String replace in file

gistfile1.rb

def string_replace(init_string, replace_string, file_name)
  file = File.new(file_name)
  lines = file.readlines
  file.close

  changes = false
  x = 0
  lines.each do |line|
    	changes = true if line.sub!(init_string, replace_string)
  end

  if changes
    file = File.new(file_name,'w')
    lines.each do |line|
      file.write(line)
    end
    file.close
  end
end