Hello betwixt,
there is a list of different software for doing this on this link, scroll down the page a little they are numbered 1-14
https://askubuntu.com/questions/3865/how-to-find-and-delete-duplicate-filesIf I make a folder and put a file in it, then create another file of the same name and extension and try to place it in the same folder it tells me it already exists and asks if I want to replace it.In so doing then you can select and place all files from a hard drive in to 1 folder, repeat with the next hard drive, afterwards you will have no duplicate files, then you can disperse the files in to the folders/directories you wish. This saves having to install a software as the functionality is already built in to detect duplicates.
If from that folder you have 100 files to move to 1 directory you can hold down Ctrl key and click x1 left mouse button on each file wherever they are in the folder to highlight them, then right click one of the selected ones and cut/paste all of them to the folder/directory you want in one action.