mirror of https://github.com/mkerrisk/man-pages
143 lines
3.5 KiB
Groff
143 lines
3.5 KiB
Groff
.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved
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.TH "UNSET" 1P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
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.\" unset
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.SH NAME
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unset \- unset values and attributes of variables and functions
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.SH SYNOPSIS
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.LP
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\fBunset\fP \fB[\fP\fB-fv\fP\fB]\fP \fIname\fP \fB...\fP
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.SH DESCRIPTION
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.LP
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Each variable or function specified by \fIname\fP shall be unset.
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.LP
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If \fB-v\fP is specified, \fIname\fP refers to a variable name and
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the shell shall unset it and remove it from the
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environment. Read-only variables cannot be unset.
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.LP
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If \fB-f\fP is specified, \fIname\fP refers to a function and the
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shell shall unset the function definition.
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.LP
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If neither \fB-f\fP nor \fB-v\fP is specified, \fIname\fP refers to
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a variable; if a variable by that name does not exist, it
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is unspecified whether a function by that name, if any, shall be unset.
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.LP
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Unsetting a variable or function that was not previously set shall
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not be considered an error and does not cause the shell to
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abort.
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.LP
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The \fIunset\fP special built-in shall support the Base Definitions
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volume of IEEE\ Std\ 1003.1-2001, Section 12.2, Utility Syntax Guidelines.
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.LP
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Note that:
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.sp
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.RS
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.nf
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\fBVARIABLE=
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\fP
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.fi
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.RE
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.LP
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is not equivalent to an \fIunset\fP of \fBVARIABLE\fP; in the example,
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\fBVARIABLE\fP is set to \fB""\fP . Also, the
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variables that can be \fIunset\fP should not be misinterpreted to
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include the special parameters (see \fISpecial Parameters\fP ).
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.SH OPTIONS
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.LP
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See the DESCRIPTION.
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.SH OPERANDS
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.LP
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See the DESCRIPTION.
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.SH STDIN
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.LP
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Not used.
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.SH INPUT FILES
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.LP
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None.
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.SH ENVIRONMENT VARIABLES
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.LP
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None.
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.SH ASYNCHRONOUS EVENTS
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.LP
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Default.
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.SH STDOUT
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.LP
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Not used.
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.SH STDERR
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.LP
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The standard error shall be used only for diagnostic messages.
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.SH OUTPUT FILES
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.LP
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None.
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.SH EXTENDED DESCRIPTION
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.LP
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None.
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.SH EXIT STATUS
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.TP 7
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\ 0
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All \fIname\fP operands were successfully unset.
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.TP 7
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>0
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At least one \fIname\fP could not be unset.
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.sp
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.SH CONSEQUENCES OF ERRORS
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.LP
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Default.
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.LP
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\fIThe following sections are informative.\fP
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.SH APPLICATION USAGE
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.LP
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None.
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.SH EXAMPLES
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.LP
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Unset \fIVISUAL\fP variable:
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.sp
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.RS
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.nf
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\fBunset -v VISUAL
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\fP
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.fi
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.RE
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.LP
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Unset the functions \fBfoo\fP and \fBbar\fP:
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.sp
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.RS
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.nf
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\fBunset -f foo bar
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\fP
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.fi
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.RE
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.SH RATIONALE
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.LP
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Consideration was given to omitting the \fB-f\fP option in favor of
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an
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\fIunfunction\fP utility, but the standard developers decided to retain
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historical
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practice.
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.LP
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The \fB-v\fP option was introduced because System V historically used
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one name space for both variables and functions. When
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\fIunset\fP is used without options, System V historically unset either
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a function or a variable, and there was no confusion about
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which one was intended. A portable POSIX application can use \fIunset\fP
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without an option to unset a variable, but not a
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function; the \fB-f\fP option must be used.
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.SH FUTURE DIRECTIONS
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.LP
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None.
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.SH SEE ALSO
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.LP
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\fISpecial Built-In Utilities\fP
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.SH COPYRIGHT
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Portions of this text are reprinted and reproduced in electronic form
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from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
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-- Portable Operating System Interface (POSIX), The Open Group Base
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Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
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Electrical and Electronics Engineers, Inc and The Open Group. In the
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event of any discrepancy between this version and the original IEEE and
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The Open Group Standard, the original IEEE and The Open Group Standard
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is the referee document. The original Standard can be obtained online at
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http://www.opengroup.org/unix/online.html .
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