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BASH-BUILTINS(7) Miscellaneous Information Manual BASH-BUILTINS(7)
NAME
bash-builtins - bash built-in commands, see bash(1)
SYNOPSIS
bash defines the following built-in commands: :, ., [, alias, bg, bind, break, builtin,
case, cd, command, compgen, complete, continue, declare, dirs, disown, echo, enable, eval,
exec, exit, export, fc, fg, getopts, hash, help, history, if, jobs, kill, let, local, lo-
gout, popd, printf, pushd, pwd, read, readonly, return, set, shift, shopt, source, sus-
pend, test, times, trap, type, typeset, ulimit, umask, unalias, unset, until, wait, while.
BASH BUILTIN COMMANDS
Unless otherwise noted, each builtin command documented in this section as accepting op-
tions preceded by - accepts -- to signify the end of the options. The :, true, false, and
test/[ builtins do not accept options and do not treat -- specially. The exit, logout,
return, break, continue, let, and shift builtins accept and process arguments beginning
with - without requiring --. Other builtins that accept arguments but are not specified
as accepting options interpret arguments beginning with - as invalid options and require
-- to prevent this interpretation.
: [arguments]
No effect; the command does nothing beyond expanding arguments and performing any
specified redirections. The return status is zero.
. filename [arguments]
source filename [arguments]
Read and execute commands from filename in the current shell environment and return
the exit status of the last command executed from filename. If filename does not
contain a slash, filenames in PATH are used to find the directory containing file-
name. The file searched for in PATH need not be executable. When bash is not in
posix mode, the current directory is searched if no file is found in PATH. If the
sourcepath option to the shopt builtin command is turned off, the PATH is not
searched. If any arguments are supplied, they become the positional parameters
when filename is executed. Otherwise the positional parameters are unchanged. If
the -T option is enabled, source inherits any trap on DEBUG; if it is not, any DE-
BUG trap string is saved and restored around the call to source, and source unsets
the DEBUG trap while it executes. If -T is not set, and the sourced file changes
the DEBUG trap, the new value is retained when source completes. The return status
is the status of the last command exited within the script (0 if no commands are
executed), and false if filename is not found or cannot be read.
alias [-p] [name[=value] ...]
Alias with no arguments or with the -p option prints the list of aliases in the
form alias name=value on standard output. When arguments are supplied, an alias is
defined for each name whose value is given. A trailing space in value causes the
next word to be checked for alias substitution when the alias is expanded. For
each name in the argument list for which no value is supplied, the name and value
of the alias is printed. Alias returns true unless a name is given for which no
alias has been defined.
bg [jobspec ...]
Resume each suspended job jobspec in the background, as if it had been started with
&. If jobspec is not present, the shell's notion of the current job is used. bg
jobspec returns 0 unless run when job control is disabled or, when run with job
control enabled, any specified jobspec was not found or was started without job
control.
bind [-m keymap] [-lpsvPSVX]
bind [-m keymap] [-q function] [-u function] [-r keyseq]
bind [-m keymap] -f filename
bind [-m keymap] -x keyseq:shell-command
bind [-m keymap] keyseq:function-name
bind [-m keymap] keyseq:readline-command
Display current readline key and function bindings, bind a key sequence to a read-
line function or macro, or set a readline variable. Each non-option argument is a
command as it would appear in .inputrc, but each binding or command must be passed
as a separate argument; e.g., '"\C-x\C-r": re-read-init-file'. Options, if sup-
plied, have the following meanings:
-m keymap
Use keymap as the keymap to be affected by the subsequent bindings. Accept-
able keymap names are emacs, emacs-standard, emacs-meta, emacs-ctlx, vi,
vi-move, vi-command, and vi-insert. vi is equivalent to vi-command (vi-move
is also a synonym); emacs is equivalent to emacs-standard.
-l List the names of all readline functions.
-p Display readline function names and bindings in such a way that they can be
re-read.
-P List current readline function names and bindings.
-s Display readline key sequences bound to macros and the strings they output
in such a way that they can be re-read.
-S Display readline key sequences bound to macros and the strings they output.
-v Display readline variable names and values in such a way that they can be
re-read.
-V List current readline variable names and values.
-f filename
Read key bindings from filename.
-q function
Query about which keys invoke the named function.
-u function
Unbind all keys bound to the named function.
-r keyseq
Remove any current binding for keyseq.
-x keyseq:shell-command
Cause shell-command to be executed whenever keyseq is entered. When
shell-command is executed, the shell sets the READLINE_LINE variable to the
contents of the readline line buffer and the READLINE_POINT and READ-
LINE_MARK variables to the current location of the insertion point and the
saved insertion point (the mark), respectively. If the executed command
changes the value of any of READLINE_LINE, READLINE_POINT, or READLINE_MARK,
those new values will be reflected in the editing state.
-X List all key sequences bound to shell commands and the associated commands
in a format that can be reused as input.
The return value is 0 unless an unrecognized option is given or an error occurred.
break [n]
Exit from within a for, while, until, or select loop. If n is specified, break n
levels. n must be >= 1. If n is greater than the number of enclosing loops, all
enclosing loops are exited. The return value is 0 unless n is not greater than or
equal to 1.
builtin shell-builtin [arguments]
Execute the specified shell builtin, passing it arguments, and return its exit sta-
tus. This is useful when defining a function whose name is the same as a shell
builtin, retaining the functionality of the builtin within the function. The cd
builtin is commonly redefined this way. The return status is false if
shell-builtin is not a shell builtin command.
caller [expr]
Returns the context of any active subroutine call (a shell function or a script ex-
ecuted with the . or source builtins). Without expr, caller displays the line num-
ber and source filename of the current subroutine call. If a non-negative integer
is supplied as expr, caller displays the line number, subroutine name, and source
file corresponding to that position in the current execution call stack. This ex-
tra information may be used, for example, to print a stack trace. The current
frame is frame 0. The return value is 0 unless the shell is not executing a sub-
routine call or expr does not correspond to a valid position in the call stack.
cd [-L|[-P [-e]] [-@]] [dir]
Change the current directory to dir. if dir is not supplied, the value of the HOME
shell variable is the default. Any additional arguments following dir are ignored.
The variable CDPATH defines the search path for the directory containing dir: each
directory name in CDPATH is searched for dir. Alternative directory names in CD-
PATH are separated by a colon (:). A null directory name in CDPATH is the same as
the current directory, i.e., ``.''. If dir begins with a slash (/), then CDPATH is
not used. The -P option causes cd to use the physical directory structure by re-
solving symbolic links while traversing dir and before processing instances of ..
in dir (see also the -P option to the set builtin command); the -L option forces
symbolic links to be followed by resolving the link after processing instances of
.. in dir. If .. appears in dir, it is processed by removing the immediately pre-
vious pathname component from dir, back to a slash or the beginning of dir. If the
-e option is supplied with -P, and the current working directory cannot be success-
fully determined after a successful directory change, cd will return an unsuccess-
ful status. On systems that support it, the -@ option presents the extended at-
tributes associated with a file as a directory. An argument of - is converted to
$OLDPWD before the directory change is attempted. If a non-empty directory name
from CDPATH is used, or if - is the first argument, and the directory change is
successful, the absolute pathname of the new working directory is written to the
standard output. The return value is true if the directory was successfully
changed; false otherwise.
command [-pVv] command [arg ...]
Run command with args suppressing the normal shell function lookup. Only builtin
commands or commands found in the PATH are executed. If the -p option is given,
the search for command is performed using a default value for PATH that is guaran-
teed to find all of the standard utilities. If either the -V or -v option is sup-
plied, a description of command is printed. The -v option causes a single word in-
dicating the command or filename used to invoke command to be displayed; the -V op-
tion produces a more verbose description. If the -V or -v option is supplied, the
exit status is 0 if command was found, and 1 if not. If neither option is supplied
and an error occurred or command cannot be found, the exit status is 127. Other-
wise, the exit status of the command builtin is the exit status of command.
compgen [option] [word]
Generate possible completion matches for word according to the options, which may
be any option accepted by the complete builtin with the exception of -p and -r, and
write the matches to the standard output. When using the -F or -C options, the
various shell variables set by the programmable completion facilities, while avail-
able, will not have useful values.
The matches will be generated in the same way as if the programmable completion
code had generated them directly from a completion specification with the same
flags. If word is specified, only those completions matching word will be dis-
played.
The return value is true unless an invalid option is supplied, or no matches were
generated.
complete [-abcdefgjksuv] [-o comp-option] [-DEI] [-A action] [-G globpat] [-W wordlist]
[-F function] [-C command] [-X filterpat] [-P prefix] [-S suffix] name [name ...]
complete -pr [-DEI] [name ...]
Specify how arguments to each name should be completed. If the -p option is sup-
plied, or if no options are supplied, existing completion specifications are
printed in a way that allows them to be reused as input. The -r option removes a
completion specification for each name, or, if no names are supplied, all comple-
tion specifications. The -D option indicates that other supplied options and ac-
tions should apply to the ``default'' command completion; that is, completion at-
tempted on a command for which no completion has previously been defined. The -E
option indicates that other supplied options and actions should apply to ``empty''
command completion; that is, completion attempted on a blank line. The -I option
indicates that other supplied options and actions should apply to completion on the
initial non-assignment word on the line, or after a command delimiter such as ; or
|, which is usually command name completion. If multiple options are supplied, the
-D option takes precedence over -E, and both take precedence over -I. If any of
-D, -E, or -I are supplied, any other name arguments are ignored; these completions
only apply to the case specified by the option.
The process of applying these completion specifications when word completion is at-
tempted is described above under Programmable Completion.
Other options, if specified, have the following meanings. The arguments to the -G,
-W, and -X options (and, if necessary, the -P and -S options) should be quoted to
protect them from expansion before the complete builtin is invoked.
-o comp-option
The comp-option controls several aspects of the compspec's behavior beyond
the simple generation of completions. comp-option may be one of:
bashdefault
Perform the rest of the default bash completions if the compspec
generates no matches.
default Use readline's default filename completion if the compspec gener-
ates no matches.
dirnames
Perform directory name completion if the compspec generates no
matches.
filenames
Tell readline that the compspec generates filenames, so it can per-
form any filename-specific processing (like adding a slash to di-
rectory names, quoting special characters, or suppressing trailing
spaces). Intended to be used with shell functions.
noquote Tell readline not to quote the completed words if they are file-
names (quoting filenames is the default).
nosort Tell readline not to sort the list of possible completions alpha-
betically.
nospace Tell readline not to append a space (the default) to words com-
pleted at the end of the line.
plusdirs
After any matches defined by the compspec are generated, directory
name completion is attempted and any matches are added to the re-
sults of the other actions.
-A action
The action may be one of the following to generate a list of possible com-
pletions:
alias Alias names. May also be specified as -a.
arrayvar
Array variable names.
binding Readline key binding names.
builtin Names of shell builtin commands. May also be specified as -b.
command Command names. May also be specified as -c.
directory
Directory names. May also be specified as -d.
disabled
Names of disabled shell builtins.
enabled Names of enabled shell builtins.
export Names of exported shell variables. May also be specified as -e.
file File names. May also be specified as -f.
function
Names of shell functions.
group Group names. May also be specified as -g.
helptopic
Help topics as accepted by the help builtin.
hostname
Hostnames, as taken from the file specified by the HOSTFILE shell
variable.
job Job names, if job control is active. May also be specified as -j.
keyword Shell reserved words. May also be specified as -k.
running Names of running jobs, if job control is active.
service Service names. May also be specified as -s.
setopt Valid arguments for the -o option to the set builtin.
shopt Shell option names as accepted by the shopt builtin.
signal Signal names.
stopped Names of stopped jobs, if job control is active.
user User names. May also be specified as -u.
variable
Names of all shell variables. May also be specified as -v.
-C command
command is executed in a subshell environment, and its output is used as
the possible completions.
-F function
The shell function function is executed in the current shell environment.
When the function is executed, the first argument ($1) is the name of the
command whose arguments are being completed, the second argument ($2) is
the word being completed, and the third argument ($3) is the word preceding
the word being completed on the current command line. When it finishes,
the possible completions are retrieved from the value of the COMPREPLY ar-
ray variable.
-G globpat
The pathname expansion pattern globpat is expanded to generate the possible
completions.
-P prefix
prefix is added at the beginning of each possible completion after all
other options have been applied.
-S suffix
suffix is appended to each possible completion after all other options have
been applied.
-W wordlist
The wordlist is split using the characters in the IFS special variable as
delimiters, and each resultant word is expanded. Shell quoting is honored
within wordlist, in order to provide a mechanism for the words to contain
shell metacharacters or characters in the value of IFS. The possible com-
pletions are the members of the resultant list which match the word being
completed.
-X filterpat
filterpat is a pattern as used for pathname expansion. It is applied to
the list of possible completions generated by the preceding options and ar-
guments, and each completion matching filterpat is removed from the list.
A leading ! in filterpat negates the pattern; in this case, any completion
not matching filterpat is removed.
The return value is true unless an invalid option is supplied, an option other than
-p or -r is supplied without a name argument, an attempt is made to remove a com-
pletion specification for a name for which no specification exists, or an error oc-
curs adding a completion specification.
compopt [-o option] [-DEI] [+o option] [name]
Modify completion options for each name according to the options, or for the cur-
rently-executing completion if no names are supplied. If no options are given,
display the completion options for each name or the current completion. The possi-
ble values of option are those valid for the complete builtin described above. The
-D option indicates that other supplied options should apply to the ``default''
command completion; that is, completion attempted on a command for which no comple-
tion has previously been defined. The -E option indicates that other supplied op-
tions should apply to ``empty'' command completion; that is, completion attempted
on a blank line. The -I option indicates that other supplied options should apply
to completion on the initial non-assignment word on the line, or after a command
delimiter such as ; or |, which is usually command name completion.
The return value is true unless an invalid option is supplied, an attempt is made
to modify the options for a name for which no completion specification exists, or
an output error occurs.
continue [n]
Resume the next iteration of the enclosing for, while, until, or select loop. If n
is specified, resume at the nth enclosing loop. n must be >= 1. If 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 n is not greater than or equal to
1.
declare [-aAfFgiIlnrtux] [-p] [name[=value] ...]
typeset [-aAfFgiIlnrtux] [-p] [name[=value] ...]
Declare variables and/or give them attributes. If no names are given then display
the values of variables. The -p option will display the attributes and values of
each name. When -p is used with name arguments, additional options, other than -f
and -F, are ignored. When -p is supplied without name arguments, it will display
the attributes and values of all variables having the attributes specified by the
additional options. If no other options are supplied with -p, declare will display
the attributes and values of all shell variables. The -f option will restrict the
display to shell functions. The -F option inhibits the display of function defini-
tions; only the function name and attributes are printed. If the extdebug shell
option is enabled using shopt, the source file name and line number where each name
is defined are displayed as well. The -F option implies -f. The -g option forces
variables to be created or modified at the global scope, even when declare is exe-
cuted in a shell function. It is ignored in all other cases. The -I option causes
local variables to inherit the attributes (except the nameref attribute) and value
of any existing variable with the same name at a surrounding scope. If there is no
existing variable, the local variable is initially unset. The following options
can be used to restrict output to variables with the specified attribute or to give
variables attributes:
-a Each name is an indexed array variable (see Arrays above).
-A Each name is an associative array variable (see Arrays above).
-f Use function names only.
-i The variable is treated as an integer; arithmetic evaluation (see ARITHMETIC
EVALUATION above) is performed when the variable is assigned a value.
-l When the variable is assigned a value, all upper-case characters are con-
verted to lower-case. The upper-case attribute is disabled.
-n Give each name the nameref attribute, making it a name reference to another
variable. That other variable is defined by the value of name. All refer-
ences, assignments, and attribute modifications to name, except those using
or changing the -n attribute itself, are performed on the variable refer-
enced by name's value. The nameref attribute cannot be applied to array
variables.
-r Make names readonly. These names cannot then be assigned values by subse-
quent assignment statements or unset.
-t Give each name the trace attribute. Traced functions inherit the DEBUG and
RETURN traps from the calling shell. The trace attribute has no special
meaning for variables.
-u When the variable is assigned a value, all lower-case characters are con-
verted to upper-case. The lower-case attribute is disabled.
-x Mark names for export to subsequent commands via the environment.
Using `+' instead of `-' turns off the attribute instead, with the exceptions that
+a and +A may not be used to destroy array variables and +r will not remove the
readonly attribute. When used in a function, declare and typeset make each name
local, as with the local command, unless the -g option is supplied. If a variable
name is followed by =value, the value of the variable is set to value. When using
-a or -A and the compound assignment syntax to create array variables, additional
attributes do not take effect until subsequent assignments. The return value is 0
unless an invalid option is encountered, an attempt is made to define a function
using ``-f foo=bar'', an attempt is made to assign a value to a readonly variable,
an attempt is made to assign a value to an array variable without using the com-
pound assignment syntax (see Arrays above), one of the names is not a valid shell
variable name, an attempt is made to turn off readonly status for a readonly vari-
able, an attempt is made to turn off array status for an array variable, or an at-
tempt is made to display a non-existent function with -f.
dirs [-clpv] [+n] [-n]
Without options, displays the list of currently remembered directories. The de-
fault display is on a single line with directory names separated by spaces. Direc-
tories are added to the list with the pushd command; the popd command removes en-
tries from the list. The current directory is always the first directory in the
stack.
-c Clears the directory stack by deleting all of the entries.
-l Produces a listing using full pathnames; the default listing format uses a
tilde to denote the home directory.
-p Print the directory stack with one entry per line.
-v Print the directory stack with one entry per line, prefixing each entry with
its index in the stack.
+n Displays the nth entry counting from the left of the list shown by dirs when
invoked without options, starting with zero.
-n Displays the nth entry counting from the right of the list shown by dirs
when invoked without options, starting with zero.
The return value is 0 unless an invalid option is supplied or n indexes beyond the
end of the directory stack.
disown [-ar] [-h] [jobspec ... | pid ... ]
Without options, remove each jobspec from the table of active jobs. If jobspec is
not present, and neither the -a nor the -r option is supplied, the current job is
used. If the -h option is given, each jobspec is not removed from the table, but
is marked so that SIGHUP is not sent to the job if the shell receives a SIGHUP. If
no jobspec is supplied, the -a option means to remove or mark all jobs; the -r op-
tion without a jobspec argument restricts operation to running jobs. The return
value is 0 unless a jobspec does not specify a valid job.
echo [-neE] [arg ...]
Output the args, separated by spaces, followed by a newline. The return status is
0 unless a write error occurs. If -n is specified, the trailing newline is sup-
pressed. If the -e option is given, interpretation of the following backslash-es-
caped characters is enabled. The -E option disables the interpretation of these
escape characters, even on systems where they are interpreted by default. The
xpg_echo shell option may be used to dynamically determine whether or not echo ex-
pands these escape characters by default. echo does not interpret -- to mean the
end of options. echo interprets the following escape sequences:
\a alert (bell)
\b backspace
\c suppress further output
\e
\E an escape character
\f form feed
\n new line
\r carriage return
\t horizontal tab
\v vertical tab
\\ backslash
\0nnn the eight-bit character whose value is the octal value nnn (zero to three
octal digits)
\xHH the eight-bit character whose value is the hexadecimal value HH (one or two
hex digits)
\uHHHH the Unicode (ISO/IEC 10646) character whose value is the hexadecimal value
HHHH (one to four hex digits)
\UHHHHHHHH
the Unicode (ISO/IEC 10646) character whose value is the hexadecimal value
HHHHHHHH (one to eight hex digits)
enable [-a] [-dnps] [-f filename] [name ...]
Enable and disable builtin shell commands. Disabling a builtin allows a disk com-
mand which has the same name as a shell builtin to be executed without specifying a
full pathname, even though the shell normally searches for builtins before disk
commands. If -n is used, each name is disabled; otherwise, names are enabled. For
example, to use the test binary found via the PATH instead of the shell builtin
version, run ``enable -n test''. The -f option means to load the new builtin com-
mand name from shared object filename, on systems that support dynamic loading.
The -d option will delete a builtin previously loaded with -f. If no name argu-
ments are given, or if the -p option is supplied, a list of shell builtins is
printed. With no other option arguments, the list consists of all enabled shell
builtins. If -n is supplied, only disabled builtins are printed. If -a is sup-
plied, the list printed includes all builtins, with an indication of whether or not
each is enabled. If -s is supplied, the output is restricted to the POSIX special
builtins. The return value is 0 unless a name is not a shell builtin or there is
an error loading a new builtin from a shared object.
eval [arg ...]
The args 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 eval. If there are no args, or only null arguments, eval returns 0.
exec [-cl] [-a name] [command [arguments]]
If command is specified, it replaces the shell. No new process is created. The
arguments become the arguments to command. If the -l option is supplied, the shell
places a dash at the beginning of the zeroth argument passed to command. This is
what login(1) does. The -c option causes command to be executed with an empty en-
vironment. If -a is supplied, the shell passes name as the zeroth argument to the
executed command. If command cannot be executed for some reason, a non-interactive
shell exits, unless the execfail shell option is enabled. In that case, it returns
failure. An interactive shell returns failure if the file cannot be executed. A
subshell exits unconditionally if exec fails. If command is not specified, any
redirections take effect in the current shell, and the return status is 0. If
there is a redirection error, the return status is 1.
exit [n]
Cause the shell to exit with a status of n. If n is omitted, the exit status is
that of the last command executed. A trap on EXIT is executed before the shell
terminates.
export [-fn] [name[=word]] ...
export -p
The supplied names are marked for automatic export to the environment of subse-
quently executed commands. If the -f option is given, the names refer to func-
tions. If no names are given, or if the -p option is supplied, a list of names of
all exported variables is printed. The -n option causes the export property to be
removed from each name. If a variable name is followed by =word, the value of the
variable is set to word. export returns an exit status of 0 unless an invalid op-
tion is encountered, one of the names is not a valid shell variable name, or -f is
supplied with a name that is not a function.
fc [-e ename] [-lnr] [first] [last]
fc -s [pat=rep] [cmd]
The first form selects a range of commands from first to last from the history list
and displays or edits and re-executes them. First and last may be specified as a
string (to locate the last command beginning with that string) or as a number (an
index into the history list, where a negative number is used as an offset from the
current command number). When listing, a first or last of 0 is equivalent to -1
and -0 is equivalent to the current command (usually the fc command); otherwise 0
is equivalent to -1 and -0 is invalid. If last is not specified, it is set to the
current command for listing (so that ``fc -l -10'' prints the last 10 commands) and
to first otherwise. If first is not specified, it is set to the previous command
for editing and -16 for listing.
The -n option suppresses the command numbers when listing. The -r option reverses
the order of the commands. If the -l option is given, the commands are listed on
standard output. Otherwise, the editor given by ename is invoked on a file con-
taining those commands. If ename is not given, the value of the FCEDIT variable is
used, and the value of EDITOR if FCEDIT is not set. If neither variable is set, vi
is used. When editing is complete, the edited commands are echoed and executed.
In the second form, command is re-executed after each instance of pat is replaced
by rep. Command is interpreted the same as first above. 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.
If the first form is used, the return value is 0 unless an invalid option is en-
countered or first or last specify history lines out of range. If the -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 cmd does not specify a
valid history line, in which case fc returns failure.
fg [jobspec]
Resume jobspec in the foreground, and make it the current job. If jobspec is not
present, the shell's notion of the current job 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 jobspec does not specify a valid
job or jobspec specifies a job that was started without job control.
getopts optstring name [arg ...]
getopts is used by shell procedures to parse positional parameters. optstring con-
tains the option characters to be recognized; if a character is followed by a
colon, the option is expected to have an argument, which should be separated from
it by white space. The colon and question mark characters may not be used as op-
tion characters. Each time it is invoked, getopts places the next option in the
shell variable name, initializing name if it does not exist, and the index of the
next argument to be processed into the variable OPTIND. OPTIND is initialized to 1
each time the shell or a shell script is invoked. When an option requires an argu-
ment, getopts places that argument into the variable OPTARG. The shell does not
reset OPTIND automatically; it must be manually reset between multiple calls to
getopts within the same shell invocation if a new set of parameters is to be used.
When the end of options is encountered, getopts exits with a return value greater
than zero. OPTIND is set to the index of the first non-option argument, and name
is set to ?.
getopts normally parses the positional parameters, but if more arguments are sup-
plied as arg values, getopts parses those instead.
getopts can report errors in two ways. If the first character of optstring is a
colon, silent error reporting is used. In normal operation, diagnostic messages
are printed when invalid options or missing option arguments are encountered. If
the variable OPTERR is set to 0, no error messages will be displayed, even if the
first character of optstring is not a colon.
If an invalid option is seen, getopts places ? into name and, if not silent, prints
an error message and unsets OPTARG. If getopts is silent, the option character
found is placed in OPTARG and no diagnostic message is printed.
If a required argument is not found, and getopts is not silent, a question mark (?)
is placed in name, OPTARG is unset, and a diagnostic message is printed. If
getopts is silent, then a colon (:) is placed in name and OPTARG is set to the op-
tion character found.
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.
hash [-lr] [-p filename] [-dt] [name]
Each time hash is invoked, the full pathname of the command name is determined by
searching the directories in $PATH and remembered. Any previously-remembered path-
name is discarded. If the -p option is supplied, no path search is performed, and
filename is used as the full filename of the command. The -r option causes the
shell to forget all remembered locations. The -d option causes the shell to forget
the remembered location of each name. If the -t option is supplied, the full path-
name to which each name corresponds is printed. If multiple name arguments are
supplied with -t, the name is printed before the hashed full pathname. The -l op-
tion causes output to be displayed in a format that may be reused as input. If no
arguments are given, or if only -l is supplied, information about remembered com-
mands is printed. The return status is true unless a name is not found or an in-
valid option is supplied.
help [-dms] [pattern]
Display helpful information about builtin commands. If pattern is specified, help
gives detailed help on all commands matching pattern; otherwise help for all the
builtins and shell control structures is printed.
-d Display a short description of each pattern
-m Display the description of each pattern in a manpage-like format
-s Display only a short usage synopsis for each pattern
The return status is 0 unless no command matches pattern.
history [n]
history -c
history -d offset
history -d start-end
history -anrw [filename]
history -p arg [arg ...]
history -s arg [arg ...]
With no options, display the command history list with line numbers. Lines listed
with a * have been modified. An argument of n lists only the last n lines. If the
shell variable HISTTIMEFORMAT is set and not null, it is used as a format string
for strftime(3) to display the time stamp associated with each displayed history
entry. No intervening blank is printed between the formatted time stamp and the
history line. If filename is supplied, it is used as the name of the history file;
if not, the value of HISTFILE is used. Options, if supplied, have the following
meanings:
-c Clear the history list by deleting all the entries.
-d offset
Delete the history entry at position offset. If offset is negative, it is
interpreted as relative to one greater than the last history position, so
negative indices count back from the end of the history, and an index of -1
refers to the current history -d command.
-d start-end
Delete the history entries between positions start and end, inclusive. Pos-
itive and negative values for start and end are interpreted as described
above.
-a Append the ``new'' history lines to the history file. These are history
lines entered since the beginning of the current bash session, but not al-
ready appended to the history file.
-n Read the history lines not already read from the history file into the cur-
rent history list. These are lines appended to the history file since the
beginning of the current bash session.
-r Read the contents of the history file and append them to the current history
list.
-w Write the current history list to the history file, overwriting the history
file's contents.
-p Perform history substitution on the following args and display the result on
the standard output. Does not store the results in the history list. Each
arg must be quoted to disable normal history expansion.
-s Store the args in the history list as a single entry. The last command in
the history list is removed before the args are added.
If the HISTTIMEFORMAT variable is set, the time stamp information associated with
each history entry is written to the history file, marked with the history comment
character. When the history file is read, lines beginning with the history comment
character followed immediately by a digit are interpreted as timestamps for the
following history entry. The return value is 0 unless an invalid option is encoun-
tered, an error occurs while reading or writing the history file, an invalid offset
is supplied as an argument to -d, or the history expansion supplied as an argument
to -p fails.
jobs [-lnprs] [ jobspec ... ]
jobs -x command [ args ... ]
The first form lists the active jobs. The options have the following meanings:
-l List process IDs in addition to the normal information.
-n Display information only about jobs that have changed status since the user
was last notified of their status.
-p List only the process ID of the job's process group leader.
-r Display only running jobs.
-s Display only stopped jobs.
If jobspec is given, output is restricted to information about that job. The re-
turn status is 0 unless an invalid option is encountered or an invalid jobspec is
supplied.
If the -x option is supplied, jobs replaces any jobspec found in command or args
with the corresponding process group ID, and executes command passing it args, re-
turning its exit status.
kill [-s sigspec | -n signum | -sigspec] [pid | jobspec] ...
kill -l|-L [sigspec | exit_status]
Send the signal named by sigspec or signum to the processes named by pid or job-
spec. sigspec is either a case-insensitive signal name such as SIGKILL (with or
without the SIG prefix) or a signal number; signum is a signal number. If sigspec
is not present, then SIGTERM is assumed. An argument of -l lists the signal names.
If any arguments are supplied when -l is given, the names of the signals corre-
sponding to the arguments are listed, and the return status is 0. The exit_status
argument to -l is a number specifying either a signal number or the exit status of
a process terminated by a signal. The -L option is equivalent to -l. kill returns
true if at least one signal was successfully sent, or false if an error occurs or
an invalid option is encountered.
let arg [arg ...]
Each arg is an arithmetic expression to be evaluated (see ARITHMETIC EVALUATION
above). If the last arg evaluates to 0, let returns 1; 0 is returned otherwise.
local [option] [name[=value] ... | - ]
For each argument, a local variable named name is created, and assigned value. The
option can be any of the options accepted by declare. When local is used within a
function, it causes the variable name to have a visible scope restricted to that
function and its children. If name is -, the set of shell options is made local to
the function in which local is invoked: shell options changed using the set builtin
inside the function are restored to their original values when the function re-
turns. The restore is effected as if a series of set commands were executed to re-
store the values that were in place before the function. With no operands, local
writes a list of local variables to the standard output. It is an error to use lo-
cal when not within a function. The return status is 0 unless local is used out-
side a function, an invalid name is supplied, or name is a readonly variable.
logout Exit a login shell.
mapfile [-d delim] [-n count] [-O origin] [-s count] [-t] [-u fd] [-C callback] [-c quan-
tum] [array]
readarray [-d delim] [-n count] [-O origin] [-s count] [-t] [-u fd] [-C callback] [-c
quantum] [array]
Read lines from the standard input into the indexed array variable array, or from
file descriptor fd if the -u option is supplied. The variable MAPFILE is the de-
fault array. Options, if supplied, have the following meanings:
-d The first character of delim is used to terminate each input line, rather
than newline. If delim is the empty string, mapfile will terminate a line
when it reads a NUL character.
-n Copy at most count lines. If count is 0, all lines are copied.
-O Begin assigning to array at index origin. The default index is 0.
-s Discard the first count lines read.
-t Remove a trailing delim (default newline) from each line read.
-u Read lines from file descriptor fd instead of the standard input.
-C Evaluate callback each time quantum lines are read. The -c option specifies
quantum.
-c Specify the number of lines read between each call to callback.
If -C is specified without -c, the default quantum is 5000. When callback is eval-
uated, it is supplied the index of the next array element to be assigned and the
line to be assigned to that element as additional arguments. callback is evaluated
after the line is read but before the array element is assigned.
If not supplied with an explicit origin, mapfile will clear array before assigning
to it.
mapfile returns successfully unless an invalid option or option argument is sup-
plied, array is invalid or unassignable, or if array is not an indexed array.
popd [-n] [+n] [-n]
Removes entries from the directory stack. With no arguments, removes the top di-
rectory from the stack, and performs a cd to the new top directory. Arguments, if
supplied, have the following meanings:
-n Suppresses the normal change of directory when removing directories from the
stack, so that only the stack is manipulated.
+n Removes the nth entry counting from the left of the list shown by dirs,
starting with zero. For example: ``popd +0'' removes the first directory,
``popd +1'' the second.
-n Removes the nth entry counting from the right of the list shown by dirs,
starting with zero. For example: ``popd -0'' removes the last directory,
``popd -1'' the next to last.
If the popd command is successful, a dirs is performed as well, and the return sta-
tus is 0. popd returns false if an invalid option is encountered, the directory
stack is empty, a non-existent directory stack entry is specified, or the directory
change fails.
printf [-v var] format [arguments]
Write the formatted arguments to the standard output under the control of the for-
mat. The -v option causes the output to be assigned to the variable var rather
than being printed to the standard output.
The format is a character string which contains three types of objects: plain char-
acters, which are simply copied to standard output, character escape sequences,
which are converted and copied to the standard output, and format specifications,
each of which causes printing of the next successive argument. In addition to the
standard printf(1) format specifications, printf interprets the following exten-
sions:
%b causes printf to expand backslash escape sequences in the corresponding ar-
gument in the same way as echo -e.
%q causes printf to output the corresponding argument in a format that can be
reused as shell input.
%(datefmt)T
causes printf to output the date-time string resulting from using datefmt as
a format string for strftime(3). The corresponding argument is an integer
representing the number of seconds since the epoch. Two special argument
values may be used: -1 represents the current time, and -2 represents the
time the shell was invoked. If no argument is specified, conversion behaves
as if -1 had been given. This is an exception to the usual printf behavior.
The %b, %q, and %T directives all use the field width and precision arguments from
the format specification and write that many bytes from (or use that wide a field
for) the expanded argument, which usually contains more characters than the origi-
nal.
Arguments to non-string format specifiers are treated as C constants, except that a
leading plus or minus sign is allowed, and if the leading character is a single or
double quote, the value is the ASCII value of the following character.
The format is reused as necessary to consume all of the arguments. If the format
requires more arguments than are supplied, the extra format specifications behave
as if a zero value or null string, as appropriate, had been supplied. The return
value is zero on success, non-zero on failure.
pushd [-n] [+n] [-n]
pushd [-n] [dir]
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, pushd
exchanges the top two directories and returns 0, unless the directory stack is
empty. Arguments, if supplied, have the following meanings:
-n Suppresses the normal change of directory when rotating or adding directo-
ries to the stack, so that only the stack is manipulated.
+n Rotates the stack so that the nth directory (counting from the left of the
list shown by dirs, starting with zero) is at the top.
-n Rotates the stack so that the nth directory (counting from the right of the
list shown by dirs, starting with zero) is at the top.
dir Adds dir to the directory stack at the top, making it the new current work-
ing directory as if it had been supplied as the argument to the cd builtin.
If the pushd command is successful, a dirs is performed as well. If the first form
is used, pushd returns 0 unless the cd to dir fails. With the second form, pushd
returns 0 unless the directory stack is empty, a non-existent directory stack ele-
ment is specified, or the directory change to the specified new current directory
fails.
pwd [-LP]
Print the absolute pathname of the current working directory. The pathname printed
contains no symbolic links if the -P option is supplied or the -o physical option
to the set builtin command is enabled. If the -L option is used, the pathname
printed may contain symbolic links. The return status is 0 unless an error occurs
while reading the name of the current directory or an invalid option is supplied.
read [-ers] [-a aname] [-d delim] [-i text] [-n nchars] [-N nchars] [-p prompt] [-t time-
out] [-u fd] [name ...]
One line is read from the standard input, or from the file descriptor fd supplied
as an argument to the -u option, split into words as described above under Word
Splitting, and the first word is assigned to the first name, the second word to the
second name, and so on. If there are more words than names, the remaining words
and their intervening delimiters are assigned to the last name. If there are fewer
words read from the input stream than names, the remaining names are assigned empty
values. The characters in IFS are used to split the line into words using the same
rules the shell uses for expansion (described above under Word Splitting). The
backslash character (\) may be used to remove any special meaning for the next
character read and for line continuation. Options, if supplied, have the following
meanings:
-a aname
The words are assigned to sequential indices of the array variable aname,
starting at 0. aname is unset before any new values are assigned. Other
name arguments are ignored.
-d delim
The first character of delim is used to terminate the input line, rather
than newline. If delim is the empty string, read will terminate a line when
it reads a NUL character.
-e If the standard input is coming from a terminal, readline (see READLINE
above) is used to obtain the line. Readline uses the current (or default,
if line editing was not previously active) editing settings, but uses Read-
line's default filename completion.
-i text
If readline is being used to read the line, text is placed into the editing
buffer before editing begins.
-n nchars
read returns after reading nchars characters rather than waiting for a com-
plete line of input, but honors a delimiter if fewer than nchars characters
are read before the delimiter.
-N nchars
read returns after reading exactly nchars characters rather than waiting for
a complete line of input, unless EOF is encountered or read times out. De-
limiter characters encountered in the input are not treated specially and do
not cause read to return until nchars characters are read. The result is
not split on the characters in IFS; the intent is that the variable is as-
signed exactly the characters read (with the exception of backslash; see the
-r option below).
-p prompt
Display prompt on standard error, without a trailing newline, before at-
tempting to read any input. The prompt is displayed only if input is coming
from a terminal.
-r Backslash does not act as an escape character. The backslash is considered
to be part of the line. In particular, a backslash-newline pair may not
then be used as a line continuation.
-s Silent mode. If input is coming from a terminal, characters are not echoed.
-t timeout
Cause read to time out and return failure if a complete line of input (or a
specified number of characters) is not read within timeout seconds. timeout
may be a decimal number with a fractional portion following the decimal
point. This option is only effective if read is reading input from a termi-
nal, pipe, or other special file; it has no effect when reading from regular
files. If read times out, read saves any partial input read into the speci-
fied variable name. If timeout is 0, read returns immediately, without try-
ing to read any data. The exit status is 0 if input is available on the
specified file descriptor, non-zero otherwise. The exit status is greater
than 128 if the timeout is exceeded.
-u fd Read input from file descriptor fd.
If no names are supplied, the line read, without the ending delimiter but otherwise
unmodified, is assigned to the variable REPLY. The exit status is zero, unless
end-of-file is encountered, read times out (in which case the status is greater
than 128), a variable assignment error (such as assigning to a readonly variable)
occurs, or an invalid file descriptor is supplied as the argument to -u.
readonly [-aAf] [-p] [name[=word] ...]
The given names are marked readonly; the values of these names may not be changed
by subsequent assignment. If the -f option is supplied, the functions correspond-
ing to the names are so marked. The -a option restricts the variables to indexed
arrays; the -A option restricts the variables to associative arrays. If both op-
tions are supplied, -A takes precedence. If no name arguments are given, or if the
-p option is supplied, a list of all readonly names is printed. The other options
may be used to restrict the output to a subset of the set of readonly names. The
-p option causes output to be displayed in a format that may be reused as input.
If a variable name is followed by =word, the value of the variable is set to word.
The return status is 0 unless an invalid option is encountered, one of the names is
not a valid shell variable name, or -f is supplied with a name that is not a func-
tion.
return [n]
Causes a function to stop executing and return the value specified by n to its
caller. If n is omitted, the return status is that of the last command executed in
the function body. If return is executed by a trap handler, the last command used
to determine the status is the last command executed before the trap handler. If
return is executed during a DEBUG trap, the last command used to determine the sta-
tus is the last command executed by the trap handler before return was invoked. If
return is used outside a function, but during execution of a script by the .
(source) command, it causes the shell to stop executing that script and return ei-
ther n or the exit status of the last command executed within the script as the
exit status of the script. If n is supplied, the return value is its least signif-
icant 8 bits. The return status is non-zero if return is supplied a non-numeric
argument, or is used outside a function and not during execution of a script by .
or source. Any command associated with the RETURN trap is executed before execu-
tion resumes after the function or script.
set [--abefhkmnptuvxBCEHPT] [-o option-name] [arg ...]
set [+abefhkmnptuvxBCEHPT] [+o option-name] [arg ...]
Without options, the name and value of each shell variable are displayed in a for-
mat that can be reused as input for setting or resetting the currently-set vari-
ables. Read-only variables cannot be reset. In posix mode, only shell variables
are listed. The output is sorted according to the current locale. When options
are specified, they set or unset shell attributes. Any arguments remaining after
option processing are treated as values for the positional parameters and are as-
signed, in order, to $1, $2, ... $n. Options, if specified, have the following
meanings:
-a Each variable or function that is created or modified is given the export
attribute and marked for export to the environment of subsequent commands.
-b Report the status of terminated background jobs immediately, rather than
before the next primary prompt. This is effective only when job control is
enabled.
-e Exit immediately if a pipeline (which may consist of a single simple com-
mand), a list, or a compound command (see SHELL GRAMMAR above), exits with
a non-zero status. The shell does not exit if the command that fails is
part of the command list immediately following a while or until keyword,
part of the test following the if or elif reserved words, part of any com-
mand executed in a && or || list except the command following the final &&
or ||, any command in a pipeline but the last, or if the command's return
value is being inverted with !. If a compound command other than a sub-
shell returns a non-zero status because a command failed while -e was being
ignored, the shell does not exit. A trap on ERR, if set, is executed be-
fore the shell exits. This option applies to the shell environment and
each subshell environment separately (see COMMAND EXECUTION ENVIRONMENT
above), and may cause subshells to exit before executing all the commands
in the subshell.
If a compound command or shell function executes in a context where -e is
being ignored, none of the commands executed within the compound command or
function body will be affected by the -e setting, even if -e is set and a
command returns a failure status. If a compound command or shell function
sets -e while executing in a context where -e is ignored, that setting will
not have any effect until the compound command or the command containing
the function call completes.
-f Disable pathname expansion.
-h Remember the location of commands as they are looked up for execution.
This is enabled by default.
-k All arguments in the form of assignment statements are placed in the envi-
ronment for a command, not just those that precede the command name.
-m Monitor mode. Job control is enabled. This option is on by default for
interactive shells on systems that support it (see JOB CONTROL above). All
processes run in a separate process group. When a background job com-
pletes, the shell prints a line containing its exit status.
-n Read commands but do not execute them. This may be used to check a shell
script for syntax errors. This is ignored by interactive shells.
-o option-name
The option-name can be one of the following:
allexport
Same as -a.
braceexpand
Same as -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 --noediting option. This also affects the editing
interface used for read -e.
errexit Same as -e.
errtrace
Same as -E.
functrace
Same as -T.
hashall Same as -h.
histexpand
Same as -H.
history Enable command history, as described above under HISTORY. This op-
tion is on by default in interactive shells.
ignoreeof
The effect is as if the shell command ``IGNOREEOF=10'' had been ex-
ecuted (see Shell Variables above).
keyword Same as -k.
monitor Same as -m.
noclobber
Same as -C.
noexec Same as -n.
noglob Same as -f.
nolog Currently ignored.
notify Same as -b.
nounset Same as -u.
onecmd Same as -t.
physical
Same as -P.
pipefail
If set, the return value of a pipeline is the value of the last
(rightmost) command to exit with a non-zero status, or zero if all
commands in the pipeline exit successfully. This option is dis-
abled by default.
posix Change the behavior of bash where the default operation differs
from the POSIX standard to match the standard (posix mode). See
SEE ALSO below for a reference to a document that details how posix
mode affects bash's behavior.
privileged
Same as -p.
verbose Same as -v.
vi Use a vi-style command line editing interface. This also affects
the editing interface used for read -e.
xtrace Same as -x.
If -o is supplied with no option-name, the values of the current options
are printed. If +o is supplied with no option-name, a series of set com-
mands to recreate the current option settings is displayed on the standard
output.
-p Turn on privileged mode. In this mode, the $ENV and $BASH_ENV files are
not processed, shell functions are not inherited from the environment, and
the SHELLOPTS, BASHOPTS, CDPATH, and GLOBIGNORE variables, if they appear
in the environment, are ignored. If the shell is started with the effec-
tive user (group) id not equal to the real user (group) id, and the -p op-
tion is not supplied, these actions are taken and the effective user id is
set to the real user id. If the -p option is supplied at startup, the ef-
fective user id is not reset. Turning this option off causes the effective
user and group ids to be set to the real user and group ids.
-t Exit after reading and executing one command.
-u Treat unset variables and parameters other than the special parameters "@"
and "*" as an error when performing parameter expansion. If expansion is
attempted on an unset variable or parameter, the shell prints an error mes-
sage, and, if not interactive, exits with a non-zero status.
-v Print shell input lines as they are read.
-x After expanding each simple command, for command, case command, select com-
mand, or arithmetic for command, display the expanded value of PS4, fol-
lowed by the command and its expanded arguments or associated word list.
-B The shell performs brace expansion (see Brace Expansion above). This is on
by default.
-C If set, bash does not overwrite an existing file with the >, >&, and <> re-
direction operators. This may be overridden when creating output files by
using the redirection operator >| instead of >.
-E If set, any trap on ERR is inherited by shell functions, command substitu-
tions, and commands executed in a subshell environment. The ERR trap is
normally not inherited in such cases.
-H Enable ! style history substitution. This option is on by default when
the shell is interactive.
-P If set, the shell does not resolve symbolic links when executing commands
such as cd that change the current working directory. It uses the physical
directory structure instead. By default, bash follows the logical chain of
directories when performing commands which change the current directory.
-T If set, any traps on DEBUG and RETURN are inherited by shell functions,
command substitutions, and commands executed in a subshell environment.
The DEBUG and RETURN traps are normally not inherited in such cases.
-- If no arguments follow this option, then the positional parameters are un-
set. Otherwise, the positional parameters are set to the args, even if
some of them begin with a -.
- Signal the end of options, cause all remaining args to be assigned to the
positional parameters. The -x and -v options are turned off. If there are
no args, the positional parameters remain unchanged.
The options are off by default unless otherwise noted. Using + rather than -
causes these options to be turned off. The options can also be specified as argu-
ments to an invocation of the shell. The current set of options may be found in
$-. The return status is always true unless an invalid option is encountered.
shift [n]
The positional parameters from n+1 ... are renamed to $1 .... Parameters repre-
sented by the numbers $# down to $#-n+1 are unset. n must be a non-negative number
less than or equal to $#. If n is 0, no parameters are changed. If n is not
given, it is assumed to be 1. If n is greater than $#, the positional parameters
are not changed. The return status is greater than zero if n is greater than $# or
less than zero; otherwise 0.
shopt [-pqsu] [-o] [optname ...]
Toggle the values of settings controlling optional shell behavior. The settings
can be either those listed below, or, if the -o option is used, those available
with the -o option to the set builtin command. With no options, or with the -p op-
tion, a list of all settable options is displayed, with an indication of whether or
not each is set; if optnames are supplied, the output is restricted to those op-
tions. The -p option causes output to be displayed in a form that may be reused as
input. Other options have the following meanings:
-s Enable (set) each optname.
-u Disable (unset) each optname.
-q Suppresses normal output (quiet mode); the return status indicates whether
the optname is set or unset. If multiple optname arguments are given with
-q, the return status is zero if all optnames are enabled; non-zero other-
wise.
-o Restricts the values of optname to be those defined for the -o option to the
set builtin.
If either -s or -u is used with no optname arguments, shopt shows only those op-
tions which are set or unset, respectively. Unless otherwise noted, the shopt op-
tions are disabled (unset) by default.
The return status when listing options is zero if all optnames are enabled, non-
zero otherwise. When setting or unsetting options, the return status is zero un-
less an optname is not a valid shell option.
The list of shopt options is:
assoc_expand_once
If set, the shell suppresses multiple evaluation of associative array sub-
scripts during arithmetic expression evaluation, while executing builtins
that can perform variable assignments, and while executing builtins that
perform array dereferencing.
autocd If set, a command name that is the name of a directory is executed as if it
were the argument to the cd command. This option is only used by interac-
tive shells.
cdable_vars
If set, an argument to the 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.
cdspell If set, minor errors in the spelling of a directory component in a cd com-
mand will be corrected. The errors checked for are transposed characters,
a missing character, and one character too many. If a correction is found,
the corrected filename is printed, and the command proceeds. This option
is only used by interactive shells.
checkhash
If set, bash checks that a command found in the hash table exists before
trying to execute it. If a hashed command no longer exists, a normal path
search is performed.
checkjobs
If set, bash lists the status of any stopped and running jobs before exit-
ing an interactive shell. If any jobs are running, this causes the exit to
be deferred until a second exit is attempted without an intervening command
(see JOB CONTROL above). The shell always postpones exiting if any jobs
are stopped.
checkwinsize
If set, bash checks the window size after each external (non-builtin) com-
mand and, if necessary, updates the values of LINES and COLUMNS. This op-
tion is enabled by default.
cmdhist If set, bash attempts to save all lines of a multiple-line command in the
same history entry. This allows easy re-editing of multi-line commands.
This option is enabled by default, but only has an effect if command his-
tory is enabled, as described above under HISTORY.
compat31
compat32
compat40
compat41
compat42
compat43
compat44
These control aspects of the shell's compatibility mode (see SHELL COMPATI-
BILITY MODE below).
complete_fullquote
If set, bash quotes all shell metacharacters in filenames and directory
names when performing completion. If not set, bash removes metacharacters
such as the dollar sign from the set of characters that will be quoted in
completed filenames when these metacharacters appear in shell variable ref-
erences in words to be completed. This means that dollar signs in variable
names that expand to directories will not be quoted; however, any dollar
signs appearing in filenames will not be quoted, either. This is active
only when bash is using backslashes to quote completed filenames. This
variable is set by default, which is the default bash behavior in versions
through 4.2.
direxpand
If set, bash replaces directory names with the results of word expansion
when performing filename completion. This changes the contents of the
readline editing buffer. If not set, bash attempts to preserve what the
user typed.
dirspell
If set, bash attempts spelling correction on directory names during word
completion if the directory name initially supplied does not exist.
dotglob If set, bash includes filenames beginning with a `.' in the results of
pathname expansion. The filenames ``.'' and ``..'' must always be
matched explicitly, even if dotglob is set.
execfail
If set, a non-interactive shell will not exit if it cannot execute the file
specified as an argument to the exec builtin command. An interactive shell
does not exit if exec fails.
expand_aliases
If set, aliases are expanded as described above under ALIASES. This option
is enabled by default for interactive shells.
extdebug
If set at shell invocation, or in a shell startup file, arrange to execute
the debugger profile before the shell starts, identical to the --debugger
option. If set after invocation, behavior intended for use by debuggers is
enabled:
1. The -F option to the declare builtin displays the source file name
and line number corresponding to each function name supplied as an
argument.
2. If the command run by the DEBUG trap returns a non-zero value, the
next command is skipped and not executed.
3. If the command run by the DEBUG trap returns a value of 2, and the
shell is executing in a subroutine (a shell function or a shell
script executed by the . or source builtins), the shell simulates a
call to return.
4. BASH_ARGC and BASH_ARGV are updated as described in their descrip-
tions above.
5. Function tracing is enabled: command substitution, shell functions,
and subshells invoked with ( command ) inherit the DEBUG and RETURN
traps.
6. Error tracing is enabled: command substitution, shell functions, and
subshells invoked with ( command ) inherit the ERR trap.
extglob If set, the extended pattern matching features described above under Path-
name Expansion are enabled.
extquote
If set, $'string' and $"string" quoting is performed within ${parameter}
expansions enclosed in double quotes. This option is enabled by default.
failglob
If set, patterns which fail to match filenames during pathname expansion
result in an expansion error.
force_fignore
If set, the suffixes specified by the FIGNORE shell variable cause words to
be ignored when performing word completion even if the ignored words are
the only possible completions. See SHELL VARIABLES above for a description
of FIGNORE. This option is enabled by default.
globasciiranges
If set, range expressions used in pattern matching bracket expressions (see
Pattern Matching above) behave as if in the traditional C locale when per-
forming comparisons. That is, the current locale's collating sequence is
not taken into account, so b will not collate between A and B, and upper-
case and lower-case ASCII characters will collate together.
globstar
If set, the pattern ** used in a pathname expansion context will match all
files and zero or more directories and subdirectories. If the pattern is
followed by a /, only directories and subdirectories match.
gnu_errfmt
If set, shell error messages are written in the standard GNU error message
format.
histappend
If set, the history list is appended to the file named by the value of the
HISTFILE variable when the shell exits, rather than overwriting the file.
histreedit
If set, and readline is being used, a user is given the opportunity to re-
edit a failed history substitution.
histverify
If set, and readline is being used, the results of history substitution are
not immediately passed to the shell parser. Instead, the resulting line is
loaded into the readline editing buffer, allowing further modification.
hostcomplete
If set, and readline is being used, bash will attempt to perform hostname
completion when a word containing a @ is being completed (see Completing
under READLINE above). This is enabled by default.
huponexit
If set, bash will send SIGHUP to all jobs when an interactive login shell
exits.
inherit_errexit
If set, command substitution inherits the value of the errexit option, in-
stead of unsetting it in the subshell environment. This option is enabled
when posix mode is enabled.
interactive_comments
If set, allow a word beginning with # to cause that word and all remaining
characters on that line to be ignored in an interactive shell (see COMMENTS
above). This option is enabled by default.
lastpipe
If set, and job control is not active, the shell runs the last command of a
pipeline not executed in the background in the current shell environment.
lithist If set, and the cmdhist option is enabled, multi-line commands are saved to
the history with embedded newlines rather than using semicolon separators
where possible.
localvar_inherit
If set, local variables inherit the value and attributes of a variable of
the same name that exists at a previous scope before any new value is as-
signed. The nameref attribute is not inherited.
localvar_unset
If set, calling unset on local variables in previous function scopes marks
them so subsequent lookups find them unset until that function returns.
This is identical to the behavior of unsetting local variables at the cur-
rent function scope.
login_shell
The shell sets this option if it is started as a login shell (see INVOCA-
TION above). The value may not be changed.
mailwarn
If set, and a file that bash is checking for mail has been accessed since
the last time it was checked, the message ``The mail in mailfile has been
read'' is displayed.
no_empty_cmd_completion
If set, and readline is being used, bash will not attempt to search the
PATH for possible completions when completion is attempted on an empty
line.
nocaseglob
If set, bash matches filenames in a case-insensitive fashion when perform-
ing pathname expansion (see Pathname Expansion above).
nocasematch
If set, bash matches patterns in a case-insensitive fashion when performing
matching while executing case or [[ conditional commands, when performing
pattern substitution word expansions, or when filtering possible comple-
tions as part of programmable completion.
nullglob
If set, bash allows patterns which match no files (see Pathname Expansion
above) to expand to a null string, rather than themselves.
progcomp
If set, the programmable completion facilities (see Programmable Completion
above) are enabled. This option is enabled by default.
progcomp_alias
If set, and programmable completion is enabled, bash treats a command name
that doesn't have any completions as a possible alias and attempts alias
expansion. If it has an alias, bash attempts programmable completion using
the command word resulting from the expanded alias.
promptvars
If set, prompt strings undergo parameter expansion, command substitution,
arithmetic expansion, and quote removal after being expanded as described
in PROMPTING above. This option is enabled by default.
restricted_shell
The shell sets this option if it is started in restricted mode (see RE-
STRICTED SHELL below). The value may not be changed. This is not reset
when the startup files are executed, allowing the startup files to discover
whether or not a shell is restricted.
shift_verbose
If set, the shift builtin prints an error message when the shift count ex-
ceeds the number of positional parameters.
sourcepath
If set, the source (.) builtin uses the value of PATH to find the directory
containing the file supplied as an argument. This option is enabled by de-
fault.
xpg_echo
If set, the echo builtin expands backslash-escape sequences by default.
suspend [-f]
Suspend the execution of this shell until it receives a SIGCONT signal. A login
shell cannot be suspended; the -f option can be used to override this and force the
suspension. The return status is 0 unless the shell is a login shell and -f is not
supplied, or if job control is not enabled.
test expr
[ expr ]
Return a status of 0 (true) or 1 (false) depending on the evaluation of the condi-
tional expression expr. Each operator and operand must be a separate argument.
Expressions are composed of the primaries described in the bash manual page under
CONDITIONAL EXPRESSIONS. test does not accept any options, nor does it accept and
ignore an argument of -- as signifying the end of options.
Expressions may be combined using the following operators, listed in decreasing or-
der of precedence. The evaluation depends on the number of arguments; see below.
Operator precedence is used when there are five or more arguments.
! expr True if expr is false.
( expr )
Returns the value of expr. This may be used to override the normal prece-
dence of operators.
expr1 -a expr2
True if both expr1 and expr2 are true.
expr1 -o expr2
True if either expr1 or expr2 is true.
test and [ evaluate conditional expressions using a set of rules based on the num-
ber of arguments.
0 arguments
The expression is false.
1 argument
The expression is true if and only if the argument is not null.
2 arguments
If the first argument is !, the expression is true if and only if the second
argument is null. If the first argument is one of the unary conditional op-
erators listed above under CONDITIONAL EXPRESSIONS, the expression is true
if the unary test is true. If the first argument is not a valid unary con-
ditional operator, the expression is false.
3 arguments
The following conditions are applied in the order listed. If the second ar-
gument is one of the binary conditional operators listed above under CONDI-
TIONAL EXPRESSIONS, the result of the expression is the result of the binary
test using the first and third arguments as operands. The -a and -o opera-
tors are considered binary operators when there are three arguments. If the
first argument is !, the value is the negation of the two-argument test us-
ing the second and third arguments. If the first argument is exactly ( and
the third argument is exactly ), the result is the one-argument test of the
second argument. Otherwise, the expression is false.
4 arguments
If the first argument is !, the result is the negation of the three-argument
expression composed of the remaining arguments. Otherwise, the expression
is parsed and evaluated according to precedence using the rules listed
above.
5 or more arguments
The expression is parsed and evaluated according to precedence using the
rules listed above.
When used with test or [, the < and > operators sort lexicographically using ASCII
ordering.
times Print the accumulated user and system times for the shell and for processes run
from the shell. The return status is 0.
trap [-lp] [[arg] sigspec ...]
The command arg is to be read and executed when the shell receives signal(s)
sigspec. If arg is absent (and there is a single sigspec) or -, each specified
signal is reset to its original disposition (the value it had upon entrance to the
shell). If arg is the null string the signal specified by each sigspec is ignored
by the shell and by the commands it invokes. If arg is not present and -p has been
supplied, then the trap commands associated with each sigspec are displayed. If no
arguments are supplied or if only -p is given, trap prints the list of commands as-
sociated with each signal. The -l option causes the shell to print a list of sig-
nal names and their corresponding numbers. Each sigspec is either a signal name
defined in <signal.h>, or a signal number. Signal names are case insensitive and
the SIG prefix is optional.
If a sigspec is EXIT (0) the command arg is executed on exit from the shell. If a
sigspec is DEBUG, the command arg is executed before every simple command, for com-
mand, case command, select command, every arithmetic for command, and before the
first command executes in a shell function (see SHELL GRAMMAR above). Refer to the
description of the extdebug option to the shopt builtin for details of its effect
on the DEBUG trap. If a sigspec is RETURN, the command arg is executed each time a
shell function or a script executed with the . or source builtins finishes execut-
ing.
If a sigspec is ERR, the command arg is executed whenever a pipeline (which may
consist of a single simple command), a list, or a compound command returns a
non-zero exit status, subject to the following conditions. The ERR trap is not ex-
ecuted if the failed command is part of the command list immediately following a
while or until keyword, part of the test in an if statement, part of a command exe-
cuted in a && or || list except the command following the final && or ||, any com-
mand in a pipeline but the last, or if the command's return value is being inverted
using !. These are the same conditions obeyed by the errexit (-e) option.
Signals ignored upon entry to the shell cannot be trapped or reset. Trapped sig-
nals that are not being ignored are reset to their original values in a subshell or
subshell environment when one is created. The return status is false if any
sigspec is invalid; otherwise trap returns true.
type [-aftpP] name [name ...]
With no options, indicate how each name would be interpreted if used as a command
name. If the -t option is used, type prints a string which is one of alias, key-
word, function, builtin, or file if name is an alias, shell reserved word, func-
tion, 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 -p option is used,
type either returns the name of the disk file that would be executed if name were
specified as a command name, or nothing if ``type -t name'' would not return file.
The -P option forces a PATH search for each name, even if ``type -t name'' would
not return file. If a command is hashed, -p and -P print the hashed value, which
is not necessarily the file that appears first in PATH. If the -a option is used,
type prints all of the places that contain an executable named name. This includes
aliases and functions, if and only if the -p option is not also used. The table of
hashed commands is not consulted when using -a. The -f option suppresses shell
function lookup, as with the command builtin. type returns true if all of the ar-
guments are found, false if any are not found.
ulimit [-HS] -a
ulimit [-HS] [-bcdefiklmnpqrstuvxPRT [limit]]
Provides control over the resources available to the shell and to processes started
by it, on systems that allow such control. The -H and -S options specify that the
hard or soft limit is set for the given resource. A hard limit cannot be increased
by a non-root user once it is set; a soft limit may be increased up to the value of
the hard limit. If neither -H nor -S is specified, both the soft and hard limits
are set. The value of limit can be a number in the unit specified for the resource
or one of the special values hard, soft, or unlimited, which stand for the current
hard limit, the current soft limit, and no limit, respectively. If limit is omit-
ted, the current value of the soft limit of the resource is printed, unless the -H
option is given. When more than one resource is specified, the limit name and
unit, if appropriate, are printed before the value. Other options are interpreted
as follows:
-a All current limits are reported; no limits are set
-b The maximum socket buffer size
-c The maximum size of core files created
-d The maximum size of a process's data segment
-e The maximum scheduling priority ("nice")
-f The maximum size of files written by the shell and its children
-i The maximum number of pending signals
-k The maximum number of kqueues that may be allocated
-l The maximum size that may be locked into memory
-m The maximum resident set size (many systems do not honor this limit)
-n The maximum number of open file descriptors (most systems do not allow this
value to be set)
-p The pipe size in 512-byte blocks (this may not be set)
-q The maximum number of bytes in POSIX message queues
-r The maximum real-time scheduling priority
-s The maximum stack size
-t The maximum amount of cpu time in seconds
-u The maximum number of processes available to a single user
-v The maximum amount of virtual memory available to the shell and, on some
systems, to its children
-x The maximum number of file locks
-P The maximum number of pseudoterminals
-R The maximum time a real-time process can run before blocking, in microsec-
onds
-T The maximum number of threads
If limit is given, and the -a option is not used, limit is the new value of the
specified resource. If no option is given, then -f is assumed. Values are in
1024-byte increments, except for -t, which is in seconds; -R, which is in microsec-
onds; -p, which is in units of 512-byte blocks; -P, -T, -b, -k, -n, and -u, which
are unscaled values; and, when in posix mode, -c and -f, which are in 512-byte in-
crements. The return status is 0 unless an invalid option or argument is supplied,
or an error occurs while setting a new limit.
umask [-p] [-S] [mode]
The user file-creation mask is set to mode. If mode begins with a digit, it is in-
terpreted as an octal number; otherwise it is interpreted as a symbolic mode mask
similar to that accepted by chmod(1). If mode is omitted, the current value of the
mask is printed. The -S option causes the mask to be printed in symbolic form; the
default output is an octal number. If the -p option is supplied, and mode is omit-
ted, the output is in a form that may be reused as input. The return status is 0
if the mode was successfully changed or if no mode argument was supplied, and false
otherwise.
unalias [-a] [name ...]
Remove each name from the list of defined aliases. If -a is supplied, all alias
definitions are removed. The return value is true unless a supplied name is not a
defined alias.
unset [-fv] [-n] [name ...]
For each name, remove the corresponding variable or function. If the -v option is
given, each name refers to a shell variable, and that variable is removed. Read-
only variables may not be unset. If -f is specified, each name refers to a shell
function, and the function definition is removed. If the -n option is supplied,
and name is a variable with the nameref attribute, name will be unset rather than
the variable it references. -n has no effect if the -f option is supplied. If no
options are supplied, each name refers to a variable; if there is no variable by
that name, a function with that name, if any, is unset. Each unset variable or
function is removed from the environment passed to subsequent commands. If any of
BASH_ALIASES, BASH_ARGV0, BASH_CMDS, BASH_COMMAND, BASH_SUBSHELL, BASHPID,
COMP_WORDBREAKS, DIRSTACK, EPOCHREALTIME, EPOCHSECONDS, FUNCNAME, GROUPS, HISTCMD,
LINENO, RANDOM, SECONDS, or SRANDOM are unset, they lose their special properties,
even if they are subsequently reset. The exit status is true unless a name is
readonly.
wait [-fn] [-p varname] [id ...]
Wait for each specified child process and return its termination status. Each id
may be a process ID or a job specification; if a job spec is given, all processes
in that job's pipeline are waited for. If id is not given, wait waits for all run-
ning background jobs and the last-executed process substitution, if its process id
is the same as $!, and the return status is zero. If the -n option is supplied,
wait waits for a single job from the list of ids or, if no ids are supplied, any
job, to complete and returns its exit status. If none of the supplied arguments is
a child of the shell, or if no arguments are supplied and the shell has no un-
waited-for children, the exit status is 127. If the -p option is supplied, the
process or job identifier of the job for which the exit status is returned is as-
signed to the variable varname named by the option argument. The variable will be
unset initially, before any assignment. This is useful only when the -n option is
supplied. Supplying the -f option, when job control is enabled, forces wait to
wait for id to terminate before returning its status, instead of returning when it
changes status. If id specifies a non-existent process or job, the return status
is 127. Otherwise, the return status is the exit status of the last process or job
waited for.
SHELL COMPATIBILITY MODE
Bash-4.0 introduced the concept of a `shell compatibility level', specified as a set of
options to the shopt builtin compat31, compat32, compat40, compat41, and so on). There is
only one current compatibility level -- each option is mutually exclusive. The compati-
bility level is intended to allow users to select behavior from previous versions that is
incompatible with newer versions while they migrate scripts to use current features and
behavior. It's intended to be a temporary solution.
This section does not mention behavior that is standard for a particular version (e.g.,
setting compat32 means that quoting the rhs of the regexp matching operator quotes special
regexp characters in the word, which is default behavior in bash-3.2 and above).
If a user enables, say, compat32, it may affect the behavior of other compatibility levels
up to and including the current compatibility level. The idea is that each compatibility
level controls behavior that changed in that version of bash, but that behavior may have
been present in earlier versions. For instance, the change to use locale-based compar-
isons with the [[ command came in bash-4.1, and earlier versions used ASCII-based compar-
isons, so enabling compat32 will enable ASCII-based comparisons as well. That granularity
may not be sufficient for all uses, and as a result users should employ compatibility lev-
els carefully. Read the documentation for a particular feature to find out the current
behavior.
Bash-4.3 introduced a new shell variable: BASH_COMPAT. The value assigned to this vari-
able (a decimal version number like 4.2, or an integer corresponding to the compatNN op-
tion, like 42) determines the compatibility level.
Starting with bash-4.4, Bash has begun deprecating older compatibility levels. Eventu-
ally, the options will be removed in favor of BASH_COMPAT.
Bash-5.0 is the final version for which there will be an individual shopt option for the
previous version. Users should use BASH_COMPAT on bash-5.0 and later versions.
The following table describes the behavior changes controlled by each compatibility level
setting. The compatNN tag is used as shorthand for setting the compatibility level to NN
using one of the following mechanisms. For versions prior to bash-5.0, the compatibility
level may be set using the corresponding compatNN shopt option. For bash-4.3 and later
versions, the BASH_COMPAT variable is preferred, and it is required for bash-5.1 and later
versions.
compat31
o quoting the rhs of the [[ command's regexp matching operator (=~) has no
special effect
compat32
o interrupting a command list such as "a ; b ; c" causes the execution of the
next command in the list (in bash-4.0 and later versions, the shell acts as
if it received the interrupt, so interrupting one command in a list aborts
the execution of the entire list)
compat40
o the < and > operators to the [[ command do not consider the current locale
when comparing strings; they use ASCII ordering. Bash versions prior to
bash-4.1 use ASCII collation and strcmp(3); bash-4.1 and later use the cur-
rent locale's collation sequence and strcoll(3).
compat41
o in posix mode, time may be followed by options and still be recognized as a
reserved word (this is POSIX interpretation 267)
o in posix mode, the parser requires that an even number of single quotes oc-
cur in the word portion of a double-quoted parameter expansion and treats
them specially, so that characters within the single quotes are considered
quoted (this is POSIX interpretation 221)
compat42
o the replacement string in double-quoted pattern substitution does not un-
dergo quote removal, as it does in versions after bash-4.2
o in posix mode, single quotes are considered special when expanding the word
portion of a double-quoted parameter expansion and can be used to quote a
closing brace or other special character (this is part of POSIX interpreta-
tion 221); in later versions, single quotes are not special within double-
quoted word expansions
compat43
o the shell does not print a warning message if an attempt is made to use a
quoted compound assignment as an argument to declare (declare -a foo='(1
2)'). Later versions warn that this usage is deprecated
o word expansion errors are considered non-fatal errors that cause the current
command to fail, even in posix mode (the default behavior is to make them
fatal errors that cause the shell to exit)
o when executing a shell function, the loop state (while/until/etc.) is not
reset, so break or continue in that function will break or continue loops in
the calling context. Bash-4.4 and later reset the loop state to prevent this
compat44
o the shell sets up the values used by BASH_ARGV and BASH_ARGC so they can ex-
pand to the shell's positional parameters even if extended debugging mode is
not enabled
o a subshell inherits loops from its parent context, so break or continue will
cause the subshell to exit. Bash-5.0 and later reset the loop state to pre-
vent the exit
o variable assignments preceding builtins like export and readonly that set
attributes continue to affect variables with the same name in the calling
environment even if the shell is not in posix mode
compat50
o Bash-5.1 changed the way $RANDOM is generated to introduce slightly more
randomness. If the shell compatibility level is set to 50 or lower, it re-
verts to the method from bash-5.0 and previous versions, so seeding the ran-
dom number generator by assigning a value to RANDOM will produce the same
sequence as in bash-5.0
o If the command hash table is empty, bash versions prior to bash-5.1 printed
an informational message to that effect, even when producing output that can
be reused as input. Bash-5.1 suppresses that message when the -l option is
supplied.
SEE ALSO
bash(1), sh(1)
GNU Bash-2.05a 2001 October 29 BASH-BUILTINS(7)
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