This is a script for dimming the backlight on my Dell laptop

dim_screen.sh

#!/bin/bash

# Since my backlight is not dimming on its own, I have resorted
# to getting a Bash script to do it for me.  This script waits
# a certain amount of seconds (passed as input) until it dims
# the screen.

# This script was found here: http://askubuntu.com/a/762994
# Jason Anderson, February 2, 2017

# This checks to see whether a number has been passed to the
# script.  It was found here: http://stackoverflow.com/a/806923
if ! [[ $1 =~ ^[0-9]+$ ]]; then
   echo "Please pass an integer." >&2
   exit 2
fi

if [ ! $(which xprintidle) ]; then
   echo "Please install xprintidle." >&2
   exit 1
fi

if [ ! $(which xbacklight) ]; then
   echo "Please install xbacklight." >&2
   exit 3
fi

if [ -f ~/config_for_dim_screen.conf ]; then
  source ~/config_for_dim_screen.conf
else
  echo "Configuration file not found." >&2
  exit 4
fi

div=1000
limit="$1"
dimmed=false
# dim_percent=6
# time_spent_fading=70
current_brightness=0

while true
do
    sleep 0.4
    let idle="$(xprintidle)"
    if [ $(($idle / $div)) -gt $limit ] && [ $dimmed == false ]; then
      current_brightness=$(xbacklight -get)
      xbacklight -dec $dim_percent -time $time_spent_fading
      dimmed=true
    elif [ $(($idle / $div)) -le $limit ] && [ $dimmed == true ]; then
      xbacklight -inc $dim_percent -time $time_spent_fading
      dimmed=false
    fi
done

exit 0