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Subject: Re: manpage searches "^\s+keyword\s" vs. ???
To: cygwin AT cygwin DOT com
References: <5C4E5F0F DOT 2090403 AT tlinx DOT org> <1210066491 DOT 20190130214043 AT yandex DOT ru> <c8f36794-db4a-8148-0547-eaad351c7795 AT redhat DOT com>
From: Eric Blake <eblake AT redhat DOT com>
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Date: Wed, 30 Jan 2019 13:35:54 -0600
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From: Eric Blake <eblake AT redhat DOT com>
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Subject: Re: manpage searches "^\s+keyword\s" vs. ???
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 <c8f36794-db4a-8148-0547-eaad351c7795 AT redhat DOT com>
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On 1/30/19 1:09 PM, Eric Blake wrote:

> \s is a non-standard regex extension - glibc provides it, Cygwin has not
> (at least, historically).  POSIX provides [[:space:]] as a portable
> alternative (although not all libc have implemented all of POSIX yet),
> but is annoyingly long to type.
>=20
> Similarly, BSD regex (which is where Cygwin derives its regex from)
> supports the non-standard regex extension [[:<:]] as a word boundary,
> while glibc has the same feature but spelled \<.  I also seem to recall
> a patch in the past to teach Cygwin to respect \< by expanding it to
> [[:<:]] before calling into the BSD-derived code (although I couldn't
> actually find one in a quick search); a similar patch to expand \s into
> [[:space:]] would be a reasonable idea.

Found it:
https://sourceware.org/git/?p=3Dnewlib-cygwin.git;a=3Dblob;f=3Dwinsup/cygwi=
n/regex/regcomp.c;h=3D180f599c#l425

and indeed, Cygwin fakes \< and \> but NOT \s or \b (for those, you'd
have to submit a patch to that spot in regcomp.c).

>=20
>> I guess this is down to compilation options at this point.
>=20
> Not so much compilation options of man and less, but rather the code
> used in Cygwin itself for handling regex.

Also a good read:

https://stackoverflow.com/questions/9792702/does-bash-support-word-boundary=
-regular-expressions

--=20
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org


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