How to add custom shortcut which pastes a fixed string into the current cursor position?

I have Ubuntu 20.04 and I would like to add a keyboard shortcut, which when I type 'asdf' quickly will copy paste a fixed string into the current cursor position. I tried adding a custom keyboard shortcut, but they can't be arbitrary keys. What are some other ways how I could achieve this? Can I somehow have arbitrary custom shortcut keys? I tried xbindkeys and xdotool but failed to shortcut a simple key:

# test
"xdotool type 'ls'"
F2

so how could I type asdf and have a fixed string copy pasted into the current cursor position and replace the just typed asdf

You are looking for a text snippet possibility, where typing a short text snippet expands to a phrase. A significant productivity booster indeed.

Your idea to do this by scripting is very valid. I run a homemade script myself based on snippy.

Before moving to scripting, you may want to evaluate a few options. Caveat: all of these options do not work on the Wayland display manager, and for now, no alternatives seem available. If you are running a standard Ubuntu desktop, you need to switch to an X11 session or try scripting yourself using the experimental tools that simulate keyboard activity under Wayland (ydotool, wtype).

Espanso: https://espanso.org/docs/get-started/ Highly recommended to try. The setup is text based. It watches what you type, and a trigger, e.g. :asdf will be replaced by your custom string. Some Wayland support already made it into the application.

Autokey: https://github.com/autokey/autokey Venerable Autokey once failed on me, after which I moved to a script based solution. I did not try it after that. However, it appears to be back and properly maintained again. This is extensively controlled using a GUI. It can do exactly what you want, i.e., replace text as you type an abbreviation you defined such as asdf.

texpander: https://github.com/leehblue/texpander This is a bash script based solution, relying on xdotool. It uses Zenity to present a menu with text fragments you saved, which you can select and paste. You could adapt this script to use a better menuing system like rofi or dmenu, or have the script first copy and delete a text fragment you typed, to replace it with the full text.