gistfile1.rb

require 'rubygems'
require 'eventmachine'

EM.run do
  memcache = EM::Protocols::Memcache.connect('127.0.0.1', 11211)

  begin
    memcache.get(:foo) do |value|
      if value.nil?
        raise Exception, "Tag :foo not found"
      end

      puts "Value Returned: #{value}"

      EM.stop_event_loop
    end
  rescue Exception => ex
    puts 'Failed to get tag...'
  end
end

# scrapcoder:~$ ruby memcache-test.rb
# em-test.rb:10: Tag :foo not found (Exception)
#	  from /home/scrapcoder/.gems/gems/eventmachine-0.12.10/lib/em/protocols/memcache.rb:63
#	  from /home/scrapcoder/.gems/gems/eventmachine-0.12.10/lib/em/protocols/memcache.rb:183:in `call'
#	  from /home/scrapcoder/.gems/gems/eventmachine-0.12.10/lib/em/protocols/memcache.rb:183:in `process_cmd'
#	  from /home/scrapcoder/.gems/gems/eventmachine-0.12.10/lib/em/protocols/memcache.rb:157:in `receive_data'
#         from /home/scrapcoder/.gems/gems/eventmachine-0.12.10/lib/eventmachine.rb:256:in `run_machine'
#	  from /home/scrapcoder/.gems/gems/eventmachine-0.12.10/lib/eventmachine.rb:256:in `run'
#	  from em-test.rb:4

See http://www.ruby-forum.com/topic/859457