How to know what is installed on a non-rpm based distribution?
 

How to know, whether some package is installed or not on a non-rpm based distribution (e.g.Debian)? On a rpm-based distribution, just the rpm -q command gives this information.

-shimsha

Try one of these 3:
find / -name program
locate program
whereis program

Since this is posted in a *BSD forum, I can give you the answer for FreeBSD (what I use).

Just type pkg_info, it will give you info on all your installed packages. Type 'man pkg_info' for more information.

Even this is a *BSD forum, I will reply to the Debian part of your question:

dpkg -l | grep ii will show you all installed packages

dpkg -l <packagename>* shows all packages whose name starts with <packagename> and the status of those packages (installed, not installed etc.)

dpkg -l <packagename>* | grep ii same as the previous one, but show only those whose status is "installed" (this would be pretty much the same as rpm -q <package>, if I am not mistaken).