Delete all of a file except for certain words that contain certain letters

Question

I have a file that contains words that I want to save, along with other junk that I do not need. I just want to delete everything except the words that contain a certain pattern. Take email addresses for example:

foo foo foo foo foo [email protected] foo foo [email protected]

Run some magic and save everything from @ to the previous and next space.

[email protected] [email protected]

This would be useful in so many applications (especially email addresses).

Answer 1

Easy way - grep

The easiest technique is to use :%!grep -o {pat}. The -o/--only-matching make grep only display the matches.

:%!grep -o 'foo\w*bar'

Note: that grep's regex's are a different variant from PCRE and Vim's.

Pure Vim method with plugin - still easy

For a pure native vim solution I suggest you look at ExtractMatches or Yankitute plugins.

(Ab)Using :s for fun and profit

You want to roll your "extract matches" command with :s with a sub-replace-expression (\=) and a list.

let lst = []
:%s/pattern/\=add(lst, submatch(0))[-1]/g
:%d
:pu=lst
:1d

The basic idea is to add each match to the list, lst, using a sub-replace-expression for the :s command. We can use some in-place array trickery to make sure the text doesn't change by always returning the last element of the array (what we just added).

This :s trick is often done in the form:

:let lst = []
:%s//\=add(lst, submatch(0))[-1]/g
:call setreg('"', join(lst, "\n"), 'l')

This will capture the current matches (uses last used pattern) into the default register. If you have Vim 7.4 then the :s can be simplified further: :%s//\=add(lst, submatch(0))/gn

More information

:h :range!
:h :s
:h sub-replace-expression
:h List
:h add()
:h submatch()
:h :d
:h :pu
:h @=

Answer 2

An applied answer (pure vim stuff) that keeps email addresses only:

:%s/\S\+@\S\+/\r\0\r/g
:v//d

1. place \r (carriage return, CR) before and after each email address (i.e. .break lines around each email found, so that each address will go on a separate line);
2. remove all lines which are not email addresses (last search pattern is used).

Less specific usage: change \S\+@\S\+ with the desired pattern.