5.19.1 Cmd Objects
A Cmd instance has the following methods:
- 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 intro class member).
If the readline module is loaded, input will automatically
inherit bash-like history-list editing (e.g. Control-P
scrolls back to the last command, Control-N forward to the next one, Control-F
moves the cursor to the right non-destructively, Control-B moves the cursor to
the left non-destructively, etc.).
An end-of-file on input is passed back as the string
An interpreter instance will recognize a command name "foo"
if and only if it has a method do_foo(). As a special case, a line
beginning with the character "?" is dispatched to the
method do_help(). As another special case, a line beginning with
the character "!" is dispatched to the method do_shell() (if such a method is defined).
If completion is enabled, completing commands will be done automatically, and
completing of commands args is done by calling 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 Cmd inherit a predefined do_help().
This method, called with an argument
'bar', invokes the corresponding method help_bar(). With no argument, do_help() lists
all available help topics (that is, all commands with corresponding help_*()
methods), and also lists any undocumented commands.
- 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 precmd()
and postcmd() methods for useful execution hooks. The return value
is a flag indicating whether interpretation of commands by the interpreter should stop.
- 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 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.
||text, line, begidx, endidx)
- Method called to complete an input line when no command-specific complete_*()
method is available. By default, it returns an empty list.
- 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 Cmd;
it exists to be overridden by subclasses. The return value is used as the command which
will be executed by the onecmd() method; the precmd()
implementation may re-write the command or simply return line unchanged.
- Hook method executed just after a command dispatch is finished. This method is a stub in
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 postcmd(); this
will be the return value of the 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.
- Hook method executed once when cmdloop() is called. This method
is a stub in Cmd; it exists to be overridden by subclasses.
- Hook method executed once when cmdloop() is about to return.
This method is a stub in Cmd; it exists to be overridden by
Instances of Cmd subclasses have some public instance variables:
- The prompt issued to solicit input.
- The string of characters accepted for the command prefix.
- The last nonempty command prefix seen.
- A string to issue as an intro or banner. May be overridden by giving the cmdloop() method an argument.
- The header to issue if the help output has a section for documented commands.
- The header to issue if the help output has a section for miscellaneous help topics (that
is, there are help_*() methods without corresponding do_*() methods).
- The header to issue if the help output has a section for undocumented commands (that is,
there are do_*() methods without corresponding help_*()
- The character used to draw separator lines under the help-message headers. If empty, no
ruler line is drawn. It defaults to "=".
- A flag, defaulting to true. If true, cmdloop() uses raw_input() to display a prompt and read the next command; if false,
sys.stdout.write() and sys.stdin.readline()
are used. (This means that by importing readline, on systems that
support it, the interpreter will automatically support Emacs-like line editing and