xcode-select -switch path when using cli toolkit

sudo xcode-select -switch /Applications/Xcode.app/Contents/Developer

I installed the CLI tools only (e.g. no Xcode) and received an error with a native gem extension build:

xcode-select: Error: No Xcode is selected. Use xcode-select -switch <path-to-xcode>, or see the xcode-select manpage (man xcode-select) for further information.

After looking at this and browsing the directories, it appears the BSD tools got installed in /usr/bin therefore:

sudo xcode-select -switch /

seems to work.