The Question is:
Is there an easy way to check the amount of data to be backuped using backup
command so that you can check to see if there is enough free space on the
The Answer is :
The OpenVMS FAQ section entitled "MISC13. How do I check for free
space on a (BACKUP) tape?" will be of interest here.
As for calculating the volume of input data -- without considering
the results of any compression used within the operation -- you can
use the DCL lexical functions, the RTL and RMS services, the $qio
calls to the file system ACP (XQP), and/or the DIRECTORY command.
BACKUP itself does not provide an API to return information to a DCL
procedure from a BACKUP (test) pass.