On: The history of documented Unix facilities

[jwilk]

unlink(1) is indeed in SUSv2/XCU5:

http://pubs.opengroup.org/onlinepubs/7908799/xcu/unlink.html

I couldn't get my hands on SUSv1/XCU4. It's supposedly available here:

https://publications.opengroup.org/c43x

But you have to log in to download, and I gave up upon seeing account creation form with 16 required fields.

"Open" in "The Open Group" is a bad joke.