How can I change brightness through terminal

adding to what Michał Šrajer says in some cases the brightness may be controlled from /sys/class/backlight/acpi_video0/brightness as is the case with my dell vostro 3400 and my the brightness range is 0-15. You may have to look for other folder in /sys/class if the same path as mine doesnot exit.

In your script you can send the equivalent keystrokes that correspond to Fn+Right Arrow and Fn+Left Arrow i.e. Brightness Up and Down respectively

Install xdotool from the Software Center

Then in your script to increase brightness:

xdotool key XF86MonBrightnessUp

To decrease Brightness

xdotool key XF86MonBrightnessDown

You could install xbacklight package $sudo apt-get install xbacklight and then if you want to increase the brightness level, type $xbacklight -inc <level in a range of 10 - 100> and vice versa: $xbacklight -dec <level in a range of 10 - 100>.

Read xbacklight --help to see more options.