my $pgrp_id=getpgrp(0) # gets the process group id of
                       # the current process

{ # scoping is important!  Otherwise
  # that signal will always be ignored
  # by the parent, which is probably bad.
  # I picked SIGINT, you might prefer something
  # else.

    local $SIG{'INT'}='IGNORE'; 
    kill 2, -$pgrp_id; # - means it's a group id.
}