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From: Eric Blake <eblake@redhat.com>
To: Stephane Chazelas <stephane@chazelas.org>
Cc: Herbert Xu <herbert@gondor.apana.org.au>,
	Harald van Dijk <harald@gigawatt.nl>,
	calestyo@scientia.org, dash@vger.kernel.org
Subject: Re: [v2 PATCH] expand: Always quote caret when using fnmatch
Date: Mon, 21 Feb 2022 10:39:08 -0600	[thread overview]
Message-ID: <20220221163908.hykzez677nlmve6x@redhat.com> (raw)
In-Reply-To: <20220220071544.7odyx5urgcwjsobd@chazelas.org>

On Sun, Feb 20, 2022 at 07:15:44AM +0000, Stephane Chazelas wrote:
> 2022-01-19 16:37:54 +1100, Herbert Xu:
> [...]
> > This patch forces ^ to be a literal when we use fnmatch.
> [...]
> The "fix" also seems incomplete and causes at least this
> regression:
> 
> $ ltrace -e fnmatch ./bin/dash -c 'case "\\" in ($1) echo match; esac' sh '[\^]'
> dash->fnmatch("[\\\\^]", "\\", 0)                              = 0
> match
> 
> See how that added \ caused it to be included in the set. Compare with:
> 
> +++ exited (status 0) +++
> $ ltrace -e fnmatch ./bin/dash -c 'case "\\" in ($1) echo match; esac' sh '[\!]'
> dash->fnmatch("[\\!]", "\\", 0)                                = 1
> +++ exited (status 0) +++
> $ ltrace -e fnmatch ./bin/dash -c 'case "\\" in ($1) echo match; esac' sh '[\x]'
> dash->fnmatch("[\\x]", "\\", 0)                                = 1
> +++ exited (status 0) +++

If you want to escape ^ to always be treated as a literal when calling
fnmatch(), you have to spell it something like [[=^=]...], not [\^...]
(that is, since \^ inside [] does NOT treat the \ as an escape
character, but as yet another literal character as part of the brakcet
group, you instead have to resort to calling out the literal character
^ via alternative spellings such as by a collation equivalent).
Another alternative is to rewrite the [] bracket exprsesion so that ^
is no longer first (but be careful if the character after ^ is -, ],
or !, as the rewrite is not always a trivial swap with the next
character).

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org


  reply	other threads:[~2022-02-21 16:41 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-01-12 16:25 possible wrong behaviour with patterns using a quoted ^ at the start of a bracket expression Christoph Anton Mitterer
2022-01-12 17:20 ` Harald van Dijk
2022-01-12 17:47   ` Christoph Anton Mitterer
2022-01-12 18:17     ` Harald van Dijk
2022-01-12 18:21       ` Christoph Anton Mitterer
2022-01-18  6:13   ` [PATCH] expand: Always quote caret when using fnmatch Herbert Xu
2022-01-18  8:44     ` Harald van Dijk
2022-01-19  5:37       ` [v2 PATCH] " Herbert Xu
2022-02-20  7:15         ` Stephane Chazelas
2022-02-21 16:39           ` Eric Blake [this message]
2022-02-21 17:06             ` Harald van Dijk
2022-02-21 19:15               ` Stephane Chazelas
2022-01-18 14:29     ` [PATCH] " Christoph Anton Mitterer
2022-01-18 14:54       ` Chet Ramey
2022-01-18 22:33       ` Herbert Xu

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