cmd2: build feature-rich command-line apps in Python

Quick start • Why cmd2? • Installation • Documentation • Projects using cmd2

cmd2 makes it quick to build powerful, polished command-line applications and REPLs in Python. Start with a subclass of the standard library's cmd.Cmd, then add commands while cmd2 handles the details that make an application pleasant to build and use: argument parsing, generated help, tab completion, command history, scripting, output styling, and much more.

You can use cmd2 for a small internal tool and grow the same application into an extensible, scriptable interface without replacing the framework or writing the usual CLI boilerplate.

Quick start

Install cmd2:

pip install cmd2

Then create app.py:

from typing import Annotated

import cmd2
from cmd2.annotated import Argument, Option


class App(cmd2.Cmd):
    """A small interactive application."""

    @cmd2.with_annotated
    def do_greet(
        self,
        name: Annotated[str, Argument(help_text="person to greet")],
        count: Annotated[int, Option(help_text="number of greetings")] = 1,
    ) -> None:
        """Greet a person."""
        for _ in range(count):
            self.poutput(f"Hello, {name}!")


if __name__ == "__main__":
    App().cmdloop()

cmd2 supports Typer-style syntax for specifying command arguments with type annotations. In this example, @cmd2.with_annotated turns name and count into a positional argument and an option.

Run it with python app.py. Your new greet command already has input validation, generated help, and tab completion for its options. The application also includes discoverable help, command history, aliases, macros, scripting, shell integration, and other built-in commands.

(Cmd) help greet
Usage: greet [-h] [--count COUNT] name

(Cmd) greet --count 2 Ada
Hello, Ada!
Hello, Ada!

See the getting started tutorial to build a more complete application.

Why cmd2?

Build more with less code

• Define commands as Python methods and use familiar argparse parsers for arguments and subcommands, or plain type hints via @with_annotated. A single parser definition drives validation, help, and completion.
• Render Rich tables and other styled objects, with consistent helpers for normal output, errors, warnings, and paging.
• Organize large applications into independently testable and dynamically loadable CommandSets, and customize the command lifecycle with hooks.
• Integrate existing Python code, shell tools, or asynchronous work instead of restructuring your application around the framework.
• Run on Windows, macOS, and Linux with a pure-Python package and a small dependency footprint.

Give users a capable interface from day one

• Tab completion: provide context-aware completion for commands, subcommands, options, choices, file paths, and custom data sources, with descriptive hints for completion candidates. Learn more about completion.
• History: search, edit, rerun, save, and optionally persist previously entered commands. Users also get familiar navigation and reverse search such as Ctrl+R. Learn more about history.
• Unicode: accept Unicode in commands, arguments, file names, and output, and run UTF-8 command scripts for applications used in any language. Learn more about command scripts.
• Shell shortcuts and hotkeys: use familiar Readline-style keyboard shortcuts for navigating and editing the command line, including Emacs-style bindings provided by prompt-toolkit. Learn more about keyboard shortcuts.
• Help: generate discoverable, categorized help for commands, subcommands, and arguments directly from their argument parsers. Learn more about help.
• Rich UI/UX: offer syntax highlighting, Fish-style history suggestions, multiline input, configurable prompts, completion menus, themes, and an optional bottom toolbar. Learn more about prompts and toolbars and themes.

Grow from exploration to automation

• Shell scripting: automate the same commands users run interactively by passing them as command arguments or standard input from shell scripts. Learn more about automating cmd2 applications.
• Python scripting: run Python scripts inside the application for loops, branching, complex control flow, and integration with the application's commands and data. Learn more about Python scripts.
• Run shell commands: execute operating-system commands without leaving the application, using the built-in shell command or its ! shortcut. Learn more about OS integration.
• Redirect output: send command output to files or the clipboard, or pipe it through one or more shell commands. Learn more about output redirection and pipes.
• Aliases, macros, and shortcuts: let users customize names, parameterized commands, and terse shortcuts for repetitive workflows without changing the application. Learn more about aliases, macros, and shortcuts.
• Startup scripts: initialize an application consistently by running saved commands every time it starts. Learn more about startup commands and scripts.
• Embedded Python and IPython shells: drop into an interactive Python or IPython session for experimentation, debugging, object introspection, and access to application state. Learn more about embedded Python shells.
• Color, style, and tables: produce readable output with Rich colors and styles, custom themes, paging, and flexible table layouts. Learn more about generating output and creating tables.

Installation

On all operating systems, the latest stable version of cmd2 can be installed using pip:

pip install -U cmd2

cmd2 works with Python 3.11+ on Windows, macOS, and Linux. It is pure Python code with few 3rd-party dependencies. It works with both conventional CPython and free-threaded variants.

For information on other installation options, see Installation Instructions in the cmd2 documentation.

[!IMPORTANT] Upgrading from an older release? Versions 3.x and 4.x include significant backwards-incompatible changes. Review the changelog and migration guide before upgrading.

Documentation

Read the latest documentation online or download it in HTML, PDF, and ePub formats. The examples directory contains focused, runnable demonstrations of individual features.

Tutorials

• cmd2 example applications
  • Basic cmd2 examples to demonstrate how to use various features
• Advanced Examples
  • More complex examples that demonstrate more features about how to put together a complete application
• Cookiecutter Templates from community
  • Basic cookiecutter template for cmd2 application : https://github.com/jayrod/cookiecutter-python-cmd2
  • Advanced cookiecutter template with external plugin support : https://github.com/jayrod/cookiecutter-python-cmd2-ext-plug

Found a bug?

If you think you've found a bug, please first read through the open Issues. If you're confident it's a new bug, go ahead and create a new GitHub issue. Be sure to include as much information as possible so we can reproduce the bug. At a minimum, please state the following:

• cmd2 version
• Python version
• OS name and version
• What you did to cause the bug to occur
• Include any traceback or error message associated with the bug

Projects using cmd2

Possibly defunct but still good examples

Note: If you have created an application based on cmd2 that you would like us to mention here, please get in touch.