How to check if running as root in a bash script

Question

I\'m writing a script that requires root level permissions, and I want to make it so that if the script is not run as root, it simply echoes \"Please run as root.\" and exit

Answer 1

id -u is much better than whoami, since some systems like android may not provide the word root.

Example:

# whoami
whoami
whoami: unknown uid 0