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<div class="section" id="module-cmd">
<h1>24.1. <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>24.1.1. 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>. 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), 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>
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<ul>
<li><a class="reference external" href="#">24.1. <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">24.1.1. Cmd Objects</a></li>
</ul>
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