Compares archive members with their counterparts in the file
system, and reports differences in file size, mode, owner,
modification date and contents. See compare.
--concatenate
-A
Appends other tar archives to the end of the archive.
See concatenate.
Adds files to the end of the archive, but only if they are newer than
their counterparts already in the archive, or if they do not already
exist in the archive. See update.