If you want to offer your customers a search engine, use a search engine.

In particular I'm fond of KinoSearch, especially the current series of developer releases add very useful features. If you want an alternative, look at Plucene.

They build an index, and do things like stemming (so that if you search for Mooses you will also find documents containing onl Moose).

If you really want to turn a search string into a regex, you could at least use the query parser from such a search engine to do the analysis of the search string for you.