Free SQL?

I need a small database to run behind a form on the WWW. Unlike the on-line databases I maintain at work, this needs to run on Linux and has a software budget of approximately zero. On the other hand, all the funcationality I need is to be able to do string searches on addresses. I've been using grep up until now, but it's beginning to get a little unweildy. I seem to remember (a long while ago) reading about someone who had written something SQL-ish in the shell. Can anyone give me a pointer to this or to any other free databases. Thankyou. Andrew -- http://www.kfs.org/kites