Subject: Re: bug#78940: REGEX wrongfully matches pattern

From: Davide Brini <[email-masked]>
Date: Wed, 2 Jul 2025 15:26:19 +0200

On Tue, 1 Jul 2025 20:26:16 +0000, "Duchesne, Alexandre"
<[email-masked]> wrote:

> Hi,
> 
> I wanted to show to my classmate the comportment of a RegEX using sed to
> capture the subgroup in a pattern match.
> 
> But, when trying with sed -E, the pattern matched even though it should
> not have.
> 
> Can someone explain to me why if this comportment turns out to be normal ?
> 
> View snippet :
> 
> $ echo abc | grep -E '(...).+' -c
> 0
> $ echo abc | sed -E 's/(...).+/\1/'
> abc

This is all expected behavior. Your regexp does not match, no sostitution
is performed, and sed prints the input line unchanged, which is the default
behavior (disable with sed -n).

-- 
D.