Building a disk

[Dale Amon]

I've a straightforward problem that recurs time after
time after time, and I am quite surprised that I have
not been able to find explicit instructions on how to
do it. I've tried again and again, occasionally 
successfully with much magic, but not terribly
repeatably.

Lets say you have a laptop with the system on /dev/sda.

You mount a hard drive via:

        * A SATA/IDE/USB converter
        * VIA a superbay on a Thinkpad
        * Via a /dev/loop0 of a blank image file

Now you build a system onto the disk:

        $ dd if=/dev/zero of=/my.host.net.raw count=20M
        $ losetup /dev/loop0 my.host.net.raw
        $ cfdisk /dev/loop0
                # create a 9G bootable linux partition and a 1G swap
        $ kpartx -a -v /dev/loop0
        $ mkfs.ext4 /dev/mapper/loop0p1 -m 0.01 -L "RecoverTest"
        $ mkdir tmp
        $ mount /dev/mapper/loop0p1 tmp

   From the backup server:
        $ rsync -av address@hidden:/srv/backup/ tmp/

Everything is really easy and straightforward so far, right?

Now... how do I install grub? The boot device I am building is 
mounted as /dev/sdb or /dev/loop0. When it is actually used it 
will be mounted as /dev/sda. How do I reliably tell that to 
grub???

This has got to be easy. I just can't believe there isn't a
simple way to do this.

Oh, and I might add that I sometimes have to do this for
grub 1 and sometimes for grub 2. So I need to understand
both environments.

I'm looking for a simple shell scriptable way of doing it.