Simple Minecraft jabber bot

jabber_bot.rb

###
# Simple jabber bot to let me talk to users of my minecraft server from gtalk

require 'xmpp4r-simple'

BOT_USERNAME = '...'
BOT_PASSWORD = '...'

ADMIN_USERNAME = '...'

SCREEN_NAME = 'minecraft'

# The idea for this method came from here but I blockified it:
#   http://stackoverflow.com/questions/1293695/watch-read-a-growing-log-file-with-ruby
def watch_file(file, &block)
  timeout = 1
  f = File.open(file, "r")
  f.seek(0, IO::SEEK_END)

  while true do
    select [f]
    yield f.gets
    sleep timeout
  end
end

def say(message)
  %x{screen -S #{SCREEN_NAME} -p 0 -X stuff "`printf "say #{message}\r"`"}
end

jabber = Jabber::Simple.new(BOT_USERNAME, BOT_PASSWORD, nil, 'Minecraft Bot')

admin_online = false

# Trap CTRL-C to logoff cleanly.
trap("INT") do
  jabber.disconnect
  puts "\nLogging off."
  exit
end

watch_file('server.log') do |line|
  case line
  when /\[INFO\] (.*?) \[[0-9\/\.:]+\] logged in/
    jabber.deliver(ADMIN_USERNAME, "#{$1} logged in")
  when /\[INFO\] (.*?) lost connection: (.*)/
    jabber.deliver(ADMIN_USERNAME, "#{$1} lost connection: #{$2}")
  when /\[INFO\] (?:\[.*?\] )?(.*?): (.*)/
    jabber.deliver(ADMIN_USERNAME, "#{$1}: #{$2}")
  end

  # Crudely determine if the admin is online
  jabber.presence_updates do |update|
    admin_online = true if update[0] == ADMIN_USERNAME && update[1] == :online
    admin_online = false if update[0] == ADMIN_USERNAME && update[1] == :unavailable
  end

  jabber.received_messages {|msg| say msg.body if admin_online }
end

No problem at all, I'm glad it's useful!