After upgrading Lion on my MacBook Air to Yosemite, I started to see the following error when running compass.
-bash: /usr/bin/compass: /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/bin/ruby: bad interpreter: No such file or directory
Now, I ended up reinstalling compass, but to do that, I had to do several updates. Not sure if I needed all of them, but here's the list of commands I entered.
Install/Update Xcode to the latest from App Store
sudo xcodebuild -license
sudo gem install compass