Searching for installed packages

A nice easy way to find out what packages you have installed on Gentoo, is a program called "equery".  This is part of the gentoolkit, so if you've not got it installed.

emerge gentoolkit

so that you have it.  After this, you can search for installed packages, like this:

[email protected] ~ $ equery list --installed gcc
[ Searching for package 'gcc' in all categories among: ]
 * installed packages
[I--] [ -] sys-devel/gcc-3.3.6-r1 (3.3)
[I--] [ -] sys-devel/gcc-4.1.2 (4.1)
[I--] [  ] sys-devel/gcc-config-1.3.16 (0)

as you can see from my example, it has matches all packages containing "gcc" in their name.  This is just one of equery's features.  Enjoy!