Can rdiff do incremental backups

I am new to ubuntu , i have installed rdiff-backup.

I have folder called sqlfiles on remote ftp server.The sql filesa are stored for last three days and then deleted. But i want to download the all copies to local computers

I want to have incremental backups on my local server so that

1)If file is same then it should not be copied 2)if different , then overwrite it 3)If file is in local directory and not in FTP , then leave as it is

How can i apply those rules to r-diff

From serverfault Master

• All 3 of your requirements can be done with rsync already.

  1. Default behavior.
  2. Default behavior.
  3. --existing (Transfer only files that already exist on the destination host.)
  

  Master : how can i enter passowrd of remote shh in rsync command

  solefald : you can use `rsync --rsh='ssh'`, so your command would look something likethis: `rsync --rsh='ssh' -a --progress --existing --dry-run /dir/to/upload/from/ user@server:/dir/to/upload/to/`. You can remove `--dry-run` and `--progress` later. pay attention to the `/` after `/dir/to/upload/from/` it will upload the **contents** of that directory, not directory itself. if you would like to upload the whole directory instead, remove trailing `/`
  From solefald