$re = '/^ID123456_(?:SIT|UAT|TRA)(?:,(SIT|UAT))*/m';
$str = ' - should match with regex
ID123456_SIT,UAT
ID123456_UAT,SIT
ID123456_SIT
ID123456_UAT
ID123456_TRA,SIT,UAT
- should match with regex';
preg_match_all($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