Basic Skill

Get current script path

script=$(readlink -f $0)

Check for root user

if [ "$(id -u)" -ne 0 ] ; then
　　echo "current user is not root "
　　exit 1
fi

Read the configured Port

read -p "please set the app port for this instance [$_APP_PORT] " APP_PORT
if ! echo $APP_PORT | egrep -q '^[0-9]+$' ; then
　　echo "setted default port: $_APP_PORT" 
　　APP_PORT=$_APP_PORT
fi