text editor to delete duplicates from pool of large files

[Snoopy]

Hello
Could you please give me an advice, which text editor or maybe other software could I use to clean duplicates in the folder filled with  a lot of .txt files, which have about 200gb total size? I mean , not the duplicates in every file separately, but to clean duplicates all over those all files in the same folder.

I am using notepad to open those 10+ GB txt files, but i need to clean them up. 
So i am thinking about using 2 ways:
merge all txt files into one large ( its size will be > RAM)
Find tools\software to clean folder with several .txt files.

just for searching fileduplicates

the onyl thing you can do progging yourself a little script or using linux basic programms like cat -> sort -> uniq