Subject: Re: bug#78883: backslash interpretation in 's' replacement text violates POSIX

From: Collin Funk <[email-masked]>
Date: Mon, 23 Jun 2025 17:30:53 -0700

Bruno Haible via <[email-masked]> writes:

> POSIX [1] is ambiguous here, I would say:
> Quoting:
>   "For each other <backslash> encountered, the following character shall
>    lose its special meaning (if any)."
> but also
>   "The meaning of an unescaped <backslash> immediately followed by any
>    character other than '&', <backslash>, a digit, <newline>, or the
>    delimiter character used for this command, is unspecified."
>
> So the interpretation of escape sequences looks like a GNU extension.
>
> By the description of the '--posix' option ("In order to simplify
> writing portable scripts"), the --posix option should turn off this
> interpretation. Or, better, emit a diagnostic.

Just want to add a strong +1 for keeping it as a GNU extension. I find
it annoying that other systems 'sed' command does not behave the same
way.

I'm fine with adding a warning for when '--posix' is used though. That
would be helpful for scripts that aim to be as portable as possible
(e.g. the old gnulib-tool).

Collin