The file dirA/a/b/c/thing1 will be copied to dirB/a/b/c/thing1 if: - dirB/a/b/c/thing1 does not exist, or - dirA/a/b/c/thing1 is newer than dirB/a/b/c/thing1 If a file is renamed, we have no record of what its original name was, and the contents of a file can't uniquely identify it as there could be multiple files with the same contents. It's all about the file's pathnames - their leading directories (location) and their filenames.