Hello!
I need to use an MQTT subscription, but I don’t understand how to use the received topic value. It can be shown in the log, but it seems impossible to save it as a variable — this is also mentioned in the manual.
How can the received value be saved as a global variable?
It can’t 
In my use of mqtt subscriptions I handle the values directly in the on-message where I use them to modify the router configuration. It may be possible to save the values to the file system as well. But I have not tried.