fibonacci() {
local x=$1
if ((x <= 1)); then
echo "$x"
return
fi
echo $(($(fibonacci $((x - 1))) + $(fibonacci $((x - 2)))))
}
f10=$(fibonacci 10)
#f10 is 55
#each $( ) starts a new process: deep recursion is slow,
#and FUNCNEST can limit the depth
echo "f10 is $f10"