Syncing Two Dirs With Rsync

[Tim Daneliuk]

I have used rsync for many years to make sure a destination
machine:directory is kept up-to-date with some source master
directory.

I now need to find a way to keep two different machine:dirs
in sync with each other.  But for any given file, I don't know
which of these is newer so I don't know "which way" to sync.

For example given:

machineA::/dir/foo      machineB:/dir/foo
machineA::/dir/bar      machineB:/dir/bar

Say the machineA has the newest foo, but machineB has the
newest bar.  At the end of syncing, I want both machines
to have the latest copies of everything.

I'm guessing there's a way to do this with rsync but I'm kind
of stumped.

Ideas?
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Tim Daneliuk