automating script to do rsync to another machine

You need to set up ssh without offering a passphrase. How to do this?

go to the

source machine
/home/your-id

ssh-keygen -t rsa

accept the default location .ssh/id_rsa and .ssh/id_rsa.pub
then do (empty passphrase)

and now you can use the generated file .ssh/id_rsa.pub

scp .ssh/id_rsa.pub distal.host.ip.address:/home/yourid/.ssh/authorized_keys

(of course we are coming from only one preimage, otherwise just add line to authorized_keys