Run task on specific path only

Hi!

**What would you like to do?**
Sometimes, when I'm working on a big project, I'd find really handy to be able to run a task only on a specific file.
That way I can make surgical changes, move forward in small steps and with high confidence. And, also, without undoing changes constantly in git.

I'd be more than happy to beta test it, if that's required/possible.