FILTER_NULL_ON_FAILURE, 'options' => ['regexp' => '/^[^<>:"\/|?]+$/'], ]); $targets = filter_input(INPUT_GET, 'targets', FILTER_VALIDATE_REGEXP, [ 'flags' => FILTER_NULL_ON_FAILURE, 'options' => ['regexp' => '/^[\da-zA-Z.:\/_ -]+$/'], ]);