grep with upper bound for middle of search pattern

Question

I'm searching for lines with occurrences of foo and one of the numbers 5, 6 or 7, but I only want lines where they (foo and one of the mentioned numbers) are no more than 20 characters apart from each other. So far, the closest thing I've come up with, to no avail, is:

grep -rniE "foo(.*){0,20}[567]" .

I'm getting something basic wrong with my pattern, I'm sure, but I just can't see it right now.

Answer 1

The problem is here:

(.*)

* is greedy. You wanted to match zero to twenty instances of any character. Say:

grep -rniE 'foo(.){0,20}[567]' .