Here you will find all the commands which will tell you about your debian packages.
1. Now, if you are looking whether you’ve downloaded packages or not , then try these commands:
apt-cache search 'foo*'
That is how you tell apt to search the packages you’ve downloaded.
2. Another command which do the same in some different way is:
dpkg-query -l 'foo*'
3. Now, if you want to see the description of your package, use something like this:
apt-cache show postgresql
This displays what the package is designed to do, version info and so forth.
4. Now, if you are wondering which all packages are installed in your system, run this on your terminal:
5. Now if you are thinking of viewing all installed packages along with there description, use this one:
dpkg -l \* dpkg -l '*'
These list all packages. (Without the star glob, dpkg only lists installed packages.)
5. To Finds installed packages marked to be purged, put this on your terminal:
dpkg -l \* | grep ^pi
6. This lists packages marked for installation, that aren’t installed yet.
dpkg -l '*' | grep "^i[^i]" dpkg -l \* | grep '^[^i]i'
7. And if you are looking for installed package with all its files(with full paths), then how about this:
dpkg -L php5 gurpinder@gurpinder:~$ dpkg -L php5 /. /usr /usr/share /usr/share/doc /usr/share/doc/php5