Safari 12 Mac: does IncludeInternalDebugMenu 1 still work?
Applications (including Terminal) do not get "full disk access" (e.g. your user files) any more in Mojave.

Try to grant Terminal access in...
System Preferences &gt; Security &amp; Privacy &gt; Privacy &gt; Full Disk Access

Unlock the system preference panel, by clicking the lock at the bottom left and filling in your password. Then either drag and drop Terminal.app onto the window, or navigate to it by clicking the plus sign (+).



Then launch Terminal and try your command again.