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Unix Specific Services</a> »</li> </ul> </div> <div class="document"> <div class="documentwrapper"> <div class="bodywrapper"> <div class="body"> <div class="section" id="module-pipes"> <span id="pipes-interface-to-shell-pipelines"></span><h1>35.11. <a class="reference internal" href="#module-pipes" title="pipes: A Python interface to Unix shell pipelines. (Unix)"><tt class="xref py py-mod docutils literal"><span class="pre">pipes</span></tt></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="http://hg.python.org/cpython/file/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)"><tt class="xref py py-mod docutils literal"><span class="pre">pipes</span></tt></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"><tt class="xref py py-func docutils literal"><span class="pre">os.system()</span></tt></a> and <a class="reference internal" href="os.html#os.popen" title="os.popen"><tt class="xref py py-func docutils literal"><span class="pre">os.popen()</span></tt></a> is required.</p> <dl class="class"> <dt id="pipes.Template"> <em class="property">class </em><tt class="descclassname">pipes.</tt><tt class="descname">Template</tt><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-python"><div class="highlight"><pre><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="s">'tr a-z A-Z'</span><span class="p">,</span> <span class="s">'--'</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="s">'pipefile'</span><span class="p">,</span> <span class="s">'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="s">'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="s">'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"> <tt class="descclassname">pipes.</tt><tt class="descname">quote</tt><big>(</big><em>s</em><big>)</big><a class="headerlink" href="#pipes.quote" title="Permalink to this definition">¶</a></dt> <dd><p class="deprecated"> <span class="versionmodified">Deprecated since version 1.6: </span>Prior to Python 2.7, this function was not publicly documented. It is finally exposed publicly in Python 3.3 as the <tt class="xref py py-func docutils literal"><span class="pre">quote</span></tt> function in the <a class="reference internal" href="shlex.html#module-shlex" title="shlex: Simple lexical analysis for Unix shell-like languages."><tt class="xref py py-mod docutils literal"><span class="pre">shlex</span></tt></a> module.</p> <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-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">filename</span> <span class="o">=</span> <span class="s">'somefile; rm -rf ~'</span> <span class="gp">>>> </span><span class="n">command</span> <span class="o">=</span> <span class="s">'ls -l {}'</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="k">print</span> <span class="n">command</span> <span class="c"># 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"><tt class="xref py py-func docutils literal"><span class="pre">quote()</span></tt></a> lets you plug the security hole:</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">command</span> <span class="o">=</span> <span class="s">'ls -l {}'</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="k">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="s">'ssh home {}'</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="k">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"><tt class="xref py py-func docutils literal"><span class="pre">shlex.split()</span></tt></a>:</p> <div class="highlight-python"><div class="highlight"><pre><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>35.11.1. 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"> <tt class="descclassname">Template.</tt><tt class="descname">reset</tt><big>(</big><big>)</big><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"> <tt class="descclassname">Template.</tt><tt class="descname">clone</tt><big>(</big><big>)</big><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"> <tt class="descclassname">Template.</tt><tt class="descname">debug</tt><big>(</big><em>flag</em><big>)</big><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 <tt class="docutils literal"><span class="pre">set</span> <span class="pre">-x</span></tt> command to be more verbose.</p> </dd></dl> <dl class="method"> <dt id="pipes.Template.append"> <tt class="descclassname">Template.</tt><tt class="descname">append</tt><big>(</big><em>cmd</em>, <em>kind</em><big>)</big><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 <tt class="docutils literal"><span class="pre">'-'</span></tt> (which means the command reads its standard input), <tt class="docutils literal"><span class="pre">'f'</span></tt> (which means the commands reads a given file on the command line) or <tt class="docutils literal"><span class="pre">'.'</span></tt> (which means the commands reads no input, and hence must be first.)</p> <p>Similarly, the second letter can be either of <tt class="docutils literal"><span class="pre">'-'</span></tt> (which means the command writes to standard output), <tt class="docutils literal"><span class="pre">'f'</span></tt> (which means the command writes a file on the command line) or <tt class="docutils literal"><span class="pre">'.'</span></tt> (which means the command does not write anything, and hence must be last.)</p> </dd></dl> <dl class="method"> <dt id="pipes.Template.prepend"> <tt class="descclassname">Template.</tt><tt class="descname">prepend</tt><big>(</big><em>cmd</em>, <em>kind</em><big>)</big><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"><tt class="xref py py-meth docutils literal"><span class="pre">append()</span></tt></a> for explanations of the arguments.</p> </dd></dl> <dl class="method"> <dt id="pipes.Template.open"> <tt class="descclassname">Template.</tt><tt class="descname">open</tt><big>(</big><em>file</em>, <em>mode</em><big>)</big><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 <tt class="docutils literal"><span class="pre">'r'</span></tt>, <tt class="docutils literal"><span class="pre">'w'</span></tt> may be given.</p> </dd></dl> <dl class="method"> <dt id="pipes.Template.copy"> <tt class="descclassname">Template.</tt><tt class="descname">copy</tt><big>(</big><em>infile</em>, <em>outfile</em><big>)</big><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> </div> <div class="sphinxsidebar"> <div class="sphinxsidebarwrapper"> <h3><a href="../contents.html">Table Of Contents</a></h3> <ul> <li><a class="reference internal" href="#">35.11. <tt class="docutils literal"><span class="pre">pipes</span></tt> — Interface to shell pipelines</a><ul> <li><a class="reference internal" href="#template-objects">35.11.1. Template Objects</a></li> </ul> </li> </ul> <h4>Previous topic</h4> <p class="topless"><a href="fcntl.html" title="previous chapter">35.10. <tt class="docutils literal"><span class="pre">fcntl</span></tt> — The <tt class="docutils literal"><span class="pre">fcntl()</span></tt> and <tt class="docutils literal"><span class="pre">ioctl()</span></tt> system calls</a></p> <h4>Next topic</h4> <p class="topless"><a href="posixfile.html" title="next chapter">35.12. <tt class="docutils literal"><span class="pre">posixfile</span></tt> — File-like objects with locking support</a></p> <h3>This Page</h3> <ul class="this-page-menu"> <li><a href="../bugs.html">Report a Bug</a></li> <li><a href="../_sources/library/pipes.txt" rel="nofollow">Show Source</a></li> </ul> <div id="searchbox" style="display: none"> <h3>Quick search</h3> <form class="search" action="../search.html" method="get"> <input type="text" name="q" /> <input type="submit" value="Go" /> <input type="hidden" name="check_keywords" value="yes" /> <input type="hidden" name="area" value="default" /> </form> <p class="searchtip" style="font-size: 90%"> Enter search terms or a module, class or function name. </p> </div> <script type="text/javascript">$('#searchbox').show(0);</script> </div> </div> <div class="clearer"></div> </div> <div class="related"> <h3>Navigation</h3> <ul> <li class="right" style="margin-right: 10px"> <a href="../genindex.html" title="General Index" >index</a></li> <li class="right" > <a href="../py-modindex.html" title="Python Module Index" >modules</a> |</li> <li class="right" > <a href="posixfile.html" title="35.12. posixfile — File-like objects with locking support" >next</a> |</li> <li class="right" > <a href="fcntl.html" title="35.10. fcntl — The fcntl() and ioctl() system calls" >previous</a> |</li> <li><img src="../_static/py.png" alt="" style="vertical-align: middle; margin-top: -1px"/></li> <li><a href="http://www.python.org/">Python</a> »</li> <li> <a href="../index.html">Python 2.7.5 documentation</a> » </li> <li><a href="index.html" >The Python Standard Library</a> »</li> <li><a href="unix.html" >35. 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