Remove everything except regex match in Vim

Question

My specific case is a text document that contains lots of text and IPv4 addresses. I want to remove everything except for the IP addresses.

I can use :vglobal<

Answer 1

In short, I'm looking for a way to do this without leaving vim

Easy enough:

:1,$! grep --extended-regexp --only-matching --regexp="([0-9]{1,3}\.){3}[0-9]{1,3}"

(though I actually voted up icecrime's substitution answer)