If you ever need to know if a specific package or a specific piece of software has been installed on a Debian system there are a variety of ways to tell, as you are probably aware of. One way that recently caught my eye, which is fast and easy to check from the command line is the search feature of aptitude.
Now, without speaking on the merits of using aptitude for package management (this is an entirely different topic) I would just like to mention here that it (aptitude) needs to be installed for this method to work. If you don’t have it installed already, it’s super simple.
sudo apt-get install aptitude
Okay, with that piece in place we just need to check that the package we are looking for is installed. So to do that, enter the following command.
aptitude search '~i' | less
Basically, this command will output a list of installed packages. I just added the | less to easily be able to scroll through the packages. In my opinion, the flexibility and usefulness of the search feature on its own is probably enough to start using aptitude, although this can be done similarly with apt-get. You may notice an “A” next to a number of these installed packages. This indicates that a package was automatically installed.
If you take a look at the output from this command it will look similar to the example posted below.
As I said, this is a quick and dirty way to view installed packages, but there are definitely other ways to go about this. I was unaware of the search functionality and well, I like aptitude so I thought that I would share the knowledge. Let me know if you know of any other cool and/or easy ways to check for installed packages.