When I run
$ gem install cocoapods
I get
Fetching: i18n-0.7.0.gem (100%)
ERROR: While executing gem ... (Gem::FilePermissi
It seems you are not using any package manager. Since, you don't have write permission to this directory, there is nothing wrong in using sudo for gem install.
However, I prefer changing ownership of that directory, so that I don't have to use sudo every time.
i.e. sudo chown -R [login name] /Library/Ruby/Gems/2.0.0
and ensure that I have write permission. sudo chmod -R u+w /Library/Ruby/Gems/2.0.0
Consider using rvm (ruby version manager) or rbenv