Linux - Bash If user is root run script

#IF USER IS ROOT THEN RUN SCRIPT
ROOT_UID=0     # Only users with $UID 0 have root privileges.
E_NOTROOT=87   # Non-root exit error.
# Run as root, of course.
if [ "$UID" -ne "$ROOT_UID" ]
then
  echo "Must be root to run this script."
  exit $E_NOTROOT
fi