To List all Installed Packages
Here "less" is a simple text reader used to scroll through the list of packages in a new buffer that opens in the existing terminal window. The list will not be mixed with other terminal commands and output. Hit 'q' to return to terminal prompt. See "man less" for more info.
dpkg -l | less
To check whether a package is installed or not:
dpkg -l {package_name}
dpkg -l vlc
To check if the package is installed or not (for example, vlc). If installed, launch the package:
dpkg -l | grep vlc
Show the location where the package is installed. The "-S" (capital S) stands for "search"
sudo dpkg -S {package_name}
sudo dpkg -S skype
To use Grep to search:
dpkg -l | grep {keywords}
dpkg -l | grep pdf