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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html><head><meta name="generator" content="HTML Tidy, see www.w3.org"><meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"><link type="text/css" rel="stylesheet" href="style.css"><!-- Generated by The Open Group's rhtm tool v1.2.1 --><!-- Copyright (c) 2001-2003 The Open Group, All Rights Reserved --><title>unset</title></head><body bgcolor="white"><basefont size="3"> <a name="unset"></a> <a name="tag_04_160"></a><!-- unset --> <!--header start--><center><font size="2">The Open Group Base Specifications Issue 6<br>IEEE Std 1003.1, 2003 Edition<br>Copyright © 2001-2003 The IEEE and The Open Group, All Rights reserved.</font></center><!--header end--><hr size="2" noshade><h4><a name="tag_04_160_01"></a>NAME</h4><blockquote>unset - unset values and attributes of variables and functions</blockquote><h4><a name="tag_04_160_02"></a>SYNOPSIS</h4><blockquote class="synopsis"><p><code><tt>unset</tt> <b>[</b><tt>-fv</tt><b>]</b> <i>name</i> <tt>...</tt></code></p></blockquote><h4><a name="tag_04_160_03"></a>DESCRIPTION</h4><blockquote><p>Each variable or function specified by <i>name</i> shall be unset.</p><p>If <b>-v</b> is specified, <i>name</i> refers to a variable name and the shell shall unset it and remove it from theenvironment. Read-only variables cannot be unset.</p><p>If <b>-f</b> is specified, <i>name</i> refers to a function and the shell shall unset the function definition.</p><p>If neither <b>-f</b> nor <b>-v</b> is specified, <i>name</i> refers to a variable; if a variable by that name does not exist, itis unspecified whether a function by that name, if any, shall be unset.</p><p>Unsetting a variable or function that was not previously set shall not be considered an error and does not cause the shell toabort.</p><p>The <i>unset</i> special built-in shall support the Base Definitions volume of IEEE Std 1003.1-2001, <a href="../basedefs/xbd_chap12.html#tag_12_02">Section 12.2, Utility Syntax Guidelines</a>.</p><p>Note that:</p><pre><tt>VARIABLE=</tt></pre><p>is not equivalent to an <i>unset</i> of <b>VARIABLE</b>; in the example, <b>VARIABLE</b> is set to <tt>""</tt> . Also, thevariables that can be <i>unset</i> should not be misinterpreted to include the special parameters (see <a href="xcu_chap02.html#tag_02_05_02"><i>Special Parameters</i></a> ).</p></blockquote><h4><a name="tag_04_160_04"></a>OPTIONS</h4><blockquote><p>See the DESCRIPTION.</p></blockquote><h4><a name="tag_04_160_05"></a>OPERANDS</h4><blockquote><p>See the DESCRIPTION.</p></blockquote><h4><a name="tag_04_160_06"></a>STDIN</h4><blockquote><p>Not used.</p></blockquote><h4><a name="tag_04_160_07"></a>INPUT FILES</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_04_160_08"></a>ENVIRONMENT VARIABLES</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_04_160_09"></a>ASYNCHRONOUS EVENTS</h4><blockquote><p>Default.</p></blockquote><h4><a name="tag_04_160_10"></a>STDOUT</h4><blockquote><p>Not used.</p></blockquote><h4><a name="tag_04_160_11"></a>STDERR</h4><blockquote><p>The standard error shall be used only for diagnostic messages.</p></blockquote><h4><a name="tag_04_160_12"></a>OUTPUT FILES</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_04_160_13"></a>EXTENDED DESCRIPTION</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_04_160_14"></a>EXIT STATUS</h4><blockquote><dl compact><dt> 0</dt><dd>All <i>name</i> operands were successfully unset.</dd><dt>>0</dt><dd>At least one <i>name</i> could not be unset.</dd></dl></blockquote><h4><a name="tag_04_160_15"></a>CONSEQUENCES OF ERRORS</h4><blockquote><p>Default.</p></blockquote><hr><div class="box"><em>The following sections are informative.</em></div><h4><a name="tag_04_160_16"></a>APPLICATION USAGE</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_04_160_17"></a>EXAMPLES</h4><blockquote><p>Unset <i>VISUAL</i> variable:</p><pre><tt>unset -v VISUAL</tt></pre><p>Unset the functions <b>foo</b> and <b>bar</b>:</p><pre><tt>unset -f foo bar</tt></pre></blockquote><h4><a name="tag_04_160_18"></a>RATIONALE</h4><blockquote><p>Consideration was given to omitting the <b>-f</b> option in favor of an<i>unfunction</i> utility, but the standard developers decided to retain historicalpractice.</p><p>The <b>-v</b> option was introduced because System V historically used one name space for both variables and functions. When<i>unset</i> is used without options, System V historically unset either a function or a variable, and there was no confusion aboutwhich one was intended. A portable POSIX application can use <i>unset</i> without an option to unset a variable, but not afunction; the <b>-f</b> option must be used.</p></blockquote><h4><a name="tag_04_160_19"></a>FUTURE DIRECTIONS</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_04_160_20"></a>SEE ALSO</h4><blockquote><p><a href="xcu_chap02.html#tag_02_14"><i>Special Built-In Utilities</i></a></p></blockquote><h4><a name="tag_04_160_21"></a>CHANGE HISTORY</h4><h4><a name="tag_04_160_22"></a>Issue 6</h4><blockquote><p>IEEE Std 1003.1-2001/Cor 1-2002, item XCU/TC1/D6/5 is applied so that the reference page sections use terms asdescribed in the Utility Description Defaults ( <a href="xcu_chap01.html#tag_01_11"><i>Utility Description Defaults</i></a> ). Nochange in behavior is intended.</p></blockquote><div class="box"><em>End of informative text.</em></div><hr><hr size="2" noshade><center><font size="2"><!--footer start-->UNIX ® is a registered Trademark of The Open Group.<br>POSIX ® is a registered Trademark of The IEEE.<br>[ <a href="../mindex.html">Main Index</a> | <a href="../basedefs/contents.html">XBD</a> | <a href="../utilities/contents.html">XCU</a> | <a href="../functions/contents.html">XSH</a> | <a href="../xrat/contents.html">XRAT</a>]</font></center><!--footer end--><hr size="2" noshade></body></html>⌨️ 快捷键说明
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