macOS with APFS: Copy-On-Write in Terminal

Question

I am writing some little script that assembles backup data into one directory. The directory content will then be uploaded to a cloud service and after that we can remove it. I was wondering how one could utilize APFS' copy-on-write feature with a command like cp in Terminal.

The Finder does a great job. But if I run cp Largefile LargeFileCopy it takes forever to copy the file and also uses the space accordingly.

Sync

Answer 1

I found it myself.

On macOS, cp supports the -c option. cp -c Largefile LargeFileCopy will then use the new clonefile(2) library and immediately return without using any additional space on the device.

Sync

cp on macOS with APFS — Interesting that copy-on-write must be opted in with -c instead of being implicitly on as it is in the Finder. What were the design considerations behind this? Does anyone know? – Foretopsail

May be it is meant to be POSIX compatible? – Sync

Seems a plausible answer. – Foretopsail