That looks like an extract from an ldap database. Have you considered instead using Net::LDAP to query the directory directly rather than parsing a dump 'by hand'?

LDAP queries support searching on loose text matches. (E.g. search key on 'maillocaladdress=test1*')

Failing that though, this looks like a fairly straightforward 'while' loop on a filehandle. If you're really insistent on hand-parsing an LDAP directory, you'll probably find the 'range' operator useful to read up on.