We can use the aptitude command to know if a package has been installed on Debian GNU/Linux or derivative
$ sudo aptitude show cmus Package: cmus New: yes State: installed Automatically installed: no Version: 2.3.3-2 Priority: optional Section: sound ...
If we don't know the exact name of the package we can search it using apt-cache
$ sudo apt-cache -n keyword
Example
$ sudo apt-cache -n cmus cmus-plugin-ffmpeg - lightweight ncurses audio player (FFmpeg plugin) cmus - lightweight ncurses audio player cmuscheme48-el - Emacs mode specialized for Scheme48
In CentOS/RHEL/Fedora you can use yum
# yum info httpd Reading repository metadata in from local files Installed Packages Name : httpd Arch : i386 Version: 2.2.6 Release: 1.fc6 Size : 2.6 M Repo : installed Summary: Apache HTTP Server ...
Furgher reading
– man apt-cache
– man aptitude
– man yum