Say you are a developer and you recently updated to OSX Sierra…
You may encounter an error like this when doing anything with ruby, even booting up IRB:
If you are a HomeBrew user, this will cause everything to break :(
After much googling, this error is the result of you having installed a newer version of ruby-gems (or a patch) against your system version of ruby. There is an easy fix!
Remove any installs of ruby-gems or any ruby-gems patches against the system version of ruby; ie: remove/rename everything in
/Library/Ruby/Gems/2.0.0 and try again.
You shouldn’t have any other gems in there (other than perhaps a runner like rake), so you shouldn’t have any gems to re-install. You should be using a ruby version manager like rbenv to manage all of your gems anyway :D