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 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 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 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, 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 .