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From: Florian Weimer <fw@deneb.enyo.de>
To: "liheng \(P\)" <liheng40@huawei.com>
Cc: Szabolcs Nagy <nsz@port70.net>,  "musl\@lists.openwall.com" <musl@lists.openwall.com>,  Rich Felker <dalias@libc.org>,  "Xiangrui \(Euler\)" <rui.xiang@huawei.com>,  Lizefan <lizefan@huawei.com>
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Date: Sun, 19 Apr 2020 15:10:34 +0200
In-Reply-To: <6D612B6AC5DCDA4580AF97B1068118AD2DD415@DGGEML501-MBX.china.huawei.com>
	(liheng's message of "Sun, 19 Apr 2020 12:26:58 +0000")
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Subject: Re: [musl] regex Back reference matching result not same as glibc and tre.

* liheng:

> But my point is that why pat[] = "(.?).?\\1" to match "aba" in
> extended regular expression mode that success in glibc and failed in
> musl?  Are musl-regex and glibc-regex different?

They are different.  Nowadays, accepting backreferences for extended
regular expressions is probably a bug: it prevents certain strategies
for implementing regular expressions because they are not, in fact,
regular.

The glibc implementation is problematic for several reasons.  I cannot
recommend to use it as a reference.