16.04 - alt+f4 script equivalent for custom keyboard shortcut?

I would like to make a new keyboard shortcut that does exactly what alt+f4 does right now. I'm using Ubuntu 16.04.

I know how to create a custom keyboard shortcut to execute a shell script, but I don't know what to do to close the current window like alt+f4does.

Just to clarify, I do not want to change what alt+f4 does, but I want to add another key combination with the same functionality.

Thanks! (I prefer a solution without installing a new program, except an apt package)

I found a solution:
http://tripie.sweb.cz/utils/wmctrl/
and
Close active window from terminal
where helpful.

You do have to run sudo apt install wmctrl but it it OK