Print CPU usage in ruby

cpu.rb

require "vmstat" # gem install vmstat

CPU_DETAIL = false # set to true if you want to see details for each cpu.

CPU_USAGE = "CPU %s: %5.1f%% sys %5.1f%% user %5.1f%% idle"

def delta prev, curr

  all = prev.cpus.zip(curr.cpus).map do |prev_cpu, curr_cpu|

    system = curr_cpu.system - prev_cpu.system
    user   = curr_cpu.user   - prev_cpu.user
    idle   = curr_cpu.idle   - prev_cpu.idle

    total = system + user + idle

    percentages = [system, user, idle].map do |ticks|
      (ticks / total.to_f) * 100.0
    end

    puts CPU_USAGE % [prev_cpu.num, *percentages] if CPU_DETAIL

    percentages
  end

  averages = all.transpose.map do |stats|
    total = stats.reduce :+
    total / stats.size.to_f
  end

  puts CPU_USAGE % ["A", *averages]

end

prev_sample = Vmstat.snapshot

loop do

  sleep 1

  sample = Vmstat.snapshot

  delta(prev_sample, sample)

  prev_sample = sample

end

Vmstat provides cumulative cpu ticks for each of the three categories (system, user, idle) since the machine booted.