Well, man says:

       read_entry ( )
           Read one entry from the file and return it as a "Net::LDAP:
+:Entry"
           object.
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So you read entries from an LDIF file, one by one, and then you write them on another, that's all. What you need to change in the script I already posted is:

• read the entries one by one from an LDIF file (not from an LDAP server, and you don't have an entries method that returns the entries all-in-a-sweep) into a variable, say $e
• write the ones you want on the other file, using $ldif->write_entry($e)

Since you say that you know how to use read_entry, you should be able to modify my script any way you like to do the job.