Invoking rsync from a script with null parameters

Joe josephj at
Mon Nov 5 00:39:06 MST 2012

Hash: SHA1

No.  I traced the heck out of it (bash -vx ...) and I was actually
sending a null parameter as the first argument to rsync and that made it
get out of bed on the wrong side.

Here are some more details as to what happened:

Essentially, rsync worked, but additionally processed all the files in
the current working directory when that wasn't expressly requested. 
Since null parameters are almost totally invisible, it took awhile to find.

Sorry I didn't include more details in my original post.

On the bright side, this is what caused me to join this list.  I've
learned a lot - mostly by lurking.


On 11/04/2012 10:35 PM, Kevin Korb wrote:
> I suspect you are missing a space somewhere and are ending up with 2
> parameters stuck together. You can have bash output the rsync command
> line it intends to run to make sure or you can just use " " instead of
> "" as extra spaces between parameters will have no effect.
> On 11/04/12 22:23, Joe wrote:
> > I'm working on a bash backup script using rsync. (kubuntu precise
> > 12.04, rsync 3.0.9-1ubuntu1)
> > To avoid having a number of slightly different rsync commands, I
> > would like to use shell variables as part of the rsync command.
> > I.e.: DRYRUN="-n" rsync "${DRYRUN}" more parameters ...
> > This does not work if DRYRUN="" - apparently because this command
> > becomes rsync "" more parameters ... instead of rsync more
> > parameters ...
> > and rsync uses the null parameter for something and does not
> > perform as expected. It does not generate any error or diagnostic
> > message.
> > Is there a way to get around this problem - other than coding each
> > permutation of the command separately?
> > I'm experimenting with putting the whole rsync command in a string
> > so I can run it after any null parameters revert to pure white
> > space. Once I get the quoting to work (preserving those quotes I
> > still need), this method should work, but it's less than elegant.
> > Is this a bug in rsync? (Shouldn't it at least complain/error exit
> > if it gets something like this that it doesn't understand?) If it
> > is, what's the best way to report it?
> > Ideally (for me anyway), I would like it to completely ignore any
> > null parameters, but I don't know what problems that might cause
> > for other people.
> > TIA
> > Joe
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