Prepend a String to a file (See related posts)

require 'tempfile'

class File
  def self.prepend(path, string)
    Tempfile.open File.basename(path) do |tempfile|
      # prepend data to tempfile
      tempfile << string

      File.open(path, 'r+') do |file|
        # append original data to tempfile
        tempfile << file.read
        # reset file positions
        file.pos = tempfile.pos = 0
        # copy all data back to original file
        file << tempfile.read
      end
    end
  end
end

class FileString < String
  extend Forwardable

  def initialize(file)
    @file = file.reopen(file.path, 'r+')
    at_exit {@file.close}
  end

  def_delegators :@file, :<<, :pos, :pos=
end