How to handle database in a gem intended for system-wide command line tool

I'm developing a gem that's basically used as a system-wide command line tool. This gem stores necessary data for the app in database. I'm wondering if there's any defacto-standard ish way to handle database in this situation.

So far, I'm thinking of using sqlite3 because I don't want users to go through these pain-in-the-ass processes to install system-wide mysql or postgress. (and yup, I'm using relational database and sqlite is more than enough in terms of performance etc, my app is just a simple small one)

If this is the right decision, the question boils down to where I should put sqlite3 database file. Definitely putting this under gem directory isn't a good idea, and so far I'm thinking of locating at /usr/local/MY_GEM/*.

Sorry the question might sound a bit vague for some people, but if I were to define a single question, it would be "Am I doing all right?" or "You guys have any better idea?".