# 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

```python
import cmd
```

## Basic 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

```python
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 types `command`. The `arg` parameter 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 types `help 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.

```python
    def do_quit(self, line):
        return True
```

[[programming/python/python]]