Summery
1lineコマンドを１つの識別子としてショートカットを作ることができる。
別名のコマンドを作成できる。
Construction
$ alian [name]=[command]
Option
[name]
任意の文字列が登録できる。
[command]
オプションも含めたワンラインのコマンドが登録できる。
Sample
# ls -la を1ワードにする
$ alias lsa='ls -la'
# 登録済みのaliasを削除する
$ unalias lsa
Discription
NAME
bash, :, ., [, alias, bg, bind, break, builtin, caller, cd, com-
mand, compgen, complete, compopt, continue, declare, dirs, dis-
own, echo, enable, eval, exec, exit, export, false, fc, fg,
getopts, hash, help, history, jobs, kill, let, local, logout,
mapfile, popd, printf, pushd, pwd, read, readonly, return, set,
shift, shopt, source, suspend, test, times, trap, true, type,
typeset, ulimit, umask, unalias, unset, wait - bash built-in
commands, see bash(1)
BASH BUILTIN COMMANDS
Unless otherwise noted, each builtin command documented in this
section as accepting options preceded by - accepts -- to signify
the end of the options. The :, true, false, and test builtins
do not accept options and do not treat -- specially. The exit,
logout, break, continue, let, and shift builtins accept and pro-
cess arguments beginning with - without requiring --. Other
builtins that accept arguments but are not specified as accept-
ing 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 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 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 sub-
stitution 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 dis-
abled or, when run with job control enabled, any speci-
fied jobspec was not found or was started without job
control.
bind [-m keymap] [-lpsvPSV]
bind [-m keymap] [-q function] [-u function] [-r keyseq]
bind [-m keymap] -f filename
bind [-m keymap] -x keyseq:shell-command
bind [-m keymap] keyseq:function-name
bind readline-command
Display current readline key and function bindings, bind
a key sequence to a readline function or macro, or set a
readline variable. Each non-option argument is a command
as it would appear in .inputrc, but each binding or com-
mand must be passed as a separate argument; e.g.,
’"\C-x\C-r": re-read-init-file’. Options, if supplied,
have the following meanings:
-m keymap
Use keymap as the keymap to be affected by the
subsequent bindings. Acceptable keymap names are
emacs, emacs-standard, emacs-meta, emacs-ctlx, vi,
vi-move, vi-command, and vi-insert. vi is equiva-
lent 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 con-
tents of the readline line buffer and the READ-
LINE_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; Otherwise, break returns 0 value.
builtin shell-builtin [arguments]
Execute the specified shell builtin, passing it argu-
ments, and return its exit status. 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 rede-
fined this way. The return status is false if
shell-builtin is not a shell builtin command.
caller [expr]
Returns the context of any active subroutine call (a
shell function or a script executed with the . or source
builtins. Without expr, caller displays the line number
and source filename of the current subroutine call. If a
non-negative integer is supplied as expr, caller displays
the line number, subroutine name, and source file corre-
sponding to that position in the current execution call
stack. This extra information may be used, for example,
to print a stack trace. The current frame is frame 0.
The return value is 0 unless the shell is not executing a
subroutine call or expr does not correspond to a valid
position in the call stack.
cd [-L|-P] [dir]
Change the current directory to dir. The variable HOME
is the default dir. The variable CDPATH defines the
search path for the directory containing dir. 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 directory structure instead of following
symbolic links (see also the -P option to the set builtin
command); the -L option forces symbolic links to be fol-
lowed. An argument of - is equivalent to $OLDPWD. If a
non-empty directory name from CDPATH is used, or if - is
the first argument, and the directory change is success-
ful, 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 func-
tion 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 util-
ities. If either the -V or -v option is supplied, 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 sup-
plied, the exit status is 0 if command was found, and 1
if not. If neither option is supplied and an error
occurred or command cannot be found, the exit status is
127. Otherwise, the exit status of the command builtin
is the exit status of command.
compgen [option] [word]
Generate possible completion matches for word according
to the options, which may be any option accepted by the
complete builtin with the exception of -p and -r, and
write the matches to the standard output. When using the
-F or -C options, the various shell variables set by the
programmable completion facilities, while available, will
not have useful values.
The matches will be generated in the same way as if the
programmable completion code had generated them directly
from a completion specification with the same flags. If
word is specified, only those completions matching word
will be displayed.
The return value is true unless an invalid option is sup-
plied, or no matches were generated.
complete [-abcdefgjksuv] [-o comp-option] [-DE] [-A action] [-G
globpat] [-W wordlist] [-F function] [-C command]
[-X filterpat] [-P prefix] [-S suffix] name [name ...]
complete -pr [-DE] [name ...]
Specify how arguments to each name should be completed.
If the -p option is supplied, or if no options are sup-
plied, existing completion specifications are printed in
a way that allows them to be reused as input. The -r
option removes a completion specification for each name,
or, if no names are supplied, all completion specifica-
tions. The -D option indicates that the remaining
options and actions should apply to the ‘‘default’’ com-
mand completion; that is, completion attempted on a com-
mand 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 nec-
essary, the -P and -S options) should be quoted to pro-
tect 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 com-
pletions if the compspec generates no
matches.
default Use readline’s default filename comple-
tion if the compspec generates no
matches.
dirnames
Perform directory name completion if the
compspec generates no matches.
filenames
Tell readline that the compspec generates
filenames, so it can perform any file-
name-specific processing (like adding a
slash to directory names, quoting special
characters, or suppressing trailing
spaces). Intended to be used with shell
functions.
nospace Tell readline not to append a space (the
default) to words completed at the end of
the line.
plusdirs
After any matches defined by the compspec
are generated, directory name completion
is attempted and any matches are added to
the results of the other actions.
-A action
The action may be one of the following to gener-
ate 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 speci-
fied 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 speci-
fied as -k.
running Names of running jobs, if job control is
active.
service Service names. May also be specified as
-s.
setopt Valid arguments for the -o option to the
set builtin.
shopt Shell option names as accepted by the
shopt builtin.
signal Signal names.
stopped Names of stopped jobs, if job control is
active.
user User names. May also be specified as -u.
variable
Names of all shell variables. May also
be specified as -v.
-G globpat
The pathname expansion pattern globpat is
expanded to generate the possible completions.
-W wordlist
The wordlist is split using the characters in the
IFS special variable as delimiters, and each
resultant word is expanded. The possible comple-
tions are the members of the resultant list which
match the word being completed.
-C command
command is executed in a subshell environment,
and its output is used as the possible comple-
tions.
-F function
The shell function function is executed in the
current shell environment. When it finishes, the
possible completions are retrieved from the value
of the COMPREPLY array variable.
-X filterpat
filterpat is a pattern as used for pathname
expansion. It is applied to the list of possible
completions generated by the preceding options
and arguments, and each completion matching fil-
terpat is removed from the list. A leading ! in
filterpat negates the pattern; in this case, any
completion not matching filterpat is removed.
-P prefix
prefix is added at the beginning of each possible
completion after all other options have been
applied.
-S suffix
suffix is appended to each possible completion
after all other options have been applied.
The return value is true unless an invalid option is sup-
plied, an option other than -p or -r is supplied without
a name argument, an attempt is made to remove a comple-
tion specification for a name for which no specification
exists, or an error occurs adding a completion specifica-
tion.
compopt [-o option] [-DE] [+o option] [name]
Modify completion options for each name according to the
options, or for the currently-execution completion if no
names are supplied. If no options are given, display the
completion options for each name or the current comple-
tion. The possible values of option are those valid for
the complete builtin described above. The -D option
indicates that the remaining options should apply to the
‘‘default’’ command completion; that is, completion
attempted on a command for which no completion has previ-
ously been defined. The -E option indicates that the
remaining options should apply to ‘‘empty’’ command com-
pletion; 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 executed outside of loop, the return value is
0.
declare [-aAfFilrtux] [-p] [name[=value] ...]
typeset [-aAfFilrtux] [-p] [name[=value] ...]
Declare variables and/or give them attributes. If no
names are given then display the values of variables.
The -p option will display the attributes and values of
each name. When -p is used with name arguments, addi-
tional options are ignored. When -p is supplied without
name arguments, it will display the attributes and values
of all variables having the attributes specified by the
additional options. If no other options are supplied
with -p, declare will display the attributes and values
of all shell variables. The -f option will restrict the
display to shell functions. The -F option inhibits the
display of function definitions; only the function name
and attributes are printed. If the extdebug shell option
is enabled using shopt, the source file name and line
number where the function is defined are displayed as
well. The -F option implies -f. The following options
can be used to restrict output to variables with the
specified attribute or to give variables attributes:
-a Each name is an indexed array variable (see Arrays
above).
-A Each name is an associative array variable (see
Arrays above).
-f Use function names only.
-i The variable is treated as an integer; arithmetic
evaluation (see ARITHMETIC EVALUATION above) is
performed when the variable is assigned a value.
-l When the variable is assigned a value, all upper-
case characters are converted to lower-case. The
upper-case attribute is disabled.
-r Make names readonly. These names cannot then be
assigned values by subsequent assignment state-
ments or unset.
-t Give each name the trace attribute. Traced func-
tions inherit the DEBUG and RETURN traps from the
calling shell. The trace attribute has no special
meaning for variables.
-u When the variable is assigned a value, all lower-
case characters are converted to upper-case. The
lower-case attribute is disabled.
-x Mark names for export to subsequent commands via
the environment.
Using ‘+’ instead of ‘-’ turns off the attribute instead,
with the exceptions that +a may not be used to destroy an
array variable and +r will not remove the readonly
attribute. When used in a function, makes each name
local, as with the local command. If a variable name is
followed by =value, the value of the variable is set to
value. The return value is 0 unless an invalid option is
encountered, an attempt is made to define a function
using ‘‘-f foo=bar’’, an attempt is made to assign a
value to a readonly variable, an attempt is made to
assign a value to an array variable without using the
compound assignment syntax (see Arrays above), one of the
names is not a valid shell variable name, an attempt is
made to turn off readonly status for a readonly variable,
an attempt is made to turn off array status for an array
variable, or an attempt is made to display a non-existent
function with -f.
dirs [+n] [-n] [-cplv]
Without options, displays the list of currently remem-
bered directories. The default display is on a single
line with directory names separated by spaces. Directo-
ries 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 sup-
plied or n indexes beyond the end of the directory stack.
disown [-ar] [-h] [jobspec ...]
Without options, each jobspec is removed from the table
of active jobs. If jobspec is not present, and neither
-a nor -r is supplied, the shell’s notion of the current
job is used. If the -h option is given, each jobspec is
not removed from the table, but is marked so that SIGHUP
is not sent to the job if the shell receives a SIGHUP.
If no jobspec is present, and neither the -a nor the -r
option is supplied, the current job is used. If no job-
spec is supplied, the -a option means to remove or mark
all jobs; the -r option without a jobspec argument
restricts operation to running jobs. The return value is
0 unless a jobspec does not specify a valid job.
echo [-neE] [arg ...]
Output the args, separated by spaces, followed by a new-
line. The return status is always 0. If -n is speci-
fied, the trailing newline is suppressed. If the -e
option is given, interpretation of the following back-
slash-escaped characters is enabled. The -E option dis-
ables 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 deter-
mine whether or not echo expands these escape characters
by default. echo does not interpret -- to mean the end
of options. echo interprets the following escape
sequences:
\a alert (bell)
\b backspace
\c suppress further output
\e an escape character
\f form feed
\n new line
\r carriage return
\t horizontal tab
\v vertical tab
\\ backslash
\0nnn the eight-bit character whose value is the octal
value nnn (zero to three octal digits)
\xHH the eight-bit character whose value is the hex-
adecimal value HH (one or two hex digits)
enable [-a] [-dnps] [-f filename] [name ...]
Enable and disable builtin shell commands. Disabling a
builtin allows a disk command which has the same name as
a shell builtin to be executed without specifying a full
pathname, even though the shell normally searches for
builtins before disk commands. If -n is used, each name
is disabled; otherwise, names are enabled. For example,
to use the test binary found via the PATH instead of the
shell builtin version, run ‘‘enable -n test’’. The -f
option means to load the new builtin command name from
shared object filename, on systems that support dynamic
loading. The -d option will delete a builtin previously
loaded with -f. If no name arguments are given, or if
the -p option is supplied, a list of shell builtins is
printed. With no other option arguments, the list con-
sists of all enabled shell builtins. If -n is supplied,
only disabled builtins are printed. If -a is supplied,
the list printed includes all builtins, with an indica-
tion of whether or not each is enabled. If -s is sup-
plied, 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 envi-
ronment. 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 shell option execfail is enabled, in
which case it returns failure. An interactive shell
returns failure if the file cannot be executed. If com-
mand 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 exe-
cuted. A trap on EXIT is executed before the shell ter-
minates.
export [-fn] [name[=word]] ...
export -p
The supplied names are marked for automatic export to the
environment of subsequently executed commands. If the -f
option is given, the names refer to functions. If no
names are given, or if the -p option is supplied, a list
of all names that are exported in this shell is printed.
The -n option causes the export property to be removed
from each name. If a variable name is followed by =word,
the value of the variable is set to word. export returns
an exit status of 0 unless an invalid option is encoun-
tered, one of the names is not a valid shell variable
name, or -f is supplied with a name that is not a func-
tion.
fc [-e ename] [-lnr] [first] [last]
fc -s [pat=rep] [cmd]
Fix Command. In the first form, a range of commands from
first to last is selected from the history list. First
and last may be specified as a string (to locate the last
command beginning with that string) or as a number (an
index into the history list, where a negative number is
used as an offset from the current command number). If
last is not specified it is set to the current command
for listing (so that ‘‘fc -l -10’’ prints the last 10
commands) and to first otherwise. If first is not speci-
fied it is set to the previous command for editing and
-16 for listing.
The -n option suppresses the command numbers when list-
ing. The -r option reverses the order of the commands.
If the -l option is given, the commands are listed on
standard output. Otherwise, the editor given by ename is
invoked on a file containing those commands. If ename is
not given, the value of the FCEDIT variable is used, and
the value of EDITOR if FCEDIT is not set. If neither
variable is set, is used. When editing is complete, the
edited commands are echoed and executed.
In the second form, command is re-executed after each
instance of pat is replaced by rep. A useful alias to
use with this is ‘‘r="fc -s"’’, so that typing ‘‘r cc’’
runs the last command beginning with ‘‘cc’’ and typing
‘‘r’’ re-executes the last command.
If the first form is used, the return value is 0 unless
an invalid option is encountered or first or last specify
history lines out of range. If the -e option is sup-
plied, 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 con-
trol enabled, if jobspec does not specify a valid job or
jobspec specifies a job that was started without job con-
trol.
getopts optstring name [args]
getopts is used by shell procedures to parse positional
parameters. optstring contains the option characters to
be recognized; if a character is followed by a colon, the
option is expected to have an argument, which should be
separated from it by white space. The colon and question
mark characters may not be used as option characters.
Each time it is invoked, getopts places the next option
in the shell variable name, initializing name if it does
not exist, and the index of the next argument to be pro-
cessed into the variable OPTIND. OPTIND is initialized
to 1 each time the shell or a shell script is invoked.
When an option requires an argument, getopts places that
argument into the variable OPTARG. The shell does not
reset OPTIND automatically; it must be manually reset
between multiple calls to getopts within the same shell
invocation if a new set of parameters is to be used.
When the end of options is encountered, getopts exits
with a return value greater than zero. OPTIND is set to
the index of the first non-option argument, and name is
set to ?.
getopts normally parses the positional parameters, but if
more arguments are given in args, getopts parses those
instead.
getopts can report errors in two ways. If the first
character of optstring is a colon, silent error reporting
is used. In normal operation diagnostic messages are
printed when invalid options or missing option arguments
are encountered. If the variable OPTERR is set to 0, no
error messages will be displayed, even if the first char-
acter 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 unspeci-
fied, is found. It returns false if the end of options
is encountered or an error occurs.
hash [-lr] [-p filename] [-dt] [name]
For each name, the full file name of the command is
determined by searching the directories in $PATH and
remembered. If the -p option is supplied, no path search
is performed, and filename is used as the full file name
of the command. The -r option causes the shell to forget
all remembered locations. The -d option causes the shell
to forget the remembered location of each name. If the
-t option is supplied, the full pathname to which each
name corresponds is printed. If multiple name arguments
are supplied with -t, the name is printed before the
hashed full pathname. The -l option causes output to be
displayed in a format that may be reused as input. If no
arguments are given, or if only -l is supplied, informa-
tion 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 man-
page-like format
-s Display only a short usage synopsis for each pat-
tern
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 sup-
plied, it is used as the name of the history file; if
not, the value of HISTFILE is used. Options, if sup-
plied, have the following meanings:
-c Clear the history list by deleting all the
entries.
-d offset
Delete the history entry at position offset.
-a Append the ‘‘new’’ history lines (history lines
entered since the beginning of the current bash
session) to the history file.
-n Read the history lines not already read from the
history file into the current history list. These
are lines appended to the history file since the
beginning of the current bash session.
-r Read the contents of the history file and use them
as the current history.
-w Write the current history to the history file,
overwriting the history file’s contents.
-p Perform history substitution on the following args
and display the result on the standard output.
Does not store the results in the history list.
Each arg must be quoted to disable normal history
expansion.
-s Store the args in the history list as a single
entry. The last command in the history list is
removed before the args are added.
If the HISTTIMEFORMAT variable is set, the time stamp
information associated with each history entry is written
to the history file, marked with the history comment
character. When the history file is read, lines begin-
ning with the history comment character followed immedi-
ately by a digit are interpreted as timestamps for the
previous history line. 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
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 infor-
mation.
-p List only the process ID of the job’s process
group leader.
-n Display information only about jobs that have
changed status since the user was last notified of
their status.
-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 pro-
cesses named by pid or jobspec. sigspec is either a
case-insensitive signal name such as SIGKILL (with or
without the SIG prefix) or a signal number; signum is a
signal number. If sigspec is not present, then SIGTERM
is assumed. An argument of -l lists the signal names.
If any arguments are supplied when -l is given, the names
of the signals corresponding to the arguments are listed,
and the return status is 0. The exit_status argument to
-l is a number specifying either a signal number or the
exit status of a process terminated by a signal. kill
returns true if at least one signal was successfully
sent, or false if an error occurs or an invalid option is
encountered.
let arg [arg ...]
Each arg is an arithmetic expression to be evaluated (see
ARITHMETIC EVALUATION above). If the last arg evaluates
to 0, let returns 1; 0 is returned otherwise.
local [option] [name[=value] ...]
For each argument, a local variable named name is cre-
ated, and assigned value. The option can be any of the
options accepted by declare. When local is used within a
function, it causes the variable name to have a visible
scope restricted to that function and its children. With
no operands, local writes a list of local variables to
the standard output. It is an error to use local when
not within a function. The return status is 0 unless
local is used outside a function, an invalid name is sup-
plied, or name is a readonly variable.
logout Exit a login shell.
mapfile [-n count] [-O origin] [-s count] [-t] [-u fd] [-C call-
back] [-c quantum] [array]
readarray [-n count] [-O origin] [-s count] [-t] [-u fd] [-C
callback] [-c quantum] [array]
Read lines from the standard input into the indexed array
variable array, or from file descriptor fd if the -u
option is supplied. The variable MAPFILE is the default
array. Options, if supplied, have the following mean-
ings:
-n Copy at most count lines. If count is 0, all
lines are copied.
-O Begin assigning to array at index origin. The
default index is 0.
-s Discard the first count lines read.
-t Remove a trailing newline from each line read.
-u Read lines from file descriptor fd instead of the
standard input.
-C Evaluate callback each time quantum lines are
read. The -c option specifies quantum.
-c Specify the number of lines read between each call
to callback.
If -C is specified without -c, the default quantum is
5000. When callback is evaluated, it is supplied the
index of the next array element to be assigned as an
additional argument. callback is evaluated after the
line is read but before the array element is assigned.
If not supplied with an explicit origin, mapfile will
clear array before assigning to it.
mapfile returns successfully unless an invalid option or
option argument is supplied, array is invalid or
unassignable, or if array is not an indexed array.
popd [-n] [+n] [-n]
Removes entries from the directory stack. With no argu-
ments, removes the top directory from the stack, and per-
forms a cd to the new top directory. Arguments, if sup-
plied, have the following meanings:
-n Suppresses the normal change of directory when
removing directories from the stack, so that only
the stack is manipulated.
+n Removes the nth entry counting from the left of
the list shown by dirs, starting with zero. For
example: ‘‘popd +0’’ removes the first directory,
‘‘popd +1’’ the second.
-n Removes the nth entry counting from the right of
the list shown by dirs, starting with zero. For
example: ‘‘popd -0’’ removes the last directory,
‘‘popd -1’’ the next to last.
If the popd command is successful, a dirs is performed as
well, and the return status is 0. popd returns false if
an invalid option is encountered, the directory stack is
empty, a non-existent directory stack entry is specified,
or the directory change fails.
printf [-v var] format [arguments]
Write the formatted arguments to the standard output
under the control of the format. The format is a charac-
ter 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) formats,
%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), and %q causes printf to output the corre-
sponding argument in a format that can be reused as shell
input.
The -v option causes the output to be assigned to the
variable var rather than being printed to the standard
output.
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 direc-
tory stack is empty. Arguments, if supplied, have the
following meanings:
-n Suppresses the normal change of directory when
adding directories to the stack, so that only the
stack is manipulated.
+n Rotates the stack so that the nth directory
(counting from the left of the list shown by dirs,
starting with zero) is at the top.
-n Rotates the stack so that the nth directory
(counting from the right of the list shown by
dirs, starting with zero) is at the top.
dir Adds dir to the directory stack at the top, making
it the new current working directory.
If the pushd command is successful, a dirs is performed
as well. If the first form is used, pushd returns 0
unless the cd to dir fails. With the second form, pushd
returns 0 unless the directory stack is empty, a non-
existent directory stack element is specified, or the
directory change to the specified new current directory
fails.
pwd [-LP]
Print the absolute pathname of the current working direc-
tory. The pathname printed contains no symbolic links if
the -P option is supplied or the -o physical option to
the set builtin command is enabled. If the -L option is
used, the pathname printed may contain symbolic links.
The return status is 0 unless an error occurs while read-
ing the name of the current directory or an invalid
option is supplied.
read [-ers] [-a aname] [-d delim] [-i text] [-n nchars] [-N
nchars] [-p prompt] [-t timeout] [-u fd] [name ...]
One line is read from the standard input, or from the
file descriptor fd supplied as an argument to the -u
option, and the first word is assigned to the first name,
the second word to the second name, and so on, with left-
over words and their intervening separators assigned to
the last name. If there are fewer words read from the
input stream than names, the remaining names are assigned
empty values. The characters in IFS are used to split
the line into words. The backslash character (\) may be
used to remove any special meaning for the next character
read and for line continuation. Options, if supplied,
have the following meanings:
-a aname
The words are assigned to sequential indices of
the array variable aname, starting at 0. aname is
unset before any new values are assigned. Other
name arguments are ignored.
-d delim
The first character of delim is used to terminate
the input line, rather than newline.
-e If the standard input is coming from a terminal,
readline (see READLINE above) is used to obtain
the line. Readline uses the current (or default,
if line editing was not previously active) editing
settings.
-i text
If readline is being used to read the line, text
is placed into the editing buffer before editing
begins.
-n nchars
read returns after reading nchars characters
rather than waiting for a complete line of input,
but honor a delimiter if fewer than nchars charac-
ters are read before the delimiter.
-N nchars
read returns after reading exactly nchars charac-
ters 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 trail-
ing newline, before attempting to read any input.
The prompt is displayed only if input is coming
from a terminal.
-r Backslash does not act as an escape character.
The backslash is considered to be part of the
line. In particular, a backslash-newline pair may
not be used as a line continuation.
-s Silent mode. If input is coming from a terminal,
characters are not echoed.
-t timeout
Cause read to time out and return failure if a
complete line of input is not read within timeout
seconds. timeout may be a decimal number with a
fractional portion following the decimal point.
This option is only effective if read is reading
input from a terminal, pipe, or other special
file; it has no effect when reading from regular
files. If timeout is 0, read returns success if
input is available on the specified file descrip-
tor, failure otherwise. The exit status is
greater than 128 if the timeout is exceeded.
-u fd Read input from file descriptor fd.
If no names are supplied, the line read is assigned to
the variable REPLY. The return code is zero, unless end-
of-file is encountered, read times out (in which case the
return code is greater than 128), or an invalid file
descriptor is supplied as the argument to -u.
readonly [-aApf] [name[=word] ...]
The given names are marked readonly; the values of these
names may not be changed by subsequent assignment. If
the -f option is supplied, the functions corresponding to
the names are so marked. The -a option restricts the
variables to indexed arrays; the -A option restricts the
variables to associative arrays. If no name arguments
are given, or if the -p option is supplied, a list of all
readonly names is printed. The -p option causes output
to be displayed in a format that may be reused as input.
If a variable name is followed by =word, the value of the
variable is set to word. The return status is 0 unless
an invalid option is encountered, one of the names is not
a valid shell variable name, or -f is supplied with a
name that is not a function.
return [n]
Causes a function to exit with the return value specified
by n. If n is omitted, the return status is that of the
last command executed in the function body. If used out-
side a function, but during execution of a script by the
. (source) command, it causes the shell to stop execut-
ing 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
executed before execution resumes after the function or
script.
set [--abefhkmnptuvxBCEHPT] [-o option] [arg ...]
set [+abefhkmnptuvxBCEHPT] [+o option] [arg ...]
Without options, the name and value of each shell vari-
able are displayed in a format 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 argu-
ments 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 envi-
ronment of subsequent commands.
-b Report the status of terminated background jobs
immediately, rather than before the next primary
prompt. This is effective only when job control
is enabled.
-e Exit immediately if a pipeline (which may consist
of a single simple command), a subshell command
enclosed in parentheses, or one of the commands
executed as part of a command list enclosed by
braces (see SHELL GRAMMAR above) exits with a
non-zero status. The shell does not exit if the
command that fails is part of the command list
immediately following a while or until keyword,
part of the test following the if or elif
reserved words, part of any command executed in a
&& or ││ list except the command following the
final && or ││, any command in a pipeline but the
last, or if the command’s return value is being
inverted with !. A trap on ERR, if set, is exe-
cuted before the shell exits. This option
applies to the shell environment and each sub-
shell environment separately (see COMMAND EXECU-
TION ENVIRONMENT above), and may cause subshells
to exit before executing all the commands in the
subshell.
-f Disable pathname expansion.
-h Remember the location of commands as they are
looked up for execution. This is enabled by
default.
-k All arguments in the form of assignment state-
ments are placed in the environment for a com-
mand, 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 suc-
cessfully. 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).
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 GLOBIG-
NORE variables, if they appear in the environ-
ment, are ignored. If the shell is started with
the effective user (group) id not equal to the
real user (group) id, and the -p option is not
supplied, these actions are taken and the effec-
tive user id is set to the real user id. If the
-p option is supplied at startup, the effective
user id is not reset. Turning this option off
causes the effective user and group ids to be set
to the real user and group ids.
-t Exit after reading and executing one command.
-u Treat unset variables and parameters other than
the special parameters "@" and "*" as an error
when performing parameter expansion. If expan-
sion is attempted on an unset variable or parame-
ter, the shell prints an error message, and, if
not interactive, exits with a non-zero status.
-v Print shell input lines as they are read.
-x After expanding each simple command, for command,
case command, select command, or arithmetic for
command, display the expanded value of PS4, 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 <> redirection operators.
This may be overridden when creating output files
by using the redirection operator >| instead of
>.
-E If set, any trap on ERR is inherited by shell
functions, command substitutions, and commands
executed in a subshell environment. The ERR trap
is normally not inherited in such cases.
-H Enable ! style history substitution. This
option is on by default when the shell is inter-
active.
-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 phys-
ical 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 inher-
ited 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 arguments to
an invocation of the shell. The current set of options
may be found in $-. The return status is always true
unless an invalid option is encountered.
shift [n]
The positional parameters from n+1 ... are renamed to $1
.... Parameters represented by the numbers $# down to
$#-n+1 are unset. n must be a non-negative number less
than or equal to $#. If n is 0, no parameters are
changed. If n is not given, it is assumed to be 1. If n
is greater than $#, the positional parameters are not
changed. The return status is greater than zero if n is
greater than $# or less than zero; otherwise 0.
shopt [-pqsu] [-o] [optname ...]
Toggle the values of variables controlling optional shell
behavior. With no options, or with the -p option, a list
of all settable options is displayed, with an indication
of whether or not each is set. The -p option causes out-
put to be displayed in a form that may be reused as
input. Other options have the following meanings:
-s Enable (set) each optname.
-u Disable (unset) each optname.
-q Suppresses normal output (quiet mode); the return
status indicates whether the optname is set or
unset. If multiple optname arguments are given
with -q, the return status is zero if all optnames
are enabled; non-zero otherwise.
-o Restricts the values of optname to be those
defined for the -o option to the set builtin.
If either -s or -u is used with no optname arguments, the
display is limited to those options which are set or
unset, respectively. Unless otherwise noted, the shopt
options are disabled (unset) by default.
The return status when listing options is zero if all
optnames are enabled, non-zero otherwise. When setting
or unsetting options, the return status is zero unless an
optname is not a valid shell option.
The list of shopt options is:
autocd If set, a command name that is the name of a
directory is executed as if it were the argument
to the cd command. This option is only used by
interactive shells.
cdable_vars
If set, an argument to the cd builtin command
that is not a directory is assumed to be the name
of a variable whose value is the directory to
change to.
cdspell If set, minor errors in the spelling of a direc-
tory component in a cd command will be corrected.
The errors checked for are transposed characters,
a missing character, and one character too many.
If a 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 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 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 mul-
tiple-line command in the same history entry.
This allows easy re-editing of multi-line com-
mands.
compat31
If set, bash changes its behavior to that of ver-
sion 3.1 with respect to quoted arguments to the
conditional command’s =~ operator.
compat32
If set, bash changes its behavior to that of ver-
sion 3.2 with respect to locale-specific string
comparison when using the conditional command’s < and > operators.
compat40
If set, bash changes its behavior to that of ver-
sion 4.0 with respect to locale-specific string
comparison when using the conditional command’s < and > operators and the effect of interrupting a
command list.
dirspell
If set, bash attempts spelling correction on
directory names during word completion if the
directory name initially supplied does not exist.
dotglob If set, bash includes filenames beginning with a
‘.’ in the results of pathname expansion.
execfail
If set, a non-interactive shell will not exit if
it cannot execute the file specified as an argu-
ment 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 dis-
plays the source file name and line number
corresponding to each function name sup-
plied 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 func-
tion or a shell script executed by the .
or source builtins), a call to return is
simulated.
4. BASH_ARGC and BASH_ARGV are updated as
described in their descriptions above.
5. Function tracing is enabled: command sub-
stitution, shell functions, and subshells
invoked with ( command ) inherit the DEBUG
and RETURN traps.
6. Error tracing is enabled: command substi-
tution, shell functions, and subshells
invoked with ( command ) inherit the ERROR
trap.
extglob If set, the extended pattern matching features
described above under Pathname Expansion are
enabled.
extquote
If set, $'string' and $"string" quoting is per-
formed 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 FIG-
NORE. This option is enabled by default.
globstar
If set, the pattern ** used in a pathname expan-
sion context will match a files and zero or more
directories and subdirectories. If the pattern
is followed by a /, only directories and subdi-
rectories 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 result-
ing 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 Com-
pleting under READLINE above). This is enabled
by default.
huponexit
If set, bash will send SIGHUP to all jobs when an
interactive login shell exits.
interactive_comments
If set, allow a word beginning with # to cause
that word and all remaining characters on that
line to be ignored in an interactive shell (see
COMMENTS above). This option is enabled by
default.
lithist If set, and the cmdhist option is enabled, multi-
line commands are saved to the history with
embedded newlines rather than using semicolon
separators where possible.
login_shell
The shell sets this option if it is started as a
login shell (see INVOCATION above). The value
may not be changed.
mailwarn
If set, and a file that bash is checking for mail
has been accessed since the last time it was
checked, the message ‘‘The mail in mailfile has
been read’’ is displayed.
no_empty_cmd_completion
If set, and readline is being used, bash will not
attempt to search the PATH for possible comple-
tions when completion is attempted on an empty
line.
nocaseglob
If set, bash matches filenames in a case-insensi-
tive fashion when performing pathname expansion
(see Pathname Expansion above).
nocasematch
If set, bash matches patterns in a case-insensi-
tive fashion when performing matching while exe-
cuting 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 expan-
sion, 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 posi-
tional parameters.
sourcepath
If set, the source (.) builtin uses the value of
PATH to find the directory containing the file
supplied as an argument. This option is enabled
by default.
xpg_echo
If set, the echo builtin expands backslash-escape
sequences by default.
suspend [-f]
Suspend the execution of this shell until it receives a
SIGCONT signal. 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
composed of the primaries described above under CONDI-
TIONAL EXPRESSIONS. test does not accept any options,
nor does it accept and ignore an argument of -- as signi-
fying the end of options.
Expressions may be combined using the following opera-
tors, listed in decreasing order of precedence. The
evaluation depends on the number of arguments; see below.
! expr True if expr is false.
( expr )
Returns the value of expr. This may be used to
override the normal precedence of operators.
expr1 -a expr2
True if both expr1 and expr2 are true.
expr1 -o expr2
True if either expr1 or expr2 is true.
test and [ evaluate conditional expressions using a set
of rules based on the number of arguments.
0 arguments
The expression is false.
1 argument
The expression is true if and only if the argument
is not null.
2 arguments
If the first argument is !, the expression is true
if and only if the second argument is null. If
the first argument is one of the unary conditional
operators listed above under CONDITIONAL EXPRES-
SIONS, 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
If the second argument is one of the binary condi-
tional 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 opera-
tors are considered binary operators when there
are three arguments. If the first argument is !,
the value is the negation of the two-argument test
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.
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 associ-
ated with each sigspec are displayed. If no arguments
are supplied or if only -p is given, trap prints the list
of commands associated with each signal. The -l option
causes the shell to print a list of signal names and
their corresponding numbers. Each sigspec is either a
signal name defined in <signal .h>, or a signal number.
Signal names are case insensitive and the SIG prefix is
optional.
If a sigspec is EXIT (0) the command arg is executed on
exit from the shell. If a sigspec is DEBUG, the command
arg is executed before every simple command, for command,
case command, select command, every arithmetic for com-
mand, and before the first command executes in a shell
function (see SHELL GRAMMAR above). Refer to the
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 executing.
If a sigspec is ERR, the command arg is executed whenever
a simple command has a non-zero exit status, subject to
the following conditions. The ERR trap is not executed
if the failed command is part of the command list immedi-
ately following a while or until keyword, part of the
test in an if statement, part of a command executed in a
&& or ││ list, or if the command’s return value is being
inverted via !. These are the same conditions obeyed by
the errexit option.
Signals ignored upon entry to the shell cannot be
trapped, 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 inter-
preted 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, function, builtin, or disk file,
respectively. If the name is not found, then nothing is
printed, and an exit status of false is returned. If the
-p option is used, type either returns the name of the
disk file that would be executed if name were specified
as a command name, or nothing if ‘‘type -t name’’ would
not return file. The -P option forces a PATH search for
each name, even if ‘‘type -t name’’ would not return
file. If a command is hashed, -p and -P print the hashed
value, not necessarily the file that appears first in
PATH. If the -a option is used, type prints all of the
places that contain an executable named name. This
includes aliases and functions, if and only if the -p
option is not also used. The table of hashed commands is
not consulted when using -a. The -f option suppresses
shell function lookup, as with the command builtin. type
returns true if all of the arguments are found, false if
any are not found.
ulimit [-HSTabcdefilmnpqrstuvx [limit]]
Provides control over the resources available to the
shell and to processes started by it, on systems that
allow such control. The -H and -S options specify that
the hard or soft limit is set for the given resource. A
hard limit cannot be increased by a non-root user once it
is set; a soft limit may be increased up to the value of
the hard limit. If neither -H nor -S is specified, both
the soft and hard limits are set. The value of limit can
be a number in the unit specified for the resource or one
of the special values hard, soft, or unlimited, which
stand for the current hard limit, the current soft limit,
and no limit, respectively. If limit is omitted, the
current value of the soft limit of the resource is
printed, unless the -H option is given. When more than
one resource is specified, the limit name and unit are
printed before the value. Other options are interpreted
as follows:
-a All current limits are reported
-b The maximum socket buffer size
-c The maximum size of core files created
-d The maximum size of a process’s data segment
-e The maximum scheduling priority ("nice")
-f The maximum size of files written by the shell and
its children
-i The maximum number of pending signals
-l The maximum size that may be locked into memory
-m The maximum resident set size (many systems do not
honor this limit)
-n The maximum number of open file descriptors (most
systems do not allow this value to be set)
-p The pipe size in 512-byte blocks (this may not be
set)
-q The maximum number of bytes in POSIX message
queues
-r The maximum real-time scheduling priority
-s The maximum stack size
-t The maximum amount of cpu time in seconds
-u The maximum number of processes available to a
single user
-v The maximum amount of virtual memory available to
the shell
-x The maximum number of file locks
-T The maximum number of threads
If limit is given, it is the new value of the specified
resource (the -a option is display only). If no option
is given, then -f is assumed. Values are in 1024-byte
increments, except for -t, which is in seconds, -p, which
is in units of 512-byte blocks, and -T, -b, -n, and -u,
which are unscaled values. The return status is 0 unless
an invalid option or argument is supplied, or an error
occurs while setting a new limit.
umask [-p] [-S] [mode]
The user file-creation mask is set to mode. If mode
begins with a digit, it is interpreted as an octal num-
ber; otherwise it is interpreted as a symbolic mode mask
similar to that accepted by chmod(1). If mode is omit-
ted, the current value of the mask is printed. The -S
option causes the mask to be printed in symbolic form;
the default output is an octal number. If the -p option
is supplied, and mode is omitted, the output is in a form
that may be reused as input. The return status is 0 if
the mode was successfully changed or if no mode argument
was supplied, and false otherwise.
unalias [-a] [name ...]
Remove each name from the list of defined aliases. If -a
is supplied, all alias definitions are removed. The
return value is true unless a supplied name is not a
defined alias.
unset [-fv] [name ...]
For each name, remove the corresponding variable or func-
tion. 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 defini-
tion is removed. Each unset variable or function is
removed from the environment passed to subsequent com-
mands. If any of COMP_WORDBREAKS, RANDOM, 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 readonly.
wait [n ...]
Wait for each specified process and return its termina-
tion status. Each n may be a process ID or a job speci-
fication; 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 processes are waited for, and the
return status is zero. If n specifies a non-existent
process or job, the return status is 127. Otherwise, the
return status is the exit status of the last process or
job waited for.
SEE ALSO
bash(1), sh(1)
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