How to show lines matching search in open folds in vim?

Question

How can I show all lines in only open folds that match "foo"?

I tried this per "search only in folded text":

:folddoopen g/foo

but got this error: E147: Cannot do :global recursive

vim version: 7.3 (2010 Aug 15)

Answer 1

:folddoopen and :g cannot be used together in a meaningful way.
Instead, use :g with foldclosed():

:g/foo/if foldclosed('.') == -1 | # | endif

For more help see:

:help :g
:help /
:help :if
:help foldclosed()
:help :#
:help :foldopen