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Date:   Wed, 12 Jan 2022 18:17:28 +0000
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From:   Harald van Dijk <harald@gigawatt.nl>
Subject: Re: possible wrong behaviour with patterns using a quoted ^ at the
 start of a bracket expression
To:     Christoph Anton Mitterer <calestyo@scientia.org>,
        dash@vger.kernel.org
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On 12/01/2022 17:47, Christoph Anton Mitterer wrote:
> On Wed, 2022-01-12 at 17:20 +0000, Harald van Dijk wrote:
>> However, whether this is the correct approach is a matter of opinion:
>> dash could alternatively choose to always take ^ as a literal and
>> always
>> escape it before passing it on to fnmatch()
> 
> Well I personally think the best would to *always* take ^ literally,
> whether quoted or not.
> 
> That would match the behaviour of bash and klibc sh, and also seems
> more in the spirit of POSIX (which, while saying that an unquoted ^
> produces undefined behaviour, also says that:
> "( '!' ) shall replace the <circumflex> character ( '^' )""
> 
> ... "replace", not complement.

Actually, in bash, unquoted ^ does act as negation. Same in ksh, which 
is the basis for a lot of POSIX. As for the spirit of POSIX, POSIX does 
say in the rationale that it's unspecified specifically in order to 
allow that:

   The restriction on a <circumflex> in a bracket expression is to allow
   implementations that support pattern matching using the <circumflex>
   as the negation character in addition to the <exclamation-mark>.

But personally, I have no opinion on which action dash should take, as 
long as it gets the right results for quoted ^.

Cheers,
Harald van Dijk