Fibonacci

#!/bin/bash
let a=0
let b=1
echo "serie de fibonacci \n"
read -p " cuantos Numeros imprimo? " N
echo $a
echo $b
let x=0
while [ x -ge $N ]; do
 let S=$a+$b
 echo $S
 let x=$x+1
 let a=$b
 let b=$S
done