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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:

../examples/environment.py

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 decorators 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()

cmd2.cmd2.Cmd.poutput

cmd2.cmd2.Cmd.perror

cmd2.cmd2.Cmd.pfeedback

cmd2.cmd2.Cmd.ppaged

Colored Output

The output methods in the previous section all honor the colors setting, which has three possible values:

Never

poutput() and pfeedback() strip all ANSI escape sequences which instruct the terminal to colorize output

Terminal

(the default value) poutput() and pfeedback() do not strip any ANSI escape sequences when the output is a terminal, but if the output is a pipe or a file the escape sequences are stripped. If you want colorized output you must add ANSI escape sequences, preferably using some python color library like plumbum.colors, colorama, blessings, or termcolor.

Always

poutput() and pfeedback() never strip ANSI escape sequences, regardless of the output destination

The previously recommended colorize method is now deprecated.

Suppressing non-essential output

The quiet setting controls whether self.pfeedback() actually produces any output. If quiet is False, then the output will be produced. If quiet is True, no output will be produced.

This makes self.pfeedback() useful for non-essential output like status messages. Users can control whether they would like to see these messages by changing the value of the quiet setting.

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).

cmd2.cmd2.Cmd.select

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!

Exit code to shell

The self.exit_code attribute of your cmd2 application controls what exit code is sent to the shell when your application exits from cmdloop().

Asynchronous Feedback

cmd2 provides two functions to provide asynchronous feedback to the user without interfering with the command line. This means the feedback is provided to the user when they are still entering text at the prompt. To use this functionality, the application must be running in a terminal that supports VT100 control characters and readline. Linux, Mac, and Windows 10 and greater all support these.

async_alert()

Used to 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 and their current input text and cursor location is left alone.

async_update_prompt()

Updates the prompt while the user is still typing at it. This is good for alerting the user to system changes dynamically in between commands. For instance you could alter the color of the prompt to indicate a system status or increase a counter to report an event.

cmd2 also provides a function to change the title of the terminal window. This feature requires the application be running in a terminal that supports VT100 control characters. Linux, Mac, and Windows 10 and greater all support these.

set_window_title()

Sets the terminal window title

The easiest way to understand these functions is to see the AsyncPrinting example for a demonstration.