Ubuntu上的软件包管理系统使安装和删除软件包极为简单，但是有时弄清楚我们实际安装了哪个版本的特定软件包很重要。

apt-get实用程序只是debian dpkg实用程序的前端，它实际上完成了实际工作。我们可以使用该实用工具来确定已安装的版本。

dpkg -s <packagename>

这是一个示例，我试图找出系统上安装了哪个版本的Ruby：

data@ubuntuServ:~$ dpkg -s ruby1.8
Package: ruby1.8
Status: install ok installed
Priority: optional
Section: interpreters
Installed-Size: 272
Maintainer: Ubuntu Core Developers <[email protected]>
Architecture: i386
Version: 1.8.4-5ubuntu1.2
Depends: libc6 (>= 2.4-1), libruby1.8 (>= 1.8.4)
Suggests: ruby1.8-examples, rdoc1.8, ri1.8
Description: Interpreter of object-oriented scripting language Ruby 1.8
Ruby is the interpreted scripting language for quick and easy
object-oriented programming. It has many features to process text
files and to do system management tasks (as in perl). It is simple,
straight-forward, and extensible.
.
This package provides version 1.8 series of Ruby.
.
On Debian, Ruby 1.8 is provided as separate packages. You can get
full Ruby 1.8 distribution by installing following packages.
.
ruby1.8 ruby1.8-dev ri1.8 rdoc1.8 irb1.8 ruby1.8-elisp
ruby1.8-examples libdbm-ruby1.8 libgdbm-ruby1.8 libtcltk-ruby1.8
libopenssl-ruby1.8 libreadline-ruby1.8
Original-Maintainer: akira yamada <[email protected]>

我们可以看到我已经安装了1.8.4版本。