diff /path/folder1 /path/folder2
diff -r /path/folder1 /path/folder2
Why don't you use Finder? Open the first folder, type .epub in the search box and drag&drop the files into the third folder. Do the same for the second folder. You will be prompted if there are files with the same name.Basically I want to copy from 2 folders, files with extension .EPUB only (ignore other extension) into a 3rd folder .