56 lines
2.0 KiB
HTML
56 lines
2.0 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>Pipelines</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>Pipelines</h2>
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<p>A pipeline is a sequence of one or more commands separated by
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the pipeline control operator (<strong>|</strong>). The standard
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output of all but the last command is connected to the standard
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input of the next command.</p>
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<p>The format for a pipeline is:</p>
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<p><strong>[ ! ]</strong> <em>command1</em> [ <strong>|</strong>
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<em>command2</em> ... ]</p>
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<p>The standard output of <em>command1</em> is connected to the
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standard input of <em>command2</em>. The standard input, standard
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output, or both of a command is considered to be assigned by the
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pipeline before any redirection specified by redirection operators
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that are part of the command. The exit status of the pipeline is
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the exit status of the last <em>command</em>.</p>
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<p>If the pipeline is not in the background (described below),
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<strong>qsh</strong> waits for all commands to complete.</p>
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<p>If the reserved word <strong>!</strong> does not precede the
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pipeline, the exit status is the exit status of the last command
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specified in the pipeline. Otherwise, the exit status is the
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logical not of the exit status of the last command. That is, if the
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last command returns zero, the exit status is 1; if the last
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command returns greater than zero, the exit status is zero.</p>
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<p>Because pipeline assignment of standard input or standard output
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or both takes place before redirection, it can be modified by
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redirection. For example:</p>
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<p>command1 2>&1 | command2</p>
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<p>sends both the standard output and standard error of <em>
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command1</em> to the standard input of <em>command2</em>.</p>
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</body>
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</html>
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