How to switch between different version of gem ins

Question

I have three version of rack installed on local machine (rack (1.4.1, 1.3.6, 1.3.5)). For some gem (such as Cucumber), it requires a lower version of rack to be activated?

I have tried with bundle but there is no good.

When executed, cucumber will still use the activated rack with version 1.4.1 of the system. Bundlespecifies which gem should be installed but doesn't ensure which gem will be activated.

How could I activate certain version of rack?

Answer 1

You can specify a version in gemfile of your project

gem "rack",  "1.3.5"

Pointed by matt:

To use gem specified in Gemfile:

bundle exec cucumber

Answer 2

Use bundler it will manage it for you.