PHP Detecting Online Users

Detecting Online Users

<?
$f = "db.dat";
$e = "30";
$i = $_SERVER['REMOTE_ADDR'];
function s($n) { if ($n == "1") return user; else return users; }
if (!$o = fopen($f,'a')) die("!db");
$a = file($f);
$o = fopen($f,'w');
foreach($a as $b) { $p = explode("|", $b); if ($p[1]+$e >= time() && $i != $p[0]) fwrite($o,$b); }
fwrite($o, "$i|".time()."\n");
fclose($o);
echo count(file($f))." ".s(count(file($file)))." online";
?>