"Cloned" from http://dzone.com/snippets/simple-irc-bot-written-ruby

simpleIRC.rb

#!/usr/local/bin/ruby

require "socket"

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

# The irc class, which talks to the server and holds the main event loop
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()
        # Connect to the IRC server
        @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