Check installed package in Raspberry Pi OS, using dpkg/dpkg-query

To list all installed packages, enter the command in Terminal:

$ dpkg -l

or

$ dpkg-query -l

To list about a specified package:

$ dpkg -l package-name-pattern

or

$ dpkg-query -l package-name-pattern

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dpkg is a tool to install, build, remove and manage Debian packages. It can also be used as a front-end to dpkg-deb and dpkg-query. 

dpkg-query is a tool to show information about packages listed in the dpkg database.

With command "-l [package-name-pattern...]" list all known packages matching one or more patterns. If no package-name-pattern is given, list all packages in /usr/local/var/lib/dpkg/status, excluding the ones marked as not-installed (i.e.  those which have been previously purged).

The first three columns of the output show the desired action, the package status, and errors, in that order.

              Desired action:

                u = Unknown

                i = Install

                h = Hold

                r = Remove

                p = Purge

              Package status:

                n = Not-installed

                c = Config-files

                H = Half-installed

                U = Unpacked

                F = Half-configured

                W = Triggers-awaiting

                t = Triggers-pending

                i = Installed

              Error flags:

                <empty> = (none)

                R = Reinst-required

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