How to execute a shell command within held{}

[sk-akiyama]

Thank you for viewing my question.

I want to execute a specific "shell command" when a key is held down (in the held{} part), but it doesn't work when I write it like
as shown in the red line in the image.

When I check the generated karabiner.json, it doesn't seem to be reflected at all, so I think the way I'm writing it is incorrect.

By the way, writing works fine for normal ":key" operations. How can I execute a shell command?

Thanks!