Help with crontab

[Thimoteus]

I'm trying to run

xbacklight -get > test.txt

every minute, but every way of doing this as a cron job doesn't seem to work. I've tried putting it into a script, setting the path variable in the cron file and the script, setting the shell variable, calling xbacklight with its absolute path, and nothing seems to work. In every case the cron job will write a file, but with nothing inside. Any ideas?

[steeldriver]

Are you setting the DISPLAY environment variable in your cron command / script? otherwise xbacklight will produce just an error (which will go to stderr not stdout, so won't be captured in your file)

$ echo $DISPLAY
:0.0
$ 
$ xbacklight -get
100.000000
$ 
$ DISPLAY= xbacklight -get
Cannot open display ""

[Thimoteus]

It worked! Thanks!

My new crontab line is:

* * * * * export DISPLAY=:0 && /usr/bin/xbacklight -get > test.txt