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

I got a similar error running Homebrew for the first time after upgrading from macOS Mojave v10.14 to Catalina v10.15.

It's never a good idea to run commands without understanding what's wrong with your installation of Homebrew and what the commands actually do. Your first and best option is to run brew doctor. This command will not only tell you if something is wrong but also how to fix the problem. In my case it showed:

Warning: Your Xcode is configured with an invalid path.
You should change it to the correct path:
  sudo xcode-select -switch /Applications/Xcode.app

Once you fix the problem(s), run brew doctor again. Basically, repeat the process until you get the all clear message.

In some cases, you get something like:

Unbrewed dylibs/header files/static libraries were found in /usr/local/....

This will happen if you've installed software outside Homebrew that also use the same location to store their files. In many cases, it's safe to ignore these warnings.