Features requiring application changes

Multiline commands

Command input may span multiple lines for the commands whose names are listed in the parameter app.multilineCommands. These commands will be executed only after the user has entered a terminator. By default, the command terminators is ;; replacing or appending to the list app.terminators allows different terminators. A blank line is always considered a command terminator (cannot be overridden).

Parsed statements

cmd2 passes arg to a do_ method (or default) as a ParsedString, a subclass of string that includes an attribute parsed. parsed is a pyparsing.ParseResults object produced by applying a pyparsing grammar applied to arg. It may include:

Name of the command called
Full input exactly as typed.
Character used to end a multiline command
Remnant of input after terminator
def do_parsereport(self, arg):
    self.stdout.write(arg.parsed.dump() + '\n')
(Cmd) parsereport A B /* C */ D; E
['parsereport', 'A B  D', ';', 'E']
- args: A B  D
- command: parsereport
- raw: parsereport A B /* C */ D; E
- statement: ['parsereport', 'A B  D', ';']
    - args: A B  D
    - command: parsereport
    - terminator: ;
- suffix: E
- terminator: ;

If parsed does not contain an attribute, querying for it will return None. (This is a characteristic of pyparsing.ParseResults.)

The parsing grammar and process currently employed by cmd2 is stable, but is likely significantly more complex than it needs to be. Future cmd2 releases may change it somewhat (hopefully reducing complexity).

(Getting arg as a ParsedString is technically “free”, in that it requires no application changes from the cmd standard, but there will be no result unless you change your application to use arg.parsed.)

Environment parameters

Your application can define user-settable parameters which your code can reference. First create a class attribute with the default value. Then update the settable dictionary with your setting name and a short description before you initialize the superclass. Here’s an example, from examples/environment.py:

#!/usr/bin/env python
# coding=utf-8
A sample application for cmd2 demonstrating customized environment parameters

from cmd2 import Cmd

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

    degrees_c = 22
    sunny = False

    def __init__(self):
        self.settable.update({'degrees_c': 'Temperature in Celsius'})
        self.settable.update({'sunny': 'Is it sunny outside?'})

    def do_sunbathe(self, arg):
        if self.degrees_c < 20:
            result = "It's {} C - are you a penguin?".format(self.degrees_c)
        elif not self.sunny:
            result = 'Too dim.'
            result = 'UV is bad for your skin.'

    def _onchange_degrees_c(self, old, new):
        # if it's over 40C, it's gotta be sunny, right?
        if new > 40:
            self.sunny = True

if __name__ == '__main__':
    c = EnvironmentApp()

If you want to be notified when a setting changes (as we do above), then define a method _onchange_{setting}(). This method will be called after the user changes a setting, and will receive both the old value and the new value.

(Cmd) set --long | grep sunny
sunny: False                # Is it sunny outside?
(Cmd) set --long | grep degrees
degrees_c: 22               # Temperature in Celsius
(Cmd) sunbathe
Too dim.
(Cmd) set degrees_c 41
degrees_c - was: 22
now: 41
(Cmd) set sunny
sunny: True
(Cmd) sunbathe
UV is bad for your skin.
(Cmd) set degrees_c 13
degrees_c - was: 41
now: 13
(Cmd) sunbathe
It's 13 C - are you a penguin?

Commands with flags

All do_ methods are responsible for interpreting the arguments passed to them. However, cmd2 lets a do_ methods accept Unix-style flags. It uses argparse to parse the flags, and they work the same way as for that module.

cmd2 defines a few decorators which change the behavior of how arguments get parsed for and passed to a do_ method. See the section Argument Processing for more information.

Controlling how arguments are parsed for commands with flags

There are a couple functions which can globally effect how arguments are parsed for commands with flags:


Allows user of cmd2 to choose between POSIX and non-POSIX splitting of args for decorated commands.

Parameters:val – bool - True => POSIX, False => Non-POSIX

Allows user of cmd2 to choose whether to automatically strip outer-quotes when POSIX_SHLEX is False.

Parameters:val – bool - True => strip quotes on args for decorated commands if POSIX_SHLEX is False.

poutput, pfeedback, perror, ppaged

Standard cmd applications produce their output with self.stdout.write('output') (or with print, but print decreases output flexibility). cmd2 applications can use self.poutput('output'), self.pfeedback('message'), self.perror('errmsg'), and self.ppaged('text') instead. These methods have these advantages:

  • Handle output redirection to file and/or pipe appropriately
  • More concise
    • .pfeedback() destination is controlled by quiet parameter.
  • Option to display long output using a pager via ppaged()
Cmd.poutput(msg, end='\n')

Convenient shortcut for self.stdout.write(); by default adds newline to end if not already present.

Also handles BrokenPipeError exceptions for when a commands’s output has been piped to another process and that process terminates before the cmd2 command is finished executing.

  • msg – str - message to print to current stdout - anything convertible to a str with ‘{}’.format() is OK
  • end – str - string appended after the end of the message if not already present, default a newline
Cmd.perror(errmsg, exception_type=None, traceback_war=True)

Print error message to sys.stderr and if debug is true, print an exception Traceback if one exists.

  • errmsg – str - error message to print out
  • exception_type – str - (optional) type of exception which precipitated this error message
  • traceback_war – bool - (optional) if True, print a message to let user know they can enable debug


For printing nonessential feedback. Can be silenced with quiet. Inclusion in redirected output is controlled by feedback_to_output.

Cmd.ppaged(msg, end='\n')

Print output using a pager if it would go off screen and stdout isn’t currently being redirected.

Never uses a pager inside of a script (Python or text) or when output is being redirected or piped or when stdout or stdin are not a fully functional terminal.

  • msg – str - message to print to current stdout - anything convertible to a str with ‘{}’.format() is OK
  • end – str - string appended after the end of the message if not already present, default a newline


Text output can be colored by wrapping it in the colorize method.

Cmd.colorize(val, color)

Given a string (val), returns that string wrapped in UNIX-style special characters that turn on (and then off) text color and style. If the colors environment parameter is False, or the application is running on Windows, will return val unchanged. color should be one of the supported strings (or styles): red/blue/green/cyan/magenta, bold, underline


Controls whether self.pfeedback('message') output is suppressed; useful for non-essential feedback that the user may not always want to read. quiet is only relevant if app.pfeedback is sometimes used.


Presents numbered options to user, as bash select.

app.select is called from within a method (not by the user directly; it is app.select, not app.do_select).

Cmd.select(opts, prompt='Your choice? ')

Presents a numbered menu to the user. Modelled after the bash shell’s SELECT. Returns the item chosen.

Argument opts can be:

a single string -> will be split into one-word options
a list of strings -> will be offered as options
a list of tuples -> interpreted as (value, text), so that the return value can differ from the text advertised to the user
def do_eat(self, arg):
    sauce = self.select('sweet salty', 'Sauce? ')
    result = '{food} with {sauce} sauce, yum!'
    result = result.format(food=arg, sauce=sauce)
    self.stdout.write(result + '\n')
(Cmd) eat wheaties
    1. sweet
    2. salty
Sauce? 2
wheaties with salty sauce, yum!