Linux: Copy Files Along with Folder Structure from Source To Target if not Exist

-parents
     Form the name of each destination file by appending to the target
     directory a slash and the specified name of the source file.  The
     last argument given to `cp' must be the name of an existing
     directory.  For example, the command:

          cp --parents a/b/c existing_dir

     copies the file `a/b/c' to `existing_dir/a/b/c', creating any
     missing intermediate directories.