Using vim to delete all lines except those that match an arbitrary set of strings

Question

I use vim to remove all lines except those that match a particular string, e.g.

:g!/[string that I want to remain in the editor]/d

Works great. But what I really want, and haven't found anywhere, is a way to use vim to remove all except for multiple strings.

For example, let's say I have a file open with the following information:

Dave came at 12PM
Lucy came at 11AM
Trish came at 5PM
John ate lunch at 2PM
Virgil left at 3PM
Dave left at 6PM

and I want to only be left with events that mention Dave and John -- what vim command could I use to just end up with:

Dave came at 12PM
John ate lunch at 2PM
Dave left at 6PM

I realize I can use command-line tools like findstr in Windows and others in *nix, but I'm in vim pretty often and haven't been able to some up with any regex or vim command that will do this. Thank you!

Answer 1

The :global command that you reference in your question actually doesn't just take literal strings, it handles any regular expression. So, you just need to come up with one that has two branches, one for John and one for Dave. Voila:

:g!/Dave\|John/d

Note that this simplistic one would also match Johnny; you probably want to limit the matches to whole keywords:

:g!/\<\(Dave\|John\)\>/d

Regular expressions are a powerful feature of Vim; it's worthwhile to learn more about them. Get started at :help regular-expression.

Answer 2

Following should do it

:v/\v(Dave|John)/d

Breakdown

:v                  matches all lines not containing the search expression 
/\vDave|John        search expression
/d                  execute delete on all those lines 

Answer 3

Use this:

:%s/^[^Dave|John].*\n//

Meaning:

%            means search the whole file
^            at the beginning of the line
[^Dave|John] something that isn't Dave nor John
.*           match anything
\n           new line character
//           replace with nothing