.light

#!/bin/bash

regexp='^[-+]?[0-9]*(\.[0-9]*)?$'
validateNumber() {
	if [[ $1 == *[0-9]* && $1 =~ $regexp ]]; then
		echo "$1"
	else
		printf >&2 '%s is not a valid number\n' "$1"
	fi
}

# compare 2 numbers, similar and faster than if (( $(bc <<<"$1 < $2") ))
isGreater() {
	local v1
	local v2
	LC_NUMERIC=C printf -v v1 '%f' "$1"
	LC_NUMERIC=C printf -v v2 '%f' "$2"
	local i1="${v1%.*}"
	local i2="${v2%.*}"
	local d1="${v1#*.}"
	local d2="${v2#*.}"
	d1="${d1:0:2}"
	d2="${d2:0:2}"
	if [[ "$d1" == 0* ]]; then d1="${d1:1}"; fi # deal with octals
	if [[ "$d2" == 0* ]]; then d2="${d2:1}"; fi
	# now compare integer parts or decimal parts if needed
	return $(( i1 == i2 ? d1 <= d2 : i1 <= i2 ))
}

# add 2 numbers (2 decimals max, similar and faster than echo "scale=2; $1 + $2" | bc)
addNum() {
	local v1
	local v2
	LC_NUMERIC=C printf -v v1 '%f' "$1"
	LC_NUMERIC=C printf -v v2 '%f' "$2"
	local i1="${v1%.*}"
	local i2="${v2%.*}"
	local d1="${v1#*.}"
	local d2="${v2#*.}"
	d1="${d1:0:2}"
	d2="${d2:0:2}"
	if [[ "$d1" == 0* ]]; then d1="${d1:1}"; fi # deal with octals
	if [[ "$d2" == 0* ]]; then d2="${d2:1}"; fi
	if [[ "$i1" == -* ]]; then d1="-$d1"; fi
	if [[ "$i2" == -* ]]; then d2="-$d2"; fi
	local d3=$(( d1 + d2 ))
	local i3=$(( i1 + i2 ))
	if (( d3 >= 100 )); then
		d3=$(( d3 - 100 ))
		i3=$(( i3 + 1 ))
	elif (( d3 <= -100 )); then
		d3=$(( -d3 - 100 ))
		i3=$(( i3 - 1 ))
	elif (( d3 < 0 && i3 > 0 )); then
		d3=$(( d3 + 100 ))
		i3=$(( i3 - 1 ))
	elif (( d3 > 0 && i3 < 0 )); then
		d3=$(( d3 - 100 ))
		i3=$(( i3 + 1 ))
	fi

	if (( d3 < 0 && i3 >= 0 )); then
		i3="-${i3#-}"
	fi

	local u="00${d3#-}"
	d3="${u:0-2}"

	echo "$i3.$d3"
}

getCurrent() {
	local bl=$(xbacklight -get)
	if [[ "$bl" == 0.* || "$bl" == 1.00* ]]; then
		xrandr --verbose | awk '/Brightness/ { print $2; exit }'
	else
		echo "$bl"
	fi
}

if [ ! "$1" ]; then
	xrandr --verbose | grep -E '(Brightness|Gamma|Backlight)'
	exit
fi

# use this to decr or incr brightness: light +/- value?
case "$1" in
[+-])
	c=$(getCurrent)
	auto=0
	step="$1$2"
	if [[ ! "$2" ]]; then
		auto=1
		step="${1}1"
		if [[ "$c" == 0.* || ("$1" == '-' && "$c" == 1.*) ]]; then
			step="$1.05"
		fi
	fi
	val=$(addNum "$c" "$step");;
*)
	val=$(validateNumber "$1");;
esac

if [[ ! $val ]]; then
	echo "nope:" "$@"
	exit
fi

if [[ $val == 0.* || $val == .* ]]; then
	# xbacklight -set 1
	tee /sys/class/backlight/intel_backlight/brightness <<< 30
	if isGreater "$val" 0.66; then
		xrandr --output eDP1 --brightness "$val" --gamma 1.0:0.8:0.65
	else
		xrandr --output eDP1 --brightness "$val" --gamma 1.0:0.7:0.45
	fi
else
	xbacklight -set "$val"
	if (( val < 3 )); then
		xrandr --output eDP1 --brightness 1 --gamma 1.0:0.9:0.82
	elif (( val < 10 )); then
		xrandr --output eDP1 --brightness 1 --gamma 1.0:0.96:0.9
	else
		xrandr --output eDP1 --brightness 1 --gamma 1.0:1.0:0.95
	fi
fi

this file above is in my home

I've added a sudoers entry to run the line 102 caub@inspiron:~$ sudo visudo -f /etc/sudoers.d/light

caub ALL=(root) NOPASSWD:/home/caub/.light

now sudo ~/.light .7 works fine, you can add a bash_alias aslias li='sudo ~/.light'