#!/bin/bash

listBacklight=`ls /sys/class/backlight`

if [ $# -gt 1 ] ; then
    echo "light2 [VALUE]"
    exit
fi
if [ -z "$1" ] ; then
    val="show"
else
    val="$1"
fi

if [ -n "$listBacklight" ] ; then
    for backlight in "$listBacklight"
    do
        if [ "$val" == "show" ]; then
          printf "${backlight}: "
          cat /sys/class/backlight/${backlight}/brightness
        else
          echo "${val}" | sudo tee "/sys/class/backlight/${backlight}/brightness" 2>/dev/null /dev/null
          if [ $? -ne 0 ]; then
            printf "%s\n" "Erreur can't write to /sys/class/backlight/${backlight}/brightness" >&2
          fi
        fi
    done
else
    echo 'No backlight detected'
fi