Match (a AND b) vs (a OR b) in PHP regex

I'm trying to search through some files in PHP and I want to give the user a choice between matching any or every term.

E.g.: Search terms: [apple,banana]

Is it possible to return only files that have both words in it?

Also my OR would use the following:

$s_terms = "(" . implode("|", explode(",", $s_terms)) . ")";

I want to separate terms with , and use it in a RegEx match like (apple|banana). Does the above code do that?

Thank you in forward

EDIT:

The other question did not answer my question, but I found something that works:
(.*apple.*banana.*)