# File lib/bundler/gem_helper.rb, line 40
    def build_gem
      file_name = nil
      sh("gem build #{spec_path}") { |out, code|
        raise out unless out[/Successfully/]
        file_name = File.basename(built_gem_path)
        FileUtils.mkdir_p(File.join(base, 'pkg'))
        FileUtils.mv(built_gem_path, 'pkg')
        Bundler.ui.confirm "#{name} #{version} built to pkg/#{file_name}"
      }
      File.join(base, 'pkg', file_name)
    end