I might drop all of the 'or's and write it like this:

my $pid = open(FROMKID, "-|");

# There are now two processes running, one with
# $pid set to the PID of the child, and the other
# with $pid set to 0 (or undefined upon an error).

unless ($pid) {
   if (!defined($pid)) {
       system_logger("Unable to fork: $!");
       die "fork: $!";       # or just exit as you were
   }

   # note that in this test, $pid is undefined,
   # which means we're the child thread, so no
   # matter what happens, we must exec or exit/die

   unless (exec(...)) {
       system_logger("Cannot exec ...: $!");
       die "exec ...: $!";   # or just exit
   }
}
[download]

It's built-in.

Hope this helps.