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Re: %q with truncating size loses safeness of %q

From: Sam Liddicott
Subject: Re: %q with truncating size loses safeness of %q
Date: Mon, 20 Apr 2020 08:36:43 +0100

On Sun, 19 Apr 2020 at 20:40, Chet Ramey <address@hidden> wrote:
> On 4/17/20 6:37 PM, Robert Elz wrote:
> > This happens only because of the cheap way we (and I presume you)
> > implement things - in any rational scheme, it would take the precision
> > chars from the source string, and then quote them.

That, or at least refuse to emit a dangling escape char. There are
arguments against both.
GNU Coreutils printf rejects size specifiers for %q and %b, probably
for this reason.

> Nobody, including POSIX, is rational, then.

Chet, I don't know that POSIX attempt to make a guarantee about output
being reusable as shell input at all, so I don't know that we need to
fallback on POSIX as a reason to break that guarantee.

I that although GNU coreutils printf doesn't exhibit this behaviour of
%q (entirely rejecting size specifiers for it) ksh does exhibit this
behaviour, I will make a report there.

This is another candidate for shellcheck I guess, which reminds me
that I forgot to submit the one for leaky named file descriptors (in
contrast to numeric ones).


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