It's been a while since I wrote a script to do that so I am trying to
recall this script off the top of my head. It went something like this.
(There may be an error with the script (is the symbol for modulo // ?),
but you should be able to understand the logic.

#!/bin/ksh
# Recycles 3 NB DB Tapes over 3 days.

NB_Tape_File=/usr/openv/netbackup/.nbtape
Number_of_Tapes=3
TAPE0=A00000
TAPE1=A00001
TAPE2=A00002

Tape_Num=`cat $NB_Tape_File`
(( Tape_Num = (Tape_Num + 1) // $Number_of_Tapes ))
echo $Tape_Num > $NB_Tape_File

TAPE=`eval TAPE$Tape_Num`
/usr/openv/netbackup/bin/admincmd/bpdbbackupdb -tpath $TAPE

Message: 3
Date: Tue, 16 Jan 2001 12:43:35 -0800
To: veritas-bu AT mailman.eng.auburn DOT edu
From: "W. Curtis Preston" <curtis AT colltech DOT com>
Subject: [Veritas-bu] NBDB backup scripts?

Does anyone have what they consider to be a good NBU database backup
script?

I've tried to write a script to do the following, but have been
unsuccessful:

1. Swap in a new DB backup tape daily
2. Protect the OLD DB backup tapes from use
3. Backup the database on demand (whenever the script is run)

Does anyone have a good script for this?