$re = '/(\bWF(?!.*(NR|TS|CD|TX))(?!.*MS[0-9]{4}SU)[A-Z]{3,4}_[A-Z_]*\b)(?!\')/';
$str = '// YES
WFFGRP_FUNCTION_GROUP
WFUIDV_USERID_VALIDATION
WFNOTE_NOTE
WFRIMH_REQUEST_IMPLEMENTATION_HISTORY
WFUIDV_USERID_VALIDATION U
// NO
WFFGRP_TOKEN_NR
WFTQUE_CREATION_TS BETWEEN @StartDate AND @EndDate
\'WFSOMETHING\'
WFUIDV_MS1234SU
WFQUEUE
WFRQST_CREATE_SOURCE_TX
WFRQST_CREATE_SOURCE_TYPE_CD
WFRQST_LAST_UPDATE_TS';
preg_match_all($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