chdir

# File lib/net/ftp.rb, line 1147
    def chdir(dirname)
      if dirname == ".."
        begin
          voidcmd("CDUP")
          return
        rescue FTPPermError => e
          if e.message[0, 3] != "500"
            raise e
          end
        end
      end
      cmd = "CWD #{dirname}"
      voidcmd(cmd)
    end