$re = '/(?<=_adv_)[\w\W]*?(?=_)/m';
$str = ' _adv_1_
Lorem ipsum dolor sit amet, consectetur adipisicing elit. Commodi consequuntur cumque eligendi et facilis ipsa perferendis possimus quasi quidem, quod rem, suscipit voluptas. Asperiores assumenda nemo repellat rerum sint, sunt?
_adv_2_
Lorem ipsum dolor sit amet, consectetur adipisicing elit. Commodi consequuntur cumque eligendi et facilis ipsa perferendis possimus quasi quidem, quod rem, suscipit voluptas. Asperiores assumenda nemo repellat rerum sint, sunt?';
preg_match_all($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