Determine which version of a gem is installed?

gem list

should give you a list of all your gems with version number in brackets behind it

StackOverflow has the answer and it might be a more useful place (for you) for Ruby architecture questions (they're still welcome here)

gem outdated

Not being a Ruby dev or having any gems installed, I'm not sure this is going to give you exactly what you're after but it should show you which ones need attention.

Otherwise I would have suggested gem query <package> (searches local) and gem query --remote to see available versions. If you only need local gem versions, the first aught to do.

You can do it like this:

bundle info { gem name }

Or look in Gemfile.lock:

grep { gem name } Gemfile.lock