def diff_dirs(dir1, dir2)
      mattching_dir_files(dir1, dir2).each do |file|
        a = File.join(dir1, file)
        b = File.join(dir2, file)
        diff_files(a,b)
      end
    end
def diff_dirs(dir1, dir2)
      mattching_dir_files(dir1, dir2).each do |file|
        a = File.join(dir1, file)
        b = File.join(dir2, file)
        diff_files(a,b)
      end
    end
Recursively diff common files between dir1 and dir2