doc.silverstripe.org/cms/tasks/FilesystemSyncTask.php

<?php
/**
 * @package cms
 * @subpackage assets
 */
class FilesystemSyncTask extends BuildTask {
	
	protected $title = "Sync Files & Images assets";
	
	protected $description = "The Files & Images system in SilverStripe maintains its own database
	 	of the contents of the assets/ folder.  This action will update that database, and
		should be called whenever files are added to the assets/ folder from outside
		SilverStripe, for example, if an author uploads files via FTP.";
	
	function run($request) {
		if(isset($_GET['folderID'])) {
			$folderID = $_GET['folderID'];
		} else {
			$folderID = null;
		}
		
		echo Filesystem::sync($folderID);
	}
	
}