How to “show desktop” from command line?

Question

I want to be able to lower all windows and show the desktop from the command line, not
Ctrl+Alt+D.

Answer 1

There is a useful command line application called xdotool which amongst other stuff, allows you to send keystrokes.

Thus - to mimic Control+Alt+D (or Super+D, or whatever the combination is you need), you can use one of the following commands:

xdotool key ctrl+alt+d
xdotool key ctrl+super+d
xdotool key super+d

To install:

sudo apt-get install xdotool

Answer 2

I'm not sure fossfreedom's answer truly satisfies the requirement to "not use Ctrl+Alt+D"

Thus I recommend to show desktop the command:

wmctrl -k on

To turn it off use

wmctrl -k off