If you’ve ever had the need to remove the duplicate lines from a long list of entries like so…

hi
bye
hi
guy
bye
hi

… and are looking for this…

hi
bye
guy

You can use the find/replace feature in Notepad++ to do it if you use the regex funcationality. Here’s the find string…

^(.*?)$\s+?^(?=.*^\1$)

Just replace with a zero length string.

If you’d like to read up on the details I found this tip here