$re = '/(PRD|prd)(?<instance>\w{2,3})/m';
$str = 'host = HYBECMPRDEU1P*
host = HYBECMPRDEU2P*
host = HYBECMPRDEU3P*
host = HYBECMPRDEU4P*
host = HYBECMPRDEU5P*
host = HYBADMPRDEU1P*
host = HYBADMPRDEU2P*
host = HYBADMPRDEU3P*
host = HYBADMPRDEU4P*
host = HYBADMPRDEU5P*
host = HYBBUSPRDAMP*
host = aks-prdap-12459421-vmss000000
host = HYBBUSPRDEU1P*
host = HYBBUSPRDEU2P*
host = HYBBUSPRDEU3P*
host = HYBBUSPRDEU4P*
host = HYBBUSPRDEU5P*
host = HYBBUSPRDAMP*
host = HYBADMPRDAMP*
host = HYBECMPRDAMP*';
preg_match_all($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