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BASH_BUILTINS(1) General Commands Manual 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 com-
mands, 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 -- specially. 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 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. 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 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. 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] [-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 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; 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 non-zero when n is <= 0; Other-
wise, break returns 0 value.
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
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 inte-
ger 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 extra information may be used, for example, to print a stack trace. The cur-
rent 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 [-e]]] [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. Alterna-
tive 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 direc-
tory structure instead of following symbolic links (see also the -P option to the
set builtin command); the -L option forces symbolic links to be followed. 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. 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 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
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 sup-
plied 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 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] [-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 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 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 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
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 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
results 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 it finishes, the possible completions are retrieved from the value of
the COMPREPLY array 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. The possible completions
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
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 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
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 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 the remaining options should apply to the ``default'' com-
mand 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. When continue is executed inside of loop, the return value is
non-zero when n is <= 0; Otherwise, continue returns 0 value. When continue is exe-
cuted outside of loop, the return value is 0.
declare [-aAfFgilrtux] [-p] [name[=value] ...]
typeset [-aAfFgilrtux] [-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 val-
ues 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 val-
ues of all shell variables. The -f option will restrict the display to shell func-
tions. The -F option inhibits the display of function definitions; only the func-
tion 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 -g option forces variables to be
created or modified at the global scope, even when declare is executed in a shell
function. It is ignored in all other cases. 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.
-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 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 com-
mand, unless the -g option is supplied, 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 assign-
ment 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] [-clpv]
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 command 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 cur-
rent 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 sup-
plied, 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 opera-
tion 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 char-
acters 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
environment. 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-inter-
active 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 exe-
cuted. 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 all names
that are exported in this shell is printed. The -n option causes the export prop-
erty 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 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]
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 num-
ber). 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, 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 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 [args]
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
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 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 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]
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 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 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
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 status 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 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 -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 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 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 history line. 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 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 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. 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 vari-
ables to the standard output. It is an error to use local when not within a func-
tion. 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 meanings:
-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 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
directory 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
argument (except that \c terminates output, backslashes in \', \", and \?
are not removed, and octal escapes beginning with \0 may contain up to four
digits).
%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.
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,
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 work-
ing 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 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, 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 inter-
vening 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 com-
plete 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 com-
ing 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 frac-
tional 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 sup-
plied 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
options 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 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) com-
mand, 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 during 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-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
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 com-
mand), 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 com-
mand 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 follow-
ing 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 environ-
ment and each subshell environment separately (see COMMAND EXECUTION ENVI-
RONMENT 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 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).
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 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
option is on by default in interactive 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 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
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 effec-
tive 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 follow 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
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 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 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 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, 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 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 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 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 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 [[ conditional 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. Bash versions prior to bash-4.1 use ASCII collation and
strcmp(3); bash-4.1 and later use the current locale's collation sequence
and strcoll(3).
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 (see previous item) and the effect of interrupting a com-
mand list.
compat41
If set, bash, when in posix mode, treats a single quote in a double-quoted
parameter expansion as a special character. The single quotes must match
(an even number) and the characters between the single quotes are consid-
ered quoted. This is the behavior of posix mode through version 4.1. The
default bash behavior remains as in previous versions.
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.
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 subroutine (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 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.
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.
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.
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.
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.
syslog_history
If set, command history is logged to syslog.
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. When the
suspended shell is a background process, it can be restarted by the fg command. For
more information, read the JOB CONTROL section. The suspend command can not suspend
the login shell. However, when -f option is specified, suspend command can suspend
even login shell. 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 operand must be a separate argument. Expressions are com-
posed of the primaries described above under CONDITIONAL EXPRESSIONS. test does
not accept any options, nor does it accept and ignore an argument of -- as signify-
ing the end of options.
Expressions may be combined using the following operators, listed in decreasing
order of precedence. The evaluation depends on the number of arguments; see below.
Operator precedence is used when there are five or more arguments.
! 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
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 con-
ditional operator, the expression is false.
3 arguments
The following conditions are applied in the order listed. If the second
argument is one of the binary conditional operators listed above under CON-
DITIONAL 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
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 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
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 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 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 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, 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, reset or listed.
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, 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, 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 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
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 and, on some
systems, to its children
-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. In POSIX Mode 512-byte blocks are used for the `-c' and `-f' options.
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 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] [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 specification; if a job spec is given, all processes in that
job's pipeline are waited for. If n is not given, all currently active child pro-
cesses are waited for, and the return status is zero. If n specifies a non-exis-
tent 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)
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