PHP script: watch & replicate a folder's content in another

#!/usr/bin/php
<?
/*
    Commands to install PHP-CLI, PEAR and iNotify plugin on Debian/Ubuntu:
        sudo apt-get install php5-cli php5-dev php-pear libnotify-bin
        sudo pecl install channel://pecl.php.net/inotify-0.1.4
        sudo echo "extension=inotify.so" > /etc/php5/cli/conf.d/inotify.ini
*/

$dirToWatch = '/mnt/files/folderToWatch/';      // don't forget trailing slash.
$destinationDir = '/mnt/files/destination/';    // don't forget trailing slash.


$fd = null;
$watch_descriptor = null;

// gracefully exit handler (unregister inotify)
function shutdown($signo) {
    global $fd, $watch_descriptor;
    print("About to gracefully exit.\n");
    if ($fd !== null) {
        if ($watch_descriptor !== null) {
            inotify_rm_watch($fd, $watch_descriptor);
            $watch_descriptor = null;
        }
        fclose($fd);
        $fd = null;
    }
}
pcntl_signal(SIGTERM, "shutdown");
pcntl_signal(SIGHUP,  "shutdown");
pcntl_signal(SIGINT, "shutdown");

$fd = inotify_init();
$watch_descriptor = inotify_add_watch($fd, $dirToWatch, IN_CREATE|IN_DELETE|IN_MOVED_TO|IN_MOVED_FROM);
$doContinue = true;
while ($doContinue) {
    $events = @inotify_read($fd);
    if ($events === false) shutdown(null);

    while (count($events)>0) {
        $event = array_shift($events);
        $filename = $event['name'];
        $filepath = $dirToWatch . $filename;

        // when a new file appears in dirToWatch
        if ( ($event['mask'] & (IN_CREATE|IN_MOVED_TO)) > 0) {
            if (!is_link($destinationDir.$filename)) {
                symlink($filepath, $destinationDir.$filename);
            }
        }
        // when a file is removed from dirToWatch
        else if ( ($event['mask'] & (IN_DELETE|IN_MOVED_FROM)) > 0) {
            if (is_link($destinationDir.$filename)) {
                unlink($destinationDir.$filename);
            }
        }
        else {
            // do nothing.
        }
    }
}

?>