Calculation in Rules

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Hi,
I try to use the dummydimmer to control the volume of my VDR. This rule works:

IF $dummydimmer.dimlevel changes THEN execute "perl /home/pi/vdr.pl VOLU $dummydimmer.dimlevel >/dev/null 2>&1 || true"

But my values are from 0 to 255, so I tried:

IF $dummydimmer.dimlevel changes THEN execute "perl /home/pi/vdr.pl VOLU ($dummydimmer.dimlevel * 2) >/dev/null 2>&1 || true"

Which did not work (used “2” to avoid having to round).
So my question is, do I have to use a seperate variable or can I do this “on the fly”?

Try to ouput to log first, so you can see what is going wrong

IF $dummydimmer.dimlevel changes THEN log "Volume is ($dummydimmer.dimlevel * 2)"

You can round directly in the rule:

IF $dummydimmer.dimlevel changes THEN execute "perl /home/pi/vdr.pl VOLU {round($dummydimmer.dimlevel/100 * 255)} >/dev/null 2>&1 || true"

Works now as it should. Thanks.