mass editing of multiple text files

hi all. i've been pulling my hair out for the last couple days and i'm starting to go bald over this...

what i need is a tool that can add a return carriage (or blank line) to the end of hundreds of text files. the only catches are, some of these files already have one inserted so there must also be a way to somehow skip those. however some of them have two blank lines at the end so there must also be a way to delete one.

example:

i know it is an odd request, but i'm sure someone must know of a way!

 

bump/tug/yoink etc.