This works for any strings that have whitespaces in them
str.downcase.tr!(" ", "_")
but strings that dont have whitespaces just get deleted
So "New School" would change into "new_school" but "color" would be "", nothing!
The docs for tr! say
Translates str in place, using the same rules as String#tr. Returns str, or nil if no changes were made.
I think you'll get the correct results if you use tr without the exclamation.