system("perl script.pl >/dev/null &");
open(CMD, "|perl script.pl > /dev/null");

##</code><code>##

system("while true; do echo boo; sleep 2; done &");
print "system done - exiting\n";

##</code><code>##

open(CMD, "|while true; do echo boo; sleep 2; done");
print "open returned - exiting\n";