$EUID is empty in /etc/init.d/celeryd

Question

I'm trying to configure the celery worker as a daemon as per Running the worker as a daemon.

Even though I work directly from root I can't run the service since the $EUID is empty and thus the condition

if [ "$EUID" != "0" ]; then
    echo "Error: This program can only be used by the root user."
    exit 1
fi

is always true.

This happens only when I try to run the service.

echo $EUID 

in the console naturally prints 0.

What's the reason of this behavior? How to solve it to make the celery worker run as a daemon?

Thanks in advance.