53807 Multiple entry tool

Im looking for a tool that can do one of 2 things, either one would work for me. Need a program that can point out duplicates in the same text document. This way I can go in and delete one. It is important that the program does not delete the entry, only points it out. I will have a list of domain names, one per line. The other way it can work is if I have text document a and text document b. It will compare the 2 and remove any domains from document b if document a already has that domain in the list. Each document will have a list of domains one per line. Preferably I would rather have it work the second way with 2 documents but either way would be fine. If you have any questions or suggestions please contact me via PMB. Thanks, Joe