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xrandr --output $(xrandr | grep " connected" | cut -f1 -d " ") --brightness 0.7
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xrandr | grep " connected" | cut -f1 -d " "
xrandr --output LVDS1 --brightness 0.7
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xrandr | grep " connected" | cut -f1 -d " " //use this command to check to find out the name of your display
xrandr --output displayname-1 --brightness 0.7 //to adjust the brightness