Call external script from udev rule - I use this mechanism to fire off xrandr rules when docking my laptop.

ext_mirror.sh

#!/bin/sh

# This script will make two connected output sources mirrors of each other:
#
#
#   +---------------+   +---------------+
#   |               |   |               |
#   |  Primary      |   | DisplayLink   |
#   |  Display      |   | (DP-2-2)      |
#   |  (e-DPI-1)    |   | (Screen 2/3)  |
#   |  (Screen 1)   |   |               |
#   |               |   |               |
#   +---------------+   +---------------+
#       ^       +---------------->
#       |       |       +---------------+
#       |       |       |               |
#       |       |       | VGA           |
#       |       |       | (DP-2-3)      |
#    +--------------+   | (Screen 2/3)  |
#    |    LAPTOP    |   |               |
#    +--------------+   |               |
#                       +---------------+

LOGFILE="/tmp/docklog-$(date +%s)"

if [[ "$ACTION" == "add" ]]; then
  DOCKED=1
  logger -t DOCKING "Detected condition: docked"
elif [[ "$ACTION" == "remove" ]]; then
  DOCKED=0
  logger -t DOCKING "Detected condition: un-docked"
else
  logger -t DOCKING "Detected condition: unknown"
  echo Please set env var \$ACTION to 'add' or 'remove'
  exit 1
fi


export DISPLAY=:0
username="bharrington"
sleep 0.5


su ${username} -c '
/usr/bin/xrandr --output DP-2-2  --right-of eDP-1;
/usr/bin/xrandr --output DP-2-3  --same-as DP-2-2 --right-of eDP-1;
notify-send -t 5000  "ext_mirror.sh executed" ;