Easy command-line interpreters with cmd and cmd2

author:Catherine Devlin

Web 2.0


But first...

../_images/sargon.jpg ../_images/akkad.png
Sargon the Great
Founder of Akkadian Empire

In between

Command-Line Interface
Unlike the Akkadian Empire, the CLI will never die.

Defining CLI

Also known as

  • “Line-oriented command interpreter”
  • “Command-line interface”
  • “Shell”
  1. Accepts free text input at prompt
  2. Outputs lines of text
  3. (repeat)


class big
  • Bash, Korn, zsh
  • Python shell
  • screen
  • Zork
  • SQL clients: psql, SQL*Plus, mysql...
  • ed

!= Command Line Utilities

class big

(ls, grep, ping, etc.)

  1. Accept arguments at invocation
  2. execute
  3. terminate

Use sys.argv, optparse

!=”Text User Interface”

  • Use entire (session) screen
  • I/O is not line-by-line
  • See curses, urwid

Decide your priorities


A cmd app: pirate.py

from cmd import Cmd

class Pirate(Cmd):

pirate = Pirate()

Fundamental prrrinciple

class huge

(Cmd) foo a b c


self.do_foo('a b c')

do_-methods: pirate2.py

class Pirate(Cmd):
    gold = 3
    def do_loot(self, arg):
        'Seize booty frrrom a passing ship.'
        self.gold += 1
        print('Now we gots {0} doubloons'
    def do_drink(self, arg):
        'Drown your sorrrows in rrrum.'
        self.gold -= 1
        print('Now we gots {0} doubloons'


self.postcmd(stop, line)

Hooks: pirate3.py

def do_loot(self, arg):
    'Seize booty from a passing ship.'
    self.gold += 1
def do_drink(self, arg):
    'Drown your sorrrows in rrrum.'
    self.gold -= 1
def precmd(self, line):
    self.initial_gold = self.gold
    return line
def postcmd(self, stop, line):
    if self.gold != self.initial_gold:
        print('Now we gots {0} doubloons'

Arguments: pirate4.py

def do_drink(self, arg):
    '''Drown your sorrrows in rrrum.

    drink [n] - drink [n] barrel[s] o' rum.'''
        self.gold -= int(arg)
        if arg:
            print('''What's "{0}"?  I'll take rrrum.'''
        self.gold -= 1

quitting: pirate5.py

def postcmd(self, stop, line):
    if self.gold != self.initial_gold:
        print('Now we gots {0} doubloons'
    if self.gold < 0:
        print("Off to debtorrr's prison.")
        stop = True
    return stop
def do_quit(self, arg):
    return True

prompts, defaults: pirate6.py

prompt = 'arrr> '
def default(self, line):
    print('What mean ye by "{0}"?'

Other CLI packages

class big
  • CmdLoop
  • cly
  • CMdO
  • pycopia
  • cmdlin
  • cmd2


class huge

Convert cmd app to cmd2



As you wish, Guido

class huge

Python 3 compatible

(um, mostly)

Absolutely free

Script files

Commands at invocation

Output redirection


Transcript testing

But wait, there’s more

  • Abbreviated commands
  • Shell commands
  • Quitting
  • Timing
  • Echo
  • Debug

Minor changes: pirate7.py

default_to_shell = True
multilineCommands = ['sing']
terminators = Cmd.terminators + ['...']
songcolor = 'blue'
settable = Cmd.settable + 'songcolor Color to ``sing`` in (red/blue/green/cyan/magenta, bold, underline)'
Cmd.shortcuts.update({'~': 'sing'})
def do_sing(self, arg):
    print(self.colorize(arg, self.songcolor))

Now how much would you pay?

options / flags

Quiet (suppress feedback)

BASH-style select

Parsing: terminators, suffixes

Options: pirate8.py

@options([make_option('--ho', type='int', default=2,
                      help="How often to chant 'ho'"),
          make_option('-c', '--commas',
                      help="Intersperse commas")])
def do_yo(self, arg, opts):
    chant = ['yo'] + ['ho'] * opts.ho
    separator = ', ' if opts.commas else ' '
    chant = separator.join(chant)
        print('{0} and a bottle of {1}'
                  .format(chant, arg))

Serious example: sqlpython

class big

cmd-based app by Luca Canali @ CERN

Replacement for Oracle SQL*Plus

Now cmd2-based; postgreSQL; MySQL

File reporter

class huge

Gather info: Python

Store: postgresql

Report: html


import glob
import os.path

for fullfilename in glob.glob('/home/cat/proj/cmd2/*.py'):
    (dirpath, fname) = os.path.split(fullfilename)
    stats = os.stat(fullfilename)
    binds['path'] = dirpath
    binds['name'] = fname
    binds['bytes'] = stats.st_size
    cmd("""INSERT INTO cat.files (path, name, bytes)
           VALUES (%(path)s, %(name)s, %(bytes)s)""")

sqlpython features

class big
  • from cmd2: scripts, redirection, py, etc.
  • multiple connections
  • UNIX: ls, cat, grep
  • Special output