NetBackup - check available space for weekend backups

You know this situation. In some remote site you have just some amount of empty tapes available and nobody to add new ones to library available. Or it’s Friday afternoon, tape library is down and you don’t know whether the space on staging disk storage unit will be enough to accomodate wekend backups? Here is a shell oneliner showing sum of last full backups for clients from list of policies (the policies configured for this particular storage unit):