Easy command-line interpreters with cmd and cmd2

Quit scribbling

Slides are already posted at catherinedevlin.pythoneers.com

Web 2.0

But first...

Sargon the Great

Founder of Akkadian Empire

In between

Command-Line Interface

Unlike the Akkadian Empire, the CLI will never die.

Defining CLI

• "Line-oriented command interpreter"
• "Command-line interface"
• "Shell"

1. Accepts free text input at prompt
2. Outputs lines of text
3. (repeat)

Examples

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

!= Command Line Utilities

(ls, grep, ping, etc.)

1. Accepts arguments at invocation
2. executes
3. terminates

Use sys.argv, optparse

!= "Text User Interfaces", "Consoles"

• Use entire (session) screen
• I/O is not line-by-line

Use curses, urwid

Priorities

A cmd app: pirate.py

from cmd import Cmd

class Pirate(Cmd):
    pass

pirate = Pirate()
pirate.cmdloop()

Fundamental prrrinciple

(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'.format(self.gold))
    def do_drink(self, arg):
        'Drown your sorrrows in rrrum.'
        self.gold -= 1
        print('Now we gots {0} doubloons'.format(self.gold))

Hooks

preloop, postloop, precmd, postcmd

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'.format(self.gold))

Arguments: pirate4.py

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

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

quitting: pirate5.py

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

prompts and defaults: pirate6.py

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

cmd2

Absolutely free

• Script files
• Commands at invocation
• Output redirection
• Python
• Transcript-based testing

But wait, there's more

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

For a few keystrokes more...

• Default to shell
• Color output
• Shortcuts
• Multiline commands
• Environment variables

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

Serious example: sqlpython

cmd-based app by Luca Canali @ CERN

Replacement for Oracle SQL*Plus

Now cmd2-based; postgreSQL; MySQL

sqlpython features

Everything in cmd2

(scripts, redirection, py)

Multi connections

ls, grep

Output to html, csv, inserts, bar graphs

py session with bind variables