I ran into this error when I tried any git operation (like git clone and git pull) on a Mac. I had just upgraded to the latest OS and suddenly my git broke!
$ git pull
xcrun: error: invalid active developer path (/Library/Developer/CommandLineTools),
missing xcrun at: /Library/Developer/CommandLineTools/usr/bin/xcrun
The fix, luckily, is pretty straight forward. Install the Xcode toolkit! Even if you had it installed before, you might have to re-register it or update it to the latest version.
$ xcode-select --install
If that doesn’t work, force it to reset. You’ll need sudo access for this one.
$ sudo xcode-select --reset
If even that fails, go to the Apple developer download section and download Xcode manually.