dir+.rb

class Dir
  @dstack = []
  
  def self.push d
    @dstack = [pwd] if @dstack.empty?
    chdir @dstack.push(d).last
    @dstack
  end
  
  def self.pop
    @dstack.pop
    chdir @dstack.last unless @dstack.empty?
    @dstack
  end
end