GNU bug report logs - #65659
RFC: changing printf(1) behavior on %b

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From: Stephane Chazelas <stephane <at> chazelas.org>
To: Eric Blake <eblake <at> redhat.com>
Cc: 65659 <at> debbugs.gnu.org, bug-bash <at> gnu.org, austin-group-l <at> opengroup.org, Chet Ramey <chet.ramey <at> case.edu>
Subject: bug#65659: RFC: changing printf(1) behavior on %b
Date: Fri, 1 Sep 2023 16:31:55 +0100

2023-09-01 07:15:14 -0500, Eric Blake:
[...]
> > Note that in bash, you need both
> > 
> > shopt -s xpg_echo
> > set -o posix
> > 
> > To get a XSI echo. Without the latter, options are still
> > recognised. You can get a XSI echo without those options with:
> > 
> > xsi_echo() {
> >   local IFS=' ' -
> >   set +o posix
> >   echo -e "$*\n\c"
> > }
> > 
> > The addition of those \n\c (noop) avoids arguments being treated as
> > options if they start with -.
> 
> As an extension, Bash (and Coreutils) happen to honor \c always, and
> not just for %b.  But POSIX only requires \c handling for %b.
> 
> And while Issue 8 has taken steps to allow implementations to support
> 'echo -e', it is still not standardized behavior; so your xsi_echo()
> is bash-specific (which is not necessarily a problem, as long as you
> are aware it is not portable).
[...]

Yes, none of local (from ash I believe), the posix option
(several shells have an option called posix all used to improve
POSIX conformance, bash may have been the first) nor -e (from
Research Unix v8) are standard, that part was about bash
specifically (as the thread is also posted on gnu.bash.bug).

BTW, that xsi_echo is not strictly equivalent to a XSI echo in
the case where the last character of the last argument is an unescaped
backslash or a character whose encoding ends in the same byte as
the encoding of backslash.

-- 
Stephane

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