cruftspy VS bgems

If you want to check your images for some common leftover files in all the layers, I made an app for that: https://github.com/viraptor/cruftspy

If you want a quick double check to verify a handful of common cleanups, check out https://github.com/viraptor/cruftspy, which reports cruft like logs, caches, and git repos.

One problem you're likely to run into is that systems using the same packaging lineage cut the same dependency up in different ways. The "right name" for a dependency can change between Ubuntu and Debian, between different releases of Ubuntu, and different architectures. It very quickly gets out of hand for any interesting set of dependencies. Now it might be that there's enough stability in the repositories these days that that's less true than it was, but I remember running into some really annoying cases at one point when I had a full gem mirror to play with.

This is one of those problems that sounds easy but gets really fiddly. I had a quick run at it from a slightly different direction a looooong time ago: binary gems (https://github.com/regularfry/bgems although heaven knows if it even still runs). Precompiled binary gems would dramatically speed up installation at the cost of a) storage; and b) getting it right once. The script I cobbled together gathers the dependencies together into a `.Depends` file which you can just pipe through to the package manager, and could happily use to strap together a package corresponding to the dependency list.

I've never really understood why a standard for precompiled gems never emerged, but it turns out it's drop-dead simple to implement. The script does some linker magic to reverse engineer the dpkg package dependency list from a compiled binary. I was quite pleased with it at the time, and while I don't think it's bullet-proof I do think it's worth having a poke at for ideas. Of course it can only detect binary dependencies, not data dependencies or anything more interesting, so there's still room for improvement.