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