UNSET(1P)						     POSIX Programmer's Manual							 UNSET(1P)

PROLOG

       This  manual page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may differ (consult the correspond-
       ing Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.

NAME

       unset -- unset values and attributes of variables and functions

SYNOPSIS

       unset [-fv] name...

DESCRIPTION

       Each variable or function specified by name shall be unset.

       If -v is specified, name refers to a variable name and the shell shall unset it and remove it from  the	environment.  Read-only  variables
       cannot be unset.

       If -f is specified, name refers to a function and the shell shall unset the function definition.

       If  neither -f nor -v is specified, name refers to a variable; if a variable by that name does not exist, it is unspecified whether a func-
       tion by that name, if any, shall be unset.

       Unsetting a variable or function that was not previously set shall not be considered an error and does not cause the shell to abort.

       The unset special built-in shall support the Base Definitions volume of POSIX.1-2008, Section 12.2, Utility Syntax Guidelines.

       Note that:

	   VARIABLE=

       is not equivalent to an unset of VARIABLE; in the example, VARIABLE is set to "".  Also, the variables that can be unset should not be mis-
       interpreted to include the special parameters (see Section 2.5.2, Special Parameters).

OPTIONS

       See the DESCRIPTION.

OPERANDS

       See the DESCRIPTION.

STDIN

       Not used.

INPUT FILES

       None.

ENVIRONMENT VARIABLES

       None.

ASYNCHRONOUS EVENTS

       Default.

STDOUT

       Not used.

STDERR

       The standard error shall be used only for diagnostic messages.

OUTPUT FILES

       None.

EXTENDED DESCRIPTION

       None.

EXIT STATUS

	0    All name operands were successfully unset.

       >0    At least one name could not be unset.

CONSEQUENCES OF ERRORS

       Default.

       The following sections are informative.

APPLICATION USAGE

       None.

EXAMPLES

       Unset VISUAL variable:

	   unset -v VISUAL

       Unset the functions foo and bar:

	   unset -f foo bar

RATIONALE

       Consideration was given to omitting the -f option in favor of an unfunction utility, but the standard developers decided to retain histori-
       cal practice.

       The -v option was introduced because System V historically used one name space for both variables and functions. When 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 unset without an option to unset a variable, but not a function; the -f option must be used.

FUTURE DIRECTIONS

       None.

SEE ALSO

       Section 2.14, Special Built-In Utilities

       The Base Definitions volume of POSIX.1-2008, Section 12.2, Utility Syntax Guidelines

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2013 Edition, Standard for Information Technol-
       ogy  --	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 Stan-
       dard 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 .

IEEE
/The Open Group						       2013								 UNSET(1P)