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 (con-
       sult the corresponding 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  unspeci-
       fied whether a function 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 IEEE Std 1003.1-2001, Section 12.2, Utility  Syn-
       tax 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 misinterpreted to include the special parameters (see 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 historical 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
       Special Built-In Utilities

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, Copy-
       right (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.open-
       group.org/unix/online.html .



IEEE/The Open Group                                           2003                                                     UNSET(1P)