210 lines
12 KiB
HTML
210 lines
12 KiB
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<!-- Created by GNU Texinfo 7.1, https://www.gnu.org/software/texinfo/ -->
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<!-- This manual documents Guile version 3.0.10.
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Copyright (C) 1996-1997, 2000-2005, 2009-2023 Free Software Foundation,
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Inc.
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Copyright (C) 2021 Maxime Devos
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Copyright (C) 2024 Tomas Volf
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Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.3 or
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any later version published by the Free Software Foundation; with no
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Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A
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copy of the license is included in the section entitled "GNU Free
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Documentation License." -->
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<title>Pipes (Guile Reference Manual)</title>
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<meta name="description" content="Pipes (Guile Reference Manual)">
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<link href="index.html" rel="start" title="Top">
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<link href="Concept-Index.html" rel="index" title="Concept Index">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="POSIX.html" rel="up" title="POSIX">
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<link href="Networking.html" rel="next" title="Networking">
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<link href="Terminals-and-Ptys.html" rel="prev" title="Terminals and Ptys">
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<link rel="stylesheet" type="text/css" href="https://www.gnu.org/software/gnulib/manual.css">
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</head>
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<body lang="en">
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<div class="subsection-level-extent" id="Pipes">
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<div class="nav-panel">
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<p>
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Next: <a href="Networking.html" accesskey="n" rel="next">Networking</a>, Previous: <a href="Terminals-and-Ptys.html" accesskey="p" rel="prev">Terminals and Ptys</a>, Up: <a href="POSIX.html" accesskey="u" rel="up"><abbr class="acronym">POSIX</abbr> System Calls and Networking</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html" title="Index" rel="index">Index</a>]</p>
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</div>
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<hr>
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<h4 class="subsection" id="Pipes-1"><span>7.2.10 Pipes<a class="copiable-link" href="#Pipes-1"> ¶</a></span></h4>
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<a class="index-entry-id" id="index-pipe-1"></a>
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<p>The following procedures are similar to the <code class="code">popen</code> and
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<code class="code">pclose</code> system routines. The code is in a separate “popen”
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module<a class="footnote" id="DOCF24" href="#FOOT24"><sup>24</sup></a>:
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</p>
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<div class="example lisp">
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<pre class="lisp-preformatted">(use-modules (ice-9 popen))
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</pre></div>
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<a class="index-entry-id" id="index-popen"></a>
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<dl class="first-deffn">
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<dt class="deffn" id="index-open_002dpipe"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">open-pipe</strong> <var class="def-var-arguments">command mode</var><a class="copiable-link" href="#index-open_002dpipe"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-open_002dpipe_002a"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">open-pipe*</strong> <var class="def-var-arguments">mode prog [args...]</var><a class="copiable-link" href="#index-open_002dpipe_002a"> ¶</a></span></dt>
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<dd><p>Execute a command in a subprocess, with a pipe to it or from it, or
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with pipes in both directions.
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</p>
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<p><code class="code">open-pipe</code> runs the shell <var class="var">command</var> using ‘<samp class="samp">/bin/sh -c</samp>’.
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<code class="code">open-pipe*</code> executes <var class="var">prog</var> directly, with the optional
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<var class="var">args</var> arguments (all strings).
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</p>
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<p><var class="var">mode</var> should be one of the following values. <code class="code">OPEN_READ</code> is
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an input pipe, ie. to read from the subprocess. <code class="code">OPEN_WRITE</code>
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is an output pipe, ie. to write to it.
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</p>
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<dl class="first-defvr first-defvar-alias-first-defvr">
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<dt class="defvr defvar-alias-defvr" id="index-OPEN_005fREAD"><span class="category-def">Variable: </span><span><strong class="def-name">OPEN_READ</strong><a class="copiable-link" href="#index-OPEN_005fREAD"> ¶</a></span></dt>
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<dt class="defvrx defvarx-alias-defvrx def-cmd-defvr" id="index-OPEN_005fWRITE"><span class="category-def">Variable: </span><span><strong class="def-name">OPEN_WRITE</strong><a class="copiable-link" href="#index-OPEN_005fWRITE"> ¶</a></span></dt>
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<dt class="defvrx defvarx-alias-defvrx def-cmd-defvr" id="index-OPEN_005fBOTH"><span class="category-def">Variable: </span><span><strong class="def-name">OPEN_BOTH</strong><a class="copiable-link" href="#index-OPEN_005fBOTH"> ¶</a></span></dt>
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</dl>
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<p>For an input pipe, the child’s standard output is the pipe and
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standard input is inherited from <code class="code">current-input-port</code>. For an
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output pipe, the child’s standard input is the pipe and standard
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output is inherited from <code class="code">current-output-port</code>. In all cases
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the child’s standard error is inherited from
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<code class="code">current-error-port</code> (see <a class="pxref" href="Default-Ports.html">Default Ports for Input, Output and Errors</a>).
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</p>
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<p>If those <code class="code">current-X-ports</code> are not files of some kind, and hence
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don’t have file descriptors for the child, then <samp class="file">/dev/null</samp> is
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used instead.
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</p>
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<p>Care should be taken with <code class="code">OPEN_BOTH</code>, a deadlock will occur if
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both parent and child are writing, and waiting until the write completes
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before doing any reading. Each direction has <code class="code">PIPE_BUF</code> bytes of
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buffering (see <a class="pxref" href="Buffering.html">Buffering</a>), which will be enough for small writes,
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but not for say putting a big file through a filter.
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</p></dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-open_002dinput_002dpipe"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">open-input-pipe</strong> <var class="def-var-arguments">command</var><a class="copiable-link" href="#index-open_002dinput_002dpipe"> ¶</a></span></dt>
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<dd><p>Equivalent to <code class="code">open-pipe</code> with mode <code class="code">OPEN_READ</code>.
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</p>
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<div class="example lisp">
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<pre class="lisp-preformatted">(let* ((port (open-input-pipe "date --utc"))
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(str (read-line port))) ; from (ice-9 rdelim)
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(close-pipe port)
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str)
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⇒ "Mon Mar 11 20:10:44 UTC 2002"
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</pre></div>
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</dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-open_002doutput_002dpipe"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">open-output-pipe</strong> <var class="def-var-arguments">command</var><a class="copiable-link" href="#index-open_002doutput_002dpipe"> ¶</a></span></dt>
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<dd><p>Equivalent to <code class="code">open-pipe</code> with mode <code class="code">OPEN_WRITE</code>.
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</p>
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<div class="example lisp">
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<pre class="lisp-preformatted">(let ((port (open-output-pipe "lpr")))
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(display "Something for the line printer.\n" port)
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(if (not (eqv? 0 (status:exit-val (close-pipe port))))
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(error "Cannot print")))
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</pre></div>
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</dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-open_002dinput_002doutput_002dpipe"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">open-input-output-pipe</strong> <var class="def-var-arguments">command</var><a class="copiable-link" href="#index-open_002dinput_002doutput_002dpipe"> ¶</a></span></dt>
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<dd><p>Equivalent to <code class="code">open-pipe</code> with mode <code class="code">OPEN_BOTH</code>.
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</p></dd></dl>
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<a class="index-entry-id" id="index-pclose"></a>
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<dl class="first-deffn">
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<dt class="deffn" id="index-close_002dpipe"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">close-pipe</strong> <var class="def-var-arguments">port</var><a class="copiable-link" href="#index-close_002dpipe"> ¶</a></span></dt>
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<dd><p>Close a pipe created by <code class="code">open-pipe</code>, wait for the process to
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terminate, and return the wait status code. The status is as per
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<code class="code">waitpid</code> and can be decoded with <code class="code">status:exit-val</code> etc
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(see <a class="pxref" href="Processes.html">Processes</a>)
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</p></dd></dl>
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<br>
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<p><code class="code">waitpid WAIT_ANY</code> should not be used when pipes are open, since
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it can reap a pipe’s child process, causing an error from a subsequent
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<code class="code">close-pipe</code>.
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</p>
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<p><code class="code">close-port</code> (see <a class="pxref" href="Ports.html">Ports</a>) can close a pipe, but it doesn’t reap
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the child process.
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</p>
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<p>The garbage collector will close a pipe no longer in use, and reap the
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child process with <code class="code">waitpid</code>. If the child hasn’t yet terminated
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the garbage collector doesn’t block, but instead checks again in the
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next GC.
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</p>
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<p>Many systems have per-user and system-wide limits on the number of
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processes, and a system-wide limit on the number of pipes, so pipes
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should be closed explicitly when no longer needed, rather than letting
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the garbage collector pick them up at some later time.
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</p>
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<dl class="first-deffn">
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<dt class="deffn" id="index-pipeline"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">pipeline</strong> <var class="def-var-arguments"><var class="var">commands</var></var><a class="copiable-link" href="#index-pipeline"> ¶</a></span></dt>
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<dd><p>Execute a pipeline of <var class="var">commands</var>, where each command is a
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list of a program and its arguments as strings, returning an input
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port to the end of the pipeline, an output port to the beginning of the
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pipeline and a list of PIDs of the processes executing the <var class="var">commands</var>.
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</p>
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<div class="example">
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<pre class="example-preformatted">(let ((commands '(("git" "ls-files")
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("tar" "-cf-" "-T-")
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("sha1sum" "-")))
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(success? (lambda (pid)
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(zero?
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(status:exit-val (cdr (waitpid pid)))))))
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(receive (from to pids) (pipeline commands)
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(let* ((sha1 (read-delimited " " from))
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(index (list-index (negate success?) (reverse pids))))
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(close to)
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(close from)
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(if (not index)
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sha1
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(string-append "pipeline failed in command: "
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(string-join (list-ref commands index)))))))
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⇒ "52f99d234503fca8c84ef94b1005a3a28d8b3bc1"
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</pre></div>
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</dd></dl>
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</div>
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<div class="footnotes-segment">
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<hr>
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<h4 class="footnotes-heading">Footnotes</h4>
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<h5 class="footnote-body-heading"><a id="FOOT24" href="#DOCF24">(24)</a></h5>
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<p>This module is only available on systems where the
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<code class="code">popen</code> feature is provided (see <a class="pxref" href="Common-Feature-Symbols.html">Common Feature Symbols</a>).</p>
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</div>
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<hr>
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<div class="nav-panel">
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<p>
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Next: <a href="Networking.html">Networking</a>, Previous: <a href="Terminals-and-Ptys.html">Terminals and Ptys</a>, Up: <a href="POSIX.html"><abbr class="acronym">POSIX</abbr> System Calls and Networking</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html" title="Index" rel="index">Index</a>]</p>
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</div>
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</body>
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</html>
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