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

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From: Rob Dyck <rob.dyck <at> telus.net>
To: 51560 <at> debbugs.gnu.org
Subject: bug#51560: Pattern matching not working as expected
Date: Mon, 01 Nov 2021 14:17:19 -0700

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Context:
sed (GNU sed) 4.8 
Copyright (C) 2020 Free Software Foundation, Inc. 
License GPLv3+: GNU GPL version 3 or later <https://gnu.org/licenses/gpl.html>. 
This is free software: you are free to change and redistribute it. 
There is NO WARRANTY, to the extent permitted by law. 

Written by Jay Fenlason, Tom Lord, Ken Pizzini, 
Paolo Bonzini, Jim Meyering, and Assaf Gordon. 

This sed program was built with SELinux support. 
SELinux is enabled on this system.

 The problem:
I am filtering the multi-line output if the ipcal command.
The full outlook looks like  --
ipcalc dead:beef::/64 
                                                                                                                                        
Full Network:   dead:beef:0000:0000:0000:0000:0000:0000/64 
Network:        dead:beef::/64 
                                                                                                                                                 
Netmask:        ffff:ffff:ffff:ffff:: = 64 
                                                                                                                                     
                                                                                                                                                                   
            
Address space:  Reserved 
HostMin:        dead:beef:: 
                                                                                                                                                    
HostMax:        dead:beef::ffff:ffff:ffff:ffff 
                                                                                                                                 
Hosts/Net:      2^(64) = 18446744073709551616

The following example is a simplified version of what I originally was trying to do.
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.
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.
I realize that sed can use various inputs to accomplish a task so I am not really interested 
here in other methods.

Why does ^Netw* match Netmask?

Am I missing something rather fundamental or is this a bug?

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