Excuse my ignorance im just curious.

  • Good. There are lists of NSFW subreddits so you can find the intersect between the two lists, or you could use the GNU utility curl to query each of the subreddits on old.reddit.com/r/<insert_subreddit_name>, use grep to isolate responses that redirected to https://old.reddit.com/over18?dest=https%3A%2F%2Fold.reddit.com%2Fr%2F<insert_subreddit_name> and then the sed command to extract subreddit names only.