if version = defined?(RAILS_GEM_VERSION) ? RAILS_GEM_VERSION : rails_gem_version
      rails_gem = Gem.cache.search('rails', "=#{version}").first

      if rails_gem
        gem "rails", "=#{version}"
        require rails_gem.full_gem_path + '/lib/initializer'
      else
        STDERR.puts %(Cannot find gem for Rails =#{version}:
    Install the missing gem with 'gem install -v=#{version} rails', or
    change environment.rb to define RAILS_GEM_VERSION with your desired version.
  )
    exit 1
end