If you want a ready-made solution I can heartily recommend the DBIx::FullTextSearch that uses MySQL as backend. It's great, it even decodes:

apples +bananas -"blue oranges"
[download]

automatically, if you want it to. It can be done as simple as this:

my @doc_ids = $fts->search(qq{apples +bananas -"blue oranges"});
[download]

It's one of these "just add water" modules at CPAN.

Another great search engine in perl is ksearch, and it does not need a database (it uses any DBM version you have access to).

/jeorgen