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From: Sam Steingold <sds AT gnu DOT org>
Subject: Re: cygwin/regex is non-POSIX
Date: Mon, 19 Jan 2004 13:54:06 -0500
Organization: disorganization
Lines: 41
Message-ID: <uoeszrcq9.fsf@gnu.org>
References: <uhdyxm0ji DOT fsf AT gnu DOT org> <20040118050449 DOT GA3672 AT efn DOT org>
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> * Yitzchak Scott-Thoennes <fgubraan AT rsa DOT bet> [2004-01-17 21:04:50 -0800]:
>
> On Thu, Jan 15, 2004 at 03:14:57PM -0500, Sam Steingold <sds AT gnu DOT org> wrote:
>> the cygwin regex is not POSIX.
>> backrefs are not available by default (apparently you need REG_BACKR for
>> that), "(a|)*" cannot be compiled because of "empty (sub)expression",
>> &c &c.
>
> SUSv3 says:
>   A vertical-line appearing first or last in an ERE, or immediately
>   following a vertical-line or a left-parenthesis, or immediately
>   preceding a right-parenthesis, produces undefined results.

Thanks, you are right, complaint is withdrawn.

> Also, it says backrefs part of basic regular expressions but not
> exteneded ones.  From your mention of | I assume you are using
> REG_EXTENDED.  If REG_EXTENDED|REG_BACKR allows backrefs, it doesn't
> appear to be documented.

I am not sure what you mean here.  I would like to interpret your words
as follows, so that I can agree with you:
<http://www.opengroup.org/onlinepubs/007904975/basedefs/xbd_chap09.html>
does not mention REG_BACKR, so it's mere presence can probably be
contrued as a violation of the standard (unless it is enabled whenever
REG_EXTENDED is).  REG_BACKR is also not mentioned in "man regex", so
it is not documented.  Right?

Now, whether I add REG_BACKR to cflags (together with REG_EXTENDED) or
eflags, I do not get back references: "^(x)+\\1$" does not match "xx"
(should be "xx" for whole and "x" for the group).

Finally, a common extension appears to be the use or "?" after a
repetition specification to mean non-greedy matching, e.g.
"a+?" will match only the first "a" in "aaaa".

-- 
Sam Steingold (http://www.podval.org/~sds) running w2k
<http://www.camera.org> <http://www.iris.org.il> <http://www.memri.org/>
<http://www.mideasttruth.com/> <http://www.honestreporting.com>
When C++ is your hammer, everything looks like a thumb.


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