Run a script on monitor connection/disconnection event

Question

I read many threads about how to do this and yet it doesn't work for me.

What I want to achieve is:

When my laptop has 2 additional displays connected when I close its lid, I don't want it to go to sleep. However, if I disconnect the displays and the lid is closed, I want to put the laptop to sleep (this way, not forgetting it on).

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Therefore, I created a BASH script that should be executed on VGA / HDMI connection events. The BASH script counts how many displays are connected and if there's only 1, it will put the laptop to sleep when the lid is closed.

I have Ubuntu 14.04 LTS. This is what I've done so far:

• Created 2 files: displays_count_sleep.sh and on_hdmi_connected.rules
  https://gist.github.com/nbtk123/9ffbf7541e47b9c0015f5c3e9f44b7c9

• Put this on_hdmi_connected.rules into /etc/udev/rules.d to catch the event:

SUBSYSTEM=="drm", RUN+="/bin/bash /home/nir/dev/scripts/displays_count_sleep.sh"

• Put the bash script I want to run, displays_count_sleep.sh, into /home/nir/dev/scripts:

#!/bin/bash

DISPLAYS_NUM=2

`touch test`

display_count=`xrandr -d :0 -q | grep ' connected' | wc -l`

echo "display count="$display_count
echo "display_num="$DISPLAYS_NUM

if [ "$display_count" -ge "$DISPLAYS_NUM" ]; then
    echo "nothing"
    `gsettings set org.gnome.settings-daemon.plugins.power lid-close-ac-action nothing`
    `gsettings set org.gnome.settings-daemon.plugins.power lid-close-battery-action nothing`
else
    echo "sleep"
    `gsettings set org.gnome.settings-daemon.plugins.power lid-close-ac-action suspend`
    `gsettings set org.gnome.settings-daemon.plugins.power lid-close-battery-action suspend`
fi

Both files have been created as root. When running "udevadm test", the output is as in the file 'udevadm_test_output' on the link.

I don't know if the event is catched, but on the real monitor (dis)connection, the script doesn't run. It works okay if I run it manually.