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BASH_BUILTINS(1) BASH_BUILTINS(1)
NAME
bash, :, ., [, alias, bg, bind, break, builtin, caller, cd, command, compgen, complete, compopt, continue, declare, dirs,
disown, echo, enable, eval, exec, exit, export, false, fc, fg, getopts, hash, help, history, jobs, kill, let, local,
logout, mapfile, popd, printf, pushd, pwd, read, readonly, return, set, shift, shopt, source, suspend, test, times, trap,
true, type, typeset, ulimit, umask, unalias, unset, wait - bash built-in commands, see bash(1)
BASH BUILTIN COMMANDS
Unless otherwise noted, each builtin command documented in this section as accepting options preceded by - accepts -- to
signify the end of the options. The :, true, false, and test builtins do not accept options and do not treat -- spe-
cially. The exit, logout, 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 begin-
ning 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. A zero
exit code is returned.
. 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, file names in PATH are used to find the
directory containing filename. 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 posi-
tional parameters when filename is executed. Otherwise the positional parameters are unchanged. The return sta-
tus is the status of the last command exited within the script (0 if no commands are executed), and false if file-
name 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] [-lpsvPSV]
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 readline-command
Display current readline key and function bindings, bind a key sequence to a readline function or macro, or set a
readline variable. Each non-option argument is a command as it would appear in .inputrc, but each binding or com-
mand must be passed as a separate argument; e.g., '"\C-x\C-r": re-read-init-file'. Options, if supplied, have the
following meanings:
-m keymap
Use keymap as the keymap to be affected by the subsequent bindings. Acceptable keymap names are emacs,
emacs-standard, emacs-meta, emacs-ctlx, vi, vi-move, vi-command, and vi-insert. vi is equivalent to
vi-command; 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 variable
to the current location of the insertion point. If the executed command changes the value of READLINE_LINE
or READLINE_POINT, those new values will be reflected in the editing state.
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 status. This is useful when defin-
ing 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 executed with the . or source
builtins. Without expr, caller displays the line number 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 corre-
sponding to that position in the current execution call stack. This extra information may be used, for example,
to print a stack trace. The current frame is frame 0. The return value is 0 unless the shell is not executing a
subroutine call or expr does not correspond to a valid position in the call stack.
cd [-L|-P] [dir]
Change the current directory to dir. The variable HOME is the default dir. The variable CDPATH defines the
search path for the directory containing dir. Alternative directory names in CDPATH 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 says to use the physical directory structure instead of following sym-
bolic links (see also the -P option to the set builtin command); the -L option forces symbolic links to be fol-
lowed. An argument of - is equivalent to $OLDPWD. 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 other-
wise.
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 guaranteed to find all of the standard utilities. If either the -V or -v option is supplied, a descrip-
tion of command is printed. The -v option causes a single word indicating the command or file name used to invoke
command to be displayed; the -V option 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. Otherwise, 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 available, 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 displayed.
The return value is true unless an invalid option is supplied, or no matches were generated.
complete [-abcdefgjksuv] [-o comp-option] [-DE] [-A action] [-G globpat] [-W wordlist] [-F function] [-C command]
[-X filterpat] [-P prefix] [-S suffix] name [name ...]
complete -pr [-DE] [name ...]
Specify how arguments to each name should be completed. If the -p option is supplied, or if no options are sup-
plied, 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 completion specifica-
tions. The -D option indicates that the remaining options and actions should apply to the ``default'' command
completion; that is, completion attempted on a command for which no completion has previously been defined. The
-E option indicates that the remaining options and actions should apply to ``empty'' command completion; that is,
completion attempted on a blank line.
The process of applying these completion specifications when word completion is attempted 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 com-
pletions. 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 generates no matches.
dirnames
Perform directory name completion if the compspec generates no matches.
filenames
Tell readline that the compspec generates filenames, so it can perform any filename-specific pro-
cessing (like adding a slash to directory names, quoting special characters, or suppressing trail-
ing spaces). Intended to be used with shell functions.
nospace Tell readline not to append a space (the default) to words completed 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 results of the other actions.
-A action
The action may be one of the following to generate a list of possible completions:
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.
-G globpat
The pathname expansion pattern globpat is expanded to generate the possible completions.
-W wordlist
The wordlist is split using the characters in the IFS special variable as delimiters, and each resultant
word is expanded. The possible completions are the members of the resultant list which match the word
being completed.
-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 it finishes, the possible
completions are retrieved from the value of the COMPREPLY array variable.
-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 arguments, and each completion matching filterpat is removed from
the list. A leading ! in filterpat negates the pattern; in this case, any completion not matching filter-
pat is removed.
-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.
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 completion specification for a name for which no specification
exists, or an error occurs adding a completion specification.
compopt [-o option] [-DE] [+o option] [name]
Modify completion options for each name according to the options, or for the currently-execution completion if no
names are supplied. If no options are given, display the completion options for each name or the current comple-
tion. The possible values of option are those valid for the complete builtin described above. The -D option
indicates that the remaining options should apply to the ``default'' command completion; that is, completion
attempted on a command for which no completion has previously been defined. The -E option indicates that the
remaining options should apply to ``empty'' command completion; that is, completion attempted on a blank line.
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 [-aAfFilrtux] [-p] [name[=value] ...]
typeset [-aAfFilrtux] [-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 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 definitions; 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 the function is defined are displayed as well. The -F option implies -f. 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 converted to lower-case. The upper-
case attribute is disabled.
-r Make names readonly. These names cannot then be assigned values by subsequent 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 converted 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 may not be used to destroy
an array variable and +r will not remove the readonly attribute. When used in a function, makes each name local,
as with the local command. If a variable name is followed by =value, the value of the variable is set to value.
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 compound 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 variable, an attempt is made to
turn off array status for an array variable, or an attempt is made to display a non-existent function with -f.
dirs [+n] [-n] [-cplv]
Without options, displays the list of currently remembered directories. The default display is on a single line
with directory names separated by spaces. Directories are added to the list with the pushd command; the popd com-
mand removes entries from the list.
+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.
-c Clears the directory stack by deleting all of the entries.
-l Produces a longer listing; 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.
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 ...]
Without options, each jobspec is removed from the table of active jobs. If jobspec is not present, and neither -a
nor -r is supplied, the shell's notion of 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 present, and neither the -a nor the -r option is supplied, the current job is used. If no jobspec is
supplied, the -a option means to remove or mark all jobs; the -r option without a jobspec argument restricts oper-
ation 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 always 0. If -n is specified,
the trailing newline is suppressed. If the -e option is given, interpretation of the following backslash-escaped
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 expands 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 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)
enable [-a] [-dnps] [-f filename] [name ...]
Enable and disable builtin shell commands. Disabling a builtin allows a disk command which has the same name as a
shell builtin to be executed without specifying a full pathname, even though the shell normally searches for
builtins before disk commands. If -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 command 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 arguments 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 supplied, 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 environment. If
-a is supplied, the shell passes name as the zeroth argument to the executed command. If command cannot be exe-
cuted for some reason, a non-interactive shell exits, unless the shell option execfail is enabled, in which case
it returns failure. An interactive shell returns failure if the file cannot be executed. If command is not spec-
ified, 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 exe-
cuted. 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 subsequently executed commands. If the
-f option is given, the names refer to functions. If no names are given, or if the -p option is supplied, a list
of all names that are exported in this shell 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 option is encountered, one of the names is not a valid shell vari-
able name, or -f is supplied with a name that is not a function.
fc [-e ename] [-lnr] [first] [last]
fc -s [pat=rep] [cmd]
Fix Command. In the first form, a range of commands from first to last is selected from the history list. 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). If
last is not specified it is set to the current command for listing (so that ``fc -l -10'' prints the last 10 com-
mands) 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 containing 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, 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. 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 encountered 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 exe-
cuted 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 [args]
getopts is used by shell procedures to parse positional parameters. optstring contains the option characters to
be recognized; if a character is followed by a colon, the option is expected to have an argument, which should be
separated from it by white space. The colon and question mark characters may not be used as option characters.
Each time it is invoked, 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 argument, 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 given in args, 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 option 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]
For each name, the full file name of the command is determined by searching the directories in $PATH and remem-
bered. If the -p option is supplied, no path search is performed, and filename is used as the full file name 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 pathname 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 option 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 commands is printed. The return sta-
tus is true unless a name is not found or an invalid option is supplied.
help [-dms] [pattern]
Display helpful information about builtin commands. If pattern is specified, help gives detailed help on all com-
mands 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 -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.
-a Append the ``new'' history lines (history lines entered since the beginning of the current bash session) to
the history file.
-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 bash session.
-r Read the contents of the history file and use them as the current history.
-w Write the current history 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 previous his-
tory line. The return value is 0 unless an invalid option is encountered, an error occurs while reading or writ-
ing 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.
-p List only the process ID of the job's process group leader.
-n Display information only about jobs that have changed status since the user was last notified of their sta-
tus.
-r Restrict output to running jobs.
-s Restrict output to stopped jobs.
If jobspec is given, output is restricted to information about that job. The return status is 0 unless an invalid
option is encountered or an invalid 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, returning its exit status.
kill [-s sigspec | -n signum | -sigspec] [pid | jobspec] ...
kill -l [sigspec | exit_status]
Send the signal named by sigspec or signum to the processes named by pid or jobspec. 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 corresponding 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. 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. With no operands, local writes a list of local variables to
the standard output. It is an error to use local when not within a function. The return status is 0 unless local
is used outside a function, an invalid name is supplied, or name is a readonly variable.
logout Exit a login shell.
mapfile [-n count] [-O origin] [-s count] [-t] [-u fd] [-C callback] [-c quantum] [array]
readarray [-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 default array. Options, if supplied, have the following mean-
ings:
-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 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 evaluated, it is supplied the index
of the next array element to be assigned as an additional argument. 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 supplied, 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 directory from the stack, and per-
forms 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 status 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 format. The format is a character
string which contains three types of objects: plain characters, which are simply copied to standard output, char-
acter 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) formats, %b causes
printf to expand backslash escape sequences in the corresponding argument (except that \c terminates output, back-
slashes in \', \", and \? are not removed, and octal escapes beginning with \0 may contain up to four digits), and
%q causes printf to output the corresponding argument in a format that can be reused as shell input.
The -v option causes the output to be assigned to the variable var rather than being printed to the standard out-
put.
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 sup-
plied. 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 cur-
rent working directory. With no arguments, 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 adding directories 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 working directory.
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 element 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 read-
ing 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 timeout] [-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,
and the first word is assigned to the first name, the second word to the second name, and so on, with leftover
words and their intervening separators 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. 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.
-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.
-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 complete line of input, but honor 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. Delimiter characters encountered in the input are not treated
specially and do not cause read to return until nchars characters are read.
-p prompt
Display prompt on standard error, without a trailing newline, before attempting to read any input. The
prompt is displayed only if input is coming from a terminal.
-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 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 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 terminal, pipe, or other special file; it has no effect when
reading from regular files. If timeout is 0, read returns success if input is available on the specified
file descriptor, failure 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 is assigned to the variable REPLY. The return code is zero, unless end-
of-file is encountered, read times out (in which case the return code is greater than 128), or an invalid file
descriptor is supplied as the argument to -u.
readonly [-aApf] [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 corresponding 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 no name arguments
are given, or if the -p option is supplied, a list of all readonly names is printed. 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 function.
return [n]
Causes a function to exit with the return value specified by n. If 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 .
(source) command, it causes the shell to stop executing that script and return either 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 dur-
ing execution of a script by ., the return status is false. Any command associated with the RETURN trap is exe-
cuted before execution resumes after the function or script.
set [--abefhkmnptuvxBCEHPT] [-o option] [arg ...]
set [+abefhkmnptuvxBCEHPT] [+o option] [arg ...]
Without options, the name and value of each shell variable are displayed in a format that can be reused as input
for setting or resetting the currently-set variables. 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 assigned, in order, to $1, $2, ... $n. Options, if specified, have the following
meanings:
-a Automatically mark variables and functions which are modified or created 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 command), a subshell command
enclosed in parentheses, or one of the commands executed as part of a command list enclosed by braces (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 command 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 !. A trap on ERR, if set, is executed before 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.
-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 environment 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). Background processes run in a separate process group and a line
containing their exit status is printed upon their completion.
-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 edit-
ing 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 option is on by default in inter-
active shells.
ignoreeof
The effect is as if the shell command ``IGNOREEOF=10'' had been executed (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).
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 commands 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 effective user (group) id
not equal to the real user (group) id, and the -p option 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 effective user
id is not reset. Turning this option off causes the effective user and group ids to be set to the real
user and group ids.
-t Exit after reading and executing one command.
-u Treat unset variables and parameters other than the special parameters "@" and "*" as an error when per-
forming parameter expansion. If expansion is attempted on an unset variable or parameter, the shell
prints an error message, and, if not interactive, exits with a non-zero status.
-v Print shell input lines as they are read.
-x After expanding each simple command, for command, case command, select command, or arithmetic for command,
display the expanded value of PS4, followed 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 <> redirection 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 substitutions, 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 follow symbolic links when executing commands such as cd that change the cur-
rent 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 com-
mands 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 unset. 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 arguments 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 represented 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 variables controlling optional shell behavior. With no options, or with the -p option, a
list of all settable options is displayed, with an indication of whether or not each is set. 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 otherwise.
-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, the display is limited to those options which are set or
unset, respectively. Unless otherwise noted, the shopt options 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 unless an optname is not a valid shell option.
The list of shopt options is:
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 interactive 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 vari-
able whose value is the directory to change to.
cdspell If set, minor errors in the spelling of a directory component in a cd command will be corrected. The
errors checked for are transposed characters, a missing character, and one character too many. If a cor-
rection is found, the corrected file name 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 exiting an interactive shell. If any
jobs are running, this causes the exit to be deferred until a second exit is attempted without an inter-
vening 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 command and, if necessary, updates the values of LINES and
COLUMNS.
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.
compat31
If set, bash changes its behavior to that of version 3.1 with respect to quoted arguments to the condi-
tional command's =~ operator.
compat32
If set, bash changes its behavior to that of version 3.2 with respect to locale-specific string comparison
when using the conditional command's < and > operators.
compat40
If set, bash changes its behavior to that of version 4.0 with respect to locale-specific string comparison
when using the conditional command's < and > operators and the effect of interrupting a command list.
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.
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, 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 subrou-
tine (a shell function or a shell script executed by the . or source builtins), a call to return is
simulated.
4. BASH_ARGC and BASH_ARGV are updated as described in their descriptions 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 ( com-
mand ) inherit the ERROR trap.
extglob If set, the extended pattern matching features described above under Pathname 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.
globstar
If set, the pattern ** used in a pathname expansion context will match a files and zero or more directo-
ries 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 substitu-
tion.
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 contain-
ing 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.
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.
lithist If set, and the cmdhist option is enabled, multi-line commands are saved to the history with embedded new-
lines rather than using semicolon separators where possible.
login_shell
The shell sets this option if it is started as a login shell (see INVOCATION 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 performing pathname expansion (see Path-
name Expansion above).
nocasematch
If set, bash matches patterns in a case-insensitive fashion when performing matching while executing case
or [[ conditional commands.
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.
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 RESTRICTED 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 exceeds 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 default.
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 or 1 depending on the evaluation of the conditional expression expr. Each operator and oper-
and must be a separate argument. Expressions are composed of the primaries described above 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 order of precedence. The evalua-
tion depends on the number of arguments; see below.
! expr True if expr is false.
( expr )
Returns the value of expr. This may be used to override the normal precedence 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 number 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 operators listed above under CONDITIONAL EXPRESSIONS, the
expression is true if the unary test is true. If the first argument is not a valid unary conditional oper-
ator, the expression is false.
3 arguments
If the second argument is one of the binary conditional operators listed above under CONDITIONAL EXPRES-
SIONS, the result of the expression is the result of the binary test using the first and third arguments as
operands. The -a and -o operators are considered binary operators when there are three arguments. If the
first argument is !, the value is the negation of the two-argument test using the second and third argu-
ments. If the first argument is exactly ( and the third argument is exactly ), the result is the one-argu-
ment 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.
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 associated with each signal. The -l option causes the shell to print a list of signal 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 command, case command, select command, every arithmetic for com-
mand, and before the first command executes in a shell function (see SHELL GRAMMAR above). Refer to the descrip-
tion 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 executing.
If a sigspec is ERR, the command arg is executed whenever a simple command has a non-zero exit status, subject to
the following conditions. The ERR trap is not executed if the failed command is part of the command list immedi-
ately following a while or until keyword, part of the test in an if statement, part of a command executed in a &&
or || list, or if the command's return value is being inverted via !. These are the same conditions obeyed by the
errexit option.
Signals ignored upon entry to the shell cannot be trapped or reset. Trapped signals that are not being ignored
are reset to their original values in a subshell or subshell environment when one is created. The return status
is false if any 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, keyword, function, builtin, or file if 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 -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, 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 arguments are found, false if any are not found.
ulimit [-HSTabcdefilmnpqrstuvx [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 omitted, 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 are printed before the value. Other options are interpreted as follows:
-a All current limits are reported
-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
-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
-x The maximum number of file locks
-T The maximum number of threads
If limit is given, it is the new value of the specified resource (the -a option is display only). If no option is
given, then -f is assumed. Values are in 1024-byte increments, except for -t, which is in seconds, -p, which is
in units of 512-byte blocks, and -T, -b, -n, and -u, which are unscaled values. 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 interpreted 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 omitted, the output is in a form that may be
reused as input. The return status is 0 if the mode was successfully changed or if no 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] [name ...]
For each name, remove the corresponding variable or function. If no options are supplied, or the -v option is
given, each name refers to a shell variable. Read-only variables may not be unset. If -f is specified, each name
refers to a shell function, and the function definition is removed. Each unset variable or function is removed
from the environment passed to subsequent commands. If any of COMP_WORDBREAKS, RANDOM, SECONDS, LINENO, HISTCMD,
FUNCNAME, GROUPS, or DIRSTACK are unset, they lose their special properties, even if they are subsequently reset.
The exit status is true unless a name is readonly.
wait [n ...]
Wait for each specified process and return its termination status. Each n may be a process ID or a job specifica-
tion; if a job spec is given, all processes in that job's pipeline are waited for. If n is not given, all cur-
rently active child processes are waited for, and the return status is zero. If n 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.
SEE ALSO
bash(1), sh(1)
GNU Bash-4.0 2004 Apr 20 BASH_BUILTINS(1)
