Edit File: cmd.html
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <title>23.1. cmd — Support for line-oriented command interpreters — Python v2.6.6 documentation</title> <link rel="stylesheet" href="../_static/default.css" type="text/css" /> <link rel="stylesheet" href="../_static/pygments.css" type="text/css" /> <script type="text/javascript"> var DOCUMENTATION_OPTIONS = { URL_ROOT: '../', VERSION: '2.6.6', COLLAPSE_MODINDEX: false, FILE_SUFFIX: '.html', HAS_SOURCE: true }; </script> <script type="text/javascript" src="../_static/jquery.js"></script> <script type="text/javascript" src="../_static/doctools.js"></script> <link rel="search" type="application/opensearchdescription+xml" title="Search within Python v2.6.6 documentation" href="../_static/opensearch.xml"/> <link rel="author" title="About these documents" href="../about.html" /> <link rel="copyright" title="Copyright" href="../copyright.html" /> <link rel="top" title="Python v2.6.6 documentation" href="../index.html" /> <link rel="up" title="23. Program Frameworks" href="frameworks.html" /> <link rel="next" title="23.2. shlex — Simple lexical analysis" href="shlex.html" /> <link rel="prev" title="23. Program Frameworks" href="frameworks.html" /> <link rel="shortcut icon" type="image/png" href="../_static/py.png" /> </head> <body> <div class="related"> <h3>Navigation</h3> <ul> <li class="right" style="margin-right: 10px"> <a href="../genindex.html" title="General Index" accesskey="I">index</a></li> <li class="right" > <a href="../modindex.html" title="Global Module Index" accesskey="M">modules</a> |</li> <li class="right" > <a href="shlex.html" title="23.2. shlex — Simple lexical analysis" accesskey="N">next</a> |</li> <li class="right" > <a href="frameworks.html" title="23. Program Frameworks" accesskey="P">previous</a> |</li> <li><img src="../_static/py.png" alt="" style="vertical-align: middle; margin-top: -1px"/></li> <li><a href="../index.html">Python v2.6.6 documentation</a> »</li> <li><a href="index.html" >The Python Standard Library</a> »</li> <li><a href="frameworks.html" accesskey="U">23. Program Frameworks</a> »</li> </ul> </div> <div class="document"> <div class="documentwrapper"> <div class="bodywrapper"> <div class="body"> <div class="section" id="module-cmd"> <h1>23.1. <tt class="xref docutils literal"><span class="pre">cmd</span></tt> — Support for line-oriented command interpreters<a class="headerlink" href="#module-cmd" title="Permalink to this headline">¶</a></h1> <p>The <a title="cmd.Cmd" class="reference internal" href="#cmd.Cmd"><tt class="xref docutils literal"><span class="pre">Cmd</span></tt></a> class provides a simple framework for writing line-oriented command interpreters. These are often useful for test harnesses, administrative tools, and prototypes that will later be wrapped in a more sophisticated interface.</p> <dl class="class"> <dt id="cmd.Cmd"> <em class="property">class </em><tt class="descclassname">cmd.</tt><tt class="descname">Cmd</tt><big>(</big><span class="optional">[</span><em>completekey</em><span class="optional">[</span>, <em>stdin</em><span class="optional">[</span>, <em>stdout</em><span class="optional">]</span><span class="optional">]</span><span class="optional">]</span><big>)</big><a class="headerlink" href="#cmd.Cmd" title="Permalink to this definition">¶</a></dt> <dd><p>A <a title="cmd.Cmd" class="reference internal" href="#cmd.Cmd"><tt class="xref docutils literal"><span class="pre">Cmd</span></tt></a> instance or subclass instance is a line-oriented interpreter framework. There is no good reason to instantiate <a title="cmd.Cmd" class="reference internal" href="#cmd.Cmd"><tt class="xref docutils literal"><span class="pre">Cmd</span></tt></a> itself; rather, it’s useful as a superclass of an interpreter class you define yourself in order to inherit <a title="cmd.Cmd" class="reference internal" href="#cmd.Cmd"><tt class="xref docutils literal"><span class="pre">Cmd</span></tt></a>‘s methods and encapsulate action methods.</p> <p>The optional argument <em>completekey</em> is the <a title="(Unix) GNU readline support for Python." class="reference external" href="readline.html#module-readline"><tt class="xref docutils literal"><span class="pre">readline</span></tt></a> name of a completion key; it defaults to <tt class="docutils literal"><span class="pre">Tab</span></tt>. If <em>completekey</em> is not <a title="None" class="reference external" href="constants.html#None"><tt class="xref xref docutils literal"><span class="pre">None</span></tt></a> and <a title="(Unix) GNU readline support for Python." class="reference external" href="readline.html#module-readline"><tt class="xref docutils literal"><span class="pre">readline</span></tt></a> is available, command completion is done automatically.</p> <p>The optional arguments <em>stdin</em> and <em>stdout</em> specify the input and output file objects that the Cmd instance or subclass instance will use for input and output. If not specified, they will default to <a title="sys.stdin" class="reference external" href="sys.html#sys.stdin"><tt class="xref docutils literal"><span class="pre">sys.stdin</span></tt></a> and <a title="sys.stdout" class="reference external" href="sys.html#sys.stdout"><tt class="xref docutils literal"><span class="pre">sys.stdout</span></tt></a>.</p> <p>If you want a given <em>stdin</em> to be used, make sure to set the instance’s <a title="cmd.Cmd.use_rawinput" class="reference internal" href="#cmd.Cmd.use_rawinput"><tt class="xref docutils literal"><span class="pre">use_rawinput</span></tt></a> attribute to <tt class="xref docutils literal"><span class="pre">False</span></tt>, otherwise <em>stdin</em> will be ignored.</p> <p class="versionchanged"> <span class="versionmodified">Changed in version 2.3: </span>The <em>stdin</em> and <em>stdout</em> parameters were added.</p> </dd></dl> <div class="section" id="cmd-objects"> <span id="id1"></span><h2>23.1.1. Cmd Objects<a class="headerlink" href="#cmd-objects" title="Permalink to this headline">¶</a></h2> <p>A <a title="cmd.Cmd" class="reference internal" href="#cmd.Cmd"><tt class="xref docutils literal"><span class="pre">Cmd</span></tt></a> instance has the following methods:</p> <dl class="method"> <dt id="cmd.Cmd.cmdloop"> <tt class="descclassname">Cmd.</tt><tt class="descname">cmdloop</tt><big>(</big><span class="optional">[</span><em>intro</em><span class="optional">]</span><big>)</big><a class="headerlink" href="#cmd.Cmd.cmdloop" title="Permalink to this definition">¶</a></dt> <dd><p>Repeatedly issue a prompt, accept input, parse an initial prefix off the received input, and dispatch to action methods, passing them the remainder of the line as argument.</p> <p>The optional argument is a banner or intro string to be issued before the first prompt (this overrides the <a title="cmd.Cmd.intro" class="reference internal" href="#cmd.Cmd.intro"><tt class="xref docutils literal"><span class="pre">intro</span></tt></a> class member).</p> <p>If the <a title="(Unix) GNU readline support for Python." class="reference external" href="readline.html#module-readline"><tt class="xref docutils literal"><span class="pre">readline</span></tt></a> module is loaded, input will automatically inherit <strong>bash</strong>-like history-list editing (e.g. <tt class="docutils literal"><span class="pre">Control-P</span></tt> scrolls back to the last command, <tt class="docutils literal"><span class="pre">Control-N</span></tt> forward to the next one, <tt class="docutils literal"><span class="pre">Control-F</span></tt> moves the cursor to the right non-destructively, <tt class="docutils literal"><span class="pre">Control-B</span></tt> moves the cursor to the left non-destructively, etc.).</p> <p>An end-of-file on input is passed back as the string <tt class="docutils literal"><span class="pre">'EOF'</span></tt>.</p> <p>An interpreter instance will recognize a command name <tt class="docutils literal"><span class="pre">foo</span></tt> if and only if it has a method <tt class="xref docutils literal"><span class="pre">do_foo()</span></tt>. As a special case, a line beginning with the character <tt class="docutils literal"><span class="pre">'?'</span></tt> is dispatched to the method <tt class="xref docutils literal"><span class="pre">do_help()</span></tt>. As another special case, a line beginning with the character <tt class="docutils literal"><span class="pre">'!'</span></tt> is dispatched to the method <tt class="xref docutils literal"><span class="pre">do_shell()</span></tt> (if such a method is defined).</p> <p>This method will return when the <a title="cmd.Cmd.postcmd" class="reference internal" href="#cmd.Cmd.postcmd"><tt class="xref docutils literal"><span class="pre">postcmd()</span></tt></a> method returns a true value. The <em>stop</em> argument to <a title="cmd.Cmd.postcmd" class="reference internal" href="#cmd.Cmd.postcmd"><tt class="xref docutils literal"><span class="pre">postcmd()</span></tt></a> is the return value from the command’s corresponding <tt class="xref docutils literal"><span class="pre">do_*()</span></tt> method.</p> <p>If completion is enabled, completing commands will be done automatically, and completing of commands args is done by calling <tt class="xref docutils literal"><span class="pre">complete_foo()</span></tt> with arguments <em>text</em>, <em>line</em>, <em>begidx</em>, and <em>endidx</em>. <em>text</em> is the string prefix we are attempting to match: all returned matches must begin with it. <em>line</em> is the current input line with leading whitespace removed, <em>begidx</em> and <em>endidx</em> are the beginning and ending indexes of the prefix text, which could be used to provide different completion depending upon which position the argument is in.</p> <p>All subclasses of <a title="cmd.Cmd" class="reference internal" href="#cmd.Cmd"><tt class="xref docutils literal"><span class="pre">Cmd</span></tt></a> inherit a predefined <tt class="xref docutils literal"><span class="pre">do_help()</span></tt>. This method, called with an argument <tt class="docutils literal"><span class="pre">'bar'</span></tt>, invokes the corresponding method <tt class="xref docutils literal"><span class="pre">help_bar()</span></tt>, and if that is not present, prints the docstring of <tt class="xref docutils literal"><span class="pre">do_bar()</span></tt>, if available. With no argument, <tt class="xref docutils literal"><span class="pre">do_help()</span></tt> lists all available help topics (that is, all commands with corresponding <tt class="xref docutils literal"><span class="pre">help_*()</span></tt> methods or commands that have docstrings), and also lists any undocumented commands.</p> </dd></dl> <dl class="method"> <dt id="cmd.Cmd.onecmd"> <tt class="descclassname">Cmd.</tt><tt class="descname">onecmd</tt><big>(</big><em>str</em><big>)</big><a class="headerlink" href="#cmd.Cmd.onecmd" title="Permalink to this definition">¶</a></dt> <dd>Interpret the argument as though it had been typed in response to the prompt. This may be overridden, but should not normally need to be; see the <a title="cmd.Cmd.precmd" class="reference internal" href="#cmd.Cmd.precmd"><tt class="xref docutils literal"><span class="pre">precmd()</span></tt></a> and <a title="cmd.Cmd.postcmd" class="reference internal" href="#cmd.Cmd.postcmd"><tt class="xref docutils literal"><span class="pre">postcmd()</span></tt></a> methods for useful execution hooks. The return value is a flag indicating whether interpretation of commands by the interpreter should stop. If there is a <tt class="xref docutils literal"><span class="pre">do_*()</span></tt> method for the command <em>str</em>, the return value of that method is returned, otherwise the return value from the <a title="cmd.Cmd.default" class="reference internal" href="#cmd.Cmd.default"><tt class="xref docutils literal"><span class="pre">default()</span></tt></a> method is returned.</dd></dl> <dl class="method"> <dt id="cmd.Cmd.emptyline"> <tt class="descclassname">Cmd.</tt><tt class="descname">emptyline</tt><big>(</big><big>)</big><a class="headerlink" href="#cmd.Cmd.emptyline" title="Permalink to this definition">¶</a></dt> <dd>Method called when an empty line is entered in response to the prompt. If this method is not overridden, it repeats the last nonempty command entered.</dd></dl> <dl class="method"> <dt id="cmd.Cmd.default"> <tt class="descclassname">Cmd.</tt><tt class="descname">default</tt><big>(</big><em>line</em><big>)</big><a class="headerlink" href="#cmd.Cmd.default" title="Permalink to this definition">¶</a></dt> <dd>Method called on an input line when the command prefix is not recognized. If this method is not overridden, it prints an error message and returns.</dd></dl> <dl class="method"> <dt id="cmd.Cmd.completedefault"> <tt class="descclassname">Cmd.</tt><tt class="descname">completedefault</tt><big>(</big><em>text</em>, <em>line</em>, <em>begidx</em>, <em>endidx</em><big>)</big><a class="headerlink" href="#cmd.Cmd.completedefault" title="Permalink to this definition">¶</a></dt> <dd>Method called to complete an input line when no command-specific <tt class="xref docutils literal"><span class="pre">complete_*()</span></tt> method is available. By default, it returns an empty list.</dd></dl> <dl class="method"> <dt id="cmd.Cmd.precmd"> <tt class="descclassname">Cmd.</tt><tt class="descname">precmd</tt><big>(</big><em>line</em><big>)</big><a class="headerlink" href="#cmd.Cmd.precmd" title="Permalink to this definition">¶</a></dt> <dd>Hook method executed just before the command line <em>line</em> is interpreted, but after the input prompt is generated and issued. This method is a stub in <a title="cmd.Cmd" class="reference internal" href="#cmd.Cmd"><tt class="xref docutils literal"><span class="pre">Cmd</span></tt></a>; it exists to be overridden by subclasses. The return value is used as the command which will be executed by the <a title="cmd.Cmd.onecmd" class="reference internal" href="#cmd.Cmd.onecmd"><tt class="xref docutils literal"><span class="pre">onecmd()</span></tt></a> method; the <a title="cmd.Cmd.precmd" class="reference internal" href="#cmd.Cmd.precmd"><tt class="xref docutils literal"><span class="pre">precmd()</span></tt></a> implementation may re-write the command or simply return <em>line</em> unchanged.</dd></dl> <dl class="method"> <dt id="cmd.Cmd.postcmd"> <tt class="descclassname">Cmd.</tt><tt class="descname">postcmd</tt><big>(</big><em>stop</em>, <em>line</em><big>)</big><a class="headerlink" href="#cmd.Cmd.postcmd" title="Permalink to this definition">¶</a></dt> <dd>Hook method executed just after a command dispatch is finished. This method is a stub in <a title="cmd.Cmd" class="reference internal" href="#cmd.Cmd"><tt class="xref docutils literal"><span class="pre">Cmd</span></tt></a>; it exists to be overridden by subclasses. <em>line</em> is the command line which was executed, and <em>stop</em> is a flag which indicates whether execution will be terminated after the call to <a title="cmd.Cmd.postcmd" class="reference internal" href="#cmd.Cmd.postcmd"><tt class="xref docutils literal"><span class="pre">postcmd()</span></tt></a>; this will be the return value of the <a title="cmd.Cmd.onecmd" class="reference internal" href="#cmd.Cmd.onecmd"><tt class="xref docutils literal"><span class="pre">onecmd()</span></tt></a> method. The return value of this method will be used as the new value for the internal flag which corresponds to <em>stop</em>; returning false will cause interpretation to continue.</dd></dl> <dl class="method"> <dt id="cmd.Cmd.preloop"> <tt class="descclassname">Cmd.</tt><tt class="descname">preloop</tt><big>(</big><big>)</big><a class="headerlink" href="#cmd.Cmd.preloop" title="Permalink to this definition">¶</a></dt> <dd>Hook method executed once when <a title="cmd.Cmd.cmdloop" class="reference internal" href="#cmd.Cmd.cmdloop"><tt class="xref docutils literal"><span class="pre">cmdloop()</span></tt></a> is called. This method is a stub in <a title="cmd.Cmd" class="reference internal" href="#cmd.Cmd"><tt class="xref docutils literal"><span class="pre">Cmd</span></tt></a>; it exists to be overridden by subclasses.</dd></dl> <dl class="method"> <dt id="cmd.Cmd.postloop"> <tt class="descclassname">Cmd.</tt><tt class="descname">postloop</tt><big>(</big><big>)</big><a class="headerlink" href="#cmd.Cmd.postloop" title="Permalink to this definition">¶</a></dt> <dd>Hook method executed once when <a title="cmd.Cmd.cmdloop" class="reference internal" href="#cmd.Cmd.cmdloop"><tt class="xref docutils literal"><span class="pre">cmdloop()</span></tt></a> is about to return. This method is a stub in <a title="cmd.Cmd" class="reference internal" href="#cmd.Cmd"><tt class="xref docutils literal"><span class="pre">Cmd</span></tt></a>; it exists to be overridden by subclasses.</dd></dl> <p>Instances of <a title="cmd.Cmd" class="reference internal" href="#cmd.Cmd"><tt class="xref docutils literal"><span class="pre">Cmd</span></tt></a> subclasses have some public instance variables:</p> <dl class="attribute"> <dt id="cmd.Cmd.prompt"> <tt class="descclassname">Cmd.</tt><tt class="descname">prompt</tt><a class="headerlink" href="#cmd.Cmd.prompt" title="Permalink to this definition">¶</a></dt> <dd>The prompt issued to solicit input.</dd></dl> <dl class="attribute"> <dt id="cmd.Cmd.identchars"> <tt class="descclassname">Cmd.</tt><tt class="descname">identchars</tt><a class="headerlink" href="#cmd.Cmd.identchars" title="Permalink to this definition">¶</a></dt> <dd>The string of characters accepted for the command prefix.</dd></dl> <dl class="attribute"> <dt id="cmd.Cmd.lastcmd"> <tt class="descclassname">Cmd.</tt><tt class="descname">lastcmd</tt><a class="headerlink" href="#cmd.Cmd.lastcmd" title="Permalink to this definition">¶</a></dt> <dd>The last nonempty command prefix seen.</dd></dl> <dl class="attribute"> <dt id="cmd.Cmd.intro"> <tt class="descclassname">Cmd.</tt><tt class="descname">intro</tt><a class="headerlink" href="#cmd.Cmd.intro" title="Permalink to this definition">¶</a></dt> <dd>A string to issue as an intro or banner. May be overridden by giving the <a title="cmd.Cmd.cmdloop" class="reference internal" href="#cmd.Cmd.cmdloop"><tt class="xref docutils literal"><span class="pre">cmdloop()</span></tt></a> method an argument.</dd></dl> <dl class="attribute"> <dt id="cmd.Cmd.doc_header"> <tt class="descclassname">Cmd.</tt><tt class="descname">doc_header</tt><a class="headerlink" href="#cmd.Cmd.doc_header" title="Permalink to this definition">¶</a></dt> <dd>The header to issue if the help output has a section for documented commands.</dd></dl> <dl class="attribute"> <dt id="cmd.Cmd.misc_header"> <tt class="descclassname">Cmd.</tt><tt class="descname">misc_header</tt><a class="headerlink" href="#cmd.Cmd.misc_header" title="Permalink to this definition">¶</a></dt> <dd>The header to issue if the help output has a section for miscellaneous help topics (that is, there are <tt class="xref docutils literal"><span class="pre">help_*()</span></tt> methods without corresponding <tt class="xref docutils literal"><span class="pre">do_*()</span></tt> methods).</dd></dl> <dl class="attribute"> <dt id="cmd.Cmd.undoc_header"> <tt class="descclassname">Cmd.</tt><tt class="descname">undoc_header</tt><a class="headerlink" href="#cmd.Cmd.undoc_header" title="Permalink to this definition">¶</a></dt> <dd>The header to issue if the help output has a section for undocumented commands (that is, there are <tt class="xref docutils literal"><span class="pre">do_*()</span></tt> methods without corresponding <tt class="xref docutils literal"><span class="pre">help_*()</span></tt> methods).</dd></dl> <dl class="attribute"> <dt id="cmd.Cmd.ruler"> <tt class="descclassname">Cmd.</tt><tt class="descname">ruler</tt><a class="headerlink" href="#cmd.Cmd.ruler" title="Permalink to this definition">¶</a></dt> <dd>The character used to draw separator lines under the help-message headers. If empty, no ruler line is drawn. It defaults to <tt class="docutils literal"><span class="pre">'='</span></tt>.</dd></dl> <dl class="attribute"> <dt id="cmd.Cmd.use_rawinput"> <tt class="descclassname">Cmd.</tt><tt class="descname">use_rawinput</tt><a class="headerlink" href="#cmd.Cmd.use_rawinput" title="Permalink to this definition">¶</a></dt> <dd>A flag, defaulting to true. If true, <a title="cmd.Cmd.cmdloop" class="reference internal" href="#cmd.Cmd.cmdloop"><tt class="xref docutils literal"><span class="pre">cmdloop()</span></tt></a> uses <a title="raw_input" class="reference external" href="functions.html#raw_input"><tt class="xref docutils literal"><span class="pre">raw_input()</span></tt></a> to display a prompt and read the next command; if false, <tt class="xref docutils literal"><span class="pre">sys.stdout.write()</span></tt> and <tt class="xref docutils literal"><span class="pre">sys.stdin.readline()</span></tt> are used. (This means that by importing <a title="(Unix) GNU readline support for Python." class="reference external" href="readline.html#module-readline"><tt class="xref docutils literal"><span class="pre">readline</span></tt></a>, on systems that support it, the interpreter will automatically support <strong>Emacs</strong>-like line editing and command-history keystrokes.)</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 external" href="#">23.1. <tt class="docutils literal"><span class="pre">cmd</span></tt> — Support for line-oriented command interpreters</a><ul> <li><a class="reference external" href="#cmd-objects">23.1.1. Cmd Objects</a></li> </ul> </li> </ul> <h4>Previous topic</h4> <p class="topless"><a href="frameworks.html" title="previous chapter">23. Program Frameworks</a></p> <h4>Next topic</h4> <p class="topless"><a href="shlex.html" title="next chapter">23.2. <tt class="docutils literal"><span class="pre">shlex</span></tt> — Simple lexical analysis</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/cmd.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" size="18" /> <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="../modindex.html" title="Global Module Index" >modules</a> |</li> <li class="right" > <a href="shlex.html" title="23.2. shlex — Simple lexical analysis" >next</a> |</li> <li class="right" > <a href="frameworks.html" title="23. 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