Comment 2 for bug 1258351

Hi, this is an interesting proposal. But I think the approach is overly limiting if we're going to allow dynamic file name specification.

The first line of a template isn't special today, and making it special will be super surprising.

This needs some design work: specifically we need to make sure this doesn't conflict with the simple case of file in -> file out, while still solving your problem (that I don't quite follow).

The pattern you've expressed is a little concerning for me because bad data could write a custom root ssh key to /root/.ssh/passwords, for instance.

So - lets gather your requirements, come up with a secure, robust design, and then this can move forward.