bug#69532: mv's new -x option should be made orthogonal to -t/-T/default

[Paul Eggert]

On 3/4/24 12:35, Pádraig Brady wrote:
> Another point worth mentioning before changing this,
> is that changing would make the --swap operation non symmetric.
> I.e. `mv -x a d` would be different to `mv -x d a` where d in a directory.

Yes, of course. It's just like mv without the -x. After you've done an 
'mv a b', 'mv b a' will undo the rename, unless b is a directory.

I realize this business of the destination being a directory is a 
hassle. That's why I put in mv's -t and -T options years ago. But at 
this point it's such a well-known hassle that we really gotta stay 
consistent with it if we add options.

The "exch" shell command (in util-linux) is a different matter, as it 
has never had the target-directory hassle (i.e., it has always assumed -T).

In looking into this a bit more, I see a bunch of other gotchas. For 
example, 'mv -b' does not work with 'mv -x'. A bunch of other mv options 
also don't work with 'mv -x'. It's a real mess as-is and we can't ship 
it this way.