($pid = fork) or last;

##</code><code>##

######### Forked, but do not know how to change a TTY. #########
  Define $DB::fork_TTY
       - or a function DB::get_fork_TTY() which will set $DB::fork_TTY.
  The value of $DB::fork_TTY should be the name of TTY to use.
  On UNIX-like systems one can get the name of a TTY for the given
   window by typing tty, and disconnect the shell from TTY by
   sleep 1000000.
  DB<4>   DB<4>