Redirect based on part of URL

[walterk]

I'm wanting to create a redirect, but I'm pretty new to regex rules. Hopefully someone can help me out.

I'd like to redirect any link containing ".nsf" to the same link, but replace "www" with "web".

Example:

www.sitename.com/mail.nsf

redirect to

web.sitename.com/mail.nsf

[g1smd]

This question [webmasterworld.com...] from yesterday is very similar - it redirects while replacing or omitting something.

It should give a good start as to the required code.

[jdMorgan]

Continued here [webmasterworld.com].