$re = '/^\_{4}[\r\n]([\s\S]+?(?=^\_{4}[\r\n]))\_{4}[\r\n]/m';
$str = '
____
____
____
fff
____
____
df123 dsfds
ggdg fsdf
____
_____
dfdsfds
gfsdf
_____
';
preg_match_all($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