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.

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

Main Features

• Searchable command history (history command and <Ctrl>+r) - optionally persistent
• Text file scripting of your application with run_script (@) and _relative_run_script (@@)
• Python scripting of your application with run_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)
• Optional py command runs interactive Python console which can be used to debug your application
• Optional ipy command runs interactive IPython console which can be used to debug your application
• 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 they can contain argument placeholders
• Ability to run commands at startup from an initialization script
• Settable environment parameters
• Parsing commands with arguments using argparse, including support for subcommands
• Unicode character support
• Good tab completion of commands, subcommands, file system paths, and shell commands
• Automatic tab completion of argparse flags when using one of the cmd2 argparse decorators
• Support for Python 3.6+ 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 or run_script -t
• Alerts that seamlessly print while user enters text at prompt
• Colored and stylized output using ansi.style()

Version 2.0 Notes

• Python 3.5 support ended
  • The last release of cmd2 to support Python 3.5 was the 1.5.0 release on January 31, 2021. Python 3.5 was released on Sept. 13, 2015 and it reached end-of-life on September 5, 2020.
• cmd2 2.0 simplifies portions of the API and introduces new features. Many of these changes are not compatible with previous versions of cmd2. For assistance with porting your current cmd2 application to version 2.0, see the CHANGELOG for a description of each breaking change and enhancement.

Installation

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

pip install -U cmd2

cmd2 works with Python 3.6+ 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.

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.

• 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."""
          self.poutput(cmd2.style('foo bar baz', fg=cmd2.fg.red))

  • 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
  • cmd2 history command provides flexible and powerful search
    • 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
  • Both of the above types of history can be optionally persistent between application runs
    • Via optional persistent_history_file argument to cmd2.Cmd initializer

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

  • See the Command Scripts 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 run_script command (or @ shortcut)

• Powerful and flexible built-in Python scripting of your application using the run_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 run_pyscript is essentially identical to what they would enter on the command line
  • See the Python Scripts section of the cmd2 docs for more info
  • Also see the python_scripting.py example in conjunction with the conditional.py script

• Parsing commands with argparse

  • The built-in cmd2.with_argparser decorator will parse arguments using argparse.ArgumentParser
    • Optionally, cmd2.with_argparser(.., with_unknown_args=True) can be used to pass all unknown arguments as a list

  from cmd2 import Cmd2ArgumentParser, with_argparser
  
  argparser = Cmd2ArgumentParser()
  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 Argument Processing in the docs for more details

  NOTE: cmd2 also provides the Cmd2ArgumentParser customization of argparse.ArgumentParser for prettier formatting of help and error messages.

• 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
  • basic_complete helper method for tab completion against a list
  • 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
  • delimiter_complete helper method for tab completion against a list but each match is split on a delimiter
    • See the basic_completion.py example for a demonstration of how to use this feature
  • flag_based_complete helper method for tab completion based on a particular flag preceding the token being completed
  • index_based_complete helper method for tab completion based on a fixed position in the input string
    • See the basic_completion.py example for a demonstration of how to use these features
    • flag_based_complete() and index_based_complete() are basic methods and should only be used if you are not familiar with argparse. The recommended approach for tab completing positional tokens and flags is to use argparse-based completion
  • cmd2 in combination with argparse also provide several advanced capabilities for automatic tab completion
    • See the argparse_completion.py example for more info

• Multi-line commands

  Any command accepts multi-line input when its name is listed the multiline_commands optional argument to cmd2.Cmd.__init. The program will keep expecting input until a line ends with any of the characters listed in the terminators optional argument to cmd2.Cmd.__init__() . 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

Tutorials

• PyOhio 2019 presentation:
  • video
  • slides
  • example code
• 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

Example Application

Example cmd2 application (examples/example.py):

#!/usr/bin/env python
# coding=utf-8
"""
A sample application for cmd2.
"""
import random
import sys
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.maxrepeats = 3
        shortcuts = dict(cmd2.DEFAULT_SHORTCUTS)
        shortcuts.update({'&': 'speak'})

        super().__init__(multiline_commands=['orate'], shortcuts=shortcuts)

        # Make maxrepeats settable at runtime
        self.add_settable(cmd2.Settable('maxrepeats', int, 'max repetitions for speak command'))

    speak_parser = cmd2.Cmd2ArgumentParser()
    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 = cmd2.Cmd2ArgumentParser()
    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__':
    app = CmdLineApp()
    sys.exit(app.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"
# Anything between two forward slashes, /, is interpreted as a regular expression (regex).
# The regex for editor will match whatever program you use.
# regexes on prompts just make the trailing space obvious
(Cmd) set
allow_style: '/(Terminal|Always|Never)/'
always_show_hint: False
debug: False
echo: False
editor: /.*?/
feedback_to_output: False
maxrepeats: 3
quiet: False
timing: False

Regular expressions can be used anywhere within a transcript file simply by enclosing them within forward slashes, /.

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

Open source projects using cmd2

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

• Jok3r
  • Network & Web Pentest Automation Framework
• CephFS Shell
  • Ceph is a distributed object, block, and file storage platform
• JSShell
  • An interactive multi-user web JavaScript shell
• psiTurk
  • An open platform for science on Amazon Mechanical Turk
• Poseidon
  • Leverages software-defined networks (SDNs) to acquire and then feed network traffic to a number of machine learning techniques
• Unipacker
  • Automatic and platform-independent unpacker for Windows binaries based on emulation
• FLASHMINGO
  • Automatic analysis of SWF files based on some heuristics. Extensible via plugins.
• tomcatmanager
  • A command line tool and python library for managing a tomcat server
• Expliot
  • Internet of Things (IoT) exploitation framework
• mptcpanalyzer
  • Tool to help analyze mptcp pcaps
• clanvas
  • Command-line client for Canvas by Instructure