to control redshift backlight

redshifted.sh

#!/bin/bash
tmp_file=/tmp/redshifted
max_tem=7000
if [ ! -f $tmp_file ];then echo $max_tem > $tmp_file ;fi
current_tem=$(cat $tmp_file)

function get_percentage () {
    echo Redshift $(( $current_tem * 100 / $max_tem  ))/100
}


case "$1" in
    1)
	if [ $current_tem -lt $max_tem ]
	then
	    tem=$(( $current_tem + 500 ))
	    redshift -O $tem > /dev/null 2>&1
	    echo $tem > $tmp_file
	    current_tem=$tem
	fi
	get_percentage
	;;
    2)
	if [ $current_tem -gt 2000 ]
	then
	    tem=$(( $current_tem - 500 ))
	    redshift -O $tem > /dev/null 2>&1
	    echo $tem > $tmp_file
	    current_tem=$tem
	fi
	get_percentage
	;;
    0)
	redshift -x > /dev/null 2>&1
	echo $max_tem > $tmp_file
	echo Diable redshift
	;;
    *)
	echo Error: input error
	echo $0 1 increase red color, 2 decrease red color, 0, disable red color
	;;
esac