implement dry-run option

[rmm-fcul]

a dry-run option would:

1. generate the relevant commands but not execute any of them, producing a transcript for executing commands manually (e.g. to inspect problems or develop parts more interactively).
2. Additionally, it would give some confidence that all files referred to are available.
3. however, note that this may require a certain number of files to be auto-generated, in a sandbox somewhere