frozen_gems.rb

require 'fileutils'

GEMFILE_TMP = 'Gemfile_tmp'

FileUtils.cp('Gemfile', GEMFILE_TMP)

regex = /^\s*gem ['"]([-\w]+)['"](,.*)?/
gems = File.read(GEMFILE_TMP).scan(regex).map do |g|
  g.first if g.last.nil?
end
gems.compact!

h = {}
`bundle exec gem list`.scan(/(\w+(\-\w+)*)\s+\((\d+\.\d+\.\d+(\.\d+)*)\)/m).each do |g|
  g.compact!
  h[g.first] = g.last if gems.include?(g.first)
end

File.open('Gemfile', 'w') {}

File.open(GEMFILE_TMP) do |tmp|
  tmp.each do |l|
    File.open('Gemfile', 'a') do |gemfile|
      name = l.scan(regex).flatten.first
      if !name.nil? && !h[name].nil?
        l.chomp! << ", '#{h[name]}'\n"
      end
      gemfile.write(l)
    end
  end
end

FileUtils.rm_f(GEMFILE_TMP)