Bash Fibonacci Recursive Function

echo works better than return + $?, since consecutive call f $(( a-1 )), f $(( a-2 )) does not set $? correctly.
the result of echo can be captured at the final step.


#!/bin/bash
f(){
 if [[ $1 -eq 1 || $1 -eq 2 ]]; then  # int differ from string compare
    echo  1
 else
    a=$1
   echo $((  $( f $((a-1)) ) + $( f $(( a-2))) ))  # $(( )) substitute var/func
 fi
}
f $1

v=$(( $(f $1) ))     # capture echo into variable
echo $v