$re = '/\b(?:(?=\w{2,3}\b)(?:\d+[a-zA-Z]*|[a-zA-Z]+\d*)-){2,}(?:\d+[a-zA-Z]*|[a-zA-Z]+\d*)\b(?!-)/m';
$str = '54-PT-001
54-PT-001A
JKS-54-002AB
KS-54-002B
JKS-64-002A
JKS-64-002B
AAA-54-002A
AAA-54-002
JKS-54-PT-002B
JKS-54-PT-002A
ABC-123-DEF-456-GHI-789
Shoudln\'t match:
only two segments:
JKS-54
mix of letter-number-letter
A1C-PT-0000
mix of number-letter-number
1A2-PT-0000
Non-final element is longer than 3 chars:
FOUR-PT-0000
XXX-FOUR-0000
Trailing dash
ABC-123-GHIJ-
';
preg_match_all($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