Helper script to set the screen brightness on a Lenovo T530

brightness.sh

#!/bin/bash

BRIGHTNESS=/sys/devices/pci0000:00/0000:00:02.0/backlight/acpi_video0/brightness
CURRENT_VALUE=$(cat $BRIGHTNESS)

value=$(echo $1 | grep -E -o '[[:digit:]]+')

if [[ $# -ne 1 ]]
	then
	echo "$0 +VALUE | -VALUE | VALUE"
	exit
fi

if [[ -z $value ]]
	then
	echo "please supply a number"
	exit
fi


if [[ $1 == -* ]]
	then
	let new_value="$CURRENT_VALUE - $value"
	if [[ $new_value -le 0 ]]
		then
		new_value=0		
	fi
	echo $new_value | sudo tee $BRIGHTNESS
elif [[ $1 == +* ]]
	then
	let new_value="$CURRENT_VALUE + $value"
	if [[ $new_value -ge 100 ]]
		then
		new_value=100
	fi
  echo $new_value | sudo tee $BRIGHTNESS
else
	echo $1 | sudo tee $BRIGHTNESS
fi