I have tested
hostname on several servers (RedHat, Ubuntu), and
hostname -f has proven unreliable, returning sometime the short name only (as described in this question).
I can see the fqn in the aliases:
hostname -a (one of the aliases is the fqn I look for), but the order of the aliases is not fixed.
Is there another way to get the fully qualified name reliably, and store it in a bash variable?