Date: Sun, 19 Apr 2020 21:26:35 -0400 From: Rich Felker <dalias@...c.org> To: "liheng (P)" <liheng40@...wei.com> Cc: Szabolcs Nagy <nsz@...t70.net>, "musl@...ts.openwall.com" <musl@...ts.openwall.com>, Florian Weimer <fw@...eb.enyo.de>, "Xiangrui (Euler)" <rui.xiang@...wei.com>, Lizefan <lizefan@...wei.com> Subject: Re: regex Back reference matching result not same as glibc and tre. On Sun, Apr 19, 2020 at 12:26:58PM +0000, liheng (P) wrote: > Ok, you are right, I retest to match "aba" by pat = > "\\(.\\?\\).\\?\\1" success without tags (basic regular expression > mode I think). regcomp1(&rbuf, pat, 0); > > 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? Having backreferences in regular expressions is inherently a bug, because it makes them non-regular and unsafe for use where the expression is user input and finishing in finite time is a requirement. They're supported in BRE because it's a historical requirement impossed by the standard, but a major *feature* of ERE is actually being regular and not having backreferences. Rich
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