Invalid active developer path on MAC OS X after installing Ruby

Question

I get this error:

xcrun: error: invalid active developer path (/Applications/Xcode.app), missing xcrun at: /Applications/Xcode.app/usr/bin/xcrun

Answer 1

For me the solution was as easy as reinstalling Xcode.

It was pointed out here: https://superuser.com/a/981126

You can (re)install Xcode via command line like the answer above suggest, or directly from the App Store.