Features requiring no modifications

These features are provided “for free” to a cmd-based application simply by replacing import cmd with import cmd2 as cmd.

Script files

Text files can serve as scripts for your cmd2-based application, with the load, _relative_load, and edit commands.

Both ASCII and UTF-8 encoded unicode text files are supported.

Simply include one command per line, typed exactly as you would inside a cmd2 application.


Comments are omitted from the argument list before it is passed to a do_ method. By default, both Python-style and C-style comments are recognized; you may change this by overriding app.commentGrammars with a different pyparsing grammar (see the arg_print example for specifically how to to this).

Comments can be useful in Script files, but would be pointless within an interactive session.

def do_speak(self, arg):
    self.stdout.write(arg + '\n')
(Cmd) speak it was /* not */ delicious! # Yuck!
it was  delicious!

Startup Initialization Script

You can load and execute commands from a startup initialization script by passing a file path to the startup_script argument to the cmd2.Cmd.__init__() method like so:

class StartupApp(cmd2.Cmd):
    def __init__(self):
        cmd2.Cmd.__init__(self, startup_script='.cmd2rc')

See the AliasStartup example for a demonstration.

Commands at invocation

You can send commands to your app as you invoke it by including them as extra arguments to the program. cmd2 interprets each argument as a separate command, so you should enclose each command in quotation marks if it is more than a one-word command.

cat@eee:~/proj/cmd2/example$ python example.py "say hello" "say Gracie" quit


If you wish to disable cmd2’s consumption of command-line arguments, you can do so by setting the allow_cli_args attribute of your cmd2.Cmd class instance to False. This would be useful, for example, if you wish to use something like Argparse to parse the overall command line arguments for your application:

from cmd2 import Cmd
class App(Cmd):
    def __init__(self):
        self.allow_cli_args = False

Output redirection

As in a Unix shell, output of a command can be redirected:

  • sent to a file with >, as in mycommand args > filename.txt
  • piped (|) as input to operating-system commands, as in mycommand args | wc
  • sent to the paste buffer, ready for the next Copy operation, by ending with a bare >, as in mycommand args >.. Redirecting to paste buffer requires software to be installed on the operating system, pywin32 on Windows or xclip on *nix.

If your application depends on mathematical syntax, > may be a bad choice for redirecting output - it will prevent you from using the greater-than sign in your actual user commands. You can override your app’s value of self.redirector to use a different string for output redirection:

class MyApp(cmd2.Cmd):
    redirector = '->'
(Cmd) say line1 -> out.txt
(Cmd) say line2 ->-> out.txt
(Cmd) !cat out.txt


If you wish to disable cmd2’s output redirection and pipes features, you can do so by setting the allow_redirection attribute of your cmd2.Cmd class instance to False. This would be useful, for example, if you want to restrict the ability for an end user to write to disk or interact with shell commands for security reasons:

from cmd2 import Cmd
class App(Cmd):
    def __init__(self):
        self.allow_redirection = False

cmd2’s parser will still treat the >, >>, and | symbols as output redirection and pipe symbols and will strip arguments after them from the command line arguments accordingly. But output from a command will not be redirected to a file or piped to a shell command.


The py command will run its arguments as a Python command. Entered without arguments, it enters an interactive Python session. That session can call “back” to your application with cmd(""). Through self, it also has access to your application instance itself which can be extremely useful for debugging. (If giving end-users this level of introspection is inappropriate, the locals_in_py parameter can be set to False and removed from the settable dictionary. See see Other user-settable parameters)

(Cmd) py print("-".join("spelling"))
(Cmd) py
Python 2.6.4 (r264:75706, Dec  7 2009, 18:45:15)
[GCC 4.4.1] on linux2
Type "help", "copyright", "credits" or "license" for more information.

    py <command>: Executes a Python command.
    py: Enters interactive Python mode.
    End with `Ctrl-D` (Unix) / `Ctrl-Z` (Windows), `quit()`, 'exit()`.
    Non-python commands can be issued with `cmd("your command")`.

>>> import os
>>> os.uname()
('Linux', 'eee', '2.6.31-19-generic', '#56-Ubuntu SMP Thu Jan 28 01:26:53 UTC 2010', 'i686')
>>> cmd("say --piglatin {os}".format(os=os.uname()[0]))
>>> self.prompt
'(Cmd) '
>>> self.prompt = 'Python was here > '
>>> quit()
Python was here >

Using the py command is tightly integrated with your main cmd2 application and any variables created or changed will persist for the life of the application:

(Cmd) py x = 5
(Cmd) py print(x)

The py command also allows you to run Python scripts via py run('myscript.py'). This provides a more complicated and more powerful scripting capability than that provided by the simple text file scripts discussed in Script files. Python scripts can include conditional control flow logic. See the python_scripting.py cmd2 application and the script_conditional.py script in the examples source code directory for an example of how to achieve this in your own applications.

Using py to run scripts directly is considered deprecated. The newer pyscript command is superior for doing this in two primary ways:

  • it supports tab-completion of file system paths
  • it has the ability to pass command-line arguments to the scripts invoked

There are no disadvantages to using pyscript as opposed to py run(). A simple example of using pyscript is shown below along with the examples/arg_printer.py script:

(Cmd) pyscript examples/arg_printer.py foo bar baz
Running Python script 'arg_printer.py' which was called with 3 arguments
arg 1: 'foo'
arg 2: 'bar'
arg 3: 'baz'


If you want to be able to pass arguments with spaces to scripts, then we strongly recommend setting the cmd2 global variable USE_ARG_LIST to True in your application using the set_use_arg_list function. This passes all arguments to @options commands as a list of strings instead of a single string.

Once this option is set, you can then put arguments in quotes like so:

(Cmd) pyscript examples/arg_printer.py hello '23 fnord'
Running Python script 'arg_printer.py' which was called with 2 arguments
arg 1: 'hello'
arg 2: '23 fnord'

IPython (optional)

If IPython is installed on the system and the cmd2.Cmd class is instantiated with use_ipython=True, then the optional ipy command will be present:

from cmd2 import Cmd
class App(Cmd):
    def __init__(self):
        Cmd.__init__(self, use_ipython=True)

The ipy command enters an interactive IPython session. Similar to an interactive Python session, this shell can access your application instance via self and any changes to your application made via self will persist. However, any local or global variable created within the ipy shell will not persist. Within the ipy shell, you cannot call “back” to your application with cmd(""), however you can run commands directly like so:


IPython provides many advantages, including:

  • Comprehensive object introspection
  • Get help on objects with ?
  • Extensible tab completion, with support by default for completion of python variables and keywords

The object introspection and tab completion make IPython particularly efficient for debugging as well as for interactive experimentation and data analysis.

Searchable command history

All cmd-based applications have access to previous commands with the up- and down- arrow keys.

All cmd-based applications on systems with the readline module also provide Readline Emacs editing mode. With this you can, for example, use Ctrl-r to search backward through the readline history.

cmd2 adds the option of making this readline history persistent via optional arguments to cmd2.Cmd.__init__():

cmd2 makes a third type of history access available with the history command:

Quitting the application

cmd2 pre-defines a quit command for you. It’s trivial, but it’s one less thing for you to remember.

Misc. pre-defined commands

Several generically useful commands are defined with automatically included do_ methods.

( ! is a shortcut for shell; thus !ls is equivalent to shell ls.)

Transcript-based testing

A transcript is both the input and output of a successful session of a cmd2-based app which is saved to a text file. The transcript can be played back into the app as a unit test.

$ python example.py --test transcript_regex.txt
Ran 1 test in 0.013s


See Transcript based testing for more details.


cmd2 adds tab-completion of file system paths for all built-in commands where it makes sense, including:

  • edit
  • load
  • pyscript
  • shell

cmd2 also adds tab-completion of shell commands to the shell command.

Additionally, it is trivial to add identical file system path completion to your own custom commands. Suppose you have defined a custom command foo by implementing the do_foo method. To enable path completion for the foo command, then add a line of code similar to the following to your class which inherits from cmd2.Cmd:

complete_foo = self.path_complete

This will effectively define the complete_foo readline completer method in your class and make it utilize the same path completion logic as the built-in commands.

The built-in logic allows for a few more advanced path completion capabilities, such as cases where you only want to match directories. Suppose you have a custom command bar implemented by the do_bar method. You can enable path completion of directories only for this command by adding a line of code similar to the following to your class which inherits from cmd2.Cmd:

# Make sure you have an "import functools" somewhere at the top
complete_bar = functools.partialmethod(cmd2.Cmd.path_complete, dir_only=True)

# Since Python 2 does not have functools.partialmethod(), you can achieve the
# same thing by implementing a tab completion function
def complete_bar(self, text, line, begidx, endidx):
    return self.path_complete(text, line, begidx, endidx, dir_only=True)