Quickly backup and deploy bootable SD cards with variable size ext4 root partitions

rapid-clone.sh

#!/bin/sh

[ -z "$PART_PREFIX" ] && PART_PREFIX=''
DD_ARGS='status=progress conv=fsync'

backup() {
	src="$1"
	dst="$2"

	sfdisk -d "${src}" > "${dst}-table.txt"
	sed -i "$ s/size=[ 0-9]*/size=+/" "${dst}-table.txt"
	e2image -ra -p "${src}${PART_PREFIX}2" "${dst}-2.img"
	e2fsck -fp "${dst}-2.img"
	# catch return codes that mean things were repaired
	case $? in
		0) ;;
		1) ;;
		2) ;;
		*) return 1;;
	esac
	resize2fs -M -p "${dst}-2.img"
	dd if="${src}${PART_PREFIX}1" of="${dst}-1.img" ${DD_ARGS} bs=4K 
}

deploy() {
	src="$1"
	dst="$2"

	sfdisk "${dst}" < "${src}-table.txt"
	e2image -ra -p "${src}-2.img" "${dst}${PART_PREFIX}2" 
	e2fsck -f "${dst}${PART_PREFIX}2"
	resize2fs -p "${dst}${PART_PREFIX}2"
	dd if="${src}-1.img" of="${dst}${PART_PREFIX}1" ${DD_ARGS} bs=4K
}

disk_image() {
	src="$1"
	dst="$2"
	start_sector_list=$(
		grep -o -P "(?<=start=)\s*\d+" "${src}-table.txt" | tr -d ' '
	)
	first_sector=$(echo "${start_sector_list}" | head -1)
	last_sector=$(echo "${start_sector_list}" | tail -1)
	echo "Using ${first_sector} - ${last_sector} as the starting image..."
	dd if=/dev/zero of="${dst}.img" count="${last_sector}"
	partition_index=1
	for start_sector in ${start_sector_list}; do
		echo "Copying partition ${partition_index} ..."
		dd if="${src}-${partition_index}.img" of="${dst}.img" \
			seek="${start_sector}" ${DD_ARGS}
		partition_index=$((partition_index+1))
	done
	sfdisk -w never -f "${dst}.img" < "${src}-table.txt"
}


help="
	[backup/deploy/disk_image] [src] [dst]

	Example: backup /dev/sdc working-image
"

if [ $# -eq 3 ]; then
	case $1 in
		"backup")
			backup "$2" "$3";;
		"deploy")
			deploy "$2" "$3";;
		"disk_image")
			disk_image "$2" "$3";;
		*)
			echo "$help"
	esac
else
	echo "$help"
fi