#!/bin/bash set -euo pipefail load_example varcounter # Read variables. varcounter FIRST SECOND THIRD varcounter FIRST &> /dev/null echo $FIRST $SECOND $FIRST echo $SECOND echo $SECOND $THIRD SECOND=1000 echo $SECOND $SECOND unset FIRST THIRD FIRST=X echo $FIRST ${THIRD:-NA} enable -d varcounter echo $FIRST echo ${SECOND:-NA}