首先安装dpkg-dev：
apt-get install dpkg-dev
设置源，将原来的源复制，但把deb改为deb-src：
#vim /etc/apt/sources.list
deb http://mirrors.163.com/ubuntu/ lucid main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ lucid-security main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ lucid-updates main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ lucid main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ lucid-security main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ lucid-updates main restricted universe multiverse
并执行apt-get update
得到命令的全路径：
# which ascii
/usr/bin/ascii
查找命令所在的包：
# dpkg -S /usr/bin/ascii
ascii: /usr/bin/ascii
下载包的源码：
# apt-get source ascii
当前目录下面既可以看到源码已经下载
# ls
ascii-3.8 ascii_3.8-4.diff.gz ascii_3.8-4.dsc ascii_3.8.orig.tar.gz