Can I easily make a host “mirror” that caches downloaded Debian packages?

We’ve got a Squid web cache set up that is used for caching package downloads, so that all the machines here don’t have to independently redownload everything. The installer prompts for a mirror and proxy. As long as every machine uses the exact same mirror (here, http.us.debian.org) and the proxy then it works.

Elegant solution to echo to either stdout or file in bash

I have a bash application that is producing some result, and I’d like to echo the result to either stdout or to a user chosen file. Because I also echo other interactive messages going to the screen, requiring the user to explicitly use the > redirection when he wants to echo the result to a file is not an option (*), as those messages would also appear in the file.