copy on content and content only

[mlh at zip.com.au]

I want to rsync on the basis of content and content only;
I don't want to copy if the file is no different and I don't
want not to copy if the file is at all different (of course).

I think the right incantation is with the -c (always checksum) option:

	rsync -rlvc here/ there

But it isn't absolutely clear whether under some circumstances
rsync might decide to copy files even if they haven't
changed; e.g. perhaps it thinks it would be more efficient
to copy small files rather than test them.

Is the -I (--ignore-times) option purely a heuristic
/efficiency thing that will not affect what is updated?

Will the -n (--dry-run) option always provide a
completely accurate prediction of what is going to be
updated if given with the -c option?  Even if
going over a network? (ssh).

It is possible for -v (verbose) to tell me why an
update is being made? (in case I'm not using the -c for instance)

Obviously here I'm using rsync for it's 'revision control'
features more than for it's efficiency features.


Regards,
Matt