Python Cmd Module
The cmd module 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.
Importing the Module
import cmdBasic Usage
To use the cmd module, you create a subclass of cmd.Cmd and implement methods for the commands you want to support.
Creating a Command Processor
import cmd
class HelloWorld(cmd.Cmd):
"""Simple command processor example."""
intro = 'Welcome to the hello shell. Type help or ? to list commands.\n'
prompt = '(hello) '
def do_greet(self, line):
"""greet [person]
Greet the named person"""
if line:
print(f"Hello, {line}")
else:
print("Hello")
def do_EOF(self, line):
return True
if __name__ == '__main__':
HelloWorld().cmdloop()Command Methods
Commands are defined by creating methods with the prefix do_. The part of the method name after do_ becomes the command name.
do_command(self, arg): This method is called when the user typescommand. Theargparameter contains the rest of the line.
Help Methods
You can provide help for your commands by defining methods with the prefix help_.
help_command(self): This method is called when the user typeshelp command.
Hooks and Overrides
The cmd.Cmd class provides several methods that can be overridden to customize behavior.
preloop(): Called once before the command loop starts.postloop(): Called once after the command loop ends.emptyline(): Called when an empty line is entered. By default, it repeats the last command.default(line): Called when an unknown command is entered.
Quitting
To exit the command loop, a command method should return True. Typically, this is done in a do_EOF or do_quit method.
def do_quit(self, line):
return True