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.

Click on image below to watch a short video demonstrating the capabilities of cmd2:

• 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 >, >>
• 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
• Macros, which are similar to aliases, but can take arguments when called
• Ability to load commands at startup from an initialization script
• Settable environment parameters
• Parsing commands with arguments using argparse, including support for sub-commands
• Unicode character support
• Good tab-completion of commands, sub-commands, file system paths, and shell commands
• Automatic tab-completion of argparse flags when using one of the cmd2 argparse decorators
• 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
• Alerts that seamlessly print while user enters text at prompt

The last version of cmd2 to support Python 2.7 is 0.8.9, released on August 21, 2018.

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

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 few 3rd-party dependencies.

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

Instructions for implementing each feature follow.

• Extension of the cmd module. So capabilities provided by cmd still exist

  • Your applicaiton inherits from cmd2.Cmd, let's say you call this class MyApp

  import cmd2
  class MyApp(cmd2.Cmd):
    pass

  • Define a command named foo by creating a method named do_foo

  class MyApp(cmd2.Cmd):
      def do_foo(self, args):
          """This docstring is the built-in help for the foo command."""
          print('foo bar baz')

  • By default the docstring for your do_foo method is the help for the foo command
    • NOTE: This doesn't apply if you use one of the argparse decorators mentioned below
  • Can provide more custom help by creating a help_foo method (except when using argparse decorators)
  • Can provide custom tab-completion for the foo command by creating a complete_foo method
  • Easy to upgrade an existing cmd app to cmd2
  • Run your cmd2 app using the built-in REPL by executing the cmdloop method

• Searchable command history

  • Readline history using <Ctrl>+r, arrow keys, and other Readline Shortcut keys
    • Readline history can be persistent between application runs via optional argument to cmd2.Cmd initializer
  • cmd2 history command provides flexible and powerful search
    • By design, this history does NOT persist between application runs
    • If you wish to exclude some of your custom commands from the history, append their names to the list at Cmd.exclude_from_history.
    • Do help history in any cmd2 application for more information

• Simple scripting using ASCII text files with one command + arguments per line

  • See the Script files section of the cmd2 docs for more info
  • See script.txt for a trivial example script that can be used in any cmd2 application with the load command (or @ shortcut)

• Powerful and flexible built-in Python scripting of your application using the pyscript command

  • Run arbitrary Python scripts within your cmd2 application with the ability to also call custom cmd2 commands
  • No separate API for your end users to learn
    • Syntax for calling cmd2 commands in a pyscript is essentially identical to what they would enter on the command line
  • See the Python section of the cmd2 docs for more info
  • Also see the python_scripting.py example in conjunciton with the conditional.py script

• Parsing commands with argparse

  • Two decorators provide built-in capability for using argparse.ArgumentParser to parse command arguments
    • cmd2.with_argparser - all arguments are parsed by the ArgumentParser
    • cmd2.with_argparser_and_unknown_args - any arguments not parsed by the ArgumentParser get passed as a list

  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

  NOTE: cmd2 also provides the ACArgumentParser customization of argparse.ArgumentParser for prettier formatting of help and RangeAction type

• cmd2 applications function like a full-featured shell in many ways (and are cross-platform)

  • Run arbitrary shell commands by preceding them with ! or shell
  • Redirect the output of any command to a file with > for overwrite or >> for append
    • If no file name provided after the >/>>, then output goes to the clipboard/pastebuffer
  • Pipe the output of any command to an arbitrary shell command with |
  • Create your own custom command aliases using the alias command
  • Create your own custom macros using the macro command (similar to aliases, but allow arguments)
  • Settable environment parameters that users can change during execution supported via set command
  • Option to display long output using a pager with cmd2.Cmd.ppaged()
  • Optionally specify a startup script that end users can use to customize their environment

• Top-notch tab-completion capabilities which are easy to use but very powerful

  • For a command foo implement a complete_foo method to provide custom tab completion for that command
    • But the helper methods within cmd2 discussed below mean you would rarely have to implement this from scratch
  • Commands which use one of the argparse decorators have automatic tab-completion of argparse flags
    • And also provide help hints for values associated with these flags
    • Experiment with the argprint.py example using the oprint and pprint commands to get a feel for how this works
  • path_complete helper method provides flexible tab-completion of file system paths
    • See the paged_output.py example for a simple use case
    • See the python_scripting.py example for a more full-featured use case
  • flag_based_complete helper method for tab completion based on a particular flag preceding the token being completed
    • See the tab_completion.py example for a demonstration of how to use this feature
  • index_based_complete helper method for tab completion based on a fixed position in the input string
    • See the tab_completion.py example for a demonstration of how to use this feature
  • basic_complete helper method for tab completion against a list
  • delimiter_complete helper method for tab completion against a list but each match is split on a delimiter
    • See the tab_autocompletion.py example for a demonstration of how to use this feature
  • cmd2 in combination with argparse also provide several advanced capabilities for automatic tab-completion - See the tab_autocompletion.py and tab_autocomp_dynamic.py examples for more info

• Multi-line commands

  Any command accepts multi-line input when its name is listed in Cmd.multiline_commands. 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.

• Asynchronous alerts based on events happening in background threads

  • cmd2 provides the following helper methods for providing information to users asynchronously even though the cmd2 REPL is a line-oriented command interpreter:
    • async_alert - display an important message to the user while they are at the prompt in between commands
      • To the user it appears as if an alert message is printed above the prompt
    • async_update_prompt - update the prompt while the user is still typing at it
      • This is good for alerting the user to system changes dynamically in between commands
    • set_window_title - set the terminal window title
      • This changes the window title of the terminal that the user is running the cmd2 app within

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 cmd2 application (examples/example.py):

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

class CmdLineApp(cmd2.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.multiline_commands = ['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
        super().__init__(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')
    @cmd2.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')
    @cmd2.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, /.

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

Here are a few examples of open-source projects which use cmd2:

• cliff
  • OpenStack Command Line Interface Formulation Framework
• tomcatmanager
  • A command line tool and python library for managing a tomcat server
• clanvas
  • Command-line client for Canvas by Instructure
• mptcpanalyzer
  • Tool to help analyze mptcp pcaps