Rsync - What on earth did I do!

I created a new document related to a course I am teaching on my netbook. I rsync'd my netbook to the desktop. To my horror, the lecture notes I had prepared on the desktop were over-written by the version on the netbook.

Why can't software prevent me from doing something so dumb.

Well, I should have examined the implications more carefully for bi-directional rsync.

Another often used flag not included in -a is -u, which says not to overwrite newer files. If we wanted to do a Briefcase style synchronization, we need -u, and we need to do the rsync in two directions:

rsync -aHu a/* b
rsync -aHu b/* a