Pop two elements, add them, leave result on top of stack and in varname
USAGE: add arrayname
add() { local arrayname=${1:?Array name required} varname=${2:-var}
Copy the array, $arrayname, to local array
eval "array=( \"\${$arrayname[@]}\" )" array[1]=$(( ${array[0]} + ${array[1]} )) eval "$varname=${array[1]}" unset array[0]
Copy array back to $arrayname
eval "$arrayname=( \"\$var\" \"\${array[@]}\" )" }