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<div class="section" id="module-pipes">
<span id="pipes-interface-to-shell-pipelines"></span><h1>36.11. <a class="reference internal" href="#module-pipes" title="pipes: A Python interface to Unix shell pipelines. (Unix)"><code class="xref py py-mod docutils literal notranslate"><span class="pre">pipes</span></code></a> — Interface to shell pipelines<a class="headerlink" href="#module-pipes" title="Permalink to this headline">¶</a></h1>
<p><strong>Source code:</strong> <a class="reference external" href="https://github.com/python/cpython/tree/2.7/Lib/pipes.py">Lib/pipes.py</a></p>
<hr class="docutils" />
<p>The <a class="reference internal" href="#module-pipes" title="pipes: A Python interface to Unix shell pipelines. (Unix)"><code class="xref py py-mod docutils literal notranslate"><span class="pre">pipes</span></code></a> module defines a class to abstract the concept of a <em>pipeline</em>
— a sequence of converters from one file to another.</p>
<p>Because the module uses <strong class="program">/bin/sh</strong> command lines, a POSIX or compatible
shell for <a class="reference internal" href="os.html#os.system" title="os.system"><code class="xref py py-func docutils literal notranslate"><span class="pre">os.system()</span></code></a> and <a class="reference internal" href="os.html#os.popen" title="os.popen"><code class="xref py py-func docutils literal notranslate"><span class="pre">os.popen()</span></code></a> is required.</p>
<dl class="class">
<dt id="pipes.Template">
<em class="property">class </em><code class="descclassname">pipes.</code><code class="descname">Template</code><a class="headerlink" href="#pipes.Template" title="Permalink to this definition">¶</a></dt>
<dd><p>An abstraction of a pipeline.</p>
</dd></dl>
<p>Example:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="kn">import</span> <span class="nn">pipes</span>
<span class="gp">>>> </span><span class="n">t</span> <span class="o">=</span> <span class="n">pipes</span><span class="o">.</span><span class="n">Template</span><span class="p">()</span>
<span class="gp">>>> </span><span class="n">t</span><span class="o">.</span><span class="n">append</span><span class="p">(</span><span class="s1">'tr a-z A-Z'</span><span class="p">,</span> <span class="s1">'--'</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">f</span> <span class="o">=</span> <span class="n">t</span><span class="o">.</span><span class="n">open</span><span class="p">(</span><span class="s1">'pipefile'</span><span class="p">,</span> <span class="s1">'w'</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">f</span><span class="o">.</span><span class="n">write</span><span class="p">(</span><span class="s1">'hello world'</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">f</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>
<span class="gp">>>> </span><span class="nb">open</span><span class="p">(</span><span class="s1">'pipefile'</span><span class="p">)</span><span class="o">.</span><span class="n">read</span><span class="p">()</span>
<span class="go">'HELLO WORLD'</span>
</pre></div>
</div>
<dl class="function">
<dt id="pipes.quote">
<code class="descclassname">pipes.</code><code class="descname">quote</code><span class="sig-paren">(</span><em>s</em><span class="sig-paren">)</span><a class="headerlink" href="#pipes.quote" title="Permalink to this definition">¶</a></dt>
<dd><div class="deprecated">
<p><span class="versionmodified deprecated">Deprecated since version 2.7: </span>Prior to Python 2.7, this function was not publicly documented. It is
finally exposed publicly in Python 3.3 as the
<code class="xref py py-func docutils literal notranslate"><span class="pre">quote</span></code> function in the <a class="reference internal" href="shlex.html#module-shlex" title="shlex: Simple lexical analysis for Unix shell-like languages."><code class="xref py py-mod docutils literal notranslate"><span class="pre">shlex</span></code></a> module.</p>
</div>
<p>Return a shell-escaped version of the string <em>s</em>. The returned value is a
string that can safely be used as one token in a shell command line, for
cases where you cannot use a list.</p>
<p>This idiom would be unsafe:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">filename</span> <span class="o">=</span> <span class="s1">'somefile; rm -rf ~'</span>
<span class="gp">>>> </span><span class="n">command</span> <span class="o">=</span> <span class="s1">'ls -l </span><span class="si">{}</span><span class="s1">'</span><span class="o">.</span><span class="n">format</span><span class="p">(</span><span class="n">filename</span><span class="p">)</span>
<span class="gp">>>> </span><span class="nb">print</span> <span class="n">command</span> <span class="c1"># executed by a shell: boom!</span>
<span class="go">ls -l somefile; rm -rf ~</span>
</pre></div>
</div>
<p><a class="reference internal" href="#pipes.quote" title="pipes.quote"><code class="xref py py-func docutils literal notranslate"><span class="pre">quote()</span></code></a> lets you plug the security hole:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">command</span> <span class="o">=</span> <span class="s1">'ls -l </span><span class="si">{}</span><span class="s1">'</span><span class="o">.</span><span class="n">format</span><span class="p">(</span><span class="n">quote</span><span class="p">(</span><span class="n">filename</span><span class="p">))</span>
<span class="gp">>>> </span><span class="nb">print</span> <span class="n">command</span>
<span class="go">ls -l 'somefile; rm -rf ~'</span>
<span class="gp">>>> </span><span class="n">remote_command</span> <span class="o">=</span> <span class="s1">'ssh home </span><span class="si">{}</span><span class="s1">'</span><span class="o">.</span><span class="n">format</span><span class="p">(</span><span class="n">quote</span><span class="p">(</span><span class="n">command</span><span class="p">))</span>
<span class="gp">>>> </span><span class="nb">print</span> <span class="n">remote_command</span>
<span class="go">ssh home 'ls -l '"'"'somefile; rm -rf ~'"'"''</span>
</pre></div>
</div>
<p>The quoting is compatible with UNIX shells and with <a class="reference internal" href="shlex.html#shlex.split" title="shlex.split"><code class="xref py py-func docutils literal notranslate"><span class="pre">shlex.split()</span></code></a>:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">remote_command</span> <span class="o">=</span> <span class="n">shlex</span><span class="o">.</span><span class="n">split</span><span class="p">(</span><span class="n">remote_command</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">remote_command</span>
<span class="go">['ssh', 'home', "ls -l 'somefile; rm -rf ~'"]</span>
<span class="gp">>>> </span><span class="n">command</span> <span class="o">=</span> <span class="n">shlex</span><span class="o">.</span><span class="n">split</span><span class="p">(</span><span class="n">remote_command</span><span class="p">[</span><span class="o">-</span><span class="mi">1</span><span class="p">])</span>
<span class="gp">>>> </span><span class="n">command</span>
<span class="go">['ls', '-l', 'somefile; rm -rf ~']</span>
</pre></div>
</div>
</dd></dl>
<div class="section" id="template-objects">
<span id="id1"></span><h2>36.11.1. Template Objects<a class="headerlink" href="#template-objects" title="Permalink to this headline">¶</a></h2>
<p>Template objects following methods:</p>
<dl class="method">
<dt id="pipes.Template.reset">
<code class="descclassname">Template.</code><code class="descname">reset</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#pipes.Template.reset" title="Permalink to this definition">¶</a></dt>
<dd><p>Restore a pipeline template to its initial state.</p>
</dd></dl>
<dl class="method">
<dt id="pipes.Template.clone">
<code class="descclassname">Template.</code><code class="descname">clone</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#pipes.Template.clone" title="Permalink to this definition">¶</a></dt>
<dd><p>Return a new, equivalent, pipeline template.</p>
</dd></dl>
<dl class="method">
<dt id="pipes.Template.debug">
<code class="descclassname">Template.</code><code class="descname">debug</code><span class="sig-paren">(</span><em>flag</em><span class="sig-paren">)</span><a class="headerlink" href="#pipes.Template.debug" title="Permalink to this definition">¶</a></dt>
<dd><p>If <em>flag</em> is true, turn debugging on. Otherwise, turn debugging off. When
debugging is on, commands to be executed are printed, and the shell is given
<code class="docutils literal notranslate"><span class="pre">set</span> <span class="pre">-x</span></code> command to be more verbose.</p>
</dd></dl>
<dl class="method">
<dt id="pipes.Template.append">
<code class="descclassname">Template.</code><code class="descname">append</code><span class="sig-paren">(</span><em>cmd</em>, <em>kind</em><span class="sig-paren">)</span><a class="headerlink" href="#pipes.Template.append" title="Permalink to this definition">¶</a></dt>
<dd><p>Append a new action at the end. The <em>cmd</em> variable must be a valid bourne shell
command. The <em>kind</em> variable consists of two letters.</p>
<p>The first letter can be either of <code class="docutils literal notranslate"><span class="pre">'-'</span></code> (which means the command reads its
standard input), <code class="docutils literal notranslate"><span class="pre">'f'</span></code> (which means the commands reads a given file on the
command line) or <code class="docutils literal notranslate"><span class="pre">'.'</span></code> (which means the commands reads no input, and hence
must be first.)</p>
<p>Similarly, the second letter can be either of <code class="docutils literal notranslate"><span class="pre">'-'</span></code> (which means the command
writes to standard output), <code class="docutils literal notranslate"><span class="pre">'f'</span></code> (which means the command writes a file on
the command line) or <code class="docutils literal notranslate"><span class="pre">'.'</span></code> (which means the command does not write anything,
and hence must be last.)</p>
</dd></dl>
<dl class="method">
<dt id="pipes.Template.prepend">
<code class="descclassname">Template.</code><code class="descname">prepend</code><span class="sig-paren">(</span><em>cmd</em>, <em>kind</em><span class="sig-paren">)</span><a class="headerlink" href="#pipes.Template.prepend" title="Permalink to this definition">¶</a></dt>
<dd><p>Add a new action at the beginning. See <a class="reference internal" href="#pipes.Template.append" title="pipes.Template.append"><code class="xref py py-meth docutils literal notranslate"><span class="pre">append()</span></code></a> for explanations of the
arguments.</p>
</dd></dl>
<dl class="method">
<dt id="pipes.Template.open">
<code class="descclassname">Template.</code><code class="descname">open</code><span class="sig-paren">(</span><em>file</em>, <em>mode</em><span class="sig-paren">)</span><a class="headerlink" href="#pipes.Template.open" title="Permalink to this definition">¶</a></dt>
<dd><p>Return a file-like object, open to <em>file</em>, but read from or written to by the
pipeline. Note that only one of <code class="docutils literal notranslate"><span class="pre">'r'</span></code>, <code class="docutils literal notranslate"><span class="pre">'w'</span></code> may be given.</p>
</dd></dl>
<dl class="method">
<dt id="pipes.Template.copy">
<code class="descclassname">Template.</code><code class="descname">copy</code><span class="sig-paren">(</span><em>infile</em>, <em>outfile</em><span class="sig-paren">)</span><a class="headerlink" href="#pipes.Template.copy" title="Permalink to this definition">¶</a></dt>
<dd><p>Copy <em>infile</em> to <em>outfile</em> through the pipe.</p>
</dd></dl>
</div>
</div>
</div>
</div>
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<h3><a href="../contents.html">Table of Contents</a></h3>
<ul>
<li><a class="reference internal" href="#">36.11. <code class="xref py py-mod docutils literal notranslate"><span class="pre">pipes</span></code> — Interface to shell pipelines</a><ul>
<li><a class="reference internal" href="#template-objects">36.11.1. Template Objects</a></li>
</ul>
</li>
</ul>
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