Where is Perl embedded in your query? What part of constructing the string is slow?
Maybe you want to talk to your database administrator about the data model and how to best access it? Most databases, and especially MySQL, are bad at doing LIKE (and, without benchmarking, even worse at doing NOT LIKE) queries, because usually there are no indices that handle substring queries and/or postfixes well.
My rough recommendation, without knowing your data model, is to read Use the Index Luke, and then to set up some benchmarks/EXPLAIN queries to find out how your data model can be improved by indices. Most likely, adding a trigger and separate column for the "8" will improve things.