sub

# File lib/pathname.rb, line 260
  def sub(pattern, *rest, &block)
    if block
      path = @path.sub(pattern, *rest) {|*args|
        begin
          old = Thread.current[:pathname_sub_matchdata]
          Thread.current[:pathname_sub_matchdata] = $~
          eval("$~ = Thread.current[:pathname_sub_matchdata]", block.binding)
        ensure
          Thread.current[:pathname_sub_matchdata] = old
        end
        yield(*args)
      }
    else
      path = @path.sub(pattern, *rest)
    end
    self.class.new(path)
  end