How to tell which version of a gem a rails app is using

Question

I\'m investigating a rails app - the prod server has two version of a specific gem installed, how can I tell which version the prod app is using?

Answer 1

gem list 

It will show all the matching gems e.g if some one do

gem list rack

Then th output will be as following

*** LOCAL GEMS ***

rack (1.6.4)
rack-mount (0.6.14)
rack-test (0.6.3, 0.6.2, 0.5.7)