Automatically Resizing a Compute Engine Disk script, http://sookocheff.com/posts/2014-11-11-automatically-resizing-a-compute-engine-disk/

gce_disk_resize.sh

STARTUP_VERSION=1
PARTITION_MARK=/var/startup.partition.$STARTUP_VERSION
RESIZE_MARK=/var/startup.resize.$STARTUP_VERSION

# Repartition the disk to full size
function partition() {
  start_sector=$(sudo fdisk -l | grep ^/dev/sda1 |  awk -F" "  '{ print $3 }')

  cat <<EOF | sudo fdisk -c -u /dev/sda
d
n
p
1
$start_sector

w
EOF

  # We've made the changes to the partition table, they haven't taken effect; we need to reboot.
  touch $PARTITION_MARK

  sudo reboot
  exit
}

# Resize the filesystem
function resize() {
  resize2fs /dev/sda1
  touch $RESIZE_MARK
}

if [ ! -f $PARTITION_MARK ]; then
  partition
fi

if [ ! -f $RESIZE_MARK ]; then
  resize
fi