PROLOG | NAME | SYNOPSIS | DESCRIPTION | OPTIONS | OPERANDS | STDIN | INPUT FILES | ENVIRONMENT VARIABLES | ASYNCHRONOUS EVENTS | STDOUT | STDERR | OUTPUT FILES | EXTENDED DESCRIPTION | EXIT STATUS | CONSEQUENCES OF ERRORS | APPLICATION USAGE | EXAMPLES | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT

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

PROLOG         top

       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         top

       unset — unset values and attributes of variables and functions

SYNOPSIS         top

       unset [−fv] name...

DESCRIPTION         top

       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         top

       See the DESCRIPTION.

OPERANDS         top

       See the DESCRIPTION.

STDIN         top

       Not used.

INPUT FILES         top

       None.

ENVIRONMENT VARIABLES         top

       None.

ASYNCHRONOUS EVENTS         top

       Default.

STDOUT         top

       Not used.

STDERR         top

       The standard error shall be used only for diagnostic messages.

OUTPUT FILES         top

       None.

EXTENDED DESCRIPTION         top

       None.

EXIT STATUS         top

        0    All name operands were successfully unset.

       >0    At least one name could not be unset.

CONSEQUENCES OF ERRORS         top

       Default.

       The following sections are informative.

APPLICATION USAGE         top

       None.

EXAMPLES         top

       Unset VISUAL variable:

           unset −v VISUAL

       Unset the functions foo and bar:

           unset −f foo bar

RATIONALE         top

       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         top

       None.

SEE ALSO         top

       Section 2.14, Special Built-In Utilities

       The Base Definitions volume of POSIX.1‐2008, Section 12.2, Utility
       Syntax Guidelines

COPYRIGHT         top

       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 .

IEEE/The Open Group                 2013                           UNSET(1P)