create shell script only run by root user

#vim script.sh

#/bin/bash

if [ $(id -u) != "0" ]; then

    echo "Error: You must be root to run this script."

else 

echo "Script is running from root user "

    exit 1

fi

#chmod o+x  script.sh

Test script from root user

# ./check.sh

Script is run by root

Test script from non root user

$ 

./check.sh

Error: You must be root to run this script.