Oil Shell

#!/usr/bin/env osh
# Fibonacci sequence in Oil Shell (OSH mode)
# OSH is backward-compatible with POSIX shell and bash

fib() {
  local -i n=$1
  if (( n <= 1 )); then
    echo $n
    return
  fi
  local -i a=0 b=1 tmp
  for (( i = 2; i <= n; i++ )); do
    tmp=$(( a + b ))
    a=$b
    b=$tmp
  done
  echo $b
}

echo "First 10 Fibonacci numbers:"
for i in $(seq 0 9); do
  printf "  fib(%d) = %d\n" "$i" "$(fib "$i")"
done