unset(1p) — Linux manual page

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

COPYRIGHT         top

       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(1P)

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