get sizes of docker image layers

sizes.rb

#!/usr/bin/env ruby

DOCKER = ENV["DOCKER"] || "/usr/bin/docker"
NO_VALUE = '<no value>'

def main(args)
  args.each do |arg|
    image_id = get_image_id(arg)
    #next if image_id.length == 0
    
    puts "#{arg} [#{image_id}]"
    loop do
      size = get_layer_size(image_id)
      puts "  %s - %f" % [image_id[0..12], size]
      p_id = get_layer_parent(image_id)
      break if p_id == NO_VALUE
      image_id = p_id
    end
  end
end

def get_layer_parent(layer_id)
  docker "inspect -f '{{.parent}}' #{layer_id}"
end

def get_layer_size(layer_id)
  docker "inspect -f '{{.Size}}' #{layer_id}"
end

def get_image_id(name)
  docker "images -q #{name}"
end

def docker(args)
  `#{DOCKER} #{args}`.chomp
end

main(ARGV)