Like perrin said, DBI is definately the way to go. With DBI you will also be able to handle the situation where your client may not have a database on the system. The DBD::CSV driver for DBI implements a rudimentory SQL database using CSV (Comma Separated Values) files. This is by no means fast, but it works the same as any other database. You can create tables, and select data using regular SQL syntax. Any real database would be preferred, but you could always fall back to this if necessary.

also it might be worthwhile to look at DBD::SQLite