$re = '/^[a-zA-Z0-9-]{5,32}$/m';
$str = 'participantone
participant1
Participant1
participant-1
participant-one
participant-one-tn
Participant1-tn
Participant-One-tn
participant.one-tn
particpant123-456-tn
participant1.worldwire.io
participant-1-worldwire-st
participant-1-worldwire-io-test-test
';
preg_match_all($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