Prepend a String to a file

boof (Florian Aßmann) — Fri, 24 Aug 2007 19:40:07 GMT

I happen to read a question on the ruby ML that inspired me to monkey patch (not really since this method does not exist...) the file class. I added a method called prepend to the File class. You need to require 'tempfile' or this patch will raise a NameError, imho.



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

Ideas (unverified):



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

DZone Snippets: file code

Prepend a String to a file