UNSET(1)                   POSIX Programmer's Manual                  UNSET(1)



PROLOG
       This manual page is part of the POSIX Programmer's Manual.  The OS
       implementation of this interface may differ (consult the corresponding
       OS manual page for details of OS behavior), or the interface may not be
       implemented on OS.

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.1-2017, 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.1-2017, Section 12.2, Utility
       Syntax Guidelines

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1-2017, Standard for Information Technology --
       Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, 2018 Edition, Copyright (C) 2018 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 .

       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 .



IEEE/The Open Group                  2017                             UNSET(1)
