-To select files newer than the modification time of a file that already
-exists, you can use the @samp{--reference} (@samp{-r}) option of @sc{gnu}
-@command{date}, available in @sc{gnu} shell utilities 1.13 or later. It returns
-the time stamp of the already-existing file; this time stamp expands to
-become the referent date which @samp{--newer} uses to determine which
-files to archive. For example, you could say,
-
-@example
-$ @kbd{tar -cf @var{archive.tar} --newer="`date -r @var{file}`" /home}
-@end example
-