bash内置文档（ubuntu20.10）
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内容图文
系统
用的是ubuntu20.10
命令
compgen -b #这个简单
man bash-builtins #显示得细节已经卸载下面文档中
文档
BASH-BUILTINS(7) Miscellaneous Information Manual BASH-BUILTINS(7)
NAME
bash-builtins - bash built-in commands, see bash(1)
SYNOPSIS
bash defines the following built-in commands: :, ., [, alias, bg, bind,
break, builtin, case, cd, command, compgen, complete, continue, de‐
clare, dirs, disown, echo, enable, eval, exec, exit, export, fc, fg,
getopts, hash, help, history, if, jobs, kill, let, local, logout, popd,
printf, pushd, pwd, read, readonly, return, set, shift, shopt, source,
suspend, test, times, trap, type, typeset, ulimit, umask, unalias, un‐
set, until, wait, while.
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, return, break, con‐
tinue, 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 interpreta‐
tion.
: [arguments]
No effect; the command does nothing beyond expanding arguments
and performing any specified redirections. The return status is
zero.
. filename [arguments]
source filename [arguments]
Read and execute commands from filename in the current shell en‐
vironment and return the exit status of the last command exe‐
cuted from filename. If filename does not contain a slash,
filenames 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 po‐
sitional parameters are unchanged. If the -T option is enabled,
source inherits any trap on DEBUG; if it is not, any DEBUG trap
string is saved and restored around the call to source, and
source unsets the DEBUG trap while it executes. If -T is not
set, and the sourced file changes the DEBUG trap, the new value
is retained when source completes. The return status is the
status of the last command exited within the script (0 if no
commands are executed), and false if filename is not found or
cannot be read.
alias [-p] [name[=value] ...]
Alias with no arguments or with the -p option prints the list of
aliases in the form alias name=value on standard output. When
arguments are supplied, an alias is defined for each name whose
value is given. A trailing space in value causes the next word
to be checked for alias substitution when the alias is expanded.
For each name in the argument list for which no value is sup‐
plied, the name and value of the alias is printed. Alias re‐
turns true unless a name is given for which no alias has been
defined.
bg [jobspec ...]
Resume each suspended job jobspec in the background, as if it
had been started with &. If jobspec is not present, the shell's
notion of the current job is used. bg jobspec returns 0 unless
run when job control is disabled or, when run with job control
enabled, any specified jobspec was not found or was started
without job control.
bind [-m keymap] [-lpsvPSVX]
bind [-m keymap] [-q function] [-u function] [-r keyseq]
bind [-m keymap] -f filename
bind [-m keymap] -x keyseq:shell-command
bind [-m keymap] keyseq:function-name
bind [-m keymap] keyseq:readline-command
Display current readline key and function bindings, bind a key
sequence to a readline function or macro, or set a readline
variable. Each non-option argument is a command as it would ap‐
pear in .inputrc, but each binding or command must be passed as
a separate argument; e.g., '"\C-x\C-r": re-read-init-file'. Op‐
tions, 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-stan‐
dard, emacs-meta, emacs-ctlx, vi, vi-move, vi-command,
and vi-insert. vi is equivalent to vi-command (vi-move
is also a synonym); emacs is equivalent to emacs-stan‐
dard.
-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 en‐
tered. When shell-command is executed, the shell sets
the READLINE_LINE variable to the contents of the read‐
line 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 READ‐
LINE_POINT, those new values will be reflected in the
editing state.
-X List all key sequences bound to shell commands and the
associated commands in a format that can be reused as in‐
put.
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 defining a function
whose name is the same as a shell builtin, retaining the func‐
tionality 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 func‐
tion or a script executed with the . or source builtins). With‐
out expr, caller displays the line number and source filename of
the current subroutine call. If a non-negative integer is sup‐
plied 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 current frame is frame 0.
The return value is 0 unless the shell is not executing a sub‐
routine call or expr does not correspond to a valid position in
the call stack.
cd [-L|[-P [-e]] [-@]] [dir]
Change the current directory to dir. if dir is not supplied,
the value of the HOME shell variable is the default. Any addi‐
tional arguments following dir are ignored. The variable CDPATH
defines the search path for the directory containing dir: each
directory name in CDPATH is searched for dir. Alternative di‐
rectory 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 causes cd to use the physical directory
structure by resolving symbolic links while traversing dir and
before processing instances of .. in dir (see also the -P option
to the set builtin command); the -L option forces symbolic links
to be followed by resolving the link after processing instances
of .. in dir. If .. appears in dir, it is processed by removing
the immediately previous pathname component from dir, back to a
slash or the beginning of dir. If the -e option is supplied
with -P, and the current working directory cannot be success‐
fully determined after a successful directory change, cd will
return an unsuccessful status. On systems that support it, the
-@ option presents the extended attributes associated with a
file as a directory. An argument of - is converted to $OLDPWD
before the directory change is attempted. If a non-empty direc‐
tory 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 guaranteed to
find all of the standard utilities. If either the -V or -v op‐
tion is supplied, a description of command is printed. The -v
option causes a single word indicating the command or filename
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 can‐
not be found, the exit status is 127. Otherwise, the exit sta‐
tus 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 fa‐
cilities, while available, will not have useful values.
The matches will be generated in the same way as if the program‐
mable completion code had generated them directly from a comple‐
tion 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] [-DEI] [-A action] [-G glob‐
pat] [-W wordlist] [-F function] [-C command]
[-X filterpat] [-P prefix] [-S suffix] name [name ...]
complete -pr [-DEI] [name ...]
Specify how arguments to each name should be completed. If the
-p option is supplied, 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 spec‐
ification for each name, or, if no names are supplied, all com‐
pletion specifications. The -D option indicates that other sup‐
plied options and actions 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 other supplied options and actions should apply
to ``empty'' command completion; that is, completion attempted
on a blank line. The -I option indicates that other supplied
options and actions should apply to completion on the inital
non-assignment word on the line, or after a command delimiter
such as ; or |, which is usually command name completion. If
multiple options are supplied, the -D option takes precedence
over -E, and both take precedence over -I. If any of -D, -E, or
-I are supplied, any other name arguments are ignored; these
completions only apply to the case specified by the option.
The process of applying these completion specifications when
word completion is attempted is described above under Program‐
mable 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 expan‐
sion before the complete builtin is invoked.
-o comp-option
The comp-option controls several aspects of the comp‐
spec's behavior beyond the simple generation of comple‐
tions. 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 comp‐
spec generates no matches.
filenames
Tell readline that the compspec generates file‐
names, so it can perform any filename-specific
processing (like adding a slash to directory
names, quoting special characters, or suppress‐
ing trailing spaces). Intended to be used with
shell functions.
noquote Tell readline not to quote the completed words
if they are filenames (quoting filenames is the
default).
nosort Tell readline not to sort the list of possible
completions alphabetically.
nospace Tell readline not to append a space (the de‐
fault) to words completed at the end of the
line.
plusdirs
After any matches defined by the compspec are
generated, directory name completion is at‐
tempted 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 spec‐
ified as -v.
-C command
command is executed in a subshell environment, and its
output is used as the possible completions.
-F function
The shell function function is executed in the current
shell environment. When the function is executed, the
first argument ($1) is the name of the command whose ar‐
guments are being completed, the second argument ($2) is
the word being completed, and the third argument ($3) is
the word preceding the word being completed on the cur‐
rent command line. When it finishes, the possible com‐
pletions 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 com‐
pletion after all other options have been applied.
-S suffix
suffix is appended to each possible completion after all
other options have been applied.
-W wordlist
The wordlist is split using the characters in the IFS
special variable as delimiters, and each resultant word
is expanded. Shell quoting is honored within wordlist,
in order to provide a mechanism for the words to contain
shell metacharacters or characters in the value of IFS.
The possible completions are the members of the resul‐
tant 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 gener‐
ated 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 argu‐
ment, 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] [-DEI] [+o option] [name]
Modify completion options for each name according to the op‐
tions, or for the currently-executing completion if no names are
supplied. If no options are given, display the completion op‐
tions for each name or the current completion. The possible
values of option are those valid for the complete builtin de‐
scribed above. The -D option indicates that other supplied op‐
tions 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 other
supplied options should apply to ``empty'' command completion;
that is, completion attempted on a blank line. The -I option
indicates that other supplied options should apply to completion
on the inital non-assignment word on the line, or after a com‐
mand delimiter such as ; or |, which is usually command name
completion.
The return value is true unless an invalid option is supplied,
an attempt is made to modify the options for a name for which no
completion specification exists, or an output error occurs.
continue [n]
Resume the next iteration of the enclosing for, while, until, or
select loop. If n is specified, resume at the nth enclosing
loop. n must be ≥ 1. If n is greater than the number of en‐
closing 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 [-aAfFgilnrtux] [-p] [name[=value] ...]
typeset [-aAfFgilnrtux] [-p] [name[=value] ...]
Declare variables and/or give them attributes. If no names are
given then display the values of variables. The -p option will
display the attributes and values of each name. When -p is used
with name arguments, additional options, other than -f and -F,
are ignored. When -p is supplied without name arguments, it
will display the attributes and values of all variables having
the attributes specified by the additional options. If no other
options are supplied with -p, declare will display the at‐
tributes 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 each
name is defined are displayed as well. The -F option implies
-f. The -g option forces variables to be created or modified at
the global scope, even when declare is executed in a shell func‐
tion. 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 evalua‐
tion (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.
-n Give each name the nameref attribute, making it a name
reference to another variable. That other variable is
defined by the value of name. All references, assign‐
ments, and attribute modifications to name, except those
using or changing the -n attribute itself, are performed
on the variable referenced by name's value. The nameref
attribute cannot be applied to array variables.
-r Make names readonly. These names cannot then be assigned
values by subsequent assignment statements or unset.
-t Give each name the trace attribute. Traced functions in‐
herit 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 en‐
vironment.
Using `+' instead of `-' turns off the attribute instead, with
the exceptions that +a and +A may not be used to destroy array
variables and +r will not remove the readonly attribute. When
used in a function, declare and typeset make each name local, as
with the local command, unless the -g option is supplied. If a
variable name is followed by =value, the value of the variable
is set to value. When using -a or -A and the compound assign‐
ment syntax to create array variables, additional attributes do
not take effect until subsequent assignments. The return value
is 0 unless an invalid option is encountered, an attempt is made
to define a function using ``-f foo=bar'', an attempt is made to
assign a value to a readonly variable, an attempt is made to as‐
sign a value to an array variable without using the compound as‐
signment syntax (see Arrays above), one of the names is not a
valid shell variable name, an attempt is made to turn off read‐
only 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 [-clpv] [+n] [-n]
Without options, displays the list of currently remembered di‐
rectories. The default display is on a single line with direc‐
tory names separated by spaces. Directories are added to the
list with the pushd command; the popd command removes entries
from the list. The current directory is always the first direc‐
tory in the stack.
-c Clears the directory stack by deleting all of the en‐
tries.
-l Produces a listing using full pathnames; the default
listing format uses a tilde to denote the home directory.
-p Print the directory stack with one entry per line.
-v Print the directory stack with one entry per line, pre‐
fixing each entry with its index in the stack.
+n Displays the nth entry counting from the left of the list
shown by dirs when invoked without options, starting with
zero.
-n Displays the nth entry counting from the right of the
list shown by dirs when invoked without options, starting
with zero.
The return value is 0 unless an invalid option is supplied or n
indexes beyond the end of the directory stack.
disown [-ar] [-h] [jobspec ... | pid ... ]
Without options, remove each jobspec from the table of active
jobs. If jobspec is not present, and neither the -a nor the -r
option is supplied, the current job is used. If the -h option
is given, each jobspec is not removed from the table, but is
marked so that SIGHUP is not sent to the job if the shell re‐
ceives a SIGHUP. If no jobspec is supplied, the -a option means
to remove or mark all jobs; the -r option without a jobspec ar‐
gument restricts operation to running jobs. The return value is
0 unless a jobspec does not specify a valid job.
echo [-neE] [arg ...]
Output the args, separated by spaces, followed by a newline.
The return status is 0 unless a write error occurs. If -n is
specified, the trailing newline is suppressed. If the -e option
is given, interpretation of the following backslash-escaped
characters is enabled. The -E option disables the interpreta‐
tion 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 es‐
cape characters by default. echo does not interpret -- to mean
the end of options. echo interprets the following escape se‐
quences:
\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 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 en‐
abled. 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 argu‐
ments, 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 indica‐
tion 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 com‐
mand. 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 begin‐
ning of the zeroth argument passed to command. This is what lo‐
gin(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 can‐
not be executed for some reason, a non-interactive shell exits,
unless the execfail shell option is enabled. In that case, it
returns failure. An interactive shell returns failure if the
file cannot be executed. A subshell exits unconditionally if
exec fails. If command is not specified, any redirections take
effect in the current shell, and the return status is 0. If
there is a redirection error, the return status is 1.
exit [n]
Cause the shell to exit with a status of n. If n is omitted,
the exit status is that of the last command executed. A trap on
EXIT is executed before the shell terminates.
export [-fn] [name[=word]] ...
export -p
The supplied names are marked for automatic export to the envi‐
ronment 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 names of all exported
variables is printed. The -n option causes the export property
to be removed from each name. If a variable name is followed by
=word, the value of the variable is set to word. export returns
an exit status of 0 unless an invalid option is encountered, one
of the names is not a valid shell variable name, or -f is sup‐
plied with a name that is not a function.
fc [-e ename] [-lnr] [first] [last]
fc -s [pat=rep] [cmd]
The first form selects a range of commands from first to last
from the history list and displays or edits and re-executes
them. First and last may be specified as a string (to locate
the last command beginning with that string) or as a number (an
index into the history list, where a negative number is used as
an offset from the current command number). 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 other‐
wise. If first is not specified, it is set to the previous com‐
mand 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. Other‐
wise, 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, vi is used. When editing is com‐
plete, the edited commands are echoed and executed.
In the second form, command is re-executed after each instance
of pat is replaced by rep. Command is interpreted the same as
first above. A useful alias to use with this is ``r="fc -s"'',
so that typing ``r cc'' runs the last command beginning with
``cc'' and typing ``r'' re-executes the last command.
If the first form is used, the return value is 0 unless an in‐
valid 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-exe‐
cuted, 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 spec‐
ify 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 parame‐
ters. optstring contains the option characters to be recog‐
nized; if a character is followed by a colon, the option is ex‐
pected 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 op‐
tion 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 re‐
turn 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 dis‐
played, 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 OP‐
TARG 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 remem‐
bered. Any previously-remembered pathname is discarded. If the
-p option is supplied, no path search is performed, and filename
is used as the full filename of the command. The -r option
causes the shell to forget all remembered locations. The -d op‐
tion 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 for‐
mat 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 -d start-end
history -anrw [filename]
history -p arg [arg ...]
history -s arg [arg ...]
With no options, display the command history list with line num‐
bers. Lines listed with a * have been modified. An argument of
n lists only the last n lines. If the shell variable HISTTIME‐
FORMAT is set and not null, it is used as a format string for
strftime(3) to display the time stamp associated with each dis‐
played history entry. No intervening blank is printed between
the formatted time stamp and the history line. If filename is
supplied, it is used as the name of the history file; if not,
the value of HISTFILE is used. Options, if supplied, have the
following meanings:
-c Clear the history list by deleting all the entries.
-d offset
Delete the history entry at position offset. If offset
is negative, it is interpreted as relative to one greater
than the last history position, so negative indices count
back from the end of the history, and an index of -1
refers to the current history -d command.
-d start-end
Delete the history entries between positions start and
end, inclusive. Positive and negative values for start
and end are interpreted as described above.
-a Append the ``new'' history lines to the history file.
These are history lines entered since the beginning of
the current bash session, but not already appended to the
history file.
-n Read the history lines not already read from the history
file into the current history list. These are lines ap‐
pended to the history file since the beginning of the
current bash session.
-r Read the contents of the history file and append them to
the current history list.
-w Write the current history list to the history file, over‐
writing 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 informa‐
tion associated with each history entry is written to the his‐
tory file, marked with the history comment character. When the
history file is read, lines beginning with the history comment
character followed immediately by a digit are interpreted as
timestamps for the following history entry. The return value is
0 unless an invalid option is encountered, an error occurs while
reading or writing the history file, an invalid offset is sup‐
plied 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 fol‐
lowing meanings:
-l List process IDs in addition to the normal information.
-n Display information only about jobs that have changed
status since the user was last notified of their status.
-p List only the process ID of the job's process group
leader.
-r Display only running jobs.
-s Display only stopped jobs.
If jobspec is given, output is restricted to information about
that job. The 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 ex‐
ecutes command passing it args, returning its exit status.
kill [-s sigspec | -n signum | -sigspec] [pid | jobspec] ...
kill -l|-L [sigspec | exit_status]
Send the signal named by sigspec or signum to the processes
named by pid or 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. The -L option is
equivalent to -l. kill returns true if at least one signal was
successfully sent, or false if an error occurs or an invalid op‐
tion is encountered.
let arg [arg ...]
Each arg is an arithmetic expression to be evaluated (see ARITH‐
METIC 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 func‐
tion and its children. If name is -, the set of shell options
is made local to the function in which local is invoked: shell
options changed using the set builtin inside the function are
restored to their original values when the function returns.
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 [-d delim] [-n count] [-O origin] [-s count] [-t] [-u fd] [-C
callback] [-c quantum] [array]
readarray [-d delim] [-n count] [-O origin] [-s count] [-t] [-u fd] [-C
callback] [-c quantum] [array]
Read lines from the standard input into the indexed array vari‐
able array, or from file descriptor fd if the -u option is sup‐
plied. The variable MAPFILE is the default array. Options, if
supplied, have the following meanings:
-d The first character of delim is used to terminate each
input line, rather than newline. If delim is the empty
string, mapfile will terminate a line when it reads a NUL
character.
-n Copy at most count lines. If count is 0, all lines are
copied.
-O Begin assigning to array at index origin. The default
index is 0.
-s Discard the first count lines read.
-t Remove a trailing delim (default newline) from each line
read.
-u Read lines from file descriptor fd instead of the stan‐
dard 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 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 ar‐
ray 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 performs a cd to
the new top directory. Arguments, if supplied, have the follow‐
ing meanings:
-n Suppresses the normal change of directory when removing
directories from the stack, so that only the stack is ma‐
nipulated.
+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-exis‐
tent 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 -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 characters, which are simply copied to standard
output, character escape sequences, which are converted and
copied to the standard output, and format specifications, each
of which causes printing of the next successive argument. In
addition to the standard printf(1) format specifications, printf
interprets the following extensions:
%b causes printf to expand backslash escape sequences in the
corresponding argument in the same way as echo -e.
%q causes printf to output the corresponding argument in a
format that can be reused as shell input.
%(datefmt)T
causes printf to output the date-time string resulting
from using datefmt as a format string for strftime(3).
The corresponding argument is an integer representing the
number of seconds since the epoch. Two special argument
values may be used: -1 represents the current time, and
-2 represents the time the shell was invoked. If no ar‐
gument is specified, conversion behaves as if -1 had been
given. This is an exception to the usual printf behav‐
ior.
Arguments to non-string format specifiers are treated as C con‐
stants, 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 argu‐
ments. If the format requires more arguments than are supplied,
the extra format specifications behave as if a zero value or
null string, as appropriate, had been supplied. The return
value is zero on success, non-zero on failure.
pushd [-n] [+n] [-n]
pushd [-n] [dir]
Adds a directory to the top of the directory stack, or rotates
the stack, making the new top of the stack the current working
directory. With no arguments, pushd exchanges the top two di‐
rectories and returns 0, unless the directory stack is empty.
Arguments, if supplied, have the following meanings:
-n Suppresses the normal change of directory when rotating
or adding 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 as if it had been supplied
as the argument to the cd builtin.
If the pushd command is successful, a dirs is performed as well.
If the first form is used, pushd returns 0 unless the cd to dir
fails. With the second form, pushd returns 0 unless the direc‐
tory 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 reading the name of the current directory or an in‐
valid 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 de‐
scriptor fd supplied as an argument to the -u option, split into
words as described above under Word Splitting, and the first
word is assigned to the first name, the second word to the sec‐
ond name, and so on. If there are more words than names, the
remaining words and their intervening delimiters are assigned to
the last name. If there are fewer words read from the input
stream than names, the remaining names are assigned empty val‐
ues. The characters in IFS are used to split the line into
words using the same rules the shell uses for expansion (de‐
scribed above under Word Splitting). The backslash character
(\) may be used to remove any special meaning for the next char‐
acter 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 ig‐
nored.
-d delim
The first character of delim is used to terminate the in‐
put line, rather than newline. If delim is the empty
string, read will terminate a line when it reads a NUL
character.
-e If the standard input is coming from a terminal, readline
(see READLINE above) is used to obtain the line. Read‐
line uses the current (or default, if line editing was
not previously active) editing settings, but uses Read‐
line's default filename completion.
-i text
If readline is being used to read the line, text is
placed into the editing buffer before editing begins.
-n nchars
read returns after reading nchars characters rather than
waiting for a complete line of input, but honors a delim‐
iter 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 charac‐
ters encountered in the input are not treated specially
and do not cause read to return until nchars characters
are read. The result is not split on the characters in
IFS; the intent is that the variable is assigned exactly
the characters read (with the exception of backslash; see
the -r option below).
-p prompt
Display prompt on standard error, without a trailing new‐
line, 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 back‐
slash is considered to be part of the line. In particu‐
lar, a backslash-newline pair may not then be used as a
line continuation.
-s Silent mode. If input is coming from a terminal, charac‐
ters are not echoed.
-t timeout
Cause read to time out and return failure if a complete
line of input (or a specified number of characters) is
not read within timeout seconds. timeout may be a deci‐
mal number with a fractional portion following the deci‐
mal 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 read times out, read saves any partial input read into
the specified variable name. If timeout is 0, read re‐
turns immediately, without trying to read any data. The
exit status is 0 if input is available on the specified
file descriptor, non-zero otherwise. The exit status is
greater than 128 if the timeout is exceeded.
-u fd Read input from file descriptor fd.
If no names are supplied, the line read is assigned to the vari‐
able REPLY. The exit status is zero, unless end-of-file is en‐
countered, read times out (in which case the status is greater
than 128), a variable assignment error (such as assigning to a
readonly variable) occurs, or an invalid file descriptor is 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 corresponding to the names are so
marked. The -a option restricts the variables to indexed ar‐
rays; the -A option restricts the variables to associative ar‐
rays. 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 stop executing and return the value speci‐
fied by n to its caller. If n is omitted, the return status is
that of the last command executed in the function body. If re‐
turn is executed by a trap handler, the last command used to de‐
termine the status is the last command executed before the trap
handler. If return is executed during a DEBUG trap, the last
command used to determine the status is the last command exe‐
cuted by the trap handler before return was invoked. If return
is used outside a function, but during execution of a script by
the . (source) command, it causes the shell to stop executing
that script and return either n or the exit status of the last
command executed within the script as the exit status of the
script. If n is supplied, the return value is its least signif‐
icant 8 bits. The return status is non-zero if return is sup‐
plied a non-numeric argument, or is used outside a function and
not during execution of a script by . or source. Any command
associated with the RETURN trap is executed before execution re‐
sumes 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 format that can be reused as input for setting or
resetting the currently-set variables. Read-only variables can‐
not be reset. In posix mode, only shell variables are listed.
The output is sorted according to the current locale. When op‐
tions are specified, they set or unset shell attributes. Any
arguments remaining after option processing are treated as val‐
ues for the positional parameters and are assigned, in order, to
$1, $2, ... $n. Options, if specified, have the following
meanings:
-a Each variable or function that is created or modified is
given the export attribute and marked for export to the
environment of subsequent commands.
-b Report the status of terminated background jobs immedi‐
ately, 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 list, or a compound command
(see SHELL GRAMMAR above), exits with a non-zero status.
The shell does not exit if the command that fails is
part of the command list immediately following a while
or until keyword, part of the test following the if or
elif reserved words, part of any 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 !. If a
compound command other than a subshell returns a non-
zero status because a command failed while -e was being
ignored, the shell does not exit. A trap on ERR, if
set, is executed before the shell exits. This option
applies to the shell environment and each subshell envi‐
ronment separately (see COMMAND EXECUTION ENVIRONMENT
above), and may cause subshells to exit before executing
all the commands in the subshell.
If a compound command or shell function executes in a
context where -e is being ignored, none of the commands
executed within the compound command or function body
will be affected by the -e setting, even if -e is set
and a command returns a failure status. If a compound
command or shell function sets -e while executing in a
context where -e is ignored, that setting will not have
any effect until the compound command or the command
containing the function call completes.
-f Disable pathname expansion.
-h Remember the location of commands as they are looked up
for execution. This is enabled by default.
-k All arguments in the form of assignment statements are
placed in the 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). All processes run
in a separate process group. When a background job com‐
pletes, the shell prints a line containing its exit sta‐
tus.
-n Read commands but do not execute them. This may be used
to check a shell script for syntax errors. This is ig‐
nored 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 inter‐
face. 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 inter‐
active shells.
ignoreeof
The effect is as if the shell command ``IG‐
NOREEOF=10'' had been executed (see Shell Vari‐
ables 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 disabled by default.
posix Change the behavior of bash where the default
operation differs from the POSIX standard to
match the standard (posix mode). See SEE ALSO
below for a reference to a document that details
how posix mode affects bash's behavior.
privileged
Same as -p.
verbose Same as -v.
vi Use a vi-style command line editing interface.
This also affects the editing interface used for
read -e.
xtrace Same as -x.
If -o is supplied with no option-name, the values of the
current options are printed. If +o is supplied with no
option-name, a series of set 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 ap‐
pear 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 sup‐
plied, these actions are taken and the effective user id
is set to the real user id. If the -p option is sup‐
plied 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 spe‐
cial parameters "@" and "*" as an error when performing
parameter expansion. If expansion is attempted on an
unset variable or parameter, the shell prints an error
message, and, if not interactive, exits with a non-zero
status.
-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, dis‐
play 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 redi‐
rection operator >| instead of >.
-E If set, any trap on ERR is inherited by shell functions,
command substitutions, and commands executed in a sub‐
shell environment. The ERR trap is normally not inher‐
ited in such cases.
-H Enable ! style history substitution. This option is on
by default when the shell is interactive.
-P If set, the shell does not resolve symbolic links when
executing commands such as cd that change the current
working directory. It uses the physical directory
structure instead. By default, bash follows the logical
chain of directories when performing commands which
change the current directory.
-T If set, any traps on DEBUG and RETURN are inherited by
shell functions, command substitutions, and commands ex‐
ecuted 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 parame‐
ters 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 posi‐
tional parameters remain unchanged.
The options are off by default unless otherwise noted. Using +
rather than - causes these options to be turned off. The op‐
tions can also be specified as arguments to an invocation of the
shell. The current set of options may be found in $-. The re‐
turn status is always true unless an invalid option is encoun‐
tered.
shift [n]
The positional parameters from n+1 ... are renamed to $1 ....
Parameters represented by the numbers $# down to $#-n+1 are un‐
set. 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 param‐
eters are not changed. The return status is greater than zero
if n is greater than $# or less than zero; otherwise 0.
shopt [-pqsu] [-o] [optname ...]
Toggle the values of settings controlling optional shell behav‐
ior. The settings can be either those listed below, or, if the
-o option is used, those available with the -o option to the set
builtin command. With no options, or with the -p option, a list
of all settable options is displayed, with an indication of
whether or not each is set; if optnames are supplied, the output
is restricted to those options. The -p option causes output to
be displayed in a form that may be reused as input. Other op‐
tions 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 multi‐
ple optname arguments are given with -q, the return sta‐
tus is zero if all optnames are enabled; non-zero other‐
wise.
-o Restricts the values of optname to be those defined for
the -o option to the set builtin.
If either -s or -u is used with no optname arguments, shopt
shows only those 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 op‐
tions, the return status is zero unless an optname is not a
valid shell option.
The list of shopt options is:
assoc_expand_once
If set, the shell suppresses multiple evaluation of as‐
sociative array subscripts during arithmetic expression
evaluation, while executing builtins that can perform
variable assignments, and while executing builtins that
perform array dereferencing.
autocd If set, a command name that is the name of a directory
is executed as if it were the argument to the cd com‐
mand. 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 variable
whose value is the directory to change to.
cdspell If set, minor errors in the spelling of a directory com‐
ponent in a cd command will be corrected. The errors
checked for are transposed characters, a missing charac‐
ter, and one character too many. If a correction is
found, the corrected filename is printed, and the com‐
mand proceeds. This option is only used by interactive
shells.
checkhash
If set, bash checks that a command found in the hash ta‐
ble exists before trying to execute it. If a hashed
command no longer exists, a normal path search is per‐
formed.
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 intervening command
(see JOB CONTROL above). The shell always postpones ex‐
iting if any jobs are stopped.
checkwinsize
If set, bash checks the window size after each external
(non-builtin) command and, if necessary, updates the
values of LINES and COLUMNS. This option is enabled by
default.
cmdhist If set, bash attempts to save all lines of a multiple-
line command in the same history entry. This allows
easy re-editing of multi-line commands. This option is
enabled by default, but only has an effect if command
history is enabled, as described above under HISTORY.
compat31
If set, bash changes its behavior to that of version 3.1
with respect to quoted arguments to the [[ conditional
command's =~ operator and locale-specific string compar‐
ison when using the [[ conditional command's < and > op‐
erators. Bash versions prior to bash-4.1 use ASCII col‐
lation and strcmp(3); bash-4.1 and later use the current
locale's collation sequence and strcoll(3).
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
(see previous item) and the effect of interrupting a
command list. Bash versions 3.2 and earlier continue
with the next command in the list after one terminates
due to an interrupt.
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 description of compat31) and the effect of inter‐
rupting a command list. Bash versions 4.0 and later in‐
terrupt the list as if the shell received the interrupt;
previous versions continue with the next command in the
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 num‐
ber) and the characters between the single quotes are
considered quoted. This is the behavior of posix mode
through version 4.1. The default bash behavior remains
as in previous versions.
compat42
If set, bash does not process the replacement string in
the pattern substitution word expansion using quote re‐
moval.
compat43
If set, bash does not print a warning message if an at‐
tempt is made to use a quoted compound array assignment
as an argument to declare, makes word expansion errors
non-fatal errors that cause the current command to fail
(the default behavior is to make them fatal errors that
cause the shell to exit), and does not reset the loop
state when a shell function is executed (this allows
break or continue in a shell function to affect loops in
the caller's context).
compat44
If set, bash saves the positional parameters to
BASH_ARGV and BASH_ARGC before they are used, regardless
of whether or not extended debugging mode is enabled.
complete_fullquote
If set, bash quotes all shell metacharacters in file‐
names and directory names when performing completion.
If not set, bash removes metacharacters such as the dol‐
lar sign from the set of characters that will be quoted
in completed filenames when these metacharacters appear
in shell variable references in words to be completed.
This means that dollar signs in variable names that ex‐
pand to directories will not be quoted; however, any
dollar signs appearing in filenames will not be quoted,
either. This is active only when bash is using back‐
slashes to quote completed filenames. This variable is
set by default, which is the default bash behavior in
versions through 4.2.
direxpand
If set, bash replaces directory names with the results
of word expansion when performing filename completion.
This changes the contents of the readline editing buf‐
fer. 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 ini‐
tially supplied does not exist.
dotglob If set, bash includes filenames beginning with a `.' in
the results of pathname expansion. The filenames ``.''
and ``..'' must always be matched explicitly, even if
dotglob is set.
execfail
If set, a non-interactive shell will not exit if it can‐
not 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 interac‐
tive shells.
extdebug
If set at shell invocation, arrange to execute the de‐
bugger profile before the shell starts, identical to the
--debugger option. If set after invocation, behavior
intended for use by debuggers is enabled:
1. The -F option to the declare builtin displays the
source file name and line number corresponding to
each function name supplied as an argument.
2. If the command run by the DEBUG trap returns a
non-zero value, the next command is skipped and
not executed.
3. If the command run by the DEBUG trap returns a
value of 2, and the shell is executing in a sub‐
routine (a shell function or a shell script exe‐
cuted by the . or source builtins), the shell
simulates a call to return.
4. BASH_ARGC and BASH_ARGV are updated as described
in their descriptions above.
5. Function tracing is enabled: command substitu‐
tion, 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 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 possi‐
ble completions. See SHELL VARIABLES above for a de‐
scription of FIGNORE. This option is enabled by de‐
fault.
globasciiranges
If set, range expressions used in pattern matching
bracket expressions (see Pattern Matching above) behave
as if in the traditional C locale when performing com‐
parisons. That is, the current locale's collating se‐
quence is not taken into account, so b will not collate
between A and B, and upper-case and lower-case ASCII
characters will collate together.
globstar
If set, the pattern ** used in a pathname expansion con‐
text 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 ex‐
its, 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 his‐
tory substitution are not immediately passed to the
shell parser. Instead, the resulting line is loaded
into the readline editing buffer, allowing further modi‐
fication.
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 inter‐
active login shell exits.
inherit_errexit
If set, command substitution inherits the value of the
errexit option, instead of unsetting it in the subshell
environment. This option is enabled when posix mode is
enabled.
interactive_comments
If set, allow a word beginning with # to cause that word
and all remaining characters on that line to be ignored
in an interactive shell (see COMMENTS above). This op‐
tion 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 back‐
ground in the current shell environment.
lithist If set, and the cmdhist option is enabled, multi-line
commands are saved to the history with embedded newlines
rather than using semicolon separators where possible.
localvar_inherit
If set, local variables inherit the value and attributes
of a variable of the same name that exists at a previous
scope before any new value is assigned. The nameref at‐
tribute is not inherited.
localvar_unset
If set, calling unset on local variables in previous
function scopes marks them so subsequent lookups find
them unset until that function returns. This is identi‐
cal to the behavior of unsetting local variables at the
current function scope.
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 dis‐
played.
no_empty_cmd_completion
If set, and readline is being used, bash will not at‐
tempt 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 Pathname
Expansion above).
nocasematch
If set, bash matches patterns in a case-insensitive
fashion when performing matching while executing case or
[[ conditional commands, when performing pattern substi‐
tution word expansions, or when filtering possible com‐
pletions as part of programmable completion.
nullglob
If set, bash allows patterns which match no files (see
Pathname Expansion above) to expand to a null string,
rather than themselves.
progcomp
If set, the programmable completion facilities (see Pro‐
grammable Completion above) are enabled. This option is
enabled by default.
progcomp_alias
If set, and programmable completion is enabled, bash
treats a command name that doesn't have any completions
as a possible alias and attempts alias expansion. If it
has an alias, bash attempts programmable completion us‐
ing the command word resulting from the expanded alias.
promptvars
If set, prompt strings undergo parameter expansion, com‐
mand substitution, arithmetic expansion, and quote re‐
moval 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 re‐
stricted 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 dis‐
cover 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 parame‐
ters.
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 se‐
quences 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 sta‐
tus is 0 unless the shell is a login shell and -f is not sup‐
plied, or if job control is not enabled.
test expr
[ expr ]
Return a status of 0 (true) or 1 (false) depending on the evalu‐
ation of the conditional expression expr. Each operator and op‐
erand 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 evaluation de‐
pends on the number of arguments; see below. Operator prece‐
dence 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 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 argu‐
ment 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 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 CONDITIONAL 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. Other‐
wise, 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 eval‐
uated 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 lexico‐
graphically 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 re‐
ceives signal(s) sigspec. If arg is absent (and there is a sin‐
gle sigspec) or -, each specified signal is reset to its origi‐
nal 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 com‐
mands 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 <sig‐
nal.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 exe‐
cuted before every simple command, for command, 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 fin‐
ishes executing.
If a sigspec is ERR, the command arg is executed whenever a
pipeline (which may consist of a single simple command), a list,
or a compound command returns a non-zero exit status, subject to
the following conditions. The ERR trap is not 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 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 using
!. These are the same conditions obeyed by the errexit (-e) op‐
tion.
Signals ignored upon entry to the shell cannot be trapped or re‐
set. 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 re‐
turned. 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 re‐
turn file. The -P option forces a PATH search for each name,
even if ``type -t name'' would not return file. If a command is
hashed, -p and -P print the hashed value, which is not necessar‐
ily 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 [-HSabcdefiklmnpqrstuvxPT [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 speci‐
fied, 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, re‐
spectively. 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 inter‐
preted 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
-k The maximum number of kqueues that may be allocated
-l The maximum size that may be locked into memory
-m The maximum resident set size (many systems do not honor
this limit)
-n The maximum number of open file descriptors (most systems
do not allow this value to be set)
-p The pipe size in 512-byte blocks (this may not be set)
-q The maximum number of bytes in POSIX message queues
-r The maximum real-time scheduling priority
-s The maximum stack size
-t The maximum amount of cpu time in seconds
-u The maximum number of processes available to a single
user
-v The maximum amount of virtual memory available to the
shell and, on some systems, to its children
-x The maximum number of file locks
-P The maximum number of pseudoterminals
-T The maximum number of threads
If limit is given, and the -a option is not used, limit is the
new value of the specified resource. If no option is given,
then -f is assumed. Values are in 1024-byte increments, except
for -t, which is in seconds; -p, which is in units of 512-byte
blocks; -P, -T, -b, -k, -n, and -u, which are unscaled values;
and, when in posix mode, -c and -f, which are in 512-byte incre‐
ments. The return status is 0 unless an invalid option or argu‐
ment 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 sym‐
bolic 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] [-n] [name ...]
For each name, remove the corresponding variable or function.
If the -v option is given, each name refers to a shell variable,
and that variable is removed. Read-only variables may not be
unset. If -f is specified, each name refers to a shell func‐
tion, and the function definition is removed. If the -n option
is supplied, and name is a variable with the nameref attribute,
name will be unset rather than the variable it references. -n
has no effect if the -f option is supplied. If no options are
supplied, each name refers to a variable; if there is no vari‐
able by that name, any function with that name is unset. Each
unset variable or function is removed from the environment
passed to subsequent commands. If any of COMP_WORDBREAKS, RAN‐
DOM, SECONDS, LINENO, HISTCMD, FUNCNAME, GROUPS, or DIRSTACK are
unset, they lose their special properties, even if they are sub‐
sequently reset. The exit status is true unless a name is read‐
only.
wait [-fn] [id ...]
Wait for each specified child process and return its termination
status. Each id may be a process ID or a job specification; if
a job spec is given, all processes in that job's pipeline are
waited for. If id is not given, all currently active child pro‐
cesses are waited for, and the return status is zero. If the -n
option is supplied, wait waits for any job to terminate and re‐
turns its exit status. If the -f option is supplied, and job
control is enabled, wait forces id to terminate before returning
its status, instead of returning when it changes status. If id
specifies a non-existent process or job, the return status is
127. Otherwise, the return status is the exit status of the
last process or job waited for.
SEE ALSO
bash(1), sh(1)
GNU Bash-2.05a 2001 October 29 BASH-BUILTINS(7)
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