[nSLUG] How to sync two directory trees

Ian Campbell ian at slu.ms
Wed May 27 04:43:05 ADT 2009

On Wed, May 27, 2009 at 03:18:41AM -0300, Mike Spencer wrote:
> Is there an easy way to sync or update two nearly identical directory
> trees?
> I have two machines.  
>  +  One, call it HD1, holds the canonical set of files in a hierarchy
>     of directories totaling nearly two gig.
>  +  The other, HD2,  holds the same set of files.  
> But some new files have been added to HD1 and some files on HD1 have
> changed.  I would like to say something like:
>     For each file, foo, in or under /home/base/<path-to-foo> (on HD1)
>       if !exist /mnt/HD2/home/base/<path-to-foo>
>          copy /home/base/<path-to-foo>  to corresponding place on HDx
>       else
>         if different          /home/base/<path-to-foo>   \
>                       /mnt/HD2/home/base/<path-to-foo>
>           delete the version on HD2 and copy over the version from HD1.
> where "different" might be as simple as different sizes or dates.

Yes, there is an easy way.


Not as well known as it should be, so spread the word :)

It tries to do things automatically but will prompt you for a decision
if it can't figure out the right thing to do, so it's not *ideal* to
run as a script... however if you need it to run without intervention
I think you can have it either pick a machine that will always
overwrite (if it's not sure) or just ignore those files.

Works similarly to rsync (think it uses the same diff backend), works
over ssh/rsh/whatever, and just like rsync requires unison to be
installed on both sides.

Nice little app.

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