I am using Rbenv to manage my ruby versions, and don't remember ever having an issue before. It's been a while since I developed at home though.
Basically this is what happens:
➣ gem install rails
ERROR: While executing gem ... (Gem::FilePermissionError)
You don't have write permissions for the /Library/Ruby/Gems/2.0.0 directory.
➣ rbenv local
➣ rbenv global
@rPat, what does the command
$ which gem
reveal? If it indicates you're using the the system gem command, try
$ rbenv rehash
and see if that resolves the issue.
Also make sure
eval "$(rbenv init -)"
is in your .bash_profile