сбросить значения и атрибуты переменных и функций (unset values and attributes of variables and functions)
Пролог (Prolog)
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.
Имя (Name)
unset — unset values and attributes of variables and functions
Синопсис (Synopsis)
unset [-fv] name...
Описание (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).
Параметры (Options)
See the DESCRIPTION.
Операнды (Operands)
See the DESCRIPTION.
Стандартный ввод (Stdin)
Not used.
Входные файлы (Input files)
None.
Переменные окружения (Environment variables)
None.
Асинхронные события (Asynchronous events)
Default.
Стандартный вывод (Stdout)
Not used.
Стандартный вывод сообщений (Stderr)
The standard error shall be used only for diagnostic messages.
Выходные файлы (Output files)
None.
Расширенное описание (Extended description)
None.
Статус выхода (Exit)
0 All name operands were successfully unset.
>0 At least one name could not be unset.
Последствия ошибок (Consequences of errors)
Default.
The following sections are informative.
Использование в приложениях (Application usage)
None.
Примеры (Examples)
Unset VISUAL variable:
unset -v VISUAL
Unset the functions foo and bar:
unset -f foo bar
Обоснование (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.
Будущие направления (Future directions)
None.
Смотри также (See also)
Section 2.14, Special Built-In Utilities
The Base Definitions volume of POSIX.1‐2017, Section 12.2,
Utility Syntax Guidelines
