monitor web response times

#!/usr/bin/ruby

def print_responses(times)
  %w{ 0.95 0.99 0.995 0.999 }.each do |percentile|
    pos = (percentile.to_f * times.length).floor
    p pos.to_s + ": " + times[pos].to_s
  end
end

num = 0
rows_to_process = 1000000
times = []

IO.popen("tail -n #{rows_to_process} /opt/nginx/logs/upstream.log | grep -v lobby.php"){|f|
  while line = f.gets
    response_time = line.split(' ')[0].to_f
    times.push response_time
    #p response_time
    num = num + 1
    break if num > rows_to_process
  end
}

times.sort!
print_responses times

p "finished"