Edit File: cmd.txt
:mod:`cmd` --- Support for line-oriented command interpreters ============================================================= .. module:: cmd :synopsis: Build line-oriented command interpreters. .. sectionauthor:: Eric S. Raymond <esr@snark.thyrsus.com> The :class:`Cmd` 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. .. class:: Cmd([completekey[, stdin[, stdout]]]) A :class:`Cmd` instance or subclass instance is a line-oriented interpreter framework. There is no good reason to instantiate :class:`Cmd` itself; rather, it's useful as a superclass of an interpreter class you define yourself in order to inherit :class:`Cmd`'s methods and encapsulate action methods. The optional argument *completekey* is the :mod:`readline` name of a completion key; it defaults to :kbd:`Tab`. If *completekey* is not :const:`None` and :mod:`readline` is available, command completion is done automatically. The optional arguments *stdin* and *stdout* 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 :data:`sys.stdin` and :data:`sys.stdout`. If you want a given *stdin* to be used, make sure to set the instance's :attr:`use_rawinput` attribute to ``False``, otherwise *stdin* will be ignored. .. versionchanged:: 2.3 The *stdin* and *stdout* parameters were added. .. _cmd-objects: Cmd Objects ----------- A :class:`Cmd` instance has the following methods: .. method:: Cmd.cmdloop([intro]) 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. The optional argument is a banner or intro string to be issued before the first prompt (this overrides the :attr:`intro` class member). If the :mod:`readline` module is loaded, input will automatically inherit :program:`bash`\ -like history-list editing (e.g. :kbd:`Control-P` scrolls back to the last command, :kbd:`Control-N` forward to the next one, :kbd:`Control-F` moves the cursor to the right non-destructively, :kbd:`Control-B` moves the cursor to the left non-destructively, etc.). An end-of-file on input is passed back as the string ``'EOF'``. An interpreter instance will recognize a command name ``foo`` if and only if it has a method :meth:`do_foo`. As a special case, a line beginning with the character ``'?'`` is dispatched to the method :meth:`do_help`. As another special case, a line beginning with the character ``'!'`` is dispatched to the method :meth:`do_shell` (if such a method is defined). This method will return when the :meth:`postcmd` method returns a true value. The *stop* argument to :meth:`postcmd` is the return value from the command's corresponding :meth:`do_\*` method. If completion is enabled, completing commands will be done automatically, and completing of commands args is done by calling :meth:`complete_foo` with arguments *text*, *line*, *begidx*, and *endidx*. *text* is the string prefix we are attempting to match: all returned matches must begin with it. *line* is the current input line with leading whitespace removed, *begidx* and *endidx* 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. All subclasses of :class:`Cmd` inherit a predefined :meth:`do_help`. This method, called with an argument ``'bar'``, invokes the corresponding method :meth:`help_bar`, and if that is not present, prints the docstring of :meth:`do_bar`, if available. With no argument, :meth:`do_help` lists all available help topics (that is, all commands with corresponding :meth:`help_\*` methods or commands that have docstrings), and also lists any undocumented commands. .. method:: Cmd.onecmd(str) 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 :meth:`precmd` and :meth:`postcmd` 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 :meth:`do_\*` method for the command *str*, the return value of that method is returned, otherwise the return value from the :meth:`default` method is returned. .. method:: Cmd.emptyline() 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. .. method:: Cmd.default(line) 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. .. method:: Cmd.completedefault(text, line, begidx, endidx) Method called to complete an input line when no command-specific :meth:`complete_\*` method is available. By default, it returns an empty list. .. method:: Cmd.precmd(line) Hook method executed just before the command line *line* is interpreted, but after the input prompt is generated and issued. This method is a stub in :class:`Cmd`; it exists to be overridden by subclasses. The return value is used as the command which will be executed by the :meth:`onecmd` method; the :meth:`precmd` implementation may re-write the command or simply return *line* unchanged. .. method:: Cmd.postcmd(stop, line) Hook method executed just after a command dispatch is finished. This method is a stub in :class:`Cmd`; it exists to be overridden by subclasses. *line* is the command line which was executed, and *stop* is a flag which indicates whether execution will be terminated after the call to :meth:`postcmd`; this will be the return value of the :meth:`onecmd` method. The return value of this method will be used as the new value for the internal flag which corresponds to *stop*; returning false will cause interpretation to continue. .. method:: Cmd.preloop() Hook method executed once when :meth:`cmdloop` is called. This method is a stub in :class:`Cmd`; it exists to be overridden by subclasses. .. method:: Cmd.postloop() Hook method executed once when :meth:`cmdloop` is about to return. This method is a stub in :class:`Cmd`; it exists to be overridden by subclasses. Instances of :class:`Cmd` subclasses have some public instance variables: .. attribute:: Cmd.prompt The prompt issued to solicit input. .. attribute:: Cmd.identchars The string of characters accepted for the command prefix. .. attribute:: Cmd.lastcmd The last nonempty command prefix seen. .. attribute:: Cmd.intro A string to issue as an intro or banner. May be overridden by giving the :meth:`cmdloop` method an argument. .. attribute:: Cmd.doc_header The header to issue if the help output has a section for documented commands. .. attribute:: Cmd.misc_header The header to issue if the help output has a section for miscellaneous help topics (that is, there are :meth:`help_\*` methods without corresponding :meth:`do_\*` methods). .. attribute:: Cmd.undoc_header The header to issue if the help output has a section for undocumented commands (that is, there are :meth:`do_\*` methods without corresponding :meth:`help_\*` methods). .. attribute:: Cmd.ruler The character used to draw separator lines under the help-message headers. If empty, no ruler line is drawn. It defaults to ``'='``. .. attribute:: Cmd.use_rawinput A flag, defaulting to true. If true, :meth:`cmdloop` uses :func:`raw_input` to display a prompt and read the next command; if false, :meth:`sys.stdout.write` and :meth:`sys.stdin.readline` are used. (This means that by importing :mod:`readline`, on systems that support it, the interpreter will automatically support :program:`Emacs`\ -like line editing and command-history keystrokes.)
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