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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 .

Any typographical or formatting errors that appear

in this page are most likely

to have been introduced during the conversion of the source files to

man page format. To report such errors, see

https://www.kernel.org/doc/man-pages/reporting_bugs.html .