Python Standard Library

The cmd Module

The cmd module (see Example 14-5) provides a simple framework for command-line interfaces (CLI). This is used by the pdb debugger module, but you can also use it for your own programs.

To implement your own command-line interface, subclass the Cmd class, and define do and help methods. The base class automatically turns all do methods into commands and uses the help methods to show help information.

Example 14-5. Using the cmd Module

File: cmd-example-1.py

import cmd
import string, sys

class CLI(cmd.Cmd):

    def _ _init_ _(self):
        cmd.Cmd._ _init_ _(self)
        self.prompt = '> '

    def do_hello(self, arg):
        print "hello again", arg, "!"

    def help_hello(self):
        print "syntax: hello [message]",
        print "-- prints a hello message"

    def do_quit(self, arg):
        sys.exit(1)

    def help_quit(self):
        print "syntax: quit",
        print "-- terminates the application"

    # shortcuts
    do_q = do_quit

#
# try it out

cli = CLI()
cli.cmdloop()

> help

Documented commands (type help <topic>):
========================================
hello           quit

Undocumented commands:
======================
help            q

> hello world
hello again world !
> q