bug#62572: Bug#1058752: bug#62572: cp --no-clobber behavior has changed

[Paul Eggert]

On 2024-01-30 03:18, Pádraig Brady wrote:
> So we now have the proposed change as:
>
>    - revert -n to old silent success behavior
>    - document -n as deprecated
>    - Leave --update=none as is (will be synonymous with -n)
>    - Provide --update=none-fail to diagnose and exit failure

Thanks, that's a better proposal, but I still see several opportunities 
for confusion.

If I understand things correctly, cp --update=none is not synonymous 
with the proposed (i.e., old-behavior) cp -n, because -n overrides 
previous -i options but --update=none does not. Also, -n overrides 
either previous or following --update=UPDATE options, but --update=none 
overrides only previous --update=UPDATE options. (For what it's worth, 
FreeBSD -n overrides

Some of this complication seems to be for consistency with how mv 
behaves with -f, -i, -n, and --update, and similarly with how rm behaves 
with -f, -i, -I, and --interactive. To be honest I don't quite 
understand the reason for all this complexity, which suggests it should 
be documented somewhere (the manual?) if it isn't already.

This raises more questions:

* If we deprecate cp -n, what about mv -n? FreeBSD mv -n behaves like 
Coreutils mv -n: it silently does nothing and exits successfully. So 
there's no compatibility argument for changing mv -n's behavior. 
However, whatever --update option we add to cp (to output a diagnostic 
and exit with failure) should surely also be added to mv, to aid 
consistency.

* Should cp --update=none be changed so that it really behaves like the 
old cp -n, in that it overrides other options in ways that differ from 
how the other --update=UPDATE options behave? I'm leaning toward "no" as 
this adds complexity that I don't see the use for.

* If we don't change cp --update=none's overriding behavior, is it still 
OK to tell users to substitute --update=none for -n even though the two 
options are not exactly equivalent? I'm leaning towards "yes" but would 
like other opinions.