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

ruby-on-rails, rubygems

Solution

In Rails 3 and Rails 4, use `bundle show`

In Rails 2, `rake gems` will print out what gems, dependencies, and versions are installed, frozen, etc.

Problem

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?

Original source