history function for ruby console (irb) sessions:

   def history(num=100)
     h = Readline::HISTORY.to_a
     start = [0,h.size-num-1].max
     h.zip((0..h.size).to_a)[start...h.size].each do |cmd,i|         
       puts " #{(i).to_s.rjust(4)}  #{cmd}"
     end
   end

I keep it in my .irbrc file, really useful to avoid stepping through command history to find previous commands.