Is there an opposite of :g in vim?

Question

I know how to do something to every line that matches a pattern, using :g. Is there a way to do something to every line that does not match the pattern?

For example, suppose I want to delete every line that does not match /foo/. I might do something like:

:G/foo/d

(:G is not the opposite of :g, but that is what I am looking for)

Any ideas?

Answer 1

I think there is a inversion within VIM as,

:g!/foo/d

or, like the grep command (below),

:v/foo/d

---

If you are ready to go to the shell prompt,

grep -v foo filename.txt > new.txt

will do this

Answer 2

Delete lines not containing "foo":

:g/^(.+)\@!.foo.$/d

It's quite tricky. Read first:

:help /\@!