def gsub!(pat, rep)
      each_with_index { |fn, i| self[i] = fn.gsub(pat, rep) }
      self
    end
def gsub!(pat, rep)
      each_with_index { |fn, i| self[i] = fn.gsub(pat, rep) }
      self
    end
Same as +gsub+ except that the original file list is modified.