How to do below in one bash command ? I mean rename file to current date
$ echo `date +"%m-%d-%y"`
01-14-16
$ mv backup1.tar 01-14-16
mv backup1.tar "$(date +"%m-%d-%y")"
$(...) is an alternative syntax to ``. This will first execute $(date +"%m-%d-%y"), so that the command line really becomes mv backup1.tar 01-14-16.
Please note that it might be good to do some checking here, e.g. if the file already exists.