Un poco largo el título del post.

Al grano, si intentando ejecutar

ionic cordova run ios -l –external

nos da el error:

[cordova] xcodebuild: Command failed with exit code 1 Error output:
[cordova] xcode-select: error: tool 'xcodebuild' requires Xcode, but active developer directory '/Library/Developer/CommandLineTools' is a command line tools instance

lo solucionaremos con

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

Volvemos a probar

ionic cordova run ios -l –external

Y funcionando