.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved 
.TH "UNSET" 1P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\" unset 
.SH PROLOG
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
.SH NAME
unset \- unset values and attributes of variables and functions
.SH SYNOPSIS
.LP
\fBunset\fP \fB[\fP\fB-fv\fP\fB]\fP \fIname\fP \fB...\fP
.SH DESCRIPTION
.LP
Each variable or function specified by \fIname\fP shall be unset.
.LP
If \fB-v\fP is specified, \fIname\fP refers to a variable name and
the shell shall unset it and remove it from the
environment. Read-only variables cannot be unset.
.LP
If \fB-f\fP is specified, \fIname\fP refers to a function and the
shell shall unset the function definition.
.LP
If neither \fB-f\fP nor \fB-v\fP is specified, \fIname\fP refers to
a variable; if a variable by that name does not exist, it
is unspecified whether a function by that name, if any, shall be unset.
.LP
Unsetting a variable or function that was not previously set shall
not be considered an error and does not cause the shell to
abort.
.LP
The \fIunset\fP special built-in shall support the Base Definitions
volume of IEEE\ Std\ 1003.1-2001, Section 12.2, Utility Syntax Guidelines.
.LP
Note that:
.sp
.RS
.nf

\fBVARIABLE=
\fP
.fi
.RE
.LP
is not equivalent to an \fIunset\fP of \fBVARIABLE\fP; in the example,
\fBVARIABLE\fP is set to \fB""\fP . Also, the
variables that can be \fIunset\fP should not be misinterpreted to
include the special parameters (see \fISpecial Parameters\fP ).
.SH OPTIONS
.LP
See the DESCRIPTION.
.SH OPERANDS
.LP
See the DESCRIPTION.
.SH STDIN
.LP
Not used.
.SH INPUT FILES
.LP
None.
.SH ENVIRONMENT VARIABLES
.LP
None.
.SH ASYNCHRONOUS EVENTS
.LP
Default.
.SH STDOUT
.LP
Not used.
.SH STDERR
.LP
The standard error shall be used only for diagnostic messages.
.SH OUTPUT FILES
.LP
None.
.SH EXTENDED DESCRIPTION
.LP
None.
.SH EXIT STATUS
.TP 7
\ 0
All \fIname\fP operands were successfully unset.
.TP 7
>0
At least one \fIname\fP could not be unset.
.sp
.SH CONSEQUENCES OF ERRORS
.LP
Default.
.LP
\fIThe following sections are informative.\fP
.SH APPLICATION USAGE
.LP
None.
.SH EXAMPLES
.LP
Unset \fIVISUAL\fP variable:
.sp
.RS
.nf

\fBunset -v VISUAL
\fP
.fi
.RE
.LP
Unset the functions \fBfoo\fP and \fBbar\fP:
.sp
.RS
.nf

\fBunset -f foo bar
\fP
.fi
.RE
.SH RATIONALE
.LP
Consideration was given to omitting the \fB-f\fP option in favor of
an
\fIunfunction\fP utility, but the standard developers decided to retain
historical
practice.
.LP
The \fB-v\fP option was introduced because System V historically used
one name space for both variables and functions. When
\fIunset\fP is used without options, System V historically unset either
a function or a variable, and there was no confusion about
which one was intended. A portable POSIX application can use \fIunset\fP
without an option to unset a variable, but not a
function; the \fB-f\fP option must be used.
.SH FUTURE DIRECTIONS
.LP
None.
.SH SEE ALSO
.LP
\fISpecial Built-In Utilities\fP
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .