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6b15476ec9
Fix grammar and spelling nits. Use .Dq and .Qq where appropriate. Divorce trailing punctuation from quoted elements. Use .Dq instead of .Xr for builtins. Remove trailing whitespace and blank lines. PR: 13340
1419 lines
48 KiB
Groff
1419 lines
48 KiB
Groff
.\" Copyright (c) 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" This code is derived from software contributed to Berkeley by
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.\" Kenneth Almquist.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the University of
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.\" California, Berkeley and its contributors.
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.\" 4. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" from: @(#)sh.1 8.6 (Berkeley) 5/4/95
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.\" $FreeBSD$
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.\"
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.Dd May 5, 1995
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.Dt SH 1
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.Os BSD 4
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.Sh NAME
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.Nm sh
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.Nd command interpreter (shell)
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.Sh SYNOPSIS
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.Nm
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.Op Fl /+abCEefIimnpsTuVvx
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.Op Fl /+o Ar longname
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.Op Fl c Ar string
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.Op Ar arg ...
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.Sh DESCRIPTION
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.Nm Sh
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is the standard command interpreter for the system.
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The current version of
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.Nm
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is in the process of being changed to
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conform with the
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.St -p1003.2
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specification for the shell. This version has many features which make
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it appear
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similar in some respects to the Korn shell, but it is not a Korn
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shell clone (run GNU's bash if you want that). Only features
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designated by POSIX, plus a few Berkeley extensions, are being
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incorporated into this shell.
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|
This man page is not intended to be a tutorial or a complete
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specification of the shell.
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|
.Ss Overview
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|
The shell is a command that reads lines from
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either a file or the terminal, interprets them, and
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generally executes other commands. It is the program that is running
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when a user logs into the system (although a user can select
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a different shell with the chsh(1) command).
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|
The shell
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|
implements a language that has flow control constructs,
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a macro facility that provides a variety of features in
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addition to data storage, along with built in history and line
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|
editing capabilities. It incorporates many features to
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aid interactive use and has the advantage that the interpretative
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|
language is common to both interactive and non-interactive
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|
use (shell scripts). That is, commands can be typed directly
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|
to the running shell or can be put into a file and the file
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|
can be executed directly by the shell.
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|
.Ss Invocation
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|
If no args are present and if the standard input of the shell
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|
is connected to a terminal (or if the -i flag is set), the shell
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|
is considered an interactive shell. An interactive shell
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|
generally prompts before each command and handles programming
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|
and command errors differently (as described below).
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|
When first starting, the shell inspects argument 0, and
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|
if it begins with a dash '-', the shell is also considered
|
|
a login shell. This is normally done automatically by the system
|
|
when the user first logs in. A login shell first reads commands
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|
from the files
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|
.Pa /etc/profile
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|
and
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|
.Pa .profile
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|
if they exist. If the environment variable
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|
.Ev ENV
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|
is set on entry to a shell, or is set in the
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|
.Pa .profile
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|
of a login shell, the shell next reads commands from the file named in
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|
.Ev ENV .
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|
Therefore, a user should place commands that are to be executed only
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|
at login time in the
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|
.Pa .profile
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file, and commands that are executed for every shell inside the
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|
.Ev ENV
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|
file. To set the
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.Ev ENV
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variable to some file, place the following line in your
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.Pa .profile
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of your home directory
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.sp
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.Dl ENV=$HOME/.shinit; export ENV
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.sp
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|
substituting for
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.Pa .shinit
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any filename you wish.
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|
If command line arguments besides the options have been
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specified, then the shell treats the first argument as the
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|
name of a file from which to read commands (a shell script), and
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the remaining arguments are set as the positional parameters
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of the shell ($1, $2, etc). Otherwise, the shell reads commands
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|
from its standard input.
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|
.Pp
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|
Unlike older versions of
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.Nm
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|
the
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|
.Ev ENV
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script is only sourced on invocation of interactive shells. This
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closes a well-known, and sometimes easily exploitable security
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|
hole related to poorly thought out
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.Ev ENV
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|
scripts.
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|
.Ss Argument List Processing
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|
All of the single letter options to
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.Nm
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|
have a corresponding name that can be used as an argument to the
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.Dq set
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|
builtin (described later). These names are provided next to the
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|
single letter option in the descriptions below. Specifying a dash
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.Dq -
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|
enables the option, while using a plus
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.Dq +
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|
disables the option. A
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|
.Dq --
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|
or plain
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.Dq -
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|
will stop option processing and will force the remaining
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|
words on the command line to be treated as arguments.
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|
.Bl -tag -width Ds
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.It Fl a Li allexport
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|
Export all variables assigned to.
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.It Fl b Li notify
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Enable asynchronous notification of background job
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completion.
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.Pq UNIMPLEMENTED
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.It Fl C Li noclobber
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|
Don't overwrite existing files with
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.Dq > .
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.Pq UNIMPLEMENTED
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.It Fl E Li emacs
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|
Enable the built-in
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.Xr emacs 1
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command line editor (disables
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.Fl V
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|
if it has been set).
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.It Fl e Li errexit
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|
If not interactive, exit immediately if any
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untested command fails.
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|
The exit status of a command is considered to be
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explicitly tested if the command is used to control
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an if, elif, while, or until; or if the command is the left
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hand operand of an
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.Dq &&
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or
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.Dq ||
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operator.
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.It Fl f Li noglob
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Disable pathname expansion.
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.It Fl I Li ignoreeof
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Ignore EOF's from input when interactive.
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.It Fl i Li interactive
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Force the shell to behave interactively.
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.It Fl m Li monitor
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|
Turn on job control (set automatically when interactive).
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.It Fl n Li noexec
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|
If not interactive, read commands but do not
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execute them. This is useful for checking the
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syntax of shell scripts.
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.It Fl p Li privileged
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|
Turn on privileged mode. This mode is enabled on startup
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if either the effective user or group id is not equal to the
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real user or group id. Turning this mode off sets the
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effective user and group ids to the real user and group ids.
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Also on interactive shells and when enabled, this mode sources
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.Pa /etc/suid_profile
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(instead of
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.Pa ~/.profile Ns )
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after
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.Pa /etc/profile
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|
and ignores the contents of the
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.Ev ENV
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variable.
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.It Fl s Li stdin
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Read commands from standard input (set automatically
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if no file arguments are present). This option has
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|
no effect when set after the shell has already started
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running (i.e. when set with the
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.Dq set
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|
command).
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.It Fl T Li asynctraps
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|
When waiting for a child, execute traps immediately. If this option is
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|
not set, traps are executed after the child exits, as specified in
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.St -p1003.2
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|
This nonstandard option is useful for putting guarding shells around
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children that block signals. The surrounding shell may kill the child
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|
or it may just return control to the tty and leave the child alone,
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|
like this:
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|
.Bd -literal -offset indent
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|
sh -T -c "trap 'exit 1' 2 ; some-blocking-program"
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|
.Ed
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|
.Pp
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|
.It Fl u Li nounset
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|
Write a message to standard error when attempting
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|
to expand a variable that is not set, and if the
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shell is not interactive, exit immediately.
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|
.Pq UNIMPLEMENTED
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|
.It Fl V Li vi
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|
Enable the built-in
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|
.Xr vi 1
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|
command line editor (disables
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.Fl E
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if it has been set).
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|
.It Fl v Li verbose
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|
The shell writes its input to standard error
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as it is read. Useful for debugging.
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.It Fl x Li xtrace
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|
Write each command to standard error (preceded
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by a '+ ') before it is executed. Useful for
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debugging.
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|
.It Fl c Ar string
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Pass the string argument to the shell to be interpreted as input.
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|
Keep in mind that this option only accepts a single string as its
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argument, hence multi-word strings must be quoted.
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|
.El
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|
.Ss Lexical Structure
|
|
The shell reads input in terms of lines from a file and breaks
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it up into words at whitespace (blanks and tabs), and at
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certain sequences of
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|
characters called
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|
.Dq operators ,
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|
which are special to the shell.
|
|
There are two types of operators: control operators and
|
|
redirection operators (their meaning is discussed later).
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|
The following is a list of valid operators:
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|
.Bl -tag -width Ds
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|
.It No Control operators:
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& && ( ) ; ;; | ||
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|
.No \en
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|
.It No Redirection operators:
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< > >| << >> <& >& <<-
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.El
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|
.Ss Quoting
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|
Quoting is used to remove the special meaning of certain characters
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|
or words to the shell, such as operators, whitespace, or
|
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keywords. There are three types of quoting: matched single quotes,
|
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matched double quotes, and backslash.
|
|
.Bl -tag -width Ds
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|
.It Single Quotes
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|
Enclosing characters in single quotes preserves the literal
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|
meaning of all the characters (except single quotes, making
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|
it impossible to put single-quotes in a single-quoted string).
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|
.It Double Quotes
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|
Enclosing characters within double quotes preserves the literal
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|
meaning of all characters except dollarsign ($), backquote (`),
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|
and backslash (\\). The backslash inside double quotes is
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|
historically weird, and serves to quote only the following
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|
characters: $ ` " \\
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.No \en .
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Otherwise it remains literal.
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|
.It Backslash
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|
A backslash preserves the literal meaning of the following
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character, with the exception of
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.No \en.
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|
A backslash preceding a
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.No \en
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is treated as a line continuation.
|
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.El
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|
.Ss Reserved Words
|
|
Reserved words are words that have special meaning to the
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shell and are recognized at the beginning of a line and
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after a control operator. The following are reserved words:
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|
.Bd -literal -offset indent
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|
! { } case do
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|
done elif else esac fi
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|
for if then until while
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|
.Ed
|
|
.Ss Aliases
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|
An alias is a name and corresponding value set using the
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.Dq alias
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|
builtin command. Whenever a reserved word may occur (see above),
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and after checking for reserved words, the shell
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checks the word to see if it matches an alias. If it does,
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it replaces it in the input stream with its value. For example,
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if there is an alias called
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.Dq lf
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with the value
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.Dq ls -F ,
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|
then the input
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|
.Bd -literal -offset indent
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lf foobar <return>
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.Ed
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|
.Pp
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|
would become
|
|
.Bd -literal -offset indent
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ls -F foobar <return>
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.Ed
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|
.Pp
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|
Aliases provide a convenient way for naive users to
|
|
create shorthands for commands without having to learn how
|
|
to create functions with arguments. They can also be
|
|
used to create lexically obscure code. This use is discouraged.
|
|
.Ss Commands
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|
The shell interprets the words it reads according to a
|
|
language, the specification of which is outside the scope
|
|
of this man page (refer to the BNF in the
|
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.St -p1003.2
|
|
document). Essentially though, a line is read and if
|
|
the first word of the line (or after a control operator)
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is not a reserved word, then the shell has recognized a
|
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simple command. Otherwise, a complex command or some
|
|
other special construct may have been recognized.
|
|
.Ss Simple Commands
|
|
If a simple command has been recognized, the shell performs
|
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the following actions:
|
|
.Bl -enum
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|
.It
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|
Leading words of the form
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|
.Dq name=value
|
|
are stripped off and assigned to the environment of
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the simple command. Redirection operators and
|
|
their arguments (as described below) are stripped
|
|
off and saved for processing.
|
|
.It
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|
The remaining words are expanded as described in
|
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the section called
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.Sx Word Expansions ,
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|
and the first remaining word is considered the command
|
|
name and the command is located. The remaining
|
|
words are considered the arguments of the command.
|
|
If no command name resulted, then the
|
|
.Dq name=value
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|
variable assignments recognized in 1) affect the
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current shell.
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.It
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Redirections are performed as described in
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the next section.
|
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.El
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|
.Ss Redirections
|
|
Redirections are used to change where a command reads its input
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|
or sends its output. In general, redirections open, close, or
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|
duplicate an existing reference to a file. The overall format
|
|
used for redirection is:
|
|
.sp
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|
.Dl [n] redir-op file
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|
.sp
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|
where redir-op is one of the redirection operators mentioned
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|
previously. The following gives some examples of how these
|
|
operators can be used. NOTE: stdin and stdout are commonly
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|
used abbreviations for standard input and standard output,
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|
respectively.
|
|
.Bl -tag -width "1234567890" -offset indent
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|
.It [n]> file
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|
redirect stdout (or n) to file
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|
.It [n]>| file
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|
same as above, but override the -C option
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|
.It [n]>> file
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|
append stdout (or n) to file
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.It [n]< file
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|
redirect stdin (or n) from file
|
|
.It [n1]<&n2
|
|
duplicate stdin (or n1) from file descriptor n2
|
|
.It [n]<&-
|
|
close stdin (or n)
|
|
.It [n1]>&n2
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|
duplicate stdout (or n1) to n2.
|
|
.It [n]>&-
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|
close stdout (or n)
|
|
.El
|
|
.Pp
|
|
The following redirection is often called a
|
|
.Dq here-document .
|
|
.Bd -literal -offset indent
|
|
[n]<< delimiter
|
|
here-doc-text...
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|
delimiter
|
|
.Ed
|
|
.Pp
|
|
All the text on successive lines up to the delimiter is
|
|
saved away and made available to the command on standard
|
|
input, or file descriptor n if it is specified. If the delimiter
|
|
as specified on the initial line is quoted, then the here-doc-text
|
|
is treated literally, otherwise the text is subjected to
|
|
parameter expansion, command substitution, and arithmetic
|
|
expansion (as described in the section on
|
|
.Sx Word Expansions ) .
|
|
If the operator is
|
|
.Dq <<-
|
|
instead of
|
|
.Dq << ,
|
|
then leading tabs
|
|
in the here-doc-text are stripped.
|
|
.Ss Search and Execution
|
|
There are three types of commands: shell functions,
|
|
builtin commands, and normal programs -- and the
|
|
command is searched for (by name) in that order. They
|
|
each are executed in a different way.
|
|
.Pp
|
|
When a shell function is executed, all of the shell positional
|
|
parameters (except $0, which remains unchanged) are
|
|
set to the arguments of the shell function.
|
|
The variables which are explicitly placed in the environment of
|
|
the command (by placing assignments to them before the
|
|
function name) are made local to the function and are set
|
|
to the values given. Then the command given in the function
|
|
definition is executed. The positional parameters are
|
|
restored to their original values when the command completes.
|
|
This all occurs within the current shell.
|
|
.Pp
|
|
Shell builtins are executed internally to the shell, without
|
|
spawning a new process.
|
|
.Pp
|
|
Otherwise, if the command name doesn't match a function
|
|
or builtin, the command is searched for as a normal
|
|
program in the filesystem (as described in the next section).
|
|
When a normal program is executed, the shell runs the program,
|
|
passing the arguments and the environment to the
|
|
program. If the program is not a normal executable file
|
|
(i.e. if it does not begin with the
|
|
.Qq magic number
|
|
whose
|
|
.Tn ASCII
|
|
representation is
|
|
.Qq #! ,
|
|
resulting in an ENOEXEC return value from
|
|
.Fn execve )
|
|
the shell
|
|
will interpret the program in a subshell. The child shell
|
|
will reinitialize itself in this case, so that the effect will
|
|
be as if a new shell had been invoked to handle the ad-hoc shell
|
|
script, except that the location of hashed commands located in
|
|
the parent shell will be remembered by the child.
|
|
.Pp
|
|
Note that previous versions of this document
|
|
and the source code itself misleadingly and sporadically
|
|
refer to a shell script without a magic number
|
|
as a
|
|
.Qq shell procedure .
|
|
.Ss Path Search
|
|
When locating a command, the shell first looks to see if
|
|
it has a shell function by that name. Then it looks for a
|
|
builtin command by that name. If a builtin command is not found,
|
|
one of two things happen:
|
|
.Bl -enum
|
|
.It
|
|
Command names containing a slash are simply executed without
|
|
performing any searches.
|
|
.It
|
|
The shell searches each entry in
|
|
.Ev PATH
|
|
in turn for the command. The value of the
|
|
.Ev PATH
|
|
variable should be a series of
|
|
entries separated by colons. Each entry consists of a
|
|
directory name.
|
|
The current directory
|
|
may be indicated implicitly by an empty directory name,
|
|
or explicitly by a single period.
|
|
.El
|
|
.Ss Command Exit Status
|
|
Each command has an exit status that can influence the behavior
|
|
of other shell commands. The paradigm is that a command exits
|
|
with zero for normal or success, and non-zero for failure,
|
|
error, or a false indication. The man page for each command
|
|
should indicate the various exit codes and what they mean.
|
|
Additionally, the builtin commands return exit codes, as does
|
|
an executed shell function.
|
|
.Pp
|
|
If a command is terminated by a signal, its exit status is 128 plus
|
|
the signal number. Signal numbers are defined in the header file
|
|
.Aq Pa sys/signal.h .
|
|
.Ss Complex Commands
|
|
Complex commands are combinations of simple commands
|
|
with control operators or reserved words, together creating a larger complex
|
|
command. More generally, a command is one of the following:
|
|
.Bl -item -offset indent
|
|
.It
|
|
simple command
|
|
.It
|
|
pipeline
|
|
.It
|
|
list or compound-list
|
|
.It
|
|
compound command
|
|
.It
|
|
function definition
|
|
.El
|
|
.Pp
|
|
Unless otherwise stated, the exit status of a command is
|
|
that of the last simple command executed by the command.
|
|
.Ss Pipelines
|
|
A pipeline is a sequence of one or more commands separated
|
|
by the control operator |. The standard output of all but
|
|
the last command is connected to the standard input
|
|
of the next command. The standard output of the last
|
|
command is inherited from the shell, as usual.
|
|
.Pp
|
|
The format for a pipeline is:
|
|
.Bd -literal -offset indent
|
|
[!] command1 [ | command2 ...]
|
|
.Ed
|
|
.Pp
|
|
The standard output of command1 is connected to the standard
|
|
input of command2. The standard input, standard output, or
|
|
both of a command is considered to be assigned by the
|
|
pipeline before any redirection specified by redirection
|
|
operators that are part of the command.
|
|
.Pp
|
|
If the pipeline is not in the background (discussed later),
|
|
the shell waits for all commands to complete.
|
|
.Pp
|
|
If the reserved word ! does not precede the pipeline, the
|
|
exit status is the exit status of the last command specified
|
|
in the pipeline. Otherwise, the exit status is the logical
|
|
NOT of the exit status of the last command. That is, if
|
|
the last command returns zero, the exit status is 1; if
|
|
the last command returns greater than zero, the exit status
|
|
is zero.
|
|
.Pp
|
|
Because pipeline assignment of standard input or standard
|
|
output or both takes place before redirection, it can be
|
|
modified by redirection. For example:
|
|
.Bd -literal -offset indent
|
|
$ command1 2>&1 | command2
|
|
.Ed
|
|
.Pp
|
|
sends both the standard output and standard error of command1
|
|
to the standard input of command2.
|
|
.Pp
|
|
A ; or <newline> terminator causes the preceding
|
|
AND-OR-list (described next) to be executed sequentially; a & causes
|
|
asynchronous execution of the preceding AND-OR-list.
|
|
.Pp
|
|
Note that unlike some other shells, each process in the
|
|
pipeline is a child of the invoking shell (unless it
|
|
is a shell builtin, in which case it executes in the
|
|
current shell -- but any effect it has on the
|
|
environment is wiped).
|
|
.Ss Background Commands -- &
|
|
If a command is terminated by the control operator ampersand
|
|
(&), the shell executes the command asynchronously -- that is,
|
|
the shell does not wait for
|
|
the command to finish before executing the next command.
|
|
.Pp
|
|
The format for running a command in background is:
|
|
.Bd -literal -offset indent
|
|
command1 & [command2 & ...]
|
|
.Ed
|
|
.Pp
|
|
If the shell is not interactive, the standard input of an
|
|
asynchronous command is set to /dev/null.
|
|
.Ss Lists -- Generally Speaking
|
|
A list is a sequence of zero or more commands separated by
|
|
newlines, semicolons, or ampersands,
|
|
and optionally terminated by one of these three characters.
|
|
The commands in a
|
|
list are executed in the order they are written.
|
|
If command is followed by an ampersand, the shell starts the
|
|
command and immediately proceed onto the next command;
|
|
otherwise it waits for the command to terminate before
|
|
proceeding to the next one.
|
|
.Ss Short-Circuit List Operators
|
|
.Dq &&
|
|
and
|
|
.Dq ||
|
|
are AND-OR list operators.
|
|
.Dq &&
|
|
executes the first command, and then executes the second command
|
|
if the exit status of the first command is zero.
|
|
.Dq ||
|
|
is similar, but executes the second command if the exit
|
|
status of the first command is nonzero.
|
|
.Dq &&
|
|
and
|
|
.Dq ||
|
|
both have the same priority.
|
|
.Ss Flow-Control Constructs -- if, while, for, case
|
|
The syntax of the if command is
|
|
.Bd -literal -offset indent
|
|
if list
|
|
then list
|
|
[ elif list
|
|
then list ] ...
|
|
[ else list ]
|
|
fi
|
|
.Ed
|
|
.Pp
|
|
The syntax of the while command is
|
|
.Bd -literal -offset indent
|
|
while list
|
|
do list
|
|
done
|
|
.Ed
|
|
.Pp
|
|
The two lists are executed repeatedly while the exit status of the
|
|
first list is zero. The until command is similar, but has the word
|
|
until in place of while, which causes it to
|
|
repeat until the exit status of the first list is zero.
|
|
.Pp
|
|
The syntax of the for command is
|
|
.Bd -literal -offset indent
|
|
for variable in word...
|
|
do list
|
|
done
|
|
.Ed
|
|
.Pp
|
|
The words are expanded, and then the list is executed
|
|
repeatedly with the variable set to each word in turn. do
|
|
and done may be replaced with
|
|
.Dq {
|
|
and
|
|
.Dq } .
|
|
.Pp
|
|
The syntax of the break and continue command is
|
|
.Bd -literal -offset indent
|
|
break [ num ]
|
|
continue [ num ]
|
|
.Ed
|
|
.Pp
|
|
Break terminates the num innermost for or while loops.
|
|
Continue continues with the next iteration of the innermost loop.
|
|
These are implemented as builtin commands.
|
|
.Pp
|
|
The syntax of the case command is
|
|
.Bd -literal -offset indent
|
|
case word in
|
|
pattern) list ;;
|
|
...
|
|
esac
|
|
.Ed
|
|
.Pp
|
|
The pattern can actually be one or more patterns (see Shell
|
|
Patterns described later), separated by
|
|
.Dq |
|
|
characters.
|
|
.Ss Grouping Commands Together
|
|
Commands may be grouped by writing either
|
|
.Bd -literal -offset indent
|
|
(list)
|
|
.Ed
|
|
.Pp
|
|
or
|
|
.Bd -literal -offset indent
|
|
{ list; }
|
|
.Ed
|
|
.Pp
|
|
The first of these executes the commands in a subshell.
|
|
Builtin commands grouped into a (list) will not affect
|
|
the current shell.
|
|
The second form does not fork another shell so is
|
|
slightly more efficient.
|
|
Grouping commands together this way allows you to
|
|
redirect their output as though they were one program:
|
|
.Bd -literal -offset indent
|
|
{ echo -n "hello"; echo " world"; } > greeting
|
|
.Ed
|
|
.Ss Functions
|
|
The syntax of a function definition is
|
|
.Bd -literal -offset indent
|
|
name ( ) command
|
|
.Ed
|
|
.Pp
|
|
A function definition is an executable statement; when
|
|
executed it installs a function named name and returns an
|
|
exit status of zero. The command is normally a list
|
|
enclosed between
|
|
.Dq {
|
|
and
|
|
.Dq } .
|
|
.Pp
|
|
Variables may be declared to be local to a function by
|
|
using a local command. This should appear as the first
|
|
statement of a function, and the syntax is
|
|
.Bd -literal -offset indent
|
|
local [ variable | - ] ...
|
|
.Ed
|
|
.Pp
|
|
Local is implemented as a builtin command.
|
|
.Pp
|
|
When a variable is made local, it inherits the initial
|
|
value and exported and readonly flags from the variable
|
|
with the same name in the surrounding scope, if there is
|
|
one. Otherwise, the variable is initially unset. The shell
|
|
uses dynamic scoping, so that if you make the variable x
|
|
local to function f, which then calls function g, references
|
|
to the variable x made inside g will refer to the
|
|
variable x declared inside f, not to the global variable
|
|
named x.
|
|
.Pp
|
|
The only special parameter than can be made local is
|
|
.Dq - .
|
|
Making
|
|
.Dq -
|
|
local causes any shell options that are
|
|
changed via the set command inside the function to be
|
|
restored to their original values when the function
|
|
returns.
|
|
.Pp
|
|
The syntax of the return command is
|
|
.Bd -literal -offset indent
|
|
return [ exitstatus ]
|
|
.Ed
|
|
.Pp
|
|
It terminates the currently executing function. Return is
|
|
implemented as a builtin command.
|
|
.Ss Variables and Parameters
|
|
The shell maintains a set of parameters. A parameter
|
|
denoted by a name is called a variable. When starting up,
|
|
the shell turns all the environment variables into shell
|
|
variables. New variables can be set using the form
|
|
.Bd -literal -offset indent
|
|
name=value
|
|
.Ed
|
|
.Pp
|
|
Variables set by the user must have a name consisting solely
|
|
of alphabetics, numerics, and underscores - the first of which
|
|
must not be numeric. A parameter can also be denoted by a number
|
|
or a special character as explained below.
|
|
.Ss Positional Parameters
|
|
A positional parameter is a parameter denoted by a number (n > 0).
|
|
The shell sets these initially to the values of its command line
|
|
arguments that follow the name of the shell script. The
|
|
.Dq set
|
|
builtin can also be used to set or reset them.
|
|
.Ss Special Parameters
|
|
A special parameter is a parameter denoted by one of the following
|
|
special characters. The value of the parameter is listed
|
|
next to its character.
|
|
.Bl -hang
|
|
.It *
|
|
Expands to the positional parameters, starting from one. When
|
|
the expansion occurs within a double-quoted string
|
|
it expands to a single field with the value of each parameter
|
|
separated by the first character of the IFS variable, or by a
|
|
<space> if IFS is unset.
|
|
.It @
|
|
Expands to the positional parameters, starting from one. When
|
|
the expansion occurs within double-quotes, each positional
|
|
parameter expands as a separate argument.
|
|
If there are no positional parameters, the
|
|
expansion of @ generates zero arguments, even when @ is
|
|
double-quoted. What this basically means, for example, is
|
|
if $1 is
|
|
.Dq abc
|
|
and $2 is
|
|
.Dq def ghi ,
|
|
then
|
|
.Qq $@
|
|
expands to
|
|
the two arguments:
|
|
.Bd -literal -offset indent
|
|
"abc" "def ghi"
|
|
.Ed
|
|
.It #
|
|
Expands to the number of positional parameters.
|
|
.It ?
|
|
Expands to the exit status of the most recent pipeline.
|
|
.It -
|
|
(hyphen) Expands to the current option flags (the single-letter
|
|
option names concatenated into a string) as specified on
|
|
invocation, by the set builtin command, or implicitly
|
|
by the shell.
|
|
.It $
|
|
Expands to the process ID of the invoked shell. A subshell
|
|
retains the same value of $ as its parent.
|
|
.It !
|
|
Expands to the process ID of the most recent background
|
|
command executed from the current shell. For a
|
|
pipeline, the process ID is that of the last command in the
|
|
pipeline.
|
|
.It 0
|
|
(zero) Expands to the name of the shell or shell script.
|
|
.El
|
|
.Ss Word Expansions
|
|
This clause describes the various expansions that are
|
|
performed on words. Not all expansions are performed on
|
|
every word, as explained later.
|
|
.Pp
|
|
Tilde expansions, parameter expansions, command substitutions,
|
|
arithmetic expansions, and quote removals that occur within
|
|
a single word expand to a single field. It is only field
|
|
splitting or pathname expansion that can create multiple
|
|
fields from a single word. The single exception to this
|
|
rule is the expansion of the special parameter @ within
|
|
double-quotes, as was described above.
|
|
.Pp
|
|
The order of word expansion is:
|
|
.Bl -enum
|
|
.It
|
|
Tilde Expansion, Parameter Expansion, Command Substitution,
|
|
Arithmetic Expansion (these all occur at the same time).
|
|
.It
|
|
Field Splitting is performed on fields
|
|
generated by step (1) unless the IFS variable is null.
|
|
.It
|
|
Pathname Expansion (unless set -f is in effect).
|
|
.It
|
|
Quote Removal.
|
|
.El
|
|
.Pp
|
|
The $ character is used to introduce parameter expansion, command
|
|
substitution, or arithmetic evaluation.
|
|
.Ss Tilde Expansion (substituting a user's home directory)
|
|
A word beginning with an unquoted tilde character (~) is
|
|
subjected to tilde expansion. All the characters up to
|
|
a slash (/) or the end of the word are treated as a username
|
|
and are replaced with the user's home directory. If the
|
|
username is missing (as in ~/foobar), the tilde is replaced
|
|
with the value of the HOME variable (the current user's
|
|
home directory).
|
|
.Ss Parameter Expansion
|
|
The format for parameter expansion is as follows:
|
|
.Bd -literal -offset indent
|
|
${expression}
|
|
.Ed
|
|
.Pp
|
|
where expression consists of all characters until the matching }. Any }
|
|
escaped by a backslash or within a quoted string, and characters in
|
|
embedded arithmetic expansions, command substitutions, and variable
|
|
expansions, are not examined in determining the matching }.
|
|
.Pp
|
|
The simplest form for parameter expansion is:
|
|
.Bd -literal -offset indent
|
|
${parameter}
|
|
.Ed
|
|
.Pp
|
|
The value, if any, of parameter is substituted.
|
|
.Pp
|
|
The parameter name or symbol can be enclosed in braces, which are
|
|
optional except for positional parameters with more than one digit or
|
|
when parameter is followed by a character that could be interpreted as
|
|
part of the name.
|
|
If a parameter expansion occurs inside double-quotes:
|
|
.Bl -enum
|
|
.It
|
|
Pathname expansion is not performed on the results of the
|
|
expansion.
|
|
.It
|
|
Field splitting is not performed on the results of the
|
|
expansion, with the exception of @.
|
|
.El
|
|
.Pp
|
|
In addition, a parameter expansion can be modified by using one of the
|
|
following formats.
|
|
.Bl -tag -width Ds
|
|
.It Li ${parameter:-word}
|
|
Use Default Values. If parameter is unset or
|
|
null, the expansion of word is
|
|
substituted; otherwise, the value of
|
|
parameter is substituted.
|
|
.It Li ${parameter:=word}
|
|
Assign Default Values. If parameter is unset
|
|
or null, the expansion of word is
|
|
assigned to parameter. In all cases, the
|
|
final value of parameter is
|
|
substituted. Only variables, not positional
|
|
parameters or special parameters, can be
|
|
assigned in this way.
|
|
.It Li ${parameter:?[word]}
|
|
Indicate Error if Null or Unset. If
|
|
parameter is unset or null, the expansion of
|
|
word (or a message indicating it is unset if
|
|
word is omitted) is written to standard
|
|
error and the shell exits with a nonzero
|
|
exit status. Otherwise, the value of
|
|
parameter is substituted. An
|
|
interactive shell need not exit.
|
|
.It Li ${parameter:+word}
|
|
Use Alternate Value. If parameter is unset
|
|
or null, null is substituted;
|
|
otherwise, the expansion of word is
|
|
substituted.
|
|
.Pp
|
|
In the parameter expansions shown previously, use of the colon in the
|
|
format results in a test for a parameter that is unset or null; omission
|
|
of the colon results in a test for a parameter that is only unset.
|
|
.It Li ${#parameter}
|
|
String Length. The length in characters of
|
|
the value of parameter.
|
|
.Pp
|
|
The following four varieties of parameter expansion provide for substring
|
|
processing. In each case, pattern matching notation (see Shell Patterns),
|
|
rather
|
|
than regular expression notation, is used to evaluate the patterns.
|
|
If parameter is * or @, the result of the expansion is unspecified.
|
|
Enclosing the full parameter expansion string in double-quotes does not
|
|
cause the following four varieties of pattern characters to be quoted,
|
|
whereas quoting characters within the braces has this effect.
|
|
.It Li ${parameter%word}
|
|
Remove Smallest Suffix Pattern. The word
|
|
is expanded to produce a pattern. The
|
|
parameter expansion then results in
|
|
parameter, with the smallest portion of the
|
|
suffix matched by the pattern deleted.
|
|
.It Li ${parameter%%word}
|
|
Remove Largest Suffix Pattern. The word
|
|
is expanded to produce a pattern. The
|
|
parameter expansion then results in
|
|
parameter, with the largest portion of the
|
|
suffix matched by the pattern deleted.
|
|
.It Li ${parameter#word}
|
|
Remove Smallest Prefix Pattern. The word
|
|
is expanded to produce a pattern. The
|
|
parameter expansion then results in
|
|
parameter, with the smallest portion of the
|
|
prefix matched by the pattern deleted.
|
|
.It Li ${parameter##word}
|
|
Remove Largest Prefix Pattern. The word
|
|
is expanded to produce a pattern. The
|
|
parameter expansion then results in
|
|
parameter, with the largest portion of the
|
|
prefix matched by the pattern deleted.
|
|
.El
|
|
.Ss Command Substitution
|
|
Command substitution allows the output of a command to be substituted in
|
|
place of the command name itself. Command substitution occurs when
|
|
the command is enclosed as follows:
|
|
.Bd -literal -offset indent
|
|
$(command)
|
|
.Ed
|
|
.Pp
|
|
or (
|
|
.Dq backquoted
|
|
version):
|
|
.Bd -literal -offset indent
|
|
`command`
|
|
.Ed
|
|
.Pp
|
|
The shell expands the command substitution by executing command in a
|
|
subshell environment and replacing the command substitution
|
|
with the
|
|
standard output of the command, removing sequences of one or more
|
|
<newline>s at the end of the substitution. (Embedded <newline>s before
|
|
the end of the output are not removed; however, during field
|
|
splitting, they may be translated into <space>s, depending on the value
|
|
of IFS and quoting that is in effect.)
|
|
.Ss Arithmetic Expansion
|
|
Arithmetic expansion provides a mechanism for evaluating an arithmetic
|
|
expression and substituting its value. The format for arithmetic
|
|
expansion is as follows:
|
|
.Bd -literal -offset indent
|
|
$((expression))
|
|
.Ed
|
|
.Pp
|
|
The expression is treated as if it were in double-quotes, except
|
|
that a double-quote inside the expression is not treated specially. The
|
|
shell expands all tokens in the expression for parameter expansion,
|
|
command substitution, and quote removal.
|
|
.Pp
|
|
Next, the shell treats this as an arithmetic expression and
|
|
substitutes the value of the expression.
|
|
.Ss White Space Splitting (Field Splitting)
|
|
After parameter expansion, command substitution, and
|
|
arithmetic expansion the shell scans the results of
|
|
expansions and substitutions that did not occur in double-quotes for
|
|
field splitting and multiple fields can result.
|
|
.Pp
|
|
The shell treats each character of the IFS as a delimiter and use
|
|
the delimiters to split the results of parameter expansion and command
|
|
substitution into fields.
|
|
.Ss Pathname Expansion (File Name Generation)
|
|
Unless the -f flag is set, file name generation is performed
|
|
after word splitting is complete. Each word is
|
|
viewed as a series of patterns, separated by slashes. The
|
|
process of expansion replaces the word with the names of
|
|
all existing files whose names can be formed by replacing
|
|
each pattern with a string that matches the specified pattern.
|
|
There are two restrictions on this: first, a pattern cannot match
|
|
a string containing a slash, and second,
|
|
a pattern cannot match a string starting with a period
|
|
unless the first character of the pattern is a period.
|
|
The next section describes the patterns used for both
|
|
Pathname Expansion and the
|
|
.Dq case
|
|
command.
|
|
.Ss Shell Patterns
|
|
A pattern consists of normal characters, which match themselves,
|
|
and meta-characters. The meta-characters are
|
|
.Dq ! ,
|
|
.Dq * ,
|
|
.Dq ? ,
|
|
and
|
|
.Dq [ .
|
|
These characters lose their special meanings if they are quoted.
|
|
When command or variable substitution is performed and the dollar sign
|
|
or back quotes are not double-quoted, the value of the
|
|
variable or the output of the command is scanned for these
|
|
characters and they are turned into meta-characters.
|
|
.Pp
|
|
An asterisk
|
|
.Dq *
|
|
matches any string of characters. A
|
|
question mark matches any single character. A left
|
|
bracket
|
|
.Dq [
|
|
introduces a character class. The end of
|
|
the character class is indicated by a
|
|
.Dq ] ;
|
|
if the
|
|
.Dq ]
|
|
is missing then the
|
|
.Dq [
|
|
matches a
|
|
.Dq [
|
|
rather than
|
|
introducing a character class. A character class matches
|
|
any of the characters between the square brackets. A
|
|
range of characters may be specified using a minus sign.
|
|
The character class may be complemented by making an
|
|
exclamation point the first character of the character
|
|
class.
|
|
.Pp
|
|
To include a
|
|
.Dq ]
|
|
in a character class, make it the first
|
|
character listed (after the
|
|
.Dq ! ,
|
|
if any). To include a
|
|
minus sign, make it the first or last character listed.
|
|
.Ss Builtins
|
|
This section lists the builtin commands which
|
|
are builtin because they need to perform some operation
|
|
that can't be performed by a separate process. In addition to
|
|
these, there are several other commands that may be
|
|
builtin for efficiency (e.g.
|
|
.Xr printf 1 ,
|
|
.Xr echo 1 ,
|
|
.Xr test 1 ,
|
|
etc).
|
|
.Bl -tag -width Ds
|
|
.It :
|
|
A null command that returns a 0 (true) exit value.
|
|
.It \&. file
|
|
The commands in the specified file are read and executed by the shell.
|
|
If
|
|
.Ar file
|
|
contains any
|
|
.Ql /
|
|
characters, it is used as is. Otherwise, the shell searches the
|
|
.Ev PATH
|
|
for the file. If it is not found in the
|
|
.Ev PATH ,
|
|
it is sought in the current working directory.
|
|
.It alias [ name[=string] ... ]
|
|
If name=string is specified, the shell defines the
|
|
alias
|
|
.Dq name
|
|
with value
|
|
.Dq string .
|
|
If just
|
|
.Dq name
|
|
is specified, the value of the alias
|
|
.Dq name
|
|
is printed.
|
|
With no arguments, the alias builtin prints the
|
|
names and values of all defined aliases (see unalias).
|
|
.It bg [ job ] ...
|
|
Continue the specified jobs (or the current job if no
|
|
jobs are given) in the background.
|
|
.It command command arg ...
|
|
Execute the specified builtin command. (This is useful when you
|
|
have a shell function with the same name
|
|
as a builtin command.)
|
|
.It cd [ directory ]
|
|
Switch to the specified directory (default $HOME).
|
|
If an entry for CDPATH appears in the environment
|
|
of the cd command or the shell variable CDPATH is set
|
|
and the directory name does not begin with a slash,
|
|
then the directories listed in CDPATH will be
|
|
searched for the specified directory. The format of
|
|
CDPATH is the same as that of PATH. In an interactive shell,
|
|
the cd command will print out the name of
|
|
the directory that it actually switched to if this is
|
|
different from the name that the user gave. These
|
|
may be different either because the CDPATH mechanism
|
|
was used or because a symbolic link was crossed.
|
|
.It eval string ...
|
|
Concatenate all the arguments with spaces. Then
|
|
re-parse and execute the
|
|
command.
|
|
.It exec [ command arg ... ]
|
|
Unless command is omitted, the shell process is
|
|
replaced with the specified program (which must be a
|
|
real program, not a shell builtin or function). Any
|
|
redirections on the exec command are marked as permanent,
|
|
so that they are not undone when the exec command finishes.
|
|
.It exit [ exitstatus ]
|
|
Terminate the shell process. If exitstatus is given
|
|
it is used as the exit status of the shell; otherwise
|
|
the exit status of the preceding command is used.
|
|
.It export name ...
|
|
The specified names are exported so that they will
|
|
appear in the environment of subsequent commands.
|
|
The only way to un-export a variable is to unset it.
|
|
The shell allows the value of a variable to be set at the
|
|
same time it is exported by writing
|
|
.Bd -literal -offset indent
|
|
export name=value
|
|
.Ed
|
|
.Pp
|
|
With no arguments the export command lists the names
|
|
of all exported variables.
|
|
.It fc [-e editor] [first [last]]
|
|
.It fc -l [-nr] [first [last]]
|
|
.It fc -s [old=new] [first]
|
|
The fc builtin lists, or edits and re-executes, commands
|
|
previously entered to an interactive shell.
|
|
.Bl -tag -width Ds
|
|
.It -e editor
|
|
Use the editor named by editor to edit the commands. The
|
|
editor string is a command name, subject to search via the
|
|
PATH variable. The value in the FCEDIT variable
|
|
is used as a default when -e is not specified. If
|
|
FCEDIT is null or unset, the value of the EDITOR
|
|
variable is used. If EDITOR is null or unset,
|
|
.Xr ed 1
|
|
is used as the editor.
|
|
.It -l (ell)
|
|
List the commands rather than invoking
|
|
an editor on them. The commands are written in the
|
|
sequence indicated by the first and last operands, as
|
|
affected by -r, with each command preceded by the command
|
|
number.
|
|
.It -n
|
|
Suppress command numbers when listing with -l.
|
|
.It -r
|
|
Reverse the order of the commands listed (with -l) or
|
|
edited (with neither -l nor -s).
|
|
.It -s
|
|
Re-execute the command without invoking an editor.
|
|
.It first
|
|
.It last
|
|
Select the commands to list or edit. The number of
|
|
previous commands that can be accessed are determined
|
|
by the value of the HISTSIZE variable. The value of first
|
|
or last or both are one of the following:
|
|
.It [+]number
|
|
A positive number representing a command
|
|
number; command numbers can be displayed
|
|
with the -l option.
|
|
.It -number
|
|
A negative decimal number representing the
|
|
command that was executed number of
|
|
commands previously. For example, -1 is
|
|
the immediately previous command.
|
|
.It string
|
|
A string indicating the most recently
|
|
entered command that begins with that
|
|
string. If the old=new operand is not also
|
|
specified with -s, the string form of the
|
|
first operand cannot contain an embedded
|
|
equal sign.
|
|
.El
|
|
.\".Pp
|
|
The following environment variables affect the execution of fc:
|
|
.Bl -tag -width Ds
|
|
.It Va FCEDIT
|
|
Name of the editor to use.
|
|
.It Va HISTSIZE
|
|
The number of previous commands that are accessible.
|
|
.El
|
|
.It fg [ job ]
|
|
Move the specified job or the current job to the
|
|
foreground.
|
|
.It getopts optstring var
|
|
The POSIX getopts command.
|
|
The getopts command deprecates the older getopt command.
|
|
The first argument should be a series of letters, each possibly
|
|
followed by a colon which indicates that the option takes an argument.
|
|
The specified variable is set to the parsed option. The index of
|
|
the next argument is placed into the shell variable OPTIND.
|
|
If an option takes an argument, it is placed into the shell variable
|
|
OPTARG. If an invalid option is encountered, var is set to '?'.
|
|
It returns a false value (1) when it encounters the end of the options.
|
|
.It hash -rv command ...
|
|
The shell maintains a hash table which remembers the
|
|
locations of commands. With no arguments whatsoever,
|
|
the hash command prints out the contents of this
|
|
table. Entries which have not been looked at since
|
|
the last cd command are marked with an asterisk; it
|
|
is possible for these entries to be invalid.
|
|
.Pp
|
|
With arguments, the hash command removes the specified commands
|
|
from the hash table (unless they are
|
|
functions) and then locates them. With the -v
|
|
option, hash prints the locations of the commands as
|
|
it finds them. The -r option causes the hash command
|
|
to delete all the entries in the hash table except
|
|
for functions.
|
|
.It jobid [ job ]
|
|
Print the process id's of the processes in the job.
|
|
If the job argument is omitted, use the current job.
|
|
.It jobs
|
|
This command lists out all the background processes
|
|
which are children of the current shell process.
|
|
.It pwd
|
|
Print the current directory. The builtin command may
|
|
differ from the program of the same name because the
|
|
builtin command remembers what the current directory
|
|
is rather than recomputing it each time. This makes
|
|
it faster. However, if the current directory is
|
|
renamed, the builtin version of pwd will continue to
|
|
print the old name for the directory.
|
|
.It Li "read [ -p prompt ] [ -t timeout ] [ -er ] variable ...
|
|
The prompt is printed if the -p option is specified
|
|
and the standard input is a terminal. Then a line is
|
|
read from the standard input. The trailing newline
|
|
is deleted from the line and the line is split as
|
|
described in the section on word splitting above, and
|
|
the pieces are assigned to the variables in order.
|
|
If there are more pieces than variables, the remaining
|
|
pieces (along with the characters in IFS that
|
|
separated them) are assigned to the last variable.
|
|
If there are more variables than pieces, the remaining
|
|
variables are assigned the null string.
|
|
.Pp
|
|
Backslashes are treated specially, unless the -r option is
|
|
specified. If a backslash is followed by
|
|
a newline, the backslash and the newline will be
|
|
deleted. If a backslash is followed by any other
|
|
character, the backslash will be deleted and the following
|
|
character will be treated as though it were
|
|
not in IFS, even if it is.
|
|
.Pp
|
|
If the -t option is specified the timeout elapses
|
|
before any input is supplied, the read command will
|
|
return without assigning any values. The timeout value
|
|
may optionally be followed by one of 's', 'm' or 'h' to
|
|
explicitly specify seconds, minutes or or hours. If none
|
|
is supplied, 's' is assumed.
|
|
.Pp
|
|
The -e option exists only for backward compatibility with older scripts.
|
|
.It readonly name ...
|
|
The specified names are marked as read only, so that
|
|
they cannot be subsequently modified or unset. The shell
|
|
allows the value of a variable to be set at the same
|
|
time it is marked read only by writing
|
|
using the following form
|
|
.Bd -literal -offset indent
|
|
readonly name=value
|
|
.Ed
|
|
.Pp
|
|
With no arguments the readonly command lists the
|
|
names of all read only variables.
|
|
.It Li "set [ { -options | +options | -- } ] arg ...
|
|
The set command performs three different functions.
|
|
.Bl -item
|
|
.It
|
|
With no arguments, it lists the values of all shell
|
|
variables.
|
|
.It
|
|
If options are given, it sets the specified option
|
|
flags, or clears them as described in the section
|
|
called
|
|
.Sx Argument List Processing .
|
|
.It
|
|
The third use of the set command is to set the values
|
|
of the shell's positional parameters to the specified
|
|
args. To change the positional parameters without
|
|
changing any options, use
|
|
.Dq --
|
|
as the first argument
|
|
to set. If no args are present, the set command
|
|
will clear all the positional parameters (equivalent
|
|
to executing
|
|
.Dq shift $# .
|
|
.El
|
|
.Pp
|
|
.It setvar variable value
|
|
Assigns value to variable. (In general it is better
|
|
to write variable=value rather than using setvar.
|
|
Setvar is intended to be used in functions that
|
|
assign values to variables whose names are passed as
|
|
parameters.)
|
|
.It shift [ n ]
|
|
Shift the positional parameters n times. A shift
|
|
sets the value of $1 to the value of $2, the value of
|
|
$2 to the value of $3, and so on, decreasing the
|
|
value of $# by one. If there are zero positional
|
|
parameters, shifting doesn't do anything.
|
|
.It trap [ action ] signal ...
|
|
Cause the shell to parse and execute action when any
|
|
of the specified signals are received. The signals
|
|
are specified by signal number. Action may be null
|
|
or omitted; the former causes the specified signal to
|
|
be ignored and the latter causes the default action
|
|
to be taken. When the shell forks off a subshell, it
|
|
resets trapped (but not ignored) signals to the
|
|
default action. The trap command has no effect on
|
|
signals that were ignored on entry to the shell.
|
|
.It type [name] ...
|
|
Interpret each name as a command and print the
|
|
resolution of the command search. Possible resolutions are:
|
|
shell keyword, alias, shell builtin, command, tracked alias
|
|
and not found. For aliases the alias expansion is printed;
|
|
for commands and tracked aliases the complete pathname of
|
|
the command is printed.
|
|
.It ulimit [ -HSacdflmnust ] [ limit ]
|
|
Set or display resource limits (see
|
|
.Xr getrlimit 2 ).
|
|
If
|
|
.Dq limit
|
|
is specified, the named resource will be set;
|
|
otherwise the current resource value will be displayed.
|
|
.Pp
|
|
If
|
|
.Dq -H
|
|
is specified, the hard limits will be
|
|
set or displayed. While everybody is allowed to reduce a
|
|
hard limit, only the superuser can increase it. Option
|
|
.Dq -S
|
|
specifies the soft limits instead. When displaying limits,
|
|
only one of
|
|
.Dq -S
|
|
or
|
|
.Dq -H
|
|
can be given. The default is
|
|
to display the soft limits, and to set both, the hard and
|
|
the soft limits.
|
|
.Pp
|
|
Option
|
|
.Dq -a
|
|
requests to display all resources. The parameter
|
|
.Dq limit
|
|
is not acceptable in this mode.
|
|
.Pp
|
|
The remaining options specify which resource value is to be
|
|
displayed or modified. They are mutually exclusive.
|
|
.Bl -tag -width Ds
|
|
.It -c coredumpsize
|
|
The maximal size of core dump files, in 512-byte blocks.
|
|
.It -d datasize
|
|
The maximal size of the data segment of a process, in kilobytes.
|
|
.It -f filesize
|
|
The maximal size of a file, in 512-byte blocks. This is the
|
|
default.
|
|
.It -l lockedmem
|
|
The maximal size of memory that can be locked by a process, in
|
|
kilobytes.
|
|
.It -m memoryuse
|
|
The maximal resident set size of a process, in kilobytes.
|
|
.It -n nofiles
|
|
The maximal number of descriptors that could be opened by a process.
|
|
.It -s stacksize
|
|
The maximal size of the stack segment, in kilobytes.
|
|
.It -t time
|
|
The maximal amount of CPU time to be used by each process, in seconds.
|
|
.It -u userproc
|
|
The maximal number of simultaneous processes for this user ID.
|
|
.El
|
|
.It umask [ mask ]
|
|
Set the value of umask (see
|
|
.Xr umask 2 )
|
|
to the specified
|
|
octal value. If the argument is omitted, the
|
|
umask value is printed.
|
|
.It unalias [-a] [name]
|
|
If
|
|
.Dq name
|
|
is specified, the shell removes that alias.
|
|
If
|
|
.Dq -a
|
|
is specified, all aliases are removed.
|
|
.It unset name ...
|
|
The specified variables and functions are unset and
|
|
unexported. If a given name corresponds to both a
|
|
variable and a function, both the variable and the
|
|
function are unset.
|
|
.It wait [ job ]
|
|
Wait for the specified job to complete and return the
|
|
exit status of the last process in the job. If the
|
|
argument is omitted, wait for all jobs to complete
|
|
and the return an exit status of zero.
|
|
.El
|
|
.Ss Commandline Editing
|
|
When
|
|
.Nm
|
|
is being used interactively from a terminal, the current command
|
|
and the command history (see fc in Builtins) can be edited using vi-mode
|
|
command line editing. This mode uses commands similar
|
|
to a subset of those described in the vi man page.
|
|
The command 'set -o vi' enables vi-mode editing and places
|
|
.Nm
|
|
into vi insert mode. With vi-mode enabled,
|
|
.Nm
|
|
can be switched between insert mode and command mode by typing <ESC>.
|
|
Hitting <return> while in command mode will pass the line to the shell.
|
|
.Pp
|
|
Similarly, the 'set -o emacs' command can be used to enable a subset of
|
|
emacs-style command line editing features.
|
|
.Sh SEE ALSO
|
|
.Xr expr 1 ,
|
|
.Xr test 1
|
|
.Sh HISTORY
|
|
A
|
|
.Nm
|
|
command appeared in
|
|
.At V.1 .
|