andy4thehuynh andy4thehuynh - 1 month ago 4x
Ruby Question

How to check if a gem is installed?

I installed data_mapper for a Sinatra project. Curious, why is it when I do

gem install brew
, I can
$ which brew
and get the path of its location and can't for data_mapper? This works for some gems and doesn't for others.

How do I verify a gem is installed properly? Would checking the version assure the gem is downloaded correctly?


Try gem list to get the list of gems that are installed. If you can't find data_mapper, it may be that the gem name is different from what you expect.

Also, if you're just doing which brew to find brew, you aren't finding the gem called brew, you're finding the location of the brew executable. Try gem which brew instead.


If you're looking for data_mapper by doing which data_mapper, you probably won't find it. which is a unix program for finding unix executables, and data_mapper probably doesn't have one.

Since your goal is to verify a gem is installed with the correct version, use gem list. You can limit to the specific gem by using gem list data_mapper.

To verify that it's installed and working, you'll have to try to require the gem and then use it in your code.