#!/bin/bash

# software toggle brightness of primary/connected monitor
# for the benefit of reading an ebook
# https://wiki.archlinux.org/index.php/xrandr

normal="1.0"
reader="0.75"

now=$(xrandr --verbose | grep -i brightness | cut -f2 -d ' ' | tail -1) # no primary selector here, some luck needed.
monitor=$(xrandr | grep -E " connected (primary )?[1-9]+" | sed -e "s/\([A-Z0-9]\+\) connected.*/\1/" | tail -1)

if [ "$now" == "$normal" ]; then
    xrandr --output "$monitor" --brightness "$reader"  
else
    xrandr --output "$monitor" --brightness "$normal" 
fi