The cp command in Linux should be treated as a stub;
The documentation says as much:
(This is an example, not a recommendation, and might not work on all platforms.)
This what would look like (I've used ai to help me that this gets written in proper english)
Getting it to update the sgml and produce a real diff file would be considerably more helpful.
I do think the point here is to be so simple as to be obviously incomplete and thus encourage the reader to find a proven backup system to plug into here instead of writing their own script.
PostgreSQL consistently tries to avoid being inherently too platform and process dependent and this is one of the key places where the community, interested in their platforms and operating systems, are expected to largely step in.
That all said, patching this part of the documentation isn't off the table. (Though given prior comments like this exist and it hasn't been updated suggests a low priority if nothing else - especially without a concrete sgml patch.)
