bash script to Download by axel with high speed

download.sh

#!/bin/bash

if ! which axel > /dev/null; then

while true; do
    read -p "Axel not found,Do you wish to install this program?" yn
    case $yn in
        [Yy]* ) sudo apt-get install axel; break;;
        [Nn]* ) exit;;
        * ) echo "Please answer yes or no.";;
    esac
done

fi

if which axel > /dev/null;then

url=$1
output=$2

if  [ -z "$url" ]  ||  [ -z "$output" ]; then
    echo "argument error"
else
    axel -s 204800 -n 10 $url >> $2;
fi


fi