foreach $element (@updevices){
        @ip = split(':',$element);
        die "Could not fork()\n" unless defined ($pid = fork);

        if ($pid) { push @pids, $pid; next;}
        # ^ this is parent code, it pushes $pid to array
        # and goes back to the top of the loop


        # below is child code
        # it does something and then exits
        system("ping $ip[2] 1 > /dev/null");
        $result = $?;
        print "ping $ip[0] $ip[2] $result\n";
        if ( $result !=  0)
        {
                print "$ip[0] is dead\n";
                push(@dead, $ip[0]);
        }
        exit; 
        # ^ child exits here
        # and basically stops (that's how exit works, after all)
        # and its exit code is 0; see perdoc -f exit
}
# after parent is done with the loop
# it continues here
# it has the array @pids
# and all other global vars that your script
# is full of...