$re = '/(?m)^.*a(?:\n.*)*?\n.*blu.*/m';
$str = '1538 a
123
skua456
789
5
g
15563 blu55g
b
456
16453 a
789
5
16524 blu
g
55
1734 a
987
987
55
aasf
552
18278 blu
ttry';
preg_match_all($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