Subject: Re: bug#33249: [PATCH] grep: grouping of patterns including back reference

From: Paul Eggert <[email-masked]>
Date: Sat, 3 Nov 2018 08:29:39 -0700

Norihiro Tanaka wrote:
> By this change, each fragment is divided into
> groups by whether the fragment includes back reference in a pattern or
> not. a frgment which includes back reference constitutes group, and all
> frgments which include back reference also constitute a group.

Surely this is not sufficient. An invocation of grep like this:

grep -E '(a
b)'

should be an error, but with the proposed patch won't it be equivalent to "grep 
-E '(a|b)'" since the pattern has no back-references?