[BoppreH]

Ouch, that is a sharp corner:

    $ echo 'aaa' > a.txt
    $ echo 'bbb' > b.txt
    $ TMP_DIR="" # Mistake! Missing arg, failed search, typo'd name, etc.
    $ cp a.txt b.txt $TMP_DIR
    $ cat b.txt
    aaa
    $ # The contents of b.txt are lost.

[nextaccountic]

cp itself should have been two commands, or at least accept two flags for those two very different semantics.

Actually there's a wave of unixy tools being written in Go and Rust and I think there might be a suitable cp replacement already, but it's up to distros to package it.