I’m guessing from your code style that you’re relatively new to Ruby? If so, welcome to the Ruby community!
Not sure I’d call this a ps clone exactly…. it’s missing a few options (grin). As far as feedback, the file structure, file naming, and method naming (is? and get) aren’t very idiomatic for Ruby projects. I also think I saw some camelcase methods in there, which is also unusual. That’s a bunch of superficial stuff, but you’ll likely find yourself converging on a consistent rubyish style the more Ruby you read/write.
I’d say more, but 1) I’m on my phone and didn’t look super closely at implementation details, and 2) not sure if you’re aiming for getting feedback here.
I’m curious, why a ps clone? Are you interested in writing command line tools in Ruby? You might find the thor gem up your alley. Or if you’re sticking with learning the standard lib there’s an OptionParser you could use.