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.TH UNSET "1P" 2013 "IEEE/The Open Group" "POSIX Programmer's Manual"
.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
\(em unset values and attributes of variables and functions
.SH SYNOPSIS
.LP
.nf
unset \fB[\fR\(mifv\fB] \fIname\fR...
.fi
.SH DESCRIPTION
Each variable or function specified by
.IR name
shall be unset.
.P
If
.BR \(miv
is specified,
.IR name
refers to a variable name and the shell shall unset it and remove it
from the environment. Read-only variables cannot be unset.
.P
If
.BR \(mif
is specified,
.IR name
refers to a function and the shell shall unset the function definition.
.P
If neither
.BR \(mif
nor
.BR \(miv
is specified,
.IR name
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.
.P
Unsetting a variable or function that was not previously set shall not
be considered an error and does not cause the shell to abort.
.P
The
.IR unset
special built-in shall support the Base Definitions volume of POSIX.1\(hy2008,
.IR "Section 12.2" ", " "Utility Syntax Guidelines".
.P
Note that:
.sp
.RS 4
.nf
\fB
VARIABLE=
.fi \fR
.P
.RE
.P
is not equivalent to an
.IR unset
of
.BR VARIABLE ;
in the example,
.BR VARIABLE
is set to
.BR \(dq\^\(dq .
Also, the variables that can be
.IR unset
should not be misinterpreted to include the special parameters (see
.IR "Section 2.5.2" ", " "Special Parameters").
.SH OPTIONS
See the DESCRIPTION.
.SH OPERANDS
See the DESCRIPTION.
.SH STDIN
Not used.
.SH "INPUT FILES"
None.
.SH "ENVIRONMENT VARIABLES"
None.
.SH "ASYNCHRONOUS EVENTS"
Default.
.SH STDOUT
Not used.
.SH STDERR
The standard error shall be used only for diagnostic messages.
.SH "OUTPUT FILES"
None.
.SH "EXTENDED DESCRIPTION"
None.
.SH "EXIT STATUS"
.IP "\00" 6
All
.IR name
operands were successfully unset.
.IP >0 6
At least one
.IR name
could not be unset.
.SH "CONSEQUENCES OF ERRORS"
Default.
.LP
.IR "The following sections are informative."
.SH "APPLICATION USAGE"
None.
.SH EXAMPLES
Unset
.IR VISUAL
variable:
.sp
.RS 4
.nf
\fB
unset \(miv VISUAL
.fi \fR
.P
.RE
.P
Unset the functions
.BR foo
and
.BR bar :
.sp
.RS 4
.nf
\fB
unset \(mif foo bar
.fi \fR
.P
.RE
.SH "RATIONALE"
Consideration was given to omitting the
.BR \(mif
option in favor of an
.IR unfunction
utility, but the standard developers decided to retain historical
practice.
.P
The
.BR \(miv
option was introduced because System V historically used one name space
for both variables and functions. When
.IR unset
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
.IR unset
without an option to unset a variable, but not a function; the
.BR \(mif
option must be used.
.SH "FUTURE DIRECTIONS"
None.
.SH "SEE ALSO"
.IR "Section 2.14" ", " "Special Built-In Utilities"
.P
The Base Definitions volume of POSIX.1\(hy2008,
.IR "Section 12.2" ", " "Utility Syntax Guidelines"
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, Copyright (C) 2013 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group.
(This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) 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.unix.org/online.html .

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