script incomplete

#!/bin/bash
DIR=/dir/$(date +%y%m)
[ -d "$DIR" ] || mkdir "$DIR"
for  D in $@ # obtem os argumentos
do
    cp /usr/home/backup
if  backup=null then

mkdir backup

done

How can I complete that script, that's not value, can someone help me complete this...
The point of the program is:

  • If the directory backup does not exist, the script must create it.
  • Inside of the backup directory the script should create a directory for each backup done with data and time...

can help me...

No double posting, thread closed
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