2 :mod:`cmd` --- Support for line-oriented command interpreters
3 =============================================================
6 :synopsis: Build line-oriented command interpreters.
7 .. sectionauthor:: Eric S. Raymond <esr@snark.thyrsus.com>
10 The :class:`Cmd` class provides a simple framework for writing line-oriented
11 command interpreters. These are often useful for test harnesses, administrative
12 tools, and prototypes that will later be wrapped in a more sophisticated
17 Latest version of the `cmd module Python source code
18 <http://svn.python.org/view/python/branches/release27-maint/Lib/cmd.py?view=markup>`_
20 .. class:: Cmd([completekey[, stdin[, stdout]]])
22 A :class:`Cmd` instance or subclass instance is a line-oriented interpreter
23 framework. There is no good reason to instantiate :class:`Cmd` itself; rather,
24 it's useful as a superclass of an interpreter class you define yourself in order
25 to inherit :class:`Cmd`'s methods and encapsulate action methods.
27 The optional argument *completekey* is the :mod:`readline` name of a completion
28 key; it defaults to :kbd:`Tab`. If *completekey* is not :const:`None` and
29 :mod:`readline` is available, command completion is done automatically.
31 The optional arguments *stdin* and *stdout* specify the input and output file
32 objects that the Cmd instance or subclass instance will use for input and
33 output. If not specified, they will default to :data:`sys.stdin` and
36 If you want a given *stdin* to be used, make sure to set the instance's
37 :attr:`use_rawinput` attribute to ``False``, otherwise *stdin* will be
40 .. versionchanged:: 2.3
41 The *stdin* and *stdout* parameters were added.
49 A :class:`Cmd` instance has the following methods:
52 .. method:: Cmd.cmdloop([intro])
54 Repeatedly issue a prompt, accept input, parse an initial prefix off the
55 received input, and dispatch to action methods, passing them the remainder of
58 The optional argument is a banner or intro string to be issued before the first
59 prompt (this overrides the :attr:`intro` class member).
61 If the :mod:`readline` module is loaded, input will automatically inherit
62 :program:`bash`\ -like history-list editing (e.g. :kbd:`Control-P` scrolls back
63 to the last command, :kbd:`Control-N` forward to the next one, :kbd:`Control-F`
64 moves the cursor to the right non-destructively, :kbd:`Control-B` moves the
65 cursor to the left non-destructively, etc.).
67 An end-of-file on input is passed back as the string ``'EOF'``.
69 An interpreter instance will recognize a command name ``foo`` if and only if it
70 has a method :meth:`do_foo`. As a special case, a line beginning with the
71 character ``'?'`` is dispatched to the method :meth:`do_help`. As another
72 special case, a line beginning with the character ``'!'`` is dispatched to the
73 method :meth:`do_shell` (if such a method is defined).
75 This method will return when the :meth:`postcmd` method returns a true value.
76 The *stop* argument to :meth:`postcmd` is the return value from the command's
77 corresponding :meth:`do_\*` method.
79 If completion is enabled, completing commands will be done automatically, and
80 completing of commands args is done by calling :meth:`complete_foo` with
81 arguments *text*, *line*, *begidx*, and *endidx*. *text* is the string prefix
82 we are attempting to match: all returned matches must begin with it. *line* is
83 the current input line with leading whitespace removed, *begidx* and *endidx*
84 are the beginning and ending indexes of the prefix text, which could be used to
85 provide different completion depending upon which position the argument is in.
87 All subclasses of :class:`Cmd` inherit a predefined :meth:`do_help`. This
88 method, called with an argument ``'bar'``, invokes the corresponding method
89 :meth:`help_bar`, and if that is not present, prints the docstring of
90 :meth:`do_bar`, if available. With no argument, :meth:`do_help` lists all
91 available help topics (that is, all commands with corresponding
92 :meth:`help_\*` methods or commands that have docstrings), and also lists any
93 undocumented commands.
96 .. method:: Cmd.onecmd(str)
98 Interpret the argument as though it had been typed in response to the prompt.
99 This may be overridden, but should not normally need to be; see the
100 :meth:`precmd` and :meth:`postcmd` methods for useful execution hooks. The
101 return value is a flag indicating whether interpretation of commands by the
102 interpreter should stop. If there is a :meth:`do_\*` method for the command
103 *str*, the return value of that method is returned, otherwise the return value
104 from the :meth:`default` method is returned.
107 .. method:: Cmd.emptyline()
109 Method called when an empty line is entered in response to the prompt. If this
110 method is not overridden, it repeats the last nonempty command entered.
113 .. method:: Cmd.default(line)
115 Method called on an input line when the command prefix is not recognized. If
116 this method is not overridden, it prints an error message and returns.
119 .. method:: Cmd.completedefault(text, line, begidx, endidx)
121 Method called to complete an input line when no command-specific
122 :meth:`complete_\*` method is available. By default, it returns an empty list.
125 .. method:: Cmd.precmd(line)
127 Hook method executed just before the command line *line* is interpreted, but
128 after the input prompt is generated and issued. This method is a stub in
129 :class:`Cmd`; it exists to be overridden by subclasses. The return value is
130 used as the command which will be executed by the :meth:`onecmd` method; the
131 :meth:`precmd` implementation may re-write the command or simply return *line*
135 .. method:: Cmd.postcmd(stop, line)
137 Hook method executed just after a command dispatch is finished. This method is
138 a stub in :class:`Cmd`; it exists to be overridden by subclasses. *line* is the
139 command line which was executed, and *stop* is a flag which indicates whether
140 execution will be terminated after the call to :meth:`postcmd`; this will be the
141 return value of the :meth:`onecmd` method. The return value of this method will
142 be used as the new value for the internal flag which corresponds to *stop*;
143 returning false will cause interpretation to continue.
146 .. method:: Cmd.preloop()
148 Hook method executed once when :meth:`cmdloop` is called. This method is a stub
149 in :class:`Cmd`; it exists to be overridden by subclasses.
152 .. method:: Cmd.postloop()
154 Hook method executed once when :meth:`cmdloop` is about to return. This method
155 is a stub in :class:`Cmd`; it exists to be overridden by subclasses.
157 Instances of :class:`Cmd` subclasses have some public instance variables:
160 .. attribute:: Cmd.prompt
162 The prompt issued to solicit input.
165 .. attribute:: Cmd.identchars
167 The string of characters accepted for the command prefix.
170 .. attribute:: Cmd.lastcmd
172 The last nonempty command prefix seen.
175 .. attribute:: Cmd.intro
177 A string to issue as an intro or banner. May be overridden by giving the
178 :meth:`cmdloop` method an argument.
181 .. attribute:: Cmd.doc_header
183 The header to issue if the help output has a section for documented commands.
186 .. attribute:: Cmd.misc_header
188 The header to issue if the help output has a section for miscellaneous help
189 topics (that is, there are :meth:`help_\*` methods without corresponding
190 :meth:`do_\*` methods).
193 .. attribute:: Cmd.undoc_header
195 The header to issue if the help output has a section for undocumented commands
196 (that is, there are :meth:`do_\*` methods without corresponding :meth:`help_\*`
200 .. attribute:: Cmd.ruler
202 The character used to draw separator lines under the help-message headers. If
203 empty, no ruler line is drawn. It defaults to ``'='``.
206 .. attribute:: Cmd.use_rawinput
208 A flag, defaulting to true. If true, :meth:`cmdloop` uses :func:`raw_input` to
209 display a prompt and read the next command; if false, :meth:`sys.stdout.write`
210 and :meth:`sys.stdin.readline` are used. (This means that by importing
211 :mod:`readline`, on systems that support it, the interpreter will automatically
212 support :program:`Emacs`\ -like line editing and command-history keystrokes.)