Bash shell script to swap two number

#!/bin/bash

function intro(){

        echo "swap shell script!"

}

function swapNum(){

        local tmp=$1

        num1=$num2 #call by value

        num2=$tmp

        return 255 #return value is 1byte

}

intro

echo "begin num is $1, $2"

num1=$1

num2=$2

swapNum num1 num2 #call fucntion

echo "result is $?"//return value

echo "artificial num is $num1, $num2"