Simple bash script to change brightness on all monitors at once

sunshine.sh

#!/usr/bin/env bash
#
# ISC License
# 
# Copyright (c) [year], [fullname]
# 
# Permission to use, copy, modify, and/or distribute this software for any
# purpose with or without fee is hereby granted, provided that the above
# copyright notice and this permission notice appear in all copies.
# 
# THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
# WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
# MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
# ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
# WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
# ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
# OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.

if [ $(xrandr --verbose | egrep -q '(Bright|Gamma)') ]; then 
	echo 'xrandr is not installed or cannot manage monitor brightness or gamma'; 
	exit;
fi

usage() { echo '$0 [-g] <0..1>'; exit; }

METHOD=brightness
VALUE=''
for param in "$@"; do
	case "$param" in
		-g|--gamma)
			METHOD='gamma'
			;;
		-h|--help)
			usage
			;;
		*)
			VALUE="$param"
			;;
	esac
done

if [ VALUE = '' ]; then
	usage
fi

if [ "$METHOD" = 'gamma' ]; then
	VALUE="$VALUE:$VALUE:$VALUE"
fi

xrandr -q | egrep "\sconnected" | cut -f1 -d ' ' | xargs -I{} xrandr --output {} --"$METHOD" "$VALUE"