bug#79714: env: always adds __CF_USER_TEXT_ENCODING var on macOS since v9.8

On 02/11/2025 09:24, Bruno Haible via GNU coreutils Bug Reports wrote:
> Andrew Marshall wrote:
>> perhaps it’s worth documenting or making it an invalid config on Darwin.
> 
> We could document that users should not use environment variables
> that start with "__", because these environment variables can be
> set by the OS and can influence the behaviour of the OS. Proposed
> patch is attached.
> 
> Once that is documented, I don't think anything is wrong with
> CoreFoundation setting or use any __FOOBAR environment variable(s).

I think the doc change is a bit too much.
The user may very well want to change OS behavior.

Sure CoreFoundation is free to set any __FOOBAR variable,
but it's unfortunate that using env to set or clear specific env vars
has the side effect of implicitly setting __CF_USER_TEXT_ENCODING.
env -i is fine BTW as we'll exec with an empty environment.

I suppose if __CF_USER_TEXT_ENCODING was problematic for users
they've a workaround of explicitly unsetting it.

So yes not a huge issue, but best avoided if possible.

cheers,
Padraig