$re = '/^PF\s*(?:(?:XAP|FNI)\s*)?O\/(?!\s*(?:VOG\+?(?:\/HSAC)?|HSAC\+?(?:\/HSAC)?)$)\s*(?:RG|VO|HS)[A-Z\s]*(?:\+\s*)?(?:\/\s*[A-Z]+)?$/m';
$str = 'Here are the records should be matched:
PF O/ HSAC + / RGETK
PFO/RGETK
PFO/RGETK+/RGETK
PFO/VOG+/RGETK
PFO/VOG+/VOG
PFO/RGETK+/VOG
PFXAPO/RGETK
PFXAPO/RGETK+/RGETK
PFXAPO/VOG+/RGETK
PFXAPO/VOG+/VOG
PFXAPO/RGETK+/VOG
PFFNIO/RGETK
PFFNIO/RGETK+/RGETK
PFFNIO/VOG+/RGETK
PFFNIO/VOG+/VOG
PFFNIO/RGETK+/VOG
PF O/RGETK+/HSAC
PF O/HSAC+/RGETK
PF O/RG+/RGETK
PF O/RG+/HSAC
Here are the records should NOT be matched:
PFO/VOG
PFO/VOG+/HSAC
PFO/HSAC+/HSAC
PFXAPO/VOG
PFXAPO/VOG+/HSAC
PFXAPO/HSAC+/HSAC
PFFNIO/VOG
PFFNIO/VOG+/HSAC
PFFNIO/HSAC+/HSAC
PF O/ HSAC
PF XAP O/HSAC
PFFNI O/ HSAC';
preg_match_all($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