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From: Stephane Chazelas <stephane.chazelas@gmail.com>
Newsgroups: gnu.bash.bug
Subject: Re: Filename expansion bug
Date: Thu, 8 Aug 2019 16:07:39 +0100
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To: Janek Mi <janekmi@gmail.com>, bug-bash@gnu.org, marcin.slusarz@gmail.com
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Xref: csiph.com gnu.bash.bug:15314

2019-08-08 10:38:48 -0400, Greg Wooledge:
[...]
> > shopt -s failglob
> > command="echo xyz\(\)"
> > $command
> > ```
> > 
> > And it was working fine. But somewhere between bash version 4 and 5 I
> > realized it generates an error:
> > no match: xyz\(\)
[...]
> And my personal response for this variant of the issue: stop putting
> shell commands in string variables and then trying to run them with
> unquoted parameter expansion.  See:
[...]

While I'd agree in this case, note that the austin-group thread
was mentionning a very similar case:
https://www.mail-archive.com/austin-group-l@opengroup.org/msg04213.html

That was in autoconf's configure script (including the one
shipped with bash) that is /broken/ by that change in 5.0:

as_echo='printf %s\n'
$as_echo x

now runs:

printf '%sn' x

if there's a file called %sn in the current directory and

printf '%s\n' x

otherwise

(and would cause an error with failglob and run printf x with
nullglob).

In that case, it's not because the autoconf authors don't know
any better but because at that point in the script where
$ac_echo is defined, they're trying to support ancient shells
that don't have function support.

-- 
Stephane