grabby.rb

require 'securerandom'
require 'thread'
mutex = Mutex.new

pause = false

pauser =  Thread.new do 
	while (true) do
    s = gets
    mutex.synchronize do
      pause = s =~ /(PAUSE|pause)?/
    end
  end
end 

opener = Thread.new do
	while (true) do
		mutex.synchronize do
 			unless pause   
                                #this line thanks to burkelibbey
				`open "http://grab.by/#{(rand 3)+2}#{SecureRandom.base64(2)[0..2]}"` 
			end	
		end
		sleep 4
	end		
end

pauser.join
opener.join