Ho risolto, posto la soluzione.

codice:
#!/bin/bash

......

mysql -uadmin -p`cat /etc/psa/.psa.shadow` -Dpsa -e "select domains.name as Domain, data_bases.name as DB from domains LEFT JOIN data_bases ON data_bases.dom_id=domains.id order by domains.name" | while read Domain DB; do
    if [ "$DB" ] | [ "$DB" != "NULL" ]; then 
        echo "BACKUP $Domain - DB : $DB"
     fi
done