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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) 2001-2004 IEEE and The Open Group, All Rights Reserved --><title>colon</title></head><body bgcolor="white"><basefont size="3"> <a name="colon"></a> <a name="tag_04_22"></a><!-- colon --> <!--header start--><center><font size="2">The Open Group Base Specifications Issue 6<br>IEEE Std 1003.1, 2004 Edition<br>Copyright © 2001-2004 The IEEE and The Open Group, All Rights reserved.</font></center><!--header end--><hr size="2" noshade><h4><a name="tag_04_22_01"></a>NAME</h4><blockquote>colon - null utility</blockquote><h4><a name="tag_04_22_02"></a>SYNOPSIS</h4><blockquote class="synopsis"><p><code><tt>:</tt> <b>[</b><i>argument</i> <tt>...</tt><b>]</b></code></p></blockquote><h4><a name="tag_04_22_03"></a>DESCRIPTION</h4><blockquote><p>This utility shall only expand command <i>argument</i>s. It is used when a command is needed, as in the <b>then</b> condition ofan <b>if</b> command, but nothing is to be done by the command.</p></blockquote><h4><a name="tag_04_22_04"></a>OPTIONS</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_04_22_05"></a>OPERANDS</h4><blockquote><p>See the DESCRIPTION.</p></blockquote><h4><a name="tag_04_22_06"></a>STDIN</h4><blockquote><p>Not used.</p></blockquote><h4><a name="tag_04_22_07"></a>INPUT FILES</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_04_22_08"></a>ENVIRONMENT VARIABLES</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_04_22_09"></a>ASYNCHRONOUS EVENTS</h4><blockquote><p>Default.</p></blockquote><h4><a name="tag_04_22_10"></a>STDOUT</h4><blockquote><p>Not used.</p></blockquote><h4><a name="tag_04_22_11"></a>STDERR</h4><blockquote><p>The standard error shall be used only for diagnostic messages.</p></blockquote><h4><a name="tag_04_22_12"></a>OUTPUT FILES</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_04_22_13"></a>EXTENDED DESCRIPTION</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_04_22_14"></a>EXIT STATUS</h4><blockquote><p>Zero.</p></blockquote><h4><a name="tag_04_22_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_22_16"></a>APPLICATION USAGE</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_04_22_17"></a>EXAMPLES</h4><blockquote><pre><tt>: ${X=abc}if falsethen :else echo $Xfi</tt><b>abc</b></pre><p>As with any of the special built-ins, the null utility can also have variable assignments and redirections associated with it,such as:</p><pre><tt>x=y : > z</tt></pre><p>which sets variable <i>x</i> to the value <i>y</i> (so that it persists after the null utility completes) and creates ortruncates file <b>z</b>.</p></blockquote><h4><a name="tag_04_22_18"></a>RATIONALE</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_04_22_19"></a>FUTURE DIRECTIONS</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_04_22_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_22_21"></a>CHANGE HISTORY</h4><h4><a name="tag_04_22_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 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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