- print_r: documentation ( source)
- preg_match_all: documentation ( source)
<?php
$out = <<<END
"CN=Administrator,CN=Users,DC=server,DC=local"
"CN=Guest,CN=Users,DC=server,DC=local"
"CN=krbtgt,CN=Users,DC=server,DC=local"
END;
$matches = array();
preg_match_all('/CN=([^,"]+)/', $out, $matches);
print_r($matches[1]);