Roberto Ragusa wrote: > Dean Messing wrote: <snip> > > Pray tell, how did you figure this out. > > I've re-read the man page and I don't see this > > this differential behaviour advertised anywhere. > > I just got it by testing and observing results. > > Actually, the "-c" is not needed at all, it's there > because I also want to know the total space used by backups. > > And... the "-s" is also not needed! It just avoids the > printing of all the subtotals of the subdirectories of > your backups. > > It looks like du simply discard everything already > found on its way when calculating disk space. > > Look at this: > > $ mkdir d > $ head -c 1000000 /dev/zero >f1 > $ ln d/f1 d/f2 > $ cp d/f1 d/f3 > > Now, this command reports only two files and not the third (hardlinked): > > $ du d > 1962 d > > And, look at this; f2 is totally ignored even if it appears on the > command line: > > $ du d/f1 d/f2 d/f3 > 981 d/f1 > 981 d/f3 > > Amazing. Indeed! I just did a bit of testing like yours using multiple directories like this: (Hope the ascii comes out on your end.) d1 d2 d3 f1 <--> f1 f2 f2 f2 (d1/d2 and d3/f2 are linked, d2/f2 is a copy). | <-----------> | f3 f3 <--> f3 `du' appears (as you implied) to construct a table of what pointer to data it's seen earlier in the arglist, and just ignore later pointers to the same data. As are all good solutions, it's simple and elegant (but evidently undocumented). Nice discovery, Roberto.
