Imported from ../bash-1.14.7.tar.gz.

[thirdparty/bash.git] / documentation / bash.1

.\"
.\" MAN PAGE COMMENTS to
.\"
.\"	Chet Ramey
.\"	Information Network Services
.\"	Case Western Reserve University
.\"	chet@ins.CWRU.Edu
.\"
.\"	Last Change: Fri May  5 10:44:39 EDT 1995
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.TH BASH 1 "1995 May 5" GNU
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..
.SH NAME
bash \- GNU Bourne\-Again SHell
.SH SYNOPSIS
.B bash
[options]
[file]
.SH COPYRIGHT
.if n Bash is Copyright (C) 1989, 1991 by the Free Software Foundation, Inc.
.if t Bash is Copyright \(co 1989, 1991 by the Free Software Foundation, Inc.
.SH DESCRIPTION
.B Bash
is an \fBsh\fR\-compatible command language interpreter that
executes commands read from the standard input or from a file.
.B Bash
also incorporates useful features from the \fIKorn\fP and \fIC\fP
shells (\fBksh\fP and \fBcsh\fP).
.PP
.B Bash
is ultimately intended to be a conformant implementation of the IEEE
Posix Shell and Tools specification (IEEE Working Group 1003\.2).
.SH OPTIONS
In addition to the single\-character shell options documented in the
description of the \fBset\fR builtin command, \fBbash\fR
interprets the following flags when it is invoked:
.PP
.PD 0
.TP 10
.BI \-c "\| string\^"
If the 
.B \-c
flag is present, then commands are read from
.IR string .
If there are arguments after the
.IR string ,
they are assigned to the positional parameters, starting with
.BR $0 .
.TP
.B \-i
If the
.B \-i
flag is present, the shell is
.IR interactive .
.TP
.B \-s
If the
.B \-s
flag is present, or if no arguments remain after option
processing, then commands are read from the standard input.
This option allows the positional parameters to be set
when invoking an interactive shell.
.TP
.B \-
A single
.B \-
signals the end of options and disables further option processing.
Any arguments after the
.B \-
are treated as filenames and arguments.  An argument of
.B \-\-
is equivalent to an argument of \fB\-\fP.
.PD
.PP
.B Bash
also interprets a number of multi\-character options.  These options must
appear on the command line before the single\-character options to be
recognized.
.PP
.PD 0
.TP 10
.B \-norc
Do not read and execute the personal initialization file
.I ~/.bashrc
if the shell is interactive.
This option is on by default if the shell is invoked as
.BR sh .
.TP
.B \-noprofile
Do not read either the system\-wide startup file
.FN /etc/profile
or any of the personal initialization files
.IR ~/.bash_profile ,
.IR ~/.bash_login ,
or
.IR ~/.profile .
By default,
.B bash
normally reads these files when it is invoked as a login shell (see
.SM
.B INVOCATION
below).
.TP
\fB\-rcfile\fP \fIfile\fP
Execute commands from
.I file
instead of the standard personal initialization file
.IR ~/.bashrc ,
if the shell is interactive (see
.SM
.B INVOCATION
below).
.TP
.B \-version
Show the version number of this instance of
.B bash
when starting.
.TP
.B \-quiet
Do not be verbose when starting up (do not show the shell version or any
other information).  This is the default.
.TP
.B \-login
Make
.B bash
act as if it had been invoked as a login shell.
.TP
.B \-nobraceexpansion
Do not perform curly brace expansion (see
.B Brace Expansion
below).
.TP
.B \-nolineediting
Do not use the GNU
.I readline
library to read command lines if interactive.
.TP
.B \-posix
Change the behavior of bash where the default operation differs
from the Posix 1003.2 standard to match the standard
.PD
.SH ARGUMENTS
If arguments remain after option processing, and neither the
.B \-c
nor the
.B \-s
option has been supplied, the first argument is assumed to
be the name of a file containing shell commands.  If
.B bash
is invoked in this fashion, 
.B $0
is set to the name of the file, and the positional parameters
are set to the remaining arguments.
.B Bash
reads and executes commands from this file, then exits.
.B Bash's
exit status is the exit status of the last command executed
in the script.
.SH DEFINITIONS
.PD 0
.TP
.B blank 
A space or tab.
.TP
.B word
A sequence of characters considered as a single unit by the shell.
Also known as a
.BR token .
.TP
.B name
A 
.I word
consisting only of alphanumeric characters and underscores, and
beginning with an alphabetic character or an underscore.  Also
referred to as an
.BR identifier .
.TP
.B metacharacter
A character that, when unquoted, separates words.  One of the following:
.br
.RS
.PP
.if t \fB|  &  ;  (  )  <  >  space  tab\fP
.if n \fB|  & ; ( ) < > space tab\fP
.RE
.PP
.TP
.B control operator
A \fItoken\fP that performs a control function.  It is one of the following
symbols:
.RS
.PP
.if t \fB\(bv\|\(bv  &  &&  ;  ;;  (  )  |  <newline>\fP
.if n \fB|| & && ; ;; ( ) | <newline>\fP
.RE
.PD
.SH "RESERVED WORDS"
\fIReserved words\fP are words that have a special meaning to the shell.
The following words are recognized as reserved when unquoted and either
the first word of a simple command (see
.SM
.B SHELL GRAMMAR
below) or the third word of a 
.B case 
or
.B for
command:
.if t .RS
.PP
.B
.if n ! case  do done elif else esac fi for function if in select then until while { }
.if t !    case    do    done    elif    else    esac    fi    for    function    if    in    select    then    until    while    {    }
.if t .RE
.RE
.SH "SHELL GRAMMAR"
.SS Simple Commands
.PP
A \fIsimple command\fP is a sequence of optional variable assignments
followed by \fIblank\fP\-separated words and redirections, and
terminated by a \fIcontrol operator\fP.  The first word
specifies the command to be executed.  The remaining words are
passed as arguments to the invoked command.
.PP
The return value of a \fIsimple command\fP is its exit status, or
128+\fIn\^\fP if the command is terminated by signal
.IR n .
.SS Pipelines
.PP
A \fIpipeline\fP is a sequence of one or more commands separated by
the character
.BR | .
The format for a pipeline is:
.RS
.PP
[ ! ] \fIcommand\fP [ \fB|\fP \fIcommand2\fP ... ]
.RE
.PP
The standard output of
.I command
is connected to the standard input of
.IR command2 .
This connection is performed before any redirections specified by the
command (see
.SM
.B REDIRECTION
below).
.PP
If the reserved word
.B !
precedes a pipeline, the exit status of that
pipeline is the logical NOT of the exit status of the last command.
Otherwise, the status of the pipeline is the exit status of the last
command.  The shell waits for all commands in the pipeline to
terminate before returning a value.
.PP
Each command in a pipeline is executed as a separate process (i.e., in a
subshell).
.SS Lists
.PP
A \fIlist\fP is a sequence of one or more pipelines separated by one
of the operators
.BR ; ,
.BR & ,
.BR && ,
or
.BR \(bv\|\(bv ,
and terminated by one of
.BR ; ,
.BR & ,
or
.BR <newline> .
.PP
Of these list operators,
.B &&
and
.B \(bv\|\(bv
have equal precedence, followed by
.B ;
and
.BR &,
which have equal precedence.
.PP
If a command is terminated by the control operator
.BR & ,
the shell executes the command in the \fIbackground\fP
in a subshell.  The shell does not wait for the command to
finish, and the return status is 0.  Commands separated by a
.B ;
are executed sequentially; the shell waits for each
command to terminate in turn.  The return status is the
exit status of the last command executed.
.PP
The control operators
.B &&
and
.B \(bv\|\(bv
denote AND lists and OR lists, respectively.
An AND list has the form
.RS
.PP
\fIcommand\fP \fB&&\fP \fIcommand2\fP
.RE
.PP
.I command2
is executed if, and only if,
.I command
returns an exit status of zero.
.PP
An OR list has the form
.RS
.PP
\fIcommand\fP \fB\(bv\|\(bv\fP \fIcommand2\fP
.PP
.RE
.PP
.I command2
is executed if and only if
.I command
returns a non\-zero exit status.  The return status of
AND and OR lists is the exit status of the last command
executed in the list.
.SS Compound Commands
.PP
A \fIcompound command\fP is one of the following:
.TP
(\fIlist\fP)
\fIlist\fP is executed in a subshell.  Variable assignments and builtin
commands that affect the shell's environment do not remain in effect
after the command completes.  The return status is the exit status of
\fIlist\fP.
.TP
{ \fIlist\fP; }
\fIlist\fP is simply executed in the current shell environment.  This is
known as a \fIgroup command\fP.  The return status is the exit status of
\fIlist\fP.
.TP
\fBfor\fP \fIname\fP [ \fBin\fP \fIword\fP; ] \fBdo\fP \fIlist\fP ; \fBdone\fP
The list of words following \fBin\fP is expanded, generating a list
of items.  The variable \fIname\fP is set to each element of this list
in turn, and \fIlist\fP is executed each time.  If the \fBin\fP
\fIword\fP is omitted, the \fBfor\fP command executes \fIlist\fP 
once for each positional parameter that is set (see
.SM
.B PARAMETERS
below).
.TP
\fBselect\fP \fIname\fP [ \fBin\fP \fIword\fP; ] \fBdo\fP \fIlist\fP ; \fBdone\fP
The list of words following \fBin\fP is expanded, generating a list
of items.  The set of expanded words is printed on the standard
error, each preceded by a number.  If the \fBin\fP
\fIword\fP is omitted, the positional parameters are printed (see
.SM
.B PARAMETERS
below).  The
.B PS3
prompt is then displayed and a line read from the standard input.
If the line consists of the number corresponding to one of
the displayed words, then the value of
.I name
is set to that word.  If the line is empty, the words and prompt
are displayed again.  If EOF is read, the command completes.  Any
other value read causes
.I name
to be set to null.  The line read is saved in the variable
.BR REPLY .
The
.I list
is executed after each selection until a
.B break
or
.B return
command is executed.
The exit status of
.B select
is the exit status of the last command executed in
.IR list ,
or zero if no commands were executed.
.TP
\fBcase\fP \fIword\fP \fBin\fP [ \fIpattern\fP [ \fB|\fP \fIpattern\fP ] \
... ) \fIlist\fP ;; ] ... \fBesac\fP
A \fBcase\fP command first expands \fIword\fP, and tries to match
it against each \fIpattern\fP in turn, using the same matching rules
as for pathname expansion (see
.B Pathname Expansion
below).  When a match is found, the
corresponding \fIlist\fP is executed.  After the first match, no
subsequent matches are attempted.  The exit status is zero if no
patterns are matches.  Otherwise, it is the exit status of the
last command executed in \fIlist\fP.
.TP
\fBif\fP \fIlist\fP \fBthen\fP \fIlist\fP \
[ \fBelif\fP \fIlist\fP \fBthen\fP \fIlist\fP ] ... \
[ \fBelse\fP \fIlist\fP ] \fBfi\fP
The
.B if 
.I list
is executed.  If its exit status is zero, the
\fBthen\fP \fIlist\fP is executed.  Otherwise, each \fBelif\fP
\fIlist\fP is executed in turn, and if its exit status is zero,
the corresponding \fBthen\fP \fIlist\fP is executed and the
command completes.  Otherwise, the \fBelse\fP \fIlist\fP is
executed, if present.  The exit status is the exit status of the
last command executed, or zero if no condition tested true.
.TP
.PD 0
\fBwhile\fP \fIlist\fP \fBdo\fP \fIlist\fP \fBdone\fP
.TP
\fBuntil\fP \fIlist\fP \fBdo\fP \fIlist\fP \fBdone\fP
.PD
The \fBwhile\fP command continuously executes the \fBdo\fP
\fIlist\fP as long as the last command in \fIlist\fP returns
an exit status of zero.  The \fBuntil\fP command is identical
to the \fBwhile\fP command, except that the test is negated;
the
.B do
.I list
is executed as long as the last command in
.I list
returns a non\-zero exit status.
The exit status of the \fBwhile\fP and \fBuntil\fP commands
is the exit status
of the last \fBdo\fP \fIlist\fP command executed, or zero if
none was executed.
.TP
[ \fBfunction\fP ] \fIname\fP () { \fIlist\fP; }
This defines a function named \fIname\fP.  The \fIbody\fP of the
function is the
.I list
of commands between { and }.  This list
is executed whenever \fIname\fP is specified as the
name of a simple command.  The exit status of a function is
the exit status of the last command executed in the body.  (See
.SM
.B FUNCTIONS
below.)
.SH COMMENTS
In a non\-interactive shell, or an interactive shell in which the
.B -o interactive\-comments
option to the \fBset\fP builtin is enabled, a word beginning with
.B #
causes that word and all remaining characters on that line to
be ignored.  An interactive shell without the
.B -o interactive\-comments
option enabled does not allow comments.
.SH QUOTING
\fIQuoting\fP is used to remove the special meaning of certain
characters or words to the shell.  Quoting can be used to 
disable special treatment for special characters, to prevent
reserved words from being recognized as such, and to prevent
parameter expansion.
.PP
Each of the \fImetacharacters\fP listed above under
.SM
.B DEFINITIONS
has special meaning to the shell and must be quoted if they are to
represent themselves.  There are three quoting mechanisms: the
.IR "escape character" ,
single quotes, and double quotes.
.PP
A non-quoted backslash (\fB\e\fP) is the
.IR "escape character" .
It preserves the literal value of the next character that follows,
with the exception of <newline>.  If a \fB\e\fP<newline> pair
appears, and the backslash is not quoted, the \fB\e\fP<newline>
is treated as a line continuation (that is, it is effectively ignored).
.PP
Enclosing characters in single quotes preserves the literal value
of each character within the quotes.  A single quote may not occur
between single quotes, even when preceded by a backslash.
.PP
Enclosing characters in double quotes preserves the literal value
of all characters within the quotes, with the exception of
.BR $ ,
.BR ` ,
and
.BR \e .
The characters
.B $
and
.B `
retain their special meaning within double quotes.  The backslash
retains its special meaning only when followed by one of the following
characters:
.BR $ ,
.BR ` ,
\^\fB"\fP\^,
.BR \e ,
or
.BR <newline> .
A double quote may be quoted within double quotes by preceding it with
a backslash.
.PP
The special parameters
.B *
and
.B @
have special meaning when in double
quotes (see
.SM
.B PARAMETERS
below).
.SH PARAMETERS
A
.I parameter
is an entity that stores values, somewhat like a
variable in a conventional programming language.  It can be a
.IR name ,
a number, or one of the special characters listed below under
.BR "Special Parameters" .
For the shell's purposes, a
.I variable
is a parameter denoted by a
.IR name .
.PP
A parameter is set if it has been assigned a value.  The null string is
a valid value.  Once a variable is set, it may be unset only by using
the
.B unset
builtin command (see
.SM
.B SHELL BUILTIN COMMANDS
below).
.PP
A
.I variable
may be assigned to by a statement of the form
.RS
.PP
\fIname\fP=[\fIvalue\fP]
.RE
.PP
If
.I value
is not given, the variable is assigned the null string.  All
.I values
undergo tilde expansion, parameter and variable expansion, command
substitution, arithmetic expansion, and quote removal.  If
the variable has its
.B \-i
attribute set (see
.B declare
below in
.SM
.BR "SHELL BUILTIN COMMANDS" )
then
.I value
is subject to arithmetic expansion even if the $[...] syntax does
not appear.  Word splitting is not performed, with the exception
of \fB"$@"\fP as explained below under
.BR "Special Parameters" .
Pathname expansion is not performed.
.SS Positional Parameters
.PP
A
.I positional parameter
is a parameter denoted by one or more
digits, other than the single digit 0.  Positional parameters are
assigned from the shell's arguments when it is invoked,
and may be reassigned using the
.B set
builtin command.  Positional parameters may not be assigned to
with assignment statements.  The positional parameters are
temporarily replaced when a shell function is executed (see
.SM
.B FUNCTIONS
below).
.PP
When a positional parameter consisting of more than a single
digit is expanded, it must be enclosed in braces (see
.SM
.B EXPANSION
below).
.SS Special Parameters
.PP
The shell treats several parameters specially.  These parameters may
only be referenced; assignment to them is not allowed.
.PD 0
.TP
.B *
Expands to the positional parameters, starting from one.  When the
expansion occurs within double quotes, it expands to a single word
with the value of each parameter separated by the first character
of the 
.SM
.B IFS
special variable.  That is, ``\fB$*\fP'' is equivalent
to ``\fB$1\fP\fIc\fP\fB$2\fP\fIc\fP\fB...\fP'', where
.I c
is the first character of the value of the
.SM
.B IFS
variable.  If
.SM
.B IFS
is null or unset, the parameters are separated by spaces.
.TP
.B @
Expands to the positional parameters, starting from one.  When the
expansion occurs within double quotes, each parameter expands as a
separate word.  That is, ``
.BR $@ ''
is equivalent to
``\fB$1\fP'' ``\fB$2\fP'' ...
When there are no positional parameters, ``\fB$@\fP'' and 
.B $@
expand to nothing (i.e., they are removed).
.TP
.B #
Expands to the number of positional parameters in decimal.
.TP
.B ?
Expands to the status of the most recently executed foreground
pipeline.
.TP
.B \-
Expands to the current option flags as specified upon invocation, 
by the
.B set
builtin command, or those set by the shell itself
(such as the
.B \-i
flag).
.TP
.B $
Expands to the process ID of the shell.  In a () subshell, it
expands to the process ID of the current shell, not the
subshell.
.TP
.B !
Expands to the process ID of the most recently executed background
(asynchronous) command.
.TP
.B 0
Expands to the name of the shell or shell script.  This is set at
shell initialization.  If
.B bash
is invoked with a file of commands,
.B $0
is set to the name of that file.  If
.B bash
is started with the
.B \-c
option, then
.B $0
is set to the first argument after the string to be
executed, if one is present.  Otherwise, it is set
to the pathname used to invoke
.BR bash ,
as given by argument zero.
.TP
.B _
Expands to the last argument to the previous command, after expansion.
Also set to the full pathname of each command executed and placed in
the environment exported to that command.
.PD
.SS Shell Variables
.PP
The following variables are set by the shell:
.PP
.PD 0
.TP
.B PPID
The process ID of the shell's parent.
.TP
.B PWD
The current working directory as set by the
.B cd
command.
.TP
.B OLDPWD
The previous working directory as set by the
.B cd
command.
.TP
.B REPLY
Set to the line of input read by the
.B read
builtin command when no arguments are supplied.
.TP
.B UID
Expands to the user ID of the current user, initialized at shell startup.
.TP
.B EUID
Expands to the effective user ID of the current user, initialized at
shell startup.
.TP
.B BASH
Expands to the full pathname used to invoke this instance of
.BR bash .
.TP
.B BASH_VERSION
Expands to the version number of this instance of
.BR bash .
.TP
.B SHLVL
Incremented by one each time an instance of
.B bash
is started.
.TP
.B RANDOM
Each time this parameter is referenced, a random integer is
generated.  The sequence of random numbers may be initialized by assigning
a value to
.SM
.BR RANDOM .
If
.SM
.B RANDOM
is unset, it loses its special properties, even if it is
subsequently reset.
.TP
.B SECONDS
Each time this parameter is
referenced, the number of seconds since shell invocation is returned.  If a
value is assigned to 
.SM
.BR SECONDS ,
the value returned upon subsequent
references is
the number of seconds since the assignment plus the value assigned.
If
.SM
.B SECONDS
is unset, it loses its special properties, even if it is
subsequently reset.
.TP
.B LINENO
Each time this parameter is referenced, the shell substitutes
a decimal number representing the current sequential line number
(starting with 1) within a script or function.  When not in a
script or function, the value substituted is not guaranteed to
be meaningful.  When in a function, the value is not
the number of the source line that the command appears
on (that information has been lost by the time the function is
executed), but is an approximation of the number of
.I simple commands
executed in the current function.
If
.SM
.B LINENO
is unset, it loses its special properties, even if it is
subsequently reset.
.TP
.B HISTCMD
The history number, or index in the history list, of the current
command.  If
.SM
.B HISTCMD
is unset, it loses its special properties, even if it is
subsequently reset.
.TP
.B OPTARG
The value of the last option argument processed by the
.B getopts
builtin command (see
.SM
.B SHELL BUILTIN COMMANDS
below).
.TP
.B OPTIND
The index of the next argument to be processed by the
.B getopts
builtin command (see
.SM
.B SHELL BUILTIN COMMANDS
below).
.TP
.B HOSTTYPE
Automatically set to a string that uniquely
describes the type of machine on which
.B bash
is executing.  The default is system-dependent.
.TP
.B OSTYPE
Automatically set to a string that
describes the operating system on which
.B bash
is executing.  The default is system-dependent.
.PD
.PP
The following variables are used by the shell.  In some cases,
.B bash
assigns a default value to a variable; these cases are noted
below.
.PP
.PD 0
.TP
.B IFS
The
.I Internal Field Separator
that is used
for word splitting after expansion and to
split lines into words with the
.B read
builtin command.  The default value is
``<space><tab><newline>''.
.TP
.B PATH
The search path for commands.  It
is a colon-separated list of directories in which
the shell looks for commands (see
.SM
.B COMMAND EXECUTION
below).  The default path is system\-dependent,
and is set by the administrator who installs
.BR bash .
A common value is ``/usr/gnu/bin:/usr/local/bin:/usr/ucb:/bin:/usr/bin:.''.
.TP
.B HOME
The home directory of the current user; the default argument for the
\fBcd\fP builtin command.
.TP
.B CDPATH
The search path for the
.B cd
command.  This is a colon-separated
list of directories in which the shell looks for destination directories
specified by the
.B cd
command.  A sample value is
``.:~:/usr''.
.TP
.B ENV
If this parameter is set when \fBbash\fP is executing a shell script,
its value is interpreted as a filename containing commands to
initialize the shell, as in
.IR .bashrc .
The value of
.SM
.B ENV
is subjected to parameter expansion, command substitution, and arithmetic
expansion before being interpreted as a pathname.
.SM
.B PATH
is not used to search for the resultant pathname.
.TP
.B MAIL
If this parameter is set to a filename and the
.SM
.B MAILPATH
variable is not set,
.B bash
informs the user of the arrival of mail in the specified file.
.TP
.B MAILCHECK
Specifies how
often (in seconds)
.B bash
checks for mail.  The default is 60 seconds.  When it is time to check
for mail, the shell does so before prompting.
If this variable is unset, the shell disables mail checking.
.TP
.B MAILPATH
A colon-separated list of pathnames to be checked for mail. 
The message to be printed may be specified by separating the pathname from
the message with a `?'.  $_ stands for the name of the current mailfile. 
Example:
.RS
.PP
\fBMAILPATH\fP='/usr/spool/mail/bfox?"You have mail":~/shell-mail?"$_ has mail!"'
.PP
.B Bash
supplies a default value for this variable, but the location of the user
mail files that it uses is system dependent (e.g., /usr/spool/mail/\fB$USER\fP).
.RE
.TP
.B MAIL_WARNING
If set, and a file that \fBbash\fP is checking for mail has been
accessed since the last time it was checked, the message ``The mail in
\fImailfile\fP has been read'' is printed.
.TP
.B PS1
The value of this parameter is expanded (see
.SM
.B PROMPTING
below) and used as the primary prompt string.  The default value is
``\fBbash\e$ \fP''.
.TP
.B PS2
The value of this parameter is expanded
and used as the secondary prompt string.  The default is
``\fB> \fP''.
.TP
.B PS3
The value of this parameter is used as the prompt for the
.I select
command (see
.SM
.B SHELL GRAMMAR
above).
.TP
.B PS4
The value of this parameter is expanded
and the value is printed before each command
.B bash
displays during an execution trace.  The first character of
.SM
.B PS4
is replicated multiple times, as necessary, to indicate multiple
levels of indirection.  The default is ``\fB+ \fP''.
.TP
.B HISTSIZE
The number of commands to remember in the command history (see
.SM
.B HISTORY
below).  The default value is 500.
.TP
.B HISTFILE
The name of the file in which command history is saved.  (See
.SM
.B HISTORY
below.)  The default value is \fI~/.bash_history\fP.  If unset, the
command history is not saved when an interactive shell exits.
.TP
.B HISTFILESIZE
The maximum number of lines contained in the history file.  When this
variable is assigned a value, the history file is truncated, if
necessary, to contain no more than that number of lines.  The default
value is 500.
.TP
.B OPTERR
If set to the value 1,
.B bash
displays error messages generated by the
.B getopts
builtin command (see
.SM
.B SHELL BUILTIN COMMANDS
below).
.SM
.B OPTERR
is initialized to 1 each time the shell is invoked or a shell
script is executed.
.TP
.B PROMPT_COMMAND
If set, the value is executed as a command prior to issuing each primary
prompt.
.TP
.B IGNOREEOF
Controls the
action of the shell on receipt of an
.SM
.B EOF
character as the sole input.  If set, the value is the number of
consecutive
.SM
.B EOF
characters typed as the first characters on an input line before
.B bash
exits.  If the variable exists but does not have a numeric value, or
has no value, the default value is 10.  If it does not exist,
.SM
.B EOF
signifies the end of input to the shell.  This is only in effect for
interactive shells.
.TP
.B TMOUT
If set to a value greater than zero, the value is interpreted as the
number of seconds to wait for input after issuing the primary prompt.
.B Bash
terminates after waiting for that number of seconds if input does
not arrive.
.TP
.B FCEDIT
The default editor for the
.B fc
builtin command.
.TP
.B FIGNORE
A colon-separated list of suffixes to ignore when performing
filename completion (see
.SM
.B READLINE
below).  A filename whose suffix matches one of the entries in 
.SM
.B FIGNORE
is excluded from the list of matched filenames.  A sample
value is ``.o:~''.
.TP
.B INPUTRC
The filename for the readline startup file, overriding the default
of
.FN ~/.inputrc
(see
.SM
.B READLINE
below).
.TP
.B notify
If set,
.B bash
reports terminated background jobs immediately, rather than waiting
until before printing the next primary prompt (see also the
.B \-b
option to the
.B set
builtin command).
.PD 0
.TP
.B history_control
.TP
.B HISTCONTROL
.PD
If set to a value of
.IR ignorespace ,
lines which begin with a
.B space
character are not entered on the history list.  If set to
a value of
.IR ignoredups ,
lines matching the last history line are not entered.
A value of
.I ignoreboth
combines the two options.
If unset, or if set to any other value than those above,
all lines read
by the parser are saved on the history list.
.TP
.B command_oriented_history
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.
.TP
.B glob_dot_filenames
If set,
.B bash
includes filenames beginning with a `.' in the results of pathname
expansion.
.TP
.B allow_null_glob_expansion
If set,
.B bash
allows pathname patterns which match no
files (see
.B Pathname Expansion
below)
to expand to a null string, rather than themselves.
.TP
.B histchars
The two or three characters which control history expansion
and tokenization (see
.SM
.B HISTORY EXPANSION
below).  The first character is the
.IR "history expansion character" ,
that is, the character which signals the start of a history
expansion, normally `\fB!\fP'.
The second character is the
.IR "quick substitution"
character, which is used as shorthand for re-running the previous
command entered, substituting one string for another in the command.
The default is `\fB^\fP'.
The optional third character is the character
which signifies that the remainder of the line is a comment, when found
as the first character of a word, normally `\fB#\fP'.  The history
comment character causes history substitution to be skipped for the
remaining words on the line.  It does not necessarily cause the shell
parser to treat the rest of the line as a comment.
.TP
.B nolinks
If set, the shell does not follow symbolic links when executing
commands 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, such as 
.BR cd .
See also the description of the \fB\-P\fP option to the \fBset\fP
builtin (
.SM
.B SHELL BUILTIN COMMANDS
below).
.PD 0
.TP
.B hostname_completion_file
.TP
.B HOSTFILE
.PD
Contains the name of a file in the same format as
.FN /etc/hosts
that should be read when the shell needs to complete a
hostname.  The file may be changed interactively; the next
time hostname completion is attempted
.B bash
adds the contents of the new file to the already existing database.
.TP
.B noclobber
If set,
.B bash
does not overwrite an existing file with the
.BR > ,
.BR >& ,
and
.B <>
redirection operators.  This variable may be overridden when 
creating output files by using the redirection operator
.B >|
instead of
.B >
(see also the \fB\-C\fP option to the
.B set
builtin command).
.TP
.B auto_resume
This variable controls how the shell interacts with the user and
job control.  If this variable is set, single word simple
commands without redirections are treated as candidates for resumption
of an existing stopped job.  There is no ambiguity allowed; if there is
more than one job beginning with the string typed, the job most recently
accessed is selected.  The
.I name
of a stopped job, in this context, is the command line used to
start it.
If set to the value
.IR exact ,
the string supplied must match the name of a stopped job exactly;
if set to
.IR substring ,
the string supplied needs to match a substring of the name of a
stopped job.  The
.I substring
value provides functionality analogous to the
.B %?
job id (see
.SM
.B JOB CONTROL
below).  If set to any other value, the supplied string must
be a prefix of a stopped job's name; this provides functionality
analogous to the
.B %
job id.
.TP
.B no_exit_on_failed_exec
If this variable exists, a non-interactive shell will not exit if
it cannot execute the file specified in the
.B exec
builtin command.  An interactive shell does not exit if
.B exec
fails.
.TP
.B cdable_vars
If this is 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.
.PD
.SH EXPANSION
Expansion is performed on the command line after it has been split into
words.  There are seven kinds of expansion performed:
.IR "brace expansion" ,
.IR "tilde expansion" ,
.IR "parameter and variable expansion" ,
.IR "command substitution" ,
.IR "arithmetic expansion" ,
.IR "word splitting" ,
and
.IR "pathname expansion" .
.PP
The order of expansions is: brace expansion, tilde expansion,
parameter, variable, command, and arithmetic substitution (done
in a left\-to\-right fashion), word splitting, and pathname
expansion.
.PP
On systems that can support it, there is an additional expansion
available: \fIprocess substitution\fP.
.PP
Only brace expansion, word splitting, and pathname expansion
can change the number of words of the expansion; other expansions
expand a single word to a single word.
The single exception to this is the expansion of
``\fB$@\fP'' as explained above (see
.SM
.BR PARAMETERS ).
.SS Brace Expansion
.PP
.I "Brace expansion"
is a mechanism by which arbitrary strings
may be generated.  This mechanism is similar to
\fIpathname expansion\fP, but the filenames generated
need not exist.  Patterns to be brace expanded take
the form of an optional
.IR preamble ,
followed by a series of comma-separated strings
between a pair of braces, followed by an optional
.IR postamble .
The preamble is prepended to each string contained
within the braces, and the postamble is then appended
to each resulting string, expanding left to right.
.PP
Brace expansions may be nested.  The results of each expanded
string are not sorted; left to right order is preserved.
For example, a\fB{\fPd,c,b\fB}\fPe expands into `ade ace abe'.
.PP
Brace expansion is performed before any other expansions,
and any characters special to other expansions are preserved
in the result.  It is strictly textual.
.B Bash
does not apply any syntactic interpretation to the context of the
expansion or the text between the braces.
.PP
A correctly-formed brace expansion must contain unquoted opening
and closing braces, and at least one unquoted comma.
Any incorrectly formed brace expansion is left unchanged.
.PP
This construct is typically used as shorthand when the common
prefix of the strings to be generated is longer than in the
above example:
.RS
.PP
mkdir /usr/local/src/bash/{old,new,dist,bugs}
.RE
or
.RS
chown root /usr/{ucb/{ex,edit},lib/{ex?.?*,how_ex}}
.RE
.PP
Brace expansion introduces a slight incompatibility with
traditional versions of
.BR sh ,
the Bourne shell.
.B sh
does not treat opening or closing braces specially when they
appear as part of a word, and preserves them in the output.
.B Bash
removes braces from words as a consequence of brace
expansion.  For example, a word entered to
.B sh
as \fIfile{1,2}\fP
appears identically in the output.  The same word is
output as
.I file1 file2
after expansion by
.BR bash .
If strict compatibility with
.B sh
is desired, start
.B bash
with the
.B \-nobraceexpansion
flag (see
.SM
.B OPTIONS
above)
or disable brace expansion with the
.B +o braceexpand
option to the
.B set
command (see
.SM
.B SHELL BUILTIN COMMANDS
below).
.SS Tilde Expansion
.PP
If a word begins with a tilde character (`\fB~\fP'), all of the characters
preceding the first slash (or all characters, if there is no slash)
are treated as a possible \fIlogin name\fP. If this \fIlogin name\fP
is the null string, the tilde is replaced with the value of the
parameter
.SM
.BR HOME .
If
.SM
.B HOME
is unset, the home directory of
the user executing the shell is substituted instead.
.PP
If a `+' follows the tilde, the value of
.SM
.B PWD
replaces the tilde and `+'.  If
a `\-' follows, the value of
.SM
.B OLDPWD
is substituted.
If the value following the tilde is a valid \fIlogin name\fP,
the tilde and \fIlogin name\fP are replaced with the home directory
associated with that name.  If the name is invalid, or the tilde
expansion fails, the word is unchanged.
.PP
Each variable assignment is checked for unquoted
instances of tildes following a
.B :
or
.BR = .
In these cases, tilde substitution is also performed.  Consequently, one
may use pathnames with tildes in assignments to
.SM
.BR PATH ,
.SM
.BR MAILPATH ,
and
.SM
.BR CDPATH ,
and the shell assigns the expanded value.
.SS Parameter Expansion
.PP
The `\fB$\fP' character introduces parameter expansion,
command substitution, or arithmetic expansion.  The parameter name
or symbol to be expanded may be enclosed in braces, which
are optional but serve to protect the variable to be expanded from
characters immediately following it which could be
interpreted as part of the name.
.PP
.PD 0
.TP
${\fIparameter\fP}
The value of \fIparameter\fP is substituted.  The braces are required
when
.I parameter
is a positional parameter with more than one digit,
or when
.I parameter
is followed by a character which is not to be
interpreted as part of its name.
.PD
.PP
In each of the cases below, \fIword\fP is subject to tilde expansion,
parameter expansion, command substitution, and arithmetic expansion.
\fBBash\fP tests for a parameter that is unset or null; omitting the
colon results in a test only for a parameter that is unset.
.PP
.PD 0
.TP
${\fIparameter\fP\fB:\-\fP\fIword\fP}
\fBUse Default Values\fP.  If
.I parameter
is unset or null, the expansion of
.I word
is substituted.  Otherwise, the value of
.I parameter
is substituted.
.TP
${\fIparameter\fP\fB:=\fP\fIword\fP}
\fBAssign Default Values\fP.
If
.I parameter
is unset or null, the expansion of
.I word
is assigned to
.IR parameter .
The value of
.I parameter
is then substituted.  Positional parameters and special parameters may
not be assigned to in this way.
.TP
${\fIparameter\fP\fB:?\fP\fIword\fP}
\fBDisplay Error if Null or Unset\fP.
If
.I parameter
is null or unset, the expansion of \fIword\fP (or a message to that effect
if
.I word
is not present) is written to the standard error and the shell, if it
is not interactive, exits.  Otherwise, the value of \fIparameter\fP is
substituted.
.TP
${\fIparameter\fP\fB:+\fP\fIword\fP}
\fBUse Alternate Value\fP.
If
.I parameter
is null or unset, nothing is substituted, otherwise the expansion of
.I word
is substituted.
.TP
${\fB#\fP\fIparameter\fP}
The length in characters of the value of \fIparameter\fP is substituted.
If \fIparameter\fP is
.B *
or 
.BR @ ,
the length substituted is the length of
.B *
expanded within double quotes.
.TP
.PD 0
${\fIparameter\fP\fB#\fP\fIword\fP}
.TP
${\fIparameter\fP\fB##\fP\fIword\fP}
.PD
The 
.I word
is expanded to produce a pattern just as in pathname
expansion.  If the pattern matches the beginning of
the value of
.IR parameter ,
then the expansion is the value of
.I parameter
with the shortest matching pattern deleted (the ``\fB#\fP''
case) or the longest
matching pattern deleted (the ``\fB##\fP'' case).
.TP
.PD 0
${\fIparameter\fP\fB%\fP\fIword\fP}
.TP
${\fIparameter\fP\fB%%\fP\fIword\fP}
.PD
The \fIword\fP is expanded to produce a pattern just as in
pathname expansion.  If the pattern matches a
trailing portion of the value of
.IR parameter ,
then the expansion is the value of
.I parameter
with the shortest matching pattern deleted
(the ``\fB%\fP'' case) or the longest
matching pattern deleted (the ``\fB%%\fP'' case).
.SS Command Substitution
.PP
\fICommand substitution\fP allows the output of a command to replace 
the command name.  There are two forms:
.PP
.RS
.PP
\fB$(\fP\fIcommand\fP\|\fB)\fP
.RE
or
.RS
\fB`\fP\fIcommand\fP\fB`\fP
.RE
.PP
. B Bash
performs the expansion by executing \fIcommand\fP and
replacing the command substitution with the standard output of the
command, with any trailing newlines deleted.
.PP
When the old\-style backquote form of substitution is used,
backslash retains its literal meaning except when followed by
.BR $ ,
.BR ` ,
or
.BR \e .
When using the $(\^\fIcommand\fP\|) form, all characters between the
parentheses make up the command; none are treated specially.
.PP
Command substitutions may be nested.  To nest when using the old form,
escape the inner backquotes with backslashes.
.PP
If the substitution appears within double quotes, word splitting and
pathname expansion are not performed on the results.
.SS Arithmetic Expansion
.PP
Arithmetic expansion allows the evaluation of an arithmetic expression
and the substitution of the result.  There are two formats for
arithmetic expansion:
.RS
.PP
\fB$[\fP\fIexpression\fP\fB]\fP
.PP
\fB$((\fP\fIexpression\fP\fB))\fP
.RE
.PP
The
.I expression
is treated as if it were within double quotes, but a double quote
inside the braces or parentheses
is not treated specially.  All tokens in the
expression undergo parameter expansion, command substitution,
and quote removal.  Arithmetic substitutions may be nested.
.PP
The evaluation is performed according to the rules listed below under
.SM
.BR "ARITHMETIC EVALUATION" .
If
.I expression
is invalid,
.B bash
prints a message indicating failure and no substitution occurs.
.SS Process Substitution
.PP
\fIProcess substitution\fP is supported on systems that support named
pipes (\fIFIFOs\fP) or the \fB/dev/fd\fP method of naming open files.
It takes the form of
\fB<(\fP\fIlist\^\fP\fB)\fP
or
\fB>(\fP\fIlist\^\fP\fB)\fP.
The process \fIlist\fP is run with its input or output connected to a
\fIFIFO\fP or some file in \fB/dev/fd\fP.  The name of this file is
passed as an argument to the current command as the result of the
expansion.  If the \fB>(\fP\fIlist\^\fP\fB)\fP form is used, writing to
the file will provide input for \fIlist\fP.  If the
\fB<(\fP\fIlist\^\fP\fB)\fP form is used, the file passed as an
argument should be read to obtain the output of \fIlist\fP.
.PP
On systems that support it, \fIprocess substitution\fP is performed
simultaneously with
.IR "parameter and variable expansion" ,
.IR "command substitution" ,
and
.IR "arithmetic expansion" .
.SS Word Splitting
.PP
The shell scans the results of
parameter expansion,
command substitution,
and
arithmetic expansion
that did not occur within double quotes for
.IR "word splitting" .
.PP
The shell treats each character of
.SM
.B IFS
as a delimiter, and splits the results of the other
expansions into words on these characters.  If the
value of
.SM
.B IFS
is exactly
.BR <space><tab><newline> ,
the default, then
any sequence of
.SM
.B IFS
characters serves to delimit words.  If
.SM
.B IFS
has a value other than the default, then sequences of
the whitespace characters
.B space
and
.B tab
are ignored at the beginning and end of the
word, as long as the whitespace character is in the
value of
.SM
.BR IFS
(an
.SM
.B IFS
whitespace character).
Any character in
.SM
.B IFS
that is not
.SM
.B IFS
whitespace, along with any adjacent
.SM
.B IFS
whitespace characters, delimits a field.
A sequence of
.SM
.B IFS
whitespace characters is also treated as a delimiter.
If the value of
.SM
.B IFS
is null, no word splitting occurs.
.SM
.B IFS
cannot be unset.
.PP
Explicit null arguments (\^\f3"\^"\fP or \^\f3'\^'\fP\^)
are retained.  Implicit null arguments, resulting from the expansion
of
.I parameters
that have no values, are removed.
.PP
Note that if no expansion occurs, no splitting
is performed.
.SS Pathname Expansion
.PP
After word splitting,
unless the
.B \-f
option has been set,
.B bash
scans each
.I word
for the characters
.BR * ,
.BR ? ,
and
.BR [ .
If one of these characters appears, then the word is
regarded as a
.IR pattern ,
and replaced with an alphabetically sorted list of
pathnames matching the pattern.
If no matching pathnames are found,
and the shell variable
.B allow_null_glob_expansion
is unset, the word is left unchanged.
If the variable is set, and no matches are found,
the word is removed.
When a pattern is used for pathname generation,
the character
.B ``.''
at the start of a name or immediately following a slash
must be matched explicitly, unless the shell variable
.B glob_dot_filenames
is set.  The slash character must always be matched
explicitly.  In other cases, the
.B ``.''
character is not treated specially.
.PP
The special pattern characters have the following meanings:
.PP
.PD 0
.TP
.B *
Matches any string, including the null string.
.TP
.B ?
Matches any single character.
.TP
.B [...]
Matches any one of the enclosed characters.  A pair of characters
separated by a minus sign denotes a
.IR range ;
any character lexically between those two characters, inclusive,
is matched.  If the first character following the
.B [
is a
.B !
or a
.B ^
then any character not enclosed is matched.  A 
.B \-
or
.B ]
may be matched by including it as the first or last character
in the set.
.PD
.SS Quote Removal
.PP
After the preceding expansions, all unquoted occurrences of the
characters
.BR \e ,
.BR ` ,
and \^\f3"\fP\^ are removed. 
.SH REDIRECTION
Before a command is executed, its input and output
may be
.I redirected
using a special notation interpreted by the shell.
Redirection may also be used to open and close files for the
current shell execution environment.  The following redirection
operators may precede or appear anywhere within a
.I simple command
or may follow a
.IR command .
Redirections are processed in the order they appear, from
left to right.
.PP
In the following descriptions, if the file descriptor number is
omitted, and the first character of the redirection operator is
.BR < ,
the redirection refers to the standard input (file descriptor
0).  If the first character of the redirection operator is
.BR > ,
the redirection refers to the standard output (file descriptor
1).
.PP
The word that follows the redirection operator in the following
descriptions is subjected to brace expansion, tilde expansion,
parameter expansion, command substitution, arithmetic expansion,
quote removal, and pathname expansion.  If it expands to more
than one word,
.B bash
reports an error.
.PP
Note that the order of redirections is significant.  For example, 
the command
.RS
.PP
ls \fB>\fP dirlist 2\fB>&\fP1
.RE
.PP
directs both standard output and standard error to the file 
.IR dirlist ,
while the command
.RS
.PP
ls 2\fB>&\fP1 \fB>\fP dirlist
.RE
.PP
directs only the standard output to file
.IR dirlist ,
because the standard error was duplicated as standard output
before the standard output was redirected to
.IR dirlist .
.SS Redirecting Input
.PP
Redirection of input causes the file whose name results from
the expansion of
.I word
to be opened for reading on file descriptor
.IR n ,
or the standard input (file descriptor 0) if
.I n
is not specified.
.PP
The general format for redirecting input is:
.RS
.PP
[\fIn\fP]\fB<\fP\fIword\fP
.RE
.SS Redirecting Output
.PP
Redirection of output causes the file whose name results from
the expansion of
.I word
to be opened for writing on file descriptor
.IR n ,
or the standard output (file descriptor 1) if
.I n
is not specified.  If the file does not exist it is created;
if it does exist it is truncated to zero size.
.PP
The general format for redirecting output is:
.RS
.PP
[\fIn\fP]\fB>\fP\fIword\fP
.RE
.PP
If the redirection operator is
.BR >| ,
then the value of the
.B -C
option to the
.B set
builtin command is not tested, and file creation is attempted.
(See also the description of
.B noclobber
under
.B "Shell Variables"
above.)
.SS Appending Redirected Output
.PP
Redirection of output in this fashion
causes the file whose name results from
the expansion of
.I word
to be opened for appending on file descriptor
.IR n ,
or the standard output (file descriptor 1) if
.I n
is not specified.  If the file does not exist it is created.
.PP
The general format for appending output is:
.RS
.PP
[\fIn\fP]\fB>>\fP\fIword\fP
.RE
.PP
.SS Redirecting Standard Output and Standard Error
.PP
.B Bash
allows both the
standard output (file descriptor 1) and
the standard error output (file descriptor 2)
to be redirected to the file whose name is the
expansion of
.I word
with this construct.
.PP
There are two formats for redirecting standard output and
standard error:
.RS
.PP
\fB&>\fP\fIword\fP
.RE
and
.RS
\fB>&\fP\fIword\fP
.RE
.PP
Of the two forms, the first is preferred.
This is semantically equivalent to
.RS
.PP
\fB>\fP\fIword\fP 2\fB>&\fP1
.RE
.SS Here Documents
.PP
This type of redirection instructs the shell to read input from the
current source until a line containing only
.I word
(with no trailing blanks)
is seen.  All of
the lines read up to that point are then used as the standard
input for a command.
.PP
The format of here-documents is as follows:
.RS
.PP
.nf
\fB<<\fP[\fB\-\fP]\fIword\fP
        \fIhere-document\fP
\fIdelimiter\fP
.fi
.RE
.PP
No parameter expansion, command substitution, pathname
expansion, or arithmetic expansion is performed on
.IR word .
If any characters in
.I word
are quoted, the
.I delimiter
is the result of quote removal on
.IR word ,
and the lines in the here-document are not expanded.  Otherwise,
all lines of the here-document are subjected to parameter expansion,
command substitution, and arithmetic expansion.  In the latter
case, the pair
.B \e<newline>
is ignored, and
.B \e
must be used to quote the characters
.BR \e ,
.BR $ ,
and
.BR ` .
.PP
If the redirection operator is
.BR <<\- ,
then all leading tab characters are stripped from input lines and the
line containing
.IR delimiter .
This allows
here-documents within shell scripts to be indented in a
natural fashion.
.SS "Duplicating File Descriptors"
.PP
The redirection operator
.RS
.PP
[\fIn\fP]\fB<&\fP\fIword\fP
.RE
.PP
is used to duplicate input file descriptors.
If
.I word
expands to one or more digits, the file descriptor denoted by
.I n
is made to be a copy of that file descriptor.  If
.I word
evaluates to
.BR \- ,
file descriptor
.I n
is closed.  If
.I n
is not specified, the standard input (file descriptor 0) is used.
.PP
The operator
.RS
.PP
[\fIn\fP]\fB>&\fP\fIword\fP
.RE
.PP
is used similarly to duplicate output file descriptors.  If
.I n
is not specified, the standard output (file descriptor 1) is used.
As a special case, if \fIn\fP is omitted, and \fIword\fP does not
expand to one or more digits, the standard output and standard
error are redirected as described previously.
.SS "Opening File Descriptors for Reading and Writing"
.PP
The redirection operator
.RS
.PP
[\fIn\fP]\fB<>\fP\fIword\fP
.RE
.PP
causes the file whose name is the expansion of
.I word
to be opened for both reading and writing on file descriptor
.IR n ,
or as the standard input and standard output if 
.I n
is not specified.  If the file does not exist, it is created.
.SH FUNCTIONS
A shell function, defined as described above under
.SM
.BR "SHELL GRAMMAR" ,
stores a series of commands for later execution.
Functions are executed in the context of the
current shell; no new process is created to interpret
them (contrast this with the execution of a shell script).
When a function is executed, the arguments to the
function become the positional parameters
during its execution.  The special parameter
.B #
is updated to reflect the change.  Positional parameter 0
is unchanged.
.PP
Variables local to the function may be declared with the
.B local
builtin command.  Ordinarily, variables and their values
are shared between the function and its caller.
.PP
If the builtin command
.B return
is executed in a function, the function completes and
execution resumes with the next command after the function
call.  When a function completes, the values of the
positional parameters and the special parameter
.B #
are restored to the values they had prior to function
execution.
.PP
Function names and definitions may be listed with the
.B \-f
option to the
.B declare
or
.B typeset
builtin commands.  Functions may be exported so that subshells
automatically have them defined with the
.B \-f
option to the 
.B export
builtin.
.PP
Functions may be recursive.  No limit is imposed on the number
of recursive calls.
.SH ALIASES
The shell maintains a list of
.I aliases
that may be set and unset with the
.B alias
and
.B unalias
builtin commands (see
.SM
.B SHELL BUILTIN COMMANDS
below).
The first word of each command, if unquoted,
is checked to see if it has an
alias.  If so, that word is replaced by the text of the alias.
The alias name and the replacement text may contain any valid
shell input, including the
.I metacharacters
listed above, with the exception that the alias name may not
contain \fI=\fP.  The first word of the replacement text is tested
for aliases, but a word that is identical to an alias being expanded
is not expanded a second time.  This means that one may alias
.B ls
to
.BR "ls \-F" ,
for instance, and
.B bash
does not try to recursively expand the replacement text.
If the last character of the alias value is a
.IR blank ,
then the next command
word following the alias is also checked for alias expansion.
.PP
Aliases are created and listed with the
.B alias
command, and removed with the
.B unalias
command.
.PP
There is no mechanism for using arguments in the replacement text,
as in
.BR csh .
If arguments are needed, a shell function should be used.
.PP
Aliases are not expanded when the shell is not interactive.
.PP
The rules concerning the definition and use of aliases are
somewhat confusing.
.B Bash
always reads at least one complete line
of input before executing any
of the commands on that line.  Aliases are expanded when a
command is read, not when it is executed.  Therefore, an
alias definition appearing on the same line as another
command does not take effect until the next line of input is read.
This means that the commands following the alias definition
on that line are not affected by the new alias.
This behavior is also an issue when functions are executed.
Aliases are expanded when the function definition is read,
not when the function is executed, because a function definition
is itself a compound command.  As a consequence, aliases
defined in a function are not available until after that
function is executed.  To be safe, always put
alias definitions on a separate line, and do not use
.B alias
in compound commands.
.PP
Note that for almost every purpose, aliases are superseded by
shell functions.
.SH "JOB CONTROL"
.I Job control
refers to the ability to selectively stop (\fIsuspend\fP)
the execution of processes and continue (\fIresume\fP)
their execution at a later point.  A user typically employs
this facility via an interactive interface supplied jointly
by the system's terminal driver and
.BR bash .
.PP
The shell associates a
.I job
with each pipeline.  It keeps a table of currently executing
jobs, which may be listed with the
.B jobs
command.  When
.B bash
starts a job asynchronously (in the
.IR background ),
it prints a line that looks like:
.RS
.PP
[1] 25647
.RE
.PP
indicating that this job is job number 1 and that the process ID
of the last process in the pipeline associated with this job is 25647.
All of the processes in a single pipeline are members of the same job.
.B Bash
uses the
.I job
abstraction as the basis for job control.
.PP
To facilitate the implementation of the user interface to job
control, the system maintains the notion of a \fIcurrent terminal
process group ID\fP.  Members of this process group (processes whose
process group ID is equal to the current terminal process group ID)
receive keyboard-generated signals such as
.SM
.BR SIGINT .
These processes are said to be in the
.IR foreground .
.I Background
processes are those whose process group ID differs from the terminal's;
such processes are immune to keyboard-generated signals.
Only foreground processes are allowed to read from or write to the
terminal.  Background processes which attempt to read from (write to) the
terminal are sent a 
.SM
.B SIGTTIN (SIGTTOU)
signal by the terminal driver, 
which, unless caught, suspends the process.
.PP
If the operating system on which
.B bash
is running supports
job control,
.B bash
allows you to use it.
Typing the
.I suspend
character (typically
.BR ^Z ,
Control-Z) while a process is running
causes that process to be stopped and returns you to 
.BR bash .
Typing the
.I "delayed suspend"
character (typically
.BR ^Y ,
Control-Y) causes the process to be stopped when it
attempts to read input from the terminal, and control to
be returned to
.BR bash .
You may then manipulate the state of this job, using the
.B bg
command to continue it in the background, the
.B fg
command to continue it in the foreground, or
the
.B kill
command to kill it.  A \fB^Z\fP takes effect immediately,
and has the additional side effect of causing pending output
and typeahead to be discarded.
.PP
There are a number of ways to refer to a job in the shell.
The character
.B %
introduces a job name.  Job number
.I n
may be referred to as
.BR %n .
A job may also be referred to using a prefix of the name used to
start it, or using a substring that appears in its command line.
For example,
.B %ce
refers to a stopped
.B ce
job.  If a prefix matches more than one job,
.B bash
reports an error.  Using
.BR %?ce ,
on the other hand, refers to any job containing the string
.B ce
in its command line.  If the substring matches more than one job,
.B bash
reports an error.  The symbols
.B %%
and
.B %+
refer to the shell's notion of the
.IR "current job" ,
which is the last job stopped while it was in
the foreground.
The 
.I "previous job"
may be referenced using
.BR %\- .
In output pertaining to jobs (e.g., the output of the
.B jobs
command), the current job is always flagged with a
.BR + ,
and the previous job with a
.BR \- .
.PP
Simply naming a job can be used to bring it into the
foreground:
.B %1
is a synonym for
\fB``fg %1''\fP,
bringing job 1 from the background into the foreground.
Similarly,
.B ``%1 &''
resumes job 1 in the background, equivalent to
\fB``bg %1''\fP.
.PP
The shell learns immediately whenever a job changes state.
Normally,
.B bash
waits until it is about to print a prompt before reporting
changes in a job's status so as to not interrupt
any other output.  If the 
.B -b
option to the
.B set
builtin command
is set,
.B bash
reports such changes immediately.  (See also the description of
.B notify
variable under
.B "Shell Variables"
above.)
.PP
If you attempt to exit
.B bash
while jobs are stopped, the shell prints a message warning you.  You
may then use the
.B jobs
command to inspect their status.  If you do this, or try to exit
again immediately, you are not warned again, and the stopped
jobs are terminated.
.SH SIGNALS
When \fBbash\fP is interactive, it ignores
.SM
.B SIGTERM
(so that \fBkill 0\fP does not kill an interactive shell),
and
.SM
.B SIGINT
is caught and handled (so that the \fBwait\fP builtin is interruptible).
In all cases, \fBbash\fP ignores
.SM
.BR SIGQUIT .
If job control is in effect,
.B bash
ignores
.SM
.BR SIGTTIN ,
.SM
.BR SIGTTOU ,
and
.SM
.BR SIGTSTP .
.PP
Synchronous jobs started by \fBbash\fP have signals set to the
values inherited by the shell from its parent.  When job control
is not in effect, background jobs (jobs started with
.BR & )
ignore
.SM
.B SIGINT
and
.SM
.BR SIGQUIT .
Commands run as a result of command substitution ignore the
keyboard-generated job control signals
.SM
.BR SIGTTIN ,
.SM
.BR SIGTTOU ,
and
.SM
.BR SIGTSTP .
.SH "COMMAND EXECUTION"
After a command has been split into words, if it results in a
simple command and an optional list of arguments, the following
actions are taken.
.PP
If the command name contains no slashes, the shell attempts to
locate it.  If there exists a shell function by that name, that
function is invoked as described above in
.SM
.BR FUNCTIONS .
If the name does not match a function, the shell searches for
it in the list of shell builtins.  If a match is found, that
builtin is invoked.
.PP
If the name is neither a shell function nor a builtin,
and contains no slashes,
.B bash
searches each element of the
.SM
.B PATH
for a directory containing an executable file by that name.
If the search is unsuccessful, the shell prints an error
message and returns a nonzero exit status.
.PP
If the search is successful, or if the command name contains
one or more slashes, the shell executes the named program.
Argument 0 is set to the name given, and the remaining arguments
to the command are set to the arguments given, if any.
.PP
If this execution fails because the file is not in executable
format, and the file is not a directory, it is assumed to be
a \fIshell script\fP, a file
containing shell commands.  A subshell is spawned to execute
it.  This subshell reinitializes itself, so
that the effect is as if a new shell had been invoked
to handle the script, with the exception that the locations of
commands remembered by the parent (see
.B hash
below under
.SM
\fBSHELL BUILTIN COMMANDS\fP)
are retained by the child.
.PP
If the program is a file beginning with
.BR #! ,
the remainder of the first line specifies an interpreter
for the program.  The shell executes the
specified interpreter on operating systems that do not
handle this executable format themselves.  The arguments to the 
interpreter consist of a single optional argument following the
interpreter name on the first line of the program, followed
by the name of the program, followed by the command
arguments, if any.
.SH ENVIRONMENT
When a program is invoked it is given an array of strings
called the
.IR environment .
This is a list of 
\fIname\fP\-\fIvalue\fP pairs, of the form
.IR "name\fR=\fPvalue" .
.PP
The shell allows you to manipulate the environment in several
ways.  On invocation, the shell scans its own environment and
creates a parameter for each name found, automatically marking
it for
.I export
to child processes.  Executed commands inherit the environment.
The
.B export
and
.B declare \-x
commands allow parameters and functions to be added to and
deleted from the environment.  If the value of a parameter
in the environment is modified, the new value becomes part
of the environment, replacing the old.  The environment
inherited by any executed command consists of the shell's
initial environment, whose values may be modified in the shell,
less any pairs removed by the
.B unset
command, plus any additions via the
.B export
and
.B declare \-x
commands.
.PP
The environment for any
.I simple command
or function may be augmented temporarily by prefixing it with
parameter assignments, as described above in
.SM
.BR PARAMETERS .
These assignment statements affect only the environment seen
by that command.
.PP
If the 
.B \-k
flag is set (see the
.B set
builtin command below), then
.I all
parameter assignments are placed in the environment for a command,
not just those that precede the command name.
.PP
When
.B bash
invokes an external command, the variable
.B _
is set to the full path name of the command and passed to that
command in its environment.
.SH "EXIT STATUS"
For the purposes of the shell, a command which exits with a 
zero exit status has succeeded.  An exit status of zero
indicates success.  A non\-zero exit status indicates failure.
When a command terminates on a fatal signal, \fBbash\fP uses
the value of 128+\fBsignal\fP as the exit status.
.PP
If a command is not found, the child process created to
execute it returns a status of 127.  If a command is found
but is not executable, the return status is 126.
.PP
\fBBash\fP itself returns the exit status of the last command
executed, unless a syntax error occurs, in which case it exits
with a non\-zero value.  See also the \fBexit\fP builtin
command below.
.SH PROMPTING
When executing interactively, 
.B bash
displays the primary prompt
.SM
.B PS1
when it is ready to read a command, and the secondary prompt
.SM
.B PS2
when it needs more input to complete a command.
.B Bash
allows these prompt strings to be customized by inserting a number of
backslash-escaped special characters that are decoded as follows:
.RS
.PD 0
.TP
.B \et
the current time in HH:MM:SS format
.TP
.B \ed
the date in "Weekday Month Date" format (e.g., "Tue May 26")
.TP
.B \en
newline
.TP
.B \es
the name of the shell, the basename of
.B $0
(the portion following the final slash)
.TP
.B \ew
the current working directory
.TP
.B \eW
the basename of the current working directory
.TP
.B \eu
the username of the current user
.TP
.B \eh
the hostname
.TP
.B \e#
the command number of this command
.TP
.B \e!
the history number of this command
.TP
.B \e$
if the effective UID is 0, a
.BR # ,
otherwise a
.B $
.TP
.B \ennn
the character corresponding to the octal number \fBnnn\fP
.TP
.B \e\e
a backslash
.TP
.B \e[
begin a sequence of non-printing characters, which could be used to
embed a terminal control sequence into the prompt
.TP
.B \e]
end a sequence of non-printing characters
.PD
.RE
.PP
The command number and the history number are usually different:
the history number of a command is its position in the history
list, which may include commands restored from the history file
(see
.SM
.B HISTORY
below), while the command number is the position in the sequence
of commands executed during the current shell session.
After the string is decoded, it is expanded via
parameter expansion,
command substitution, arithmetic expansion, and word splitting.
.SH READLINE
This is the library that handles reading input when using an interactive
shell, unless the
.B \-nolineediting
option is given.  By default, the line editing commands
are similar to those of emacs.
A vi-style line editing interface is also available.
.PP
In this section, the emacs-style notation is used to denote
keystrokes.  Control keys are denoted by C\-\fIkey\fR, e.g., C\-n
means Control\-N.  Similarly, 
.I meta
keys are denoted by M\-\fIkey\fR, so M\-x means Meta\-X.  (On keyboards
without a 
.I meta
key, M\-\fIx\fP means ESC \fIx\fP, i.e., press the Escape key
then the
.I x
key.  This makes ESC the \fImeta prefix\fP.
The combination M\-C\-\fIx\fP means ESC\-Control\-\fIx\fP,
or press the Escape key
then hold the Control key while pressing the
.I x
key.)
.PP
The default key-bindings may be changed with an
.FN ~/.inputrc 
file.  The value of the shell variable
.SM
.BR INPUTRC ,
if set, is used instead of
.IR ~/.inputrc .
Other programs that use this library may add their own commands
and bindings.
.PP
For example, placing
.RS
.PP
M\-Control\-u: universal\-argument
.RE
or
.RS
C\-Meta\-u: universal\-argument
.RE
into the 
.FN ~/.inputrc
would make M\-C\-u execute the readline command
.IR universal\-argument .
.PP
The following symbolic character names are recognized:
.IR RUBOUT ,
.IR DEL ,
.IR ESC ,
.IR LFD ,
.IR NEWLINE ,
.IR RET ,
.IR RETURN ,
.IR SPC ,
.IR SPACE ,
and
.IR TAB .
In addition to command names, readline allows keys to be bound
to a string that is inserted when the key is pressed (a \fImacro\fP).
.PP
Readline is customized by putting commands in an initialization
file.  The name of this file is taken from the value of the
.SM
.B INPUTRC
variable.  If that variable is unset, the default is
.IR ~/.inputrc .
When a program which uses the readline library starts up, the
init file is read, and the key bindings and variables are set.
There are only a few basic constructs allowed in the
readline init file.  Blank lines are ignored.
Lines beginning with a \fB#\fP are comments.
Lines beginning with a \fB$\fP indicate conditional
constructs.  Other lines
denote key bindings and variable settings.
.PP
The syntax for controlling key bindings in the
.I ~/.inputrc
file is simple.  All that is required is the name of the
command or the text of a macro and a key sequence to which
it should be bound. The name may be specified in one of two ways:
as a symbolic key name, possibly with \fIMeta-\fP or \fIControl-\fP
prefixes, or as a key sequence.
When using the form \fBkeyname\fP:\fIfunction-name\fP or \fImacro\fP,
.I keyname
is the name of a key spelled out in English.  For example:
.sp
.RS
Control-u: universal\-argument
.br
Meta-Rubout: backward-kill-word
.br
Control-o: ">&output"
.RE
.LP
In the above example,
.I C-u
is bound to the function
.BR universal\-argument ,
.I M-DEL
is bound to the function
.BR backward\-kill\-word ,
and
.I C-o
is bound to run the macro
expressed on the right hand side (that is, to insert the text
.I >&output
into the line).
.PP
In the second form, \fB"keyseq"\fP:\fIfunction-name\fP or \fImacro\fP,
.B keyseq
differs from
.B keyname
above in that strings denoting
an entire key sequence may be specified by placing the sequence
within double quotes.  Some GNU Emacs style key escapes can be
used, as in the following example.
.sp
.RS
"\eC-u": universal\-argument
.br
"\eC-x\eC-r": re\-read\-init\-file
.br
"\ee[11~": "Function Key 1"
.RE
.PP
In this example,
.I C-u
is again bound to the function
.BR universal\-argument .
.I "C-x C-r"
is bound to the function
.BR re\-read\-init\-file ,
and 
.I "ESC [ 1 1 ~"
is bound to insert the text
.BR "Function Key 1" .
The full set of escape sequences is
.RS
.TP
.B \eC\-
control prefix
.TP
.B \eM-
meta prefix
.TP
.B \ee
an escape character
.TP
.B \e\e
backslash
.TP
.B \e"
literal "
.TP
.B \e'
literal '
.RE
.PP
When entering the text of a macro, single or double quotes should
be used to indicate a macro definition.  Unquoted text
is assumed to be a function name.  Backslash
will quote any character in the macro text, including " and '.
.PP
.B Bash
allows the current readline key bindings to be displayed or modified
with the
.B bind
builtin command.  The editing mode may be switched during interactive
use by using the
.B \-o
option to the
.B set
builtin command (see
.SM
.B SHELL BUILTIN COMMANDS
below).
.PP
Readline has variables that can be used to further customize its
behavior.  A variable may be set in the
.I inputrc
file with a statement of the form
.RS
.PP
\fBset\fP \fIvariable\-name\fP \fIvalue\fP
.RE
.PP
Except where noted, readline variables can take the values
.B On
or
.BR Off .
The variables and their default values are:
.PP
.PD 0
.TP
.B horizontal\-scroll\-mode (Off)
When set to \fBOn\fP, makes readline use a single line for display,
scrolling the input horizontally on a single screen line when it
becomes longer than the screen width rather than wrapping to a new line.
.TP
.B editing\-mode (emacs)
Controls whether readline begins with a set of key bindings similar
to \fIemacs\fP or \fIvi\fP.
.B editing\-mode
can be set to either
.B emacs
or
.BR vi .
.TP
.B mark\-modified\-lines (Off)
If set to \fBOn\fP, history lines that have been modified are displayed
with a preceding asterisk (\fB*\fP).
.TP
.B bell\-style (audible)
Controls what happens when readline wants to ring the terminal bell.
If set to \fBnone\fP, readline never rings the bell.  If set to
\fBvisible\fP, readline uses a visible bell if one is available.
If set to \fBaudible\fP, readline attempts to ring the terminal's bell.
.TP
.B comment\-begin (``#'')
The string that is inserted in \fBvi\fP mode when the
.B vi\-comment
command is executed.
.TP
.B meta\-flag (Off)
If set to \fBOn\fP, readline will enable eight-bit input (that is,
it will not strip the high bit from the characters it reads),
regardless of what the terminal claims it can support.
.TP
.B convert\-meta (On)
If set to \fBOn\fP, readline will convert characters with the
eighth bit set to an ASCII key sequence
by stripping the eighth bit and prepending an
escape character (in effect, using escape as the \fImeta prefix\fP).
.TP
.B output\-meta (Off)
If set to \fBOn\fP, readline will display characters with the
eighth bit set directly rather than as a meta-prefixed escape
sequence.
.TP
.B completion\-query\-items (100)
This determines when the user is queried about viewing
the number of possible completions
generated by the \fBpossible\-completions\fP command.
It may be set to any integer value greater than or equal to
zero.  If the number of possible completions is greater than
or equal to the value of this variable, the user is asked whether
or not he wishes to view them; otherwise they are simply listed
on the terminal.
.TP
.B keymap (emacs)
Set the current readline keymap.  The set of legal keymap names is
\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; \fIemacs\fP is
equivalent to \fIemacs-standard\fP.  The default value is
.IR emacs ;
the value of
.B editing\-mode
also affects the default keymap.
.TP
.B show\-all\-if\-ambiguous (Off)
This alters the default behavior of the completion functions.  If
set to
.BR on ,
words which have more than one possible completion cause the
matches to be listed immediately instead of ringing the bell.
.TP
.B expand\-tilde (Off)
If set to \fBon\fP, tilde expansion is performed when readline
attempts word completion.
.PD
.PP
Readline implements a facility similar in spirit to the conditional
compilation features of the C preprocessor which allows key
bindings and variable settings to be performed as the result
of tests.  There are three parser directives used.
.IP \fB$if\fP
The 
.B $if
construct allows bindings to be made based on the
editing mode, the terminal being used, or the application using
readline.  The text of the test extends to the end of the line;
no characters are required to isolate it.
.RS
.IP \fBmode\fP
The \fBmode=\fP form of the \fB$if\fP directive is used to test
whether readline is in emacs or vi mode.
This may be used in conjunction
with the \fBset keymap\fP command, for instance, to set bindings in
the \fIemacs-standard\fP and \fIemacs-ctlx\fP keymaps only if
readline is starting out in emacs mode.
.IP \fBterm\fP
The \fBterm=\fP form may be used to include terminal-specific
key bindings, perhaps to bind the key sequences output by the
terminal's function keys.  The word on the right side of the
.B =
is tested against the full name of the terminal and the portion
of the terminal name before the first \fB\-\fP.  This allows
.I sun
to match both
.I sun
and
.IR sun\-cmd ,
for instance.
.IP \fBapplication\fP
The \fBapplication\fP construct is used to include
application\-specific settings.  Each program using the readline
library sets the \fIapplication name\fP, and an initialization
file can test for a particular value.
This could be used to bind key sequences to functions useful for
a specific program.  For instance, the following command adds a
key sequence that quotes the current or previous word in Bash:
.RS
.nf
\fB$if\fP Bash
# Quote the current or previous word
"\eC-xq": "\eeb\e"\eef\e""
\fB$endif\fP
.fi
.RE
.RE
.IP \fB$endif\fP
This command, as you saw in the previous example, terminates an
\fB$if\fP command.
.IP \fB$else\fP
Commands in this branch of the \fB$if\fP directive are executed if
the test fails.
.PP
Readline commands may be given numeric
.IR arguments ,
which normally act as a repeat count.  Sometimes, however, it is the
sign of the argument that is significant.  Passing a negative argument
to a command that acts in the forward direction (e.g., \fBkill\-line\fP)
causes that command to act in a backward direction.  Commands whose
behavior with arguments deviates from this are noted.
.PP
When a command is described as \fIkilling\fP text, the text
deleted is saved for possible future retrieval
(\fIyanking\fP).  The killed text is saved in a
\fIkill\-ring\fP.  Consecutive kills cause the text to be
accumulated into one unit, which can be yanked all at once. 
Commands which do not kill text separate the chunks of text
on the kill\-ring.
.PP
The following is a list of the names of the commands and the default
key sequences to which they are bound.
.SS Commands for Moving
.PP
.PD 0
.TP
.B beginning\-of\-line (C\-a)
Move to the start of the current line.
.TP
.B end\-of\-line (C\-e)
Move to the end of the line.
.TP
.B forward\-char (C\-f)
Move forward a character.
.TP
.B backward\-char (C\-b)
Move back a character.
.TP
.B forward\-word (M\-f)
Move forward to the end of the next word.  Words are composed of
alphanumeric characters (letters and digits).
.TP
.B backward\-word (M\-b)
Move back to the start of this, or the previous, word.  Words are
composed of alphanumeric characters (letters and digits).
.TP
.B clear\-screen (C\-l)
Clear the screen leaving the current line at the top of the screen.
With an argument, refresh the current line without clearing the
screen.
.TP
.B redraw\-current\-line
Refresh the current line.  By default, this is unbound.
.PD
.SS Commands for Manipulating the History
.PP
.PD 0
.TP
.B accept\-line (Newline, Return)
Accept the line regardless of where the cursor is.  If this line is
non\-empty, add it to the history list according to the state of the
.SM
.B HISTCONTROL
variable.  If the line is a modified history
line, then restore the history line to its original state.
.TP
.B previous\-history (C\-p)
Fetch the previous command from the history list, moving back in
the list.
.TP
.B next\-history (C\-n)
Fetch the next command from the history list, moving forward in the
list.
.TP
.B beginning\-of\-history (M\-<)
Move to the first line in the history.
.TP
.B end\-of\-history (M\->)
Move to the end of the input history, i.e., the line currently being
entered.
.TP
.B reverse\-search\-history (C\-r)
Search backward starting at the current line and moving `up' through
the history as necessary.  This is an incremental search.
.TP
.B forward\-search\-history (C\-s)
Search forward starting at the current line and moving `down' through
the history as necessary.  This is an incremental search.
.TP
.B non\-incremental\-reverse\-search\-history (M\-p)
Search backward through the history starting at the current line
using a non\-incremental search for a string supplied by the user.
.TP
.B non\-incremental\-forward\-search\-history (M\-n)
Search forward through the history using a non\-incremental search for
a string supplied by the user.
.TP
.B history\-search\-forward
Search forward through the history for the string of characters
between the start of the current line and the current point.  This
is a non-incremental search.  By default, this command is unbound.
.TP
.B history\-search\-backward
Search backward through the history for the string of characters
between the start of the current line and the current point.  This
is a non-incremental search.  By default, this command is unbound.
.TP
.B yank\-nth\-arg (M\-C\-y)
Insert the first argument to the previous command (usually
the second word on the previous line) at point (the current
cursor position).  With an argument
.IR n ,
insert the \fIn\fPth word from the previous command (the words
in the previous command begin with word 0).  A negative argument
inserts the \fIn\fPth word from the end of the previous command.
.TP
.B
yank\-last\-arg (M\-.\^, M\-_\^)
Insert the last argument to the previous command (the last word on
the previous line).  With an argument,
behave exactly like \fByank-nth-arg\fP.
.TP
.B shell\-expand\-line (M\-C\-e)
Expand the line the way the shell does when it reads it.  This
performs alias and history expansion as well as all of the shell
word expansions.  See
.SM
.B HISTORY EXPANSION
below for a description of history expansion.
.TP
.B history\-expand\-line (M\-^)
Perform history expansion on the current line.  See
.SM
.B HISTORY EXPANSION
below for a description of history expansion.
.TP
.B insert\-last\-argument (M\-.\^, M\-_\^)
A synonym for \fByank\-last\-arg\fP.
.TP
.B operate-and-get-next (C\-o)
Accept the current line for execution and fetch the next line
relative to the current line from the history for editing.  Any
argument is ignored.
.PD
.SS Commands for Changing Text
.PP
.PD 0
.TP
.B delete\-char (C\-d)
Delete the character under the cursor.  If point is at the
beginning of the line, there are no characters in the line, and
the last character typed was not
.BR C\-d ,
then return
.SM
.BR EOF .
.TP
.B backward\-delete\-char (Rubout)
Delete the character behind the cursor.  When given a numeric argument,
save the deleted text on the kill\-ring.
.TP
.B quoted\-insert (C\-q, C\-v)
Add the next character that you type to the line verbatim.  This is
how to insert characters like \fBC\-q\fP, for example.
.TP
.B tab\-insert (C-v TAB)
Insert a tab character.
.TP
.B self\-insert (a,\ b,\ A,\ 1,\ !,\ ...)
Insert the character typed.
.TP
.B transpose\-chars (C\-t)
Drag the character before point forward over the character at point.
Point moves forward as well.  If point is at the end of the line, then
transpose the two characters before point.  Negative arguments don't work.
.TP
.B transpose\-words (M\-t)
Drag the word behind the cursor past the word in front of the cursor
moving the cursor over that word as well.
.TP
.B upcase\-word (M\-u)
Uppercase the current (or following) word.  With a negative argument,
do the previous word, but do not move point.
.TP
.B downcase\-word (M\-l)
Lowercase the current (or following) word.  With a negative argument,
do the previous word, but do not move point.
.TP
.B capitalize\-word (M\-c)
Capitalize the current (or following) word.  With a negative argument,
do the previous word, but do not move point.
.PD
.SS Killing and Yanking
.PP
.PD 0
.TP
.B kill\-line (C\-k)
Kill the text from the current cursor position to the end of the line.
.TP
.B backward\-kill\-line (C\-x C\-Rubout)
Kill backward to the beginning of the line.
.TP
.B unix\-line\-discard (C\-u)
Kill backward from point to the beginning of the line.
.\" There is no real difference between this and backward-kill-line
.TP
.B kill\-whole\-line
Kill all characters on the current line, no matter where the
cursor is.  By default, this is unbound.
.TP
.B kill\-word  (M\-d)
Kill from the cursor to the end of the current word, or if between
words, to the end of the next word.  Word boundaries are the same as
those used by \fBforward\-word\fP.
.TP
.B backward\-kill\-word (M\-Rubout)
Kill the word behind the cursor.  Word boundaries are the same as
those used by \fBbackward\-word\fP.
.TP
.B unix\-word\-rubout (C\-w)
Kill the word behind the cursor, using white space as a word boundary.
The word boundaries are different from backward\-kill\-word.
.TP
.B delete\-horizontal\-space
Delete all spaces and tabs around point.  By default, this is unbound.
.TP
.B yank (C\-y)
Yank the top of the kill ring into the buffer at the cursor.
.TP
.B yank\-pop (M\-y)
Rotate the kill\-ring, and yank the new top.  Only works following
.B yank
or
.BR yank\-pop .
.PD
.SS Numeric Arguments
.PP
.PD 0
.TP
.B digit\-argument (M\-0, M\-1, ..., M\-\-)
Add this digit to the argument already accumulating, or start a new
argument.  M\-\- starts a negative argument.
.TP
.B universal\-argument
Each time this is executed, the argument count is multiplied by four.
The argument count is initially one, so executing this function the
first time makes the argument count four.  By default, this is not
bound to a key.
.PD
.SS Completing
.PP
.PD 0
.TP
.B complete (TAB)
Attempt to perform completion on the text before point.
.B Bash
attempts completion treating the text as a variable (if the
text begins with \fB$\fP), username (if the text begins with
\fB~\fP), hostname (if the text begins with \fB@\fP), or
command (including aliases and functions) in turn.  If none
of these produces a match, filename completion is attempted.
.TP
.B possible\-completions (M-?)
List the possible completions of the text before point.
.TP
.B insert\-completions
Insert all completions of the text before point
that would have been generated by
\fBpossible\-completions\fP.  By default, this
is not bound to a key.
.TP
.B complete\-filename (M\-/)
Attempt filename completion on the text before point.
.TP
.B possible\-filename\-completions (C\-x /)
List the possible completions of the text before point,
treating it as a filename.
.TP
.B complete\-username (M\-~)
Attempt completion on the text before point, treating
it as a username.
.TP
.B possible\-username\-completions (C\-x ~)
List the possible completions of the text before point,
treating it as a username.
.TP
.B complete\-variable (M\-$)
Attempt completion on the text before point, treating
it as a shell variable.
.TP
.B possible\-variable\-completions (C\-x $)
List the possible completions of the text before point,
treating it as a shell variable.
.TP
.B complete\-hostname (M\-@)
Attempt completion on the text before point, treating
it as a hostname.
.TP
.B possible\-hostname\-completions (C\-x @)
List the possible completions of the text before point,
treating it as a hostname.
.TP
.B complete\-command (M\-!)
Attempt completion on the text before point, treating
it as a command name.  Command completion attempts to
match the text against aliases, reserved words, shell
functions, builtins, and finally executable filenames,
in that order.
.TP
.B possible\-command\-completions (C\-x !)
List the possible completions of the text before point,
treating it as a command name.
.TP
.B dynamic\-complete\-history (M-TAB)
Attempt completion on the text before point, comparing
the text against lines from the history list for possible
completion matches.
.TP
.B complete\-into\-braces (M\-{)
Perform filename completion and return the list of possible completions
enclosed within braces so the list is available to the shell (see
.B Brace Expansion
above).
.PD
.SS Keyboard Macros
.PP
.PD 0
.TP
.B start\-kbd\-macro (C-x (\^)
Begin saving the characters typed into the current keyboard macro.
.TP
.B end\-kbd\-macro (C-x )\^)
Stop saving the characters typed into the current keyboard macro
and save the definition.
.TP
.B call\-last\-kbd\-macro (C-x e)
Re-execute the last keyboard macro defined, by making the characters
in the macro appear as if typed at the keyboard.
.PD
.SS Miscellaneous
.PP
.PD 0
.TP
.B re\-read\-init\-file (C\-x C\-r)
Read in the contents of your init file, and incorporate
any bindings or variable assignments found there.
.TP
.B abort (C\-g)
Abort the current editing command and
ring the terminal's bell (subject to the setting of
.BR bell\-style ).
.TP
.B do\-uppercase\-version (M\-a, M\-b, ...)
Run the command that is bound to the corresponding uppercase
character.
.TP
.B prefix\-meta (ESC)
Metafy the next character typed.
.SM
.B ESC
.B f
is equivalent to
.BR Meta\-f .
.TP
.B undo (C\-_, C\-x C\-u)
Incremental undo, separately remembered for each line.
.TP
.B revert\-line (M\-r)
Undo all changes made to this line.  This is like typing the
.B undo
command enough times to return the line to its initial state.
.TP
.B tilde\-expand (M\-~)
Perform tilde expansion on the current word.
.TP
.B dump\-functions
Print all of the functions and their key bindings to the
readline output stream.  If a numeric argument is supplied,
the output is formatted in such a way that it can be made part
of an \fIinputrc\fP file.
.TP
.B display\-shell\-version (C\-x C\-v)
Display version information about the current instance of
.BR bash .
.PD
.SH HISTORY
When interactive, the shell provides access to the \fIcommand history\fP,
the list of commands previously typed.  The text of the last
.SM
.B HISTSIZE
commands (default 500) is saved in a history list.  The shell
stores each command in the history list prior to parameter and
variable expansion (see
.SM
.B EXPANSION
above) but after history expansion is performed, subject to the
values of the shell variables
.B command_oriented_history
and
.SM
.BR HISTCONTROL .
On startup, the history is initialized from the file named by
the variable
.SM
.B HISTFILE
(default \fI~/.bash_history\fP).
.SM
.B HISTFILE
is truncated, if necessary, to contain no more than
.SM
.B HISTFILESIZE
lines.
The builtin command
.B fc
(see
.SM
.B SHELL BUILTIN COMMANDS
below) may be used to list or edit and re-execute a portion of
the history list.
The
.B history
builtin can be used to display the history list and manipulate the
history file.  When using the command-line editing, search commands
are available in each editing mode that provide access to the
history list.  When an interactive shell exits, the last
.SM
.B HISTSIZE
lines are copied from the history list to
.SM
.BR HISTFILE .
If
.SM
.B HISTFILE
is unset, or if the history file is unwritable, the history is
not saved.
.SH "HISTORY EXPANSION"
.PP
The shell supports a history expansion feature that
is similar to the history expansion in
.BR csh.
This section describes what syntax features are available.  This
feature is enabled by default for interactive shells, and can be
disabled using the
.B \+H
option to the
.B set
builtin command (see
.SM
.B SHELL BUILTIN COMMANDS
below).  Non-interactive shells do not perform history expansion.
.PP
History expansion is performed immediately after a complete line
is read, before the shell breaks it into words.
It takes place in two parts.  The first is to determine
which line from the previous history to use during
substitution.  The second is to select portions of that line for
inclusion into the current one.  The line selected from the
previous history is the \fIevent\fP, and the portions of that
line that are acted upon are \fIwords\fP.  The line is broken
into words in the same fashion as when reading input, so that
several \fImetacharacter\fP\-separated words surrounded by quotes
are considered as one word.  Only backslash (\^\fB\e\fP\^)
and single quotes can quote
the history escape character, which is \^\fB!\fP\^ by default.
.PP
The shell allows control of the various characters used by the
history expansion mechanism (see the description of
.B histchars
above under
.BR "Shell Variables" ).
.SS Event Designators
.PP
An event designator is a reference to a command line entry in the
history list.
.PP
.PD 0
.TP
.B !
Start a history substitution, except when followed by a
.BR blank ,
newline, = or (.
.TP
.B !!
Refer to the previous command.  This is a synonym for `!\-1'.
.TP
.B !\fIn\fR
Refer to command line
.IR n .
.TP
.B !\-\fIn\fR
Refer to the current command line minus
.IR n .
.TP
.B !\fIstring\fR
Refer to the most recent command starting with 
.IR string .
.TP
.B !?\fIstring\fR\fB[?]\fR
Refer to the most recent command containing
.IR string .
.TP
.B \d\s+2^\s-2\u\fIstring1\fP\d\s+2^\s-2\u\fIstring2\fP\d\s+2^\s-2\u
Quick substitution.  Repeat the last command, replacing
.I string1
with
.IR string2 .
Equivalent to
``!!:s/\fIstring1\fP/\fIstring2\fP/''
(see \fBModifiers\fP below).
.TP
.B !#
The entire command line typed so far.
.PD
.SS Word Designators
.PP
A 
.B :
separates the event specification from the word
designator.  It can be omitted if the word designator begins with a
.BR ^ ,
.BR $ ,
.BR * ,
or
.BR % .
Words are numbered from the beginning of the line,
with the first word being denoted by a 0 (zero).
.PP
.PD 0
.TP
.B 0 (zero)
The zeroth word.  For the shell, this is the command
word.
.TP
.I n
The \fIn\fRth word.
.TP
.B ^
The first argument.  That is, word 1.
.TP
.B $
The last argument.
.TP
.B %
The word matched by the most recent `?\fIstring\fR?' search.
.TP
.I x\fB\-\fPy
A range of words; `\-\fIy\fR' abbreviates `0\-\fIy\fR'.
.TP
.B *
All of the words but the zeroth.  This is a synonym
for `\fI1\-$\fP'.  It is not an error to use
.B *
if there is just one
word in the event; the empty string is returned in that case.
.TP
.B x*
Abbreviates \fIx\-$\fP.
.TP
.B x\-
Abbreviates \fIx\-$\fP like \fBx*\fP, but omits the last word.
.PD
.SS Modifiers
.PP
After the optional word designator, you can add a sequence of one
or more of the following modifiers, each preceded by a `:'.
.PP
.PD 0
.PP
.TP
.B h
Remove a trailing pathname component, leaving only the head.
.TP
.B r
Remove a trailing suffix of the form \fI.xxx\fP, leaving the
basename.
.TP
.B e
Remove all but the trailing suffix.
.TP
.B t
Remove all leading pathname components, leaving the tail.
.TP
.B p
Print the new command but do not execute it.
.TP
.B q
Quote the substituted words, escaping further substitutions.
.TP
.B x
Quote the substituted words as with
.BR q ,
but break into words at
.B blanks
and newlines.
.TP
.B s/\fIold\fP/\fInew\fP/
Substitute
.I new
for the first occurrence of
.I old
in the event line.  Any delimiter can be used in place of /.  The
final delimiter is optional if it is the last character of the
event line.  The delimiter may be quoted in
.I old
and
.I new
with a single backslash.  If & appears in
.IR new ,
it is replaced by
.IR old .
A single backslash will quote the &.
.TP
.B &
Repeat the previous substitution.
.TP
.B g
Cause changes to be applied over the entire event line.  This is
used in conjunction with `\fB:s\fP' (e.g., `\fB:gs/\fIold\fP/\fInew\fP/\fR')
or `\fB:&\fP'.  If used with
`\fB:s\fP', any delimiter can be used
in place of /, and the final delimiter is optional
if it is the last character of the event line.
.PD
.SH "ARITHMETIC EVALUATION"
The shell allows arithmetic expressions to be evaluated, under
certain circumstances (see the \fBlet\fP builtin command and
\fBArithmetic Expansion\fP).
Evaluation
is done in long integers with no check for overflow, though division
by 0 is trapped and flagged as an error.  The following list of
operators is grouped into levels of equal-precedence operators.
The levels are listed in order of decreasing precedence.
.PP
.PD 0
.TP
.B \- +
unary minus and plus
.TP
.B ! ~
logical and bitwise negation
.TP
.B * / %
multiplication, division, remainder
.TP
.B + \-
addition, subtraction
.TP
.B << >>
left and right bitwise shifts
.TP
.B <= >= < >
comparison
.TP
.B == !=
equality and inequality
.TP
.B &
bitwise AND
.TP
.B ^
bitwise exclusive OR
.TP
.B |
bitwise OR
.TP
.B &&
logical AND
.TP
.B ||
logical OR
.TP
.B = *= /= %= += \-= <<= >>= &= ^= |=
assignment
.PD
.PP
Shell variables are allowed as operands; parameter expansion is
performed before the expression is evaluated. 
The value of a parameter is coerced to a long integer within
an expression.  A shell variable need not have its integer attribute
turned on to be used in an expression.
.PP
Constants with a leading 0 are interpreted as octal numbers.
A leading \fI0x\fP or \fI0X\fP denotes hexadecimal.  Otherwise,
numbers take the form [\fIbase#\fP]n, where \fIbase\fP is a
decimal number between 2 and 36 representing the arithmetic
base, and \fIn\fP is a number in that base.  If \fIbase\fP is
omitted, then base 10 is used.
.PP
Operators are evaluated in order of precedence.  Sub-expressions in
parentheses are evaluated first and may override the precedence
rules above.
.SH "SHELL BUILTIN COMMANDS"
.\" start of bash_builtins
.zZ
.PD 0
.TP
\fB:\fP [\fIarguments\fP]
.PD
No effect; the command does nothing beyond expanding
.I arguments
and performing any specified
redirections.  A zero exit code is returned.
.TP
.PD 0
\fB .\| \fP \fIfilename\fP [\fIarguments\fP]
.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, pathnames in
.SM
.B PATH
are used to find the directory containing
.IR filename .
The file searched for in
.SM
.B PATH
need not be executable.  The current directory is
searched if no file is found in
.SM
.BR PATH .
If any \fIarguments\fP are supplied, they become the positional
parameters when \fIfile\fP is executed.  Otherwise the positional
parameters are unchanged.
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.
.TP
\fBalias\fP [\fIname\fP[=\fIvalue\fP] ...]
\fBAlias\fP with no arguments prints the list of aliases in the form
\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]
Place \fIjobspec\fP in the background, as if it had been started with
.BR & .
If \fIjobspec\fP 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, if \fIjobspec\fP was not found or started without
job control.
.TP
.PD 0
\fBbind\fP [\fB\-m\fP \fIkeymap\fP] [\fB\-lvd\fP] [\fB-q\fP \fIname\fP]
.TP
\fBbind\fP [\fB\-m\fP \fIkeymap\fP] \fB-f\fP \fIfilename\fP
.TP
\fBbind\fP [\fB\-m\fP \fIkeymap\fP] \fIkeyseq\fP:\fIfunction-name\fP
.PD
Display current
.B readline
key and function bindings, or bind a key sequence to a
.B readline
function or macro.  The binding syntax accepted is identical to that of
.IR .inputrc ,
but each binding 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; \fIemacs\fP is
equivalent to \fIemacs-standard\fP.
.TP
.B \-l
List the names of all \fBreadline\fP functions
.TP
.B \-v
List current function names and bindings
.TP
.B \-d
Dump function names and bindings in such a way that they can be re-read
.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
.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 ,
or
.B until
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 the shell is not executing
a loop when
.B break
is executed.
.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 you wish to define a
function whose name is the same as a shell builtin,
but need the functionality of the
builtin within the function itself.  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
\fBcd\fP [\fIdir\fP]
Change the current directory to \fIdir\fP.  The variable
.SM
.B HOME
is the
default
.IR dir .
The variable
.SM
.B CDPATH
defines the search path for
the directory containing
.IR dir .
Alternative directory names 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.  An argument of
.B \-
is equivalent to
.SM
.BR $OLDPWD .
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
.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 pathname
used to invoke
.I command
to be printed; the
.B \-V
option produces a more verbose description.
An argument of
.B \-\-
disables option checking for the rest of the arguments.
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
\fBcontinue\fP [\fIn\fP]
Resume the next iteration of the enclosing
.BR for ,
.BR while ,
or
.B until
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 the
shell is not executing a loop when
.B continue
is executed.
.TP
.PD 0
\fBdeclare\fP [\fB\-frxi\fP] [\fIname\fP[=\fIvalue\fP]]
.TP
\fBtypeset\fP [\fB\-frxi\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 instead.  The options can
be used to restrict output to variables with the specified attribute.
.RS
.PD 0
.TP
.B \-f
Use function names only
.TP
.B \-r
Make \fIname\fPs readonly.  These names cannot then be assigned values
by subsequent assignment statements.
.TP
.B \-x
Mark \fIname\fPs for export to subsequent commands via the environment.
.TP
.B \-i
The variable is treated as an integer; arithmetic evaluation (see
.SM
.B "ARITHMETIC EVALUATION" ") "
is performed when the variable is assigned a value.
.PD
.PP
Using `+' instead of `\-'
turns off the attribute instead.  When used in a function, makes
\fIname\fPs local, as with the 
.B local
command.  The return value is 0 unless an illegal option is encountered,
an attempt is made to define a function using "-f foo=bar",
one of the \fInames\fP is not a legal shell variable name,
an attempt is made to turn off readonly status for a readonly variable,
or an attempt is made to display a non-existant function with -f.
.RE
.TP
.B dirs [\fB-l\fP] [\fB+/\-n\fP]
Display the list of currently remembered directories.  Directories
are added to the list with the 
.B pushd
command; the
.B popd
command moves back up through the list.
.RS
.PD 0
.TP
.B +n
displays the \fIn\fPth entry counting from the left of the list
shown by
.B dirs
when invoked without options, starting with zero.
.TP
.B \-n
displays the \fIn\fPth entry counting from the right of the list
shown by
.B dirs
when invoked without options, starting with zero.
.TP
.B \-l
produces a longer listing; the default listing format uses a 
tilde to denote the home directory.
.PD
.PP
The return value is 0 unless an
illegal option is supplied or \fIn\fP indexes beyond the end
of the directory stack.
.RE
.TP
\fBecho\fP [\fB\-neE\fP] [\fIarg\fP ...]
Output the \fIarg\fPs, separated by spaces.  The return status is
always 0.  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.
.RS
.PD 0
.TP
.B \ea
alert (bell)
.TP
.B \eb
backspace
.TP
.B \ec
suppress trailing newline
.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 \ennn
the character whose ASCII code is \fInnn\fP (octal)
.PD
.RE
.TP
\fBenable\fP [\fB\-n\fP] [\fB\-all\fP] [\fIname\fP ...]
Enable and disable builtin shell commands.  This allows
the execution of a disk command which has the same name as a shell
builtin without specifying a full pathname.
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, type
``enable -n test''.  If no arguments are given,
a list of all enabled shell builtins is printed.
If only \fB\-n\fP is supplied, a list of all disabled
builtins is printed.  If only \fB\-all\fP is supplied,
the list printed includes all builtins, with an
indication of whether or not each is enabled.
.B enable
accepts
.B \-a
as a synonym for
.BR \-all .
The return value is 0 unless a
.I name
is not a shell builtin.
.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 the
.B eval
command.  If there are no
.IR args ,
or only null arguments,
.B eval
returns true.
.TP
\fBexec\fP [[\fB\-\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 first argument is 
.BR \- ,
the shell places a dash in the zeroth arg passed to 
.IR command .
This is what login does.  If the file
cannot be executed for some reason, a non-interactive shell exits,
unless the shell variable \fBno_exit_on_failed_exec\fP exists, in
which case it returns failure.  An interactive shell returns failure
if the file cannot be executed.
If
.I command
is not specified, any redirections take effect in the current shell,
and the return status is 0.
.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
.PD 0
\fBexport\fP [\fB\-nf\fP\^] [\fIname\fP[=\fIword\fP]] ...
.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 all names that are exported in this shell is printed.
The
.B \-n
option causes the export property to be removed from the
named variables.  An argument of
.B \-\-
disables option checking for the rest of the arguments.
.B export
returns an exit status of 0 unless an illegal option is
encountered,
one of the \fInames\fP is not a legal shell variable name, or
.B \-f
is supplied with a
.I name
that is not a function.
.TP
.PD 0
\fBfc\fP [\fB\-e\fP \fIename\fP] [\fB\-nlr\fP] [\fIfirst\fP] [\fIlast\fP]
.TP
\fBfc\fP \fB\-s\fP [\fIpat\fP=\fIrep\fP] [\fIcmd\fP]
.PD
Fix Command.  In the first form, a range of commands from
.I first
to
.I last
is selected from the history list.
.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).  If 
.I last
is not specified it is set to
the current command for listing (so that
.B fc \-l \-10
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
flag suppresses
the command numbers when listing.  The
.B \-r
flag reverses the order of
the commands.  If the
.B \-l
flag 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.
A useful alias to use with this is ``r=fc \-s'',
so that typing ``r cc''
runs the last command beginning with ``cc'' and typing ``r''
re-executes the last command.
.sp 1
If the first form is used, the return value is 0 unless an illegal
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]
Place
.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 [\fIargs\fP]
.B getopts
is used by shell procedures to parse positional parameters.
.I optstring
contains the option letters to be recognized; if a letter
is followed by a colon, the option is expected to have an
argument, which should be separated from it by white space.
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
.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 illegal options or missing option arguments are
encountered.
If the variable
.SM
.B OPTERR
is set to 0, no error message will be displayed, even if the first
character of 
.I optstring
is not a colon.
.sp 1
If an illegal 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 ,
.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
normally parses the positional parameters, but if more arguments are
given in
.IR args ,
.B getopts
parses those instead.
.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\-r\fP] [\fIname\fP]
For each
.IR name ,
the full pathname of the command is determined
and remembered.  The
.B \-r
option causes the shell to forget all
remembered locations.  If no arguments are given, information
about remembered commands is printed.
An argument of
.B \-\-
disables option checking for the rest of the arguments.  The return
status is true unless a
.I name
is not found or an illegal option is supplied.
.TP
\fBhelp\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 a list of the builtins is printed.  The return status is 0
unless no command matches
.IR pattern .
.TP
.PD 0
\fBhistory\fP [\fIn\fP]
.TP
\fBhistory\fP \fB\-rwan\fP [\fIfilename\fP]
.\".TP
.\"\fBhistory\fP \fB\-s\fP \fIargs\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 a non-option argument 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 \-a
Append the ``new'' history lines (history lines entered since the
beginning of the current \fBbash\fP session) 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 use them as the current history
.TP
.B \-w
Write the current history to the history file, overwriting the
history file's contents.
.\".TP
.\".B \-s
.\"perform history
.\"substitution on the following \fIargs\fP and display
.\"the result on the standard output.
.PD
.PP
The return value is 0 unless an illegal option is encountered or an
error occurs while reading or writing the history file.
.RE
.TP
.PD 0
\fBjobs\fP [\fB\-lnp\fP] [ \fIjobspec\fP ... ]
.TP
\fBjobs\fP \fB\-x\fP \fIcommand\fP [ \fIargs\fP ... ]
.PD
The first form lists the active jobs.  The
.B \-l
option lists process IDs
in addition to the normal information; the
.B \-p
option lists only the process ID of the job's process group
leader.  The
.B \-n
option displays only jobs that have changed status since
last notified.  If
.I jobspec
is given, output is restricted to information about that job.
The return status is 0 unless an illegal option is encountered
or an illegal
.I jobspec
is supplied.
.sp 1
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.
.TP
.PD 0
\fBkill\fP [\fB-s sigspec\fP | \fB\-sigspec\fP] [\fIpid\fP | \fIjobspec\fP] ...
.TP
\fBkill\fP \fB\-l\fP [\fIsignum\fP]
.PD
Send the signal named by
.I sigspec
to the processes named by
.I pid
or
.IR jobspec .
.I sigspec
is either a signal name such as
.SM
.B SIGKILL
or a signal number.  If
.I sigspec
is a signal name, the name is case insensitive and may be
given with or without the
.SM
.B SIG
prefix.
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 specified signals are listed, and
the return status is 0.
An argument of
.B \-\-
disables option checking for the rest of the arguments.
.B kill
returns true if at least one signal was successfully sent, or false
if an error occurs or an illegal option is encountered.
.TP
\fBlet\fP \fIarg\fP [\fIarg\fP ...]
Each
.I arg
is an arithmetic expression to be evaluated (see
.SM
.BR "ARITHMETIC EVALUATION" ).
If the last
.I arg
evaluates to 0,
.B let
returns 1; 0 is returned otherwise.
.TP
\fBlocal\fP [\fIname\fP[=\fIvalue\fP] ...]
For each argument, create a local variable named
.IR name ,
and assign it
.IR value .
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.
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, or an illegal
.I name
is supplied.
.TP
.B logout
Exit a login shell.
.TP
\fBpopd\fP [\fB+/\-n\fP]
Removes entries from the directory stack.  With no arguments,
removes the top directory from the stack, and performs a
.B cd
to the new top directory.
.RS
.PD 0
.TP
.B +n
removes the \fIn\fPth entry counting from the left of the list
shown by
.BR dirs ,
starting with zero.  For example: ``popd +0''
removes the first directory, ``popd +1'' the second.
.TP
.B \-n
removes the \fIn\fPth entry counting from the right of the list
shown by
.BR dirs ,
starting with zero.  For example: ``popd -0''
removes the last directory, ``popd -1'' the next to last.
.PD
.PP
If the
.B popd
command is successful, a 
.B dirs
is performed as well, and the return status is 0.
.B popd
returns false if an illegal option is encountered, the directory stack
is empty, a non-existent directory stack entry is specified, or the
directory change fails.
.RE
.TP
.PD 0
\fBpushd\fP [\fIdir\fP]
.TP
\fBpushd\fP \fB+/\-n\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, exchanges the top two directories
and returns 0, unless the directory stack is empty.
.RS
.PD 0
.TP
.B +n
Rotates the stack so that the \fIn\fPth directory
(counting from the left of the list shown by
.BR dirs )
is at the top.
.TP
.B \-n
Rotates the stack so that the \fIn\fPth directory
(counting from the right) is at the top.
.TP
.B dir
adds
.I dir
to the directory stack at the top, making it the
new current working directory.
.PD
.PP
If the
.B pushd
command is successful, a 
.B dirs
is performed as well.
If the first form is used,
.B pushd
returns 0 unless the cd to
.I dir
fails.  With the second form,
.B pushd
returns 0 unless the directory stack is empty,
a non-existant directory stack element is specified,
or the directory change to the specified new current directory
fails.
.RE
.TP
\fBpwd\fP
Print the absolute pathname of the current working directory.
The path printed contains no symbolic links if the
.B \-P
option to the
.B set
builtin command is set.
See also the description of 
.B nolinks
under
.B Shell Variables
above).  The return status is 0 unless an error occurs while
reading the pathname of the current directory.
.TP
\fBread\fP [\fB\-r\fP] [\fIname\fP ...]
One line is read from the standard input, and the first word
is assigned to the first
.IR name ,
the second word to the second
.IR name ,
and so on, with leftover words assigned to the last
.IR name .
Only the
characters in 
.SM
.B IFS
are recognized as word delimiters.  If no
.I names
are supplied, the line read is assigned to the variable
.SM
.BR REPLY .
The return code is zero, unless end-of-file is encountered.  If the
.B \-r
option
is given, a backslash-newline pair is not ignored, and
the backslash is considered to be part of the line.
.TP
.PD 0
\fBreadonly\fP [\fB\-f\fP] [\fIname\fP ...]
.TP
\fBreadonly -p\fP
.PD
The given
\fInames\fP are marked readonly and the values of these
\fInames\fP
may not be changed by subsequent assignment.
If the
.B \-f
option is supplied, the functions corresponding to the
\fInames\fP are so
marked.  If no arguments are given, or if the
.B \-p
option is supplied, a list of all readonly names
is printed.
An argument of
.B \-\-
disables option checking for the rest of the arguments.  The
return status is 0 unless an illegal option is encountered,
one of the \fInames\fP is not a legal 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 exit with the return value specified by
.IR n .
If 
.I n
is omitted, the return status is that of the last command
executed in the function body.  If 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 used outside a
function and not during execution of a script by \fB.\fP\^,
the return status is false.
.TP
\fBset\fP [\fB\-\-abefhkmnptuvxldCHP\fP] [\fB-o\fP \fIoption\fP] [\fIarg\fP ...]
.RS
.PD 0
.TP 8
.B \-a
Automatically mark variables which are modified or created for export
to the environment of subsequent commands.
.TP 8
.B \-b
Cause the status of terminated background jobs to be reported
immediately, rather than before the next primary prompt.
(Also see
.B notify
under
.B Shell Variables
above).
.TP 8
.B \-e
Exit immediately if a \fIsimple-command\fP (see
.SM
.B SHELL GRAMMAR
above) exits with a non\-zero status.  The shell does not exit if the
command that fails is part of an
.I until
or
.I while
loop,
part of an
.I if
statement, part of a
.B &&
or
.B \(bv\|\(bv
list, or if the command's return value is
being inverted via
.BR ! .
.TP 8
.B \-f
Disable pathname expansion.
.TP 8 
.B \-h
Locate and remember function commands as functions are
defined.  Function commands are normally looked up when
the function is executed.
.TP 8
.B \-k
All keyword arguments 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 flag is on
by default for interactive shells on systems that support
it (see
.SM
.B JOB CONTROL
above).  Background processes run in a separate process
group and a line containing their exit status is printed
upon their completion.
.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 for
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
The shell performs brace expansion (see
.B Brace Expansion
above).  This is on by default.
.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 \-nolineediting
option.
.TP 8
.B errexit
Same as
.BR \-e .
.TP 8
.B histexpand
Same as
.BR \-H .
.TP 8
.B ignoreeof
The effect is as if the shell command `IGNOREEOF=10' had been executed
(see
.B Shell Variables
above).
.TP 8
.B interactive\-comments
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
above).
.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 nohash
Same as
.BR \-d .
.TP 8
.B notify
Same as
.BR \-b .
.TP 8
.B nounset
Same as
.BR \-u .
.TP 8
.B physical
Same as
.BR \-P .
.TP 8
.B posix
Change the behavior of bash where the default operation differs
from the Posix 1003.2 standard to match the standard.
.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.
.TP 8
.B xtrace
Same as
.BR \-x .
.PP
If no \fIoption-name\fP is supplied, the values of the current options are
printed.
.RE
.TP 8
.B \-p
Turn on
.I privileged
mode.  In this mode, the
.B $ENV
file is not processed, and shell functions
are not inherited from the environment.  This is enabled automatically
on startup if the effective user (group) id is not equal to the real
user (group) id.  Turning this option off causes the effective user
and group ids to be set to the real user and group ids.
.TP 8
.B \-t
Exit after reading and executing one command.
.TP 8
.B \-u
Treat unset variables as an error when performing
parameter expansion.  If expansion is attempted on an
unset variable, 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
.IR simple-command ,
.B bash
displays the expanded value of
.SM
.BR PS4 ,
followed by the command and its expanded arguments.
.TP 8
.B \-l
Save and restore the binding of \fIname\fP in a
\fBfor\fP \fIname\fP [in \fBword\fP] command (see
.SM
.B SHELL GRAMMAR
above).
.TP 8
.B \-d
Disable the hashing of commands that are looked up for execution.
Normally, commands are remembered in a hash table, and once
found, do not have to be looked up again.
.TP 8
.B \-C
The effect is as if the shell command `noclobber=' had been executed
(see
.B Shell Variables
above).
.TP 8
.B \-H
Enable
.B !
style history substitution.  This flag is on by
default when the shell is interactive.
.TP 8
.B \-P
If set, do not follow symbolic links when performing commands such as
.B cd
which change the current directory.  The physical directory is
used instead.
.TP 8
.B \-\-
If no arguments follow this flag, 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 flags are off by default
unless otherwise noted.
Using + rather than \- causes these flags
to be turned off.  The
flags can also be specified as options to an
invocation of the shell.  The current
set of flags may be found in
.BR $\- .
After the option arguments are processed,
the remaining \fIn\fP \fIarg\fPs are treated
as values for the positional
parameters and are assigned, in order, to 
.BR $1 ,
.BR $2 ,
.B ...
.BR $\fIn\fP .
If no options or \fIarg\fPs are supplied,
all shell variables are printed.  The return status is always true
unless an illegal 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$#\fP\-\fIn\fP+1 are unset.
If
.I n
is 0, no parameters are changed.
If
.I n 
is not given, it is assumed to be 1.
.I n
must be a non-negative number less than or equal to \fB$#\fP.
If
.I n
is greater than \fB$#\fP, the positional parameters are not changed.
The return status is greater than 0 if
.I n
is greater than
.B $#
or less than 0; otherwise 0.
.TP
\fBsuspend\fP [\fB\-f\fP]
Suspend the execution of this shell until it receives a
.SM
.B SIGCONT
signal.  The
.B \-f
option says not to complain if this is 
a login shell; just suspend anyway.  The return status is 0 unless
the shell is a login shell and
.B \-f
is not supplied, or if job control is not enabled.
.TP
.PD 0
\fBtest\fP \fIexpr\fP
.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 .
Expressions may be unary or binary.  Unary
expressions are often used to examine the status of a file.  There
are string operators and numeric comparison operators as well.  Each
operator and operand must be a separate argument.  If \fIfile\fP
is of the form /dev/fd/\fIn\fP, then file descriptor \fIn\fP is
checked.
.RS
.PD 0
.TP
.B \-b \fIfile\fP
True if \fIfile\fP exists and is block special.
.TP
.B \-c \fIfile\fP
True if \fIfile\fP exists and is character special.
.TP
.B \-d \fIfile\fP
True if \fIfile\fP exists and is a directory.
.TP
.B \-e \fIfile\fP
True if \fIfile\fP exists.
.TP
.B \-f \fIfile\fP
True if \fIfile\fP exists and is a regular file.
.TP
.B \-g \fIfile\fP
True if \fIfile\fP exists and is set-group-id.
.TP
.B \-k \fIfile\fP
True if \fIfile\fP has its ``sticky'' bit set.
.TP
.B \-L \fIfile\fP
True if \fIfile\fP exists and is a symbolic link.
.TP
.B \-p \fIfile\fP
True if \fIfile\fP exists and is a named pipe.
.TP
.B \-r \fIfile\fP
True if \fIfile\fP exists and is readable.
.TP
.B \-s \fIfile\fP
True if \fIfile\fP exists and has a size greater than zero.
.TP
.B \-S \fIfile\fP
True if \fIfile\fP exists and is a socket.
.TP
.B \-t \fIfd\fP
True if
.I fd
is opened on a terminal.
.TP
.B \-u \fIfile\fP
True if \fIfile\fP exists and its set-user-id bit is set.
.TP
.B \-w \fIfile\fP
True if \fIfile\fP exists and is writable.
.TP
.B \-x \fIfile\fP
True if \fIfile\fP exists and is executable.
.TP
.B \-O \fIfile\fP
True if \fIfile\fP exists and is owned by the effective user id.
.TP
.B \-G \fIfile\fP
True if \fIfile\fP exists and is owned by the effective group id.
.TP
\fIfile1\fP \-\fBnt\fP \fIfile2\fP
True if \fIfile1\fP is newer (according to
modification date) than \fIfile2\fP.
.TP
\fIfile1\fP \-\fBot\fP \fIfile2\fP
True if \fIfile1\fP is older than file2.
.TP
\fIfile1\fP \fB\-ef\fP \fIfile\fP
True if \fIfile1\fP and \fIfile2\fP have the same device and
inode numbers.
.TP
.B \-z \fIstring\fP
True if the length of \fIstring\fP is zero.
.TP
.B \-n \fIstring\fP
.TP
\fIstring\fP
True if the length of
.I string
is non\-zero.
.TP
\fIstring1\fP \fB=\fP \fIstring2\fP
True if the strings are equal.
.TP
\fIstring1\fP \fB!=\fP \fIstring2\fP
True if the strings are not equal.
.TP
.B ! \fIexpr\fP
True if
.I expr
is false.
.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.
.TP
.I arg1 \fBOP\fP arg2
.SM
.B OP
is one of
.BR \-eq ,
.BR \-ne ,
.BR \-lt ,
.BR \-le ,
.BR \-gt ,
or
.BR \-ge .
These arithmetic binary operators return true if \fIarg1\fP
is equal, not-equal, less-than, less-than-or-equal,
greater-than, or greater-than-or-equal than \fIarg2\fP,
respectively.
.I Arg1
and
.I arg2
may be positive integers, negative integers, or the special
expression \fB\-l\fP \fIstring\fP, which evaluates to the
length of 
.IR string .
.PD
.RE
.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\-l\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 or
.BR \- ,
all specified signals are
reset to their original values (the values they had
upon entrance to the shell).  If 
.I arg
is the null string this
signal is ignored by the shell and by the
commands it invokes.
.I sigspec
is either
a signal name defined in <\fIsignal.h\fP>, or a signal number. 
If
.I sigspec
is
.SM
.B EXIT
(0) the command
.I arg
is executed on exit from
the shell.  With no arguments,
.B trap
prints the list of commands associated with each signal number.
The 
.B \-l
option causes the shell to
print a list of signal names and their corresponding
numbers.  An argument of
.B \-\-
disables option checking for the rest of the arguments.
Signals ignored upon entry to the shell cannot be trapped or reset.
Trapped signals are reset to their original values in a child
process when it is created.  The return status is false if either
the trap name or number is invalid; otherwise
.B trap
returns true.
.TP
\fBtype\fP [\fB\-all\fP] [\fB\-type\fP | \fB\-path\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 \-type
flag is used,
.B type
prints a phrase 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 name is not found, then nothing is printed,
and an exit status of false is returned.
If the
.B \-path
flag 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
.B \-type
would not return
.IR file .
If a command is hashed,
.B \-path
prints the hashed value, not necessarily the file that appears
first in 
.SM
.BR PATH .
If the
.B \-all
flag 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 \-path
flag is not also used.
The table of hashed commands is not consulted
when using
.BR \-all .
.B type
accepts
.BR \-a ,
.BR \-t ,
and
.B \-p
in place of
.BR \-all ,
.BR \-type ,
and
.BR \-path ,
respectively.
An argument of
.B \-\-
disables option checking for the rest of the arguments.
.B type
returns true if any of the arguments are found, false if
none are found.
.TP
\fBulimit\fP [\fB\-SHacdfmstpnuv\fP [\fIlimit\fP]]
.B Ulimit
provides control over the resources available to the shell and to
processes started by it, on systems that allow such control.  The
value of
.I limit
can be a number in the unit specified for the resource, or the
value
.BR unlimited .
The \fBH\fP and \fBS\fP options specify that the hard or soft limit is
set for the given resource.  A hard limit cannot be increased once it
is set; a soft limit may be increased up to the value of the hard limit.
If neither \fBH\fP nor \fBS\fP is specified, the command applies to the
soft limit.  If
.I limit
is omitted, the current value of the soft limit of the resource is
printed, unless the \fBH\fP option is given.  When more than one resource
is specified, the limit name and unit is printed before the value.
Other options are interpreted as follows:
.RS
.PD 0
.TP
.B \-a
all current limits are reported
.TP
.B \-c
the maximum size of core files created
.TP
.B \-d
the maximum size of a process's data segment
.TP
.B \-f
the maximum size of files created by the shell
.TP
.B \-m
the maximum resident set size
.TP
.B \-s
the maximum stack size
.TP
.B \-t
the maximum amount of cpu time in seconds
.TP
.B \-p
the pipe size in 512-byte blocks (this may not be set)
.TP
.B \-n
the maximum number of open file descriptors (most systems do not
allow this value to be set, only displayed)
.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
.PD
.PP
An argument of
.B \-\-
disables option checking for the rest of the arguments.  If
.I limit
is given, it is the new value of the specified resource (the
.B \-a
option is display only).
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 \-p ,
which is in units of 512-byte blocks,
and
.B \-n
and
.BR \-u ,
which are unscaled values.  The return status is 0
unless an illegal option is encountered, a non-numeric argument
other than \fBunlimited\fP is supplied as \fIlimit\fP, or an
error occurs while setting a new limit.
.RE
.TP
\fBumask\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, or if the 
.B \-S
option is supplied, 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.
An argument of
.B \-\-
disables option checking for the rest of the arguments.  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 \fIname\fPs 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] [\fIname\fP ...]
For each
.IR name ,
remove the corresponding variable or, given the
.B \-f
option, function.
An argument of
.B \-\-
disables option checking for the rest of the arguments.
Note that
.SM
.BR PATH ,
.SM
.BR IFS ,
.SM
.BR PPID ,
.SM
.BR PS1 ,
.SM
.BR PS2 ,
.SM
.BR UID ,
and
.SM
.B EUID
cannot be unset.  If any of
.SM
.BR RANDOM ,
.SM
.BR SECONDS ,
.SM
.BR LINENO ,
or
.SM
.B HISTCMD
are unset, they lose their special properties, even if they are
subsequently reset.  The exit status is true unless a
.I name
does not exist or is non-unsettable.
.TP
\fBwait\fP [\fIn\fP]
Wait for the specified process and return its termination
status.
.I n
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 n
is not given, all currently active child processes
are waited for, and the return status is zero.  If
.I n
specifies a non-existant process or job, the return status is
127.  Otherwise, the return status is the exit status of the last
process or job waited for.
.\" bash_builtins
.if \n(zZ=1 .ig zZ
.SH INVOCATION
A \fIlogin shell\fP is one whose first character of argument zero is a
.BR \- ,
or one started with the 
.B \-login
flag.
.PP
An \fIinteractive\fP shell is one whose standard input and output are
both connected to terminals (as determined by
.IR isatty (3)),
or one started with the
.B \-i
option.
.SM
.B PS1
is set and
.B $\-
includes
.B i
if
.B bash
is interactive,
allowing a shell script or a startup file to test this state.
.PP
.nf
Login shells:
  On login (subject to the \fB\-noprofile\fP option):
        if \fI/etc/profile\fP exists, source it.

        if \fI~/.bash_profile\fP exists, source it,
          else if \fI~/.bash_login\fP exists, source it,
            else if \fI~/.profile\fP exists, source it.

  On exit:
        if \fI~/.bash_logout\fP exists, source it.

Non-login interactive shells:
  On startup (subject to the \fB\-norc\fP and \fB\-rcfile\fP options):
        if \fI~/.bashrc\fP exists, source it.

Non-interactive shells:
  On startup:
        if the environment variable \fBENV\fP is non-null, expand
        it and source the file it names, as if the command
                if [ "$ENV" ]; then . $ENV; fi
        had been executed, but do not use \fBPATH\fP to search
        for the pathname.  When not started in Posix mode, bash
        looks for \fBBASH_ENV\fP before \fBENV\fP.
.PP
.fi
.PP
If Bash is invoked as
.BR sh ,
it tries to mimic the behavior of
.B sh
as closely as possible.  For a login shell, it attempts to
source only
.I /etc/profile
and
.IR ~/.profile ,
in that order.  The
.B \-noprofile
option may still be used to disable this behavior.
A shell invoked as 
.B sh
does not attempt to source any other startup files.
.PP
When
.B bash 
is started in
.I posix
mode, as with the
.B \-posix
command line option, it follows the Posix standard for
startup files.  In this mode, the
.B ENV
variable is expanded and that file sourced; no other startup
files are read.
.SH "SEE ALSO"
.PD 0
.TP
\fIBash Features\fP, Brian Fox and Chet Ramey
.TP
\fIThe Gnu Readline Library\fP, Brian Fox and Chet Ramey
.TP
\fIThe Gnu History Library\fP, Brian Fox and Chet Ramey
.TP
\fIA System V Compatible Implementation of 4.2\s-1BSD\s+1 Job Control\fP, David Lennert
.TP
\fIPortable Operating System Interface (POSIX) Part 2: Shell and Utilities\fP, IEEE
.TP
\fIsh\fP(1), \fIksh\fP(1), \fIcsh\fP(1)
.TP
\fIemacs\fP(1), \fIvi\fP(1)
.TP
\fIreadline\fP(3)
.PD
.SH FILES
.PD 0
.TP
.FN /bin/bash
The \fBbash\fP executable
.TP
.FN /etc/profile
The systemwide initialization file, executed for login shells
.TP
.FN ~/.bash_profile
The personal initialization file, executed for login shells
.TP
.FN ~/.bashrc
The individual per-interactive-shell startup file
.TP
.FN ~/.inputrc
Individual \fIreadline\fP initialization file
.PD
.SH AUTHORS
.RS
Brian Fox, Free Software Foundation (primary author)
.br
bfox@ai.MIT.Edu
.PP
Chet Ramey, Case Western Reserve University
.br
chet@ins.CWRU.Edu
.SH BUG REPORTS
If you find a bug in
.B bash,
you should report it.  But first, you should
make sure that it really is a bug, and that it appears in the latest
version of
.B bash
that you have.
.PP
Once you have determined that a bug actually exists, use the
.I bashbug
command to submit a bug report.
If you have a fix, you are welcome to mail that
as well!
Suggestions and `philosophical' bug reports may be mailed
to \fPbug-bash\fP@\fIprep.ai.MIT.Edu\fP or posted to the Usenet
newsgroup
.BR gnu.bash.bug .
.PP
ALL bug reports should include:
.PP
.PD 0
.TP 20
The version number of \fBbash\fR
.TP
The hardware and operating system
.TP
The compiler used to compile
.TP
A description of the bug behaviour
.TP
A short script or `recipe' which exercises the bug
.PD
.PP
.I bashbug
inserts the first three items automatically into the template
it provides for filing a bug report.
.PP
Comments and bug reports concerning
this manual page should be directed to
.IR chet@ins.CWRU.Edu .
.SH BUGS
.PP
It's too big and too slow.
.PP
There are some subtle differences between 
.B bash
and traditional versions of
.BR sh ,
mostly because of the
.SM
.B POSIX
specification.
.PP
Aliases are confusing in some uses.
.zZ