>I'm definitely not in favor of fossilizing Unix, but there's a difference between avoiding fossilization and the kind of minimal, mathematical purity that we see GNU Grep trying to impose here.

I can't really see the difference. Adding a deprecation warning to stderr in a non-POSIX command 15 years after deprecation notice is among the smallest possible changes to [GNU's Not] Unix I can think of. Even then, the change is trivially silenced by deleting a single line in a shell script or two[1] and seems that some distros already do that for you[2].

Yes, this will break something for someone[3] and I might well be that someone. You truly have my sympathies. But if you want to run a system for a decade and a half without ever needing changes, stick to POSIX. You can't have your fossils and eat them too.

[1] https://git.savannah.gnu.org/cgit/grep.git/commit/src/egrep.... [2] https://github.com/void-linux/void-packages/pull/39340 [3] https://xkcd.com/1172/