217 lines
5.5 KiB
HTML
217 lines
5.5 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<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>exec</title>
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<body bgcolor="white">
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<basefont size="3"> <a name="exec"></a> <a name="tag_04_46"></a><!-- exec -->
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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_46_01"></a>NAME</h4>
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<blockquote>exec - execute commands and open, close, or copy file descriptors</blockquote>
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<h4><a name="tag_04_46_02"></a>SYNOPSIS</h4>
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<blockquote class="synopsis">
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<p><code><tt>exec</tt> <b>[</b><i>command</i> <b>[</b><i>argument</i> <tt>...</tt><b>]]</b></code></p>
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</blockquote>
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<h4><a name="tag_04_46_03"></a>DESCRIPTION</h4>
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<blockquote>
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<p>The <i>exec</i> utility shall open, close, and/or copy file descriptors as specified by any redirections as part of the
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command.</p>
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<p>If <i>exec</i> is specified without <i>command</i> or <i>argument</i>s, and any file descriptors with numbers greater than 2 are
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opened with associated redirection statements, it is unspecified whether those file descriptors remain open when the shell invokes
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another utility. Scripts concerned that child shells could misuse open file descriptors can always close them explicitly, as shown
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in one of the following examples.</p>
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<p>If <i>exec</i> is specified with <i>command</i>, it shall replace the shell with <i>command</i> without creating a new process.
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If <i>argument</i>s are specified, they shall be arguments to <i>command</i>. Redirection affects the current shell execution
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environment.</p>
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</blockquote>
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<h4><a name="tag_04_46_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_46_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_46_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_46_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_46_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_46_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_46_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_46_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_46_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_46_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_46_14"></a>EXIT STATUS</h4>
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<blockquote>
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<p>If <i>command</i> is specified, <i>exec</i> shall not return to the shell; rather, the exit status of the process shall be the
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exit status of the program implementing <i>command</i>, which overlaid the shell. If <i>command</i> is not found, the exit status
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shall be 127. If <i>command</i> is found, but it is not an executable utility, the exit status shall be 126. If a redirection error
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occurs (see <a href="xcu_chap02.html#tag_02_08_01"><i>Consequences of Shell Errors</i></a> ), the shell shall exit with a value in
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the range 1-125. Otherwise, <i>exec</i> shall return a zero exit status.</p>
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</blockquote>
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<h4><a name="tag_04_46_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_46_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_46_17"></a>EXAMPLES</h4>
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<blockquote>
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<p>Open <i>readfile</i> as file descriptor 3 for reading:</p>
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<pre>
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<tt>exec 3< readfile
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</tt>
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</pre>
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<p>Open <i>writefile</i> as file descriptor 4 for writing:</p>
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<pre>
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<tt>exec 4> writefile
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</tt>
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</pre>
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<p>Make file descriptor 5 a copy of file descriptor 0:</p>
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<pre>
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<tt>exec 5<&0
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</tt>
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</pre>
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<p>Close file descriptor 3:</p>
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<pre>
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<tt>exec 3<&-
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</tt>
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</pre>
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<p>Cat the file <b>maggie</b> by replacing the current shell with the <a href="../utilities/cat.html"><i>cat</i></a> utility:</p>
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<pre>
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<tt>exec cat maggie
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</tt>
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</pre>
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</blockquote>
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<h4><a name="tag_04_46_18"></a>RATIONALE</h4>
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<blockquote>
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<p>Most historical implementations were not conformant in that:</p>
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<pre>
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<tt>foo=bar exec cmd
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</tt>
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</pre>
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<p>did not pass <b>foo</b> to <b>cmd</b>.</p>
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</blockquote>
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<h4><a name="tag_04_46_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_46_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_46_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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