Section: POSIX Programmer's Manual (1P)
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.
--- unset values and attributes of variables and functions
unset [-fv] name...
Each variable or function specified by
shall be unset.
refers to a variable name and the shell shall unset it and remove it
from the environment. Read-only variables cannot be unset.
refers to a function and the shell shall unset the function definition.
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.
special built-in shall support the Base Definitions volume of POSIX.1-2017,
Section 12.2, Utility Syntax Guidelines.
is not equivalent to an
in the example,
is set to
Also, the variables that can be
should not be misinterpreted to include the special parameters (see
Section 2.5.2, Special Parameters).
See the DESCRIPTION.
See the DESCRIPTION.
The standard error shall be used only for diagnostic messages.
operands were successfully unset.
At least one
could not be unset.
CONSEQUENCES OF ERRORS
The following sections are informative.
unset -v VISUAL
Unset the functions
unset -f foo bar
Consideration was given to omitting the
option in favor of an
utility, but the standard developers decided to retain historical
option was introduced because System V historically used one name space
for both variables and functions. When
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
without an option to unset a variable, but not a function; the
option must be used.
, Special Built-In Utilities
The Base Definitions volume of POSIX.1-2017,
Section 12.2, Utility Syntax Guidelines
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
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