command substitution with the standard output of the
command, with any trailing newlines deleted.
Embedded newlines are not deleted, but they may be removed during
word splitting.
The command substitution \fB$(cat \fIfile\fP)\fR can be replaced by
the equivalent but faster \fB$(< \fIfile\fP)\fR.
.PP
When the old-style backquote form of substitution is used,
backslash retains its literal meaning except when followed by
.BR $ ,
.BR \` ,
or
.BR \e .
The first backquote not preceded by a backslash terminates the
command substitution.
When using the $(\^\fIcommand\fP\|) form, all characters between the
parentheses make up the command; none are treated specially.
.PP
Command substitutions may be nested.  To nest when using the backquoted form,
escape the inner backquotes with backslashes.
.PP
If the substitution appears within double quotes, word splitting and
pathname expansion are not performed on the results.
.SS Arithmetic Expansion
.PP
Arithmetic expansion allows the evaluation of an arithmetic expression
and the substitution of the result.  The format for arithmetic expansion is:
.RS
.PP
\fB$((\fP\fIexpression\fP\fB))\fP
.RE
.PP
The old format \fB$[\fP\fIexpression\fP\fB]\fP is deprecated and will
be removed in upcoming versions of bash.
.PP
The
.I expression
is treated as if it were within double quotes, but a double quote
inside the parentheses is not treated specially.
All tokens in the expression undergo parameter and variable expansion,
command substitution, and quote removal.
The result is treated as the arithmetic expression to be evaluated.
Arithmetic expansions may be nested.
.PP
The evaluation is performed according to the rules listed below under
.SM
.BR "ARITHMETIC EVALUATION" .
If
.I expression
is invalid,
.B bash
prints a message indicating failure and no substitution occurs.
.SS Process Substitution
.PP
\fIProcess substitution\fP allows a process's input or output to be
referred to using a filename.
It takes the form of
\fB<(\fP\fIlist\^\fP\fB)\fP
or
\fB>(\fP\fIlist\^\fP\fB)\fP.
The process \fIlist\fP is run asynchronously, and its input or output
appears as a filename.
This filename is
passed as an argument to the current command as the result of the
expansion.
If the \fB>(\fP\fIlist\^\fP\fB)\fP form is used, writing to
the file will provide input for \fIlist\fP.  If the
\fB<(\fP\fIlist\^\fP\fB)\fP form is used, the file passed as an
argument should be read to obtain the output of \fIlist\fP.
Process substitution is supported on systems that support named
pipes (\fIFIFOs\fP) or the \fB/dev/fd\fP method of naming open files.
.PP
When available, process substitution is performed
simultaneously with parameter and variable expansion,
command substitution,
and arithmetic expansion.
.SS Word Splitting
.PP
The shell scans the results of
parameter expansion,
command substitution,
and
arithmetic expansion
that did not occur within double quotes for
.IR "word splitting" .
.PP
The shell treats each character of
.SM
.B IFS
as a delimiter, and splits the results of the other
expansions into words using these characters as field terminators.
If
.SM
.B IFS
is unset, or its
value is exactly
.BR <space><tab><newline> ,
the default, then
sequences of
.BR <space> ,
.BR <tab> ,
and
.B <newline>
at the beginning and end of the results of the previous
expansions are ignored, and
any sequence of
.SM
.B IFS
characters not at the beginning or end serves to delimit words.
If
.SM
.B IFS
has a value other than the default, then sequences of
the whitespace characters
.BR space ,
.BR tab ,
and
.B newline
are ignored at the beginning and end of the
word, as long as the whitespace character is in the
value of
.SM
.B IFS
(an
.SM
.B IFS
whitespace character).
Any character in
.SM
.B IFS
that is not
.SM
.B IFS
whitespace, along with any adjacent
.SM
.B IFS
whitespace characters, delimits a field.
A sequence of
.SM
.B IFS
whitespace characters is also treated as a delimiter.
If the value of
.SM
.B IFS
is null, no word splitting occurs.
.PP
Explicit null arguments (\^\f3"\^"\fP or \^\f3\(aq\^\(aq\fP\^) are retained
and passed to commands as empty strings.
Unquoted implicit null arguments, resulting from the expansion of
parameters that have no values, are removed.
If a parameter with no value is expanded within double quotes, a
null argument results and is retained
and passed to a command as an empty string.
When a quoted null argument appears as part of a word whose expansion is
non-null, the null argument is removed.
That is, the word
\f(CW\-d\(aq\^\(aq\fP becomes \f(CW\-d\fP after word splitting and
null argument removal.
.PP
Note that if no expansion occurs, no splitting
is performed.
.SS Pathname Expansion
.PP
After word splitting,
unless the
.B \-f
option has been set,
.B bash
scans each word for the characters
.BR * ,
.BR ? ,
and
.BR [ .
If one of these characters appears, then the word is
regarded as a
.IR pattern ,
and replaced with an alphabetically sorted list of
filenames matching the pattern
(see
.SM
.B "Pattern Matching"
below).
If no matching filenames are found,
and the shell option
.B nullglob
is not enabled, the word is left unchanged.
If the
.B nullglob
option is set, and no matches are found,
the word is removed.
If the
.B 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
.B nocaseglob
is enabled, the match is performed without regard to the case
of alphabetic characters.
Note that when using range expressions like
[a-z] (see below), letters of the other case may be included,
depending on the setting of
.B LC_COLLATE.
When a pattern is used for pathname expansion,
the character
.B ``.''
at the start of a name or immediately following a slash
must be matched explicitly, unless the shell option
.B dotglob
is set.
The filenames
.B ``.''
and
.B ``..''
must always be matched explicitly, even if
.B dotglob
is set.
In other cases, the
.B ``.''
character is not treated specially.
When matching a pathname, the slash character must always be
matched explicitly by a slash in the pattern, but in other matching
contexts it can be matched by a special pattern character as described
below under
.SM
.BR "Pattern Matching" .
See the description of
.B shopt
below under
.SM
.B SHELL BUILTIN COMMANDS
for a description of the
.BR nocaseglob ,
.BR nullglob ,
.BR failglob ,
and
.B dotglob
shell options.
.PP
The
.SM
.B GLOBIGNORE
shell variable may be used to restrict the set of file names matching a
.IR pattern .
If
.SM
.B GLOBIGNORE
is set, each matching file name that also matches one of the patterns in
.SM
.B GLOBIGNORE
is removed from the list of matches.
If the \fBnocaseglob\fP option is set, the matching against the patterns in
.SM
.B GLOBIGNORE
is performed without regard to case.
The filenames
.B ``.''
and
.B ``..''
are always ignored when
.SM
.B GLOBIGNORE
is set and not null.  However, setting
.SM
.B GLOBIGNORE
to a non-null value has the effect of enabling the
.B dotglob
shell option, so all other filenames beginning with a
.B ``.''
will match.
To get the old behavior of ignoring filenames beginning with a
.BR ``.'' ,
make
.B ``.*''
one of the patterns in
.SM
.BR GLOBIGNORE .
The
.B dotglob
option is disabled when
.SM
.B GLOBIGNORE
is unset.
The pattern matching honors the setting of the \fBextglob\fP shell
option.
.PP
\fBPattern Matching\fP
.PP
Any character that appears in a pattern, other than the special pattern
characters described below, matches itself.  The NUL character may not
occur in a pattern.  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.
.PP
The special pattern characters have the following meanings:
.PP
.PD 0
.RS
.TP
.B *
Matches any string, including the null string.
When the \fBglobstar\fP shell option is enabled, and \fB*\fP is used in
a pathname expansion context, two adjacent \fB*\fPs used as a single
pattern will match all files and zero or more directories and
subdirectories.
If followed by a \fB/\fP, two adjacent \fB*\fPs will match only directories
and subdirectories.
.TP
.B ?
Matches any single character.
.TP
.B [...]
Matches any one of the enclosed characters.  A pair of characters
separated by a hyphen denotes a
\fIrange expression\fP;
any character that falls between those two characters, inclusive,
using the current locale's collating sequence and character set,
is matched.  If the first character following the
.B [
is a
.B !
or a
.B ^
then any character not enclosed is matched.
The sorting order of characters in range expressions is determined by
the current locale and the values of the
.SM
.B LC_COLLATE
or
.SM
.B LC_ALL
shell variables, if set.
To obtain the traditional interpretation of range expressions, where
.B [a\-d]
is equivalent to
.BR [abcd] ,
set value of the
.B LC_ALL
shell variable to
.BR C ,
or enable the
.B globasciiranges
shell option.
A
.B \-
may be matched by including it as the first or last character
in the set.
A
.B ]
may be matched by including it as the first character
in the set.
.br
.if t .sp 0.5
.if n .sp 1
Within
.B [
and
.BR ] ,
\fIcharacter classes\fP can be specified using the syntax
\fB[:\fP\fIclass\fP\fB:]\fP, where \fIclass\fP is one of the
following classes defined in the POSIX standard:
.PP
.RS
.B
.if n alnum alpha ascii blank cntrl digit graph lower print punct space upper word xdigit
.if t alnum   alpha   ascii   blank   cntrl   digit   graph   lower   print   punct   space   upper   word   xdigit
.br
A character class matches any character belonging to that class.
The \fBword\fP character class matches letters, digits, and the character _.
.br
.if t .sp 0.5
.if n .sp 1
Within
.B [
and
.BR ] ,
an \fIequivalence class\fP can be specified using the syntax
\fB[=\fP\fIc\fP\fB=]\fP, which matches all characters with the
same collation weight (as defined by the current locale) as
the character \fIc\fP.
.br
.if t .sp 0.5
.if n .sp 1
Within
.B [
and
.BR ] ,
the syntax \fB[.\fP\fIsymbol\fP\fB.]\fP matches the collating symbol
\fIsymbol\fP.
.RE
.RE
.PD
.PP
If the \fBextglob\fP shell option is enabled using the \fBshopt\fP
builtin, several extended pattern matching operators are recognized.
In the following description, a \fIpattern-list\fP is a list of one
or more patterns separated by a \fB|\fP.
Composite patterns may be formed using one or more of the following
sub-patterns:
.sp 1
.PD 0
.RS
.TP
\fB?(\fP\^\fIpattern-list\^\fP\fB)\fP
Matches zero or one occurrence of the given patterns
.TP
\fB*(\fP\^\fIpattern-list\^\fP\fB)\fP
Matches zero or more occurrences of the given patterns
.TP
\fB+(\fP\^\fIpattern-list\^\fP\fB)\fP
Matches one or more occurrences of the given patterns
.TP
\fB@(\fP\^\fIpattern-list\^\fP\fB)\fP
Matches one of the given patterns
.TP
\fB!(\fP\^\fIpattern-list\^\fP\fB)\fP
Matches anything except one of the given patterns
.RE
.PD
.PP
Complicated extended pattern matching against long strings is slow,
especially when the patterns contain alternations and the strings
contain multiple matches.
Using separate matches against shorter strings, or using arrays of
strings instead of a single long string, may be faster.
.SS Quote Removal
.PP
After the preceding expansions, all unquoted occurrences of the
characters
.BR \e ,
.BR \(aq ,
and \^\f3"\fP\^ that did not result from one of the above
expansions are removed.
.SH REDIRECTION
Before a command is executed, its input and output
may be
.I redirected
using a special notation interpreted by the shell.
Redirection allows commands' file handles to be
duplicated, opened, closed,
made to refer to different files,
and can change the files the command reads from and writes to.
Redirection may also be used to modify file handles in the
current shell execution environment.
The following redirection
operators may precede or appear anywhere within a
.I simple command
or may follow a
.IR command .
Redirections are processed in the order they appear, from
left to right.
.PP
Each redirection that may be preceded by a file descriptor number
may instead be preceded by a word of the form {\fIvarname\fP}.
In this case, for each redirection operator except
>&- and <&-, the shell will allocate a file descriptor greater
than or equal to 10 and assign it to \fIvarname\fP.
If >&- or <&- is preceded
by {\fIvarname\fP}, the value of \fIvarname\fP defines the file
descriptor to close.
If {\fIvarname\fP} is supplied, the redirection persists beyond
the scope of the command, allowing the shell programmer to manage
the file descriptor himself.
.PP
In the following descriptions, if the file descriptor number is
omitted, and the first character of the redirection operator is
.BR < ,
the redirection refers to the standard input (file descriptor
0).  If the first character of the redirection operator is
.BR > ,
the redirection refers to the standard output (file descriptor
1).
.PP
The word following the redirection operator in the following
descriptions, unless otherwise noted, is subjected to
brace expansion, tilde expansion, parameter and variable expansion,
command substitution, arithmetic expansion, quote removal,
pathname expansion, and word splitting.
If it expands to more than one word,
.B bash
reports an error.
.PP
Note that the order of redirections is significant.  For example,
the command
.RS
.PP
ls \fB>\fP dirlist 2\fB>&\fP1
.RE
.PP
directs both standard output and standard error to the file
.IR dirlist ,
while the command
.RS
.PP
ls 2\fB>&\fP1 \fB>\fP dirlist
.RE
.PP
directs only the standard output to file
.IR dirlist ,
because the standard error was duplicated from the standard output
before the standard output was redirected to
.IR dirlist .
.PP
\fBBash\fP handles several filenames specially when they are used in
redirections, as described in the following table.
If the operating system on which \fBbash\fP is running provides these
special files, bash will use them; otherwise it will emulate them
internally with the behavior described below.
.RS
.PP
.PD 0
.TP
.B /dev/fd/\fIfd\fP
If \fIfd\fP is a valid integer, file descriptor \fIfd\fP is duplicated.
.TP
.B /dev/stdin
File descriptor 0 is duplicated.
.TP
.B /dev/stdout
File descriptor 1 is duplicated.
.TP
.B /dev/stderr
File descriptor 2 is duplicated.
.TP
.B /dev/tcp/\fIhost\fP/\fIport\fP
If \fIhost\fP is a valid hostname or Internet address, and \fIport\fP
is an integer port number or service name, \fBbash\fP attempts to open
the corresponding TCP socket.
.TP
.B /dev/udp/\fIhost\fP/\fIport\fP
If \fIhost\fP is a valid hostname or Internet address, and \fIport\fP
is an integer port number or service name, \fBbash\fP attempts to open
the corresponding UDP socket.
.PD
.RE
.PP
A failure to open or create a file causes the redirection to fail.
.PP
Redirections using file descriptors greater than 9 should be used with
care, as they may conflict with file descriptors the shell uses
internally.
.PP
Note that the
.B exec
builtin command can make redirections take effect in the current shell.
.SS Redirecting Input
.PP
Redirection of input causes the file whose name results from
the expansion of
.I word
to be opened for reading on file descriptor
.IR n ,
or the standard input (file descriptor 0) if
.I n
is not specified.
.PP
The general format for redirecting input is:
.RS
.PP
[\fIn\fP]\fB<\fP\fIword\fP
.RE
.SS Redirecting Output
.PP
Redirection of output causes the file whose name results from
the expansion of
.I word
to be opened for writing on file descriptor
.IR n ,
or the standard output (file descriptor 1) if
.I n
is not specified.  If the file does not exist it is created;
if it does exist it is truncated to zero size.
.PP
The general format for redirecting output is:
.RS
.PP
[\fIn\fP]\fB>\fP\fIword\fP
.RE
.PP
If the redirection operator is
.BR > ,
and the
.B noclobber
option to the
.B set
builtin has been enabled, the redirection will fail if the file
whose name results from the expansion of \fIword\fP exists and is
a regular file.
If the redirection operator is
.BR >| ,
or the redirection operator is
.B >
and the
.B noclobber
option to the
.B set
builtin command is not enabled, the redirection is attempted even
if the file named by \fIword\fP exists.
.SS Appending Redirected Output
.PP
Redirection of output in this fashion
causes the file whose name results from
the expansion of
.I word
to be opened for appending on file descriptor
.IR n ,
or the standard output (file descriptor 1) if
.I n
is not specified.  If the file does not exist it is created.
.PP
The general format for appending output is:
.RS
.PP
[\fIn\fP]\fB>>\fP\fIword\fP
.RE
.PP
.SS Redirecting Standard Output and Standard Error
.PP
This construct allows both the
standard output (file descriptor 1) and
the standard error output (file descriptor 2)
to be redirected to the file whose name is the
expansion of
.IR word .
.PP
There are two formats for redirecting standard output and
standard error:
.RS
.PP
\fB&>\fP\fIword\fP
.RE
and
.RS
\fB>&\fP\fIword\fP
.RE
.PP
Of the two forms, the first is preferred.
This is semantically equivalent to
.RS
.PP
\fB>\fP\fIword\fP 2\fB>&\fP1
.RE
.PP
When using the second form, \fIword\fP may not expand to a number or
\fB\-\fP.  If it does, other redirection operators apply
(see \fBDuplicating File Descriptors\fP below) for compatibility
reasons.
.SS Appending Standard Output and Standard Error
.PP
This construct allows both the
standard output (file descriptor 1) and
the standard error output (file descriptor 2)
to be appended to the file whose name is the
expansion of
.IR word .
.PP
The format for appending standard output and standard error is:
.RS
.PP
\fB&>>\fP\fIword\fP
.RE
.PP
This is semantically equivalent to
.RS
.PP
\fB>>\fP\fIword\fP 2\fB>&\fP1
.RE
.PP
(see \fBDuplicating File Descriptors\fP below).
.SS Here Documents
.PP
This type of redirection instructs the shell to read input from the
current source until a line containing only
.I delimiter
(with no trailing blanks)
is seen.  All of
the lines read up to that point are then used as the standard
input (or file descriptor \fIn\fP if \fIn\fP is specified) for a command.
.PP
The format of here-documents is:
.RS
.PP
.nf
[\fIn\fP]\fB<<\fP[\fB\-\fP]\fIword\fP
        \fIhere-document\fP
\fIdelimiter\fP
.fi
.RE
.PP
No parameter and variable expansion, command substitution,
arithmetic expansion, or pathname expansion is performed on
.IR word .
If any part of
.I word
is quoted, the
.I delimiter
is the result of quote removal on
.IR word ,
and the lines in the here-document are not expanded.
If \fIword\fP is unquoted,
all lines of the here-document are subjected to
parameter expansion, command substitution, and arithmetic expansion,
the character sequence
.B \e<newline>
is ignored, and
.B \e
must be used to quote the characters
.BR \e ,
.BR $ ,
and
.BR \` .
.PP
If the redirection operator is
.BR <<\- ,
then all leading tab characters are stripped from input lines and the
line containing
.IR delimiter .
This allows
here-documents within shell scripts to be indented in a
natural fashion.
.SS "Here Strings"
A variant of here documents, the format is:
.RS
.PP
.nf
[\fIn\fP]\fB<<<\fP\fIword\fP
.fi
.RE
.PP
The \fIword\fP undergoes
tilde expansion, parameter and variable expansion,
command substitution, arithmetic expansion, and quote removal.
Pathname expansion and word splitting are not performed.
The result is supplied as a single string, with a newline appended,
to the command on its
standard input (or file descriptor \fIn\fP if \fIn\fP is specified).
.SS "Duplicating File Descriptors"
.PP
The redirection operator
.RS
.PP
[\fIn\fP]\fB<&\fP\fIword\fP
.RE
.PP
is used to duplicate input file descriptors.
If
.I word
expands to one or more digits, the file descriptor denoted by
.I n
is made to be a copy of that file descriptor.
If the digits in
.I word
do not specify a file descriptor open for input, a redirection error occurs.
If
.I word
evaluates to
.BR \- ,
file descriptor
.I n
is closed.  If
.I n
is not specified, the standard input (file descriptor 0) is used.
.PP
The operator
.RS
.PP
[\fIn\fP]\fB>&\fP\fIword\fP
.RE
.PP
is used similarly to duplicate output file descriptors.  If
.I n
is not specified, the standard output (file descriptor 1) is used.
If the digits in
.I word
do not specify a file descriptor open for output, a redirection error occurs.
If
.I word
evaluates to
.BR \- ,
file descriptor
.I n
is closed.
As a special case, if \fIn\fP is omitted, and \fIword\fP does not
expand to one or more digits or \fB\-\fP, the standard output and standard
error are redirected as described previously.
.SS "Moving File Descriptors"
.PP
The redirection operator
.RS
.PP
[\fIn\fP]\fB<&\fP\fIdigit\fP\fB\-\fP
.RE
.PP
moves the file descriptor \fIdigit\fP to file descriptor
.IR n ,
or the standard input (file descriptor 0) if \fIn\fP is not specified.
\fIdigit\fP is closed after being duplicated to \fIn\fP.
.PP
Similarly, the redirection operator
.RS
.PP
[\fIn\fP]\fB>&\fP\fIdigit\fP\fB\-\fP
.RE
.PP
moves the file descriptor \fIdigit\fP to file descriptor
.IR n ,
or the standard output (file descriptor 1) if \fIn\fP is not specified.
.SS "Opening File Descriptors for Reading and Writing"
.PP
The redirection operator
.RS
.PP
[\fIn\fP]\fB<>\fP\fIword\fP
.RE
.PP
causes the file whose name is the expansion of
.I word
to be opened for both reading and writing on file descriptor
.IR n ,
or on file descriptor 0 if
.I n
is not specified.  If the file does not exist, it is created.
.SH ALIASES
\fIAliases\fP allow a string to be substituted for a word when it is used
as the first word of a simple command.
The shell maintains a list of aliases that may be set and unset with the
.B alias
and
.B unalias
builtin commands (see
.SM
.B SHELL BUILTIN COMMANDS
below).
The first word of each simple command, if unquoted,
is checked to see if it has an
alias.  If so, that word is replaced by the text of the alias.
The characters \fB/\fP, \fB$\fP, \fB\`\fP, and \fB=\fP and
any of the shell \fImetacharacters\fP 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
.B ls
to
.BR "ls \-F" ,
for instance, and
.B bash
does not try to recursively expand the replacement text.
If the last character of the alias value is a
.IR blank ,
then the next command
word following the alias is also checked for alias expansion.
.PP
Aliases are created and listed with the
.B alias
command, and removed with the
.B unalias
command.
.PP
There is no mechanism for using arguments in the replacement text.
If arguments are needed, a shell function should be used (see
.SM
.B FUNCTIONS
below).
.PP
Aliases are not expanded when the shell is not interactive, unless
the
.B expand_aliases
shell option is set using
.B shopt
(see the description of
.B shopt
under
.SM
\fBSHELL BUILTIN COMMANDS\fP
below).
.PP
The rules concerning the definition and use of aliases are
somewhat confusing.
.B Bash
always reads at least one complete line of input,
and all lines that make up a compound command,
before executing any of the commands on that line or the compound command.
Aliases are expanded when a
command is read, not when it is executed.  Therefore, an
alias definition appearing on the same line as another
command does not take effect until the next line of input is read.
The commands following the alias definition
on that line are not affected by the new alias.
This behavior is also an issue when functions are executed.
Aliases are expanded when a function definition is read,
not when the function is executed, because a function definition
is itself a command.  As a consequence, aliases
defined in a function are not available until after that
function is executed.  To be safe, always put
alias definitions on a separate line, and do not use
.B alias
in compound commands.
.PP
For almost every purpose, aliases are superseded by
shell functions.
.SH FUNCTIONS
A shell function, defined as described above under
.SM
.BR "SHELL GRAMMAR" ,
stores a series of commands for later execution.
When the name of a shell function is used as a simple command name,
the list of commands associated with that function name is executed.
Functions are executed in the context of the
current shell; no new process is created to interpret
them (contrast this with the execution of a shell script).
When a function is executed, the arguments to the
function become the positional parameters
during its execution.
The special parameter
.B #
is updated to reflect the change.  Special parameter \fB0\fP
is unchanged.
The first element of the
.SM
.B FUNCNAME
variable is set to the name of the function while the function
is executing.
.PP
All other aspects of the shell execution
environment are identical between a function and its caller
with these exceptions: the
.SM
.B DEBUG
and
.B RETURN
traps (see the description of the
.B trap
builtin under
.SM
.B SHELL BUILTIN COMMANDS
below) are not inherited unless the function has been given the
\fBtrace\fP attribute (see the description of the
.SM
.B declare
builtin below) or the
\fB\-o functrace\fP shell option has been enabled with
the \fBset\fP builtin
(in which case all functions inherit the \fBDEBUG\fP and \fBRETURN\fP traps),
and the
.SM
.B ERR
trap is not inherited unless the \fB\-o errtrace\fP shell option has
been enabled.
.PP
Variables local to the function may be declared with the
.B local
builtin command.  Ordinarily, variables and their values
are shared between the function and its caller.
If a variable is declared \fBlocal\fP, the variable's visible scope
is restricted to that function and its children (including the functions
it calls).
Local variables "shadow" variables with the same name declared at
previous scopes.
For instance, a local variable declared in a function
hides a global variable of the same name: references and assignments
refer to the local variable, leaving the global variable unmodified.
When the function returns, the global variable is once again visible.
.PP
The shell uses \fIdynamic scoping\fP to control a variable's visibility
within functions.
With dynamic scoping, visible variables and their values
are a result of the sequence of function calls that caused execution
to reach the current function.
The value of a variable that a function sees depends
on its value within its caller, if any, whether that caller is
the "global" scope or another shell function.
This is also the value that a local variable
declaration "shadows", and the value that is restored when the function
returns.
.PP
For example, if a variable \fIvar\fP is declared as local in function
\fIfunc1\fP, and \fIfunc1\fP calls another function \fIfunc2\fP,
references to \fIvar\fP made from within \fIfunc2\fP will resolve to the
local variable \fIvar\fP from \fIfunc1\fP, shadowing any global variable
named \fIvar\fP.
.PP
The \fBunset\fP builtin also acts using the same dynamic scope: if a
variable is local to the current scope, \fBunset\fP will unset it;
otherwise the unset will refer to the variable found in any calling scope
as described above.
If a variable at the current local scope is unset, it will remain so
until it is reset in that scope or until the function returns.
Once the function returns, any instance of the variable at a previous
scope will become visible.
If the unset acts on a variable at a previous scope, any instance of a
variable with that name that had been shadowed will become visible.
.PP
The \fBFUNCNEST\fP variable, if set to a numeric value greater
than 0, defines a maximum function nesting level.  Function
invocations that exceed the limit cause the entire command to
abort.
.PP
If the builtin command
.B return
is executed in a function, the function completes and
execution resumes with the next command after the function
call.
Any command associated with the \fBRETURN\fP trap is executed
before execution resumes.
When a function completes, the values of the
positional parameters and the special parameter
.B #
are restored to the values they had prior to the function's
execution.
.PP
Function names and definitions may be listed with the
.B \-f
option to the
.B declare
or
.B typeset
builtin commands.  The
.B \-F
option to
.B declare
or
.B typeset
will list the function names only
(and optionally the source file and line number, if the \fBextdebug\fP
shell option is enabled).
Functions may be exported so that subshells
automatically have them defined with the
.B \-f
option to the 
.B export
builtin.
A function definition may be deleted using the \fB\-f\fP option to
the
.B unset
builtin.
.PP
Functions may be recursive.
The \fBFUNCNEST\fP variable may be used to limit the depth of the
function call stack and restrict the number of function invocations.
By default, no limit is imposed on the number of recursive calls.
.SH "ARITHMETIC EVALUATION"
The shell allows arithmetic expressions to be evaluated, under
certain circumstances (see the \fBlet\fP and \fBdeclare\fP builtin
commands, the \fB((\fP compound command, and \fBArithmetic Expansion\fP).
Evaluation is done in fixed-width integers with no check for overflow,
though division by 0 is trapped and flagged as an error.
The operators and their precedence, associativity, and values
are the same as in the C language.
The following list of operators is grouped into levels of
equal-precedence operators.
The levels are listed in order of decreasing precedence.
.PP
.PD 0
.TP
.B \fIid\fP++ \fIid\fP\-\-
variable post-increment and post-decrement
.TP
.B \- +
unary minus and plus
.TP
.B ++\fIid\fP \-\-\fIid\fP
variable pre-increment and pre-decrement
.TP
.B ! ~
logical and bitwise negation
.TP
.B **
exponentiation
.TP
.B * / %
multiplication, division, remainder
.TP
.B + \-
addition, subtraction
.TP
.B << >>
left and right bitwise shifts
.TP
.B <= >= < >
comparison
.TP
.B == !=
equality and inequality
.TP
.B &
bitwise AND
.TP
.B ^
bitwise exclusive OR
.TP
.B |
bitwise OR
.TP
.B &&
logical AND
.TP
.B ||
logical OR
.TP
.B \fIexpr\fP?\fIexpr\fP:\fIexpr\fP
conditional operator
.TP
.B = *= /= %= += \-= <<= >>= &= ^= |=
assignment
.TP
.B \fIexpr1\fP , \fIexpr2\fP
comma
.PD
.PP
Shell variables are allowed as operands; parameter expansion is
performed before the expression is evaluated.
Within an expression, shell variables may also be referenced by name
without using the parameter expansion syntax.
A shell variable that is null or unset evaluates to 0 when referenced
by name without using the parameter expansion syntax.
The value of a variable is evaluated as an arithmetic expression
when it is referenced, or when a variable which has been given the
\fIinteger\fP attribute using \fBdeclare \-i\fP is assigned a value.
A null value evaluates to 0.
A shell variable need not have its \fIinteger\fP attribute
turned on to be used in an expression.
.PP
Constants with a leading 0 are interpreted as octal numbers.
A leading 0x or 0X denotes hexadecimal.
Otherwise, numbers take the form [\fIbase#\fP]n, where the optional \fIbase\fP
is a decimal number between 2 and 64 representing the arithmetic
base, and \fIn\fP is a number in that base.
If \fIbase#\fP is omitted, then base 10 is used.
When specifying \fIn\fP,
the digits greater than 9 are represented by the lowercase letters,
the uppercase letters, @, and _, in that order.
If \fIbase\fP is less than or equal to 36, lowercase and uppercase
letters may be used interchangeably to represent numbers between 10
and 35.
.PP
Operators are evaluated in order of precedence.  Sub-expressions in
parentheses are evaluated first and may override the precedence
rules above.
.SH "CONDITIONAL EXPRESSIONS"
Conditional expressions are used by the \fB[[\fP compound command and
the \fBtest\fP and \fB[\fP builtin commands to test file attributes
and perform string and arithmetic comparisons.
The \fBtest\fP abd \fB[\fP commands determine their behavior based on
the number of arguments; see the descriptions of those commands for any
other command-specific actions.
.PP
Expressions are formed from the following unary or binary primaries.
\fBBash\fP handles several filenames specially when they are used in
expressions.
If the operating system on which \fBbash\fP is running provides these
special files, bash will use them; otherwise it will emulate them
internally with this behavior:
If any \fIfile\fP argument to one of the primaries is of the form
\fI/dev/fd/n\fP, then file descriptor \fIn\fP is checked.
If the \fIfile\fP argument to one of the primaries is one of
\fI/dev/stdin\fP, \fI/dev/stdout\fP, or \fI/dev/stderr\fP, file
descriptor 0, 1, or 2, respectively, is checked.
.PP
Unless otherwise specified, primaries that operate on files follow symbolic
links and operate on the target of the link, rather than the link itself.
.if t .sp 0.5
.if n .sp 1
When used with \fB[[\fP, the \fB<\fP and \fB>\fP operators sort
lexicographically using the current locale.
The \fBtest\fP command sorts using ASCII ordering.
.sp 1
.PD 0
.TP
.B \-a \fIfile\fP
True if \fIfile\fP exists.
.TP
.B \-b \fIfile\fP
True if \fIfile\fP exists and is a block special file.
.TP
.B \-c \fIfile\fP
True if \fIfile\fP exists and is a character special file.
.TP
.B \-d \fIfile\fP
True if \fIfile\fP exists and is a directory.
.TP
.B \-e \fIfile\fP
True if \fIfile\fP exists.
.TP
.B \-f \fIfile\fP
True if \fIfile\fP exists and is a regular file.
.TP
.B \-g \fIfile\fP
True if \fIfile\fP exists and is set-group-id.
.TP
.B \-h \fIfile\fP
True if \fIfile\fP exists and is a symbolic link.
.TP
.B \-k \fIfile\fP
True if \fIfile\fP exists and its ``sticky'' bit is set.
.TP
.B \-p \fIfile\fP
True if \fIfile\fP exists and is a named pipe (FIFO).
.TP
.B \-r \fIfile\fP
True if \fIfile\fP exists and is readable.
.TP
.B \-s \fIfile\fP
True if \fIfile\fP exists and has a size greater than zero.
.TP
.B \-t \fIfd\fP
True if file descriptor
.I fd
is open and refers to a terminal.
.TP
.B \-u \fIfile\fP
True if \fIfile\fP exists and its set-user-id bit is set.
.TP
.B \-w \fIfile\fP
True if \fIfile\fP exists and is writable.
.TP
.B \-x \fIfile\fP
True if \fIfile\fP exists and is executable.
.TP
.B \-G \fIfile\fP
True if \fIfile\fP exists and is owned by the effective group id.
.TP
.B \-L \fIfile\fP
True if \fIfile\fP exists and is a symbolic link.
.TP
.B \-N \fIfile\fP
True if \fIfile\fP exists and has been modified since it was last read.
.TP
.B \-O \fIfile\fP
True if \fIfile\fP exists and is owned by the effective user id.
.TP
.B \-S \fIfile\fP
True if \fIfile\fP exists and is a socket.
.TP
\fIfile1\fP \fB\-ef\fP \fIfile2\fP
True if \fIfile1\fP and \fIfile2\fP refer to the same device and
inode numbers.
.TP
\fIfile1\fP \-\fBnt\fP \fIfile2\fP
True if \fIfile1\fP is newer (according to modification date) than \fIfile2\fP,
or if \fIfile1\fP exists and \fPfile2\fP does not.
.TP
\fIfile1\fP \-\fBot\fP \fIfile2\fP
True if \fIfile1\fP is older than \fIfile2\fP, or if \fIfile2\fP exists
and \fIfile1\fP does not.
.TP
.B \-o \fIoptname\fP
True if the shell option
.I optname
is enabled.
See the list of options under the description of the
.B \-o
option to the
.B set
builtin below.
.TP
.B \-v \fIvarname\fP
True if the shell variable
.I varname
is set (has been assigned a value).
.TP
.B \-R \fIvarname\fP
True if the shell variable
.I varname
is set and is a name reference.
.TP
.B \-z \fIstring\fP
True if the length of \fIstring\fP is zero.
.TP
\fIstring\fP
.PD 0
.TP
.B \-n \fIstring\fP
.PD
True if the length of
.I string
is non-zero.
.TP
\fIstring1\fP \fB==\fP \fIstring2\fP
.PD 0
.TP
\fIstring1\fP \fB=\fP \fIstring2\fP
.PD
True if the strings are equal.  \fB=\fP should be used
with the \fBtest\fP command for POSIX conformance.
When used with the \fB[[\fP command, this performs pattern matching as
described above (\fBCompound Commands\fP).
.TP
\fIstring1\fP \fB!=\fP \fIstring2\fP
True if the strings are not equal.
.TP
\fIstring1\fP \fB<\fP \fIstring2\fP
True if \fIstring1\fP sorts before \fIstring2\fP lexicographically.
.TP
\fIstring1\fP \fB>\fP \fIstring2\fP
True if \fIstring1\fP sorts after \fIstring2\fP lexicographically.
.TP
.I \fIarg1\fP \fBOP\fP \fIarg2\fP
.SM
.B OP
is one of
.BR \-eq ,
.BR \-ne ,
.BR \-lt ,
.BR \-le ,
.BR \-gt ,
or
.BR \-ge .
These arithmetic binary operators return true if \fIarg1\fP
is equal to, not equal to, less than, less than or equal to,
greater than, or greater than or equal to \fIarg2\fP, respectively.
.I Arg1
and
.I arg2
may be positive or negative integers.
When used with the \fB[[\fP command,
.I Arg1
and
.I Arg2
are evaluated as arithmetic expressions  (see
.SM
.B "ARITHMETIC EVALUATION"
above).
.PD
.SH "SIMPLE COMMAND EXPANSION"
When a simple command is executed, the shell performs the following
expansions, assignments, and redirections, from left to right.
.IP 1.
The words that the parser has marked as variable assignments (those
preceding the command name) and redirections are saved for later
processing.
.IP 2.
The words that are not variable assignments or redirections are
expanded.  If any words remain after expansion, the first word
is taken to be the name of the command and the remaining words are
the arguments.
.IP 3.
Redirections are performed as described above under
.SM
.BR REDIRECTION .
.IP 4.
The text after the \fB=\fP in each variable assignment undergoes tilde
expansion, parameter expansion, command substitution, arithmetic expansion,
and quote removal before being assigned to the variable.
.PP
If no command name results, the variable assignments affect the current
shell environment.  Otherwise, the variables are added to the environment
of the executed command and do not affect the current shell environment.
If any of the assignments attempts to assign a value to a readonly variable,
an error occurs, and the command exits with a non-zero status.
.PP
If no command name results, redirections are performed, but do not
affect the current shell environment.  A redirection error causes the
command to exit with a non-zero status.
.PP
If there is a command name left after expansion, execution proceeds as
described below.  Otherwise, the command exits.  If one of the expansions
contained a command substitution, the exit status of the command is
the exit status of the last command substitution performed.  If there
were no command substitutions, the command exits with a status of zero.
.SH "COMMAND EXECUTION"
After a command has been split into words, if it results in a
simple command and an optional list of arguments, the following
actions are taken.
.PP
If the command name contains no slashes, the shell attempts to
locate it.  If there exists a shell function by that name, that
function is invoked as described above in
.SM
.BR FUNCTIONS .
If the name does not match a function, the shell searches for
it in the list of shell builtins.  If a match is found, that
builtin is invoked.
.PP
If the name is neither a shell function nor a builtin,
and contains no slashes,
.B bash
searches each element of the
.SM
.B PATH
for a directory containing an executable file by that name.
.B Bash
uses a hash table to remember the full pathnames of executable
files (see
.B hash
under
.SM
.B "SHELL BUILTIN COMMANDS"
below).
A full search of the directories in
.SM
.B PATH
is performed only if the command is not found in the hash table.
If the search is unsuccessful, the shell searches for a defined shell
function named \fBcommand_not_found_handle\fP.
If that function exists, it is invoked in a separate execution environment
with the original command and
the original command's arguments as its arguments, and the function's
exit status becomes the exit status of that subshell.
If that function is not defined, the shell prints an error
message and returns an exit status of 127.
.PP
If the search is successful, or if the command name contains
one or more slashes, the shell executes the named program in a
separate execution environment.
Argument 0 is set to the name given, and the remaining arguments
to the command are set to the arguments given, if any.
.PP
If this execution fails because the file is not in executable
format, and the file is not a directory, it is assumed to be
a \fIshell script\fP, a file
containing shell commands.  A subshell is spawned to execute
it.  This subshell reinitializes itself, so
that the effect is as if a new shell had been invoked
to handle the script, with the exception that the locations of
commands remembered by the parent (see
.B hash
below under
.SM
\fBSHELL BUILTIN COMMANDS\fP)
are retained by the child.
.PP
If the program is a file beginning with
.BR #! ,
the remainder of the first line specifies an interpreter
for the program.  The shell executes the
specified interpreter on operating systems that do not
handle this executable format themselves.  The arguments to the
interpreter consist of a single optional argument following the
interpreter name on the first line of the program, followed
by the name of the program, followed by the command
arguments, if any.
.SH COMMAND EXECUTION ENVIRONMENT
The shell has an \fIexecution environment\fP, which consists of the
following:
.IP \(bu
open files inherited by the shell at invocation, as modified by
redirections supplied to the \fBexec\fP builtin
.IP \(bu
the current working directory as set by \fBcd\fP, \fBpushd\fP, or
\fBpopd\fP, or inherited by the shell at invocation
.IP \(bu
the file creation mode mask as set by \fBumask\fP or inherited from
the shell's parent
.IP \(bu
current traps set by \fBtrap\fP
.IP \(bu
shell parameters that are set by variable assignment or with \fBset\fP
or inherited from the shell's parent in the environment
.IP \(bu
shell functions defined during execution or inherited from the shell's
parent in the environment
.IP \(bu
options enabled at invocation (either by default or with command-line
arguments) or by \fBset\fP
.IP \(bu
options enabled by \fBshopt\fP
.IP \(bu
shell aliases defined with \fBalias\fP
.IP \(bu
various process IDs, including those of background jobs, the value
of \fB$$\fP, and the value of
.SM
.B PPID
.PP
When a simple command other than a builtin or shell function
is to be executed, it
is invoked in a separate execution environment that consists of
the following.  Unless otherwise noted, the values are inherited
from the shell.
.if n .sp 1
.IP \(bu
the shell's open files, plus any modifications and additions specified
by redirections to the command
.IP \(bu
the current working directory
.IP \(bu
the file creation mode mask
.IP \(bu
shell variables and functions marked for export, along with variables
exported for the command, passed in the environment
.IP \(bu
traps caught by the shell are reset to the values inherited from the
shell's parent, and traps ignored by the shell are ignored
.PP
A command invoked in this separate environment cannot affect the
shell's execution environment.
.PP
Command substitution, commands grouped with parentheses,
and asynchronous commands are invoked in a
subshell environment that is a duplicate of the shell environment,
except that traps caught by the shell are reset to the values
that the shell inherited from its parent at invocation.  Builtin
commands that are invoked as part of a pipeline are also executed in a
subshell environment.  Changes made to the subshell environment
cannot affect the shell's execution environment.
.PP
Subshells spawned to execute command substitutions inherit the value of
the \fB\-e\fP option from the parent shell.  When not in \fIposix mode\fP,
\fBbash\fP clears the \fB\-e\fP option in such subshells.
.PP
If a command is followed by a \fB&\fP and job control is not active, the
default standard input for the command is the empty file \fI/dev/null\fP.
Otherwise, the invoked command inherits the file descriptors of the calling
shell as modified by redirections.
.SH ENVIRONMENT
When a program is invoked it is given an array of strings
called the
.IR environment .
This is a list of
\fIname\fP\-\fIvalue\fP pairs, of the form
.IR "name\fR=\fPvalue" .
.PP
The shell provides several ways to manipulate the environment.
On invocation, the shell scans its own environment and
creates a parameter for each name found, automatically marking
it for
.I export
to child processes.  Executed commands inherit the environment.
The
.B export
and
.B declare \-x
commands allow parameters and functions to be added to and
deleted from the environment.  If the value of a parameter
in the environment is modified, the new value becomes part
of the environment, replacing the old.  The environment
inherited by any executed command consists of the shell's
initial environment, whose values may be modified in the shell,
less any pairs removed by the
.B unset
command, plus any additions via the
.B export
and
.B declare \-x
commands.
.PP
The environment for any
.I simple command
or function may be augmented temporarily by prefixing it with
parameter assignments, as described above in
.SM
.BR PARAMETERS .
These assignment statements affect only the environment seen
by that command.
.PP
If the
.B \-k
option is set (see the
.B set
builtin command below), then
.I all
parameter assignments are placed in the environment for a command,
not just those that precede the command name.
.PP
When
.B bash
invokes an external command, the variable
.B _
is set to the full filename of the command and passed to that
command in its environment.
.SH "EXIT STATUS"
.PP
The exit status of an executed command is the value returned by the
\fIwaitpid\fP system call or equivalent function.  Exit statuses
fall between 0 and 255, though, as explained below, the shell may
use values above 125 specially.  Exit statuses from shell builtins and
compound commands are also limited to this range.  Under certain
circumstances, the shell will use special values to indicate specific
failure modes.
.PP
For the shell's purposes, a command which exits with a
zero exit status has succeeded.  An exit status of zero
indicates success.  A non-zero exit status indicates failure.
When a command terminates on a fatal signal \fIN\fP, \fBbash\fP uses
the value of 128+\fIN\fP as the exit status.
.PP
If a command is not found, the child process created to
execute it returns a status of 127.  If a command is found
but is not executable, the return status is 126.
.PP
If a command fails because of an error during expansion or redirection,
the exit status is greater than zero.
.PP
Shell builtin commands return a status of 0 (\fItrue\fP) if
successful, and non-zero (\fIfalse\fP) if an error occurs
while they execute.
All builtins return an exit status of 2 to indicate incorrect usage,
generally invalid options or missing arguments.
.PP
\fBBash\fP itself returns the exit status of the last command
executed, unless a syntax error occurs, in which case it exits
with a non-zero value.  See also the \fBexit\fP builtin
command below.
.SH SIGNALS
When \fBbash\fP is interactive, in the absence of any traps, it ignores
.SM
.B SIGTERM
(so that \fBkill 0\fP does not kill an interactive shell),
and
.SM
.B SIGINT
is caught and handled (so that the \fBwait\fP builtin is interruptible).
In all cases, \fBbash\fP ignores
.SM
.BR SIGQUIT .
If job control is in effect,
.B bash
ignores
.SM
.BR SIGTTIN ,
.SM
.BR SIGTTOU ,
and
.SM
.BR SIGTSTP .
.PP
Non-builtin commands run by \fBbash\fP have signal handlers
set to the values inherited by the shell from its parent.
When job control is not in effect, asynchronous commands
ignore
.SM
.B SIGINT
and
.SM
.B SIGQUIT
in addition to these inherited handlers.
Commands run as a result of command substitution ignore the
keyboard-generated job control signals
.SM
.BR SIGTTIN ,
.SM
.BR SIGTTOU ,
and
.SM
.BR SIGTSTP .
.PP
The shell exits by default upon receipt of a
.SM
.BR SIGHUP .
Before exiting, an interactive shell resends the
.SM
.B SIGHUP
to all jobs, running or stopped.
Stopped jobs are sent
.SM
.B SIGCONT
to ensure that they receive the
.SM
.BR SIGHUP .
To prevent the shell from
sending the signal to a particular job, it should be removed from the
jobs table with the
.B disown
builtin (see
.SM
.B "SHELL BUILTIN COMMANDS"
below) or marked
to not receive
.SM
.B SIGHUP
using
.BR "disown \-h" .
.PP
If the
.B huponexit
shell option has been set with
.BR shopt ,
.B bash
sends a
.SM
.B SIGHUP
to all jobs when an interactive login shell exits.
.PP
If \fBbash\fP 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 \fBbash\fP is waiting for an asynchronous command via the \fBwait\fP
builtin, the reception of a signal for which a trap has been set will
cause the \fBwait\fP builtin to return immediately with an exit status
greater than 128, immediately after which the trap is executed.
.SH "JOB CONTROL"
.I Job control
refers to the ability to selectively stop (\fIsuspend\fP)
the execution of processes and continue (\fIresume\fP)
their execution at a later point.  A user typically employs
this facility via an interactive interface supplied jointly
by the operating system kernel's terminal driver and
.BR bash .
.PP
The shell associates a
.I job
with each pipeline.  It keeps a table of currently executing
jobs, which may be listed with the
.B jobs
command.  When
.B bash
starts a job asynchronously (in the
.IR background ),
it prints a line that looks like:
.RS
.PP
[1] 25647
.RE
.PP
indicating that this job is job number 1 and that the process ID
of the last process in the pipeline associated with this job is 25647.
All of the processes in a single pipeline are members of the same job.
.B Bash
uses the
.I job
abstraction as the basis for job control.
.PP
To facilitate the implementation of the user interface to job
control, the operating system maintains the notion of a \fIcurrent terminal
process group ID\fP.  Members of this process group (processes whose
process group ID is equal to the current terminal process group ID)
receive keyboard-generated signals such as
.SM
.BR SIGINT .
These processes are said to be in the
.IR foreground .
.I Background
processes are those whose process group ID differs from the terminal's;
such processes are immune to keyboard-generated signals.
Only foreground processes are allowed to read from or, if the
user so specifies with \f(CWstty tostop\fP, write to the
terminal.
Background processes which attempt to read from (write to when
\f(CWstty tostop\fP is in effect) the
terminal are sent a
.SM
.B SIGTTIN (SIGTTOU)
signal by the kernel's terminal driver, 
which, unless caught, suspends the process.
.PP
If the operating system on which
.B bash
is running supports
job control,
.B bash
contains facilities to use it.
Typing the
.I suspend
character (typically
.BR ^Z ,
Control-Z) while a process is running
causes that process to be stopped and returns control to
.BR bash .
Typing the
.I "delayed suspend"
character (typically
.BR ^Y ,
Control-Y) causes the process to be stopped when it
attempts to read input from the terminal, and control to
be returned to
.BR bash .
The user may then manipulate the state of this job, using the
.B bg
command to continue it in the background, the
.B fg
command to continue it in the foreground, or
the
.B kill
command to kill it.  A \fB^Z\fP takes effect immediately,
and has the additional side effect of causing pending output
and typeahead to be discarded.
.PP
There are a number of ways to refer to a job in the shell.
The character
.B %
introduces a job specification (\fIjobspec\fP).  Job number
.I n
may be referred to as
.BR %n .
A job may also be referred to using a prefix of the name used to
start it, or using a substring that appears in its command line.
For example,
.B %ce
refers to a stopped
.B ce
job.  If a prefix matches more than one job,
.B bash
reports an error.  Using
.BR %?ce ,
on the other hand, refers to any job containing the string
.B ce
in its command line.  If the substring matches more than one job,
.B bash
reports an error.  The symbols
.B %%
and
.B %+
refer to the shell's notion of the
.IR "current job" ,
which is the last job stopped while it was in
the foreground or started in the background.
The
.I "previous job"
may be referenced using
.BR %\- .
If there is only a single job, \fB%+\fP and \fB%\-\fP can both be used
to refer to that job.
In output pertaining to jobs (e.g., the output of the
.B jobs
command), the current job is always flagged with a
.BR + ,
and the previous job with a
.BR \- .
A single % (with no accompanying job specification) also refers to the
current job.
.PP
Simply naming a job can be used to bring it into the
foreground:
.B %1
is a synonym for
\fB``fg %1''\fP,
bringing job 1 from the background into the foreground.
Similarly,
.B ``%1 &''
resumes job 1 in the background, equivalent to
\fB``bg %1''\fP.
.PP
The shell learns immediately whenever a job changes state.
Normally,
.B bash
waits until it is about to print a prompt before reporting
changes in a job's status so as to not interrupt
any other output.  If the
.B \-b
option to the
.B set
builtin command
is enabled,
.B bash
reports such changes immediately.
Any trap on
.SM
.B SIGCHLD
is executed for each child that exits.
.PP
If an attempt to exit
.B bash
is made while jobs are stopped (or, if the \fBcheckjobs\fP shell option has
been enabled using the \fBshopt\fP builtin, running), the shell prints a
warning message, and, if the \fBcheckjobs\fP option is enabled, lists the
jobs and their statuses.
The
.B jobs
command may then be used to inspect their status.
If a second attempt to exit is made without an intervening command,
the shell does not print another warning, and any stopped
jobs are terminated.
.PP
When the shell is waiting for a job or process using the \fBwait\fP
builtin, and job control is enabled, \fBwait\fP will return when the
job changes state. The \fB\-f\fP option will force \fBwait\fP to wait
until the job or process terminates before returning.
.SH PROMPTING
When executing interactively,
.B bash
displays the primary prompt
.SM
.B PS1
when it is ready to read a command, and the secondary prompt
.SM
.B PS2
when it needs more input to complete a command.
.B Bash
displays
.SM
.B PS0
after it reads a command but before executing it.
.B Bash
displays
.SM
.B PS4
as described above
before tracing each command when the \fB\-x\fP option is enabled.
.B Bash
allows these prompt strings to be customized by inserting a number of
backslash-escaped special characters that are decoded as follows:
.RS
.PD 0
.TP
.B \ea
an ASCII bell character (07)
.TP
.B \ed
the date in "Weekday Month Date" format (e.g., "Tue May 26")
.TP
.B \eD{\fIformat\fP}
the \fIformat\fP is passed to \fIstrftime\fP(3) and the result is inserted
into the prompt string; an empty \fIformat\fP results in a locale-specific
time representation.  The braces are required
.TP
.B \ee
an ASCII escape character (033)
.TP
.B \eh
the hostname up to the first `.'
.TP
.B \eH
the hostname
.TP
.B \ej
the number of jobs currently managed by the shell
.TP
.B \el
the basename of the shell's terminal device name
.TP
.B \en
newline
.TP
.B \er
carriage return
.TP
.B \es
the name of the shell, the basename of
.B $0
(the portion following the final slash)
.TP
.B \et
the current time in 24-hour HH:MM:SS format
.TP
.B \eT
the current time in 12-hour HH:MM:SS format
.TP
.B \e@
the current time in 12-hour am/pm format
.TP
.B \eA
the current time in 24-hour HH:MM format
.TP
.B \eu
the username of the current user
.TP
.B \ev
the version of \fBbash\fP (e.g., 2.00)
.TP
.B \eV
the release of \fBbash\fP, version + patch level (e.g., 2.00.0)
.TP
.B \ew
the current working directory, with
.SM
.B $HOME
abbreviated with a tilde
(uses the value of the
.SM
.B PROMPT_DIRTRIM
variable)
.TP
.B \eW
the basename of the current working directory, with
.SM
.B $HOME
abbreviated with a tilde
.TP
.B \e!
the history number of this command
.TP
.B \e#
the command number of this command
.TP
.B \e$
if the effective UID is 0, a
.BR # ,
otherwise a
.B $
.TP
.B \e\fInnn\fP
the character corresponding to the octal number \fInnn\fP
.TP
.B \e\e
a backslash
.TP
.B \e[
begin a sequence of non-printing characters, which could be used to
embed a terminal control sequence into the prompt
.TP
.B \e]
end a sequence of non-printing characters
.PD
.RE
.PP
The command number and the history number are usually different:
the history number of a command is its position in the history
list, which may include commands restored from the history file
(see
.SM
.B HISTORY
below), while the command number is the position in the sequence
of commands executed during the current shell session.
After the string is decoded, it is expanded via
parameter expansion, command substitution, arithmetic
expansion, and quote removal, subject to the value of the
.B promptvars
shell option (see the description of the
.B shopt
command under
.SM
.B "SHELL BUILTIN COMMANDS"
below).
.SH READLINE
This is the library that handles reading input when using an interactive
shell, unless the
.B \-\-noediting
option is given at shell invocation.
Line editing is also used when using the \fB\-e\fP option to the
\fBread\fP builtin.
By default, the line editing commands are similar to those of Emacs.
A vi-style line editing interface is also available.
Line editing can be enabled at any time using the
.B \-o emacs
or
.B \-o vi
options to the
.B set
builtin (see
.SM
.B SHELL BUILTIN COMMANDS
below).
To turn off line editing after the shell is running, use the
.B +o emacs
or
.B +o vi
options to the
.B set
builtin.
.SS "Readline Notation"
.PP
In this section, the Emacs-style notation is used to denote
keystrokes.  Control keys are denoted by C\-\fIkey\fR, e.g., C\-n
means Control\-N.  Similarly,
.I meta
keys are denoted by M\-\fIkey\fR, so M\-x means Meta\-X.  (On keyboards
without a
.I meta
key, M\-\fIx\fP means ESC \fIx\fP, i.e., press the Escape key
then the
.I x
key.  This makes ESC the \fImeta prefix\fP.
The combination M\-C\-\fIx\fP means ESC\-Control\-\fIx\fP,
or press the Escape key
then hold the Control key while pressing the
.I x
key.)
.PP
Readline commands may be given numeric
.IR arguments ,
which normally act as a repeat count.
Sometimes, however, it is the sign of the argument that is significant.
Passing a negative argument to a command that acts in the forward
direction (e.g., \fBkill\-line\fP) causes that command to act in a
backward direction.
Commands whose behavior with arguments deviates from this are noted
below.
.PP
When a command is described as \fIkilling\fP text, the text
deleted is saved for possible future retrieval
(\fIyanking\fP).  The killed text is saved in a
\fIkill ring\fP.  Consecutive kills cause the text to be
accumulated into one unit, which can be yanked all at once.
Commands which do not kill text separate the chunks of text
on the kill ring.
.SS "Readline Initialization"
.PP
Readline is customized by putting commands in an initialization
file (the \fIinputrc\fP file).
The name of this file is taken from the value of the
.SM
.B INPUTRC
variable.  If that variable is unset, the default is
.IR ~/.inputrc .
When a program which uses the readline library starts up, the
initialization file is read, and the key bindings and variables
are set.
There are only a few basic constructs allowed in the
readline initialization file.
Blank lines are ignored.
Lines beginning with a \fB#\fP are comments.
Lines beginning with a \fB$\fP indicate conditional constructs.
Other lines denote key bindings and variable settings.
.PP
The default key-bindings may be changed with an
.I inputrc
file.
Other programs that use this library may add their own commands
and bindings.
.PP
For example, placing
.RS
.PP
M\-Control\-u: universal\-argument
.RE
or
.RS
C\-Meta\-u: universal\-argument
.RE
into the
.I inputrc
would make M\-C\-u execute the readline command
.IR universal\-argument .
.PP
The following symbolic character names are recognized:
.IR RUBOUT ,
.IR DEL ,
.IR ESC ,
.IR LFD ,
.IR NEWLINE ,
.IR RET ,
.IR RETURN ,
.IR SPC ,
.IR SPACE ,
and
.IR TAB .
.PP
In addition to command names, readline allows keys to be bound
to a string that is inserted when the key is pressed (a \fImacro\fP).
.SS "Readline Key Bindings"
.PP
The syntax for controlling key bindings in the
.I inputrc
file is simple.  All that is required is the name of the
command or the text of a macro and a key sequence to which
it should be bound.  The name may be specified in one of two ways:
as a symbolic key name, possibly with \fIMeta\-\fP or \fIControl\-\fP
prefixes, or as a key sequence.
.PP
When using the form \fBkeyname\fP:\^\fIfunction\-name\fP or \fImacro\fP,
.I keyname
is the name of a key spelled out in English.  For example:
.sp
.RS
Control-u: universal\-argument
.br
Meta-Rubout: backward-kill-word
.br
Control-o: "> output"
.RE
.LP
In the above example,
.I C\-u
is bound to the function
.BR universal\-argument ,
.I M\-DEL
is bound to the function
.BR backward\-kill\-word ,
and
.I C\-o
is bound to run the macro
expressed on the right hand side (that is, to insert the text
.if t \f(CW> output\fP
.if n ``> output''
into the line).
.PP
In the second form, \fB"keyseq"\fP:\^\fIfunction\-name\fP or \fImacro\fP,
.B keyseq
differs from
.B keyname
above in that strings denoting
an entire key sequence may be specified by placing the sequence
within double quotes.  Some GNU Emacs style key escapes can be
used, as in the following example, but the symbolic character names
are not recognized.
.sp
.RS
"\eC\-u": universal\-argument
.br
"\eC\-x\eC\-r": re\-read\-init\-file
.br
"\ee[11~": "Function Key 1"
.RE
.PP
In this example,
.I C\-u
is again bound to the function
.BR universal\-argument .
.I "C\-x C\-r"
is bound to the function
.BR re\-read\-init\-file ,
and
.I "ESC [ 1 1 ~"
is bound to insert the text
.if t \f(CWFunction Key 1\fP.
.if n ``Function Key 1''.
.PP
The full set of GNU Emacs style escape sequences is
.RS
.PD 0
.TP
.B \eC\-
control prefix
.TP
.B \eM\-
meta prefix
.TP
.B \ee
an escape character
.TP
.B \e\e
backslash
.TP
.B \e"
literal "
.TP
.B \e\(aq
literal \(aq
.RE
.PD
.PP
In addition to the GNU Emacs style escape sequences, a second
set of backslash escapes is available:
.RS
.PD 0
.TP
.B \ea
alert (bell)
.TP
.B \eb
backspace
.TP
.B \ed
delete
.TP
.B \ef
form feed
.TP
.B \en
newline
.TP
.B \er
carriage return
.TP
.B \et
horizontal tab
.TP
.B \ev
vertical tab
.TP
.B \e\fInnn\fP
the eight-bit character whose value is the octal value \fInnn\fP
(one to three digits)
.TP
.B \ex\fIHH\fP
the eight-bit character whose value is the hexadecimal value \fIHH\fP
(one or two hex digits)
.RE
.PD
.PP
When entering the text of a macro, single or double quotes must
be used to indicate a macro definition.
Unquoted text is assumed to be a function name.
In the macro body, the backslash escapes described above are expanded.
Backslash will quote any other character in the macro text,
including " and \(aq.
.PP
.B Bash
allows the current readline key bindings to be displayed or modified
with the
.B bind
builtin command.  The editing mode may be switched during interactive
use by using the
.B \-o
option to the
.B set
builtin command (see
.SM
.B SHELL BUILTIN COMMANDS
below).
.SS "Readline Variables"
.PP
Readline has variables that can be used to further customize its
behavior.  A variable may be set in the
.I inputrc
file with a statement of the form
.RS
.PP
\fBset\fP \fIvariable\-name\fP \fIvalue\fP
.RE
.PP
Except where noted, readline variables can take the values
.B On
or
.B Off
(without regard to case).
Unrecognized variable names are ignored.
When a variable value is read, empty or null values, "on" (case-insensitive),
and "1" are equivalent to \fBOn\fP.  All other values are equivalent to
\fBOff\fP.
The variables and their default values are:
.PP
.PD 0
.TP
.B bell\-style (audible)
Controls what happens when readline wants to ring the terminal bell.
If set to \fBnone\fP, readline never rings the bell.  If set to
\fBvisible\fP, readline uses a visible bell if one is available.
If set to \fBaudible\fP, readline attempts to ring the terminal's bell.
.TP
.B bind\-tty\-special\-chars (On)
If set to \fBOn\fP, readline attempts to bind the control characters
treated specially by the kernel's terminal driver to their readline
equivalents.
.TP
.B blink\-matching\-paren (Off)
If set to \fBOn\fP, readline attempts to briefly move the cursor to an
opening parenthesis when a closing parenthesis is inserted.
.TP
.B colored\-completion\-prefix (Off)
If set to \fBOn\fP, when listing completions, readline displays the
common prefix of the set of possible completions using a different color.
The color definitions are taken from the value of the \fBLS_COLORS\fP
environment variable.
.TP
.B colored\-stats (Off)
If set to \fBOn\fP, readline displays possible completions using different
colors to indicate their file type.
The color definitions are taken from the value of the \fBLS_COLORS\fP
environment variable.
.TP
.B comment\-begin (``#'')
The string that is inserted when the readline
.B insert\-comment
command is executed.
This command is bound to
.B M\-#
in emacs mode and to
.B #
in vi command mode.
.TP
.B completion\-display\-width (\-1)
The number of screen columns used to display possible matches
when performing completion.
The value is ignored if it is less than 0 or greater than the terminal
screen width.
A value of 0 will cause matches to be displayed one per line.
The default value is \-1.
.TP
.B completion\-ignore\-case (Off)
If set to \fBOn\fP, readline performs filename matching and completion
in a case\-insensitive fashion.
.TP
.B completion\-map\-case (Off)
If set to \fBOn\fP, and \fBcompletion\-ignore\-case\fP is enabled, readline
treats hyphens (\fI\-\fP) and underscores (\fI_\fP) as equivalent when
performing case\-insensitive filename matching and completion.
.TP
.B completion\-prefix\-display\-length (0)
The length in characters of the common prefix of a list of possible
completions that is displayed without modification.  When set to a
value greater than zero, common prefixes longer than this value are
replaced with an ellipsis when displaying possible completions.
.TP
.B completion\-query\-items (100)
This determines when the user is queried about viewing
the number of possible completions
generated by the \fBpossible\-completions\fP command.
It may be set to any integer value greater than or equal to
zero.  If the number of possible completions is greater than
or equal to the value of this variable, the user is asked whether
or not he wishes to view them; otherwise they are simply listed
on the terminal.
.TP
.B convert\-meta (On)
If set to \fBOn\fP, readline will convert characters with the
eighth bit set to an ASCII key sequence
by stripping the eighth bit and prefixing an
escape character (in effect, using escape as the \fImeta prefix\fP).
The default is \fIOn\fP, but readline will set it to \fIOff\fP if the
locale contains eight-bit characters.
.TP
.B disable\-completion (Off)
If set to \fBOn\fP, readline will inhibit word completion.  Completion
characters will be inserted into the line as if they had been
mapped to \fBself-insert\fP.
.TP
.B echo\-control\-characters (On)
When set to \fBOn\fP, on operating systems that indicate they support it,
readline echoes a character corresponding to a signal generated from the
keyboard.
.TP
.B editing\-mode (emacs)
Controls whether readline begins with a set of key bindings similar
to \fIEmacs\fP or \fIvi\fP.
.B editing\-mode
can be set to either
.B emacs
or
.BR vi .
.TP
.B emacs\-mode\-string (@)
If the \fIshow\-mode\-in\-prompt\fP variable is enabled,
this string is displayed immediately before the last line of the primary
prompt when emacs editing mode is active.  The value is expanded like a
key binding, so the standard set of meta- and control prefixes and
backslash escape sequences is available.
Use the \e1 and \e2 escapes to begin and end sequences of
non-printing characters, which can be used to embed a terminal control
sequence into the mode string.
.TP
.B enable\-bracketed\-paste (Off)
When set to \fBOn\fP, readline will configure the terminal in a way
that will enable it to insert each paste into the editing buffer as a
single string of characters, instead of treating each character as if
it had been read from the keyboard.  This can prevent pasted characters
from being interpreted as editing commands.
.TP
.B enable\-keypad (Off)
When set to \fBOn\fP, readline will try to enable the application
keypad when it is called.  Some systems need this to enable the
arrow keys.
.TP
.B enable\-meta\-key (On)
When set to \fBOn\fP, readline will try to enable any meta modifier
key the terminal claims to support when it is called.  On many terminals,
the meta key is used to send eight-bit characters.
.TP
.B expand\-tilde (Off)
If set to \fBOn\fP, tilde expansion is performed when readline
attempts word completion.
.TP
.B history\-preserve\-point (Off)
If set to \fBOn\fP, the history code attempts to place point at the
same location on each history line retrieved with \fBprevious-history\fP
or \fBnext-history\fP.
.TP
.B history\-size (unset)
Set the maximum number of history entries saved in the history list.
If set to zero, any existing history entries are deleted and no new entries
are saved.
If set to a value less than zero, the number of history entries is not
limited.
By default, the number of history entries is set to the value of the
\fBHISTSIZE\fP shell variable.
If an attempt is made to set \fIhistory\-size\fP to a non-numeric value,
the maximum number of history entries will be set to 500.
.TP
.B horizontal\-scroll\-mode (Off)
When set to \fBOn\fP, makes readline use a single line for display,
scrolling the input horizontally on a single screen line when it
becomes longer than the screen width rather than wrapping to a new line.
.TP
.B input\-meta (Off)
If set to \fBOn\fP, readline will enable eight-bit input (that is,
it will not strip the eighth bit from the characters it reads),
regardless of what the terminal claims it can support.  The name
.B meta\-flag
is a synonym for this variable.
The default is \fIOff\fP, but readline will set it to \fIOn\fP if the
locale contains eight-bit characters.
.TP
.B isearch\-terminators (``C\-[C\-J'')
The string of characters that should terminate an incremental
search without subsequently executing the character as a command.
If this variable has not been given a value, the characters
\fIESC\fP and \fIC\-J\fP will terminate an incremental search.
.TP
.B keymap (emacs)
Set the current readline keymap.  The set of valid keymap names is
\fIemacs, emacs\-standard, emacs\-meta, emacs\-ctlx, vi,
vi\-command\fP, and
.IR vi\-insert .
\fIvi\fP is equivalent to \fIvi\-command\fP; \fIemacs\fP is
equivalent to \fIemacs\-standard\fP.  The default value is
.IR emacs ;
the value of
.B editing\-mode
also affects the default keymap.
.TP
.B keyseq\-timeout (500)
Specifies the duration \fIreadline\fP will wait for a character when reading an
ambiguous key sequence (one that can form a complete key sequence using
the input read so far, or can take additional input to complete a longer
key sequence).
If no input is received within the timeout, \fIreadline\fP will use the shorter
but complete key sequence.
The value is specified in milliseconds, so a value of 1000 means that
\fIreadline\fP will wait one second for additional input.
If this variable is set to a value less than or equal to zero, or to a
non-numeric value, \fIreadline\fP will wait until another key is pressed to
decide which key sequence to complete.
.TP
.B mark\-directories (On)
If set to \fBOn\fP, completed directory names have a slash
appended.
.TP
.B mark\-modified\-lines (Off)
If set to \fBOn\fP, history lines that have been modified are displayed
with a preceding asterisk (\fB*\fP).
.TP
.B mark\-symlinked\-directories (Off)
If set to \fBOn\fP, completed names which are symbolic links to directories
have a slash appended (subject to the value of
\fBmark\-directories\fP).
.TP
.B match\-hidden\-files (On)
This variable, when set to \fBOn\fP, causes readline to match files whose
names begin with a `.' (hidden files) when performing filename
completion.
If set to \fBOff\fP, the leading `.' must be
supplied by the user in the filename to be completed.
.TP
.B menu\-complete\-display\-prefix (Off)
If set to \fBOn\fP, menu completion displays the common prefix of the
list of possible completions (which may be empty) before cycling through
the list.
.TP
.B output\-meta (Off)
If set to \fBOn\fP, readline will display characters with the
eighth bit set directly rather than as a meta-prefixed escape
sequence.
The default is \fIOff\fP, but readline will set it to \fIOn\fP if the
locale contains eight-bit characters.
.TP
.B page\-completions (On)
If set to \fBOn\fP, readline uses an internal \fImore\fP-like pager
to display a screenful of possible completions at a time.
.TP
.B print\-completions\-horizontally (Off)
If set to \fBOn\fP, readline will display completions with matches
sorted horizontally in alphabetical order, rather than down the screen.
.TP
.B revert\-all\-at\-newline (Off)
If set to \fBOn\fP, readline will undo all changes to history lines
before returning when \fBaccept\-line\fP is executed.  By default,
history lines may be modified and retain individual undo lists across
calls to \fBreadline\fP.
.TP
.B show\-all\-if\-ambiguous (Off)
This alters the default behavior of the completion functions.  If
set to
.BR On ,
words which have more than one possible completion cause the
matches to be listed immediately instead of ringing the bell.
.TP
.B show\-all\-if\-unmodified (Off)
This alters the default behavior of the completion functions in
a fashion similar to \fBshow\-all\-if\-ambiguous\fP.
If set to
.BR On ,
words which have more than one possible completion without any
possible partial completion (the possible completions don't share
a common prefix) cause the matches to be listed immediately instead
of ringing the bell.
.TP
.B show\-mode\-in\-prompt (Off)
If set to \fBOn\fP, add a string to the beginning of the prompt
indicating the editing mode: emacs, vi command, or vi insertion.
The mode strings are user-settable (e.g., \fIemacs\-mode\-string\fP).
.TP
.B skip\-completed\-text (Off)
If set to \fBOn\fP, this alters the default completion behavior when
inserting a single match into the line.  It's only active when
performing completion in the middle of a word.  If enabled, readline
does not insert characters from the completion that match characters
after point in the word being completed, so portions of the word
following the cursor are not duplicated.
.TP
.B vi\-cmd\-mode\-string ((cmd))
If the \fIshow\-mode\-in\-prompt\fP variable is enabled,
this string is displayed immediately before the last line of the primary
prompt when vi editing mode is active and in command mode.
The value is expanded like a
key binding, so the standard set of meta- and control prefixes and
backslash escape sequences is available.
Use the \e1 and \e2 escapes to begin and end sequences of
non-printing characters, which can be used to embed a terminal control
sequence into the mode string.
.TP
.B vi\-ins\-mode\-string ((ins))
If the \fIshow\-mode\-in\-prompt\fP variable is enabled,
this string is displayed immediately before the last line of the primary
prompt when vi editing mode is active and in insertion mode.
The value is expanded like a
key binding, so the standard set of meta- and control prefixes and
backslash escape sequences is available.
Use the \e1 and \e2 escapes to begin and end sequences of
non-printing characters, which can be used to embed a terminal control
sequence into the mode string.
.TP
.B visible\-stats (Off)
If set to \fBOn\fP, a character denoting a file's type as reported
by \fIstat\fP(2) is appended to the filename when listing possible
completions.
.PD
.SS "Readline Conditional Constructs"
.PP
Readline implements a facility similar in spirit to the conditional
compilation features of the C preprocessor which allows key
bindings and variable settings to be performed as the result
of tests.  There are four parser directives used.
.IP \fB$if\fP
The
.B $if
construct allows bindings to be made based on the
editing mode, the terminal being used, or the application using
readline.  The text of the test, after any comparison operator,
 extends to the end of the line;
unless otherwise noted, no characters are required to isolate it.
.RS
.IP \fBmode\fP
The \fBmode=\fP form of the \fB$if\fP directive is used to test
whether readline is in emacs or vi mode.
This may be used in conjunction
with the \fBset keymap\fP command, for instance, to set bindings in
the \fIemacs\-standard\fP and \fIemacs\-ctlx\fP keymaps only if
readline is starting out in emacs mode.
.IP \fBterm\fP
The \fBterm=\fP form may be used to include terminal-specific
key bindings, perhaps to bind the key sequences output by the
terminal's function keys.  The word on the right side of the
.B =
is tested against both the full name of the terminal and the portion
of the terminal name before the first \fB\-\fP.  This allows
.I sun
to match both
.I sun
and
.IR sun\-cmd ,
for instance.
.IP \fBversion\fP
The \fBversion\fP test may be used to perform comparisons against
specific readline versions.
The \fBversion\fP expands to the current readline version.
The set of comparison operators includes
.BR = ,
(and
.BR == ),
.BR != ,
.BR <= ,
.BR >= ,
.BR < ,
and
.BR > .
The version number supplied on the right side of the operator consists
of a major version number, an optional decimal point, and an optional
minor version (e.g., \fB7.1\fP). If the minor version is omitted, it
is assumed to be \fB0\fP.
The operator may be separated from the string \fBversion\fP   
and from the version number argument by whitespace.
.IP \fBapplication\fP
The \fBapplication\fP construct is used to include
application-specific settings.  Each program using the readline
library sets the \fIapplication name\fP, and an initialization
file can test for a particular value.
This could be used to bind key sequences to functions useful for
a specific program.  For instance, the following command adds a
key sequence that quotes the current or previous word in \fBbash\fP:
.sp 1
.RS
.nf
\fB$if\fP Bash
# Quote the current or previous word
"\eC\-xq": "\eeb\e"\eef\e""
\fB$endif\fP
.fi
.RE
.IP \fIvariable\fP
The \fIvariable\fP construct provides simple equality tests for readline
variables and values.
The permitted comparison operators are \fI=\fP, \fI==\fP, and \fI!=\fP.
The variable name must be separated from the comparison operator by
whitespace; the operator may be separated from the value on the right hand
side by whitespace.
Both string and boolean variables may be tested. Boolean variables must be
tested against the values \fIon\fP and \fIoff\fP.
.RE
.IP \fB$endif\fP
This command, as seen in the previous example, terminates an
\fB$if\fP command.
.IP \fB$else\fP
Commands in this branch of the \fB$if\fP directive are executed if
the test fails.
.IP \fB$include\fP
This directive takes a single filename as an argument and reads commands
and bindings from that file.  For example, the following directive
would read \fI/etc/inputrc\fP:
.sp 1
.RS
.nf
\fB$include\fP \^ \fI/etc/inputrc\fP
.fi
.RE
.SS Searching
.PP
Readline provides commands for searching through the command history
(see
.SM
.B HISTORY
below) for lines containing a specified string.
There are two search modes:
.I incremental
and
.IR non-incremental .
.PP
Incremental searches begin before the user has finished typing the
search string.
As each character of the search string is typed, readline displays
the next entry from the history matching the string typed so far.
An incremental search requires only as many characters as needed to
find the desired history entry.
The characters present in the value of the \fBisearch-terminators\fP
variable are used to terminate an incremental search.
If that variable has not been assigned a value the Escape and
Control-J characters will terminate an incremental search.
Control-G will abort an incremental search and restore the original
line.
When the search is terminated, the history entry containing the
search string becomes the current line.
.PP
To find other matching entries in the history list, type Control-S or
Control-R as appropriate.
This will search backward or forward in the history for the next
entry matching the search string typed so far.
Any other key sequence bound to a readline command will terminate
the search and execute that command.
For instance, a \fInewline\fP will terminate the search and accept
the line, thereby executing the command from the history list.
.PP
Readline remembers the last incremental search string.  If two
Control-Rs are typed without any intervening characters defining a
new search string, any remembered search string is used.
.PP
Non-incremental searches read the entire search string before starting
to search for matching history lines.  The search string may be
typed by the user or be part of the contents of the current line.
.SS "Readline Command Names"
.PP
The following is a list of the names of the commands and the default
key sequences to which they are bound.
Command names without an accompanying key sequence are unbound by default.
In the following descriptions, \fIpoint\fP refers to the current cursor
position, and \fImark\fP refers to a cursor position saved by the
\fBset\-mark\fP command.
The text between the point and mark is referred to as the \fIregion\fP.
.SS Commands for Moving
.PP
.PD 0
.TP
.B beginning\-of\-line (C\-a)
Move to the start of the current line.
.TP
.B end\-of\-line (C\-e)
Move to the end of the line.
.TP
.B forward\-char (C\-f)
Move forward a character.
.TP
.B backward\-char (C\-b)
Move back a character.
.TP
.B forward\-word (M\-f)
Move forward to the end of the next word.  Words are composed of
alphanumeric characters (letters and digits).
.TP
.B backward\-word (M\-b)
Move back to the start of the current or previous word.
Words are composed of alphanumeric characters (letters and digits).
.TP
.B shell\-forward\-word
Move forward to the end of the next word.
Words are delimited by non-quoted shell metacharacters.
.TP
.B shell\-backward\-word
Move back to the start of the current or previous word.
Words are delimited by non-quoted shell metacharacters.
.TP
.B previous\-screen\-line
Attempt to move point to the same physical screen column on the previous
physical screen line. This will not have the desired effect if the current
Readline line does not take up more than one physical line or if point is not  
greater than the length of the prompt plus the screen width.
.TP
.B next\-screen\-line
Attempt to move point to the same physical screen column on the next
physical screen line. This will not have the desired effect if the current
Readline line does not take up more than one physical line or if the length
of the current Readline line is not greater than the length of the prompt
plus the screen width.
.TP
.B clear\-screen (C\-l)
Clear the screen leaving the current line at the top of the screen.
With an argument, refresh the current line without clearing the
screen.
.TP
.B redraw\-current\-line
Refresh the current line.
.PD
.SS Commands for Manipulating the History
.PP
.PD 0
.TP
.B accept\-line (Newline, Return)
Accept the line regardless of where the cursor is.  If this line is
non-empty, add it to the history list according to the state of the
.SM
.B HISTCONTROL
variable.  If the line is a modified history
line, then restore the history line to its original state.
.TP
.B previous\-history (C\-p)
Fetch the previous command from the history list, moving back in
the list.
.TP
.B next\-history (C\-n)
Fetch the next command from the history list, moving forward in the
list.
.TP
.B beginning\-of\-history (M\-<)
Move to the first line in the history.
.TP
.B end\-of\-history (M\->)
Move to the end of the input history, i.e., the line currently being
entered.
.TP
.B reverse\-search\-history (C\-r)
Search backward starting at the current line and moving `up' through
the history as necessary.  This is an incremental search.
.TP
.B forward\-search\-history (C\-s)
Search forward starting at the current line and moving `down' through
the history as necessary.  This is an incremental search.
.TP
.B non\-incremental\-reverse\-search\-history (M\-p)
Search backward through the history starting at the current line
using a non-incremental search for a string supplied by the user.
.TP
.B non\-incremental\-forward\-search\-history (M\-n)
Search forward through the history using a non-incremental search for
a string supplied by the user.
.TP
.B history\-search\-forward
Search forward through the history for the string of characters
between the start of the current line and the point.
This is a non-incremental search.
.TP
.B history\-search\-backward
Search backward through the history for the string of characters
between the start of the current line and the point.
This is a non-incremental search.
.TP
.B history\-substring\-search\-backward
Search backward through the history for the string of characters   
between the start of the current line and the current cursor
position (the \fIpoint\fP).
The search string may match anywhere in a history line.
This is a non-incremental search.
.TP
.B history\-substring\-search\-forward
Search forward through the history for the string of characters
between the start of the current line and the point.
The search string may match anywhere in a history line.
This is a non-incremental search.
.TP
.B yank\-nth\-arg (M\-C\-y)
Insert the first argument to the previous command (usually
the second word on the previous line) at point.
With an argument
.IR n ,
insert the \fIn\fPth word from the previous command (the words
in the previous command begin with word 0).  A negative argument
inserts the \fIn\fPth word from the end of the previous command.
Once the argument \fIn\fP is computed, the argument is extracted
as if the "!\fIn\fP" history expansion had been specified.
.TP
.B
yank\-last\-arg (M\-.\^, M\-_\^)
Insert the last argument to the previous command (the last word of
the previous history entry).
With a numeric argument, behave exactly like \fByank\-nth\-arg\fP.
Successive calls to \fByank\-last\-arg\fP move back through the history
list, inserting the last word (or the word specified by the argument to
the first call) of each line in turn.
Any numeric argument supplied to these successive calls determines
the direction to move through the history.  A negative argument switches
the direction through the history (back or forward).
The history expansion facilities are used to extract the last word,
as if the "!$" history expansion had been specified.
.TP
.B shell\-expand\-line (M\-C\-e)
Expand the line as the shell does.  This
performs alias and history expansion as well as all of the shell
word expansions.  See
.SM
.B HISTORY EXPANSION
below for a description of history expansion.
.TP
.B history\-expand\-line (M\-^)
Perform history expansion on the current line.
See
.SM
.B HISTORY EXPANSION
below for a description of history expansion.
.TP
.B magic\-space
Perform history expansion on the current line and insert a space.
See
.SM
.B HISTORY EXPANSION
below for a description of history expansion.
.TP
.B alias\-expand\-line
Perform alias expansion on the current line.
See
.SM
.B ALIASES
above for a description of alias expansion.
.TP
.B history\-and\-alias\-expand\-line
Perform history and alias expansion on the current line.
.TP
.B insert\-last\-argument (M\-.\^, M\-_\^)
A synonym for \fByank\-last\-arg\fP.
.TP
.B operate\-and\-get\-next (C\-o)
Accept the current line for execution and fetch the next line
relative to the current line from the history for editing.
A numeric argument, if supplied, specifies the history entry to use instead
of the current line.
.TP
.B edit\-and\-execute\-command (C\-x C\-e)
Invoke an editor on the current command line, and execute the result as shell
commands.
\fBBash\fP attempts to invoke
.SM
.BR $VISUAL ,
.SM
.BR $EDITOR ,
and \fIemacs\fP as the editor, in that order.
.PD
.SS Commands for Changing Text
.PP
.PD 0
.TP
.B \fIend\-of\-file\fP (usually C\-d)
The character indicating end-of-file as set, for example, by
.if t \f(CWstty\fP.
.if n ``stty''.
If this character is read when there are no characters
on the line, and point is at the beginning of the line, Readline
interprets it as the end of input and returns
.SM
.BR EOF .
.TP
.B delete\-char (C\-d)
Delete the character at point.
If this function is bound to the
same character as the tty \fBEOF\fP character, as \fBC\-d\fP
commonly is, see above for the effects.
.TP
.B backward\-delete\-char (Rubout)
Delete the character behind the cursor.  When given a numeric argument,
save the deleted text on the kill ring.
.TP
.B forward\-backward\-delete\-char
Delete the character under the cursor, unless the cursor is at the
end of the line, in which case the character behind the cursor is
deleted.
.TP
.B quoted\-insert (C\-q, C\-v)
Add the next character typed to the line verbatim.  This is
how to insert characters like \fBC\-q\fP, for example.
.TP
.B tab\-insert (C\-v TAB)
Insert a tab character.
.TP
.B self\-insert (a,\ b,\ A,\ 1,\ !,\ ...)
Insert the character typed.
.TP
.B transpose\-chars (C\-t)
Drag the character before point forward over the character at point,
moving point forward as well.
If point is at the end of the line, then this transposes
the two characters before point.
Negative arguments have no effect.
.TP
.B transpose\-words (M\-t)
Drag the word before point past the word after point,
moving point over that word as well.
If point is at the end of the line, this transposes
the last two words on the line.
.TP
.B upcase\-word (M\-u)
Uppercase the current (or following) word.  With a negative argument,
uppercase the previous word, but do not move point.
.TP
.B downcase\-word (M\-l)
Lowercase the current (or following) word.  With a negative argument,
lowercase the previous word, but do not move point.
.TP
.B capitalize\-word (M\-c)
Capitalize the current (or following) word.  With a negative argument,
capitalize the previous word, but do not move point.
.TP
.B overwrite\-mode
Toggle overwrite mode.  With an explicit positive numeric argument,
switches to overwrite mode.  With an explicit non-positive numeric
argument, switches to insert mode.  This command affects only
\fBemacs\fP mode; \fBvi\fP mode does overwrite differently.
Each call to \fIreadline()\fP starts in insert mode.
In overwrite mode, characters bound to \fBself\-insert\fP replace
the text at point rather than pushing the text to the right.
Characters bound to \fBbackward\-delete\-char\fP replace the character
before point with a space.  By default, this command is unbound.
.PD
.SS Killing and Yanking
.PP
.PD 0
.TP
.B kill\-line (C\-k)
Kill the text from point to the end of the line.
.TP
.B backward\-kill\-line (C\-x Rubout)
Kill backward to the beginning of the line.
.TP
.B unix\-line\-discard (C\-u)
Kill backward from point to the beginning of the line.
The killed text is saved on the kill-ring.
.\" There is no real difference between this and backward-kill-line
.TP
.B kill\-whole\-line
Kill all characters on the current line, no matter where point is.
.TP
.B kill\-word (M\-d)
Kill from point to the end of the current word, or if between
words, to the end of the next word.
Word boundaries are the same as those used by \fBforward\-word\fP.
.TP
.B backward\-kill\-word (M\-Rubout)
Kill the word behind point.
Word boundaries are the same as those used by \fBbackward\-word\fP.
.TP
.B shell\-kill\-word
Kill from point to the end of the current word, or if between
words, to the end of the next word.
Word boundaries are the same as those used by \fBshell\-forward\-word\fP.
.TP
.B shell\-backward\-kill\-word
Kill the word behind point.
Word boundaries are the same as those used by \fBshell\-backward\-word\fP.
.TP
.B unix\-word\-rubout (C\-w)
Kill the word behind point, using white space as a word boundary.
The killed text is saved on the kill-ring.
.TP
.B unix\-filename\-rubout
Kill the word behind point, using white space and the slash character
as the word boundaries.
The killed text is saved on the kill-ring.
.TP
.B delete\-horizontal\-space (M\-\e)
Delete all spaces and tabs around point.
.TP
.B kill\-region
Kill the text in the current region.
.TP
.B copy\-region\-as\-kill
Copy the text in the region to the kill buffer.
.TP
.B copy\-backward\-word
Copy the word before point to the kill buffer.
The word boundaries are the same as \fBbackward\-word\fP.
.TP
.B copy\-forward\-word
Copy the word following point to the kill buffer.
The word boundaries are the same as \fBforward\-word\fP.
.TP
.B yank (C\-y)
Yank the top of the kill ring into the buffer at point.
.TP
.B yank\-pop (M\-y)
Rotate the kill ring, and yank the new top.  Only works following
.B yank
or
.BR yank\-pop .
.PD
.SS Numeric Arguments
.PP
.PD 0
.TP
.B digit\-argument (M\-0, M\-1, ..., M\-\-)
Add this digit to the argument already accumulating, or start a new
argument.  M\-\- starts a negative argument.
.TP
.B universal\-argument
This is another way to specify an argument.
If this command is followed by one or more digits, optionally with a
leading minus sign, those digits define the argument.
If the command is followed by digits, executing
.B universal\-argument
again ends the numeric argument, but is otherwise ignored.
As a special case, if this command is immediately followed by a
character that is neither a digit nor minus sign, the argument count
for the next command is multiplied by four.
The argument count is initially one, so executing this function the
first time makes the argument count four, a second time makes the
argument count sixteen, and so on.
.PD
.SS Completing
.PP
.PD 0
.TP
.B complete (TAB)
Attempt to perform completion on the text before point.
.B Bash
attempts completion treating the text as a variable (if the
text begins with \fB$\fP), username (if the text begins with
\fB~\fP), hostname (if the text begins with \fB@\fP), or
command (including aliases and functions) in turn.  If none
of these produces a match, filename completion is attempted.
.TP
.B possible\-completions (M\-?)
List the possible completions of the text before point.
.TP
.B insert\-completions (M\-*)
Insert all completions of the text before point
that would have been generated by
\fBpossible\-completions\fP.
.TP
.B menu\-complete
Similar to \fBcomplete\fP, but replaces the word to be completed
with a single match from the list of possible completions.
Repeated execution of \fBmenu\-complete\fP steps through the list
of possible completions, inserting each match in turn.
At the end of the list of completions, the bell is rung
(subject to the setting of \fBbell\-style\fP)
and the original text is restored.
An argument of \fIn\fP moves \fIn\fP positions forward in the list
of matches; a negative argument may be used to move backward
through the list.
This command is intended to be bound to \fBTAB\fP, but is unbound
by default.
.TP
.B menu\-complete\-backward
Identical to \fBmenu\-complete\fP, but moves backward through the list
of possible completions, as if \fBmenu\-complete\fP had been given a
negative argument.  This command is unbound by default.
.TP
.B delete\-char\-or\-list
Deletes the character under the cursor if not at the beginning or
end of the line (like \fBdelete\-char\fP).
If at the end of the line, behaves identically to
\fBpossible\-completions\fP.
This command is unbound by default.
.TP
.B complete\-filename (M\-/)
Attempt filename completion on the text before point.
.TP
.B possible\-filename\-completions (C\-x /)
List the possible completions of the text before point,
treating it as a filename.
.TP
.B complete\-username (M\-~)
Attempt completion on the text before point, treating
it as a username.
.TP
.B possible\-username\-completions (C\-x ~)
List the possible completions of the text before point,
treating it as a username.
.TP
.B complete\-variable (M\-$)
Attempt completion on the text before point, treating
it as a shell variable.
.TP
.B possible\-variable\-completions (C\-x $)
List the possible completions of the text before point,
treating it as a shell variable.
.TP
.B complete\-hostname (M\-@)
Attempt completion on the text before point, treating
it as a hostname.
.TP
.B possible\-hostname\-completions (C\-x @)
List the possible completions of the text before point,
treating it as a hostname.
.TP
.B complete\-command (M\-!)
Attempt completion on the text before point, treating
it as a command name.  Command completion attempts to
match the text against aliases, reserved words, shell
functions, shell builtins, and finally executable filenames,
in that order.
.TP
.B possible\-command\-completions (C\-x !)
List the possible completions of the text before point,
treating it as a command name.
.TP
.B dynamic\-complete\-history (M\-TAB)
Attempt completion on the text before point, comparing
the text against lines from the history list for possible
completion matches.
.TP
.B dabbrev\-expand
Attempt menu completion on the text before point, comparing
the text against lines from the history list for possible
completion matches.
.TP
.B complete\-into\-braces (M\-{)
Perform filename completion and insert the list of possible completions
enclosed within braces so the list is available to the shell (see
.B Brace Expansion
above).
.PD
.SS Keyboard Macros
.PP
.PD 0
.TP
.B start\-kbd\-macro (C\-x (\^)
Begin saving the characters typed into the current keyboard macro.
.TP
.B end\-kbd\-macro (C\-x )\^)
Stop saving the characters typed into the current keyboard macro
and store the definition.
.TP
.B call\-last\-kbd\-macro (C\-x e)
Re-execute the last keyboard macro defined, by making the characters
in the macro appear as if typed at the keyboard.
.TP
.B print\-last\-kbd\-macro ()
Print the last keyboard macro defined in a format suitable for the
\fIinputrc\fP file.
.PD
.SS Miscellaneous
.PP
.PD 0
.TP
.B re\-read\-init\-file (C\-x C\-r)
Read in the contents of the \fIinputrc\fP file, and incorporate
any bindings or variable assignments found there.
.TP
.B abort (C\-g)
Abort the current editing command and
ring the terminal's bell (subject to the setting of
.BR bell\-style ).
.TP
.B do\-lowercase\-version (M\-A, M\-B, M\-\fIx\fP, ...)
If the metafied character \fIx\fP is uppercase, run the command
that is bound to the corresponding metafied lowercase character. 
The behavior is undefined if \fIx\fP is already lowercase. 
.TP
.B prefix\-meta (ESC)
Metafy the next character typed.
.SM
.B ESC
.B f
is equivalent to
.BR Meta\-f .
.TP
.B undo (C\-_, C\-x C\-u)
Incremental undo, separately remembered for each line.
.TP
.B revert\-line (M\-r)
Undo all changes made to this line.  This is like executing the
.B undo
command enough times to return the line to its initial state.
.TP
.B tilde\-expand (M\-&)
Perform tilde expansion on the current word.
.TP
.B set\-mark (C\-@, M\-<space>)
Set the mark to the point.  If a
numeric argument is supplied, the mark is set to that position.
.TP
.B exchange\-point\-and\-mark (C\-x C\-x)
Swap the point with the mark.  The current cursor position is set to
the saved position, and the old cursor position is saved as the mark.
.TP
.B character\-search (C\-])
A character is read and point is moved to the next occurrence of that
character.  A negative count searches for previous occurrences.
.TP
.B character\-search\-backward (M\-C\-])
A character is read and point is moved to the previous occurrence of that
character.  A negative count searches for subsequent occurrences.
.TP
.B skip\-csi\-sequence
Read enough characters to consume a multi-key sequence such as those
defined for keys like Home and End.  Such sequences begin with a
Control Sequence Indicator (CSI), usually ESC\-[.  If this sequence is
bound to "\e[", keys producing such sequences will have no effect
unless explicitly bound to a readline command, instead of inserting
stray characters into the editing buffer.  This is unbound by default,
but usually bound to ESC\-[.
.TP
.B insert\-comment (M\-#)
Without a numeric argument, the value of the readline
.B comment\-begin
variable is inserted at the beginning of the current line.
If a numeric argument is supplied, this command acts as a toggle: if
the characters at the beginning of the line do not match the value
of \fBcomment\-begin\fP, the value is inserted, otherwise
the characters in \fBcomment\-begin\fP are deleted from the beginning of
the line.
In either case, the line is accepted as if a newline had been typed.
The default value of
\fBcomment\-begin\fP causes this command to make the current line
a shell comment.
If a numeric argument causes the comment character to be removed, the line
will be executed by the shell.
.TP
.B glob\-complete\-word (M\-g)
The word before point is treated as a pattern for pathname expansion,
with an asterisk implicitly appended.  This pattern is used to
generate a list of matching filenames for possible completions.
.TP
.B glob\-expand\-word (C\-x *)
The word before point is treated as a pattern for pathname expansion,
and the list of matching filenames is inserted, replacing the word.
If a numeric argument is supplied, an asterisk is appended before
pathname expansion.
.TP
.B glob\-list\-expansions (C\-x g)
The list of expansions that would have been generated by
.B glob\-expand\-word
is displayed, and the line is redrawn.
If a numeric argument is supplied, an asterisk is appended before
pathname expansion.
.TP
.B dump\-functions
Print all of the functions and their key bindings to the
readline output stream.  If a numeric argument is supplied,
the output is formatted in such a way that it can be made part
of an \fIinputrc\fP file.
.TP
.B dump\-variables
Print all of the settable readline variables and their values to the
readline output stream.  If a numeric argument is supplied,
the output is formatted in such a way that it can be made part
of an \fIinputrc\fP file.
.TP
.B dump\-macros
Print all of the readline key sequences bound to macros and the
strings they output.  If a numeric argument is supplied,
the output is formatted in such a way that it can be made part
of an \fIinputrc\fP file.
.TP
.B display\-shell\-version (C\-x C\-v)
Display version information about the current instance of
.BR bash .
.PD
.SS Programmable Completion
.PP
When word completion is attempted for an argument to a command for
which a completion specification (a \fIcompspec\fP) has been defined
using the \fBcomplete\fP builtin (see
.SM
.B "SHELL BUILTIN COMMANDS"
below), the programmable completion facilities are invoked.
.PP
First, the command name is identified.
If the command word is the empty string (completion attempted at the
beginning of an empty line), any compspec defined with
the \fB\-E\fP option to \fBcomplete\fP is used.
If a compspec has been defined for that command, the
compspec is used to generate the list of possible completions for the word.
If the command word is a full pathname, a compspec for the full
pathname is searched for first.
If no compspec is found for the full pathname, an attempt is made to
find a compspec for the portion following the final slash.
If those searches do not result in a compspec, any compspec defined with
the \fB\-D\fP option to \fBcomplete\fP is used as the default.
If there is no default compspec, \fBbash\fP attempts alias expansion
on the command word as a final resort, and attempts to find a compspec
for the command word from any successful expansion.
.PP
Once a compspec has been found, it is used to generate the list of
matching words.
If a compspec is not found, the default \fBbash\fP completion as
described above under \fBCompleting\fP is performed.
.PP
First, the actions specified by the compspec are used.
Only matches which are prefixed by the word being completed are
returned.
When the
.B \-f
or
.B \-d
option is used for filename or directory name completion, the shell
variable
.SM
.B FIGNORE
is used to filter the matches.
.PP
Any completions specified by a pathname expansion pattern to the
\fB\-G\fP option are generated next.
The words generated by the pattern need not match the word
being completed.
The
.SM
.B GLOBIGNORE
shell variable is not used to filter the matches, but the
.SM
.B FIGNORE
variable is used.
.PP
Next, the string specified as the argument to the \fB\-W\fP option
is considered.
The string is first split using the characters in the
.SM
.B IFS
special variable as delimiters.
Shell quoting is honored.
Each word is then expanded using
brace expansion, tilde expansion, parameter and variable expansion,
command substitution, and arithmetic expansion,
as described above under
.SM
.BR EXPANSION .
The results are split using the rules described above under
\fBWord Splitting\fP.
The results of the expansion are prefix-matched against the word being
completed, and the matching words become the possible completions.
.PP
After these matches have been generated, any shell function or command
specified with the \fB\-F\fP and \fB\-C\fP options is invoked.
When the command or function is invoked, the
.SM
.BR COMP_LINE ,
.SM
.BR COMP_POINT ,
.SM
.BR COMP_KEY ,
and
.SM
.B COMP_TYPE
variables are assigned values as described above under
\fBShell Variables\fP.
If a shell function is being invoked, the
.SM
.B COMP_WORDS
and
.SM
.B COMP_CWORD
variables are also set.
When the function or command is invoked,
the first argument (\fB$1\fP) is the name of the command whose arguments are
being completed,
the second argument (\fB$2\fP) is the word being completed,
and the third argument (\fB$3\fP) is the word preceding the word being
completed on the current command line.
No filtering of the generated completions against the word being completed
is performed; the function or command has complete freedom in generating
the matches.
.PP
Any function specified with \fB\-F\fP is invoked first.
The function may use any of the shell facilities, including the
\fBcompgen\fP builtin described below, to generate the matches.
It must put the possible completions in the
.SM
.B COMPREPLY
array variable, one per array element.
.PP
Next, any command specified with the \fB\-C\fP option is invoked
in an environment equivalent to command substitution.
It should print a list of completions, one per line, to the
standard output.
Backslash may be used to escape a newline, if necessary.
.PP
After all of the possible completions are generated, any filter
specified with the \fB\-X\fP option is applied to the list.
The filter is a pattern as used for pathname expansion; a \fB&\fP
in the pattern is replaced with the text of the word being completed.
A literal \fB&\fP may be escaped with a backslash; the backslash
is removed before attempting a match.
Any completion that matches the pattern will be removed from the list.
A leading \fB!\fP negates the pattern; in this case any completion
not matching the pattern will be removed.
If the
.B nocasematch
shell option is enabled, the match is performed without regard to the case
of alphabetic characters.
.PP
Finally, any prefix and suffix specified with the \fB\-P\fP and \fB\-S\fP
options are added to each member of the completion list, and the result is
returned to the readline completion code as the list of possible
completions.
.PP
If the previously-applied actions do not generate any matches, and the
\fB\-o dirnames\fP option was supplied to \fBcomplete\fP when the
compspec was defined, directory name completion is attempted.
.PP
If the \fB\-o plusdirs\fP option was supplied to \fBcomplete\fP when the
compspec was defined, directory name completion is attempted and any
matches are added to the results of the other actions.
.PP
By default, if a compspec is found, whatever it generates is returned
to the completion code as the full set of possible completions.
The default \fBbash\fP completions are not attempted, and the readline
default of filename completion is disabled.
If the \fB\-o bashdefault\fP option was supplied to \fBcomplete\fP when
the compspec was defined, the \fBbash\fP default completions are attempted
if the compspec generates no matches.
If the \fB\-o default\fP option was supplied to \fBcomplete\fP when the
compspec was defined, readline's default completion will be performed
if the compspec (and, if attempted, the default \fBbash\fP completions)
generate no matches.
.PP
When a compspec indicates that directory name completion is desired,
the programmable completion functions force readline to append a slash
to completed names which are symbolic links to directories, subject to
the value of the \fBmark\-directories\fP readline variable, regardless
of the setting of the \fBmark-symlinked\-directories\fP readline variable.
.PP
There is some support for dynamically modifying completions.  This is
most useful when used in combination with a default completion specified
with \fBcomplete \-D\fP.
It's possible for shell functions executed as completion
handlers to indicate that completion should be retried by returning an
exit status of 124.  If a shell function returns 124, and changes
the compspec associated with the command on which completion is being
attempted (supplied as the first argument when the function is executed),
programmable completion restarts from the beginning, with an
attempt to find a new compspec for that command.  This allows a set of
completions to be built dynamically as completion is attempted, rather than
being loaded all at once.
.PP
For instance, assuming that there is a library of compspecs, each kept in a
file corresponding to the name of the command, the following default
completion function would load completions dynamically:
.PP
\f(CW_completion_loader()
.br
{
.br
	. "/etc/bash_completion.d/$1.sh" >/dev/null 2>&1 && return 124
.br
}
.br
complete -D -F _completion_loader -o bashdefault -o default
.br
\fP
.SH HISTORY
When the
.B \-o history
option to the
.B set
builtin is enabled, the shell provides access to the
\fIcommand history\fP,
the list of commands previously typed.
The value of the
.SM
.B HISTSIZE
variable is used as the
number of commands to save in a history list.
The text of the last
.SM
.B HISTSIZE
commands (default 500) is saved.  The shell
stores each command in the history list prior to parameter and
variable expansion (see
.SM
.B EXPANSION
above) but after history expansion is performed, subject to the
values of the shell variables
.SM
.B HISTIGNORE
and
.SM
.BR HISTCONTROL .
.PP
On startup, the history is initialized from the file named by
the variable
.SM
.B HISTFILE
(default \fI~/.bash_history\fP).
The file named by the value of
.SM
.B HISTFILE
is truncated, if necessary, to contain no more than
the number of lines specified by the value of
.SM
.BR HISTFILESIZE .
If \fBHISTFILESIZE\fP is unset, or set to null, a non-numeric value,
or a numeric value less than zero, the history file is not truncated.
When the history file is read,
lines beginning with the history comment character followed immediately
by a digit are interpreted as timestamps for the following history line.
These timestamps are optionally displayed depending on the value of the
.SM
.B HISTTIMEFORMAT
variable.
When a shell with history enabled exits, the last
.SM
.B $HISTSIZE
lines are copied from the history list to
.SM
.BR $HISTFILE .
If the
.B histappend
shell option is enabled
(see the description of
.B shopt
under
.SM
.B "SHELL BUILTIN COMMANDS"
below), the lines are appended to the history file,
otherwise the history file is overwritten.
If
.SM
.B HISTFILE
is unset, or if the history file is unwritable, the history is
not saved.
If the
.SM
.B HISTTIMEFORMAT
variable is set, time stamps are written to the history file, marked
with the history comment character, so
they may be preserved across shell sessions.
This uses the history comment character to distinguish timestamps from
other history lines.
After saving the history, the history file is truncated
to contain no more than
.SM
.B HISTFILESIZE
lines.  If
.SM
.B HISTFILESIZE
is unset, or set to null, a non-numeric value,
or a numeric value less than zero, the history file is not truncated.
.PP
The builtin command
.B fc
(see
.SM
.B SHELL BUILTIN COMMANDS
below) may be used to list or edit and re-execute a portion of
the history list.
The
.B history
builtin may be used to display or modify the history list and
manipulate the history file.
When using command-line editing, search commands
are available in each editing mode that provide access to the
history list.
.PP
The shell allows control over which commands are saved on the history
list.  The
.SM
.B HISTCONTROL
and
.SM
.B HISTIGNORE
variables may be set to cause the shell to save only a subset of the
commands entered.
The
.B cmdhist
shell option, if enabled, causes the shell to attempt to save each
line of a multi-line command in the same history entry, adding
semicolons where necessary to preserve syntactic correctness.
The
.B lithist
shell option causes the shell to save the command with embedded newlines
instead of semicolons.  See the description of the
.B shopt
builtin below under
.SM
.B "SHELL BUILTIN COMMANDS"
for information on setting and unsetting shell options.
.SH "HISTORY EXPANSION"
.PP
The shell supports a history expansion feature that
is similar to the history expansion in
.BR csh .
This section describes what syntax features are available.  This
feature is enabled by default for interactive shells, and can be
disabled using the
.B +H
option to the
.B set
builtin command (see
.SM
.B SHELL BUILTIN COMMANDS
below).  Non-interactive shells do not perform history expansion
by default.
.PP
History expansions introduce words from the history list into
the input stream, making it easy to repeat commands, insert the
arguments to a previous command into the current input line, or
fix errors in previous commands quickly.
.PP
History expansion is performed immediately after a complete line
is read, before the shell breaks it into words, and is performed
on each line individually without taking quoting on previous lines into
account.
It takes place in two parts.
The first is to determine which line from the history list
to use during substitution.
The second is to select portions of that line for inclusion into
the current one.
The line selected from the history is the \fIevent\fP,
and the portions of that line that are acted upon are \fIwords\fP.
Various \fImodifiers\fP are available to manipulate the selected words.
The line is broken into words in the same fashion as when reading input,
so that several \fImetacharacter\fP-separated words surrounded by
quotes are considered one word.
History expansions are introduced by the appearance of the
history expansion character, which is \^\fB!\fP\^ by default.
Only backslash (\^\fB\e\fP\^) and single quotes can quote
the history expansion character, but the history expansion character is
also treated as quoted if it immediately precedes the closing double quote
in a double-quoted string.
.PP
Several characters inhibit history expansion if found immediately
following the history expansion character, even if it is unquoted:
space, tab, newline, carriage return, and \fB=\fP.
If the \fBextglob\fP shell option is enabled, \fB(\fP will also
inhibit expansion.
.PP
Several shell options settable with the
.B shopt
builtin may be used to tailor the behavior of history expansion.
If the
.B histverify
shell option is enabled (see the description of the
.B shopt
builtin below), and
.B readline
is being used, history substitutions are not immediately passed to
the shell parser.
Instead, the expanded line is reloaded into the
.B readline
editing buffer for further modification.
If
.B readline
is being used, and the
.B histreedit
shell option is enabled, a failed history substitution will be reloaded
into the
.B readline
editing buffer for correction.
The
.B \-p
option to the
.B history
builtin command may be used to see what a history expansion will
do before using it.
The
.B \-s
option to the
.B history
builtin may be used to add commands to the end of the history list
without actually executing them, so that they are available for
subsequent recall.
.PP
The shell allows control of the various characters used by the
history expansion mechanism (see the description of
.B histchars
above under
.BR "Shell Variables" ).
The shell uses
the history comment character to mark history timestamps when
writing the history file.
.SS Event Designators
.PP
An event designator is a reference to a command line entry in the
history list.
Unless the reference is absolute, events are relative to the current
position in the history list.
.PP
.PD 0
.TP
.B !
Start a history substitution, except when followed by a
.BR blank ,
newline, carriage return, =
or ( (when the \fBextglob\fP shell option is enabled using
the \fBshopt\fP builtin).
.TP
.B !\fIn\fR
Refer to command line
.IR n .
.TP
.B !\-\fIn\fR
Refer to the current command minus
.IR n .
.TP
.B !!
Refer to the previous command.  This is a synonym for `!\-1'.
.TP
.B !\fIstring\fR
Refer to the most recent command preceding the current position in the
history list starting with
.IR string .
.TP
.B !?\fIstring\fR\fB[?]\fR
Refer to the most recent command preceding the current position in the
history list containing
.IR string .
The trailing \fB?\fP may be omitted if
.I string
is followed immediately by a newline.
.TP
.B \d\s+2^\s-2\u\fIstring1\fP\d\s+2^\s-2\u\fIstring2\fP\d\s+2^\s-2\u
Quick substitution.  Repeat the previous command, replacing
.I string1
with
.IR string2 .
Equivalent to
``!!:s/\fIstring1\fP/\fIstring2\fP/''
(see \fBModifiers\fP below).
.TP
.B !#
The entire command line typed so far.
.PD
.SS Word Designators
.PP
Word designators are used to select desired words from the event.
A
.B :
separates the event specification from the word designator.
It may be omitted if the word designator begins with a
.BR ^ ,
.BR $ ,
.BR * ,
.BR \- ,
or
.BR % .
Words are numbered from the beginning of the line,
with the first word being denoted by 0 (zero).
Words are inserted into the current line separated by single spaces.
.PP
.PD 0
.TP
.B 0 (zero)
The zeroth word.  For the shell, this is the command
word.
.TP
.I n
The \fIn\fRth word.
.TP
.B ^
The first argument.  That is, word 1.
.TP
.B $
The last word.  This is usually the last argument, but will expand to the
zeroth word if there is only one word in the line.
.TP
.B %
The word matched by the most recent `?\fIstring\fR?' search.
.TP
.I x\fB\-\fPy
A range of words; `\-\fIy\fR' abbreviates `0\-\fIy\fR'.
.TP
.B *
All of the words but the zeroth.  This is a synonym
for `\fI1\-$\fP'.  It is not an error to use
.B *
if there is just one
word in the event; the empty string is returned in that case.
.TP
.B x*
Abbreviates \fIx\-$\fP.
.TP
.B x\-
Abbreviates \fIx\-$\fP like \fBx*\fP, but omits the last word.
.PD
.PP
If a word designator is supplied without an event specification, the
previous command is used as the event.
.SS Modifiers
.PP
After the optional word designator, there may appear a sequence of
one or more of the following modifiers, each preceded by a `:'.
.PP
.PD 0
.PP
.TP
.B h
Remove a trailing filename component, leaving only the head.
.TP
.B t
Remove all leading filename components, leaving the tail.
.TP
.B r
Remove a trailing suffix of the form \fI.xxx\fP, leaving the
basename.
.TP
.B e
Remove all but the trailing suffix.
.TP
.B p
Print the new command but do not execute it.
.TP
.B q
Quote the substituted words, escaping further substitutions.
.TP
.B x
Quote the substituted words as with
.BR q ,
but break into words at
.B blanks
and newlines.
.TP
.B s/\fIold\fP/\fInew\fP/
Substitute
.I new
for the first occurrence of
.I old
in the event line.  Any delimiter can be used in place of /.  The
final delimiter is optional if it is the last character of the
event line.  The delimiter may be quoted in
.I old
and
.I new
with a single backslash.  If & appears in
.IR new ,
it is replaced by
.IR old .
A single backslash will quote the &.  If
.I old
is null, it is set to the last
.I old
substituted, or, if no previous history substitutions took place,
the last
.I string
in a
.B !?\fIstring\fR\fB[?]\fR
search.
.TP
.B &
Repeat the previous substitution.
.TP
.B g
Cause changes to be applied over the entire event line.  This is
used in conjunction with `\fB:s\fP' (e.g., `\fB:gs/\fIold\fP/\fInew\fP/\fR')
or `\fB:&\fP'.  If used with
`\fB:s\fP', any delimiter can be used
in place of /, and the final delimiter is optional
if it is the last character of the event line.
An \fBa\fP may be used as a synonym for \fBg\fP.
.TP
.B G
Apply the following `\fBs\fP' modifier once to each word in the event line.
.PD
.SH "SHELL BUILTIN COMMANDS"
.\" start of bash_builtins
.zZ
.PP
Unless otherwise noted, each builtin command documented in this
section as accepting options preceded by
.B \-
accepts
.B \-\-
to signify the end of the options.
The \fB:\fP, \fBtrue\fP, \fBfalse\fP, and \fBtest\fP/\fB[\fP builtins
do not accept options and do not treat \fB\-\-\fP specially.
The \fBexit\fP, \fBlogout\fP, \fBreturn\fP,
\fBbreak\fP, \fBcontinue\fP, \fBlet\fP,
and \fBshift\fP builtins accept and process arguments beginning with
\fB\-\fP without requiring \fB\-\-\fP.
Other builtins that accept arguments but are not specified as accepting
options interpret arguments beginning with \fB\-\fP as invalid options and
require \fB\-\-\fP to prevent this interpretation.
.sp .5
.PD 0
.TP
\fB:\fP [\fIarguments\fP]
.PD
No effect; the command does nothing beyond expanding
.I arguments
and performing any specified
redirections.
The return status is zero.
.TP
\fB .\| \fP \fIfilename\fP [\fIarguments\fP]
.PD 0
.TP
\fBsource\fP \fIfilename\fP [\fIarguments\fP]
.PD
Read and execute commands from
.I filename
in the current
shell environment and return the exit status of the last command
executed from
.IR filename .
If
.I filename
does not contain a slash, filenames in
.SM
.B PATH
are used to find the directory containing
.IR filename .
The file searched for in
.SM
.B PATH
need not be executable.
When \fBbash\fP is not in \fIposix mode\fP, the current directory is
searched if no file is found in
.SM
.BR PATH .
If the
.B sourcepath
option to the
.B shopt
builtin command is turned off, the
.SM
.B PATH
is not searched.
If any \fIarguments\fP are supplied, they become the positional
parameters when \fIfilename\fP is executed.  Otherwise the positional
parameters are unchanged.
If the \fB\-T\fP option is enabled, \fBsource\fP inherits any trap on
\fBDEBUG\fP; if it is not, any \fBDEBUG\fP trap string is saved and
restored around the call to \fBsource\fP, and \fBsource\fP unsets the
\fBDEBUG\fP trap while it executes.
If \fB\-T\fP is not set, and the sourced file changes
the \fBDEBUG\fP trap, the new value is retained when \fBsource\fP completes.
The return status is the status of the last command exited within
the script (0 if no commands are executed), and false if
.I filename
is not found or cannot be read.
.TP
\fBalias\fP [\fB\-p\fP] [\fIname\fP[=\fIvalue\fP] ...]
\fBAlias\fP with no arguments or with the
.B \-p
option prints the list of aliases in the form
\fBalias\fP \fIname\fP=\fIvalue\fP on standard output.
When arguments are supplied, an alias is defined for
each \fIname\fP whose \fIvalue\fP is given.
A trailing space in \fIvalue\fP causes the next word to be
checked for alias substitution when the alias is expanded.
For each \fIname\fP in the argument list for which no \fIvalue\fP
is supplied, the name and value of the alias is printed.
\fBAlias\fP returns true unless a \fIname\fP is given for which
no alias has been defined.
.TP
\fBbg\fP [\fIjobspec\fP ...]
Resume each suspended job \fIjobspec\fP in the background, as if it
had been started with
.BR & .
If
.I jobspec
is not present, the shell's notion of the \fIcurrent job\fP is used.
.B bg
.I jobspec
returns 0 unless run when job control is disabled or, when run with
job control enabled, any specified \fIjobspec\fP was not found
or was started without job control.
.TP
\fBbind\fP [\fB\-m\fP \fIkeymap\fP] [\fB\-lpsvPSVX\fP]
.PD 0
.TP
\fBbind\fP [\fB\-m\fP \fIkeymap\fP] [\fB\-q\fP \fIfunction\fP] [\fB\-u\fP \fIfunction\fP] [\fB\-r\fP \fIkeyseq\fP]
.TP
\fBbind\fP [\fB\-m\fP \fIkeymap\fP] \fB\-f\fP \fIfilename\fP
.TP
\fBbind\fP [\fB\-m\fP \fIkeymap\fP] \fB\-x\fP \fIkeyseq\fP:\fIshell\-command\fP
.TP
\fBbind\fP [\fB\-m\fP \fIkeymap\fP] \fIkeyseq\fP:\fIfunction\-name\fP
.TP
\fBbind\fP [\fB\-m\fP \fIkeymap\fP] \fIkeyseq\fP:\fIreadline\-command\fP
.PD
Display current
.B readline
key and function bindings, bind a key sequence to a
.B readline
function or macro, or set a
.B readline
variable.
Each non-option argument is a command as it would appear in
.IR .inputrc ,
but each binding or command must be passed as a separate argument;
e.g., '"\eC\-x\eC\-r": re\-read\-init\-file'.
Options, if supplied, have the following meanings:
.RS
.PD 0
.TP
.B \-m \fIkeymap\fP
Use
.I keymap
as the keymap to be affected by the subsequent bindings.
Acceptable
.I keymap
names are
\fIemacs, emacs\-standard, emacs\-meta, emacs\-ctlx, vi,
vi\-move, vi\-command\fP, and
.IR vi\-insert .
\fIvi\fP is equivalent to \fIvi\-command\fP (\fIvi\-move\fP is also
a synonym); \fIemacs\fP is
equivalent to \fIemacs\-standard\fP.
.TP
.B \-l
List the names of all \fBreadline\fP functions.
.TP
.B \-p
Display \fBreadline\fP function names and bindings in such a way
that they can be re-read.
.TP
.B \-P
List current \fBreadline\fP function names and bindings.
.TP
.B \-s
Display \fBreadline\fP key sequences bound to macros and the strings
they output in such a way that they can be re-read.
.TP
.B \-S
Display \fBreadline\fP key sequences bound to macros and the strings
they output.
.TP
.B \-v
Display \fBreadline\fP variable names and values in such a way that they
can be re-read.
.TP
.B \-V
List current \fBreadline\fP variable names and values.
.TP
.B \-f \fIfilename\fP
Read key bindings from \fIfilename\fP.
.TP
.B \-q \fIfunction\fP
Query about which keys invoke the named \fIfunction\fP.
.TP
.B \-u \fIfunction\fP
Unbind all keys bound to the named \fIfunction\fP.
.TP
.B \-r \fIkeyseq\fP
Remove any current binding for \fIkeyseq\fP.
.TP
.B \-x \fIkeyseq\fP:\fIshell\-command\fP
Cause \fIshell\-command\fP to be executed whenever \fIkeyseq\fP is
entered.
When \fIshell\-command\fP is executed, the shell sets the
.SM
.B READLINE_LINE
variable to the contents of the \fBreadline\fP line buffer and the
.SM
.B READLINE_POINT
variable to the current location of the insertion point.
If the executed command changes the value of
.SM
.B READLINE_LINE
or
.SM
.BR READLINE_POINT ,
those new values will be reflected in the editing state.
.TP
.B \-X
List all key sequences bound to shell commands and the associated commands
in a format that can be reused as input.
.PD
.PP
The return value is 0 unless an unrecognized option is given or an
error occurred.
.RE
.TP
\fBbreak\fP [\fIn\fP]
Exit from within a
.BR for ,
.BR while ,
.BR until ,
or
.B select
loop.  If \fIn\fP is specified, break \fIn\fP levels.
.I n
must be \(>= 1.  If
.I n
is greater than the number of enclosing loops, all enclosing loops
are exited.
The return value is 0 unless \fIn\fP is not greater than or equal to 1.
.TP
\fBbuiltin\fP \fIshell\-builtin\fP [\fIarguments\fP]
Execute the specified shell builtin, passing it
.IR arguments ,
and return its exit status.
This is useful when defining a
function whose name is the same as a shell builtin,
retaining the functionality of the builtin within the function.
The \fBcd\fP builtin is commonly redefined this way.
The return status is false if
.I shell\-builtin
is not a shell builtin command.
.TP
\fBcaller\fP [\fIexpr\fP]
Returns the context of any active subroutine call (a shell function or
a script executed with the \fB.\fP or \fBsource\fP builtins).
Without \fIexpr\fP, \fBcaller\fP displays the line number and source
filename of the current subroutine call.
If a non-negative integer is supplied as \fIexpr\fP, \fBcaller\fP
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 \fIexpr\fP does not correspond to a valid position in the
call stack.
.TP
\fBcd\fP [\fB\-L\fP|[\fB\-P\fP [\fB\-e\fP]] [\-@]] [\fIdir\fP]
Change the current directory to \fIdir\fP.
if \fIdir\fP is not supplied, the value of the
.SM
.B HOME
shell variable is the default.
Any additional arguments following \fIdir\fP are ignored.
The variable
.SM
.B CDPATH
defines the search path for the directory containing
.IR dir :
each directory name in
.SM
.B CDPATH
is searched for \fIdir\fP.
Alternative directory names in
.SM
.B CDPATH
are separated by a colon (:).  A null directory name in
.SM
.B CDPATH
is the same as the current directory, i.e., ``\fB.\fP''.  If
.I dir
begins with a slash (/),
then
.SM
.B CDPATH
is not used.  The
.B \-P
option causes \fBcd\fP to use the physical directory structure
by resolving symbolic links while traversing \fIdir\fP and
before processing instances of \fI..\fP in \fIdir\fP (see also the
.B \-P
option to the
.B set
builtin command); the
.B \-L
option forces symbolic links to be followed by resolving the link
after processing instances of \fI..\fP in \fIdir\fP.
If \fI..\fP appears in \fIdir\fP, it is processed by removing the
immediately previous pathname component from \fIdir\fP, back to a slash
or the beginning of \fIdir\fP.
If the
.B \-e
option is supplied with
.BR \-P ,
and the current working directory cannot be successfully determined
after a successful directory change, \fBcd\fP will return an unsuccessful
status.
On systems that support it, the \fB\-@\fP option presents the extended
attributes associated with a file as a directory.
An argument of
.B \-
is converted to
.SM
.B $OLDPWD
before the directory change is attempted.
If a non-empty directory name from
.SM
.B CDPATH
is used, or if
\fB\-\fP 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 value is true if the directory was successfully changed;
false otherwise.
.TP
\fBcommand\fP [\fB\-pVv\fP] \fIcommand\fP [\fIarg\fP ...]
Run
.I command
with
.I args
suppressing the normal shell function lookup.
Only builtin commands or commands found in the
.SM
.B PATH
are executed.  If the
.B \-p
option is given, the search for
.I command
is performed using a default value for
.SM
.B PATH
that is guaranteed to find all of the standard utilities.
If either the
.B \-V
or
.B \-v
option is supplied, a description of
.I command
is printed.  The
.B \-v