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 |e,i|
    puts " #{(i).to_s.rjust(4)}  #{e}"
  end;nil
end

>> history(7)
  483  def history(num=100)
  484    h = Readline::HISTORY.to_a
  485    start = [0,h.size-num-1].max
  486    h.zip((0..h.size).to_a)[start...h.size].each do |e,i|
  487      puts " #{(i).to_s.rjust(4)}  #{e}"
  488    end;nil
  489  end
  490  history(7)