Data counters, sysfs reader

I was trying to write a Tasker profile that switches WiFi hotspot on when Bluetooth tethering transferred more than defined limit in a time interval.

With a bare Tasker it is a complicated task. It would be nice to have:

Data counters with atomical read and reset, and event/state, when particular interface appears/disappears.

And generic sysfs readers that reads value to a variable and handles missing file. This would be possible with a bare Tasker, but it does not have check File Exists.