gmail_idle.rb

require 'net/imap'

class Net::IMAP
   def idle
     cmd = "IDLE"
     synchronize do
       tag = generate_tag
       put_string(tag + " " + cmd)
       put_string(CRLF)
     end
   end
   def done
     cmd = "DONE"
     synchronize do
       put_string(cmd)
       put_string(CRLF)
     end
   end
end

imap = Net::IMAP.new('imap.gmail.com', '993', true)
imap.login('you@yomammashouse.com', 'slappy')
imap.select('Inbox')
imap.add_response_handler { |resp|
  if resp.kind_of?(Net::IMAP::UntaggedResponse) and resp.name == "EXISTS"
    puts "Mailbox now has #{resp.data} messages"
  end
}
imap.idle

loop do
end