Features requiring application changes¶

Multiline commands¶

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

In multiline commands, output redirection characters like > and | are part of the command arguments unless they appear after the terminator.

Parsed statements¶

cmd2 passes arg to a do_ method (or default) as a Statement, a subclass of string that includes many attributes of the parsed input:

command: Name of the command called
args: The arguments to the command with output redirection or piping to shell commands removed
command_and_args: A string of just the command and the arguments, with output redirection or piping to shell commands removed
argv: A list of arguments a-la sys.argv, including the command as argv[0] and the subsequent arguments as additional items in the list. Quotes around arguments will be stripped as will any output redirection or piping portions of the command
raw: Full input exactly as typed.
terminator: Character used to end a multiline command

If Statement does not contain an attribute, querying for it will return None.

(Getting arg as a Statement 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 any of the additional attributes.)

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
"""

import cmd2


class EnvironmentApp(cmd2.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?'})
        super().__init__()

    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.'
        else:
            result = 'UV is bad for your skin.'
        self.poutput(result)

    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()
    c.cmdloop()

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.

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.

Parameters:	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.

Parameters:	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
Returns:

Cmd.pfeedback(msg)¶: 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.

Parameters:	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

color¶

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

quiet¶

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.

select¶

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!