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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


       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 .