Linux File mv -u
When you'll use mv *, it moves all the files to the destination directory. But when you use 'u' option, files that already exist in the destination directory will be automtically skipped and all the other files will be copied.
Look at the above figure. In 'file1' there are three files 'new1, new2, new3'. And in 'file2', file 'new3' already exist.
Now we want to move all the files of 'file1' to 'file2'. With the 'u' option, file'new3' will be skipped while other two files will be moved.
Now 'file2' has all the three files without over writing.