sh-posix(1) sh-posix(1)
NAME [Toc] [Back]
sh-posix: sh, rsh - standard and restricted POSIX.2-conformant command
shells
SYNOPSIS [Toc] [Back]
sh [{-|+}aefhikmnprstuvx] [{-|+}o option]... [-c string] [arg]...
rsh [{-|+}aefhikmnprstuvx] [{-|+}o option]... [-c string] [arg]...
Remarks [Toc] [Back]
This shell is intended to conform to the shell specification of the
POSIX.2 Shell and Utility standards. Check any standards conformance
documents shipped with your system for information on the conformance
of this shell to any other standards.
List of Subheadings in DESCRIPTION [Toc] [Back]
Shell Invocation Tilde Substitution Environment
Options Command Substitution Functions
rsh Restrictions Parameter Substitution Jobs
Definitions Blank Interpretation Signals
Commands File Name Generation Execution
Simple Commands Quoting Command Reentry
Compound Commands Arithmetic Evaluation Command Line Editing
Special Commands Prompting emacs/gmacs Editing Mode
Comments Conditional Expressions vi Editing Mode
Aliasing Input/Output
DESCRIPTION [Toc] [Back]
sh is a command programming language that executes commands read from
a terminal or a file.
rsh is a restricted version of sh. See the rsh Restrictions
subsection below.
Shell Invocation [Toc] [Back]
If the shell is invoked by an exec*() system call and the first
character of argument zero (shell parameter 0) is dash (-), the shell
is assumed to be a login shell and commands are read first from
/etc/profile, then from either .profile in the current directory or
$HOME/.profile if either file exists, and finally from the file named
by performing parameter substitution on the value of the environment
parameter ENV, if the file exists. If the -s option is not present
and an arg is, a path search is performed on the first arg to
determine the name of the script to execute. When running sh with
arg, the script arg must have read permission and any setuid and
setgid settings will be ignored. Commands are read as described
below.
Shell output, except for the output of some of the commands listed in
the Special Commands subsection, is written to standard error (file
descriptor 2).
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Options [Toc] [Back]
The following options are interpreted by the shell when it is invoked.
-c string Read commands from string.
-i If -i is present or if the shell input and output are
attached to a terminal (as reported by tty()), the
shell is interactive. In this case SIGTERM is ignored
and SIGINT is caught and ignored (so that wait is
interruptible). In all cases, SIGQUIT is ignored by
the shell. See signal(5).
-r The shell is a restricted shell.
-s If -s is present or if no arguments remain, commands
are read from the standard input.
The remaining options and operands are described under the set command
in the Special Commands subsection.
rsh Restrictions
rsh is used to set up login names and execution environments where
capabilities are more controlled than those of the standard shell.
The actions of rsh are identical to those of sh, except that the
following are forbidden:
+ Changing directory (see the cd special command and cd(1))
+ Setting the value of SHELL, ENV, or PATH
+ Specifying path or command names containing /
+ Redirecting output (>, >|, <>, and >>)
The restrictions above are enforced after the .profile and ENV files
are interpreted.
When a command to be executed is found to be a shell procedure, rsh
invokes sh to execute it. Thus, the end-user is provided with shell
procedures accessible to the full power of the standard shell, while
being restricted to a limited menu of commands. This scheme assumes
that the end-user does not have write and execute permissions in the
same directory.
These rules effectively give the writer of the .profile file complete
control over user actions, by performing guaranteed set-up actions and
leaving the user in an appropriate directory (probably not the login
directory).
The system administrator often sets up a directory of commands
(usually /usr/rbin) that can be safely invoked by rsh. HP-UX systems
provide a restricted editor red (see ed(1)), suitable for restricted
users.
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Definitions [Toc] [Back]
metacharacter One of the following characters:
; & ( ) | < > newline space tab
blank A tab or a space.
identifier A sequence of letters, digits, or underscores
starting with a letter or underscore. Identifiers
are used as names for functions and named
parameters.
word A sequence of characters separated by one or more
nonquoted metacharacters.
command A sequence of characters in the syntax of the
shell language. The shell reads each command and
carries out the desired action, either directly or
by invoking separate utilities.
special command A command that is carried out by the shell without
creating a separate process. Except for
documented side effects, most special commands can
be implemented as separate utilities.
# Comment delimiter. A word beginning with # and
all following characters up to a newline are
ignored.
parameter An identifier, a decimal number, or one of the
characters !, #, $, *, -, ?, @, and _. See the
Parameter Substitution subsection.
named parameter A parameter that can be assigned a value. See the
Parameter Substitution subsection.
variable A parameter.
environment variable
A parameter that is known outside the local shell,
usually by means of the export special command.
Commands [Toc] [Back]
A command can be a simple command that executes an executable file, a
special command that executes within the shell, or a compound command
that provides flow of control for groups of simple, special, and
compound commands.
Simple Commands [Toc] [Back]
A simple command is a sequence of blank-separated words that may be
preceded by a parameter assignment list. (See the Environment
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subsection). The first word specifies the name of the command to be
executed. Except as specified below, the remaining words are passed
as arguments to the invoked command. The command name is passed as
argument 0 (see exec(2)). The value of a simple command is its exit
status if it terminates normally, or 128+errorstatus if it terminates
abnormally (see signal(5) for a list of errorstatus values).
A pipeline is a sequence of one or more commands separated by a bar
(|) and optionally preceded by an exclamation mark (!). The standard
output of each command but the last is connected by a pipe (see
pipe(2)) to the standard input of the next command. Each command is
run as a separate process; the shell waits for the last command to
terminate. If ! does not precede the pipeline, the exit status of the
pipeline is the exit status of the last command in the pipeline.
Otherwise, the exit status of the pipeline is the logical negation of
the exit status of the last command in the pipeline.
A list is a sequence of one or more pipelines separated by ;, &, &&,
or ||, and optionally terminated by ;, &, or |&.
; Causes sequential execution of the preceding pipeline. An
arbitrary number of newlines can appear in a list, instead
of semicolons, to delimit commands.
& Causes asynchronous execution of the preceding pipeline
(that is, the shell does not wait for that pipeline to
finish).
|& Causes asynchronous execution of the preceding command or
pipeline with a two-way pipe established to the parent
shell. The standard input and output of the spawned command
can be written to and read from by the parent shell using
the -p option of the special commands read and print.
&& Causes the list following it to be executed only if the
preceding pipeline returns a zero value.
|| Causes the list following it to be executed only if the
preceding pipeline returns a nonzero value.
Of these five symbols, ;, &, and |& have equal precedence, which is
lower than that of && and ||. The symbols && and || also have equal
precedence.
Compound Commands [Toc] [Back]
Unless otherwise stated, the value returned by a compound command is
that of the last simple command executed in the compound command. The
; segment separator can be replaced by one or more newlines.
The following keywords are recognized only as the first word of a
command and when not quoted:
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! } elif for then
[[ case else function time
]] do esac if until
{ done fi select while
A compound command is one of the following.
case word in [[;] [(] pattern [| pattern]...) list ;;]... ; esac
Execute the list associated with the first pattern that matches
word. The form of the patterns is identical to that used for
file name generation (see the File Name Generation subsection).
The ;; case terminator cannot be replaced by newlines.
for identifier [in word ...] ; do list ; done
Set identifier to each word in sequence and execute the do list.
If in word ... is omitted, set identifier to each set positional
parameter instead. See the Parameter Substitution subsection.
Execution ends when there are no more positional parameters or
words in the list.
function identifier { list ; }
identifier () { list ; }
Define a function named by identifier. A function is called by
executing its identifier as a command. The body of the function
is the list of commands between { and }. See the Functions
subsection.
if list ; then list ; [elif list ; then list ;]... [else list ;] fi
Execute the if list and, if its exit status is zero, execute the
first then list. Otherwise, execute the elif list (if any) and,
if its exit status is zero, execute the next then list. Failing
that, execute the else list (if any). If no else list or then
list is executed, if returns a zero exit status.
select identifier [in word ...] ; do list ; done
Print the set of words on standard error (file descriptor 2),
each preceded by a number. If in word ... is omitted, print the
positional parameters instead (see the Parameter Substitution
subsection). Print the PS3 prompt and read a line from standard
input into the parameter REPLY. If this line consists of the
number of one of the listed words, set identifier to the
corresponding word, execute list, and repeat the PS3 prompt. If
the line is empty, print the selection list again, and repeat the
PS3 prompt. Otherwise, set identifier to null, execute list, and
repeat the PS3 prompt. The select loop repeats until a break
special command or end-of-file is encountered.
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time pipeline
Execute the pipeline and print the elapsed time, the user time,
and the system time on standard error. Note that the time
keyword can appear anywhere in the pipeline to time the entire
pipeline. To time a particular command in a pipeline, see
time(1).
until list ; do list ; done
Execute the until list. If the exit status of the last command
in the list is nonzero, execute the do list and execute the until
list again. When the exit status of the last command in the
until list is zero, terminate the loop. If no commands in the do
list are executed, until returns a zero exit status.
while list ; do list ; done
Execute the while list. If the exit status of the last command
in the list is zero, execute the do list and execute the while
list again. When the exit status of the last command in the
while list is nonzero, terminate the loop. If no commands in the
do list are executed, while returns a nonzero exit status.
( list )
Execute list in a separate environment. If two adjacent open
parentheses are needed for nesting, a space must be inserted
between them to avoid arithmetic evaluation.
{ list ; }
Execute list, but not in a separate environment. Note that { is
a keyword and requires a trailing blank to be recognized.
[[ expression ]]
Evaluate expression and return a zero exit status when expression
is true. See the Conditional Expressions subsection for a
description of expression. Note that [[ and ]] are keywords and
require blanks between them and expression.
Special Commands [Toc] [Back]
Special commands are simple commands that are executed in the shell
process. They permit input/output redirection. Unless otherwise
indicated, file descriptor 1 (standard output) is the default output
location and the exit status, when there are no syntax errors, is
zero.
Commands that are marked with "%" are treated specially in the
following ways:
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1. Variable assignment lists preceding the command remain in
effect when the command completes.
2. I/O redirections are processed after variable assignments.
3. Certain errors cause a script that contains them to abort.
Words following commands marked with "&" that are in the format of a
variable assignment are expanded with the same rules as a variable
assignment. This means that tilde substitution is performed after the
= sign and word-splitting and file-name generation are not performed.
% : [arg]...
(colon) Only expand parameters. A zero exit status is returned.
% . file [arg]...
(period) Read and execute commands from file and return. The
commands are executed in the current shell environment. The
search path specified by PATH is used to find the directory
containing file. If any arguments arg are given, they become the
positional parameters. Otherwise, the positional parameters are
unchanged. The exit status is the exit status of the last
command executed.
& alias [-tx] [name[=value]]...
With name=value specified, define name as an alias and assign it
the value value. A trailing space in value causes the next word
to be checked for alias substitution.
With name=value omitted, print the list of aliases in the form
name=value on standard output.
With name specified without =value, print the specified alias.
With -t, set tracked aliases. The value of a tracked alias is
the full path name corresponding to the given name. The value of
a tracked alias becomes undefined when the value of PATH is
reset, but the alias remains tracked. With name=value omitted,
print the list of tracked aliases in the form name=pathname on
standard output.
With -x, set exported aliases. An exported alias is defined
across subshell environments. With name=value omitted, print the
list of exported aliases in the form name=value on standard
output.
Alias returns true unless a name is given for which no alias has
been defined.
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See also the unalias special command.
bg [job]...
Put the specified jobs into the background. The current job is
put in the background if job is unspecified. See the Jobs
subsection for a description of the format of job. See also the
fg special command.
% break [n]
Exit from the enclosing for, select, until, or while loop, if
any. If n is specified, exit from n levels.
cd [-L|-P] [arg]
cd old new
In the first form, change the current working directory (PWD) to
arg. If arg is -, the directory is changed to the previous
directory (OLDPWD). The shell parameter HOME is the default arg.
After the cd, the PWD and OLDPWD environment variables are set to
the new current directory and the former directory respectively.
With -L (default), preserve logical naming when treating symbolic
links. cd -L .. moves the current directory one path component
closer to the root directory.
With -P, preserve the physical path when treating symbolic links.
cd -P .. changes the working directory to the actual parent
directory of the current directory.
The shell parameter CDPATH defines the search path for the
directory containing arg. Alternative directory names are
separated by a colon (:). If CDPATH is null or undefined, the
default value is the current directory. Note that the current
directory is specified by a null path name, which can appear
immediately after the equal sign or between the colon delimiters
anywhere else in the path list. If arg begins with a /, the
search path is not used. Otherwise, each directory in the path
is searched for arg. See also cd(1).
The second form of cd substitutes the string new for the string
old in the current directory name, PWD, and tries to change to
this new directory.
command [arg]...
Treat arg as a command, but disable function lookup on arg. See
command(1) for usage and description.
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% continue [n]
Resume the next iteration of the enclosing for, select, until, or
while loop. If n is specified, resume at the nth enclosing loop.
echo [arg]...
Print arg on standard output. See echo(1) for usage and
description. See also the print special command.
% eval [arg]...
Read the arguments as input to the shell and execute the
resulting commands. Allows parameter substitution for keywords
and characters that would otherwise be unrecognized in the
resulting commands.
% exec [arg]...
Parameter assignments remain in effect after the command
completes. If arg is given, execute the command specified by the
arguments in place of this shell without creating a new process.
Input/output arguments may appear and affect the current process.
If no arguments are given, modify file descriptors as prescribed
by the input/output redirection list. In this case, any file
descriptor numbers greater than 2 that are opened with this
mechanism are closed when another program is invoked.
% exit [n]
Exit from the shell with the exit status specified by n. If n is
omitted, the exit status is that of the last command executed.
An end-of-file also causes the shell to exit, except when a shell
has the ignoreeof option set. (See the set special command.)
%& export [name[=value]]...
%& export -p
Mark the given variable names for automatic export to the
environment of subsequently executed commands. Optionally,
assign values to the variables.
With no arguments, write the names and values of all exported
variables to standard output,
With -p, write the names and values of all exported variables to
standard output, in a format with the proper use of quoting, so
that it is suitable for re-input to the shell as commands that
achieve the same exporting results.
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fc [-r] [-e ename] [first [last]]
fc -l [-nr] [first [last]]
fc -s [old=new] [first]
fc -e - [old=new] [command]
List, or edit and reexecute, commands previously entered to an
interactive shell. A range of commands from first to last is
selected from the last HISTSIZE commands typed at the terminal.
The arguments first and last can be specified as a number or
string. A given string is used to locate the most recent
command. A negative number is used to offset the current command
number.
With -l, list the commands on standard output. Without -l,
invoke the editor program ename on a file containing these
keyboard commands. If ename is not supplied, the value of the
parameter FCEDIT (default /usr/bin/ed) is used as the editor.
Once editing has ended, the commands (if any) are executed. If
last is omitted, only the command specified by first is used. If
first is not specified, the default is the previous command for
editing and -16 for listing.
With -r, reverse the order of the commands.
With -n, suppress command numbers when listing.
With -s, reexecute the command without invoking an editor.
The old=new argument replaces the first occurrence of string old
in the command to be reexecuted by the string new.
fg [job]...
Bring each job into the foreground in the order specified. If no
job is specified, bring the current job into the foreground. See
the Jobs subsection for a description of the format of job. See
also the bg special command.
getopts optstring name [arg]...
Parse the argument list, or the positional parameters if no
arguments, for valid options. On each execution, return the next
option in name. See getopts(1) for usage and description.
An option begins with a + or a -. An argument not beginning with
+ or -, or the argument --, ends the options. optstring contains
the letters that getopts recognizes. If a letter is followed by
a :, that option is expected to have an argument. The options
can be separated from the argument by blanks.
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For an option specified as -letter, name is set to letter. For
an option specified as +letter, name is set to +letter. The
index of the next arg is stored in OPTIND. The option argument,
if any, is stored in OPTARG. If no option argument is found, or
the option found does not take an argument, OPTARG is unset.
A leading : in optstring causes getopts to store the letter of an
invalid option in OPTARG, and to set name to ? for an unknown
option and to : when a required option argument is missing.
Otherwise, getopts prints an error message. The exit status is
nonzero when there are no more options.
& hash [utility]...
& hash -r
Affect the way the current shell environment remembers the
locations of utilities. With utility, add utility locations to a
list of remembered locations. With no arguments, print the
contents of the list. With -r, forget all previously remembered
utility locations.
jobs [-lnp] [job]...
List information about each given job, or all active jobs if job
is not specified. With -l, list process IDs in addition to the
normal information. With -n, display only jobs that have stopped
or exited since last notified. With -p, list only the process
group. See the Jobs subsection for a description of the format
of job.
kill [-s signal] process ...
kill -l
kill [-signal] process ...
Send either signal 15 (SIGTERM, terminate) or the specified
signal to the specified jobs or processes. If the signal being
sent is TERM (terminate) or HUP (hangup), the job or process is
sent a CONT (continue) signal when stopped. See kill(1) for
usage and description.
With -l, list the signal names and numbers.
let arg ...
(( arg ...))
Evaluate each arg as a separate arithmetic expression. See the
Arithmetic Evaluation subsection for a description of arithmetic
expression evaluation. The exit status is 0 if the value of the
last expression is nonzero, and 1 otherwise.
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% newgrp [-] [group]
Replace the current shell with a new one having group as the
user's group. The default group is the user's login group. With
-, also execute the user's .profile and $ENV files. See
newgrp(1) for usage and description. Equivalent to
exec newgrp arg ....
print [-nprRsu[n]] [arg]...
The shell output mechanism. With no options or with option - or
--, print the arguments on standard output as described in
echo(1). See also printf(1).
With -n, do not add a newline character to the output.
With -p, write the arguments onto the pipe of the process spawned
with |& instead of standard output.
With -R or -r (raw mode), ignore the escape conventions of echo.
With -R, print all subsequent arguments and options other than
-n.
With -s, write the arguments into the history file instead of to
standard output.
With -u, specify a one-digit file descriptor unit number n on
which the output will be placed. The default is 1 (standard
output).
pwd [-L|-P]
Print the name of the current working directory (equivalent to
print -r - $PWD). With -L (the default), preserve the logical
meaning of the current directory. With -P, preserve the physical
meaning of the current directory if it is a symbolic link. See
also the cd special command, cd(1), ln(1), and pwd(1).
read [-prsu[n]] [name?prompt] [name]...
The shell input mechanism. Read one line (by default, from
standard input) and break it up into words using the characters
in IFS as separators. The first word is assigned to the first
name, the second word to the second name, and so on; the
remaining words are assigned to the last name. See also read(1).
The return code is 0, unless an end-of-file is encountered.
With -p, take the input line from the input pipe of a process
spawned by the shell using |&. An end-of-file with -p causes
cleanup for this process so that another process can be spawned.
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With -r (raw mode), a \ at the end of a line does not signify
line continuation.
With -s, save the input as a command in the history file.
With -u, specify a one-digit file descriptor unit to read from.
The file descriptor can be opened with the exec special command.
The default value of n is 0 (standard input). If name is
omitted, REPLY is used as the default name.
If the first argument contains a ?, the remainder of the argument
is used as a prompt when the shell is interactive.
If the given file descriptor is open for writing and is a
terminal device, the prompt is placed on that unit. Otherwise,
the prompt is issued on file descriptor 2 (standard error).
%& readonly [name[=value]]...
%& readonly -p
Mark the given names read only. These names cannot be changed by
subsequent assignment.
With -p, write the names and values of all read-only variables to
standard output in a format with the proper use of quoting so
that it is suitable for re-input to the shell as commands that
achieve the same attribute-setting results.
% return [n]
Cause a shell function to return to the invoking script with the
return status specified by n. If n is omitted, the return status
is that of the last command executed. Only the low 8 bits of n
(decimal 0 to 255) are passed back to the caller. If return is
invoked while not in a function or a . script (see the . special
command), it has the same effect as an exit command.
% set [{-|+}abCefhkmnopstuvx] [{-|+}o option]...
[{-|+}A name] [arg]...
Set (-) or clear (+) execution options or perform array
assignments (-A, +A). All options except -A and +A can be
supplied in a shell invocation (see the SYNOPSIS section and the
Shell Invocation subsection).
Using + instead of - before an option causes the option to be
turned off. These options can also be used when invoking the
shell. The current list of set single-letter options is
contained in the shell variable -. It can be examined with the
command echo $-.
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The - and + options can be intermixed in the same command, except
that there can be only one -A or +A option.
Unless -A or +A is specified, the remaining arg arguments are
assigned consecutively to the positional parameters 1, 2, ....
The set command with neither arguments nor options displays the
names and values of all shell parameters on standard output. See
also env(1).
The options are defined as follows.
-A Array assignment. Unset the variable name and assign values
sequentially from the list arg. With +A, do not unset the
variable name first.
-a Automatically export subsequently defined parameters.
-b Cause the shell to notify the user asynchronously of
background jobs as they are completed. When the shell
notifies the user that a job has been completed, it can
remove the job's process ID from the list of those known in
the current shell execution environment.
-C Prevent redirection > from truncating existing files.
Requires >| to truncate a file when turned on.
-e Execute the ERR trap, if set, and exit if a command has a
nonzero exit status, and is not part of the compound list
following a if, until, or while keyword, and is not part of
an AND or OR list, and is not a pipeline preceded by the !
reserved word. This mode is disabled while reading
profiles.
-f Disable file name generation.
-h Specify that each command whose name is an identifier
becomes a tracked alias when first encountered.
-k Place all parameter assignment arguments (not just those
that precede the command name) into the environment for a
command.
-m Run background jobs in a separate process group and print a
line upon completion. The exit status of background jobs is
reported in a completion message. This option is turned on
automatically for interactive shells.
-n Read commands and check them for syntax errors, but do not
execute them. The -n option is ignored for interactive
shells.
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-o Set an option argument from the following list. Repeat the
-o option to specify additional option arguments.
allexport Same as -a.
bgnice Run all background jobs at a lower priority.
emacs Use a emacs-style inline editor for command
entry.
errexit Same as -e.
gmacs Use a gmacs-style inline editor for command
entry.
ignoreeof Do not exit from the shell on end-of-file
(eof, as defined by stty; default is ^D).
The exit special command must be used.
keyword Same as -k.
markdirs Append a trailing / to all directory names
resulting from file name generation.
monitor Same as -m.
noclobber Same as -C.
noexec Same as -n.
noglob Same as -f.
nolog Do not save function definitions in history
file.
notify Same as -b.
nounset Same as -u.
privileged Same as -p.
trackall Same as -h.
verbose Same as -v.
vi Use a vi-style inline editor for command
entry.
viraw Process each character as it is typed in vi
mode (always on).
xtrace Same as -x.
-p Disable processing of the $HOME/.profile file and uses the
file /etc/suid_profile instead of the ENV file. This mode
is on whenever the effective user ID (group ID) is not equal
to the real user ID (group ID). Turning this off causes the
effective user ID and group ID to be set to the real user ID
and group ID.
-s Sort the positional parameters.
-t Exit after reading and executing one command.
-u Treat unset parameters as an error when substituting.
-v Print shell input lines as they are read.
-x Print commands and their arguments as they are executed.
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- Turn off -x and -v options and stop examining arguments for
options.
-- Do not change any of the options; useful in setting
parameter 1 to a value beginning with -. If no arguments
follow this option, the positional parameters are unset.
% shift [n]
Rename the positional parameters from n+1 ... to 1 .... The
default value of n is 1. n can be any arithmetic expression that
evaluates to a nonnegative number less than or equal to $#.
test [expr]
Evaluate conditional expression expr. See test(1) for usage and
description. See also the Conditional Expressions subsection.
The arithmetic comparison operators are not restricted to
integers. They allow any arithmetic expression. The following
additional primitive expressions are allowed:
-L file True if file is a symbolic link.
-e file True if file exists.
file1 -nt file2 True if file1 is newer than file2.
file1 -ot file2 True if file1 is older than file2.
file1 -ef file2 True if file1 has the same device and
i-node number as file2.
% times
Print the accumulated user and system times for the shell and for
processes run from the shell.
% trap [arg] [sig]...
Set arg as a command that is read and executed when the shell
receives a sig signal. (Note that arg is scanned once when the
trap is set and once when the trap is taken.) Each sig can be
given as the number or name of a signal. Letter case is ignored.
For example, 3, QUIT, quit, and SIGQUIT all specify the same
signal. Use kill -l to get a list of signals.
Trap commands are executed in signal number order. Any attempt
to set a trap on a signal that was ignored upon entering the
current shell is ineffective. Traps remain in effect for a given
shell until explicitly changed with another trap command; that
is, a trap set within a function will remain in effect even after
the function returns.
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If arg is - (or if arg is omitted and the first sig is numeric),
reset all traps for each sig to their original values.
If arg is the null string ('' or ""), each sig is ignored by the
shell and by the commands it invokes.
If sig is DEBUG, then arg is executed after each command. If sig
is ERR, arg is executed whenever a command has a nonzero exit
code. If sig is 0 or EXIT, the command arg is executed on exit
from the shell.
With no arguments, print a list of commands associated with each
signal name.
& typeset [{-|+}LRZfilrtux[n]] [name[=value]]...
name=value [name=value]...
Assign types and a value to a local named parameter name. See
also the export special command. Parameter assignments remain in
effect after the command completes. When invoked inside a
function, create a new instance of the parameter name. The
parameter value and type are restored when the function
completes.
The following list of attributes can be specified. Use + instead
of - to turn the options off.
-L Left justify and remove leading blanks from value. If n is
nonzero, it defines the width of the field; otherwise, it is
determined by the width of the value of first assignment.
When name is assigned, the value is filled on the right with
blanks or truncated, if necessary, to fit into the field.
Leading zeros are removed if the -Z option is also set. The
-R option is turned off. Flagged as leftjust n.
-R Right justify and fill with leading blanks. If n is
nonzero, it defines the width of the field; otherwise, it is
determined by the width of the value of first assignment.
The field is left-filled with blanks or truncated from the
end if the parameter is reassigned. The -L option is turned
off. Flagged as rightjust n.
-Z Right justify and fill with leading zeros if the first
nonblank character is a digit and the -L option has not been
set. If n is nonzero it defines the width of the field;
otherwise, it is determined by the width of the value of
first assignment. Flagged as zerofill n plus the flag for
-L or -R.
-f Cause name to refer to function names rather than parameter
names. No assignments can be made to the name declared with
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the typeset statement. The only other valid options are -t
(which turns on execution tracing for this function) and -x
(which allows the function to remain in effect across shell
procedures executed in the same process environment).
Flagged as function.
-i Parameter is an integer. This makes arithmetic faster. If
n is nonzero it defines the output arithmetic base;
otherwise, the first assignment determines the output base.
Flagged as integer [base n].
-l Convert all uppercase characters to lowercase. The
uppercase -u option is turned off. Flagged as lowercase.
-r Mark any given name as "read only". The name cannot be
changed by subsequent assignment. Flagged as readonly.
-t Tag the named parameters. Tags are user-definable and have
no special meaning to the shell. Flagged as tagged.
-u Convert all lowercase characters to uppercase characters.
The lowercase -l option is turned off. Flagged as
uppercase.
-x Mark any given name for automatic export to the environment
of subsequently executed commands. Flagged as export.
typeset alone displays a list of parameter names, prefixed by any
flags specified above.
typeset - displays the parameter names followed by their values.
Specify one or more of the option letters to restrict the list.
Some options are incompatible with others.
typeset + displays the parameter names alone. Specify one or
more of the option letters to restrict the list. Some options
are incompatible with others.
ulimit [-HSacdfnst] [limit]
Set or display a resource limit. The limit for a specified
resource is set when limit is specified. The value of limit can
be a number in the unit specified with each resource, or the
keyword unlimited.
The -H and -S flags specify whether the hard limit or the soft
limit is set for the given resource. A hard limit cannot be
increased once it is set. A soft limit can be increased up to
the hard limit. If neither -H nor -S is specified, the limit
applies to both. The current resource limit is printed when
limit is omitted. In this case, the soft limit is printed unless
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-H is specified. When more than one resource is specified, the
limit name and unit are printed before the value.
If no option is given, -f is assumed.
-a List all of the current resource limits.
-c The number of 512-byte blocks in the size of core
dumps.
-d The number of kilobytes in the size of the data area.
-f The number of 512-byte blocks in files written by child
processes (files of any size can be read).
-n The number of file descriptors.
-s The number of kilobytes in the size of the stack area.
-t The number of seconds to be used by each process.
umask [-S] [mask]
Set the user file-creation mask mask. mask can be either an
octal number or a symbolic value as described in umask(1). A
symbolic value shows permissions that are unmasked. An octal
value shows permissions that are masked off.
Without mask, print the current value of the mask. With -S,
print the value in symbolic format. Without -S, print the value
as an octal number. The output from either form can be used as
the mask of a subsequent invocation of umask.
unalias name ...
unalias -a
Remove each name from the alias list. With -a, remove all alias
definitions from the current shell execution environment. See
also the alias special command.
% unset [-fv] name ...
Remove the named shell parameters from the parameter list. Their
values and attributes are erased. Read-only variables cannot be
unset. With -f, names refer to function names. With -v, names
refer to variable names. Unsetting _, ERRNO, LINENO, MAILCHECK,
OPTARG, OPTIND, RANDOM, SECONDS, and TMOUT removes their special
meaning, even if they are subsequently assigned to.
wait [job]
Wait for the specified job to terminate or stop, and report its
status. This status becomes the return code for the wait
command. Without job, wait for all currently active child
processes to terminate or stop. The termination status returned
is that of the last process. See the Jobs subsection for a
description of the format of job.
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whence [-pv] name ...
For each name, indicate how it would be interpreted if used as a
command name. With -v, produce a more verbose report. With -p
do a path search for name, disregarding any use as an alias, a
function, or a reserved word.
Comments [Toc] [Back]
A word beginning with # causes that word and all the following
characters up to a newline to be ignored.
Aliasing [Toc] [Back]
The first word of each command is replaced by the text of an alias, if
an alias for this word has been defined. An alias name consists of
any number of characters excluding metacharacters, quoting characters,
file expansion characters, parameter and command substitution
characters, and =. The replacement string can contain any valid shell
script, including the metacharacters listed above. The first word of
each command in the replaced text, other than any that are in the
process of being replaced, will be tested for additional aliases. If
the last character of the alias value is a blank, the word following
the alias is also checked for alias substitution. Aliases can be used
to redefine specia
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