Idiom #344 Extract filename extension
Assign to ext the fragment of the string f after the last dot character, or the empty string if f does not contain a dot.
E.g. "photo.jpg" -> "jpg"
ext must not contain the dot character.
Assign to ext the fragment of the string f after the last dot character, or the empty string if f does not contain a dot.
E.g. "photo.jpg" -> "jpg"
ext must not contain the dot character.