Re: Bug Report: \y, \B, \<, \> do not work with _

[Paul Eggert]

> From: Aharon Robbins <address@hidden>
> Date: Thu, 07 Dec 2000 16:11:53 +0200

> Now, why grep needs regex, I don't know, but I haven't looked at the code.

To implement features that the DFA code can't implement, e.g. regular
expressions like "\(a+\)b\1" that contain backreferences.

There are also some subtle questions of nonconformance with POSIX.2 in
the area of bracket expressions, which I'm trying to address by
helping the POSIX committee revise POSIX.  My opinion is that the
POSIX.2 spec is currently unimplementable in portable code, and is
anyway not what users expect.

For example, in a Danish locale where "aa" is a collating element,
POSIX.2 clearly says that [^[:lower:]]+ must match "aa" (!).
None of the GNU tools do this; nor does Solaris or Tru64;
and Danish users do not expect it.