I have tried installing Sass three times on Mac OS Sierra(10.12) from the terminal typing the following code:
sudo gem install sass
Then it
I used to have the same problem installing the Sass. After installing Xcode with
Sass
Xcode
xcode-select --install
I agree the license with
sudo xcodebuild -license
and finally run the app Xcode and finished installing. After that I write sudo gem install sass and it works.