GNU bug report logs - #51560
Pattern matching not working as expected

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Message #11 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Rob Dyck <rob.dyck <at> telus.net>
To: 51560 <at> debbugs.gnu.org, bug-sed <at> gnu.org
Cc: Davide Brini <dave_br <at> gmx.com>
Subject: Re: bug#51560: Pattern matching not working as expected
Date: Tue, 02 Nov 2021 07:39:33 -0700

Thank you. I was missing something fundamental. my previous experience with 
something similar to regular expressions was with telephone apps. For instance 
00* represented the international dialing code followed by any number of 
digits.

On Tuesday, November 2, 2021 3:12:18 A.M. PDT Davide Brini wrote:
> On Mon, 01 Nov 2021 14:17:19 -0700, Rob Dyck <rob.dyck <at> telus.net> wrote:
> > Extract the lines that start with Network
> > This works as expected --~]$ ipcalc dead:beef::/64 | sed -n '/^Netwo*/p'
> > Network:        dead:beef::/64
> > So ^Netwo* finds the only line that starts with Network.
> 
> Remember that the * quantifier applies to the preceding element, so more
> correctly, "^Netwo*" fins the lines starting with:
> 
> N, e, t, w, zero or more o
> 
> (you probably see where this is going already)
> 
> > My reasoning is that ^Netw shoud give the same result ( elimate o ).
> > But no
> > ipcalc dead:beef::/64 | sed -n '/^Netw*/p'
> > Network:        dead:beef::/64
> > Netmask:        ffff:ffff:ffff:ffff:: = 64
> > 
> > Netmask get pulled in.
> 
> Because "^Netw*" finds lines staring with:
> 
> N, e, t, zero or more w
> 
> So sed is correct.
> 
> --
> D.

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