symbolic_modes_to_i

# File lib/fileutils.rb, line 904
  def symbolic_modes_to_i(mode_sym, path)  #:nodoc:
    mode_sym.split(/,/).inject(File.stat(path).mode & 07777) do |current_mode, clause|
      target, *actions = clause.split(/([=+-])/)
      raise ArgumentError, "invalid file mode: #{mode_sym}" if actions.empty?
      target = 'a' if target.empty?
      user_mask = user_mask(target)
      actions.each_slice(2) do |op, perm|
        need_apply = op == '='
        mode_mask = (perm || '').each_char.inject(0) do |mask, chr|
          case chr
          when "r"
            mask | 0444
          when "w"
            mask | 0222
          when "x"
            mask | 0111
          when "X"
            if FileTest.directory? path
              mask | 0111
            else
              mask
            end
          when "s"
            mask | 06000
          when "t"
            mask | 01000
          when "u", "g", "o"
            if mask.nonzero?
              current_mode = apply_mask(current_mode, user_mask, op, mask)
            end
            need_apply = false
            copy_mask = user_mask(chr)
            (current_mode & copy_mask) / (copy_mask & 0111) * (user_mask & 0111)
          else
            raise ArgumentError, "invalid `perm' symbol in file mode: #{chr}"
          end
        end

        if mode_mask.nonzero? || need_apply
          current_mode = apply_mask(current_mode, user_mask, op, mode_mask)
        end
      end
      current_mode
    end
  end