$re = '/(?i)\b([\w]{3}(?=[\w]*;))/m';
$str = 'd;dd;abc;def;ghi;jkl;ff,sd;cv;s;asdfasdf;s;asdf;asdfasdfad;trhegdas;sd;';
preg_match_all($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