cmd2: a tool for building interactive command line apps

cmd2 is a tool for building interactive command line applications in Python. Its goal is to make it quick and easy for developers to build feature-rich and user-friendly interactive command line applications. It provides a simple API which is an extension of Python's built-in cmd module. cmd2 provides a wealth of features on top of cmd to make your life easier and eliminates much of the boilerplate code which would be necessary when using cmd.

Main Features

• Searchable command history (history command and <Ctrl>+r) - optionally persistent
• Text file scripting of your application with load (@) and _relative_load (@@)
• Python scripting of your application with pyscript
• Run shell commands with !
• Pipe command output to shell commands with |
• Redirect command output to file with >, >>; input from file with <
• Bare >, >> with no filename send output to paste buffer (clipboard)
• py enters interactive Python console (opt-in ipy for IPython console)
• Option to display long output using a pager with cmd2.Cmd.ppaged()
• Multi-line commands
• Special-character command shortcuts (beyond cmd's ? and !)
• Command aliasing similar to bash alias command
• Ability to load commands at startup from an initialization script
• Settable environment parameters
• Parsing commands with arguments using argparse, including support for sub-commands
• Sub-menu support via the AddSubmenu decorator
• Unicode character support
• Good tab-completion of commands, sub-commands, file system paths, and shell commands
• Support for Python 3.4+ on Windows, macOS, and Linux
• Trivial to provide built-in help for all commands
• Built-in regression testing framework for your applications (transcript-based testing)
• Transcripts for use with built-in regression can be automatically generated from history -t

Python 2.7 support is EOL

Support for adding new features to the Python 2.7 release of cmd2 was discontinued on April 15, 2018. Bug fixes will be supported for Python 2.7 via 0.8.x until August 31, 2018.

Supporting Python 2 was an increasing burden on our limited resources. Switching to support only Python 3 will allow us to clean up the codebase, remove some cruft, and focus on developing new features.

Installation

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

pip install -U cmd2

cmd2 works with Python 3.4+ on Windows, macOS, and Linux. It is pure Python code with the only 3rd-party dependencies being on pyparsing, and pyperclip. Windows has an additional dependency on pyreadline. Non-Windows platforms have an additional dependency on wcwidth. Finally, Python 3.4 has an additional dependency on contextlib2.

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

Documentation

The latest documentation for cmd2 can be read online here: https://cmd2.readthedocs.io/en/latest/

It is available in HTML, PDF, and ePub formats.

Feature Overview

Instructions for implementing each feature follow.

• Searchable command history

  All commands will automatically be tracked in the session's history, unless the command is listed in Cmd's exclude_from_history attribute. The history is accessed through the history command. If you wish to exclude some of your custom commands from the history, append their names to the list at Cmd.exclude_from_history.

• Load commands from file, save to file, edit commands in file

  Type help load, help history for details.

• Multi-line commands

  Any command accepts multi-line input when its name is listed in Cmd.multilineCommands. The program will keep expecting input until a line ends with any of the characters in Cmd.terminators . The default terminators are ; and /n (empty newline).

• Special-character shortcut commands (beyond cmd's "@" and "!")

  To create a single-character shortcut for a command, update Cmd.shortcuts.

• Settable environment parameters

  To allow a user to change an environment parameter during program execution, append the parameter's name to `Cmd.settable``

• Parsing commands with argparse

  import argparse
  from cmd2 import with_argparser
  
  argparser = argparse.ArgumentParser()
  argparser.add_argument('-p', '--piglatin', action='store_true', help='atinLay')
  argparser.add_argument('-s', '--shout', action='store_true', help='N00B EMULATION MODE')
  argparser.add_argument('words', nargs='+', help='words to say')
  @with_argparser(argparser)
  def do_speak(self, args):
      """Repeats what you tell me to."""
      words = []
      for word in args.words:
          if args.piglatin:
              word = '%s%say' % (word[1:], word[0])
          if args.shout:
              word = word.upper()
          words.append(word)
      self.stdout.write('{}\n'.format(' '.join(words)))

  See https://cmd2.readthedocs.io/en/latest/argument_processing.html for more details

Tutorials

A few tutorials on using cmd2 exist:

• Florida PyCon 2017 talk: slides, video
• PyCon 2010 talk by Catherine Devlin, the original author: video
• A nice brief step-by-step tutorial: blog

Example Application

Example cmd2 application (examples/example.py):

#!/usr/bin/env python
# coding=utf-8
"""
A sample application for cmd2.
"""

import random
import argparse

from cmd2 import Cmd, with_argparser


class CmdLineApp(Cmd):
    """ Example cmd2 application. """

    # Setting this true makes it run a shell command if a cmd2/cmd command doesn't exist
    # default_to_shell = True
    MUMBLES = ['like', '...', 'um', 'er', 'hmmm', 'ahh']
    MUMBLE_FIRST = ['so', 'like', 'well']
    MUMBLE_LAST = ['right?']

    def __init__(self):
        self.multilineCommands = ['orate']
        self.maxrepeats = 3

        # Add stuff to settable and shortcuts before calling base class initializer
        self.settable['maxrepeats'] = 'max repetitions for speak command'
        self.shortcuts.update({'&': 'speak'})

        # Set use_ipython to True to enable the "ipy" command which embeds and interactive IPython shell
        Cmd.__init__(self, use_ipython=False)

    speak_parser = argparse.ArgumentParser()
    speak_parser.add_argument('-p', '--piglatin', action='store_true', help='atinLay')
    speak_parser.add_argument('-s', '--shout', action='store_true', help='N00B EMULATION MODE')
    speak_parser.add_argument('-r', '--repeat', type=int, help='output [n] times')
    speak_parser.add_argument('words', nargs='+', help='words to say')
    @with_argparser(speak_parser)
    def do_speak(self, args):
        """Repeats what you tell me to."""
        words = []
        for word in args.words:
            if args.piglatin:
                word = '%s%say' % (word[1:], word[0])
            if args.shout:
                word = word.upper()
            words.append(word)
        repetitions = args.repeat or 1
        for i in range(min(repetitions, self.maxrepeats)):
            # .poutput handles newlines, and accommodates output redirection too
            self.poutput(' '.join(words))

    do_say = do_speak  # now "say" is a synonym for "speak"
    do_orate = do_speak  # another synonym, but this one takes multi-line input

    mumble_parser = argparse.ArgumentParser()
    mumble_parser.add_argument('-r', '--repeat', type=int, help='how many times to repeat')
    mumble_parser.add_argument('words', nargs='+', help='words to say')
    @with_argparser(mumble_parser)
    def do_mumble(self, args):
        """Mumbles what you tell me to."""
        repetitions = args.repeat or 1
        for i in range(min(repetitions, self.maxrepeats)):
            output = []
            if (random.random() < .33):
                output.append(random.choice(self.MUMBLE_FIRST))
            for word in args.words:
                if (random.random() < .40):
                    output.append(random.choice(self.MUMBLES))
                output.append(word)
            if (random.random() < .25):
                output.append(random.choice(self.MUMBLE_LAST))
            self.poutput(' '.join(output))

if __name__ == '__main__':
    c = CmdLineApp()
    c.cmdloop()

The following is a sample session running example.py. Thanks to Cmd2's built-in transcript testing capability, it also serves as a test suite for example.py when saved as transcript_regex.txt. Running

python example.py -t transcript_regex.txt

will run all the commands in the transcript against example.py, verifying that the output produced matches the transcript.

example/transcript_regex.txt:

# Run this transcript with "python example.py -t transcript_regex.txt"
# The regex for colors is because no color on Windows.
# The regex for editor will match whatever program you use.
# regexes on prompts just make the trailing space obvious
(Cmd) set
colors: /(True|False)/
continuation_prompt: >/ /
debug: False
echo: False
editor: /.*?/
feedback_to_output: False
locals_in_py: True
maxrepeats: 3
prompt: (Cmd)/ /
quiet: False
timing: False

Note how a regular expression /(True|False)/ is used for output of the show color command since colored text is currently not available for cmd2 on Windows. Regular expressions can be used anywhere within a transcript file simply by enclosing them within forward slashes, /.