215 lines
5.6 KiB
HTML
215 lines
5.6 KiB
HTML
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<link type="text/css" rel="stylesheet" href="style.css"><!-- Generated by The Open Group's rhtm tool v1.2.1 -->
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<!-- Copyright (c) 2001 The Open Group, All Rights Reserved -->
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<title>unset</title>
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<body bgcolor="white">
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<basefont size="3"> <a name="unset"></a> <a name="tag_04_160"></a><!-- unset -->
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<!--header start-->
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<center><font size="2">The Open Group Base Specifications Issue 6<br>
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IEEE Std 1003.1-2001<br>
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Copyright © 2001 The IEEE and The Open Group, All Rights reserved.</font></center>
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<!--header end-->
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<hr size="2" noshade>
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<h4><a name="tag_04_160_01"></a>NAME</h4>
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<blockquote>unset - unset values and attributes of variables and functions</blockquote>
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<h4><a name="tag_04_160_02"></a>SYNOPSIS</h4>
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<blockquote class="synopsis">
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<p><code><tt>unset</tt> <b>[</b><tt>-fv</tt><b>]</b> <i>name</i> <tt>...</tt></code></p>
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</blockquote>
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<h4><a name="tag_04_160_03"></a>DESCRIPTION</h4>
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<blockquote>
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<p>Each variable or function specified by <i>name</i> shall be unset.</p>
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<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 the
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environment. Read-only variables cannot be unset.</p>
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<p>If <b>-f</b> is specified, <i>name</i> refers to a function and the shell shall unset the function definition.</p>
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<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, it
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is unspecified whether a function by that name, if any, shall be unset.</p>
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<p>Unsetting a variable or function that was not previously set shall not be considered an error and does not cause the shell to
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abort.</p>
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<p>The <i>unset</i> special built-in shall support the Base Definitions volume of IEEE Std 1003.1-2001, <a href=
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"../basedefs/xbd_chap12.html#tag_12_02">Section 12.2, Utility Syntax Guidelines</a>.</p>
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<p>Note that:</p>
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<pre>
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<tt>VARIABLE=
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</tt>
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</pre>
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<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, the
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variables that can be <i>unset</i> should not be misinterpreted to include the special parameters (see <a href=
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"xcu_chap02.html#tag_02_05_02"><i>Special Parameters</i></a> ).</p>
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</blockquote>
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<h4><a name="tag_04_160_04"></a>OPTIONS</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_04_160_05"></a>OPERANDS</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_04_160_06"></a>STDIN</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_04_160_07"></a>INPUT FILES</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_04_160_08"></a>ENVIRONMENT VARIABLES</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_04_160_09"></a>ASYNCHRONOUS EVENTS</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_04_160_10"></a>STDOUT</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_04_160_11"></a>STDERR</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_04_160_12"></a>OUTPUT FILES</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_04_160_13"></a>EXTENDED DESCRIPTION</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_04_160_14"></a>EXIT STATUS</h4>
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<blockquote>
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<dl compact>
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<dt> 0</dt>
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<dd>All <i>name</i> operands were successfully unset.</dd>
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<dt>>0</dt>
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<dd>At least one <i>name</i> could not be unset.</dd>
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</dl>
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</blockquote>
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<h4><a name="tag_04_160_15"></a>CONSEQUENCES OF ERRORS</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<hr>
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<div class="box"><em>The following sections are informative.</em></div>
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<h4><a name="tag_04_160_16"></a>APPLICATION USAGE</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_04_160_17"></a>EXAMPLES</h4>
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<blockquote>
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<p>Unset <i>VISUAL</i> variable:</p>
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<pre>
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<tt>unset -v VISUAL
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</tt>
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</pre>
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<p>Unset the functions <b>foo</b> and <b>bar</b>:</p>
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<pre>
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<tt>unset -f foo bar
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</tt>
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</pre>
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</blockquote>
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<h4><a name="tag_04_160_18"></a>RATIONALE</h4>
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<blockquote>
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<p>Consideration was given to omitting the <b>-f</b> option in favor of an
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<i>unfunction</i> utility, but the standard developers decided to retain historical
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practice.</p>
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<p>The <b>-v</b> option was introduced because System V historically used one name space for both variables and functions. When
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<i>unset</i> is used without options, System V historically unset either 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 <i>unset</i> without an option to unset a variable, but not a
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function; the <b>-f</b> option must be used.</p>
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</blockquote>
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<h4><a name="tag_04_160_19"></a>FUTURE DIRECTIONS</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_04_160_20"></a>SEE ALSO</h4>
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<blockquote>
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<p><a href="xcu_chap02.html#tag_02_14"><i>Special Built-In Utilities</i></a></p>
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</blockquote>
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<h4><a name="tag_04_160_21"></a>CHANGE HISTORY</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<div class="box"><em>End of informative text.</em></div>
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<hr>
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UNIX ® is a registered Trademark of The Open Group.<br>
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POSIX ® is a registered Trademark of The IEEE.<br>
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[ <a href="../mindex.html">Main Index</a> | <a href="../basedefs/contents.html">XBD</a> | <a href=
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"../utilities/contents.html">XCU</a> | <a href="../functions/contents.html">XSH</a> | <a href="../xrat/contents.html">XRAT</a>
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]</font></center>
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