Command Interpreter in Python with CMD Module

Introduction: Command-line interface (CLI) is a text-based interface used for interacting with a computer system. It is used by system administrators and developers to interact with the operating system or to run commands. Python has a module called cmd that provides support for line-oriented command interpreters. In this article, we will explore the cmd module in Python and how it can be used to create a CLI.

What is cmd module in Python? The cmd module in Python is a built-in module that provides a framework for building line-oriented command interpreters. It makes it easy to build CLI applications in Python by providing a base class called Cmd that can be extended to create a command interpreter.

The Cmd class has several methods that can be overridden to customize the behavior of the interpreter. These methods include preloop, postloop, precmd, postcmd, default, and emptyline.

Let’s create a simple command-line interface using the cmd module in Python.

import cmd

class MyCLI(cmd.Cmd): 
prompt = 'mycli> '
 
def do_hello(self, arg): 
print('Hello, world!')
 
def do_quit(self, arg): 
return True

if __name__ == '__main__': 
MyCLI().cmdloop()
  1. Import cmd module: We start by importing the cmd module in Python.
  2. Create a class: We create a class called MyCLI that extends the Cmd class.
  3. Set the prompt: We set the prompt to ‘mycli> ‘ using the prompt variable.
  4. Define commands: We define two commands, ‘hello’ and ‘quit’ using the do_hello and do_quit methods respectively.
  5. Implement commands: The do_hello method simply prints ‘Hello, world!’ to the console. The do_quit method returns True, which exits the command interpreter.
  6. Run the CLI: We run the command interpreter using the cmdloop method of the MyCLI class.

When you run the code, it will start a command-line interface with the prompt “mycli>”. You can enter the command “hello” to see the output “Hello, world!” on the command line. Similarly, if you enter the command “quit”, the program will exit the command-line interface.

Conclusion: In this article, we have explored the cmd module in Python and how it can be used to create a CLI. The cmd module provides a simple and easy-to-use framework for building command interpreters in Python. By extending the Cmd class and implementing the required methods, developers can create powerful and customizable CLI applications.