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

This effect can be accomplished by using sub-replace-special substitution and setreg() linewise

:let @a=""
:%s//\=setreg('A', submatch(0), 'l')/g
:%d _
:pu a
:0d _

or all in one line as such:

:let @a=""|%s//\=setreg('A', submatch(0), 'l')/g|%d _|pu a|0d _

Overview: Using a substitution to append each match into register "a" linewise then replace the entire buffer with the contents of register "a"

Explanation:

1. let @a="" empty the "a" register that we will be appending into
2. %s//\=setreg('A', submatch(0), 'l')/g substitute globally using the last pattern
3. the \=expr will replace the pattern with the contents of the expression
4. submatch(0) get the entire string of what just matched
5. setreg('A', submatch(0), 'l') append (note: the capital "a") to @a the matched string, but linewise
6. %d _ delete every line into the black hole register (aka @_)
7. pu a put the contents of @a into the buffer
8. 0d _ delete the first line

Concerns:

• This will trash one of your registers. This example trashed @a
• Uses the last search pattern. Although you can modify the substitute command with whatever pattern you want: %s/<pattern>/\=setreg('A', submatch(0), 'l')/g

For more help

:h :s\=
:h :let-@
:h submatch()
:h setreg()
:h :d
:h :p

Answer 2

Assuming <ip> is your regex to match an IP address, I presume you could do something like :

:%s/.\{-}\(<ip>\).*/\1/g

where \1 is the first matched group (the address alone), and .\{-} used for non-greedy matching.

Answer 3

:set nowrapscan
:let @a=""
gg0qac/\v(\d{1,3}\.){3}\d{1,3}<CR><CR><Esc>//e+1<CR>@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}<CR>: change until pattern.
6. c{motion}<CR><ESC>: replace text with newline (here {motion} is /{pat}<CR>).
7. //e+1<CR>: search for last pattern, go one character left past its end (wraps around a newline, but if your lines looks like this: IP<newline>IP, 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.

Answer 4

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)