Resize partition within disk image file

resize.sh

#!/bin/bash

DATA_SIZE=$(du -s \
  --exclude="*_[A-Z][A-Z].*" \
  --exclude="*_[A-Z][A-Z]_*" \
  --exclude="*_[A-Z][A-Z][A-Z].*" \
  --exclude="*_[A-Z][A-Z][A-Z]_*" \
  /data/ | cut -f1)

#########################################################################
# This is about the simplest way to resize a partition:
#   1. Append the required space to the disk image
#   2. Resize partition "2" to use the appended space
#   3. Expose the partitions as devices (synchronously, so that we don't encounter race conditions)
#   4. Modify the super block of the resized partition to match the new size
#########################################################################
truncate -s "+$(echo "(${DATA_SIZE} * 1024) + (1024 * 1024)" | bc)" "/tmp/raspbian.img"
echo ",+" | sfdisk -N 2 "/tmp/raspbian.img"
kpartx -a -s -v "/tmp/raspbian.img"
resize2fs -f /dev/mapper/loop*p2

BOOT_PARTITION=$(basename /dev/mapper/loop*p1)
DATA_PARTITION=$(basename /dev/mapper/loop*p2)

mkdir -p "/mnt/${BOOT_PARTITION}" "/mnt/${DATA_PARTITION}"
mount "/dev/mapper/${BOOT_PARTITION}" "/mnt/${BOOT_PARTITION}"
mount "/dev/mapper/${DATA_PARTITION}" "/mnt/${DATA_PARTITION}"