Script to monitor the state of the NumLock key and notify the user whenever it changes.

I bought a new laptop which has a numerical keypad (no, I don´t like numerical keypads, but that was the model that was in stock). Obviously the keypad's behaviour changes depending on the state of the NumLock key, however the laptop came with no LEDs to indicate when that key is On or Off.

That proved to be annoying because I was constantly getting a 7 when I pressed the Home key, or a 1 when I pressed the End key, etc. That's why I decided to develop this script, so now I get instant feedback about the NumLock state whenever I press it. :)

This script was written in BASH which should come pre-installed on almost all Linux distributions. It depends on Gnome's GLib (gsettings) and Gnome's libnotify (notify-send).

It was successfully tested on a Fedora 31 Workstation running GNU BASH 5.0.7, GLib 2.62.1 and libnotify 0.7.8.

• For other Linux distributions you might want to adjust the the path to the input-keyboard-symbolic.svg file inside the shell script, because it will likely be different.

Note: the brief instructions below assume the reader has some basic knowledge of how to use a Linux Desktop system running Gnome.

Simply copy the io.techwords.numlock-notifier.desktop file into the ${HOME}/.config/autostart directory and the numlock-notifier.sh script into a directory of your choice (suggestion: ${HOME}/bin), set the execute permission on the .sh script (e.g. chmod u+x numlock-notifier.sh), and adjust the Exec= line inside the .desktop file so it points to where you copied the .sh script. Restart Gnome or reboot your computer.

The easiest way to test this, after restarting Gnome or your computer, is simply pressing the NumLock key on your keyboard and see if you get a notification at the top of your screen like the one shown below:

You can also check if the necessary processes are running by executing the following command:

$ pstree -aT $(pgrep -x flock)

You should then see something like the following:

flock -en /run/user/1000/numlock-notifier.lock /home/me/bin/numlock-notifier.sh
  └─numlock-notifie /home/me/bin/numlock-notifier.sh
      └─gsettings monitor org.gnome.desktop.peripherals.keyboard numlock-state

Moreover, you can check if the two necessary files were also created by executing the following command:

$ ls -F ${XDG_RUNTIME_DIR:-/tmp}/numlock-notifier*

Which should produce something like the following output:

/run/user/1000/numlock-notifier|  /run/user/1000/numlock-notifier.lock

If the tests above succeeded there is nothing else to do. Simply press the NumLock key and get a desktop notification indicating its current status.

The .sh script uses a lock file to prevent multiple instances of itself. It also cleans-up after itself if it's terminated so no files should be left on the system if it's not running. The gsettings command continuously monitor the state of NumLock and sends any changes into a FIFO file which is continuously polled by the .sh script. The .sh script generates a desktop notification using notify-send whenever it reads a change from the FIFO file.

More visible notifications can be achieved by replacing notify-send with zenity (Gnome) or kdialog (KDE).

This project is licensed under the MIT License - see the LICENSE file for details.