$re = '/^
(?:OOO) # "OOO"
(ABC|DEF) # "ABC" or "DEF"
(RR|AA|DD|EE) # "RR" or "AA" or "DD" ior :"EE)
(
(?:AAA|BBC|CCC)(?=\d{3}\b) # "AAA" or "BBB" or "CCC" if followed by 3 digits
| # or
(?:ZZ|XX|YY)(?=\d{2}\b) # "ZZ" or "XX" or "YY" if followed by 2 digits
)
.* # anything up to the end
$/xm';
$str = 'OOODEFDDAAA011
OOODEFDDZZ01
OOODEFDDZZ011
OOODEFDDZZ01 words at the end?';
preg_match_all($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