$re = '/(?<=SKU:\s)(.{13})/m';
$str = '<li class="cart__item">SKU: MLB2046549757 | NAME: Notebook Multilaser Legacy Book Pc310 Preta 14.1 , Intel Celeron N3000 4gb De Ram 64gb Ssd, Intel Hd Graphics 1366x768px Windows 10 Home | PRICE: $1415</li><li class="cart__item">SKU: MLB2046549757 | NAME: Notebook Multilaser Legacy Book Pc310 Preta 14.1 , Intel Celeron N3000 4gb De Ram 64gb Ssd, Intel Hd Graphics 1366x768px Windows 10 Home | PRICE: $1415</li>';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php