# Find your VM name
VBoxManage list vms
VMNAME="YOUR_VM_NAME"

# Get VM disk path.
VMDISK1=$(VBoxManage showvminfo "${VMNAME}" --machinereadable | grep -E '^\"SATA' | head -n1 | cut -d'=' -f2 | sed -e 's/^"//' -e 's/"$//')

# Convert disk to VDI
if [ "${VMDISK##*.}" != "vdi" ]; then
  VMDISK2="${VMDISK1%%.*}.$(cat /dev/urandom | env LC_CTYPE=C tr -dc 'a-zA-Z0-9' | fold -w 32 | head -n 1).vdi"
  VBoxManage clonemedium "${VMDISK1}" "${VMDISK2}" --format VDI

  # Attach new disk
  VMDISK_INFO=$(VBoxManage showvminfo "${VMNAME}" --machinereadable | grep -E '^\"SATA' | head -n1 | cut -d'=' -f1 | sed -e 's/^"//' -e 's/"$//')
  VMDISK_CONTROLLER=$(echo "${VMDISK_INFO}" | cut -d'-' -f1)
  VMDISK_PORT=$(echo "${VMDISK_INFO}" | cut -d'-' -f2)
  VMDISK_DEVICE=$(echo "${VMDISK_INFO}" | cut -d'-' -f3)

  VBoxManage storageattach "${VMNAME}" \
              --storagectl "${VMDISK_CONTROLLER}" \
              --port "${VMDISK_PORT}" \
              --device "${VMDISK_DEVICE}" \
              --type hdd \
              --medium "${VMDISK2}"
else
  VMDISK2="${VMDISK1}"
fi

# Resize disk
VBoxManage modifymedium "${VMDISK2}" --resize NEW_SIZE

# Resize primary partition with GParted Live CD.