Which programs use which libraries and vice-versa
 

I recently tried the newest version of crunchbang, and immediately after discovering iceweasel, I went straight back to my Ubuntu 10.10 install and found the .deb file online. When I tried to install, dpkg told me that it conflicts with hunspell-en-ca. I'm not really sure what this library does, (probably a spell-checker of sorts) but I would like to know which programs would be affected if I were to uninstall it. Is there a command to show which programs use which libraries and which libraries furnish to which programs (sorry for the awkward wording)?

Thanks

Iceweasel is simply Firefox with the branding removed.

http://wiki.debian.org/Iceweasel

According to the listing in Synaptic, hunspell-en-ca is the Canadian English dictionary for hunspell.

Okay, well that works. But, now that I'm interested, does anyone know how to achieve the original goal of finding the ties between libraries and programs?

Well, I think your question is not so much focused on libraries as it is general package dependencies.

I'll give you an approach for that in one second, but there is a very low-level approach for libraries specifically.

There's a program called "ldd" (not sure what package(s) provide it). If you run ldd on an executable binary (i.e. not a text script), it should tell you what libraries the binary might load at runtime. For example:
However, there is no way to go in reverse--that is, find all programs that depend on linux-vdso.so.1 for instance.

Back to the package dependency versus library dependency. Check out this page if you use Debian-style deb packages. The examples show how to create a dependency graph. For this to work, you need to have the "dot" program installed (which is included in the graphviz package).

It will generate a PNG file depicting what one (or more) packages are needed by any number of top-level packages. The web page also describes how to go in reverse (find all packages that depend on a specific package).

EDIT:
Be careful though. Some high level packages will generate a LOT of dependencies. For instance, I just ran the commands for package openvpn. The data file for the dot program was 200+ kilobytes in size. That will create a massive graph (and likely require a LONG time to process).

EDIT2:
I should also point out that you can get the package dependency information through apt-cache by itself (without the use of dot). See the man page for apt-cache and the "showpkg" action. For me, I prefer the visuals.