simplifiable.rb

  def replace_line_in_file(old,new,file)
    File.open(file) do |f|
      File.open(file + ".new", "w") do |f2|
        f.each_line do |line|
          f2.puts line.gsub(old, new)
        end
      end
    end
    File.rename(file + ".new", file)
  end