Deleting all special characters from a string - ruby

I was doing the challenges from pythonchallenge writing code in ruby, specifically this one. It contains a really long string in page source with special characters. I was trying to find a way to delete them/check for the alphabetical chars. I tried using scan method, but I think I might not use it properly. I also tried `delete!` like that: ``` a = "PAGE SOURCE CODE PASTED HERE" a.delete! "!", "@" #and so on with special chars, does not work(?) a ``` How can I do that? Thanks