.lf 1 ./builtins.1
.\" This is a hack to force bash builtins into the whatis database
.\" and to get the list of builtins to come up with the man command.
.\"
.\" 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
..
.TH BASH_BUILTINS 1 "2021 November 22" "GNU Bash 5.2"
.SH NAME
:, ., [, alias, bg, bind, break, builtin, caller,
cd, command, compgen, complete, compopt,
continue, declare, dirs, disown, echo, enable, eval, exec, exit,
export, false, fc, fg, getopts, hash, help, history, jobs, kill,
let, local, logout, mapfile, popd, printf, pushd, pwd, read,
readarray, readonly, return, set,
shift, shopt, source, suspend, test, times, trap, true, type, typeset,
ulimit, umask, unalias, unset, wait \- bash built-in commands, see \fBbash\fR(1)
.SH BASH BUILTIN COMMANDS
.nr zZ 1
.lf 1 ./bash.1
.\"
.\" MAN PAGE COMMENTS to
.\"
.\"	Chet Ramey
.\"	Case Western Reserve University
.\"	chet.ramey@case.edu
.\"
.\"	Last Change: Mon Sep 19 11:13:21 EDT 2022
.\"
.\" bash_builtins, strip all but Built-Ins section
.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 ,
but \fIfilename\fP does not need to be executable.
The file searched for in
.SM
.B PATH
need not be executable.
When \fBbash\fP is not in \fIposix mode\fP, it searches
the current directory 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, \fB.\fP inherits any trap on
\fBDEBUG\fP; if it is not, any \fBDEBUG\fP trap string is saved and
restored around the call to \fB.\fP, and \fB.\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 \fB.\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
.TP
\fBbind\fP \fIreadline-command-line\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 a
.B readline
initialization file such as
.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
and
.SM
.B READLINE_MARK
variables to the current location of the insertion point and the saved
insertion point (the mark), respectively.
The shell assigns any numeric argument the user supplied to the     
.SM
.B READLINE_ARGUMENT
variable.
If there was no argument, that variable is not set.
If the executed command changes the value of any of
.SM
.BR READLINE_LINE ,
.SM
.BR READLINE_POINT ,
or
.SM
.BR READLINE_MARK ,
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.
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.
If the directory change is successful, \fBcd\fP sets the value of the
\fBPWD\fP environment variable to the new directory name, and sets the
\fBOLDPWD\fP environment variable to the value of the current working
directory before the change.
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
option causes a single word indicating the command or filename
used to invoke
.I command
to be displayed; the
.B \-V
option produces a more verbose description.
If the
.B \-V
or
.B \-v
option is supplied, the exit status is 0 if
.I command
was found, and 1 if not.  If neither option is supplied and
an error occurred or
.I command
cannot be found, the exit status is 127.  Otherwise, the exit status of the
.B command
builtin is the exit status of
.IR command .
.TP
\fBcompgen\fP [\fIoption\fP] [\fIword\fP]
Generate possible completion matches for \fIword\fP according to
the \fIoption\fPs, which may be any option accepted by the
.B complete
builtin with the exception of \fB\-p\fP and \fB\-r\fP, and write
the matches to the standard output.
When using the \fB\-F\fP or \fB\-C\fP options, the various shell variables
set by the programmable completion facilities, while available, will not
have useful values.
.sp 1
The matches will be generated in the same way as if the programmable
completion code had generated them directly from a completion specification
with the same flags.
If \fIword\fP is specified, only those completions matching \fIword\fP
will be displayed.
.sp 1
The return value is true unless an invalid option is supplied, or no
matches were generated.
.TP
\fBcomplete\fP [\fB\-abcdefgjksuv\fP] [\fB\-o\fP \fIcomp-option\fP] [\fB\-DEI\fP] [\fB\-A\fP \fIaction\fP] [\fB\-G\fP \fIglobpat\fP] [\fB\-W\fP \fIwordlist\fP]
.br
[\fB\-F\fP \fIfunction\fP] [\fB\-C\fP \fIcommand\fP] [\fB\-X\fP \fIfilterpat\fP] [\fB\-P\fP \fIprefix\fP] [\fB\-S\fP \fIsuffix\fP] \fIname\fP [\fIname ...\fP]
.PD 0
.TP
\fBcomplete\fP \fB\-pr\fP [\fB\-DEI\fP] [\fIname\fP ...]
.PD
Specify how arguments to each \fIname\fP should be completed.
If the \fB\-p\fP option is supplied, or if no options are supplied,
existing completion specifications are printed in a way that allows
them to be reused as input.
The \fB\-r\fP option removes a completion specification for
each \fIname\fP, or, if no \fIname\fPs are supplied, all
completion specifications.
The \fB\-D\fP option indicates that other supplied options and actions should
apply to the ``default'' command completion; that is, completion attempted
on a command for which no completion has previously been defined.
The \fB\-E\fP option indicates that other supplied options and actions should
apply to ``empty'' command completion; that is, completion attempted on a
blank line.
The \fB\-I\fP option indicates that other supplied options and actions should
apply to completion on the initial non-assignment word on the line, or after
a command delimiter such as \fB;\fP or \fB|\fP, which is usually command
name completion.
If multiple options are supplied, the \fB\-D\fP option takes precedence
over \fB\-E\fP, and both take precedence over \fB\-I\fP.
If any of \fB\-D\fP, \fB\-E\fP, or \fB\-I\fP are supplied, any other
\fIname\fP arguments are ignored; these completions only apply to the case
specified by the option.
.sp 1
The process of applying these completion specifications when word completion
is attempted is described
.ie \n(zZ=1 in \fIbash(1)\fP.
.el above under \fBProgrammable Completion\fP.
.sp 1
Other options, if specified, have the following meanings.
The arguments to the \fB\-G\fP, \fB\-W\fP, and \fB\-X\fP options
(and, if necessary, the \fB\-P\fP and \fB\-S\fP options)
should be quoted to protect them from expansion before the
.B complete
builtin is invoked.
.RS
.PD 0
.TP 8
\fB\-o\fP \fIcomp-option\fP
The \fIcomp-option\fP controls several aspects of the compspec's behavior
beyond the simple generation of completions.
\fIcomp-option\fP may be one of:
.RS
.TP 8
.B bashdefault
Perform the rest of the default \fBbash\fP completions if the compspec
generates no matches.
.TP 8
.B default
Use readline's default filename completion if the compspec generates
no matches.
.TP 8
.B dirnames
Perform directory name completion if the compspec generates no matches.
.TP 8
.B filenames
Tell readline that the compspec generates filenames, so it can perform any
filename\-specific processing (like adding a slash to directory names,
quoting special characters, or suppressing trailing spaces).
Intended to be used with shell functions.
.TP 8
.B noquote
Tell readline not to quote the completed words if they are filenames
(quoting filenames is the default).
.TP 8
.B nosort
Tell readline not to sort the list of possible completions alphabetically.
.TP 8
.B nospace
Tell readline not to append a space (the default) to words completed at
the end of the line.
.TP 8
.B plusdirs
After any matches defined by the compspec are generated,
directory name completion is attempted and any
matches are added to the results of the other actions.
.RE
.TP 8
\fB\-A\fP \fIaction\fP
The \fIaction\fP may be one of the following to generate a list of possible
completions:
.RS
.TP 8
.B alias
Alias names.  May also be specified as \fB\-a\fP.
.TP 8
.B arrayvar
Array variable names.
.TP 8
.B binding
\fBReadline\fP key binding names.
.TP 8
.B builtin
Names of shell builtin commands.  May also be specified as \fB\-b\fP.
.TP 8
.B command
Command names.  May also be specified as \fB\-c\fP.
.TP 8
.B directory
Directory names.  May also be specified as \fB\-d\fP.
.TP 8
.B disabled
Names of disabled shell builtins.
.TP 8
.B enabled
Names of enabled shell builtins.
.TP 8
.B export
Names of exported shell variables.  May also be specified as \fB\-e\fP.
.TP 8
.B file
File names.  May also be specified as \fB\-f\fP.
.TP 8
.B function
Names of shell functions.
.TP 8
.B group
Group names.  May also be specified as \fB\-g\fP.
.TP 8
.B helptopic
Help topics as accepted by the \fBhelp\fP builtin.
.TP 8
.B hostname
Hostnames, as taken from the file specified by the
.SM
.B HOSTFILE
shell variable.
.TP 8
.B job
Job names, if job control is active.  May also be specified as \fB\-j\fP.
.TP 8
.B keyword
Shell reserved words.  May also be specified as \fB\-k\fP.
.TP 8
.B running
Names of running jobs, if job control is active.
.TP 8
.B service
Service names.  May also be specified as \fB\-s\fP.
.TP 8
.B setopt
Valid arguments for the \fB\-o\fP option to the \fBset\fP builtin.
.TP 8
.B shopt
Shell option names as accepted by the \fBshopt\fP builtin.
.TP 8
.B signal
Signal names.
.TP 8
.B stopped
Names of stopped jobs, if job control is active.
.TP 8
.B user
User names.  May also be specified as \fB\-u\fP.
.TP 8
.B variable
Names of all shell variables.  May also be specified as \fB\-v\fP.
.RE
.TP 8
\fB\-C\fP \fIcommand\fP
\fIcommand\fP is executed in a subshell environment, and its output is
used as the possible completions.
Arguments are passed as with the \fB\-F\fP option.
.TP 8
\fB\-F\fP \fIfunction\fP
The shell function \fIfunction\fP is executed in the current shell
environment.
When the function is executed,
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.
When it finishes, the possible completions are retrieved from the value
of the
.SM
.B COMPREPLY
array variable.
.TP 8
\fB\-G\fP \fIglobpat\fP
The pathname expansion pattern \fIglobpat\fP is expanded to generate
the possible completions.
.TP 8
\fB\-P\fP \fIprefix\fP
\fIprefix\fP is added at the beginning of each possible completion
after all other options have been applied.
.TP 8
\fB\-S\fP \fIsuffix\fP
\fIsuffix\fP is appended to each possible completion
after all other options have been applied.
.TP 8
\fB\-W\fP \fIwordlist\fP
The \fIwordlist\fP is split using the characters in the
.SM
.B IFS
special variable as delimiters, and each resultant word is expanded.
Shell quoting is honored within \fIwordlist\fP,
in order to provide a
mechanism for the words to contain shell metacharacters or characters
in the value of
.SM
.BR IFS .
The possible completions are the members of the resultant list which
match the word being completed.
.TP 8
\fB\-X\fP \fIfilterpat\fP
\fIfilterpat\fP is a pattern as used for pathname expansion.
It is applied to the list of possible completions generated by the
preceding options and arguments, and each completion matching
\fIfilterpat\fP is removed from the list.
A leading \fB!\fP in \fIfilterpat\fP negates the pattern; in this
case, any completion not matching \fIfilterpat\fP is removed.
.PD
.PP
The return value is true unless an invalid option is supplied, an option
other than \fB\-p\fP or \fB\-r\fP is supplied without a \fIname\fP
argument, an attempt is made to remove a completion specification for
a \fIname\fP for which no specification exists, or
an error occurs adding a completion specification.
.RE
.TP
\fBcompopt\fP [\fB\-o\fP \fIoption\fP] [\fB\-DEI\fP] [\fB+o\fP \fIoption\fP] [\fIname\fP]
Modify completion options for each \fIname\fP according to the
\fIoption\fPs, or for the
currently-executing completion if no \fIname\fPs are supplied.
If no \fIoption\fPs are given, display the completion options for each
\fIname\fP or the current completion.
The possible values of \fIoption\fP are those valid for the \fBcomplete\fP
builtin described above.
The \fB\-D\fP option indicates that other supplied options should
apply to the ``default'' command completion; that is, completion attempted
on a command for which no completion has previously been defined.
The \fB\-E\fP option indicates that other supplied options should
apply to ``empty'' command completion; that is, completion attempted on a
blank line.
The \fB\-I\fP option indicates that other supplied options should
apply to completion on the initial non-assignment word on the line,
or after a command delimiter such as \fB;\fP or \fB|\fP, which is usually
command name completion.
.sp 1
The return value is true unless an invalid option is supplied, an attempt
is made to modify the options for a \fIname\fP for which no completion
specification exists, or an output error occurs.
.TP
\fBcontinue\fP [\fIn\fP]
Resume the next iteration of the enclosing
.BR for ,
.BR while ,
.BR until ,
or
.B select
loop.
If
.I n
is specified, resume at the \fIn\fPth enclosing loop.
.I n
must be \(>= 1.  If
.I n
is greater than the number of enclosing loops, the last enclosing loop
(the ``top-level'' loop) is resumed.
The return value is 0 unless \fIn\fP is not greater than or equal to 1.
.TP
\fBdeclare\fP [\fB\-aAfFgiIlnrtux\fP] [\fB\-p\fP] [\fIname\fP[=\fIvalue\fP] ...]
.PD 0
.TP
\fBtypeset\fP [\fB\-aAfFgiIlnrtux\fP] [\fB\-p\fP] [\fIname\fP[=\fIvalue\fP] ...]
.PD
Declare variables and/or give them attributes.
If no \fIname\fPs are given then display the values of variables.
The
.B \-p
option will display the attributes and values of each
.IR name .
When
.B \-p
is used with \fIname\fP arguments, additional options,
other than \fB\-f\fP and \fB\-F\fP, are ignored.
When
.B \-p
is supplied without \fIname\fP arguments, it will display the attributes
and values of all variables having the attributes specified by the
additional options.
If no other options are supplied with \fB\-p\fP, \fBdeclare\fP will display
the attributes and values of all shell variables.  The \fB\-f\fP option
will restrict the display to shell functions.
The
.B \-F
option inhibits the display of function definitions; only the
function name and attributes are printed.
If the \fBextdebug\fP shell option is enabled using \fBshopt\fP,
the source file name and line number where each \fIname\fP
is defined are displayed as well.  The
.B \-F
option implies
.BR \-f .
The
.B \-g
option forces variables to be created or modified at the global scope,
even when \fBdeclare\fP is executed in a shell function.
It is ignored in all other cases.
The
.B \-I
option causes local variables to inherit the attributes
(except the \fInameref\fP attribute) 
and value of any existing variable with the same
\fIname\fP at a surrounding scope.
If there is no existing variable, the local variable is initially unset.
The following options can
be used to restrict output to variables with the specified attribute or
to give variables attributes:
.RS
.PD 0
.TP
.B \-a
Each \fIname\fP is an indexed array variable (see
.B Arrays
.ie \n(zZ=1 in \fIbash(1)\fP).
.el above).
.TP
.B \-A
Each \fIname\fP is an associative array variable (see
.B Arrays
.ie \n(zZ=1 in \fIbash(1)\fP).
.el above).
.TP
.B \-f
Use function names only.
.TP
.B \-i
The variable is treated as an integer; arithmetic evaluation (see
.SM
.B "ARITHMETIC EVALUATION"
.ie \n(zZ=1 in \fIbash(1)\fP)
.el above)
is performed when the variable is assigned a value.
.TP
.B \-l
When the variable is assigned a value, all upper-case characters are
converted to lower-case.
The upper-case attribute is disabled.
.TP
.B \-n
Give each \fIname\fP the \fInameref\fP attribute, making
it a name reference to another variable.
That other variable is defined by the value of \fIname\fP.
All references, assignments, and attribute modifications
to \fIname\fP, except those using or changing the
\fB\-n\fP attribute itself, are performed on the variable referenced by
\fIname\fP's value.
The nameref attribute cannot be applied to array variables.
.TP
.B \-r
Make \fIname\fPs readonly.  These names cannot then be assigned values
by subsequent assignment statements or unset.
.TP
.B \-t
Give each \fIname\fP the \fItrace\fP attribute.
Traced functions inherit the \fBDEBUG\fP and \fBRETURN\fP traps from
the calling shell.
The trace attribute has no special meaning for variables.
.TP
.B \-u
When the variable is assigned a value, all lower-case characters are
converted to upper-case.
The lower-case attribute is disabled.
.TP
.B \-x
Mark \fIname\fPs for export to subsequent commands via the environment.
.PD
.PP
Using `+' instead of `\-'
turns off the attribute instead,
with the exceptions that \fB+a\fP and \fB+A\fP
may not be used to destroy array variables and \fB+r\fP will not
remove the readonly attribute.
When used in a function,
.B declare
and
.B typeset
make each
\fIname\fP local, as with the
.B local
command,
unless the \fB\-g\fP option is supplied.
If a variable name is followed by =\fIvalue\fP, the value of
the variable is set to \fIvalue\fP.
When using \fB\-a\fP or \fB\-A\fP and the compound assignment syntax to
create array variables, additional attributes do not take effect until
subsequent assignments.
The return value is 0 unless an invalid option is encountered,
an attempt is made to define a function using
.if n ``\-f foo=bar'',
.if t \f(CW\-f foo=bar\fP,
an attempt is made to assign a value to a readonly variable,
an attempt is made to assign a value to an array variable without
using the compound assignment syntax (see
.B Arrays
.ie \n(zZ=1 in \fIbash(1)\fP),
.el above),
one of the \fInames\fP is not a valid shell variable name,
an attempt is made to turn off readonly status for a readonly variable,
an attempt is made to turn off array status for an array variable,
or an attempt is made to display a non-existent function with \fB\-f\fP.
.RE
.TP
.B dirs [\fB\-clpv\fP] [+\fIn\fP] [\-\fIn\fP]
Without options, displays the list of currently remembered directories.
The default display is on a single line with directory names separated
by spaces.
Directories are added to the list with the
.B pushd
command; the
.B popd
command removes entries from the list.
The current directory is always the first directory in the stack.
.RS
.PD 0
.TP
.B \-c
Clears the directory stack by deleting all of the entries.
.TP
.B \-l
Produces a listing using full pathnames;
the default listing format uses a tilde to denote the home directory.
.TP
.B \-p
Print the directory stack with one entry per line.
.TP
.B \-v
Print the directory stack with one entry per line,
prefixing each entry with its index in the stack.
.TP
\fB+\fP\fIn\fP
Displays the \fIn\fPth entry counting from the left of the list
shown by
.B dirs
when invoked without options, starting with zero.
.TP
\fB\-\fP\fIn\fP
Displays the \fIn\fPth entry counting from the right of the list
shown by
.B dirs
when invoked without options, starting with zero.
.PD
.PP
The return value is 0 unless an
invalid option is supplied or \fIn\fP indexes beyond the end
of the directory stack.
.RE
.TP
\fBdisown\fP [\fB\-ar\fP] [\fB\-h\fP] [\fIjobspec\fP ... | \fIpid\fP ... ]
Without options, remove each
.I jobspec
from the table of active jobs.
If
.I jobspec
is not present, and neither the \fB\-a\fP nor the \fB\-r\fP option
is supplied, the \fIcurrent job\fP is used.
If the \fB\-h\fP option is given, each
.I jobspec
is not removed from the table, but is marked so that
.SM
.B SIGHUP
is not sent to the job if the shell receives a
.SM
.BR SIGHUP .
If no
.I jobspec
is supplied, the
.B \-a
option means to remove or mark all jobs; the
.B \-r
option without a
.I jobspec
argument restricts operation to running jobs.
The return value is 0 unless a
.I jobspec
does not specify a valid job.
.TP
\fBecho\fP [\fB\-neE\fP] [\fIarg\fP ...]
Output the \fIarg\fPs, separated by spaces, followed by a newline.
The return status is 0 unless a write error occurs.
If \fB\-n\fP is specified, the trailing newline is
suppressed.  If the \fB\-e\fP option is given, interpretation of
the following backslash-escaped characters is enabled.  The
.B \-E
option disables the interpretation of these escape characters,
even on systems where they are interpreted by default.
The \fBxpg_echo\fP shell option may be used to
dynamically determine whether or not \fBecho\fP expands these
escape characters by default.
.B echo
does not interpret \fB\-\-\fP to mean the end of options.
.B echo
interprets the following escape sequences:
.RS
.PD 0
.TP
.B \ea
alert (bell)
.TP
.B \eb
backspace
.TP
.B \ec
suppress further output
.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 \e0\fInnn\fP
the eight-bit character whose value is the octal value \fInnn\fP
(zero 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)
.PD
.RE
.TP
\fBenable\fP [\fB\-a\fP] [\fB\-dnps\fP] [\fB\-f\fP \fIfilename\fP] [\fIname\fP ...]
Enable and disable builtin shell commands.
Disabling a builtin allows a disk command which has the same name
as a shell builtin to be executed without specifying a full pathname,
even though the shell normally searches for builtins before disk commands.
If \fB\-n\fP is used, each \fIname\fP
is disabled; otherwise,
\fInames\fP are enabled.  For example, to use the
.B test
binary found via the
.SM
.B PATH
instead of the shell builtin version, run
.if t \f(CWenable -n test\fP.
.if n ``enable -n test''.
The
.B \-f
option means to load the new builtin command
.I name
from shared object
.IR filename ,
on systems that support dynamic loading.
Bash will use the value of the \fBBASH_LOADABLES_PATH\fP variable as a
colon-separated list of directories in which to search for \fIfilename\fP.
The default is system-dependent.
The
.B \-d
option will delete a builtin previously loaded with
.BR \-f .
If no \fIname\fP arguments are given, or if the
.B \-p
option is supplied, a list of shell builtins is printed.
With no other option arguments, the list consists of all enabled
shell builtins.
If \fB\-n\fP is supplied, only disabled builtins are printed.
If \fB\-a\fP is supplied, the list printed includes all builtins, with an
indication of whether or not each is enabled.
If \fB\-s\fP is supplied, the output is restricted to the POSIX
\fIspecial\fP builtins.
If no options are supplied and a \fIname\fP is not a shell builtin,
\fBenable\fP will attempt to load \fIname\fP from a shared object named
\fIname\fP, as if the command were
.if t \f(CWenable \-f\fP \fIname name\fP .
.if n ``enable -f \fIname name\fP .
The return value is 0 unless a
.I name
is not a shell builtin or there is an error loading a new builtin
from a shared object.
.TP
\fBeval\fP [\fIarg\fP ...]
The \fIarg\fPs are read and concatenated together into a single
command.  This command is then read and executed by the shell, and
its exit status is returned as the value of
.BR eval .
If there are no
.IR args ,
or only null arguments,
.B eval
returns 0.
.TP
\fBexec\fP [\fB\-cl\fP] [\fB\-a\fP \fIname\fP] [\fIcommand\fP [\fIarguments\fP]]
If
.I command
is specified, it replaces the shell.
No new process is created.  The
.I arguments
become the arguments to \fIcommand\fP.
If the
.B \-l
option is supplied,
the shell places a dash at the beginning of the zeroth argument passed to
.IR command .
This is what
.IR login (1)
does.  The
.B \-c
option causes
.I command
to be executed with an empty environment.  If
.B \-a
is supplied, the shell passes
.I name
as the zeroth argument to the executed command.
If
.I command
cannot be executed for some reason, a non-interactive shell exits,
unless the
.B execfail
shell option
is enabled.  In that case, it returns failure.
An interactive shell returns failure if the file cannot be executed.
A subshell exits unconditionally if \fBexec\fP fails.
If
.I command
is not specified, any redirections take effect in the current shell,
and the return status is 0.  If there is a redirection error, the
return status is 1.
.TP
\fBexit\fP [\fIn\fP]
Cause the shell to exit
with a status of \fIn\fP.  If
.I n
is omitted, the exit status
is that of the last command executed.
A trap on
.SM
.B EXIT
is executed before the shell terminates.
.TP
\fBexport\fP [\fB\-fn\fP\^] [\fIname\fP[=\fIword\fP]] ...
.PD 0
.TP
.B export \-p
.PD
The supplied
.I names
are marked for automatic export to the environment of
subsequently executed commands.  If the
.B \-f
option is given, the
.I names
refer to functions.
If no
.I names
are given, or if the
.B \-p
option is supplied, a list
of names of all exported variables is printed.
The
.B \-n
option causes the export property to be removed from each
\fIname\fP.
If a variable name is followed by =\fIword\fP, the value of
the variable is set to \fIword\fP.
.B export
returns an exit status of 0 unless an invalid option is
encountered,
one of the \fInames\fP is not a valid shell variable name, or
.B \-f
is supplied with a
.I name
that is not a function.
.TP
\fBfc\fP [\fB\-e\fP \fIename\fP] [\fB\-lnr\fP] [\fIfirst\fP] [\fIlast\fP]
.PD 0
.TP
\fBfc\fP \fB\-s\fP [\fIpat\fP=\fIrep\fP] [\fIcmd\fP]
.PD
The first form selects a range of commands from
.I first
to
.I last
from the history list and displays or edits and re-executes them.
.I First
and
.I last
may be specified as a string (to locate the last command beginning
with that string) or as a number (an index into the history list,
where a negative number is used as an offset from the current
command number).
When listing, a \fIfirst\fP or \fIlast\fP of
0 is equivalent to \-1 and \-0 is equivalent to the current
command (usually the \fBfc\fP command); otherwise 0 is equivalent to \-1
and \-0 is invalid.
If
.I last
is not specified, it is set to
the current command for listing (so that
.if n ``fc \-l \-10''
.if t \f(CWfc \-l \-10\fP
prints the last 10 commands) and to
.I first
otherwise.
If
.I first
is not specified, it is set to the previous
command for editing and \-16 for listing.
.sp 1
The
.B \-n
option suppresses
the command numbers when listing.  The
.B \-r
option reverses the order of
the commands.  If the
.B \-l
option is given,
the commands are listed on
standard output.  Otherwise, the editor given by
.I ename
is invoked
on a file containing those commands.  If
.I ename
is not given, the
value of the
.SM
.B FCEDIT
variable is used, and
the value of
.SM
.B EDITOR
if
.SM
.B FCEDIT
is not set.  If neither variable is set,
.FN vi
is used.  When editing is complete, the edited commands are
echoed and executed.
.sp 1
In the second form, \fIcommand\fP is re-executed after each instance
of \fIpat\fP is replaced by \fIrep\fP.
\fICommand\fP is interpreted the same as \fIfirst\fP above.
A useful alias to use with this is
.if n ``r="fc -s"'',
.if t \f(CWr='fc \-s'\fP,
so that typing
.if n ``r cc''
.if t \f(CWr cc\fP
runs the last command beginning with
.if n ``cc''
.if t \f(CWcc\fP
and typing
.if n ``r''
.if t \f(CWr\fP
re-executes the last command.
.sp 1
If the first form is used, the return value is 0 unless an invalid
option is encountered or
.I first
or
.I last
specify history lines out of range.
If the
.B \-e
option is supplied, the return value is the value of the last
command executed or failure if an error occurs with the temporary
file of commands.  If the second form is used, the return status
is that of the command re-executed, unless
.I cmd
does not specify a valid history line, in which case
.B fc
returns failure.
.TP
\fBfg\fP [\fIjobspec\fP]
Resume
.I jobspec
in the foreground, and make it the current job.
If
.I jobspec
is not present, the shell's notion of the \fIcurrent job\fP is used.
The return value is that of the command placed into the foreground,
or failure if run when job control is disabled or, when run with
job control enabled, if
.I jobspec
does not specify a valid job or
.I jobspec
specifies a job that was started without job control.
.TP
\fBgetopts\fP \fIoptstring\fP \fIname\fP [\fIarg ...\fP]
.B getopts
is used by shell procedures to parse positional parameters.
.I optstring
contains the option characters to be recognized; if a character
is followed by a colon, the option is expected to have an
argument, which should be separated from it by white space.
The colon and question mark characters may not be used as
option characters.
Each time it is invoked,
.B getopts
places the next option in the shell variable
.IR name ,
initializing
.I name
if it does not exist,
and the index of the next argument to be processed into the
variable
.SM
.BR OPTIND .
.SM
.B OPTIND
is initialized to 1 each time the shell or a shell script
is invoked.  When an option requires an argument,
.B getopts
places that argument into the variable
.SM
.BR OPTARG .
The shell does not reset
.SM
.B OPTIND
automatically; it must be manually reset between multiple
calls to
.B getopts
within the same shell invocation if a new set of parameters
is to be used.
.sp 1
When the end of options is encountered, \fBgetopts\fP exits with a
return value greater than zero.
.SM
.B OPTIND
is set to the index of the first non-option argument,
and \fIname\fP is set to ?.
.sp 1
.B getopts
normally parses the positional parameters, but if more arguments are
supplied as
.I arg
values,
.B getopts
parses those instead.
.sp 1
.B getopts
can report errors in two ways.  If the first character of
.I optstring
is a colon,
.I silent
error reporting is used.  In normal operation, diagnostic messages
are printed when invalid options or missing option arguments are
encountered.
If the variable
.SM
.B OPTERR
is set to 0, no error messages will be displayed, even if the first
character of
.I optstring
is not a colon.
.sp 1
If an invalid option is seen,
.B getopts
places ? into
.I name
and, if not silent,
prints an error message and unsets
.SM
.BR OPTARG .
If
.B getopts
is silent,
the option character found is placed in
.SM
.B OPTARG
and no diagnostic message is printed.
.sp 1
If a required argument is not found, and
.B getopts
is not silent,
a question mark (\^\fB?\fP\^) is placed in
.IR name ,
.SM
.B OPTARG
is unset, and a diagnostic message is printed.
If
.B getopts
is silent, then a colon (\^\fB:\fP\^) is placed in
.I name
and
.SM
.B OPTARG
is set to the option character found.
.sp 1
.B getopts
returns true if an option, specified or unspecified, is found.
It returns false if the end of options is encountered or an
error occurs.
.TP
\fBhash\fP [\fB\-lr\fP] [\fB\-p\fP \fIfilename\fP] [\fB\-dt\fP] [\fIname\fP]
Each time \fBhash\fP is invoked,
the full pathname of the command
.I name
is determined by searching
the directories in
.B $PATH
and remembered.  Any previously-remembered pathname is discarded.
If the
.B \-p
option is supplied, no path search is performed, and
.I filename
is used as the full filename of the command.
The
.B \-r
option causes the shell to forget all
remembered locations.
The
.B \-d
option causes the shell to forget the remembered location of each \fIname\fP.
If the
.B \-t
option is supplied, the full pathname to which each \fIname\fP corresponds
is printed.  If multiple \fIname\fP arguments are supplied with \fB\-t\fP,
the \fIname\fP is printed before the hashed full pathname.
The
.B \-l
option causes output to be displayed in a format that may be reused as input.
If no arguments are given, or if only \fB\-l\fP is supplied,
information about remembered commands is printed.
The return status is true unless a
.I name
is not found or an invalid option is supplied.
.TP
\fBhelp\fP [\fB\-dms\fP] [\fIpattern\fP]
Display helpful information about builtin commands.  If
.I pattern
is specified,
.B help
gives detailed help on all commands matching
.IR pattern ;
otherwise help for all the builtins and shell control structures
is printed.
.RS
.PD 0
.TP
.B \-d
Display a short description of each \fIpattern\fP
.TP
.B \-m
Display the description of each \fIpattern\fP in a manpage-like format
.TP
.B \-s
Display only a short usage synopsis for each \fIpattern\fP
.PD
.PP
The return status is 0 unless no command matches
.IR pattern .
.RE
.TP
\fBhistory [\fIn\fP]
.PD 0
.TP
\fBhistory\fP \fB\-c\fP
.TP
\fBhistory \-d\fP \fIoffset\fP
.TP
\fBhistory \-d\fP \fIstart\fP\-\fIend\fP
.TP
\fBhistory\fP \fB\-anrw\fP [\fIfilename\fP]
.TP
\fBhistory\fP \fB\-p\fP \fIarg\fP [\fIarg ...\fP]
.TP
\fBhistory\fP \fB\-s\fP \fIarg\fP [\fIarg ...\fP]
.PD
With no options, display the command
history list with line numbers.  Lines listed
with a
.B *
have been modified.  An argument of
.I n
lists only the last
.I n
lines.
If the shell variable
.SM
.B HISTTIMEFORMAT
is set and not null,
it is used as a format string for \fIstrftime\fP(3) to display
the time stamp associated with each displayed history entry.
No intervening blank is printed between the formatted time stamp
and the history line.
If \fIfilename\fP is supplied, it is used as the
name of the history file; if not, the value of
.SM
.B HISTFILE
is used.  Options, if supplied, have the following meanings:
.RS
.PD 0
.TP
.B \-c
Clear the history list by deleting all the entries.
.TP
\fB\-d\fP \fIoffset\fP
Delete the history entry at position \fIoffset\fP.
If \fIoffset\fP is negative, it is interpreted as relative to one greater
than the last history position, so negative indices count back from the
end of the history, and an index of \-1 refers to the current
\fBhistory -d\fP command.
.TP
\fB\-d\fP \fIstart\fP\-\fIend\fP
Delete the range of history entries between positions \fIstart\fP and
\fIend\fP, inclusive.
Positive and negative values for \fIstart\fP and \fIend\fP
are interpreted as described above.
.TP
.B \-a
Append the ``new'' history lines to the history file.
These are history lines entered since the beginning of the current
\fBbash\fP session, but not already appended to the history file.
.TP
.B \-n
Read the history lines not already read from the history
file into the current history list.  These are lines
appended to the history file since the beginning of the
current \fBbash\fP session.
.TP
.B \-r
Read the contents of the history file
and append them to the current history list.
.TP
.B \-w
Write the current history list to the history file, overwriting the
history file's contents.
.TP
.B \-p
Perform history substitution on the following \fIargs\fP and display
the result on the standard output.
Does not store the results in the history list.
Each \fIarg\fP must be quoted to disable normal history expansion.
.TP
.B \-s
Store the
.I args
in the history list as a single entry.  The last command in the
history list is removed before the
.I args
are added.
.PD
.PP
If the
.SM
.B HISTTIMEFORMAT
variable is set, the time stamp information
associated with each history entry is written to the history file,
marked with the history comment character.
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 entry.
The return value is 0 unless an invalid option is encountered, an
error occurs while reading or writing the history file, an invalid
\fIoffset\fP or range is supplied as an argument to \fB\-d\fP, or the
history expansion supplied as an argument to \fB\-p\fP fails.
.RE
.TP
\fBjobs\fP [\fB\-lnprs\fP] [ \fIjobspec\fP ... ]
.PD 0
.TP
\fBjobs\fP \fB\-x\fP \fIcommand\fP [ \fIargs\fP ... ]
.PD
The first form lists the active jobs.  The options have the following
meanings:
.RS
.PD 0
.TP
.B \-l
List process IDs
in addition to the normal information.
.TP
.B \-n
Display information only about jobs that have changed status since
the user was last notified of their status.
.TP
.B \-p
List only the process ID of the job's process group
leader.
.TP
.B \-r
Display only running jobs.
.TP
.B \-s
Display only stopped jobs.
.PD
.PP
If
.I jobspec
is given, output is restricted to information about that job.
The return status is 0 unless an invalid option is encountered
or an invalid
.I jobspec
is supplied.
.PP
If the
.B \-x
option is supplied,
.B jobs
replaces any
.I jobspec
found in
.I command
or
.I args
with the corresponding process group ID, and executes
.I command
passing it
.IR args ,
returning its exit status.
.RE
.TP
\fBkill\fP [\fB\-s\fP \fIsigspec\fP | \fB\-n\fP \fIsignum\fP | \fB\-\fP\fIsigspec\fP] [\fIpid\fP | \fIjobspec\fP] ...
.PD 0
.TP
\fBkill\fP \fB\-l\fP|\fB\-L\fP [\fIsigspec\fP | \fIexit_status\fP]
.PD
Send the signal named by
.I sigspec
or
.I signum
to the processes named by
.I pid
or
.IR jobspec .
.I sigspec
is either a case-insensitive signal name such as
.SM
.B SIGKILL
(with or without the
.SM
.B SIG
prefix) or a signal number;
.I signum
is a signal number.
If
.I sigspec
is not present, then
.SM
.B SIGTERM
is assumed.
An argument of
.B \-l
lists the signal names.
If any arguments are supplied when
.B \-l
is given, the names of the signals corresponding to the arguments are
listed, and the return status is 0.
The \fIexit_status\fP argument to
.B \-l
is a number specifying either a signal number or the exit status of
a process terminated by a signal.
The
.B \-L
option is equivalent to \fB\-l\fP.
.B kill
returns true if at least one signal was successfully sent, or false
if an error occurs or an invalid option is encountered.
.TP
\fBlet\fP \fIarg\fP [\fIarg\fP ...]
Each
.I arg
is an arithmetic expression to be evaluated (see
.SM
.B "ARITHMETIC EVALUATION"
.ie \n(zZ=1 in \fIbash(1)\fP).
.el above).
If the last
.I arg
evaluates to 0,
.B let
returns 1; 0 is returned otherwise.
.TP
\fBlocal\fP [\fIoption\fP] [\fIname\fP[=\fIvalue\fP] ... | \- ]
For each argument, a local variable named
.I name
is created, and assigned
.IR value .
The \fIoption\fP can be any of the options accepted by \fBdeclare\fP.
When
.B local
is used within a function, it causes the variable
.I name
to have a visible scope restricted to that function and its children.
If \fIname\fP is \-, the set of shell options is made local to the function
in which \fBlocal\fP is invoked: shell options changed using the
\fBset\fP builtin inside the function are restored to their original values
when the function returns.
The restore is effected as if a series of \fBset\fP commands were executed
to restore the values that were in place before the function.
With no operands,
.B local
writes a list of local variables to the standard output.  It is
an error to use
.B local
when not within a function.  The return status is 0 unless
.B local
is used outside a function, an invalid
.I name
is supplied, or
\fIname\fP is a readonly variable.
.TP
.B logout
Exit a login shell.
.TP
\fBmapfile\fP [\fB\-d\fP \fIdelim\fP] [\fB\-n\fP \fIcount\fP] [\fB\-O\fP \fIorigin\fP] [\fB\-s\fP \fIcount\fP] [\fB\-t\fP] [\fB\-u\fP \fIfd\fP] [\fB\-C\fP \fIcallback\fP] [\fB\-c\fP \fIquantum\fP] [\fIarray\fP]
.PD 0
.TP
\fBreadarray\fP [\fB\-d\fP \fIdelim\fP] [\fB\-n\fP \fIcount\fP] [\fB\-O\fP \fIorigin\fP] [\fB\-s\fP \fIcount\fP] [\fB\-t\fP] [\fB\-u\fP \fIfd\fP] [\fB\-C\fP \fIcallback\fP] [\fB\-c\fP \fIquantum\fP] [\fIarray\fP]
.PD
Read lines from the standard input into the indexed array variable
.IR array ,
or from file descriptor
.I fd
if the
.B \-u
option is supplied.
The variable
.SM
.B MAPFILE
is the default \fIarray\fP.
Options, if supplied, have the following meanings:
.RS
.PD 0
.TP
.B \-d
The first character of \fIdelim\fP is used to terminate each input line,
rather than newline.
If \fIdelim\fP is the empty string, \fBmapfile\fP will terminate a line
when it reads a NUL character.
.TP
.B \-n
Copy at most
.I count
lines.  If \fIcount\fP is 0, all lines are copied.
.TP
.B \-O
Begin assigning to
.I array
at index
.IR origin .
The default index is 0.
.TP
.B \-s
Discard the first \fIcount\fP lines read.
.TP
.B \-t
Remove a trailing \fIdelim\fP (default newline) from each line read.
.TP
.B \-u
Read lines from file descriptor \fIfd\fP instead of the standard input.
.TP
.B \-C
Evaluate
.I callback
each time \fIquantum\fP lines are read.  The \fB\-c\fP option specifies
.IR quantum .
.TP
.B \-c
Specify the number of lines read between each call to
.IR callback .
.PD
.PP
If
.B \-C
is specified without
.BR \-c ,
the default quantum is 5000.
When \fIcallback\fP is evaluated, it is supplied the index of the next
array element to be assigned and the line to be assigned to that element
as additional arguments.
\fIcallback\fP is evaluated after the line is read but before the
array element is assigned.
.PP
If not supplied with an explicit origin, \fBmapfile\fP will clear \fIarray\fP
before assigning to it.
.PP
\fBmapfile\fP returns successfully unless an invalid option or option
argument is supplied, \fIarray\fP is invalid or unassignable, or if
\fIarray\fP is not an indexed array.
.RE
.TP
\fBpopd\fP [\-\fBn\fP] [+\fIn\fP] [\-\fIn\fP]
Removes entries from the directory stack.
The elements are numbered from 0 starting at the first directory
listed by \fBdirs\fP.
With no arguments, \fBpopd\fP
removes the top directory from the stack, and
changes to the new top directory.
Arguments, if supplied, have the following meanings:
.RS
.PD 0
.TP
.B \-n
Suppresses the normal change of directory when removing directories
from the stack, so that only the stack is manipulated.
.TP
\fB+\fP\fIn\fP
Removes the \fIn\fPth entry counting from the left of the list
shown by
.BR dirs ,
starting with zero, from the stack.
For example:
.if n ``popd +0''
.if t \f(CWpopd +0\fP
removes the first directory,
.if n ``popd +1''
.if t \f(CWpopd +1\fP
the second.
.TP
\fB\-\fP\fIn\fP
Removes the \fIn\fPth entry counting from the right of the list
shown by
.BR dirs ,
starting with zero.  For example:
.if n ``popd -0''
.if t \f(CWpopd -0\fP
removes the last directory,
.if n ``popd -1''
.if t \f(CWpopd -1\fP
the next to last.
.PD
.PP
If the top element of the directory stack is modified, and
the \fI-n\fP option was not supplied, \fBpopd\fP uses the \fBcd\fP
builtin to change to the directory at the top of the stack.
If the \fBcd\fP fails, \fBpopd\fP returns a non-zero value.
.PP
Otherwise,
.B popd
returns false if an invalid option is encountered, the directory stack
is empty, or a non-existent directory stack entry is specified.
.PP
If the
.B popd
command is successful,
bash runs
.B dirs
to show the final contents of the directory stack,
and the return status is 0.
.RE
.TP
\fBprintf\fP [\fB\-v\fP \fIvar\fP] \fIformat\fP [\fIarguments\fP]
Write the formatted \fIarguments\fP to the standard output under the
control of the \fIformat\fP.
The \fB\-v\fP option causes the output to be assigned to the variable
\fIvar\fP rather than being printed to the standard output.
.sp 1
The \fIformat\fP is a character string which contains three types of objects:
plain characters, which are simply copied to standard output, character
escape sequences, which are converted and copied to the standard output, and
format specifications, each of which causes printing of the next successive
\fIargument\fP.
In addition to the standard \fIprintf\fP(1) format specifications,
\fBprintf\fP interprets the following extensions:
.RS
.PD 0
.TP
.B %b
causes
\fBprintf\fP to expand backslash escape sequences in the corresponding
\fIargument\fP
in the same way as \fBecho \-e\fP.
.TP
.B %q
causes \fBprintf\fP to output the corresponding
\fIargument\fP in a format that can be reused as shell input.
.TP
.B %Q
like \fB%q\fP, but applies any supplied precision to the \fIargument\fP
before quoting it.
.TP
.B %(\fIdatefmt\fP)T
causes \fBprintf\fP to output the date-time string resulting from using
\fIdatefmt\fP as a format string for \fIstrftime\fP(3).
The corresponding \fIargument\fP is an integer representing the number of
seconds since the epoch.
Two special argument values may be used: \-1 represents the current
time, and \-2 represents the time the shell was invoked.
If no argument is specified, conversion behaves as if \-1 had been given.
This is an exception to the usual \fBprintf\fP behavior.
.PD
.PP
The %b, %q, and %T directives all use the field width and precision
arguments from the format specification and write that many bytes from
(or use that wide a field for) the expanded argument, which usually
contains more characters than the original.
.PP
Arguments to non-string format specifiers are treated as C constants,
except that a leading plus or minus sign is allowed, and if the leading
character is a single or double quote, the value is the ASCII value of
the following character.
.PP
The \fIformat\fP is reused as necessary to consume all of the \fIarguments\fP.
If the \fIformat\fP requires more \fIarguments\fP than are supplied, the
extra format specifications behave as if a zero value or null string, as
appropriate, had been supplied.
The return value is zero on success, non-zero on failure.
.RE
.TP
\fBpushd\fP [\fB\-n\fP] [+\fIn\fP] [\-\fIn\fP]
.PD 0
.TP
\fBpushd\fP [\fB\-n\fP] [\fIdir\fP]
.PD
Adds a directory to the top of the directory stack, or rotates
the stack, making the new top of the stack the current working
directory.
With no arguments, \fBpushd\fP exchanges the top two elements of
the directory stack.
Arguments, if supplied, have the following meanings:
.RS
.PD 0
.TP
.B \-n
Suppresses the normal change of directory when rotating or
adding directories to the stack, so that only the stack is manipulated.
.TP
\fB+\fP\fIn\fP
Rotates the stack so that the \fIn\fPth directory
(counting from the left of the list shown by
.BR dirs ,
starting with zero)
is at the top.
.TP
\fB\-\fP\fIn\fP
Rotates the stack so that the \fIn\fPth directory
(counting from the right of the list shown by
.BR dirs ,
starting with zero) is at the top.
.TP
.I dir
Adds
.I dir
to the directory stack at the top
.PD
.PP
After the stack has been modified, if the \fB\-n\fP option was not
supplied, \fBpushd\fP uses the \fBcd\fP builtin to change to the
directory at the top of the stack.
If the \fBcd\fP fails, \fBpushd\fP returns a non-zero value.
.PP
Otherwise, if no arguments are supplied,
.B pushd
returns 0 unless the directory stack is empty.
When rotating the directory stack,
.B pushd
returns 0 unless the directory stack is empty or
a non-existent directory stack element is specified.
.PP
If the
.B pushd
command is successful,
bash runs
.B dirs
to show the final contents of the directory stack.
.RE
.TP
\fBpwd\fP [\fB\-LP\fP]
Print the absolute pathname of the current working directory.
The pathname printed contains no symbolic links if the
.B \-P
option is supplied or the
.B \-o physical
option to the
.B set
builtin command is enabled.
If the
.B \-L
option is used, the pathname printed may contain symbolic links.
The return status is 0 unless an error occurs while
reading the name of the current directory or an
invalid option is supplied.
.TP
\fBread\fP [\fB\-ers\fP] [\fB\-a\fP \fIaname\fP] [\fB\-d\fP \fIdelim\fP] [\fB\-i\fP \fItext\fP] [\fB\-n\fP \fInchars\fP] [\fB\-N\fP \fInchars\fP] [\fB\-p\fP \fIprompt\fP] [\fB\-t\fP \fItimeout\fP] [\fB\-u\fP \fIfd\fP] [\fIname\fP ...]
One line is read from the standard input, or from the file descriptor
\fIfd\fP supplied as an argument to the \fB\-u\fP option,
split into words as described
.ie \n(zZ=1 in \fIbash(1)\fP
.el above
under \fBWord Splitting\fP,
and the first word
is assigned to the first
.IR name ,
the second word to the second
.IR name ,
and so on.
If there are more words than names, the remaining words and their
intervening delimiters are assigned to the last
.IR name .
If there are fewer words read from the input stream than names,
the remaining names are assigned empty values.
The characters in
.SM
.B IFS
are used to split the line into words using the same rules the shell
uses for expansion (described
.ie \n(zZ=1 in \fIbash(1)\fP
.el above
under \fBWord Splitting\fP).
The backslash character (\fB\e\fP) may be used to remove any special
meaning for the next character read and for line continuation.
Options, if supplied, have the following meanings:
.RS
.PD 0
.TP
.B \-a \fIaname\fP
The words are assigned to sequential indices
of the array variable
.IR aname ,
starting at 0.
.I aname
is unset before any new values are assigned.
Other \fIname\fP arguments are ignored.
.TP
.B \-d \fIdelim\fP
The first character of \fIdelim\fP is used to terminate the input line,
rather than newline.
If \fIdelim\fP is the empty string, \fBread\fP will terminate a line
when it reads a NUL character.
.TP
.B \-e
If the standard input
is coming from a terminal,
.B readline
(see
.SM
.B READLINE
.ie \n(zZ=1 in \fIbash(1)\fP)
.el above)
is used to obtain the line.
Readline uses the current (or default, if line editing was not previously
active) editing settings, but uses readline's default filename completion.
.TP
.B \-i \fItext\fP
If
.B readline
is being used to read the line, \fItext\fP is placed into the editing
buffer before editing begins.
.TP
.B \-n \fInchars\fP
\fBread\fP returns after reading \fInchars\fP characters rather than
waiting for a complete line of input, but honors a delimiter if fewer
than \fInchars\fP characters are read before the delimiter.
.TP
.B \-N \fInchars\fP
\fBread\fP returns after reading exactly \fInchars\fP characters rather
than waiting for a complete line of input, unless EOF is encountered or
\fBread\fP times out.
Delimiter characters encountered in the input are
not treated specially and do not cause \fBread\fP to return until
\fInchars\fP characters are read.
The result is not split on the characters in \fBIFS\fP; the intent is
that the variable is assigned exactly the characters read
(with the exception of backslash; see the \fB\-r\fP option below).
.TP
.B \-p \fIprompt\fP
Display \fIprompt\fP on standard error, without a
trailing newline, before attempting to read any input.  The prompt
is displayed only if input is coming from a terminal.
.TP
.B \-r
Backslash does not act as an escape character.
The backslash is considered to be part of the line.
In particular, a backslash-newline pair may not then be used as a line
continuation.
.TP
.B \-s
Silent mode.  If input is coming from a terminal, characters are
not echoed.
.TP
.B \-t \fItimeout\fP
Cause \fBread\fP to time out and return failure if a complete line of
input (or a specified number of characters)
is not read within \fItimeout\fP seconds.
\fItimeout\fP may be a decimal number with a fractional portion following
the decimal point.
This option is only effective if \fBread\fP is reading input from a
terminal, pipe, or other special file; it has no effect when reading
from regular files.
If \fBread\fP times out, \fBread\fP saves any partial input read into
the specified variable \fIname\fP.
If \fItimeout\fP is 0, \fBread\fP returns immediately, without trying to
read any data.
The exit status is 0 if input is available on the specified file descriptor,
or the read will return EOF,
non-zero otherwise.
The exit status is greater than 128 if the timeout is exceeded.
.TP
.B \-u \fIfd\fP
Read input from file descriptor \fIfd\fP.
.PD
.PP
If no
.I names
are supplied, the line read,
without the ending delimiter but otherwise unmodified,
is assigned to the variable
.SM
.BR REPLY .
The exit status is zero, unless end-of-file is encountered, \fBread\fP
times out (in which case the status is greater than 128),
a variable assignment error (such as assigning to a readonly variable) occurs,
or an invalid file descriptor is supplied as the argument to \fB\-u\fP.
.RE
.TP
\fBreadonly\fP [\fB\-aAf\fP] [\fB\-p\fP] [\fIname\fP[=\fIword\fP] ...]
.PD
The given
\fInames\fP are marked readonly; the values of these
.I names
may not be changed by subsequent assignment.
If the
.B \-f
option is supplied, the functions corresponding to the
\fInames\fP are so
marked.
The
.B \-a
option restricts the variables to indexed arrays; the
.B \-A
option restricts the variables to associative arrays.
If both options are supplied,
.B \-A
takes precedence.
If no
.I name
arguments are given, or if the
.B \-p
option is supplied, a list of all readonly names is printed.
The other options may be used to restrict the output to a subset of
the set of readonly names.
The
.B \-p
option causes output to be displayed in a format that
may be reused as input.
If a variable name is followed by =\fIword\fP, the value of
the variable is set to \fIword\fP.
The return status is 0 unless an invalid option is encountered,
one of the
.I names
is not a valid shell variable name, or
.B \-f
is supplied with a
.I name
that is not a function.
.TP
\fBreturn\fP [\fIn\fP]
Causes a function to stop executing and return the value specified by
.I n
to its caller.
If
.I n
is omitted, the return status is that of the last command
executed in the function body.
If \fBreturn\fP is executed by a trap handler, the last command used to
determine the status is the last command executed before the trap handler.
If \fBreturn\fP is executed during a \fBDEBUG\fP trap, the last command
used to determine the status is the last command executed by the trap
handler before \fBreturn\fP was invoked.
If
.B return
is used outside a function,
but during execution of a script by the
.B .
(\fBsource\fP) command, it causes the shell to stop executing
that script and return either
.I n
or the exit status of the last command executed within the
script as the exit status of the script.
If \fIn\fP is supplied, the return value is its least significant
8 bits.
The return status is non-zero if
.B return
is supplied a non-numeric argument, or
is used outside a
function and not during execution of a script by \fB.\fP\^ or \fBsource\fP.
Any command associated with the \fBRETURN\fP trap is executed
before execution resumes after the function or script.
.TP
\fBset\fP [\fB\-abefhkmnptuvxBCEHPT\fP] [\fB\-o\fP \fIoption\-name\fP] [\fB\-\-\fP] [\fB\-\fP] [\fIarg\fP ...]
.PD 0
.TP
\fBset\fP [\fB+abefhkmnptuvxBCEHPT\fP] [\fB+o\fP \fIoption\-name\fP] [\fB\-\-\fP] [\fB\-\fP] [\fIarg\fP ...]
.PD
Without options, display the name and value of each shell variable
in a format that can be reused as input
for setting or resetting the currently-set variables.
Read-only variables cannot be reset.
In \fIposix mode\fP, only shell variables are listed.
The output is sorted according to the current locale.
When options are specified, they set or unset shell attributes.
Any arguments remaining after option processing are treated
as values for the positional parameters and are assigned, in order, to
.BR $1 ,
.BR $2 ,
.B ...
.BR $\fIn\fP .
Options, if specified, have the following meanings:
.RS
.PD 0
.TP 8
.B \-a
Each variable or function that is created or modified is given the
export attribute and marked for export to the environment of
subsequent commands.
.TP 8
.B \-b
Report the status of terminated background jobs
immediately, rather than before the next primary prompt.  This is
effective only when job control is enabled.
.TP 8
.B \-e
Exit immediately if a
\fIpipeline\fP (which may consist of a single \fIsimple command\fP),
a \fIlist\fP,
or a \fIcompound command\fP
(see
.SM
.B SHELL GRAMMAR
.ie \n(zZ=1 in \fIbash(1)\fP),
.el above),
exits with a non-zero status.
The shell does not exit if the
command that fails is part of the command list immediately following a
.B while
or
.B until
keyword,
part of the test following the
.B if
or
.B elif
reserved words, part of any command executed in a
.B &&
or
.B ||
list except the command following the final \fB&&\fP or \fB||\fP,
any command in a pipeline but the last,
or if the command's return value is
being inverted with
.BR ! .
If a compound command other than a subshell
returns a non-zero status because a command failed
while \fB\-e\fP was being ignored, the shell does not exit.
A trap on \fBERR\fP, if set, is executed before the shell exits.
This option applies to the shell environment and each subshell environment
separately (see
.SM
.B "COMMAND EXECUTION ENVIRONMENT"
.ie \n(zZ=1 in \fIbash(1)\fP),
.el above),
and may cause
subshells to exit before executing all the commands in the subshell.
.if t .sp 0.5
.if n .sp 1
If a compound command or shell function executes in a context
where \fB\-e\fP is being ignored,
none of the commands executed within the compound command or function body
will be affected by the \fB\-e\fP setting, even if \fB\-e\fP is set
and a command returns a failure status.
If a compound command or shell function sets \fB\-e\fP while executing in
a context where \fB\-e\fP is ignored, that setting will not have any
effect until the compound command or the command containing the function
call completes.
.TP 8
.B \-f
Disable pathname expansion.
.TP 8
.B \-h
Remember the location of commands as they are looked up for execution.
This is enabled by default.
.TP 8
.B \-k
All arguments in the form of assignment statements
are placed in the environment for a command, not just
those that precede the command name.
.TP 8
.B \-m
Monitor mode.  Job control is enabled.  This option is on
by default for interactive shells on systems that support
it (see
.SM
.B JOB CONTROL
.ie \n(zZ=1 in \fIbash(1)\fP).
.el above).
All processes run in a separate process group.
When a background job completes, the shell prints a line
containing its exit status.
.TP 8
.B \-n
Read commands but do not execute them.
This may be used to check a shell script for syntax errors.
This is ignored by interactive shells.
.TP 8
.B \-o \fIoption\-name\fP
The \fIoption\-name\fP can be one of the following:
.RS
.TP 8
.B allexport
Same as
.BR \-a .
.TP 8
.B braceexpand
Same as
.BR \-B .
.TP 8
.B emacs
Use an emacs-style command line editing interface.  This is enabled
by default when the shell is interactive, unless the shell is started
with the
.B \-\-noediting
option.
This also affects the editing interface used for \fBread \-e\fP.
.TP 8
.B errexit
Same as
.BR \-e .
.TP 8
.B errtrace
Same as
.BR \-E .
.TP 8
.B functrace
Same as
.BR \-T .
.TP 8
.B hashall
Same as
.BR \-h .
.TP 8
.B histexpand
Same as
.BR \-H .
.TP 8
.B history
Enable command history, as described
.ie \n(zZ=1 in \fIbash(1)\fP
.el above
under
.SM
.BR HISTORY .
This option is on by default in interactive shells.
.TP 8
.B ignoreeof
The effect is as if the shell command
.if t \f(CWIGNOREEOF=10\fP
.if n ``IGNOREEOF=10''
had been executed
(see
.B Shell Variables
.ie \n(zZ=1 in \fIbash(1)\fP).
.el above).
.TP 8
.B keyword
Same as
.BR \-k .
.TP 8
.B monitor
Same as
.BR \-m .
.TP 8
.B noclobber
Same as
.BR \-C .
.TP 8
.B noexec
Same as
.BR \-n .
.TP 8
.B noglob
Same as
.BR \-f .
.TP 8
.B nolog
Currently ignored.
.TP 8
.B notify
Same as
.BR \-b .
.TP 8
.B nounset
Same as
.BR \-u .
.TP 8
.B onecmd
Same as
.BR \-t .
.TP 8
.B physical
Same as
.BR \-P .
.TP 8
.B pipefail
If set, the return value of a pipeline is the value of the last
(rightmost) command to exit with a non-zero status, or zero if all
commands in the pipeline exit successfully.
This option is disabled by default.
.TP 8
.B posix
Change the behavior of
.B bash
where the default operation differs
from the POSIX standard to match the standard (\fIposix mode\fP).
See
.SM
.B "SEE ALSO"
.ie \n(zZ=1 in \fIbash(1)\fP
.el below
for a reference to a document that details how posix mode affects
bash's behavior.
.TP 8
.B privileged
Same as
.BR \-p .
.TP 8
.B verbose
Same as
.BR \-v .
.TP 8
.B vi
Use a vi-style command line editing interface.
This also affects the editing interface used for \fBread \-e\fP.
.TP 8
.B xtrace
Same as
.BR \-x .
.sp .5
.PP
If
.B \-o
is supplied with no \fIoption\-name\fP, the values of the current options are
printed.
If
.B +o
is supplied with no \fIoption\-name\fP, a series of
.B set
commands to recreate the current option settings is displayed on
the standard output.
.RE
.TP 8
.B \-p
Turn on
.I privileged
mode.  In this mode, the
.SM
.B $ENV
and
.SM
.B $BASH_ENV
files are not processed, shell functions are not inherited from the
environment, and the
.SM
.BR SHELLOPTS ,
.SM
.BR BASHOPTS ,
.SM
.BR CDPATH ,
and
.SM
.B GLOBIGNORE
variables, if they appear in the environment, are ignored.
If the shell is started with the effective user (group) id not equal to the
real user (group) id, and the \fB\-p\fP option is not supplied, these actions
are taken and the effective user id is set to the real user id.
If the \fB\-p\fP option is supplied at startup, the effective user id is
not reset.
Turning this option off causes the effective user
and group ids to be set to the real user and group ids.
.TP 8
.B \-r
Enable restricted shell mode.
This option cannot be unset once it has been set.
.TP 8
.B \-t
Exit after reading and executing one command.
.TP 8
.B \-u
Treat unset variables and parameters other than the special
parameters "@" and "*",
or array variables subscripted with "@" or "*",
as an error when performing
parameter expansion.  If expansion is attempted on an
unset variable or parameter, the shell prints an error message, and,
if not interactive, exits with a non-zero status.
.TP 8
.B \-v
Print shell input lines as they are read.
.TP 8
.B \-x
After expanding each \fIsimple command\fP,
\fBfor\fP command, \fBcase\fP command, \fBselect\fP command, or
arithmetic \fBfor\fP command, display the expanded value of
.SM
.BR PS4 ,
followed by the command and its expanded arguments
or associated word list.
.TP 8
.B \-B
The shell performs brace expansion (see
.B Brace Expansion
.ie \n(zZ=1 in \fIbash(1)\fP).
.el above).
This is on by default.
.TP 8
.B \-C
If set,
.B bash
does not overwrite an existing file with the
.BR > ,
.BR >& ,
and
.B <>
redirection operators.  This may be overridden when
creating output files by using the redirection operator
.B >|
instead of
.BR > .
.TP 8
.B \-E
If set, any trap on \fBERR\fP is inherited by shell functions, command
substitutions, and commands executed in a subshell environment.
The \fBERR\fP trap is normally not inherited in such cases.
.TP 8
.B \-H
Enable
.B !
style history substitution.  This option is on by
default when the shell is interactive.
.TP 8
.B \-P
If set, the shell does not resolve symbolic links when executing
commands such as
.B cd
that change the current working directory.  It uses the
physical directory structure instead.  By default,
.B bash
follows the logical chain of directories when performing commands
which change the current directory.
.TP 8
.B \-T
If set, any traps on \fBDEBUG\fP and \fBRETURN\fP are inherited by shell
functions, command substitutions, and commands executed in a
subshell environment.
The \fBDEBUG\fP and \fBRETURN\fP traps are normally not inherited
in such cases.
.TP 8
.B \-\-
If no arguments follow this option, then the positional parameters are
unset.  Otherwise, the positional parameters are set to the
\fIarg\fPs, even if some of them begin with a
.BR \- .
.TP 8
.B \-
Signal the end of options, cause all remaining \fIarg\fPs to be
assigned to the positional parameters.  The
.B \-x
and
.B \-v
options are turned off.
If there are no \fIarg\fPs,
the positional parameters remain unchanged.
.PD
.PP
The options are off by default unless otherwise noted.
Using + rather than \- causes these options to be turned off.
The options can also be specified as arguments to an invocation of
the shell.
The current set of options may be found in
.BR $\- .
The return status is always true unless an invalid option is encountered.
.RE
.TP
\fBshift\fP [\fIn\fP]
The positional parameters from \fIn\fP+1 ... are renamed to
.B $1
.B ....
Parameters represented by the numbers \fB$#\fP
down to \fB$#\fP\-\fIn\fP+1 are unset.
.I n
must be a non-negative number less than or equal to \fB$#\fP.
If
.I n
is 0, no parameters are changed.
If
.I n
is not given, it is assumed to be 1.
If
.I n
is greater than \fB$#\fP, the positional parameters are not changed.
The return status is greater than zero if
.I n
is greater than
.B $#
or less than zero; otherwise 0.
.TP
\fBshopt\fP [\fB\-pqsu\fP] [\fB\-o\fP] [\fIoptname\fP ...]
Toggle the values of settings controlling optional shell behavior.
The settings can be either those listed below, or, if the
.B \-o
option is used, those available with the
.B \-o
option to the \fBset\fP builtin command.
With no options, or with the
.B \-p
option, a list of all settable options is displayed, with
an indication of whether or not each is set;
if \fIoptnames\fP are supplied, the output is restricted to those options.
The \fB\-p\fP option causes output to be displayed in a form that
may be reused as input.
Other options have the following meanings:
.RS
.PD 0
.TP
.B \-s
Enable (set) each \fIoptname\fP.
.TP
.B \-u
Disable (unset) each \fIoptname\fP.
.TP
.B \-q
Suppresses normal output (quiet mode); the return status indicates
whether the \fIoptname\fP is set or unset.
If multiple \fIoptname\fP arguments are given with
.BR \-q ,
the return status is zero if all \fIoptnames\fP are enabled; non-zero
otherwise.
.TP
.B \-o
Restricts the values of \fIoptname\fP to be those defined for the
.B \-o
option to the
.B set
builtin.
.PD
.PP
If either
.B \-s
or
.B \-u
is used with no \fIoptname\fP arguments,
.B shopt
shows only those options which are set or unset, respectively.
Unless otherwise noted, the \fBshopt\fP options are disabled (unset)
by default.
.PP
The return status when listing options is zero if all \fIoptnames\fP
are enabled, non-zero otherwise.  When setting or unsetting options,
the return status is zero unless an \fIoptname\fP is not a valid shell
option.
.PP
The list of \fBshopt\fP options is:
.if t .sp .5v
.if n .sp 1v
.PD 0
.TP 8
.B assoc_expand_once
If set, the shell suppresses multiple evaluation of associative array
subscripts during arithmetic expression evaluation, while executing
builtins that can perform variable assignments,
and while executing builtins that perform array dereferencing.
.TP 8
.B autocd
If set, a command name that is the name of a directory is executed as if
it were the argument to the \fBcd\fP command.
This option is only used by interactive shells.
.TP 8
.B cdable_vars
If set, an argument to the
.B cd
builtin command that
is not a directory is assumed to be the name of a variable whose
value is the directory to change to.
.TP 8
.B cdspell
If set, minor errors in the spelling of a directory component in a
.B cd
command will be corrected.
The errors checked for are transposed characters,
a missing character, and one character too many.
If a correction is found, the corrected filename is printed,
and the command proceeds.
This option is only used by interactive shells.
.TP 8
.B checkhash
If set, \fBbash\fP checks that a command found in the hash
table exists before trying to execute it.  If a hashed command no
longer exists, a normal path search is performed.
.TP 8
.B checkjobs
If set, \fBbash\fP lists the status of any stopped and running jobs before
exiting an interactive shell.  If any jobs are running, this causes
the exit to be deferred until a second exit is attempted without an
intervening command (see
.SM
.B "JOB CONTROL"
.ie \n(zZ=1 in \fIbash(1)\fP).
.el above).
The shell always postpones exiting if any jobs are stopped.
.TP 8
.B checkwinsize
If set, \fBbash\fP checks the window size after each external (non-builtin)
command and, if necessary, updates the values of
.SM
.B LINES
and
.SM
.BR COLUMNS .
This option is enabled by default.
.TP 8
.B cmdhist
If set,
.B bash
attempts to save all lines of a multiple-line
command in the same history entry.  This allows
easy re-editing of multi-line commands.
This option is enabled by default, but only has an effect if command
history is enabled, as described
.ie \n(zZ=1 in \fIbash(1)\fP
.el above
under
.SM
.BR HISTORY .
.PD 0
.TP 8
.B compat31
.TP 8
.B compat32
.TP 8
.B compat40
.TP 8
.B compat41
.TP 8
.B compat42
.TP 8
.B compat43
.TP 8
.B compat44
.TP 8
.B compat50
.PD
These control aspects of the shell's compatibility mode
(see
.SM
.B "SHELL COMPATIBILITY MODE"
.ie \n(zZ=1 in \fIbash(1)\fP).
.el below).
.TP 8
.B complete_fullquote
If set,
.B bash
quotes all shell metacharacters in filenames and directory names when
performing completion.
If not set,
.B bash
removes metacharacters such as the dollar sign from the set of
characters that will be quoted in completed filenames
when these metacharacters appear in shell variable references in words to be
completed.
This means that dollar signs in variable names that expand to directories
will not be quoted;
however, any dollar signs appearing in filenames will not be quoted, either.
This is active only when bash is using backslashes to quote completed
filenames.
This variable is set by default, which is the default bash behavior in
versions through 4.2.
.TP 8
.B direxpand
If set,
.B bash
replaces directory names with the results of word expansion when performing
filename completion.  This changes the contents of the readline editing
buffer.
If not set,
.B bash
attempts to preserve what the user typed.
.TP 8
.B dirspell
If set,
.B bash
attempts spelling correction on directory names during word completion
if the directory name initially supplied does not exist.
.TP 8
.B dotglob
If set,
.B bash
includes filenames beginning with a `.' in the results of pathname
expansion.
The filenames
.B ``.''
and
.B ``..''
must always be matched explicitly, even if
.B dotglob
is set.
.TP 8
.B execfail
If set, a non-interactive shell will not exit if
it cannot execute the file specified as an argument to the
.B exec
builtin command.  An interactive shell does not exit if
.B exec
fails.
.TP 8
.B expand_aliases
If set, aliases are expanded as described
.ie \n(zZ=1 in \fIbash(1)\fP
.el above
under
.SM
.BR ALIASES .
This option is enabled by default for interactive shells.
.TP 8
.B extdebug
If set at shell invocation,
or in a shell startup file,
arrange to execute the debugger profile
before the shell starts, identical to the \fB\-\-debugger\fP option.
If set after invocation, behavior intended for use by debuggers is enabled:
.RS
.TP
.B 1.
The \fB\-F\fP option to the \fBdeclare\fP builtin displays the source
file name and line number corresponding to each function name supplied
as an argument.
.TP
.B 2.
If the command run by the \fBDEBUG\fP trap returns a non-zero value, the
next command is skipped and not executed.
.TP
.B 3.
If the command run by the \fBDEBUG\fP trap returns a value of 2, and the
shell is executing in a subroutine (a shell function or a shell script
executed by the \fB.\fP or \fBsource\fP builtins), the shell simulates
a call to \fBreturn\fP.
.TP
.B 4.
.SM
.B BASH_ARGC
and
.SM
.B BASH_ARGV
are updated as described in their descriptions
.ie \n(zZ=1 in \fIbash(1)\fP).
.el above).
.TP
.B 5.
Function tracing is enabled: command substitution, shell functions, and
subshells invoked with \fB(\fP \fIcommand\fP \fB)\fP inherit the
\fBDEBUG\fP and \fBRETURN\fP traps.
.TP
.B 6.
Error tracing is enabled: command substitution, shell functions, and
subshells invoked with \fB(\fP \fIcommand\fP \fB)\fP inherit the
\fBERR\fP trap.
.RE
.TP 8
.B extglob
If set, the extended pattern matching features described
.ie \n(zZ=1 in \fIbash(1)\fP
.el above
under
\fBPathname Expansion\fP are enabled.
.TP 8
.B extquote
If set, \fB$\fP\(aq\fIstring\fP\(aq and \fB$\fP"\fIstring\fP" quoting is
performed within \fB${\fP\fIparameter\fP\fB}\fP expansions
enclosed in double quotes.  This option is enabled by default.
.TP 8
.B failglob
If set, patterns which fail to match filenames during pathname expansion
result in an expansion error.
.TP 8
.B force_fignore
If set, the suffixes specified by the
.SM
.B FIGNORE
shell variable
cause words to be ignored when performing word completion even if
the ignored words are the only possible completions.
See
.SM
\fBSHELL VARIABLES\fP
.ie \n(zZ=1 in \fIbash(1)\fP
.el above
for a description of
.SM
.BR FIGNORE .
This option is enabled by default.
.TP 8
.B globasciiranges
If set, range expressions used in pattern matching bracket expressions (see
.SM
.B Pattern Matching
.ie \n(zZ=1 in \fIbash(1)\fP)
.el above)
behave as if in the traditional C locale when performing
comparisons.  That is, the current locale's collating sequence
is not taken into account, so
.B b
will not collate between
.B A
and
.BR B ,
and upper-case and lower-case ASCII characters will collate together.
.TP 8
.B globskipdots
If set, pathname expansion will never match the filenames
.B ``.''
and
.BR ``..'' ,
even if the pattern begins with a
.BR ``.'' .
This option is enabled by default.
.TP 8
.B globstar
If set, the pattern \fB**\fP used in a pathname expansion context will
match all files and zero or more directories and subdirectories.
If the pattern is followed by a \fB/\fP, only directories and
subdirectories match.
.TP 8
.B gnu_errfmt
If set, shell error messages are written in the standard GNU error
message format.
.TP 8
.B histappend
If set, the history list is appended to the file named by the value
of the
.SM
.B HISTFILE
variable when the shell exits, rather than overwriting the file.
.TP 8
.B histreedit
If set, and
.B readline
is being used, a user is given the opportunity to re-edit a
failed history substitution.
.TP 8
.B histverify
If set, and
.B readline
is being used, the results of history substitution are not immediately
passed to the shell parser.  Instead, the resulting line is loaded into
the \fBreadline\fP editing buffer, allowing further modification.
.TP 8
.B hostcomplete
If set, and
.B readline
is being used, \fBbash\fP will attempt to perform hostname completion when a
word containing a \fB@\fP is being completed (see
.B Completing
under
.SM
.B READLINE
.ie \n(zZ=1 in \fIbash(1)\fP).
.el above).
This is enabled by default.
.TP 8
.B huponexit
If set, \fBbash\fP will send
.SM
.B SIGHUP
to all jobs when an interactive login shell exits.
.TP 8
.B inherit_errexit
If set, command substitution inherits the value of the \fBerrexit\fP option,
instead of unsetting it in the subshell environment.
This option is enabled when \fIposix mode\fP is enabled.
.TP 8
.B interactive_comments
If set, allow a word beginning with
.B #
to cause that word and all remaining characters on that
line to be ignored in an interactive shell (see
.SM
.B COMMENTS
.ie \n(zZ=1 in \fIbash(1)\fP).
.el above).
This option is enabled by default.
.TP 8
.B lastpipe
If set, and job control is not active, the shell runs the last command of
a pipeline not executed in the background in the current shell environment.
.TP 8
.B lithist
If set, and the
.B cmdhist
option is enabled, multi-line commands are saved to the history with
embedded newlines rather than using semicolon separators where possible.
.TP 8
.B localvar_inherit
If set, local variables inherit the value and attributes of a variable of
the same name that exists at a previous scope before any new value is
assigned.  The nameref attribute is not inherited.
.TP 8
.B localvar_unset
If set, calling \fBunset\fP on local variables in previous function scopes
marks them so subsequent lookups find them unset until that function
returns. This is identical to the behavior of unsetting local variables
at the current function scope.
.TP 8
.B login_shell
The shell sets this option if it is started as a login shell (see
.SM
.B "INVOCATION"
.ie \n(zZ=1 in \fIbash(1)\fP).
.el above).
The value may not be changed.
.TP 8
.B mailwarn
If set, and a file that \fBbash\fP is checking for mail has been
accessed since the last time it was checked, the message ``The mail in
\fImailfile\fP has been read'' is displayed.
.TP 8
.B no_empty_cmd_completion
If set, and
.B readline
is being used,
.B bash
will not attempt to search the
.SM
.B PATH
for possible completions when
completion is attempted on an empty line.
.TP 8
.B nocaseglob
If set,
.B bash
matches filenames in a case\-insensitive fashion when performing pathname
expansion (see
.B Pathname Expansion
.ie \n(zZ=1 in \fIbash(1)\fP).
.el above).
.TP 8
.B nocasematch
If set,
.B bash
matches patterns in a case\-insensitive fashion when performing matching
while executing \fBcase\fP or \fB[[\fP conditional commands,
when performing pattern substitution word expansions,
or when filtering possible completions as part of programmable completion.
.TP 8
.B noexpand_translation
If set,
.B bash
encloses the translated results of $"..." quoting in single quotes
instead of double quotes.
If the string is not translated, this has no effect.
.TP 8
.B nullglob
If set,
.B bash
allows patterns which match no
files (see
.B Pathname Expansion
.ie \n(zZ=1 in \fIbash(1)\fP)
.el above)
to expand to a null string, rather than themselves.
.TP 8
.B patsub_replacement
If set, \fBbash\fP
expands occurrences of \fB&\fP in the replacement string of pattern
substitution to the text matched by the pattern, as described
under \fBParameter Expansion\fP
.ie \n(zZ=1 in \fIbash(1)\fP.
.el above.
This option is enabled by default.
.TP 8
.B progcomp
If set, the programmable completion facilities (see
\fBProgrammable Completion\fP
.ie \n(zZ=1 in \fIbash(1)\fP)
.el above)
are enabled.
This option is enabled by default.
.TP 8
.B progcomp_alias
If set, and programmable completion is enabled, \fBbash\fP treats a command
name that doesn't have any completions as a possible alias and attempts
alias expansion. If it has an alias, \fBbash\fP attempts programmable
completion using the command word resulting from the expanded alias.
.TP 8
.B promptvars
If set, prompt strings undergo
parameter expansion, command substitution, arithmetic
expansion, and quote removal after being expanded as described in
.SM
.B PROMPTING
.ie \n(zZ=1 in \fIbash(1)\fP.
.el above.
This option is enabled by default.
.TP 8
.B restricted_shell
The shell sets this option if it is started in restricted mode
(see
.SM
.B "RESTRICTED SHELL"
.ie \n(zZ=1 in \fIbash(1)\fP).
.el below).
The value may not be changed.
This is not reset when the startup files are executed, allowing
the startup files to discover whether or not a shell is restricted.
.TP 8
.B shift_verbose
If set, the
.B shift
builtin prints an error message when the shift count exceeds the
number of positional parameters.
.TP 8
.B sourcepath
If set, the
\fB.\fP (\fBsource\fP) builtin uses the value of
.SM
.B PATH
to find the directory containing the file supplied as an argument.
This option is enabled by default.
.TP 8
.B varredir_close
If set, the shell automatically closes file descriptors assigned using the
\fI{varname}\fP redirection syntax (see
.SM
.B REDIRECTION
.ie \n(zZ=1 in \fIbash(1)\fP)
.el above)
instead of leaving them open when the command completes.
.TP 8
.B xpg_echo
If set, the \fBecho\fP builtin expands backslash-escape sequences
by default.
.RE
.PD
.TP
\fBsuspend\fP [\fB\-f\fP]
Suspend the execution of this shell until it receives a
.SM
.B SIGCONT
signal.  A login shell,
or a shell without job control enabled,
cannot be suspended; the
.B \-f
option can be used to override this and force the suspension.
The return status is 0 unless the shell is a login shell
or job control is not enabled
and
.B \-f
is not supplied.
.TP
\fBtest\fP \fIexpr\fP
.PD 0
.TP
\fB[\fP \fIexpr\fP \fB]\fP
Return a status of 0 (true) or 1 (false) depending on
the evaluation of the conditional expression
.IR expr .
Each operator and operand must be a separate argument.
Expressions are composed of the primaries described 
.ie \n(zZ=1 in \fIbash(1)\fP
.el above
under
.SM
.BR "CONDITIONAL EXPRESSIONS" .
\fBtest\fP does not accept any options, nor does it accept and ignore
an argument of \fB\-\-\fP as signifying the end of options.
.if t .sp 0.5
.if n .sp 1
Expressions may be combined using the following operators, listed
in decreasing order of precedence.
The evaluation depends on the number of arguments; see below.
Operator precedence is used when there are five or more arguments.
.RS
.PD 0
.TP
.B ! \fIexpr\fP
True if
.I expr
is false.
.TP
.B ( \fIexpr\fP )
Returns the value of \fIexpr\fP.
This may be used to override the normal precedence of operators.
.TP
\fIexpr1\fP \-\fBa\fP \fIexpr2\fP
True if both
.I expr1
and
.I expr2
are true.
.TP
\fIexpr1\fP \-\fBo\fP \fIexpr2\fP
True if either
.I expr1
or
.I expr2
is true.
.PD
.PP
\fBtest\fP and \fB[\fP evaluate conditional
expressions using a set of rules based on the number of arguments.
.if t .sp 0.5
.if n .sp 1
.PD 0
.TP
0 arguments
The expression is false.
.TP
1 argument
The expression is true if and only if the argument is not null.
.TP
2 arguments
If the first argument is \fB!\fP, the expression is true if and
only if the second argument is null.
If the first argument is one of the unary conditional operators listed
.ie \n(zZ=1 in \fIbash(1)\fP
.el above
under
.SM
.BR "CONDITIONAL EXPRESSIONS" ,
the expression is true if the unary test is true.
If the first argument is not a valid unary conditional operator, the expression
is false.
.TP
3 arguments
The following conditions are applied in the order listed.
If the second argument is one of the binary conditional operators listed
.ie \n(zZ=1 in \fIbash(1)\fP
.el above
under
.SM
.BR "CONDITIONAL EXPRESSIONS" ,
the result of the expression is the result of the binary test using
the first and third arguments as operands.
The \fB\-a\fP and \fB\-o\fP operators are considered binary operators
when there are three arguments.
If the first argument is \fB!\fP, the value is the negation of
the two-argument test using the second and third arguments.
If the first argument is exactly \fB(\fP and the third argument is
exactly \fB)\fP, the result is the one-argument test of the second
argument.
Otherwise, the expression is false.
.TP
4 arguments
The following conditions are applied in the order listed.
If the first argument is \fB!\fP, the result is the negation of
the three-argument expression composed of the remaining arguments.
the two-argument test using the second and third arguments.
If the first argument is exactly \fB(\fP and the fourth argument is
exactly \fB)\fP, the result is the two-argument test of the second
and third arguments.
Otherwise, the expression is parsed and evaluated according to
precedence using the rules listed above.
.TP
5 or more arguments
The expression is parsed and evaluated according to precedence
using the rules listed above.
.if t .sp 0.5
.if n .sp 1
.LP
When used with \fBtest\fP or \fB[\fP, the \fB<\fP and \fB>\fP operators
sort lexicographically using ASCII ordering.
.RE
.PD
.TP
.B times
Print the accumulated user and system times for the shell and
for processes run from the shell.  The return status is 0.
.TP
\fBtrap\fP [\fB\-lp\fP] [[\fIarg\fP] \fIsigspec\fP ...]
The command
.I arg
is to be read and executed when the shell receives
signal(s)
.IR sigspec .
If
.I arg
is absent (and there is a single \fIsigspec\fP) or
.BR \- ,
each specified signal is
reset to its original disposition (the value it had
upon entrance to the shell).
If
.I arg
is the null string the signal specified by each
.I sigspec
is ignored by the shell and by the commands it invokes.
If
.I arg
is not present and
.B \-p
has been supplied, then the trap commands associated with each
.I sigspec
are displayed.
If no arguments are supplied or if only
.B \-p
is given,
.B trap
prints the list of commands associated with each signal.
The
.B \-l
option causes the shell to print a list of signal names and
their corresponding numbers.
Each
.I sigspec
is either
a signal name defined in <\fIsignal.h\fP>, or a signal number.
Signal names are case insensitive and the
.SM
.B SIG
prefix is optional.
.if t .sp 0.5
.if n .sp 1
If a
.I sigspec
is
.SM
.B EXIT
(0) the command
.I arg
is executed on exit from the shell.
If a
.I sigspec
is
.SM
.BR DEBUG ,
the command
.I arg
is executed before every \fIsimple command\fP, \fIfor\fP command,
\fIcase\fP command, \fIselect\fP command, every arithmetic \fIfor\fP
command, and before the first command executes in a shell function (see
.SM
.B SHELL GRAMMAR
.ie \n(zZ=1 in \fIbash(1)\fP).
.el above).
Refer to the description of the \fBextdebug\fP option to the
\fBshopt\fP builtin for details of its effect on the \fBDEBUG\fP trap.
If a
.I sigspec
is
.SM
.BR RETURN ,
the command
.I arg
is executed each time a shell function or a script executed with
the \fB.\fP or \fBsource\fP builtins finishes executing.
.if t .sp 0.5
.if n .sp 1
If a
.I sigspec
is
.SM
.BR ERR ,
the command
.I arg
is executed whenever
a pipeline (which may consist of a single simple
command), a list, or a compound command returns a
non\-zero exit status,
subject to the following conditions.
The
.SM
.B ERR
trap is not executed if the failed
command is part of the command list immediately following a
.B while
or
.B until
keyword,
part of the test in an
.I if
statement, part of a command executed in a
.B &&
or
.B ||
list except the command following the final \fB&&\fP or \fB||\fP,
any command in a pipeline but the last,
or if the command's return value is
being inverted using
.BR ! .
These are the same conditions obeyed by the \fBerrexit\fP (\fB\-e\fP) option.
.if t .sp 0.5
.if n .sp 1
Signals ignored upon entry to the shell cannot be trapped or reset.
Trapped signals that are not being ignored are reset to their original
values in a subshell or subshell environment when one is created.
The return status is false if any
.I sigspec
is invalid; otherwise
.B trap
returns true.
.TP
\fBtype\fP [\fB\-aftpP\fP] \fIname\fP [\fIname\fP ...]
With no options,
indicate how each
.I name
would be interpreted if used as a command name.
If the
.B \-t
option is used,
.B type
prints a string which is one of
.IR alias ,
.IR keyword ,
.IR function ,
.IR builtin ,
or
.I file
if
.I name
is an alias, shell reserved word, function, builtin, or disk file,
respectively.
If the
.I name
is not found, then nothing is printed, and an exit status of false
is returned.
If the
.B \-p
option is used,
.B type
either returns the name of the disk file
that would be executed if
.I name
were specified as a command name,
or nothing if
.if t \f(CWtype -t name\fP
.if n ``type -t name''
would not return
.IR file .
The
.B \-P
option forces a
.SM
.B PATH
search for each \fIname\fP, even if
.if t \f(CWtype -t name\fP
.if n ``type -t name''
would not return
.IR file .
If a command is hashed,
.B \-p
and
.B \-P
print the hashed value, which is not necessarily the file that appears
first in
.SM
.BR PATH .
If the
.B \-a
option is used,
.B type
prints all of the places that contain
an executable named
.IR name .
This includes aliases and functions,
if and only if the
.B \-p
option is not also used.
The table of hashed commands is not consulted
when using
.BR \-a .
The
.B \-f
option suppresses shell function lookup, as with the \fBcommand\fP builtin.
.B type
returns true if all of the arguments are found, false if
any are not found.
.TP
\fBulimit\fP [\fB\-HS\fP] \fB\-a\fP
.PD 0
.TP
\fBulimit\fP [\fB\-HS\fP] [\fB\-bcdefiklmnpqrstuvxPRT\fP [\fIlimit\fP]]
.PD
Provides control over the resources available to the shell and to
processes started by it, on systems that allow such control.
The \fB\-H\fP and \fB\-S\fP options specify that the hard or soft limit is
set for the given resource.
A hard limit cannot be increased by a non-root user once it is set;
a soft limit may be increased up to the value of the hard limit.
If neither \fB\-H\fP nor \fB\-S\fP is specified, both the soft and hard
limits are set.
The value of
.I limit
can be a number in the unit specified for the resource
or one of the special values
.BR hard ,
.BR soft ,
or
.BR unlimited ,
which stand for the current hard limit, the current soft limit, and
no limit, respectively.
If
.I limit
is omitted, the current value of the soft limit of the resource is
printed, unless the \fB\-H\fP option is given.  When more than one
resource is specified, the limit name and unit, if appropriate,
are printed before the value.
Other options are interpreted as follows:
.RS
.PD 0
.TP
.B \-a
All current limits are reported; no limits are set
.TP
.B \-b
The maximum socket buffer size
.TP
.B \-c
The maximum size of core files created
.TP
.B \-d
The maximum size of a process's data segment
.TP
.B \-e
The maximum scheduling priority ("nice")
.TP
.B \-f
The maximum size of files written by the shell and its children
.TP
.B \-i
The maximum number of pending signals
.TP
.B \-k
The maximum number of kqueues that may be allocated
.TP
.B \-l
The maximum size that may be locked into memory
.TP
.B \-m
The maximum resident set size (many systems do not honor this limit)
.TP
.B \-n
The maximum number of open file descriptors (most systems do not
allow this value to be set)
.TP
.B \-p
The pipe size in 512-byte blocks (this may not be set)
.TP
.B \-q
The maximum number of bytes in POSIX message queues
.TP
.B \-r
The maximum real-time scheduling priority
.TP
.B \-s
The maximum stack size
.TP
.B \-t
The maximum amount of cpu time in seconds
.TP
.B \-u
The maximum number of processes available to a single user
.TP
.B \-v
The maximum amount of virtual memory available to the shell and, on
some systems, to its children
.TP
.B \-x
The maximum number of file locks
.TP
.B \-P
The maximum number of pseudoterminals
.TP
.B \-R
The maximum time a real-time process can run before blocking, in microseconds
.TP
.B \-T
The maximum number of threads
.PD
.PP
If
.I limit
is given, and the
.B \-a
option is not used,
\fIlimit\fP is the new value of the specified resource.
If no option is given, then
.B \-f
is assumed.  Values are in 1024-byte increments, except for
.BR \-t ,
which is in seconds;
.BR \-R ,
which is in microseconds;
.BR \-p ,
which is in units of 512-byte blocks;
.BR \-P ,
.BR \-T ,
.BR \-b ,
.BR \-k ,
.BR \-n ,
and
.BR \-u ,
which are unscaled values;
and, when in posix mode,
.B \-c
and
.BR \-f ,
which are in 512-byte increments.
The return status is 0 unless an invalid option or argument is supplied,
or an error occurs while setting a new limit.
.RE
.TP
\fBumask\fP [\fB\-p\fP] [\fB\-S\fP] [\fImode\fP]
The user file-creation mask is set to
.IR mode .
If
.I mode
begins with a digit, it
is interpreted as an octal number; otherwise
it is interpreted as a symbolic mode mask similar
to that accepted by
.IR chmod (1).
If
.I mode
is omitted, the current value of the mask is printed.
The
.B \-S
option causes the mask to be printed in symbolic form; the
default output is an octal number.
If the
.B \-p
option is supplied, and
.I mode
is omitted, the output is in a form that may be reused as input.
The return status is 0 if the mode was successfully changed or if
no \fImode\fP argument was supplied, and false otherwise.
.TP
\fBunalias\fP [\-\fBa\fP] [\fIname\fP ...]
Remove each \fIname\fP from the list of defined aliases.  If
.B \-a
is supplied, all alias definitions are removed.  The return
value is true unless a supplied
.I name
is not a defined alias.
.TP
\fBunset\fP [\-\fBfv\fP] [\-\fBn\fP] [\fIname\fP ...]
For each
.IR name ,
remove the corresponding variable or function.
If the
.B \-v
option is given, each
.I name
refers to a shell variable, and that variable is removed.
Read-only variables may not be unset.
If
.B \-f
is specified, each
.I name
refers to a shell function, and the function definition
is removed.
If the
.B \-n
option is supplied, and \fIname\fP is a variable with the \fInameref\fP
attribute, \fIname\fP will be unset rather than the variable it
references.
\fB\-n\fP has no effect if the \fB\-f\fP option is supplied.
If no options are supplied, each \fIname\fP refers to a variable; if
there is no variable by that name, a function with that name, if any, is
unset.
Each unset variable or function is removed from the environment
passed to subsequent commands.
If any of
.SM
.BR BASH_ALIASES ,
.SM
.BR BASH_ARGV0 ,
.SM
.BR BASH_CMDS ,
.SM
.BR BASH_COMMAND ,
.SM
.BR BASH_SUBSHELL ,
.SM
.BR BASHPID ,
.SM
.BR COMP_WORDBREAKS ,
.SM
.BR DIRSTACK ,
.SM
.BR EPOCHREALTIME ,
.SM
.BR EPOCHSECONDS ,
.SM
.BR FUNCNAME ,
.SM
.BR GROUPS ,
.SM
.BR HISTCMD ,
.SM
.BR LINENO ,
.SM
.BR RANDOM ,
.SM
.BR SECONDS ,
or
.SM
.B SRANDOM
are unset, they lose their special properties, even if they are
subsequently reset.  The exit status is true unless a
.I name
is readonly or may not be unset.
.TP
\fBwait\fP [\fB\-fn\fP] [\fP\-p\fP \fIvarname\fP] [\fIid ...\fP]
Wait for each specified child process and return its termination status.
Each
.I id
may be a process
ID or a job specification; if a job spec is given, all processes
in that job's pipeline are waited for.  If
.I id
is not given,
\fBwait\fP waits for all running background jobs and
the last-executed process substitution, if its process id is the same as
\fB$!\fP,
and the return status is zero.
If the \fB\-n\fP option is supplied,
\fBwait\fP waits for a single job
from the list of \fIid\fPs or, if no \fIid\fPs are supplied, any job,
to complete and returns its exit status.
If none of the supplied arguments is a child of the shell, or if no arguments
are supplied and the shell has no unwaited-for children, the exit status
is 127.
If the \fB\-p\fP option is supplied, the process or job identifier of the job
for which the exit status is returned is assigned to the variable
\fIvarname\fP named by the option argument.
The variable will be unset initially, before any assignment.
This is useful only when the \fB\-n\fP option is supplied.
Supplying the \fB\-f\fP option, when job control is enabled,
forces \fBwait\fP to wait for \fIid\fP to terminate before returning
its status, instead of returning when it changes status.
If
.I id
specifies a non-existent process or job, the return status is 127.
If \fBwait\fP is interrupted by a signal, the return status will be greater
than 128, as described under
.B SIGNALS
.ie \n(zZ=1 in \fIbash(1)\fP.
.el above.
Otherwise, the return status is the exit status of the last
process or job waited for.
.SH "SHELL COMPATIBILITY MODE"
Bash-4.0 introduced the concept of a \fIshell compatibility level\fP,
specified as a set of options to the shopt builtin (
.BR compat31 ,
.BR compat32 ,
.BR compat40 ,
.BR compat41 ,
and so on).
There is only one current
compatibility level -- each option is mutually exclusive.
The compatibility level is intended to allow users to select behavior
from previous versions that is incompatible with newer versions
while they migrate scripts to use current features and
behavior. It's intended to be a temporary solution.
.PP
This section does not mention behavior that is standard for a particular
version (e.g., setting \fBcompat32\fP means that quoting the rhs of the regexp
matching operator quotes special regexp characters in the word, which is
default behavior in bash-3.2 and subsequent versions). 
.PP
If a user enables, say, \fBcompat32\fP, it may affect the behavior of other
compatibility levels up to and including the current compatibility level.
The idea is that each compatibility level controls behavior that changed
in that version of \fBbash\fP,
but that behavior may have been present in earlier versions.
For instance, the change to use locale-based comparisons with the \fB[[\fP
command came in bash-4.1, and earlier versions used ASCII-based comparisons,
so enabling \fBcompat32\fP will enable ASCII-based comparisons as well.
That granularity may not be sufficient for
all uses, and as a result users should employ compatibility levels carefully.
Read the documentation for a particular feature to find out the
current behavior.
.PP
Bash-4.3 introduced a new shell variable:
.SM
.BR BASH_COMPAT .
The value assigned
to this variable (a decimal version number like 4.2, or an integer
corresponding to the \fBcompat\fP\fINN\fP option, like 42) determines the
compatibility level.
.PP
Starting with bash-4.4, Bash has begun deprecating older compatibility
levels.
Eventually, the options will be removed in favor of
.SM
.BR BASH_COMPAT .
.PP
Bash-5.0 is the final version for which there will be an individual shopt
option for the previous version. Users should use
.SM
.B BASH_COMPAT
on bash-5.0 and later versions.
.PP
The following table describes the behavior changes controlled by each
compatibility level setting.
The \fBcompat\fP\fINN\fP tag is used as shorthand for setting the
compatibility level
to \fINN\fP using one of the following mechanisms.
For versions prior to bash-5.0, the compatibility level may be set using
the corresponding \fBcompat\fP\fINN\fP shopt option.
For bash-4.3 and later versions, the
.SM
.B BASH_COMPAT
variable is preferred,
and it is required for bash-5.1 and later versions.
.TP
\fBcompat31\fP
.PD 0
.RS
.IP \(bu
quoting the rhs of the \fB[[\fP command's regexp matching operator (=~)
has no special effect
.RE
.PD
.TP
\fBcompat32\fP
.PD 0
.RS
.IP \(bu
interrupting a command list such as "a ; b ; c" causes the execution
of the next command in the list (in bash-4.0 and later versions,
the shell acts as if it received the interrupt, so
interrupting one command in a list aborts the execution of the
entire list)
.RE
.PD
.TP
\fBcompat40\fP
.PD 0
.RS
.IP \(bu
the \fB<\fP and \fB>\fP operators to the \fB[[\fP command do not
consider the current locale when comparing strings; they use ASCII
ordering.
Bash versions prior to bash-4.1 use ASCII collation and
.IR strcmp (3);
bash-4.1 and later use the current locale's collation sequence and
.IR strcoll (3).
.RE
.PD
.TP
\fBcompat41\fP
.PD 0
.RS
.IP \(bu
in \fIposix\fP mode, \fBtime\fP may be followed by options and still be
recognized as a reserved word (this is POSIX interpretation 267)
.IP \(bu
in \fIposix\fP mode, the parser requires that an even number of single
quotes occur in the \fIword\fP portion of a double-quoted
parameter expansion and treats them specially, so that characters within
the single quotes are considered quoted
(this is POSIX interpretation 221)
.RE
.PD
.TP
\fBcompat42\fP
.PD 0
.RS
.IP \(bu
the replacement string in double-quoted pattern substitution does not
undergo quote removal, as it does in versions after bash-4.2
.IP \(bu
in posix mode, single quotes are considered special when expanding
the \fIword\fP portion of a double-quoted parameter expansion
and can be used to quote a closing brace or other special character
(this is part of POSIX interpretation 221);
in later versions, single quotes
are not special within double-quoted word expansions
.RE
.PD
.TP
\fBcompat43\fP
.PD 0
.RS
.IP \(bu
the shell does not print a warning message if an attempt is made to
use a quoted compound assignment as an argument to declare
(e.g., declare -a foo=\(aq(1 2)\(aq). Later versions warn that this usage is
deprecated
.IP \(bu
word expansion errors are considered non-fatal errors that cause the
current command to fail, even in posix mode
(the default behavior is to make them fatal errors that cause the shell
to exit)
.IP \(bu
when executing a shell function, the loop state (while/until/etc.)
is not reset, so \fBbreak\fP or \fBcontinue\fP in that function will break
or continue loops in the calling context. Bash-4.4 and later reset
the loop state to prevent this
.RE
.PD
.TP
\fBcompat44\fP
.PD 0
.RS
.IP \(bu
the shell sets up the values used by
.SM
.B BASH_ARGV
and
.SM
.B BASH_ARGC
so they can expand to the shell's positional parameters even if extended
debugging mode is not enabled
.IP \(bu
a subshell inherits loops from its parent context, so \fBbreak\fP
or \fBcontinue\fP will cause the subshell to exit.
Bash-5.0 and later reset the loop state to prevent the exit
.IP \(bu
variable assignments preceding builtins like \fBexport\fP and \fBreadonly\fP
that set attributes continue to affect variables with the same
name in the calling environment even if the shell is not in posix
mode
.RE
.PD
.TP
\fBcompat50\fP
.PD 0
.RS
.IP \(bu
Bash-5.1 changed the way
.SM
.B $RANDOM
is generated to introduce slightly
more randomness. If the shell compatibility level is set to 50 or
lower, it reverts to the method from bash-5.0 and previous versions,
so seeding the random number generator by assigning a value to
.SM
.B RANDOM
will produce the same sequence as in bash-5.0
.IP \(bu
If the command hash table is empty, bash versions prior to bash-5.1
printed an informational message to that effect, even when producing
output that can be reused as input. Bash-5.1 suppresses that message
when the \fB\-l\fP option is supplied.
.RE
.PD
.TP
\fBcompat51\fP
.PD 0
.RS
.IP \(bu
The \fBunset\fP builtin treats attempts to unset array subscripts \fB@\fP
and \fB*\fP differently depending on whether the array is indexed or
associative, and differently than in previous versions.
.RE
.PD
.\" bash_builtins
.zY
.lf 23 ./builtins.1
.SH SEE ALSO
bash(1), sh(1)