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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

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 .