append something into middle of file

append.rb

def append_config_to_file
    tempfile = File.open("file.rb", 'w')
    f = File.new("config/application.rb")
    f.each do |line|
      tempfile << line
      if line.match(/class Application/)
        tempfile << "    config.autoload_paths += %W(\#{config.root}/searches)\n"
      end
    end
    f.close
    tempfile.close

    FileUtils.mv("file.rb", "config/application.rb")
  end