How to check if running as root in a bash script

The $EUID environment variable holds the current user’s UID. Root’s UID is 0. Use something like this in your script:

if [ "$EUID" -ne 0 ]
  then echo "Please run as root"
  exit
fi

Note: If you get 2: [: Illegal number: check if you have #!/bin/sh at the top and change it to #!/bin/bash.