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       This  manual  page  is part of the POSIX Programmer's Manual.  The Linux implementation of
       this interface may differ (consult 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 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 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 misinterpreted 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 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

       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 Technology  --  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 Standard 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 .