155 lines
3.6 KiB
HTML
155 lines
3.6 KiB
HTML
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">
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<html>
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<head>
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<meta name="generator" content="HTML Tidy, see www.w3.org">
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<meta http-equiv="Content-Type" content=
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"text/html; charset=utf-8">
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<title>trap - Trap signals</title>
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<LINK rel="stylesheet" type="text/css" href="../rzahg/ic.css">
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</HEAD>
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<body bgcolor="#FFFFFF">
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<!-- Java sync-link -->
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<SCRIPT LANGUAGE="Javascript" SRC="../rzahg/synch.js" TYPE="text/javascript"></SCRIPT>
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<h2>trap - Trap signals</h2>
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<strong>Synopsis</strong>
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<p><strong>trap</strong> [ <em>action condition</em> ... ]</p>
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<p><strong>trap -p</strong> [ <em>condition</em> ... ]</p>
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<p>
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<strong>trap -l</strong>
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</p>
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<p><strong>Description</strong></p>
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<p>The <strong>trap</strong> utility sets the <em>action</em>
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for <strong>qsh</strong> to take when a <em>condition</em> arises.
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<strong>qsh</strong> expands <em>action</em> once when running
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<strong>trap</strong> and again when <em>condition</em> arises.</p>
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<p>When the <strong>-p</strong> option is specified, <strong>
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trap</strong> displays the current <em>action</em> for the specified
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<em>conditions</em>.</p>
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<p>
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When the <strong>-l</strong> option is specified,
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<strong>trap</strong> displays a list of all of the signal names and their
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corresponding numbers.
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</p>
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<p>When no arguments are specified, <strong>trap</strong> displays a list
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of the currently defined traps.</p>
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<p><strong>Options</strong></p>
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<dl>
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<dt>
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<strong>-l</strong></dt>
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<dd>Display a list of all of the signal names and their corresponding numbers.
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</dd>
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<dt><strong>-p</strong></dt>
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<dd>Display each trap in a re-enterable format.</dd>
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</dl>
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<p><strong>Operands</strong></p>
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<p>For <em>action</em>, you can specify:</p>
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<ul>
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<li>Null to ignore <em>condition</em> when it arises</li>
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<li>Minus (<strong>-</strong>) to reset <em>condition</em> to its
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original value.</li>
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<li>A command to be run each time <em>condition</em> arises.</li>
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</ul>
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<p>For <em>condition,</em> you can specify:</p>
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<ul>
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<li>Name or number of a signal. You can use <strong>trap
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-l</strong> to display a list of valid signals. For portability,
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you should always specify the signal name.</li>
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<li><strong>0</strong> or <strong>EXIT</strong>. <strong>
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qsh</strong> runs <em>action</em> when the shell exits.</li>
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<li><strong>ERR</strong>. <strong>qsh</strong> runs <em>action</em>
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when a command has a non-zero exit status.</li>
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<li><strong>DEBUG</strong>. <strong>qsh</strong> runs <em>
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action</em> after each simple command.</li>
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</ul>
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<p>If more than one condition arises at the same time, <strong>
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qsh</strong> runs the traps in this order:</p>
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<ol>
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<li><strong>DEBUG</strong>, if it is specified, then</li>
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<li><strong>ERR</strong>, if it is specified and applicable,
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then</li>
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<li>Any other specified traps in signal number order, then</li>
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<li><strong>EXIT</strong>.</li>
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</ol>
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<p><strong>Exit Status</strong></p>
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<ul>
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<li>0 when successful.</li>
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<li>>0 when an invalid <em>condition</em> is specified.</li>
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</ul>
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<p><strong>Related information</strong></p>
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<ul>
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<li><a href="kill.htm">kill - Terminate or signal
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processes</a></li>
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<li><a href="wait.htm">wait - Wait for process completion</a></li>
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</ul>
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<strong>Examples</strong>
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<ol>
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<li>Set a trap for the ERR condition:
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<pre>
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trap `print Command failed' ERR
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</pre></li>
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<li>Ignore the ERR condition:
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<pre>
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trap "" ERR
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</pre></li>
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<li>Reset the ERR condition to its original value:
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<pre>
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trap - ERR
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</pre></li>
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<li>Display the current action for the ERR condition:
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<pre>
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trap -p ERR
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</pre></li>
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<li>Display all of the currently defined traps:
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<pre>
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trap
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</pre></li>
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</ol>
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</body>
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</html>
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