mjhjmtu

Once upon a time, I cast this shellspell,

# tail -f /sys/devices/platform/applesmc.768/light

and it does produce,

(0,0)

Those file I read is light sensor abstraction file of Macbook Pro.

Unfortunately, when I give some light into the sensor (in the same place as camera), It didn't update the value!

It does show the change when read manually,

# cat /sys/devices/platform/applesmc.768/light
(50,0)

The quest is as to why?!
Cause I want to do some polling into the value and get the notification when it changed. Using python too doesn't work.

Use watch around cat or a while loop instead:

watch cat /sys/devices/platform/applesmc.768/light

while sleep 0.5; do cat /sys/devices/platform/applesmc.768/light; done

The file is not being appended to with new values, it is being replaced so inorder to reread the values you need to reread the file. Thus tail will not work as it is waiting for more lines to be appended to the file.

In python you could try skipping to the beginning of the opened file, but that will likely just allow you to reread the old value again. Closing and reopening the file should work as you want it to however.