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<title>5.20.1 Cmd Objects</title>
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<H2><A NAME="SECTION0072010000000000000000"></A>
<A NAME="Cmd-objects"></A>
<BR>
5.20.1 Cmd Objects
</H2>

<P>
A <tt class="class">Cmd</tt> instance has the following methods:

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-1461' xml:id='l2h-1461' class="method">cmdloop</tt></b>(</nobr></td>
  <td><var></var><big>[</big><var>intro</var><big>]</big><var></var>)</td></tr></table></dt>
<dd>
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>
The optional argument is a banner or intro string to be issued before the
first prompt (this overrides the <tt class="member">intro</tt> class member).

<P>
If the <tt class="module"><a href="module-readline.html">readline</a></tt> module is loaded, input will automatically
inherit <b class="program">bash</b>-like history-list editing (e.g. <kbd>Control-P</kbd>
scrolls back to the last command, <kbd>Control-N</kbd> forward to the next
one, <kbd>Control-F</kbd> moves the cursor to the right non-destructively,
<kbd>Control-B</kbd> moves the cursor to the left non-destructively, etc.).

<P>
An end-of-file on input is passed back as the string <code>'EOF'</code>.

<P>
An interpreter instance will recognize a command name "<tt class="samp">foo</tt>" if
and only if it has a method <tt class="method">do_foo()</tt>.  As a special case,
a line beginning with the character "<tt class="character">?</tt>" is dispatched to
the method <tt class="method">do_help()</tt>.  As another special case, a line
beginning with the character "<tt class="character">!</tt>" is dispatched to the
method <tt class="method">do_shell()</tt> (if such a method is defined).

<P>
This method will return when the <tt class="method">postcmd()</tt> method returns a
true value.  The <var>stop</var> argument to <tt class="method">postcmd()</tt> is the
return value from the command's corresponding <tt class="method">do_*()</tt> method.

<P>
If completion is enabled, completing commands will be done
automatically, and completing of commands args is done by calling
<tt class="method">complete_foo()</tt> with arguments <var>text</var>, <var>line</var>,
<var>begidx</var>, and <var>endidx</var>.  <var>text</var> is the string prefix we
are attempting to match: all returned matches must begin with it.
<var>line</var> is the current input line with leading whitespace removed,
<var>begidx</var> and <var>endidx</var> 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>
All subclasses of <tt class="class">Cmd</tt> inherit a predefined <tt class="method">do_help()</tt>.
This method, called with an argument <code>'bar'</code>, invokes the
corresponding method <tt class="method">help_bar()</tt>.  With no argument,
<tt class="method">do_help()</tt> lists all available help topics (that is, all
commands with corresponding <tt class="method">help_*()</tt> methods), and also lists
any undocumented commands.
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-1462' xml:id='l2h-1462' class="method">onecmd</tt></b>(</nobr></td>
  <td><var>str</var>)</td></tr></table></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 <tt class="method">precmd()</tt> and <tt class="method">postcmd()</tt> 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="method">do_*()</tt> method for the command <var>str</var>, the return
value of that method is returned, otherwise the return value from the
<tt class="method">default()</tt> method is returned.
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-1463' xml:id='l2h-1463' class="method">emptyline</tt></b>(</nobr></td>
  <td><var></var>)</td></tr></table></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.
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-1464' xml:id='l2h-1464' class="method">default</tt></b>(</nobr></td>
  <td><var>line</var>)</td></tr></table></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.
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-1465' xml:id='l2h-1465' class="method">completedefault</tt></b>(</nobr></td>
  <td><var>text, line, begidx, endidx</var>)</td></tr></table></dt>
<dd>
Method called to complete an input line when no command-specific
<tt class="method">complete_*()</tt> method is available.  By default, it returns an
empty list.
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-1466' xml:id='l2h-1466' class="method">precmd</tt></b>(</nobr></td>
  <td><var>line</var>)</td></tr></table></dt>
<dd>
Hook method executed just before the command line <var>line</var> is
interpreted, but after the input prompt is generated and issued.  This
method is a stub in <tt class="class">Cmd</tt>; it exists to be overridden by
subclasses.  The return value is used as the command which will be
executed by the <tt class="method">onecmd()</tt> method; the <tt class="method">precmd()</tt>
implementation may re-write the command or simply return <var>line</var>
unchanged.
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-1467' xml:id='l2h-1467' class="method">postcmd</tt></b>(</nobr></td>
  <td><var>stop, line</var>)</td></tr></table></dt>
<dd>
Hook method executed just after a command dispatch is finished.  This
method is a stub in <tt class="class">Cmd</tt>; it exists to be overridden by
subclasses.  <var>line</var> is the command line which was executed, and
<var>stop</var> is a flag which indicates whether execution will be
terminated after the call to <tt class="method">postcmd()</tt>; this will be the
return value of the <tt class="method">onecmd()</tt> method.  The return value of
this method will be used as the new value for the internal flag which
corresponds to <var>stop</var>; returning false will cause interpretation
to continue.
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-1468' xml:id='l2h-1468' class="method">preloop</tt></b>(</nobr></td>
  <td><var></var>)</td></tr></table></dt>
<dd>
Hook method executed once when <tt class="method">cmdloop()</tt> is called.  This
method is a stub in <tt class="class">Cmd</tt>; it exists to be overridden by
subclasses.
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-1469' xml:id='l2h-1469' class="method">postloop</tt></b>(</nobr></td>
  <td><var></var>)</td></tr></table></dt>
<dd>
Hook method executed once when <tt class="method">cmdloop()</tt> is about to return.
This method is a stub in <tt class="class">Cmd</tt>; it exists to be overridden by
subclasses.
</dl>

<P>
Instances of <tt class="class">Cmd</tt> subclasses have some public instance variables:

<P>
<dl><dt><b><tt id='l2h-1470' xml:id='l2h-1470' class="member">prompt</tt></b></dt>
<dd>
The prompt issued to solicit input.
</dl>

<P>
<dl><dt><b><tt id='l2h-1471' xml:id='l2h-1471' class="member">identchars</tt></b></dt>
<dd>
The string of characters accepted for the command prefix.
</dl>

<P>
<dl><dt><b><tt id='l2h-1472' xml:id='l2h-1472' class="member">lastcmd</tt></b></dt>
<dd>
The last nonempty command prefix seen.
</dl>

<P>
<dl><dt><b><tt id='l2h-1473' xml:id='l2h-1473' class="member">intro</tt></b></dt>
<dd>
A string to issue as an intro or banner.  May be overridden by giving
the <tt class="method">cmdloop()</tt> method an argument.
</dl>

<P>
<dl><dt><b><tt id='l2h-1474' xml:id='l2h-1474' class="member">doc_header</tt></b></dt>
<dd>
The header to issue if the help output has a section for documented
commands.
</dl>

<P>
<dl><dt><b><tt id='l2h-1475' xml:id='l2h-1475' class="member">misc_header</tt></b></dt>
<dd>
The header to issue if the help output has a section for miscellaneous
help topics (that is, there are <tt class="method">help_*()</tt> methods without
corresponding <tt class="method">do_*()</tt> methods).
</dl>

<P>
<dl><dt><b><tt id='l2h-1476' xml:id='l2h-1476' class="member">undoc_header</tt></b></dt>
<dd>
The header to issue if the help output has a section for undocumented
commands (that is, there are <tt class="method">do_*()</tt> methods without
corresponding <tt class="method">help_*()</tt> methods).
</dl>

<P>
<dl><dt><b><tt id='l2h-1477' xml:id='l2h-1477' class="member">ruler</tt></b></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="character">=</tt>".
</dl>

<P>
<dl><dt><b><tt id='l2h-1478' xml:id='l2h-1478' class="member">use_rawinput</tt></b></dt>
<dd>
A flag, defaulting to true.  If true, <tt class="method">cmdloop()</tt> uses
<tt class="function">raw_input()</tt> to display a prompt and read the next command;
if false, <tt class="method">sys.stdout.write()</tt> and
<tt class="method">sys.stdin.readline()</tt> are used. (This means that by
importing <tt class="module"><a href="module-readline.html">readline</a></tt>, on systems that support it, the
interpreter will automatically support <b class="program">Emacs</b>-like line editing
and command-history keystrokes.)
</dl>

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<span class="release-info">Release 2.4.2, documentation updated on 28 September 2005.</span>
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