Set correct primary monitor for login screen when lightdm greeter starts up on Elementary OS

set-primary-monitor-pantheon-greeter

#!/bin/bash
#
# Created: 2017-07-02 16:20
# Updated: 2018-02-09 12:23
# Creator: Ryan Miller
# Website: http://devopsmachine.com/
# File:    /usr/local/bin/set-primary-monitor-pantheon-greeter
# 
# Set correct primary monitor for login screen when lightdm greeter starts up on Elementary OS.
#
# Make sure to add the following line into /usr/share/lightdm/lightdm.conf.d/40-pantheon-greeter.conf (without the #)
# greeter-setup-script=/usr/local/bin/set-primary-monitor-pantheon-greeter
# 

# Change this variable to your primary display (Run 'xrandr -q' to see available displays)
PRIMARY_DISPLAY='HDMI-0'

# Get list of connected monitors
x_out=$(xrandr -q | grep -e '\( \)connected' | awk -F' ' '{ print $1 }')

# Safety - Check if PRIMARY_DISPLAY is connected; if not, bail out of script
[[ $(grep ${PRIMARY_DISPLAY} <<< ${x_out}) ]] || exit 0
     
# Iterate over x_out and disable all monitors except for PRIMARY_DISPLAY
for monitor in ${x_out[@]} ; do
    if [[ ${monitor} = ${PRIMARY_DISPLAY} ]] ; then
        xrandr --output ${monitor} --primary
    else
        xrandr --output ${monitor} --off
    fi
done

if the screen turn to black. Just make sure the computer boot failed several time you will get into Grub2 and enter to recovery mode after that remove 2 file above /usr/local/bin/set-primary-monitor-pantheon-greeter and /usr/share/lightdm/lightdm.conf.d/40-pantheon-greeter.conf now black screen gone. Also all solution doesn't work for me.