A simple Ruby IRC bot

ircbot.rb

#!/usr/local/bin/ruby

require "socket"

# Don't allow use of "tainted" data by potentially dangerous operations
$SAFE = 1

class IRC

  def initialize(server, port, nick, channel)
    @server = server
    @port = port
    @nick = nick
    @channel = channel
  end

  def send(s)
    # Send a message to the irc server and print it to the screen
    puts "--> #{s}"
    @irc.send "#{s}\n", 0
  end

  def connect
    @irc = TCPSocket.open(@server, @port)
    send "USER blah blah blah :blah blah"
    send "NICK #{@nick}"
    send "JOIN #{@channel}"
  end

  def evaluate(s)
    # Make sure we have a valid expression (for security reasons), and
    # evaluate it if we do, otherwise return an error message
    if s =~ /^[-+*\/\d\s\eE.()]*$/ then
      begin
        s.untaint
        return eval(s).to_s
      rescue Exception => detail
        puts detail.message()
      end
    end
    return "Error"
  end

  def handle_server_input(s)
    # This isn't at all efficient, but it shows what we can do with Ruby
    # (Dave Thomas calls this construct "a multiway if on steroids")
    case s.strip
    when /^PING :(.+)$/i
      puts "[ Server ping ]"
      send "PONG :#{$1}"
    when /^:(.+?)!(.+?)@(.+?)\sPRIVMSG\s.+\s:[\001]PING (.+)[\001]$/i
      puts "[ CTCP PING from #{$1}!#{$2}@#{$3} ]"
      send "NOTICE #{$1} :\001PING #{$4}\001"
    when /^:(.+?)!(.+?)@(.+?)\sPRIVMSG\s.+\s:[\001]VERSION[\001]$/i
      puts "[ CTCP VERSION from #{$1}!#{$2}@#{$3} ]"
      send "NOTICE #{$1} :\001VERSION Ruby-irc v0.042\001"
    when /^:(.+?)!(.+?)@(.+?)\sPRIVMSG\s(.+)\s:EVAL (.+)$/i
      puts "[ EVAL #{$5} from #{$1}!#{$2}@#{$3} ]"
      send "PRIVMSG #{(($4==@nick)?$1:$4)} :#{evaluate($5)}"
    else
      puts s
    end
  end

  def main_loop
    # Just keep on truckin' until we disconnect
    while true
      ready = select([@irc, $stdin], nil, nil, nil)
      next if !ready
      for s in ready[0]
        if s == $stdin then
          return if $stdin.eof
          s = $stdin.gets
          send s
        elsif s == @irc then
          return if @irc.eof
          s = @irc.gets
          handle_server_input(s)
        end
      end
    end
  end

end

# The main program. If we get an exception, then print it out and keep
# going (we do NOT want to disconnect unexpectedly!)
irc = IRC.new('efnet.skynet.be', 6667, 'Alt-255', '#cout')
irc.connect()

begin
  irc.main_loop()
rescue Interrupt
rescue Exception => detail
  puts detail.message()
  print detail.backtrace.join("\n")
  retry
end