UNIX for Advanced & Expert Users

I have lines like:

Mg2.qns W=0.175u
Mg2.qpsb W=0.175u
Mg4.qns W=0.175u
Mg4.qpsb W=0.175u

Which I need to become:
Mg2.qns W=wmg2qns
Mg2.qpsb W=wmg2qpsb
Mg4.qns W=wmg4qns
Mg4.qpsb W=wmg4qpsb

To acheive this individually line by line I use a command like:
:g/Mg2\.qns/s/W=.*/W=wmg2qns/

However I wish to acheive this for all lines in one command

I can find all the lines containing the concerned words by using:

:g/Mg[24]\.q[np]s/s/??????????????????????

I do not know how to fill up the second part of the command represented by question marks. Any idea?

Not clear why there's a colon at the start; is this vim? Here's how to do it in vim:

Code:

:%s/Mg\([24]\).\(q[np]s[b]?\) W=0\.175u/Mg\1.\2 W=wmg\1\2/g

Thanks!
I am using Vi.
I tried using the command but it did not execute. (Even tried in vim)
I tried searching for
/Mg\([24]\).\(q[np][as]\)

and it could find all the lines.

But when I search for

/Mg\([24]\).\(q[np][as][b]?\) It cannot find anything. How can I make the presence of that last charachter b optional in the substitution command?

One more question: How do I substitute in case I have some charachters in between Mg...... and W=175u like below. These in between charachters should not be disturbed.


Mg2.qns A B C L=123u W=0.175u
Mg2.qpsb DE 12 c1 L=123u W=0.175u
Mg4.qns M N O W=0.175u
Mg4.qpsb W=0.175u

Code:

sed 's/\(.*\)\.\(.*\) W=\(.*\)./\1.\2 W=w\1\2/' filename