PARAM=abcdefg

echo ${PARAM:1 ? 4 : 2}
echo ${PARAM:1 ? 4 : 2:1}

echo ${PARAM: 4<5 ? 4 : 2}
echo ${PARAM: 5>4 ? 4 : 2:1}

echo ${PARAM:${OFFSET:-0}}
OFFSET=4
echo ${PARAM:${OFFSET:-0}}