[Lvlug] How to confirm that cp -u option is working as it should?

[Randy Kramer]

Background:

I'm using cp -a for some of my backups.  I tried using cp -ax but it 
didn't work as I expected--I had a ram disk mounted within the 
directory and I expected the -x option to avoid copying the stuff on 
the ram disk and it didn't.  (So now I umounted the ramdisk before the 
copy.)

Then I tried to use cp -au to do an incremental backup.  It seemed the 
command took almost as long as the full backup (I didn't time either 
one), which raises the question--does anybody have either:
   * suggestions on how to confirm that cp copied only the new files 
(now that the cp is complete, the dates on the files in both places 
will be the same, so checking those doesn't help)
   * reasons (that I might check) why the -u option might not work as 
expected--afaict, the only alias active in my system is alias 
ls='ls --color=auto'

Thanks!
Randy Kramer