UbuntuSolutions

Searching the local cache of repositories apt-cache search

$ apt-cache search activerecord
libactiveldap-ruby1.8 - an object-oriented interface to LDAP for Ruby
libactiverecord-ruby - Ruby library that ties database tables to classes
libactiverecord-ruby1.8 - Tie database tables to classes (Ruby 1.8)
...

Finding information about a non installed package

apt-cache showpkg

$ apt-cache showpkg libactiverecord-ruby1.8
Package: libactiverecord-ruby1.8
Versions:
2.1.0-3 (/var/lib/apt/lists/us.archive.ubuntu.com_ubuntu_dists_intrepid_universe_binary-i386_Packages)
Description Language:
        File: /var/lib/apt/lists/us.archive.ubuntu.com_ubuntu_dists_intrepid_universe_binary-i386_Packages
         MD5: 4eabc44d09608d0156c42018917a2881

Reverse Depends:
libactiverecord-ruby,libactiverecord-ruby1.8
Dependencies:
2.1.0-3 - libruby1.8 (0 (null)) libactivesupport-ruby1.8 (2 2.1.0-3) libsqlite3-ruby1.8 (16 (null)) libpgsql-ruby1.8 (16 (null)) libmysql-ruby1.8 (0 (null))
Provides:
2.1.0-3 -
Reverse Provides:

Listing all available packages matching a pattern

The packages matching the patterns may or may not be installed. dpkg -l

$ dpkg -l ruby*
Desired=Unknown/Install/Remove/Purge/Hold
| Status=Not/Inst/Cfg-files/Unpacked/Failed-cfg/Half-inst/trig-aWait/Trig-pend
|/ Err?=(none)/Hold/Reinst-required/X=both-problems (Status,Err: uppercase=bad)
||/ Name             Version          Description
+++-================-================-================================================
ii  ruby             4.2              An interpreter of object-oriented scripting lang
un  ruby-elisp                  (no description available)
ii  ruby-full        4.2              Ruby full installation
ii  ruby1.8          1.8.7.72-1       Interpreter of object-oriented scripting languag
ii  ruby1.8-dev      1.8.7.72-1       Header files for compiling extension modules for
un  ruby1.8-examples            (no description available)
ii  rubygems         1.3.0~RC1really1 package management framework for Ruby libraries/
un  rubygems-doc                (no description available)
ii  rubygems1.8      1.3.0~RC1really1 package management framework for Ruby libraries/

Finding information about an installed package

dpkg -s

$ dpkg -s ruby1.8
Package: ruby1.8
Status: install ok installed
Priority: optional
Section: interpreters
Installed-Size: 136
Maintainer: Ubuntu Core Developers 

Listing all files belonging to an installed package

dpkg -L

$ dpkg -L ruby1.8
/.
/usr
/usr/bin
/usr/bin/ruby1.8
/usr/bin/erb1.8
/usr/bin/testrb1.8
/usr/share
/usr/share/man
/usr/share/man/man1
/usr/share/man/man1/erb1.8.1.gz
/usr/share/man/man1/testrb1.8.1.gz
/usr/share/man/man1/ruby1.8.1.gz
/usr/share/doc
/usr/share/doc/ruby1.8
/usr/share/doc/ruby1.8/README
/usr/share/doc/ruby1.8/README.ja.gz
/usr/share/doc/ruby1.8/ToDo.gz
/usr/share/doc/ruby1.8/README.Debian
/usr/share/doc/ruby1.8/copyright
/usr/share/doc/ruby1.8/LEGAL.gz
/usr/share/doc/ruby1.8/NEWS-1.8.0.gz
/usr/share/doc/ruby1.8/NEWS.gz
/usr/share/doc/ruby1.8/NEWS.Debian.gz
/usr/share/doc/ruby1.8/changelog.Debian.gz