Install with

gem install --user-install -n~/bin **gem_name**

This assumes you want the gems in your ~/bin folder, and that you have it added to your PATH

Sources:

• https://stackoverflow.com/questions/31596273/install-gem-in-local-folder
• https://guides.rubygems.org/faqs/#i-installed-gems-with---user-install-and-their-commands-are-not-available