Mag Tape Duplication Problems

[Geoff Clare]

When I actually got round to trying out the script I posted, there
were a few problems with it I had not forseen (OK, I know I should
have tried it *before* I posted it, but I was short of time, sorry).

The main problem was that because the first loop was on the end of a pipe
it was executed in a subshell, so all those carefully stored block
counts were not available to the second loop.  This has been
cured by having the entire script from that point down executed as
a subshell receiving the data from the pipe.

Here is the updated version:

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:
# shell script to copy mag tape to multiple cartridge volumes and back

BLOCKSIZE=10k		# mag tape block size required
MAGTAPE=/dev/rmt8	# name of mag tape device
CARTRIDGE=/dev/rct	# name of cartridge device
BLOCKSPERVOL=40000	# no. of 512 byte blocks to fill cartridge tape

IFS="+$IFS"	# add '+' to field seperator list to ease splitting of
		# dd block counts

# direct dd output into remainder of script as single subshell, instead of
# just the first loop, to allow $b1 $b2 etc. to be accessed in the second loop

dd if="$MAGTAPE" ibs="$BLOCKSIZE" | (

	# write cartridges until < requested no. of blocks are transferred

	blocks="$BLOCKSPERVOL"
	vol=1
	while test "$blocks" -eq "$BLOCKSPERVOL"
	do
		echo "insert cartridge $vol and press RETURN"
		read a </dev/tty
		a=`dd count="$BLOCKSPERVOL" of="$CARTRIDGE" 2>&1`
		echo "$a"
		set -- $a
		blocks=`expr $1 \+ $2`
		eval b"$vol"="$blocks"
		vol=`expr $vol \+ 1`
	done

	echo "insert blank mag tape to receive copy and press RETURN"
	read a </dev/tty

	# write back cartridges - no of blocks on each volume is in b$vol

	outvol=1
	while test "$outvol" -lt "$vol"
	do
		echo >&2 "insert cartridge $outvol and press RETURN"
		read a </dev/tty
		eval blocks=\$b"$outvol"
		echo >&2 "block count should be $blocks"
		dd count="$blocks" if="$CARTRIDGE"
		outvol=`expr $outvol \+ 1`
	done | dd obs="$BLOCKSIZE" of="$MAGTAPE"
)

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-- 

Geoff Clare    UniSoft Limited, Saunderson House, Hayne Street, London EC1A 9HH
gwc at root.co.uk   ...!mcvax!ukc!root44!gwc   +44-1-606-7799  FAX: +44-1-726-2750