199 lines
7.9 KiB
HTML
199 lines
7.9 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<meta name="generator" content="HTML Tidy, see www.w3.org">
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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>pclose</title>
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</head>
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<body bgcolor="white">
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<script type="text/javascript" language="JavaScript" src="../jscript/codes.js">
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<basefont size="3"> <a name="pclose"></a> <a name="tag_03_416"></a><!-- pclose -->
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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_03_416_01"></a>NAME</h4>
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<blockquote>pclose - close a pipe stream to or from a process</blockquote>
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<h4><a name="tag_03_416_02"></a>SYNOPSIS</h4>
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<blockquote class="synopsis">
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<div class="box"><code><tt><sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src="../images/opt-start.gif" alt=
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"[Option Start]" border="0"> #include <<a href="../basedefs/stdio.h.html">stdio.h</a>><br>
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<br>
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int pclose(FILE *</tt><i>stream</i><tt>); <img src="../images/opt-end.gif" alt="[Option End]" border="0"></tt></code></div>
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<tt><br>
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</tt></blockquote>
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<h4><a name="tag_03_416_03"></a>DESCRIPTION</h4>
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<blockquote>
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<p>The <i>pclose</i>() function shall close a stream that was opened by <a href="../functions/popen.html"><i>popen</i>()</a>, wait
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for the command to terminate, and return the termination status of the process that was running the command language interpreter.
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However, if a call caused the termination status to be unavailable to <i>pclose</i>(), then <i>pclose</i>() shall return -1 with
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<i>errno</i> set to [ECHILD] to report this situation. This can happen if the application calls one of the following functions:</p>
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<ul>
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<li>
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<p><a href="../functions/wait.html"><i>wait</i>()</a></p>
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</li>
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<li>
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<p><a href="../functions/waitpid.html"><i>waitpid</i>()</a> with a <i>pid</i> argument less than or equal to 0 or equal to the
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process ID of the command line interpreter</p>
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</li>
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<li>
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<p>Any other function not defined in this volume of IEEE Std 1003.1-2001 that could do one of the above</p>
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</li>
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</ul>
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<p>In any case, <i>pclose</i>() shall not return before the child process created by <a href=
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"../functions/popen.html"><i>popen</i>()</a> has terminated.</p>
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<p>If the command language interpreter cannot be executed, the child termination status returned by <i>pclose</i>() shall be as if
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the command language interpreter terminated using <i>exit</i>(127) or <i>_exit</i>(127).</p>
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<p>The <i>pclose</i>() function shall not affect the termination status of any child of the calling process other than the one
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created by <a href="../functions/popen.html"><i>popen</i>()</a> for the associated stream.</p>
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<p>If the argument <i>stream</i> to <i>pclose</i>() is not a pointer to a stream created by <a href=
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"../functions/popen.html"><i>popen</i>()</a>, the result of <i>pclose</i>() is undefined.</p>
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</blockquote>
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<h4><a name="tag_03_416_04"></a>RETURN VALUE</h4>
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<blockquote>
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<p>Upon successful return, <i>pclose</i>() shall return the termination status of the command language interpreter. Otherwise,
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<i>pclose</i>() shall return -1 and set <i>errno</i> to indicate the error.</p>
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</blockquote>
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<h4><a name="tag_03_416_05"></a>ERRORS</h4>
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<blockquote>
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<p>The <i>pclose</i>() function shall fail if:</p>
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<dl compact>
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<dt>[ECHILD]</dt>
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<dd>The status of the child process could not be obtained, as described above.</dd>
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</dl>
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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_03_416_06"></a>EXAMPLES</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_03_416_07"></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_03_416_08"></a>RATIONALE</h4>
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<blockquote>
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<p>There is a requirement that <i>pclose</i>() not return before the child process terminates. This is intended to disallow
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implementations that return [EINTR] if a signal is received while waiting. If <i>pclose</i>() returned before the child terminated,
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there would be no way for the application to discover which child used to be associated with the stream, and it could not do the
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cleanup itself.</p>
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<p>If the stream pointed to by <i>stream</i> was not created by <a href="../functions/popen.html"><i>popen</i>()</a>, historical
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implementations of <i>pclose</i>() return -1 without setting <i>errno</i>. To avoid requiring <i>pclose</i>() to set <i>errno</i>
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in this case, IEEE Std 1003.1-2001 makes the behavior unspecified. An application should not use <i>pclose</i>() to close
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any stream that was not created by <a href="../functions/popen.html"><i>popen</i>()</a>.</p>
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<p>Some historical implementations of <i>pclose</i>() either block or ignore the signals SIGINT, SIGQUIT, and SIGHUP while waiting
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for the child process to terminate. Since this behavior is not described for the <i>pclose</i>() function in
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IEEE Std 1003.1-2001, such implementations are not conforming. Also, some historical implementations return [EINTR] if a
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signal is received, even though the child process has not terminated. Such implementations are also considered non-conforming.</p>
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<p>Consider, for example, an application that uses:</p>
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<pre>
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<tt>popen("command", "r")
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</tt>
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</pre>
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<p>to start <i>command</i>, which is part of the same application. The parent writes a prompt to its standard output (presumably
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the terminal) and then reads from the <a href="../functions/popen.html"><i>popen</i>()</a>ed stream. The child reads the response
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from the user, does some transformation on the response (pathname expansion, perhaps) and writes the result to its standard output.
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The parent process reads the result from the pipe, does something with it, and prints another prompt. The cycle repeats. Assuming
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that both processes do appropriate buffer flushing, this would be expected to work.</p>
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<p>To conform to IEEE Std 1003.1-2001, <i>pclose</i>() must use <a href="../functions/waitpid.html"><i>waitpid</i>()</a>,
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or some similar function, instead of <a href="../functions/wait.html"><i>wait</i>()</a>.</p>
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<p>The code sample below illustrates how the <i>pclose</i>() function might be implemented on a system conforming to
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IEEE Std 1003.1-2001.</p>
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<pre>
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<tt>int pclose(FILE *stream)
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{
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int stat;
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pid_t pid;
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<br>
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pid = <pid for process created for stream by popen()>
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(void) fclose(stream);
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while (waitpid(pid, &stat, 0) == -1) {
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if (errno != EINTR){
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stat = -1;
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break;
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}
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}
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return(stat);
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}
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</tt>
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</pre>
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</blockquote>
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<h4><a name="tag_03_416_09"></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_03_416_10"></a>SEE ALSO</h4>
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<blockquote>
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<p><a href="fork.html"><i>fork</i>()</a> , <a href="popen.html"><i>popen</i>()</a> , <a href="waitpid.html"><i>waitpid</i>()</a> ,
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the Base Definitions volume of IEEE Std 1003.1-2001, <a href="../basedefs/stdio.h.html"><i><stdio.h></i></a></p>
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</blockquote>
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<h4><a name="tag_03_416_11"></a>CHANGE HISTORY</h4>
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<blockquote>
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<p>First released in Issue 1. Derived from Issue 1 of the SVID.</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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<hr size="2" noshade>
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<center><font size="2"><!--footer start-->
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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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