- substr: documentation ( source)
- strpos: documentation ( source)
- strrev: documentation ( source)
<?php
$dn = "CN=devops,OU=Groups,OU=US,DC=vice,DC=com;CN=WebDev,OU=GlobalGroups,DC=vice,DC=com;CN=UKOffice,OU=Groups,OU=UK,DC=vice,DC=com;CN=GoogleApps,OU=GlobalGroups,DC=vice,DC=com;CN=UKStaff,OU=Groups,OU=UK,DC=vice,DC=com";
echo substr($dn, (strlen($dn) - strpos(strrev($dn), strrev('OU='))), 2);