ldapdata: Want to set "Common name" when user edits profile

Hi,

I am trying to use ldapdata to store my edited profile fields in LDAP. It works perfectly for LDAP fields that are mapped to profile fields. What I want to do is, when a user changes his profile (possibly first name, and last name), I want to set the common name (first name followed by last name). I tried using the "PHP to filter attributes: " section, and that doesn't seem to work.

What is the best way to set the Common name?

Thanks,
Arun