I\'m getting this error when I try to run any brew command.
Holger-Sindbaeks-MacBook-Air:~ holgersindbaek$ brew help
-bash: /usr/local/bin/brew: /usr/bin/rub
I got the same issue when updated to MacOSX High Sierra & using Xcode 9 with that. High Sierra update ruby gem to version 2.3 but xcpreety command of Xcode 9 still using Ruby 2.0 which is unable to find now & gives bad interpreter. Just go to Terminal & run
sudo gem install xcpretty
Restart Xcode & do fresh clean build it works for me. Hope it helps!!!