How do I fix the “You don't have write permissions into the /usr/bin directory” error when installing Rails?

Question

I\'m trying to install Rails 3 on a brand new MacBook Pro running OS X 10.6.3, Ruby 1.8.7, and Rails 2.3.5 and I\'m wondering if I\'ve hosed myself. So far, I\'ve run these

Answer 1

On macOS High Sierra, this solved my issue:

sudo gem update --system -n /usr/local/bin/gem