<?php
$users = "Username1, Username2 , Username3 ";
preg_match_all('/([\w]{4,25})(?:\s+)?,?/m', $users, $result, PREG_PATTERN_ORDER
); foreach($result[1] as $user) {
echo $user;
}
PD9waHAKJHVzZXJzID0gIlVzZXJuYW1lMSwgVXNlcm5hbWUyICAgICAgLCBVc2VybmFtZTMgICAgICAgIjsKCnByZWdfbWF0Y2hfYWxsKCcvKFtcd117NCwyNX0pKD86XHMrKT8sPy9tJywgJHVzZXJzLCAkcmVzdWx0LCBQUkVHX1BBVFRFUk5fT1JERVIpOwpmb3JlYWNoKCRyZXN1bHRbMV0gYXMgJHVzZXIpIHsKCWVjaG8gJHVzZXI7Cn0=