Log CPU usage percentage per core

cpu_cores.rb

#!/usr/bin/env ruby

$stdout.sync = true

cpu_last = {}
cpu_last_sum = {}

loop do
  cpus = IO.readlines('/proc/stat').select { |line| line.start_with?('cpu') }

  current = {}

  cpus.each do |cpu|
    stats = cpu.split(' ')
    name  = stats[0]

    cpu_now = stats[1..].map(&:to_i)
    cpu_last[name] ||= cpu_now

    cpu_sum = cpu_now.inject(:+)

    cpu_delta      = cpu_sum - cpu_last_sum[name].to_i
    cpu_idle_delta = cpu_now[3] - cpu_last[name][3].to_i

    cpu_used = cpu_delta - cpu_idle_delta

    cpu_usage = (100 * cpu_used / cpu_delta)

    current[name] = cpu_usage

    cpu_last[name]     = cpu_now
    cpu_last_sum[name] = cpu_sum
  end

  puts "#{Time.now} #{current.map { |name, usage| "#{name}: #{usage}%" }.join(' ')}"

  sleep(1)
end