I still don't get locking. I just want to increment the number in the file. How can I do this?

Didn't anyone ever tell you web-page hit counters were useless? They don't count number of hits, they're a waste of time, and they serve only to stroke the writer's vanity. It's better to pick a random number; they're more realistic.

Anyway, this is what you can do if you can't help yourself.

    use Fcntl qw(:DEFAULT :flock);
    sysopen(FH, "numfile", O_RDWR|O_CREAT) 	 or die "can't open numfile: $!";
    flock(FH, LOCK_EX) 				 or die "can't flock numfile: $!";
    $num = <FH> || 0;
    seek(FH, 0, 0) 				 or die "can't rewind numfile: $!";
    truncate(FH, 0) 				 or die "can't truncate numfile: $!";
    (print FH $num+1, "\n")			 or die "can't write numfile: $!";
    close FH 					 or die "can't close numfile: $!";

    $hits = int( (time() - 850_000_000) / rand(1_000) );