Bash - Get Sudoer Username?

Question

Say I have the following bash script:

#!/bin/bash

echo $( whoami )

This is what it outputs with and without sudo:

alix@netbook:~$ ./test.sh 
alix
alix@netbook:~$ sudo ./test.sh 
root

The script executes several commands that require superuser priviledges, but I also want to add the original executing user to a group. Is there any command that returns alix if I run sudo ./test.sh?

Answer 1

Found the solution in a related answer:

#!/bin/bash

echo $( whoami )
echo $SUDO_USER

And the output:

alix@netbook:~$ ./test.sh 
alix

alix@netbook:~$ sudo ./test.sh 
root
alix