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

:set nowrapscan
:let @a=""
gg0qac/\v(\d{1,3}\.){3}\d{1,3}//e+1@aq@adG

Explanation:

1. set nowrapscan disables ability to seek «past the end of file».
2. let @a="": empty the a register.
3. gg0: go to the first column (0) of the first line (gg).
4. qa: start writing macros.
5. c/{pattern}: change until pattern.
6. c{motion}: replace text with newline (here {motion} is /{pat}).
7. //e+1: search for last pattern, go one character left past its end (wraps around a newline, but if your lines looks like this: IPIP, there may be problems).
8. @a: execute @a macros (it is empty when you are recording it, but when you are finished it will repeat steps 1-7 until it gets an error).
9. q: end recording @a.
10. @a: execute @a macros.
11. dG: delete to the end of file.