Lenovo Thinkpad P50, dock with external monitor, udev + xrandr auto switching

README

This switches between the laptop monitor ($intern) when undocked and a two monitor setup when docked ($extern right of $intern).

ENV{ID_VENDOR_ID}, ENV{ID_MODEL_ID}, x_user and intern need to be set.

Based on the Arch wiki, StackExchange and Google.

66-auto_xrandr.rules

SUBSYSTEM=="usb", ACTION=="add|remove", ENV{ID_VENDOR_ID}=="17ef", ENV{ID_MODEL_ID}=="305a", RUN+="/usr/local/bin/auto_xrandr.sh dock"

auto_xrandr.sh

#!/usr/bin/env bash

readonly ty="$1"

x_user=some_user
intern="DP-4"

extern="$(xrandr|grep '\bconnected\b'|grep -v "^$intern connected"|head -n1|cut -d' ' -f1)"
export DISPLAY=:0.0
export XAUTHORITY="$(getent passwd "$x_user"|cut -d: -f6)/.Xauthority"
export DBUS_SESSION_BUS_ADDRESS="unix:path=/run/user/$(id -u "$x_user")/bus"

sleep 2

if [[ -z "$extern" ]]; then
    xrandr --output "$extern" --off --output "$intern" --auto --panning 0x0
else
    case "$ty" in
        dock) xrandr --output "$extern" --primary --auto --output "$intern" --left-of "$extern" --auto;;
        *) xrandr --output "$extern" --primary --auto --output "$intern" --off;;
    esac
fi