creating bootable image with a script

[Kevin Hunter]

Hi List,

I'm currently trying to create a bootable USB disk.

Goal 1: create a bootable disk image with a GPT partition label.

Goal 1 is what is giving me trouble.

Goal 2: script this, so I can create a disk image on the fly and shove
it out to any random disk

With goal 2, what I want to be able to do is dynamically create disk
images.  Specifically, I'd like to avoid the step of "mastering" an
actual disk and then copying over with dd.  I do *not* want to do this:

(1) dd if=/dev/sdb of=./disk.img bs=1M
(2) dd if=disk.img of=/dev/sdb bs=1M

I want to completely forgo step 1.

I think I'm 9/10ths of the way there.  I have everything except for the
booting part.  Grub continues to be a mystery to me, and I'm hoping
someone can educate me.  Here's my script so far:

http://cs.earlham.edu/~kevin/tmp/make_bootable_img.sh

It's an explanatory call for help, so please excuse the lack of error
handling, and other coding neophyte-isms.

Thanks much!

Kevin