How to create script to flash USB drive.

Hello,

I am using unassigned devices to mount USB flash drives on unRAID 6.11.5. My goal is to format it with FAT32, copy the contents of an ISO file, copy the contents of a folder from unRAID, and then change a few files and parameters.

I seem to have most of the needed commands, but cannot make the device bootable. Here is what I have so far.

#!/bin/bash
PATH=/usr/local/sbin:/usr/sbin:/sbin:/usr/local/bin:/usr/bin:/bin
## Available variables:
# ACTION - if mounting, ADD; if unmounting, UNMOUNT; if unmounted, REMOVE; if error, ERROR_MOUNT, ERROR_UNMOUNT
# DEVICE - partition device, e.g. /dev/sda1
# UD_DEVICE - unassigned devX designation
# SERIAL - disk serial number
# LABEL - partition label
# LUKS - if the device is encrypted, this is the partition device, e.g. /dev/sda1
# FSTYPE - partition filesystem
# MOUNTPOINT - where the partition is mounted
# OWNER - "udev" if executed by UDEV, otherwise "user"
# PROG_NAME - program name of this script
# LOGFILE - log file for this script

ISO=/mnt/user/Images/Deployments/USB/apps/Hiren\'s.BootCD.15.2.iso
ROOTDRV=/mnt/user/Images/Deployments/USB/Root

/usr/local/emhttp/webGui/scripts/notify -e "unRAID Server Notice" -s "USB Script" -d "Starting USB Creation" -i "normal"

sleep 10

/usr/local/sbin/rc.unassigned umount ${DEVICE}
sfdisk --delete ${DEVICE}
echo ',,c;' | sfdisk ${DEVICE}
/usr/local/sbin/rc.unassigned mount ${DEVICE}
sleep 10
sfdisk -A ${MOUNTPOINT}
mlabel -i ${MOUNTPOINT} ::${LABEL}

isoinfo -f -R -i $ISO | while read line; do
  d=$(dirname $line)
  od=${MOUNTPOINT}${d}
  [ -f $od ] && rm -f $od
  [ -d $od ] || mkdir -p $od
  isoinfo -R -i ${ISO} -x $line > ${MOUNTPOINT}${line}
done

rsync -a -v ${ROOTDRV} $MOUNTPOINT/ 2>&1

mlabel -i ${MOUNTPOINT} ::MYBOOT

/usr/local/sbin/rc.unassigned umount ${DEVICE}

/usr/local/emhttp/webGui/scripts/notify -e "unRAID Server Notice" -s "USB Script" -d "USB Drive is ready for use." -i "normal"

These are commands I picked up from around the web. They all seem to work so far except the device is not bootable. Or, rather, it does boot, but gives an error instead of the HBCD boot menu.