File cache in PHP

Here is example for the file caching in php:

$cachefile = 'cache.php';
$cachetime = 1800;

// Serve from the cache if it is younger than $cachetime
if (file_exists($cachefile) && time() - $cachetime < filemtime($cachefile)) {
    echo " Cached copy, generated ".date('H:i', filemtime($cachefile))."";
    include($cachefile);
}else{
  ob_start(); 

  $cached = fopen($cachefile, 'w');
  fwrite($cached, ob_get_contents());
  fclose($cached);
  ob_end_flush();
}

?>