SD Card image shrinker

gistfile1.sh

#!/bin/bash

IMG="$1"

if [[ -e $IMG ]]; then
	P_START=$( fdisk -lu $IMG | grep Linux | awk '{print $2}' ) # Start of 2nd partition in 512 byte sectors
	P_SIZE=$(( $( fdisk -lu $IMG | grep Linux | awk '{print $3}' ) * 1024 )) # Partition size in bytes
	losetup /dev/loop2 $IMG -o $(($P_START * 512)) --sizelimit $P_SIZE
	fsck -f /dev/loop2
	resize2fs -M /dev/loop2 # Make the filesystem as small as possible
	fsck -f /dev/loop2
	P_NEWSIZE=$( dumpe2fs /dev/loop2 2>/dev/null | grep '^Block count:' | awk '{print $3}' ) # In 4k blocks
	P_NEWEND=$(( $P_START + ($P_NEWSIZE * 8) + 1 )) # in 512 byte sectors
	losetup -d /dev/loop2
	echo -e "p\nd\n2\nn\np\n2\n$P_START\n$P_NEWEND\np\nW\n" | fdisk $IMG
	I_SIZE=$((($P_NEWEND + 1) * 512)) # New image size in bytes
	truncate -s $I_SIZE $IMG 
else
	echo "Usage: $0 filename"
fi

fdisk didn't like the capital W for me.

$ fdisk --version
fdisk from util-linux 2.28.2