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2875 lines
72 KiB
Groff
2875 lines
72 KiB
Groff
.\"-
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.\" 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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.\" 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 30, 2016
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.Dt SH 1
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.Os
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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 /+abCEefhIimnPpTuVvx
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.Op Fl /+o Ar longname
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.Oo
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.Ar script
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.Op Ar arg ...
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.Oc
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.Nm
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.Op Fl /+abCEefhIimnPpTuVvx
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.Op Fl /+o Ar longname
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.Fl c Ar string
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.Oo
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.Ar name
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.Op Ar arg ...
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.Oc
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.Nm
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.Op Fl /+abCEefhIimnPpTuVvx
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.Op Fl /+o Ar longname
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|
.Fl s
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.Op Ar arg ...
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.Sh DESCRIPTION
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|
The
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.Nm
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|
utility is the standard command interpreter for the system.
|
|
The current version of
|
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.Nm
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|
is close to the
|
|
.St -p1003.1
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|
specification for the shell.
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|
It only supports features
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|
designated by
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.Tn POSIX ,
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plus a few Berkeley extensions.
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|
This man page is not intended to be a tutorial nor a complete
|
|
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.
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|
It is the program that is started when a user logs into the system,
|
|
although a user can select a different shell with the
|
|
.Xr chsh 1
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|
command.
|
|
The shell
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|
implements a language that has flow control constructs,
|
|
a macro facility that provides a variety of features in
|
|
addition to data storage, along with built-in history and line
|
|
editing capabilities.
|
|
It incorporates many features to
|
|
aid interactive use and has the advantage that the interpretative
|
|
language is common to both interactive and non-interactive
|
|
use (shell scripts).
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|
That is, commands can be typed directly
|
|
to the running shell or can be put into a file,
|
|
which can be executed directly by the shell.
|
|
.Ss Invocation
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|
.\"
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|
.\" XXX This next sentence is incredibly confusing.
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|
.\"
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|
If no arguments are present and if the standard input of the shell
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|
is connected to a terminal
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|
(or if the
|
|
.Fl i
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|
option is set),
|
|
the shell is considered an interactive shell.
|
|
An interactive shell
|
|
generally prompts before each command and handles programming
|
|
and command errors differently (as described below).
|
|
When first starting, the shell inspects argument 0, and
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|
if it begins with a dash
|
|
.Pq Ql - ,
|
|
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
|
|
from the files
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|
.Pa /etc/profile
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|
and then
|
|
.Pa .profile
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|
in a user's home directory,
|
|
if they exist.
|
|
If the environment variable
|
|
.Ev ENV
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|
is set on entry to a shell, or is set in the
|
|
.Pa .profile
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|
of a login shell, the shell then subjects its value to parameter expansion
|
|
and arithmetic expansion and reads commands from the named file.
|
|
Therefore, a user should place commands that are to be executed only
|
|
at login time in the
|
|
.Pa .profile
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|
file, and commands that are executed for every shell inside the
|
|
.Ev ENV
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|
file.
|
|
The user can set the
|
|
.Ev ENV
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|
variable to some file by placing the following line in the file
|
|
.Pa .profile
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|
in the home directory,
|
|
substituting for
|
|
.Pa .shrc
|
|
the filename desired:
|
|
.Pp
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|
.Dl "ENV=$HOME/.shrc; export ENV"
|
|
.Pp
|
|
The first non-option argument specified on the command line
|
|
will be treated as the
|
|
name of a file from which to read commands (a shell script), and
|
|
the remaining arguments are set as the positional parameters
|
|
of the shell
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|
.Li ( $1 , $2 ,
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|
etc.).
|
|
Otherwise, the shell reads commands
|
|
from its standard input.
|
|
.Pp
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|
Unlike older versions of
|
|
.Nm
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|
the
|
|
.Ev ENV
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|
script is only sourced on invocation of interactive shells.
|
|
This
|
|
closes a well-known, and sometimes easily exploitable security
|
|
hole related to poorly thought out
|
|
.Ev ENV
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|
scripts.
|
|
.Ss Argument List Processing
|
|
All of the single letter options to
|
|
.Nm
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|
have a corresponding long name,
|
|
with the exception of
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|
.Fl c
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|
and
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|
.Fl /+o .
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|
These long names are provided next to the single letter options
|
|
in the descriptions below.
|
|
The long name for an option may be specified as an argument to the
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|
.Fl /+o
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|
option of
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|
.Nm .
|
|
Once the shell is running,
|
|
the long name for an option may be specified as an argument to the
|
|
.Fl /+o
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|
option of the
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|
.Ic set
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|
built-in command
|
|
(described later in the section called
|
|
.Sx Built-in Commands ) .
|
|
Introducing an option with a dash
|
|
.Pq Ql -
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|
enables the option,
|
|
while using a plus
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|
.Pq Ql +
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|
disables the option.
|
|
A
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|
.Dq Li --
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|
or plain
|
|
.Ql -
|
|
will stop option processing and will force the remaining
|
|
words on the command line to be treated as arguments.
|
|
The
|
|
.Fl /+o
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|
and
|
|
.Fl c
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|
options do not have long names.
|
|
They take arguments and are described after the single letter options.
|
|
.Bl -tag -width indent
|
|
.It Fl a Li allexport
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|
Flag variables for export when assignments are made to them.
|
|
.It Fl b Li notify
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|
Enable asynchronous notification of background job
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|
completion.
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|
(UNIMPLEMENTED)
|
|
.It Fl C Li noclobber
|
|
Do not overwrite existing files with
|
|
.Ql > .
|
|
.It Fl E Li emacs
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|
Enable the built-in
|
|
.Xr emacs 1
|
|
command line editor (disables the
|
|
.Fl V
|
|
option if it has been set;
|
|
set automatically when interactive on terminals).
|
|
.It Fl e Li errexit
|
|
Exit immediately if any untested command fails in non-interactive mode.
|
|
The exit status of a command is considered to be
|
|
explicitly tested if the command is part of the list used to control
|
|
an
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|
.Ic if , elif , while ,
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|
or
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|
.Ic until ;
|
|
if the command is the left
|
|
hand operand of an
|
|
.Dq Li &&
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|
or
|
|
.Dq Li ||
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|
operator; or if the command is a pipeline preceded by the
|
|
.Ic !\&
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|
keyword.
|
|
If a shell function is executed and its exit status is explicitly
|
|
tested, all commands of the function are considered to be tested as
|
|
well.
|
|
.Pp
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|
It is recommended to check for failures explicitly
|
|
instead of relying on
|
|
.Fl e
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|
because it tends to behave in unexpected ways,
|
|
particularly in larger scripts.
|
|
.It Fl f Li noglob
|
|
Disable pathname expansion.
|
|
.It Fl h Li trackall
|
|
A do-nothing option for
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|
.Tn POSIX
|
|
compliance.
|
|
.It Fl I Li ignoreeof
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|
Ignore
|
|
.Dv EOF Ap s
|
|
from input when in interactive mode.
|
|
.It Fl i Li interactive
|
|
Force the shell to behave interactively.
|
|
.It Fl m Li monitor
|
|
Turn on job control (set automatically when interactive).
|
|
A new process group is created for each pipeline (called a job).
|
|
It is possible to suspend jobs or to have them run in the foreground or
|
|
in the background.
|
|
In a non-interactive shell,
|
|
this option can be set even if no terminal is available
|
|
and is useful to place processes in separate process groups.
|
|
.It Fl n Li noexec
|
|
If not interactive, read commands but do not
|
|
execute them.
|
|
This is useful for checking the
|
|
syntax of shell scripts.
|
|
.It Fl P Li physical
|
|
Change the default for the
|
|
.Ic cd
|
|
and
|
|
.Ic pwd
|
|
commands from
|
|
.Fl L
|
|
(logical directory layout)
|
|
to
|
|
.Fl P
|
|
(physical directory layout).
|
|
.It Fl p Li privileged
|
|
Turn on privileged mode.
|
|
This mode is enabled on startup
|
|
if either the effective user or group ID is not equal to the
|
|
real user or group ID.
|
|
Turning this mode off sets the
|
|
effective user and group IDs to the real user and group IDs.
|
|
When this mode is enabled for interactive shells, the file
|
|
.Pa /etc/suid_profile
|
|
is sourced instead of
|
|
.Pa ~/.profile
|
|
after
|
|
.Pa /etc/profile
|
|
is sourced, and the contents of the
|
|
.Ev ENV
|
|
variable are ignored.
|
|
.It Fl s Li stdin
|
|
Read commands from standard input (set automatically
|
|
if no file arguments are present).
|
|
This option has
|
|
no effect when set after the shell has already started
|
|
running (i.e., when set with the
|
|
.Ic set
|
|
command).
|
|
.It Fl T Li trapsasync
|
|
When waiting for a child, execute traps immediately.
|
|
If this option is not set,
|
|
traps are executed after the child exits,
|
|
as specified in
|
|
.St -p1003.2 .
|
|
This nonstandard option is useful for putting guarding shells around
|
|
children that block signals.
|
|
The surrounding shell may kill the child
|
|
or it may just return control to the tty and leave the child alone,
|
|
like this:
|
|
.Bd -literal -offset indent
|
|
sh -T -c "trap 'exit 1' 2 ; some-blocking-program"
|
|
.Ed
|
|
.It Fl u Li nounset
|
|
Write a message to standard error when attempting
|
|
to expand a variable, a positional parameter or
|
|
the special parameter
|
|
.Va \&!
|
|
that is not set, and if the
|
|
shell is not interactive, exit immediately.
|
|
.It Fl V Li vi
|
|
Enable the built-in
|
|
.Xr vi 1
|
|
command line editor (disables
|
|
.Fl E
|
|
if it has been set).
|
|
.It Fl v Li verbose
|
|
The shell writes its input to standard error
|
|
as it is read.
|
|
Useful for debugging.
|
|
.It Fl x Li xtrace
|
|
Write each command
|
|
(preceded by the value of the
|
|
.Va PS4
|
|
variable subjected to parameter expansion and arithmetic expansion)
|
|
to standard error before it is executed.
|
|
Useful for debugging.
|
|
.It nolog
|
|
Another do-nothing option for
|
|
.Tn POSIX
|
|
compliance.
|
|
It only has a long name.
|
|
.El
|
|
.Pp
|
|
The
|
|
.Fl c
|
|
option causes the commands to be read from the
|
|
.Ar string
|
|
operand instead of from the standard input.
|
|
Keep in mind that this option only accepts a single string as its
|
|
argument, hence multi-word strings must be quoted.
|
|
.Pp
|
|
The
|
|
.Fl /+o
|
|
option takes as its only argument the long name of an option
|
|
to be enabled or disabled.
|
|
For example, the following two invocations of
|
|
.Nm
|
|
both enable the built-in
|
|
.Xr emacs 1
|
|
command line editor:
|
|
.Bd -literal -offset indent
|
|
set -E
|
|
set -o emacs
|
|
.Ed
|
|
.Pp
|
|
If used without an argument, the
|
|
.Fl o
|
|
option displays the current option settings in a human-readable format.
|
|
If
|
|
.Cm +o
|
|
is used without an argument, the current option settings are output
|
|
in a format suitable for re-input into the shell.
|
|
.Ss Lexical Structure
|
|
The shell reads input in terms of lines from a file and breaks
|
|
it up into words at whitespace (blanks and tabs), and at
|
|
certain sequences of
|
|
characters called
|
|
.Dq operators ,
|
|
which are special to the shell.
|
|
There are two types of operators: control operators and
|
|
redirection operators (their meaning is discussed later).
|
|
The following is a list of valid operators:
|
|
.Bl -tag -width indent
|
|
.It Control operators:
|
|
.Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact
|
|
.It Li & Ta Li && Ta Li \&( Ta Li \&) Ta Li \en
|
|
.It Li ;; Ta Li ;& Ta Li \&; Ta Li \&| Ta Li ||
|
|
.El
|
|
.It Redirection operators:
|
|
.Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact
|
|
.It Li < Ta Li > Ta Li << Ta Li >> Ta Li <>
|
|
.It Li <& Ta Li >& Ta Li <<- Ta Li >| Ta \&
|
|
.El
|
|
.El
|
|
.Pp
|
|
The character
|
|
.Ql #
|
|
introduces a comment if used at the beginning of a word.
|
|
The word starting with
|
|
.Ql #
|
|
and the rest of the line are ignored.
|
|
.Pp
|
|
.Tn ASCII
|
|
.Dv NUL
|
|
characters (character code 0) are not allowed in shell input.
|
|
.Ss Quoting
|
|
Quoting is used to remove the special meaning of certain characters
|
|
or words to the shell, such as operators, whitespace, keywords,
|
|
or alias names.
|
|
.Pp
|
|
There are four types of quoting: matched single quotes,
|
|
dollar-single quotes,
|
|
matched double quotes, and backslash.
|
|
.Bl -tag -width indent
|
|
.It Single Quotes
|
|
Enclosing characters in single quotes preserves the literal
|
|
meaning of all the characters (except single quotes, making
|
|
it impossible to put single-quotes in a single-quoted string).
|
|
.It Dollar-Single Quotes
|
|
Enclosing characters between
|
|
.Li $'
|
|
and
|
|
.Li '
|
|
preserves the literal meaning of all characters
|
|
except backslashes and single quotes.
|
|
A backslash introduces a C-style escape sequence:
|
|
.Bl -tag -width xUnnnnnnnn
|
|
.It \ea
|
|
Alert (ring the terminal bell)
|
|
.It \eb
|
|
Backspace
|
|
.It \ec Ns Ar c
|
|
The control character denoted by
|
|
.Li ^ Ns Ar c
|
|
in
|
|
.Xr stty 1 .
|
|
If
|
|
.Ar c
|
|
is a backslash, it must be doubled.
|
|
.It \ee
|
|
The ESC character
|
|
.Tn ( ASCII
|
|
0x1b)
|
|
.It \ef
|
|
Formfeed
|
|
.It \en
|
|
Newline
|
|
.It \er
|
|
Carriage return
|
|
.It \et
|
|
Horizontal tab
|
|
.It \ev
|
|
Vertical tab
|
|
.It \e\e
|
|
Literal backslash
|
|
.It \e\&'
|
|
Literal single-quote
|
|
.It \e\&"
|
|
Literal double-quote
|
|
.It \e Ns Ar nnn
|
|
The byte whose octal value is
|
|
.Ar nnn
|
|
(one to three digits)
|
|
.It \ex Ns Ar nn
|
|
The byte whose hexadecimal value is
|
|
.Ar nn
|
|
(one or more digits only the last two of which are used)
|
|
.It \eu Ns Ar nnnn
|
|
The Unicode code point
|
|
.Ar nnnn
|
|
(four hexadecimal digits)
|
|
.It \eU Ns Ar nnnnnnnn
|
|
The Unicode code point
|
|
.Ar nnnnnnnn
|
|
(eight hexadecimal digits)
|
|
.El
|
|
.Pp
|
|
The sequences for Unicode code points are currently only useful with
|
|
UTF-8 locales.
|
|
They reject code point 0 and UTF-16 surrogates.
|
|
.Pp
|
|
If an escape sequence would produce a byte with value 0,
|
|
that byte and the rest of the string until the matching single-quote
|
|
are ignored.
|
|
.Pp
|
|
Any other string starting with a backslash is an error.
|
|
.It Double Quotes
|
|
Enclosing characters within double quotes preserves the literal
|
|
meaning of all characters except dollar sign
|
|
.Pq Ql $ ,
|
|
backquote
|
|
.Pq Ql ` ,
|
|
and backslash
|
|
.Pq Ql \e .
|
|
The backslash inside double quotes is historically weird.
|
|
It remains literal unless it precedes the following characters,
|
|
which it serves to quote:
|
|
.Pp
|
|
.Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact
|
|
.It Li $ Ta Li ` Ta Li \&" Ta Li \e Ta Li \en
|
|
.El
|
|
.It Backslash
|
|
A backslash preserves the literal meaning of the following
|
|
character, with the exception of the newline character
|
|
.Pq Ql \en .
|
|
A backslash preceding a newline is treated as a line continuation.
|
|
.El
|
|
.Ss Keywords
|
|
Keywords or reserved words are words that have special meaning to the
|
|
shell and are recognized at the beginning of a line and
|
|
after a control operator.
|
|
The following are keywords:
|
|
.Bl -column "doneXX" "elifXX" "elseXX" "untilXX" "whileX" -offset center
|
|
.It Li \&! Ta { Ta } Ta Ic case Ta Ic do
|
|
.It Ic done Ta Ic elif Ta Ic else Ta Ic esac Ta Ic fi
|
|
.It Ic for Ta Ic if Ta Ic then Ta Ic until Ta Ic while
|
|
.El
|
|
.Ss Aliases
|
|
An alias is a name and corresponding value set using the
|
|
.Ic alias
|
|
built-in command.
|
|
Wherever the command word of a simple command may occur,
|
|
and after checking for keywords if a keyword may occur, the shell
|
|
checks the word to see if it matches an alias.
|
|
If it does, it replaces it in the input stream with its value.
|
|
For example, if there is an alias called
|
|
.Dq Li lf
|
|
with the value
|
|
.Dq Li "ls -F" ,
|
|
then the input
|
|
.Pp
|
|
.Dl "lf foobar"
|
|
.Pp
|
|
would become
|
|
.Pp
|
|
.Dl "ls -F foobar"
|
|
.Pp
|
|
Aliases are also recognized after an alias
|
|
whose value ends with a space or tab.
|
|
For example, if there is also an alias called
|
|
.Dq Li nohup
|
|
with the value
|
|
.Dq Li "nohup " ,
|
|
then the input
|
|
.Pp
|
|
.Dl "nohup lf foobar"
|
|
.Pp
|
|
would become
|
|
.Pp
|
|
.Dl "nohup ls -F foobar"
|
|
.Pp
|
|
Aliases provide a convenient way for naive users to
|
|
create shorthands for commands without having to learn how
|
|
to create functions with arguments.
|
|
Using aliases in scripts is discouraged
|
|
because the command that defines them must be executed
|
|
before the code that uses them is parsed.
|
|
This is fragile and not portable.
|
|
.Pp
|
|
An alias name may be escaped in a command line, so that it is not
|
|
replaced by its alias value, by using quoting characters within or
|
|
adjacent to the alias name.
|
|
This is most often done by prefixing
|
|
an alias name with a backslash to execute a function, built-in, or
|
|
normal program with the same name.
|
|
See the
|
|
.Sx Quoting
|
|
subsection.
|
|
.Ss Commands
|
|
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
|
|
.St -p1003.2
|
|
document).
|
|
Essentially though, a line is read and if
|
|
the first word of the line (or after a control operator)
|
|
is not a keyword, then the shell has recognized a
|
|
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
|
|
the following actions:
|
|
.Bl -enum
|
|
.It
|
|
Leading words of the form
|
|
.Dq Li name=value
|
|
are stripped off and assigned to the environment of
|
|
the simple command
|
|
(they do not affect expansions).
|
|
Redirection operators and
|
|
their arguments (as described below) are stripped
|
|
off and saved for processing.
|
|
.It
|
|
The remaining words are expanded as described in
|
|
the section called
|
|
.Sx Word Expansions ,
|
|
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 Li name=value
|
|
variable assignments recognized in 1) affect the
|
|
current shell.
|
|
.It
|
|
Redirections are performed as described in
|
|
the next section.
|
|
.El
|
|
.Ss Redirections
|
|
Redirections are used to change where a command reads its input
|
|
or sends its output.
|
|
In general, redirections open, close, or
|
|
duplicate an existing reference to a file.
|
|
The overall format
|
|
used for redirection is:
|
|
.Pp
|
|
.D1 Oo Ar n Oc Ar redir-op file
|
|
.Pp
|
|
The
|
|
.Ar redir-op
|
|
is one of the redirection operators mentioned
|
|
previously.
|
|
The following gives some examples of how these
|
|
operators can be used.
|
|
Note that stdin and stdout are commonly used abbreviations
|
|
for standard input and standard output respectively.
|
|
.Bl -tag -width "1234567890XX" -offset indent
|
|
.It Oo Ar n Oc Ns Li > Ar file
|
|
redirect stdout (or file descriptor
|
|
.Ar n )
|
|
to
|
|
.Ar file
|
|
.It Oo Ar n Oc Ns Li >| Ar file
|
|
same as above, but override the
|
|
.Fl C
|
|
option
|
|
.It Oo Ar n Oc Ns Li >> Ar file
|
|
append stdout (or file descriptor
|
|
.Ar n )
|
|
to
|
|
.Ar file
|
|
.It Oo Ar n Oc Ns Li < Ar file
|
|
redirect stdin (or file descriptor
|
|
.Ar n )
|
|
from
|
|
.Ar file
|
|
.It Oo Ar n Oc Ns Li <> Ar file
|
|
redirect stdin (or file descriptor
|
|
.Ar n )
|
|
to and from
|
|
.Ar file
|
|
.It Oo Ar n1 Oc Ns Li <& Ns Ar n2
|
|
duplicate stdin (or file descriptor
|
|
.Ar n1 )
|
|
from file descriptor
|
|
.Ar n2
|
|
.It Oo Ar n Oc Ns Li <&-
|
|
close stdin (or file descriptor
|
|
.Ar n )
|
|
.It Oo Ar n1 Oc Ns Li >& Ns Ar n2
|
|
duplicate stdout (or file descriptor
|
|
.Ar n1 )
|
|
to file descriptor
|
|
.Ar n2
|
|
.It Oo Ar n Oc Ns Li >&-
|
|
close stdout (or file descriptor
|
|
.Ar n )
|
|
.El
|
|
.Pp
|
|
The following redirection is often called a
|
|
.Dq here-document .
|
|
.Bd -unfilled -offset indent
|
|
.Oo Ar n Oc Ns Li << Ar delimiter
|
|
.Ar here-doc-text
|
|
.Ar ...
|
|
.Ar 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
|
|
.Ar n
|
|
if it is specified.
|
|
If the
|
|
.Ar delimiter
|
|
as specified on the initial line is quoted, then the
|
|
.Ar 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 Li <<-
|
|
instead of
|
|
.Dq Li << ,
|
|
then leading tabs
|
|
in the
|
|
.Ar here-doc-text
|
|
are stripped.
|
|
.Ss Search and Execution
|
|
There are three types of commands: shell functions,
|
|
built-in commands, and normal programs.
|
|
The command is searched for (by name) in that order.
|
|
The three types of commands are all executed in a different way.
|
|
.Pp
|
|
When a shell function is executed, all of the shell positional
|
|
parameters (except
|
|
.Li $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 built-in commands are executed internally to the shell, without
|
|
spawning a new process.
|
|
There are two kinds of built-in commands: regular and special.
|
|
Assignments before special builtins persist after they finish
|
|
executing and assignment errors, redirection errors and certain
|
|
operand errors cause a script to be aborted.
|
|
Special builtins cannot be overridden with a function.
|
|
Both regular and special builtins can affect the shell in ways
|
|
normal programs cannot.
|
|
.Pp
|
|
Otherwise, if the command name does not match a function
|
|
or built-in command, the command is searched for as a normal
|
|
program in the file system (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
|
|
.Dq "magic number"
|
|
whose
|
|
.Tn ASCII
|
|
representation is
|
|
.Dq Li #! ,
|
|
resulting in an
|
|
.Er ENOEXEC
|
|
return value from
|
|
.Xr execve 2 )
|
|
but appears to be a text file,
|
|
the shell will run a new instance of
|
|
.Nm
|
|
to interpret it.
|
|
.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
|
|
.Dq "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
|
|
built-in command by that name.
|
|
If a built-in 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 the
|
|
.Va PATH
|
|
variable
|
|
in turn for the command.
|
|
The value of the
|
|
.Va 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 built-in commands return exit codes, as does
|
|
an executed shell function.
|
|
.Pp
|
|
If a command is terminated by a signal, its exit status is greater than 128.
|
|
The signal name can be found by passing the exit status to
|
|
.Li kill -l .
|
|
.Pp
|
|
If there is no command word,
|
|
the exit status is the exit status of the last command substitution executed,
|
|
or zero if the command does not contain any command substitutions.
|
|
.Ss Complex Commands
|
|
Complex commands are combinations of simple commands
|
|
with control operators or keywords, 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,
|
|
or zero if no simple command was executed.
|
|
.Ss Pipelines
|
|
A pipeline is a sequence of one or more commands separated
|
|
by the control operator
|
|
.Ql \&| .
|
|
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:
|
|
.Pp
|
|
.D1 Oo Li \&! Oc Ar command1 Op Li \&| Ar command2 ...
|
|
.Pp
|
|
The standard output of
|
|
.Ar command1
|
|
is connected to the standard input of
|
|
.Ar 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
|
|
Note that unlike some other shells,
|
|
.Nm
|
|
executes each process in a pipeline with more than one command
|
|
in a subshell environment and as a child of the
|
|
.Nm
|
|
process.
|
|
.Pp
|
|
If the pipeline is not in the background (discussed later),
|
|
the shell waits for all commands to complete.
|
|
.Pp
|
|
If the keyword
|
|
.Ic !\&
|
|
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:
|
|
.Pp
|
|
.Dl "command1 2>&1 | command2"
|
|
.Pp
|
|
sends both the standard output and standard error of
|
|
.Ar command1
|
|
to the standard input of
|
|
.Ar command2 .
|
|
.Pp
|
|
A
|
|
.Ql \&;
|
|
or newline terminator causes the preceding
|
|
AND-OR-list
|
|
(described below in the section called
|
|
.Sx Short-Circuit List Operators )
|
|
to be executed sequentially;
|
|
an
|
|
.Ql &
|
|
causes asynchronous execution of the preceding AND-OR-list.
|
|
.Ss Background Commands (&)
|
|
If a command is terminated by the control operator ampersand
|
|
.Pq Ql & ,
|
|
the shell executes the command in a subshell environment (see
|
|
.Sx Grouping Commands Together
|
|
below) and asynchronously;
|
|
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:
|
|
.Pp
|
|
.D1 Ar command1 Li & Op Ar command2 Li & Ar ...
|
|
.Pp
|
|
If the shell is not interactive, the standard input of an
|
|
asynchronous command is set to
|
|
.Pa /dev/null .
|
|
.Pp
|
|
The exit status is zero.
|
|
.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 proceeds onto the next command;
|
|
otherwise it waits for the command to terminate before
|
|
proceeding to the next one.
|
|
.Ss Short-Circuit List Operators
|
|
.Dq Li &&
|
|
and
|
|
.Dq Li ||
|
|
are AND-OR list operators.
|
|
.Dq Li &&
|
|
executes the first command, and then executes the second command
|
|
if the exit status of the first command is zero.
|
|
.Dq Li ||
|
|
is similar, but executes the second command if the exit
|
|
status of the first command is nonzero.
|
|
.Dq Li &&
|
|
and
|
|
.Dq Li ||
|
|
both have the same priority.
|
|
.Ss Flow-Control Constructs (if, while, for, case)
|
|
The syntax of the
|
|
.Ic if
|
|
command is:
|
|
.Bd -unfilled -offset indent -compact
|
|
.Ic if Ar list
|
|
.Ic then Ar list
|
|
.Oo Ic elif Ar list
|
|
.Ic then Ar list Oc Ar ...
|
|
.Op Ic else Ar list
|
|
.Ic fi
|
|
.Ed
|
|
.Pp
|
|
The exit status is that of selected
|
|
.Ic then
|
|
or
|
|
.Ic else
|
|
list,
|
|
or zero if no list was selected.
|
|
.Pp
|
|
The syntax of the
|
|
.Ic while
|
|
command is:
|
|
.Bd -unfilled -offset indent -compact
|
|
.Ic while Ar list
|
|
.Ic do Ar list
|
|
.Ic done
|
|
.Ed
|
|
.Pp
|
|
The two lists are executed repeatedly while the exit status of the
|
|
first list is zero.
|
|
The
|
|
.Ic until
|
|
command is similar, but has the word
|
|
.Ic until
|
|
in place of
|
|
.Ic while ,
|
|
which causes it to
|
|
repeat until the exit status of the first list is zero.
|
|
.Pp
|
|
The exit status is that of the last execution of the second list,
|
|
or zero if it was never executed.
|
|
.Pp
|
|
The syntax of the
|
|
.Ic for
|
|
command is:
|
|
.Bd -unfilled -offset indent -compact
|
|
.Ic for Ar variable Op Ic in Ar word ...
|
|
.Ic do Ar list
|
|
.Ic done
|
|
.Ed
|
|
.Pp
|
|
If
|
|
.Ic in
|
|
and the following words are omitted,
|
|
.Ic in Li \&"$@\&"
|
|
is used instead.
|
|
The words are expanded, and then the list is executed
|
|
repeatedly with the variable set to each word in turn.
|
|
The
|
|
.Ic do
|
|
and
|
|
.Ic done
|
|
commands may be replaced with
|
|
.Ql {
|
|
and
|
|
.Ql } .
|
|
.Pp
|
|
The syntax of the
|
|
.Ic break
|
|
and
|
|
.Ic continue
|
|
commands is:
|
|
.D1 Ic break Op Ar num
|
|
.D1 Ic continue Op Ar num
|
|
.Pp
|
|
The
|
|
.Ic break
|
|
command terminates the
|
|
.Ar num
|
|
innermost
|
|
.Ic for
|
|
or
|
|
.Ic while
|
|
loops.
|
|
The
|
|
.Ic continue
|
|
command continues with the next iteration of the innermost loop.
|
|
These are implemented as special built-in commands.
|
|
.Pp
|
|
The syntax of the
|
|
.Ic case
|
|
command is:
|
|
.Bd -unfilled -offset indent -compact
|
|
.Ic case Ar word Ic in
|
|
.Ar pattern Ns Li ) Ar list Li ;;
|
|
.Ar ...
|
|
.Ic esac
|
|
.Ed
|
|
.Pp
|
|
The pattern can actually be one or more patterns
|
|
(see
|
|
.Sx Shell Patterns
|
|
described later),
|
|
separated by
|
|
.Ql \&|
|
|
characters.
|
|
Tilde expansion, parameter expansion, command substitution,
|
|
arithmetic expansion and quote removal are applied to the word.
|
|
Then, each pattern is expanded in turn using tilde expansion,
|
|
parameter expansion, command substitution and arithmetic expansion and
|
|
the expanded form of the word is checked against it.
|
|
If a match is found, the corresponding list is executed.
|
|
If the selected list is terminated by the control operator
|
|
.Ql ;&
|
|
instead of
|
|
.Ql ;; ,
|
|
execution continues with the next list,
|
|
continuing until a list terminated with
|
|
.Ql ;;
|
|
or the end of the
|
|
.Ic case
|
|
command.
|
|
.Ss Grouping Commands Together
|
|
Commands may be grouped by writing either
|
|
.Pp
|
|
.D1 Li \&( Ns Ar list Ns Li \%)
|
|
.Pp
|
|
or
|
|
.Pp
|
|
.D1 Li { Ar list Ns Li \&; }
|
|
.Pp
|
|
The first form executes the commands in a subshell environment.
|
|
A subshell environment has its own copy of:
|
|
.Bl -enum
|
|
.It
|
|
The current working directory as set by
|
|
.Ic cd .
|
|
.It
|
|
The file creation mask as set by
|
|
.Ic umask .
|
|
.It
|
|
Resource limits as set by
|
|
.Ic ulimit .
|
|
.It
|
|
References to open files.
|
|
.It
|
|
Traps as set by
|
|
.Ic trap .
|
|
.It
|
|
Known jobs.
|
|
.It
|
|
Positional parameters and variables.
|
|
.It
|
|
Shell options.
|
|
.It
|
|
Shell functions.
|
|
.It
|
|
Shell aliases.
|
|
.El
|
|
.Pp
|
|
These are copied from the parent shell environment,
|
|
except that trapped (but not ignored) signals are reset to the default action
|
|
and known jobs are cleared.
|
|
Any changes do not affect the parent shell environment.
|
|
.Pp
|
|
A subshell environment may be implemented as a child process or differently.
|
|
If job control is enabled in an interactive shell,
|
|
commands grouped in parentheses can be suspended and continued as a unit.
|
|
.Pp
|
|
For compatibility with other shells,
|
|
two open parentheses in sequence should be separated by whitespace.
|
|
.Pp
|
|
The second form never forks another shell,
|
|
so it is slightly more efficient.
|
|
Grouping commands together this way allows the user 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
|
|
.Pp
|
|
.D1 Ar name Li \&( \&) Ar command
|
|
.Pp
|
|
A function definition is an executable statement; when
|
|
executed it installs a function named
|
|
.Ar name
|
|
and returns an
|
|
exit status of zero.
|
|
The
|
|
.Ar command
|
|
is normally a list
|
|
enclosed between
|
|
.Ql {
|
|
and
|
|
.Ql } .
|
|
.Pp
|
|
Variables may be declared to be local to a function by
|
|
using the
|
|
.Ic local
|
|
command.
|
|
This should appear as the first statement of a function,
|
|
and the syntax is:
|
|
.Pp
|
|
.D1 Ic local Oo Ar variable ... Oc Op Fl
|
|
.Pp
|
|
The
|
|
.Ic local
|
|
command is implemented as a built-in command.
|
|
The exit status is zero
|
|
unless the command is not in a function or a variable name is invalid.
|
|
.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 the variable
|
|
.Va x
|
|
is made local to function
|
|
.Em f ,
|
|
which then calls function
|
|
.Em g ,
|
|
references to the variable
|
|
.Va x
|
|
made inside
|
|
.Em g
|
|
will refer to the variable
|
|
.Va x
|
|
declared inside
|
|
.Em f ,
|
|
not to the global variable named
|
|
.Va x .
|
|
.Pp
|
|
The only special parameter that can be made local is
|
|
.Ql - .
|
|
Making
|
|
.Ql -
|
|
local causes any shell options
|
|
(including those that only have long names)
|
|
that are
|
|
changed via the
|
|
.Ic set
|
|
command inside the function to be
|
|
restored to their original values when the function
|
|
returns.
|
|
.Pp
|
|
The syntax of the
|
|
.Ic return
|
|
command is
|
|
.Pp
|
|
.D1 Ic return Op Ar exitstatus
|
|
.Pp
|
|
It terminates the current executional scope, returning from the closest
|
|
nested function or sourced script;
|
|
if no function or sourced script is being executed,
|
|
it exits the shell instance.
|
|
The
|
|
.Ic return
|
|
command is implemented as a special built-in command.
|
|
.Ss Variables and Parameters
|
|
The shell maintains a set of parameters.
|
|
A parameter
|
|
denoted by a name
|
|
(consisting solely
|
|
of alphabetics, numerics, and underscores,
|
|
and starting with an alphabetic or an underscore)
|
|
is called a variable.
|
|
When starting up,
|
|
the shell turns all environment variables with valid names into shell
|
|
variables.
|
|
New variables can be set using the form
|
|
.Pp
|
|
.D1 Ar name Ns = Ns Ar value
|
|
.Pp
|
|
A parameter can also be denoted by a number
|
|
or a special character as explained below.
|
|
.Pp
|
|
Assignments are expanded differently from other words:
|
|
tilde expansion is also performed after the equals sign and after any colon
|
|
and usernames are also terminated by colons,
|
|
and field splitting and pathname expansion are not performed.
|
|
.Pp
|
|
This special expansion applies not only to assignments that form a simple
|
|
command by themselves or precede a command word,
|
|
but also to words passed to the
|
|
.Ic export ,
|
|
.Ic local
|
|
or
|
|
.Ic readonly
|
|
built-in commands that have this form.
|
|
For this, the builtin's name must be literal
|
|
(not the result of an expansion)
|
|
and may optionally be preceded by one or more literal instances of
|
|
.Ic command
|
|
without options.
|
|
.Ss Positional Parameters
|
|
A positional parameter is a parameter denoted by a number greater than zero.
|
|
The shell sets these initially to the values of its command line
|
|
arguments that follow the name of the shell script.
|
|
The
|
|
.Ic set
|
|
built-in command can also be used to set or reset them.
|
|
.Ss Special Parameters
|
|
Special parameters are parameters denoted by a single special character
|
|
or the digit zero.
|
|
They are shown in the following list, exactly as they would appear in input
|
|
typed by the user or in the source of a shell script.
|
|
.Bl -hang
|
|
.It Li $*
|
|
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
|
|
.Va IFS
|
|
variable,
|
|
or by a space if
|
|
.Va IFS
|
|
is unset.
|
|
.It Li $@
|
|
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
|
|
.Li @
|
|
generates zero arguments, even when
|
|
.Li @
|
|
is double-quoted.
|
|
What this basically means, for example, is
|
|
if
|
|
.Li $1
|
|
is
|
|
.Dq Li abc
|
|
and
|
|
.Li $2
|
|
is
|
|
.Dq Li "def ghi" ,
|
|
then
|
|
.Li \&"$@\&"
|
|
expands to
|
|
the two arguments:
|
|
.Bd -literal -offset indent
|
|
"abc" "def ghi"
|
|
.Ed
|
|
.It Li $#
|
|
Expands to the number of positional parameters.
|
|
.It Li $?
|
|
Expands to the exit status of the most recent pipeline.
|
|
.It Li $-
|
|
(hyphen) Expands to the current option flags (the single-letter
|
|
option names concatenated into a string) as specified on
|
|
invocation, by the
|
|
.Ic set
|
|
built-in command, or implicitly
|
|
by the shell.
|
|
.It Li $$
|
|
Expands to the process ID of the invoked shell.
|
|
A subshell
|
|
retains the same value of
|
|
.Va $
|
|
as its parent.
|
|
.It Li $!
|
|
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.
|
|
If this parameter is referenced, the shell will remember
|
|
the process ID and its exit status until the
|
|
.Ic wait
|
|
built-in command reports completion of the process.
|
|
.It Li $0
|
|
(zero) Expands to the name of the shell script if passed on the command line,
|
|
the
|
|
.Ar name
|
|
operand if given (with
|
|
.Fl c )
|
|
or otherwise argument 0 passed to the shell.
|
|
.El
|
|
.Ss Special Variables
|
|
The following variables are set by the shell or
|
|
have special meaning to it:
|
|
.Bl -tag -width ".Va HISTSIZE"
|
|
.It Va CDPATH
|
|
The search path used with the
|
|
.Ic cd
|
|
built-in.
|
|
.It Va EDITOR
|
|
The fallback editor used with the
|
|
.Ic fc
|
|
built-in.
|
|
If not set, the default editor is
|
|
.Xr ed 1 .
|
|
.It Va FCEDIT
|
|
The default editor used with the
|
|
.Ic fc
|
|
built-in.
|
|
.It Va HISTSIZE
|
|
The number of previous commands that are accessible.
|
|
.It Va HOME
|
|
The user's home directory,
|
|
used in tilde expansion and as a default directory for the
|
|
.Ic cd
|
|
built-in.
|
|
.It Va IFS
|
|
Input Field Separators.
|
|
The default value is
|
|
.Aq space ,
|
|
.Aq tab ,
|
|
and
|
|
.Aq newline
|
|
in that order.
|
|
This default also applies if
|
|
.Va IFS
|
|
is unset, but not if it is set to the empty string.
|
|
See the
|
|
.Sx White Space Splitting
|
|
section for more details.
|
|
.It Va LINENO
|
|
The current line number in the script or function.
|
|
.It Va MAIL
|
|
The name of a mail file, that will be checked for the arrival of new
|
|
mail.
|
|
Overridden by
|
|
.Va MAILPATH .
|
|
.It Va MAILPATH
|
|
A colon
|
|
.Pq Ql \&:
|
|
separated list of file names, for the shell to check for incoming
|
|
mail.
|
|
This variable overrides the
|
|
.Va MAIL
|
|
setting.
|
|
There is a maximum of 10 mailboxes that can be monitored at once.
|
|
.It Va OPTIND
|
|
The index of the next argument to be processed by
|
|
.Ic getopts .
|
|
This is initialized to 1 at startup.
|
|
.It Va PATH
|
|
The default search path for executables.
|
|
See the
|
|
.Sx Path Search
|
|
section for details.
|
|
.It Va PPID
|
|
The parent process ID of the invoked shell.
|
|
This is set at startup
|
|
unless this variable is in the environment.
|
|
A later change of parent process ID is not reflected.
|
|
A subshell retains the same value of
|
|
.Va PPID .
|
|
.It Va PS1
|
|
The primary prompt string, which defaults to
|
|
.Dq Li "$ " ,
|
|
unless you are the superuser, in which case it defaults to
|
|
.Dq Li "# " .
|
|
.Va PS1
|
|
may include any of the following formatting sequences,
|
|
which are replaced by the given information:
|
|
.Bl -tag -width indent
|
|
.It Li \eH
|
|
This system's fully-qualified hostname (FQDN).
|
|
.It Li \eh
|
|
This system's hostname.
|
|
.It Li \eW
|
|
The final component of the current working directory.
|
|
.It Li \ew
|
|
The entire path of the current working directory.
|
|
.It Li \e$
|
|
Superuser status.
|
|
.Dq Li "$ "
|
|
for normal users and
|
|
.Dq Li "# "
|
|
for superusers.
|
|
.It Li \e\e
|
|
A literal backslash.
|
|
.El
|
|
.It Va PS2
|
|
The secondary prompt string, which defaults to
|
|
.Dq Li "> " .
|
|
.Va PS2
|
|
may include any of the formatting sequences from
|
|
.Va PS1 .
|
|
.It Va PS4
|
|
The prefix for the trace output (if
|
|
.Fl x
|
|
is active).
|
|
The default is
|
|
.Dq Li "+ " .
|
|
.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
|
|
.Va @
|
|
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
|
|
.Va IFS
|
|
variable is null.
|
|
.It
|
|
Pathname Expansion (unless the
|
|
.Fl f
|
|
option is in effect).
|
|
.It
|
|
Quote Removal.
|
|
.El
|
|
.Pp
|
|
The
|
|
.Ql $
|
|
character is used to introduce parameter expansion, command
|
|
substitution, or arithmetic expansion.
|
|
.Ss Tilde Expansion (substituting a user's home directory)
|
|
A word beginning with an unquoted tilde character
|
|
.Pq Ql ~
|
|
is
|
|
subjected to tilde expansion.
|
|
All the characters up to a slash
|
|
.Pq Ql /
|
|
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
|
|
.Pa ~/foobar ) ,
|
|
the tilde is replaced with the value of the
|
|
.Va HOME
|
|
variable (the current user's home directory).
|
|
.Ss Parameter Expansion
|
|
The format for parameter expansion is as follows:
|
|
.Pp
|
|
.D1 Li ${ Ns Ar expression Ns Li }
|
|
.Pp
|
|
where
|
|
.Ar expression
|
|
consists of all characters until the matching
|
|
.Ql } .
|
|
Any
|
|
.Ql }
|
|
escaped by a backslash or within a single-quoted or double-quoted
|
|
string, and characters in
|
|
embedded arithmetic expansions, command substitutions, and variable
|
|
expansions, are not examined in determining the matching
|
|
.Ql } .
|
|
If the variants with
|
|
.Ql + ,
|
|
.Ql - ,
|
|
.Ql =
|
|
or
|
|
.Ql ?\&
|
|
occur within a double-quoted string,
|
|
as an extension there may be unquoted parts
|
|
(via double-quotes inside the expansion);
|
|
.Ql }
|
|
within such parts are also not examined in determining the matching
|
|
.Ql } .
|
|
.Pp
|
|
The simplest form for parameter expansion is:
|
|
.Pp
|
|
.D1 Li ${ Ns Ar parameter Ns Li }
|
|
.Pp
|
|
The value, if any, of
|
|
.Ar 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
|
|
Field splitting is not performed on the results of the
|
|
expansion, with the exception of the special parameter
|
|
.Va @ .
|
|
.It
|
|
Pathname expansion is not performed on the results of the
|
|
expansion.
|
|
.El
|
|
.Pp
|
|
In addition, a parameter expansion can be modified by using one of the
|
|
following formats.
|
|
.Bl -tag -width indent
|
|
.It Li ${ Ns Ar parameter Ns Li :- Ns Ar word Ns Li }
|
|
Use Default Values.
|
|
If
|
|
.Ar parameter
|
|
is unset or null, the expansion of
|
|
.Ar word
|
|
is substituted; otherwise, the value of
|
|
.Ar parameter
|
|
is substituted.
|
|
.It Li ${ Ns Ar parameter Ns Li := Ns Ar word Ns Li }
|
|
Assign Default Values.
|
|
If
|
|
.Ar parameter
|
|
is unset or null, the expansion of
|
|
.Ar word
|
|
is assigned to
|
|
.Ar parameter .
|
|
In all cases, the
|
|
final value of
|
|
.Ar parameter
|
|
is substituted.
|
|
Quoting inside
|
|
.Ar word
|
|
does not prevent field splitting or pathname expansion.
|
|
Only variables, not positional
|
|
parameters or special parameters, can be
|
|
assigned in this way.
|
|
.It Li ${ Ns Ar parameter Ns Li :? Ns Oo Ar word Oc Ns Li }
|
|
Indicate Error if Null or Unset.
|
|
If
|
|
.Ar parameter
|
|
is unset or null, the expansion of
|
|
.Ar word
|
|
(or a message indicating it is unset if
|
|
.Ar word
|
|
is omitted) is written to standard
|
|
error and the shell exits with a nonzero
|
|
exit status.
|
|
Otherwise, the value of
|
|
.Ar parameter
|
|
is substituted.
|
|
An
|
|
interactive shell need not exit.
|
|
.It Li ${ Ns Ar parameter Ns Li :+ Ns Ar word Ns Li }
|
|
Use Alternate Value.
|
|
If
|
|
.Ar parameter
|
|
is unset or null, null is substituted;
|
|
otherwise, the expansion of
|
|
.Ar word
|
|
is substituted.
|
|
.El
|
|
.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.
|
|
.Pp
|
|
The
|
|
.Ar word
|
|
inherits the type of quoting
|
|
(unquoted, double-quoted or here-document)
|
|
from the surroundings,
|
|
with the exception that a backslash that quotes a closing brace is removed
|
|
during quote removal.
|
|
.Bl -tag -width indent
|
|
.It Li ${# Ns Ar parameter Ns Li }
|
|
String Length.
|
|
The length in characters of
|
|
the value of
|
|
.Ar parameter .
|
|
.El
|
|
.Pp
|
|
The following four varieties of parameter expansion provide for substring
|
|
processing.
|
|
In each case, pattern matching notation
|
|
(see
|
|
.Sx Shell Patterns ) ,
|
|
rather than regular expression notation,
|
|
is used to evaluate the patterns.
|
|
If parameter is one of the special parameters
|
|
.Va *
|
|
or
|
|
.Va @ ,
|
|
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.
|
|
.Bl -tag -width indent
|
|
.It Li ${ Ns Ar parameter Ns Li % Ns Ar word Ns Li }
|
|
Remove Smallest Suffix Pattern.
|
|
The
|
|
.Ar word
|
|
is expanded to produce a pattern.
|
|
The
|
|
parameter expansion then results in
|
|
.Ar parameter ,
|
|
with the smallest portion of the
|
|
suffix matched by the pattern deleted.
|
|
.It Li ${ Ns Ar parameter Ns Li %% Ns Ar word Ns Li }
|
|
Remove Largest Suffix Pattern.
|
|
The
|
|
.Ar word
|
|
is expanded to produce a pattern.
|
|
The
|
|
parameter expansion then results in
|
|
.Ar parameter ,
|
|
with the largest portion of the
|
|
suffix matched by the pattern deleted.
|
|
.It Li ${ Ns Ar parameter Ns Li # Ns Ar word Ns Li }
|
|
Remove Smallest Prefix Pattern.
|
|
The
|
|
.Ar word
|
|
is expanded to produce a pattern.
|
|
The
|
|
parameter expansion then results in
|
|
.Ar parameter ,
|
|
with the smallest portion of the
|
|
prefix matched by the pattern deleted.
|
|
.It Li ${ Ns Ar parameter Ns Li ## Ns Ar word Ns Li }
|
|
Remove Largest Prefix Pattern.
|
|
The
|
|
.Ar word
|
|
is expanded to produce a pattern.
|
|
The
|
|
parameter expansion then results in
|
|
.Ar 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:
|
|
.Pp
|
|
.D1 Li $( Ns Ar command Ns Li )\&
|
|
.Pp
|
|
or the backquoted version:
|
|
.Pp
|
|
.D1 Li ` Ns Ar command Ns Li `
|
|
.Pp
|
|
The shell expands the command substitution by executing command
|
|
and replacing the command substitution
|
|
with the standard output of the command,
|
|
removing sequences of one or more newlines at the end of the substitution.
|
|
Embedded newlines before the end of the output are not removed;
|
|
however, during field splitting, they may be translated into spaces
|
|
depending on the value of
|
|
.Va IFS
|
|
and the quoting that is in effect.
|
|
The command is executed in a subshell environment,
|
|
except that the built-in commands
|
|
.Ic jobid ,
|
|
.Ic jobs ,
|
|
and
|
|
.Ic trap
|
|
return information about the parent shell environment
|
|
and
|
|
.Ic times
|
|
returns information about the same process
|
|
if they are the only command in a command substitution.
|
|
.Pp
|
|
If a command substitution of the
|
|
.Li $(
|
|
form begins with a subshell,
|
|
the
|
|
.Li $(
|
|
and
|
|
.Li (\&
|
|
must be separated by whitespace
|
|
to avoid ambiguity with arithmetic expansion.
|
|
.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:
|
|
.Pp
|
|
.D1 Li $(( Ns Ar expression Ns Li ))
|
|
.Pp
|
|
The
|
|
.Ar 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
|
|
.Ar expression
|
|
for parameter expansion,
|
|
command substitution,
|
|
arithmetic expansion
|
|
and quote removal.
|
|
.Pp
|
|
The allowed expressions are a subset of C expressions,
|
|
summarized below.
|
|
.Bl -tag -width "Variables" -offset indent
|
|
.It Values
|
|
All values are of type
|
|
.Ft intmax_t .
|
|
.It Constants
|
|
Decimal, octal (starting with
|
|
.Li 0 )
|
|
and hexadecimal (starting with
|
|
.Li 0x )
|
|
integer constants.
|
|
.It Variables
|
|
Shell variables can be read and written
|
|
and contain integer constants.
|
|
.It Unary operators
|
|
.Li "! ~ + -"
|
|
.It Binary operators
|
|
.Li "* / % + - << >> < <= > >= == != & ^ | && ||"
|
|
.It Assignment operators
|
|
.Li "= += -= *= /= %= <<= >>= &= ^= |="
|
|
.It Conditional operator
|
|
.Li "? :"
|
|
.El
|
|
.Pp
|
|
The result of the expression is substituted in decimal.
|
|
.Ss White Space Splitting (Field Splitting)
|
|
In certain contexts,
|
|
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
|
|
Characters in
|
|
.Va IFS
|
|
that are whitespace
|
|
.Po
|
|
.Aq space ,
|
|
.Aq tab ,
|
|
and
|
|
.Aq newline
|
|
.Pc
|
|
are treated differently from other characters in
|
|
.Va IFS .
|
|
.Pp
|
|
Whitespace in
|
|
.Va IFS
|
|
at the beginning or end of a word is discarded.
|
|
.Pp
|
|
Subsequently, a field is delimited by either
|
|
.Bl -enum
|
|
.It
|
|
a non-whitespace character in
|
|
.Va IFS
|
|
with any whitespace in
|
|
.Va IFS
|
|
surrounding it, or
|
|
.It
|
|
one or more whitespace characters in
|
|
.Va IFS .
|
|
.El
|
|
.Pp
|
|
If a word ends with a non-whitespace character in
|
|
.Va IFS ,
|
|
there is no empty field after this character.
|
|
.Pp
|
|
If no field is delimited, the word is discarded.
|
|
In particular, if a word consists solely of an unquoted substitution
|
|
and the result of the substitution is null,
|
|
it is removed by field splitting even if
|
|
.Va IFS
|
|
is null.
|
|
.Ss Pathname Expansion (File Name Generation)
|
|
Unless the
|
|
.Fl f
|
|
option 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
|
|
Pathname Expansion,
|
|
the four varieties of parameter expansion for substring processing and the
|
|
.Ic case
|
|
command.
|
|
.Ss Shell Patterns
|
|
A pattern consists of normal characters, which match themselves,
|
|
and meta-characters.
|
|
The meta-characters are
|
|
.Ql * ,
|
|
.Ql \&? ,
|
|
and
|
|
.Ql \&[ .
|
|
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
|
|
.Pq Ql *
|
|
matches any string of characters.
|
|
A question mark
|
|
.Pq Ql \&?
|
|
matches any single character.
|
|
A left bracket
|
|
.Pq Ql \&[
|
|
introduces a character class.
|
|
The end of the character class is indicated by a
|
|
.Ql \&] ;
|
|
if the
|
|
.Ql \&]
|
|
is missing then the
|
|
.Ql \&[
|
|
matches a
|
|
.Ql \&[
|
|
rather than introducing a character class.
|
|
A character class matches any of the characters between the square brackets.
|
|
A locale-dependent range of characters may be specified using a minus sign.
|
|
A named class of characters (see
|
|
.Xr wctype 3 )
|
|
may be specified by surrounding the name with
|
|
.Ql \&[:
|
|
and
|
|
.Ql :\&] .
|
|
For example,
|
|
.Ql \&[\&[:alpha:\&]\&]
|
|
is a shell pattern that matches a single letter.
|
|
The character class may be complemented by making an exclamation point
|
|
.Pq Ql !\&
|
|
the first character of the character class.
|
|
A caret
|
|
.Pq Ql ^
|
|
has the same effect but is non-standard.
|
|
.Pp
|
|
To include a
|
|
.Ql \&]
|
|
in a character class, make it the first character listed
|
|
(after the
|
|
.Ql \&!
|
|
or
|
|
.Ql ^ ,
|
|
if any).
|
|
To include a
|
|
.Ql - ,
|
|
make it the first or last character listed.
|
|
.Ss Built-in Commands
|
|
This section lists the built-in commands.
|
|
.Bl -tag -width indent
|
|
.It Ic \&:
|
|
A null command that returns a 0 (true) exit value.
|
|
.It Ic \&. Ar file
|
|
The commands in the specified file are read and executed by the shell.
|
|
The
|
|
.Ic return
|
|
command may be used to return to the
|
|
.Ic \&.
|
|
command's caller.
|
|
If
|
|
.Ar file
|
|
contains any
|
|
.Ql /
|
|
characters, it is used as is.
|
|
Otherwise, the shell searches the
|
|
.Va PATH
|
|
for the file.
|
|
If it is not found in the
|
|
.Va PATH ,
|
|
it is sought in the current working directory.
|
|
.It Ic \&[
|
|
A built-in equivalent of
|
|
.Xr test 1 .
|
|
.It Ic alias Oo Ar name Ns Oo = Ns Ar string Oc ... Oc
|
|
If
|
|
.Ar name Ns = Ns Ar string
|
|
is specified, the shell defines the alias
|
|
.Ar name
|
|
with value
|
|
.Ar string .
|
|
If just
|
|
.Ar name
|
|
is specified, the value of the alias
|
|
.Ar name
|
|
is printed.
|
|
With no arguments, the
|
|
.Ic alias
|
|
built-in command prints the names and values of all defined aliases
|
|
(see
|
|
.Ic unalias ) .
|
|
Alias values are written with appropriate quoting so that they are
|
|
suitable for re-input to the shell.
|
|
Also see the
|
|
.Sx Aliases
|
|
subsection.
|
|
.It Ic bg Op Ar job ...
|
|
Continue the specified jobs
|
|
(or the current job if no jobs are given)
|
|
in the background.
|
|
.It Ic bind Oo Fl aeklrsv Oc Oo Ar key Oo Ar command Oc Oc
|
|
List or alter key bindings for the line editor.
|
|
This command is documented in
|
|
.Xr editrc 5 .
|
|
.It Ic break Op Ar num
|
|
See the
|
|
.Sx Flow-Control Constructs
|
|
subsection.
|
|
.It Ic builtin Ar cmd Op Ar arg ...
|
|
Execute the specified built-in command,
|
|
.Ar cmd .
|
|
This is useful when the user wishes to override a shell function
|
|
with the same name as a built-in command.
|
|
.It Ic cd Oo Fl L | P Oc Oo Fl e Oc Op Ar directory
|
|
.It Ic cd Fl
|
|
Switch to the specified
|
|
.Ar directory ,
|
|
to the directory specified in the
|
|
.Va HOME
|
|
environment variable if no
|
|
.Ar directory
|
|
is specified or
|
|
to the directory specified in the
|
|
.Va OLDPWD
|
|
environment variable if
|
|
.Ar directory
|
|
is
|
|
.Fl .
|
|
If
|
|
.Ar directory
|
|
does not begin with
|
|
.Pa / , \&. ,
|
|
or
|
|
.Pa .. ,
|
|
then the directories listed in the
|
|
.Va CDPATH
|
|
variable will be
|
|
searched for the specified
|
|
.Ar directory .
|
|
If
|
|
.Va CDPATH
|
|
is unset, the current directory is searched.
|
|
The format of
|
|
.Va CDPATH
|
|
is the same as that of
|
|
.Va PATH .
|
|
In an interactive shell,
|
|
the
|
|
.Ic cd
|
|
command will print out the name of the directory
|
|
that it actually switched to
|
|
if the
|
|
.Va CDPATH
|
|
mechanism was used or if
|
|
.Ar directory
|
|
was
|
|
.Fl .
|
|
.Pp
|
|
If the
|
|
.Fl P
|
|
option is specified,
|
|
.Pa ..
|
|
is handled physically and symbolic links are resolved before
|
|
.Pa ..
|
|
components are processed.
|
|
If the
|
|
.Fl L
|
|
option is specified,
|
|
.Pa ..
|
|
is handled logically.
|
|
This is the default.
|
|
.Pp
|
|
The
|
|
.Fl e
|
|
option causes
|
|
.Ic cd
|
|
to return exit status 1 if the full pathname of the new directory
|
|
cannot be determined reliably or at all.
|
|
Normally this is not considered an error,
|
|
although a warning is printed.
|
|
.It Ic chdir
|
|
A synonym for the
|
|
.Ic cd
|
|
built-in command.
|
|
.It Ic command Oo Fl p Oc Op Ar utility Op Ar argument ...
|
|
.It Ic command Oo Fl p Oc Fl v Ar utility
|
|
.It Ic command Oo Fl p Oc Fl V Ar utility
|
|
The first form of invocation executes the specified
|
|
.Ar utility ,
|
|
ignoring shell functions in the search.
|
|
If
|
|
.Ar utility
|
|
is a special builtin,
|
|
it is executed as if it were a regular builtin.
|
|
.Pp
|
|
If the
|
|
.Fl p
|
|
option is specified, the command search is performed using a
|
|
default value of
|
|
.Va PATH
|
|
that is guaranteed to find all of the standard utilities.
|
|
.Pp
|
|
If the
|
|
.Fl v
|
|
option is specified,
|
|
.Ar utility
|
|
is not executed but a description of its interpretation by the shell is
|
|
printed.
|
|
For ordinary commands the output is the path name; for shell built-in
|
|
commands, shell functions and keywords only the name is written.
|
|
Aliases are printed as
|
|
.Dq Ic alias Ar name Ns = Ns Ar value .
|
|
.Pp
|
|
The
|
|
.Fl V
|
|
option is identical to
|
|
.Fl v
|
|
except for the output.
|
|
It prints
|
|
.Dq Ar utility Ic is Ar description
|
|
where
|
|
.Ar description
|
|
is either
|
|
the path name to
|
|
.Ar utility ,
|
|
a special shell builtin,
|
|
a shell builtin,
|
|
a shell function,
|
|
a shell keyword
|
|
or
|
|
an alias for
|
|
.Ar value .
|
|
.It Ic continue Op Ar num
|
|
See the
|
|
.Sx Flow-Control Constructs
|
|
subsection.
|
|
.It Ic echo Oo Fl e | n Oc Op Ar string ...
|
|
Print a space-separated list of the arguments to the standard output
|
|
and append a newline character.
|
|
.Bl -tag -width indent
|
|
.It Fl n
|
|
Suppress the output of the trailing newline.
|
|
.It Fl e
|
|
Process C-style backslash escape sequences.
|
|
The
|
|
.Ic echo
|
|
command understands the following character escapes:
|
|
.Bl -tag -width indent
|
|
.It \ea
|
|
Alert (ring the terminal bell)
|
|
.It \eb
|
|
Backspace
|
|
.It \ec
|
|
Suppress the trailing newline (this has the side-effect of truncating the
|
|
line if it is not the last character)
|
|
.It \ee
|
|
The ESC character
|
|
.Tn ( ASCII
|
|
0x1b)
|
|
.It \ef
|
|
Formfeed
|
|
.It \en
|
|
Newline
|
|
.It \er
|
|
Carriage return
|
|
.It \et
|
|
Horizontal tab
|
|
.It \ev
|
|
Vertical tab
|
|
.It \e\e
|
|
Literal backslash
|
|
.It \e0nnn
|
|
(Zero) The character whose octal value is
|
|
.Ar nnn
|
|
.El
|
|
.Pp
|
|
If
|
|
.Ar string
|
|
is not enclosed in quotes then the backslash itself must be escaped
|
|
with a backslash to protect it from the shell.
|
|
For example
|
|
.Bd -literal -offset indent
|
|
$ echo -e "a\evb"
|
|
a
|
|
b
|
|
$ echo -e a\e\evb
|
|
a
|
|
b
|
|
$ echo -e "a\e\eb"
|
|
a\eb
|
|
$ echo -e a\e\e\e\eb
|
|
a\eb
|
|
.Ed
|
|
.El
|
|
.Pp
|
|
Only one of the
|
|
.Fl e
|
|
and
|
|
.Fl n
|
|
options may be specified.
|
|
.It Ic eval Ar string ...
|
|
Concatenate all the arguments with spaces.
|
|
Then re-parse and execute the command.
|
|
.It Ic exec Op Ar command Op arg ...
|
|
Unless
|
|
.Ar command
|
|
is omitted,
|
|
the shell process is replaced with the specified program
|
|
(which must be a real program, not a shell built-in command or function).
|
|
Any redirections on the
|
|
.Ic exec
|
|
command are marked as permanent,
|
|
so that they are not undone when the
|
|
.Ic exec
|
|
command finishes.
|
|
.It Ic exit Op Ar exitstatus
|
|
Terminate the shell process.
|
|
If
|
|
.Ar exitstatus
|
|
is given
|
|
it is used as the exit status of the shell.
|
|
Otherwise, if the shell is executing an
|
|
.Cm EXIT
|
|
trap, the exit status of the last command before the trap is used;
|
|
if the shell is executing a trap for a signal,
|
|
the shell exits by resending the signal to itself.
|
|
Otherwise, the exit status of the preceding command is used.
|
|
The exit status should be an integer between 0 and 255.
|
|
.It Ic export Ar name ...
|
|
.It Ic export Op Fl p
|
|
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
|
|
.Ic unset
|
|
it.
|
|
The shell allows the value of a variable to be set
|
|
at the same time as it is exported by writing
|
|
.Pp
|
|
.D1 Ic export Ar name Ns = Ns Ar value
|
|
.Pp
|
|
With no arguments the
|
|
.Ic export
|
|
command lists the names
|
|
of all exported variables.
|
|
If the
|
|
.Fl p
|
|
option is specified, the exported variables are printed as
|
|
.Dq Ic export Ar name Ns = Ns Ar value
|
|
lines, suitable for re-input to the shell.
|
|
.It Ic false
|
|
A null command that returns a non-zero (false) exit value.
|
|
.It Ic fc Oo Fl e Ar editor Oc Op Ar first Op Ar last
|
|
.It Ic fc Fl l Oo Fl nr Oc Op Ar first Op Ar last
|
|
.It Ic fc Fl s Oo Ar old Ns = Ns Ar new Oc Op Ar first
|
|
The
|
|
.Ic fc
|
|
built-in command lists, or edits and re-executes,
|
|
commands previously entered to an interactive shell.
|
|
.Bl -tag -width indent
|
|
.It Fl e Ar editor
|
|
Use the editor named by
|
|
.Ar editor
|
|
to edit the commands.
|
|
The
|
|
.Ar editor
|
|
string is a command name,
|
|
subject to search via the
|
|
.Va PATH
|
|
variable.
|
|
The value in the
|
|
.Va FCEDIT
|
|
variable is used as a default when
|
|
.Fl e
|
|
is not specified.
|
|
If
|
|
.Va FCEDIT
|
|
is null or unset, the value of the
|
|
.Va EDITOR
|
|
variable is used.
|
|
If
|
|
.Va EDITOR
|
|
is null or unset,
|
|
.Xr ed 1
|
|
is used as the editor.
|
|
.It Fl l No (ell)
|
|
List the commands rather than invoking
|
|
an editor on them.
|
|
The commands are written in the
|
|
sequence indicated by the
|
|
.Ar first
|
|
and
|
|
.Ar last
|
|
operands, as affected by
|
|
.Fl r ,
|
|
with each command preceded by the command number.
|
|
.It Fl n
|
|
Suppress command numbers when listing with
|
|
.Fl l .
|
|
.It Fl r
|
|
Reverse the order of the commands listed
|
|
(with
|
|
.Fl l )
|
|
or edited
|
|
(with neither
|
|
.Fl l
|
|
nor
|
|
.Fl s ) .
|
|
.It Fl s
|
|
Re-execute the command without invoking an editor.
|
|
.It Ar first
|
|
.It Ar last
|
|
Select the commands to list or edit.
|
|
The number of previous commands that can be accessed
|
|
are determined by the value of the
|
|
.Va HISTSIZE
|
|
variable.
|
|
The value of
|
|
.Ar first
|
|
or
|
|
.Ar last
|
|
or both are one of the following:
|
|
.Bl -tag -width indent
|
|
.It Oo Cm + Oc Ns Ar num
|
|
A positive number representing a command number;
|
|
command numbers can be displayed with the
|
|
.Fl l
|
|
option.
|
|
.It Fl Ar num
|
|
A negative decimal number representing the
|
|
command that was executed
|
|
.Ar num
|
|
of
|
|
commands previously.
|
|
For example, \-1 is the immediately previous command.
|
|
.It Ar string
|
|
A string indicating the most recently entered command
|
|
that begins with that string.
|
|
If the
|
|
.Ar old Ns = Ns Ar new
|
|
operand is not also specified with
|
|
.Fl s ,
|
|
the string form of the first operand cannot contain an embedded equal sign.
|
|
.El
|
|
.El
|
|
.Pp
|
|
The following variables affect the execution of
|
|
.Ic fc :
|
|
.Bl -tag -width ".Va HISTSIZE"
|
|
.It Va FCEDIT
|
|
Name of the editor to use for history editing.
|
|
.It Va HISTSIZE
|
|
The number of previous commands that are accessible.
|
|
.El
|
|
.It Ic fg Op Ar job
|
|
Move the specified
|
|
.Ar job
|
|
or the current job to the foreground.
|
|
.It Ic getopts Ar optstring var
|
|
The
|
|
.Tn POSIX
|
|
.Ic getopts
|
|
command.
|
|
The
|
|
.Ic getopts
|
|
command deprecates the older
|
|
.Xr getopt 1
|
|
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
|
|
.Va OPTIND .
|
|
If an option takes an argument, it is placed into the shell variable
|
|
.Va OPTARG .
|
|
If an invalid option is encountered,
|
|
.Ar var
|
|
is set to
|
|
.Ql \&? .
|
|
It returns a false value (1) when it encounters the end of the options.
|
|
A new set of arguments may be parsed by assigning
|
|
.Li OPTIND=1 .
|
|
.It Ic hash Oo Fl rv Oc Op Ar command ...
|
|
The shell maintains a hash table which remembers the locations of commands.
|
|
With no arguments whatsoever, the
|
|
.Ic hash
|
|
command prints out the contents of this table.
|
|
.Pp
|
|
With arguments, the
|
|
.Ic hash
|
|
command removes each specified
|
|
.Ar command
|
|
from the hash table (unless they are functions) and then locates it.
|
|
With the
|
|
.Fl v
|
|
option,
|
|
.Ic hash
|
|
prints the locations of the commands as it finds them.
|
|
The
|
|
.Fl r
|
|
option causes the
|
|
.Ic hash
|
|
command to delete all the entries in the hash table except for functions.
|
|
.It Ic jobid Op Ar job
|
|
Print the process IDs of the processes in the specified
|
|
.Ar job .
|
|
If the
|
|
.Ar job
|
|
argument is omitted, use the current job.
|
|
.It Ic jobs Oo Fl lps Oc Op Ar job ...
|
|
Print information about the specified jobs, or all jobs if no
|
|
.Ar job
|
|
argument is given.
|
|
The information printed includes job ID, status and command name.
|
|
.Pp
|
|
If the
|
|
.Fl l
|
|
option is specified, the PID of each job is also printed.
|
|
If the
|
|
.Fl p
|
|
option is specified, only the process IDs for the process group leaders
|
|
are printed, one per line.
|
|
If the
|
|
.Fl s
|
|
option is specified, only the PIDs of the job commands are printed, one per
|
|
line.
|
|
.It Ic kill
|
|
A built-in equivalent of
|
|
.Xr kill 1
|
|
that additionally supports sending signals to jobs.
|
|
.It Ic local Oo Ar variable ... Oc Op Fl
|
|
See the
|
|
.Sx Functions
|
|
subsection.
|
|
.It Ic printf
|
|
A built-in equivalent of
|
|
.Xr printf 1 .
|
|
.It Ic pwd Op Fl L | P
|
|
Print the path of the current directory.
|
|
The built-in command may
|
|
differ from the program of the same name because the
|
|
built-in 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 built-in version of
|
|
.Xr pwd 1
|
|
will continue to print the old name for the directory.
|
|
.Pp
|
|
If the
|
|
.Fl P
|
|
option is specified, symbolic links are resolved.
|
|
If the
|
|
.Fl L
|
|
option is specified, the shell's notion of the current directory
|
|
is printed (symbolic links are not resolved).
|
|
This is the default.
|
|
.It Ic read Oo Fl p Ar prompt Oc Oo
|
|
.Fl t Ar timeout Oc Oo Fl er Oc Ar variable ...
|
|
The
|
|
.Ar prompt
|
|
is printed if the
|
|
.Fl 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
|
|
.Sx White Space Splitting (Field 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
|
|
.Va 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
|
|
.Fl 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
|
|
.Va IFS ,
|
|
even if it is.
|
|
.Pp
|
|
If the
|
|
.Fl t
|
|
option is specified and the
|
|
.Ar timeout
|
|
elapses before a complete line of input is supplied,
|
|
the
|
|
.Ic read
|
|
command will return an exit status as if terminated by
|
|
.Dv SIGALRM
|
|
without assigning any values.
|
|
The
|
|
.Ar timeout
|
|
value may optionally be followed by one of
|
|
.Ql s ,
|
|
.Ql m
|
|
or
|
|
.Ql h
|
|
to explicitly specify seconds, minutes or hours.
|
|
If none is supplied,
|
|
.Ql s
|
|
is assumed.
|
|
.Pp
|
|
The
|
|
.Fl e
|
|
option exists only for backward compatibility with older scripts.
|
|
.Pp
|
|
The exit status is 0 on success, 1 on end of file,
|
|
between 2 and 128 if an error occurs
|
|
and greater than 128 if a trapped signal interrupts
|
|
.Ic read .
|
|
.It Ic readonly Oo Fl p Oc Op Ar name ...
|
|
Each specified
|
|
.Ar name
|
|
is marked as read only,
|
|
so that it cannot be subsequently modified or unset.
|
|
The shell allows the value of a variable to be set
|
|
at the same time as it is marked read only
|
|
by using the following form:
|
|
.Pp
|
|
.D1 Ic readonly Ar name Ns = Ns Ar value
|
|
.Pp
|
|
With no arguments the
|
|
.Ic readonly
|
|
command lists the names of all read only variables.
|
|
If the
|
|
.Fl p
|
|
option is specified, the read-only variables are printed as
|
|
.Dq Ic readonly Ar name Ns = Ns Ar value
|
|
lines, suitable for re-input to the shell.
|
|
.It Ic return Op Ar exitstatus
|
|
See the
|
|
.Sx Functions
|
|
subsection.
|
|
.It Ic set Oo Fl /+abCEefIimnpTuVvx Oc Oo Fl /+o Ar longname Oc Oo
|
|
.Fl c Ar string Oc Op Fl - Ar arg ...
|
|
The
|
|
.Ic 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,
|
|
either in short form or using the long
|
|
.Dq Fl /+o Ar longname
|
|
form,
|
|
it sets or clears the specified options as described in the section called
|
|
.Sx Argument List Processing .
|
|
.It
|
|
If the
|
|
.Dq Fl -
|
|
option is specified,
|
|
.Ic set
|
|
will replace the shell's positional parameters with the subsequent
|
|
arguments.
|
|
If no arguments follow the
|
|
.Dq Fl -
|
|
option,
|
|
all the positional parameters will be cleared,
|
|
which is equivalent to executing the command
|
|
.Dq Li "shift $#" .
|
|
The
|
|
.Dq Fl -
|
|
flag may be omitted when specifying arguments to be used
|
|
as positional replacement parameters.
|
|
This is not recommended,
|
|
because the first argument may begin with a dash
|
|
.Pq Ql -
|
|
or a plus
|
|
.Pq Ql + ,
|
|
which the
|
|
.Ic set
|
|
command will interpret as a request to enable or disable options.
|
|
.El
|
|
.It Ic setvar Ar variable value
|
|
Assigns the specified
|
|
.Ar value
|
|
to the specified
|
|
.Ar variable .
|
|
The
|
|
.Ic setvar
|
|
command is intended to be used in functions that
|
|
assign values to variables whose names are passed as parameters.
|
|
In general it is better to write
|
|
.Dq Ar variable Ns = Ns Ar value
|
|
rather than using
|
|
.Ic setvar .
|
|
.It Ic shift Op Ar n
|
|
Shift the positional parameters
|
|
.Ar n
|
|
times, or once if
|
|
.Ar n
|
|
is not specified.
|
|
A shift sets the value of
|
|
.Li $1
|
|
to the value of
|
|
.Li $2 ,
|
|
the value of
|
|
.Li $2
|
|
to the value of
|
|
.Li $3 ,
|
|
and so on,
|
|
decreasing the value of
|
|
.Li $#
|
|
by one.
|
|
For portability, shifting if there are zero positional parameters
|
|
should be avoided, since the shell may abort.
|
|
.It Ic test
|
|
A built-in equivalent of
|
|
.Xr test 1 .
|
|
.It Ic times
|
|
Print the amount of time spent executing the shell process and its children.
|
|
The first output line shows the user and system times for the shell process
|
|
itself, the second one contains the user and system times for the
|
|
children.
|
|
.It Ic trap Oo Ar action Oc Ar signal ...
|
|
.It Ic trap Fl l
|
|
Cause the shell to parse and execute
|
|
.Ar action
|
|
when any specified
|
|
.Ar signal
|
|
is received.
|
|
The signals are specified by name or number.
|
|
In addition, the pseudo-signal
|
|
.Cm EXIT
|
|
may be used to specify an
|
|
.Ar action
|
|
that is performed when the shell terminates.
|
|
The
|
|
.Ar action
|
|
may be an empty string or a dash
|
|
.Pq Ql - ;
|
|
the former causes the specified signal to be ignored
|
|
and the latter causes the default action to be taken.
|
|
Omitting the
|
|
.Ar action
|
|
and using only signal numbers is another way to request the default action.
|
|
In a subshell or utility environment,
|
|
the shell resets trapped (but not ignored) signals to the default action.
|
|
The
|
|
.Ic trap
|
|
command has no effect on signals that were ignored on entry to the shell.
|
|
.Pp
|
|
Option
|
|
.Fl l
|
|
causes the
|
|
.Ic trap
|
|
command to display a list of valid signal names.
|
|
.It Ic true
|
|
A null command that returns a 0 (true) exit value.
|
|
.It Ic type Op Ar name ...
|
|
Interpret each
|
|
.Ar name
|
|
as a command and print the resolution of the command search.
|
|
Possible resolutions are:
|
|
shell keyword, alias, special shell builtin, 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 Ic ulimit Oo Fl HSabcdfklmnopstuvw Oc Op Ar limit
|
|
Set or display resource limits (see
|
|
.Xr getrlimit 2 ) .
|
|
If
|
|
.Ar limit
|
|
is specified, the named resource will be set;
|
|
otherwise the current resource value will be displayed.
|
|
.Pp
|
|
If
|
|
.Fl 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.
|
|
The
|
|
.Fl S
|
|
option
|
|
specifies the soft limits instead.
|
|
When displaying limits,
|
|
only one of
|
|
.Fl S
|
|
or
|
|
.Fl H
|
|
can be given.
|
|
The default is to display the soft limits,
|
|
and to set both the hard and the soft limits.
|
|
.Pp
|
|
Option
|
|
.Fl a
|
|
causes the
|
|
.Ic ulimit
|
|
command to display all resources.
|
|
The parameter
|
|
.Ar 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 indent
|
|
.It Fl b Ar sbsize
|
|
The maximum size of socket buffer usage, in bytes.
|
|
.It Fl c Ar coredumpsize
|
|
The maximal size of core dump files, in 512-byte blocks.
|
|
.It Fl d Ar datasize
|
|
The maximal size of the data segment of a process, in kilobytes.
|
|
.It Fl f Ar filesize
|
|
The maximal size of a file, in 512-byte blocks.
|
|
.It Fl k Ar kqueues
|
|
The maximal number of kqueues
|
|
(see
|
|
.Xr kqueue 2 )
|
|
for this user ID.
|
|
.It Fl l Ar lockedmem
|
|
The maximal size of memory that can be locked by a process, in
|
|
kilobytes.
|
|
.It Fl m Ar memoryuse
|
|
The maximal resident set size of a process, in kilobytes.
|
|
.It Fl n Ar nofiles
|
|
The maximal number of descriptors that could be opened by a process.
|
|
.It Fl o Ar umtxp
|
|
The maximal number of process-shared locks
|
|
(see
|
|
.Xr pthread 3 )
|
|
for this user ID.
|
|
.It Fl p Ar pseudoterminals
|
|
The maximal number of pseudo-terminals for this user ID.
|
|
.It Fl s Ar stacksize
|
|
The maximal size of the stack segment, in kilobytes.
|
|
.It Fl t Ar time
|
|
The maximal amount of CPU time to be used by each process, in seconds.
|
|
.It Fl u Ar userproc
|
|
The maximal number of simultaneous processes for this user ID.
|
|
.It Fl v Ar virtualmem
|
|
The maximal virtual size of a process, in kilobytes.
|
|
.It Fl w Ar swapuse
|
|
The maximum amount of swap space reserved or used for this user ID,
|
|
in kilobytes.
|
|
.El
|
|
.It Ic umask Oo Fl S Oc Op Ar mask
|
|
Set the file creation mask (see
|
|
.Xr umask 2 )
|
|
to the octal or symbolic (see
|
|
.Xr chmod 1 )
|
|
value specified by
|
|
.Ar mask .
|
|
If the argument is omitted, the current mask value is printed.
|
|
If the
|
|
.Fl S
|
|
option is specified, the output is symbolic, otherwise the output is octal.
|
|
.It Ic unalias Oo Fl a Oc Op Ar name ...
|
|
The specified alias names are removed.
|
|
If
|
|
.Fl a
|
|
is specified, all aliases are removed.
|
|
.It Ic unset Oo Fl fv Oc Ar name ...
|
|
The specified variables or functions are unset and unexported.
|
|
If the
|
|
.Fl v
|
|
option is specified or no options are given, the
|
|
.Ar name
|
|
arguments are treated as variable names.
|
|
If the
|
|
.Fl f
|
|
option is specified, the
|
|
.Ar name
|
|
arguments are treated as function names.
|
|
.It Ic wait Op Ar job ...
|
|
Wait for each specified
|
|
.Ar job
|
|
to complete and return the exit status of the last process in the
|
|
last specified
|
|
.Ar job .
|
|
If any
|
|
.Ar job
|
|
specified is unknown to the shell, it is treated as if it
|
|
were a known job that exited with exit status 127.
|
|
If no operands are given, wait for all jobs to complete
|
|
and 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
|
|
.Ic fc
|
|
in
|
|
.Sx Built-in Commands )
|
|
can be edited using
|
|
.Nm vi Ns -mode
|
|
command line editing.
|
|
This mode uses commands similar
|
|
to a subset of those described in the
|
|
.Xr vi 1
|
|
man page.
|
|
The command
|
|
.Dq Li "set -o vi"
|
|
(or
|
|
.Dq Li "set -V" )
|
|
enables
|
|
.Nm vi Ns -mode
|
|
editing and places
|
|
.Nm
|
|
into
|
|
.Nm vi
|
|
insert mode.
|
|
With
|
|
.Nm vi Ns -mode
|
|
enabled,
|
|
.Nm
|
|
can be switched between insert mode and command mode by typing
|
|
.Aq ESC .
|
|
Hitting
|
|
.Aq return
|
|
while in command mode will pass the line to the shell.
|
|
.Pp
|
|
Similarly, the
|
|
.Dq Li "set -o emacs"
|
|
(or
|
|
.Dq Li "set -E" )
|
|
command can be used to enable a subset of
|
|
.Nm emacs Ns -style
|
|
command line editing features.
|
|
.Sh ENVIRONMENT
|
|
The following environment variables affect the execution of
|
|
.Nm :
|
|
.Bl -tag -width ".Ev LANGXXXXXX"
|
|
.It Ev ENV
|
|
Initialization file for interactive shells.
|
|
.It Ev LANG , Ev LC_*
|
|
Locale settings.
|
|
These are inherited by children of the shell,
|
|
and is used in a limited manner by the shell itself.
|
|
.It Ev OLDPWD
|
|
The previous current directory.
|
|
This is used and updated by
|
|
.Ic cd .
|
|
.It Ev PWD
|
|
An absolute pathname for the current directory,
|
|
possibly containing symbolic links.
|
|
This is used and updated by the shell.
|
|
.It Ev TERM
|
|
The default terminal setting for the shell.
|
|
This is inherited by children of the shell, and is used in the history
|
|
editing modes.
|
|
.El
|
|
.Pp
|
|
Additionally, environment variables are turned into shell variables
|
|
at startup,
|
|
which may affect the shell as described under
|
|
.Sx Special Variables .
|
|
.Sh FILES
|
|
.Bl -tag -width "/etc/suid_profileXX" -compact
|
|
.It Pa ~/.profile
|
|
User's login profile.
|
|
.It Pa /etc/profile
|
|
System login profile.
|
|
.It Pa /etc/shells
|
|
Shell database.
|
|
.It Pa /etc/suid_profile
|
|
Privileged shell profile.
|
|
.El
|
|
.Sh EXIT STATUS
|
|
Errors that are detected by the shell, such as a syntax error, will
|
|
cause the shell to exit with a non-zero exit status.
|
|
If the shell is not an interactive shell, the execution of the shell
|
|
file will be aborted.
|
|
Otherwise the shell will return the exit status of the last command
|
|
executed, or if the
|
|
.Ic exit
|
|
builtin is used with a numeric argument, it
|
|
will return the argument.
|
|
.Sh SEE ALSO
|
|
.Xr builtin 1 ,
|
|
.Xr chsh 1 ,
|
|
.Xr echo 1 ,
|
|
.Xr ed 1 ,
|
|
.Xr emacs 1 ,
|
|
.Xr kill 1 ,
|
|
.Xr printf 1 ,
|
|
.Xr pwd 1 ,
|
|
.Xr test 1 ,
|
|
.Xr vi 1 ,
|
|
.Xr execve 2 ,
|
|
.Xr getrlimit 2 ,
|
|
.Xr umask 2 ,
|
|
.Xr wctype 3 ,
|
|
.Xr editrc 5 ,
|
|
.Xr shells 5
|
|
.Sh HISTORY
|
|
A
|
|
.Nm
|
|
command, the Thompson shell, appeared in
|
|
.At v1 .
|
|
It was superseded in
|
|
.At v7
|
|
by the Bourne shell, which inherited the name
|
|
.Nm .
|
|
.Pp
|
|
This version of
|
|
.Nm
|
|
was rewritten in 1989 under the
|
|
.Bx
|
|
license after the Bourne shell from
|
|
.At V.4 .
|
|
.Sh AUTHORS
|
|
This version of
|
|
.Nm
|
|
was originally written by
|
|
.An Kenneth Almquist .
|
|
.Sh BUGS
|
|
The
|
|
.Nm
|
|
utility does not recognize multibyte characters other than UTF-8.
|
|
Splitting using
|
|
.Va IFS
|
|
does not recognize multibyte characters.
|