How can I run a command when the container shuts down, to perform clean-up work?

[JaneSmith]

Hello. As the title says, my goal is run a command when the dev container shuts down. I want to perform clean-up work, such as deleting the /node_modules/ directory in the project folder.

The devcontainer.json file has convenient postCreateCommand and postStartCommand options, but apparently nothing for shutdown. There is a shutdownAction defined, but seemingly unrelated. I'm essentially looking for a way to set up a shutdownCommand.

I attempted to do this by trapping EXIT in the postStartCommand, e.g.:

"postStartCommand": "trap \"rm -rf ${containerWorkspaceFolder}/node_modules\" EXIT"

Unfortunately, this didn't work as intended. Instead of running on shutdown, it runs at the end of the startup sequence, as it catches the startup sequence exiting.

What is the proper way to handle this?