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

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From: Steffen Nurpmeso <steffen <at> sdaoden.eu>
To: "Stephane Chazelas via austin-group-l at The Open Group" <austin-group-l <at> opengroup.org>
Cc: chet.ramey <at> case.edu, Phi Debian <phi.debian <at> gmail.com>, bug-bash <at> gnu.org, 65659 <at> debbugs.gnu.org, Eric Blake <eblake <at> redhat.com>, Steffen Nurpmeso <steffen <at> sdaoden.eu>
Subject: bug#65659: RFC: changing printf(1) behavior on %b
Date: Fri, 01 Sep 2023 23:28:50 +0200

Stephane Chazelas via austin-group-l at The Open Group wrote in
 <20230901181024.pwx4plwclz7ijv5a <at> chazelas.org>:
 |2023-09-01 07:54:02 -0500, Eric Blake via austin-group-l at The Open Group:
 ...
 |> How many scripts in the wild actually use %b, though?  And if there
 |> are such scripts, anything we can do to make it easy to do a drop-in
 |> replacement that still preserves the old behavior (such as changing %b
 |> to %#s) is going to be easier to audit than the only other
 |> currently-portable alternative of actually analyzing the string to see
 |> if it uses any octal or \c escapes that have to be re-written to
 |> portably function as a printf format argument.
 |[...]
 |
 |FWIW, a "printf %b" github shell code search returns ~ 29k
 |entries
 |(https://github.com/search?q=printf+%25b+language%3AShell&type=code&l=Sh\
 |ell)
 |
 |That likely returns only a small subset of the code that uses
 |printf with %b inside the format and probably a few false
 |positives, but that gives many examples of how printf %b is used
 |in practice.

Actually this returns a huge amount of false positives where
printf(1) and %b are not on the same line, let alone the same
command, if you just scroll down a bit it starts like neovim match

 pr_title="${pr_title// /,}" # Replace spaces with commas.
 pr_title="$(printf 'vim-patch:%s' "${pr_title#,}")"

(bash only btw).
Furthermore it shows a huge amount of false use cases like

 printf >&2 "%b\n" "The following warnings and non-fatal errors were encountered during the installation process:"

This is only the first result page.
It seems people think you need this to get colours mostly, which
then, it has to be said, is also practically mislead.  (To the
best of *my* knowledge that is.)

Ah it is a copy&paste world, and for one Stephane at stackoverflow
there are 99 that fool and mislead you, or do not know for sure
themselves, but also copy and paste!

--steffen
|
|Der Kragenbaer,                The moon bear,
|der holt sich munter           he cheerfully and one by one
|einen nach dem anderen runter  wa.ks himself off
|(By Robert Gernhardt)

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