MediaWiki/Sql
Here is a query that will show you the pages in your wiki that contain a particular string. In this example, I wanted to find all pages that were using the 'Icon' extension parser extension magic word '#icon'.
SELECT DISTINCT page_title
FROM page
RIGHT JOIN revision ON page_id = rev_page
WHERE rev_text_id
IN (
SELECT old_id
FROM `text`
WHERE old_text LIKE '%#icon%'
)