[comp.os.vms] Tape Motion Commands?

JWS@PSUARLC.BITNET (06/29/88)

I've used a magnetic tape oriented minicomputer that had tape motion built into
its command language.  These commands were rewind, forward file, back file,
forward record, back record and write file mark.

I'm starting a project on our VAX which uses multifile foreign tapes as input.
The tape motion commands mentioned above would give me a lot of needed
flexibility.  Do you have or know of such a facility.

carl@CITHEX.CALTECH.EDU (Carl J Lydick) (07/04/88)

 > I've used a magnetic tape oriented minicomputer that had tape motion built into
 > its command language.  These commands were rewind, forward file, back file,
 > forward record, back record and write file mark.
 > 
 > I'm starting a project on our VAX which uses multifile foreign tapes as input.
 > The tape motion commands mentioned above would give me a lot of needed
 > flexibility.  Do you have or know of such a facility.

It would behoove you to familiarize yourself with the VMS HELP utility.
HELP HINTS has an entry for "Physical devices" which refers you to the
"SET MAGTAPE" command for setting tape characteristics.  The commands you want
to use are:
	For rewind:
		$ SET MAGTAPE/REWIND tape
	To skip files:
		$ SET MAGTAPE/SKIP=FILE:n tape
	To skip records:
		$ SET MAGTAPE/SKIP=RECORD:n tape
	To write file mark:
		$ SET MAGTAPE/END_OF_FILE tape
	To skip blocks:
		$ SET MAGTAPE/SKIP=BLOCK:n tape
	To skip to the end of the tape:
		$ SET MAGTAPE/SKIP=END_OF_TAPE tape
where "tape" is the name of the tape, and "n" is tne number of files/records
you want to skip.  "n" can be negative to skip backwards.  I seem to recall
that there is an off-by-one error in the case of skipping negative numbers
of files; I think you have to, e.g., skip -2 files to go back one file.
For more information, type "HELP SET MAGTAPE".