No need for overlays.
Instead create own packages and call them via callPackage.
That will keep them simpler and allows dependency injection.
I can follow existing patterns from nixpkgs, etc.
No longer have all of them as files and apply sed.
Instead define dependencies via nix expression.
Also allow to write the scripts within nix expression.
Some are still large and separate .sh files, but loaded within
expression.
Also only the main file is exposed as others are only dependencies.
Still all can now be installed as all are separate derivations.
The new writeShellApplication also executes shellcheck as another
benefit. And it makes script executable.
Daniel Siepmann