有多个功能类似的脚本，用到同一个变量，但是这个变量有可能会根据需要改变，如果每个脚本文件定义一个这个变量，修改的时候每个脚本都要修改，很麻烦，所以想将这个变量定义在一个common.sh脚本里面，然后在功能脚本里面引用这个脚本，代码如下：
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#获取脚本所在的路径 script_folder=$(cd "$(dirname "$0")"; pwd) #引用脚本 source ${script_folder}/common.sh |
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script_folder=$(cd "$(dirname "$0")"; pwd) echo ${script_folder} |
使用apt-get下载软件慢的话，可以换成国内的一些源，这样就可以节省很多时间了
修改方法：
1. 先备份系统的源文件，然后编辑源列表文件
cp /etc/apt/sources.list /etc/apt/sources.list.bak
vi /etc/apt/sources.list
在打开的编辑器中加入以下内容
deb http://mirrors.sohu.com/ubuntu/ precise-updates main restricted
deb-src http://mirrors.sohu.com/ubuntu/ precise-updates main restricted
deb http://mirrors.sohu.com/ubuntu/ precise universe
deb-src http://mirrors.sohu.com/ubuntu/ precise universe
deb http://mirrors.sohu.com/ubuntu/ precise-updates universe
deb-src http://mirrors.sohu.com/ubuntu/ precise-updates universe
deb http://mirrors.sohu.com/ubuntu/ precise multiverse
deb-src http://mirrors.sohu.com/ubuntu/ precise multiverse
deb http://mirrors.sohu.com/ubuntu/ precise-updates multiverse
deb-src http://mirrors.sohu.com/ubuntu/ precise-updates multiverse
deb http://mirrors.sohu.com/ubuntu/ precise-backports main restricted universe multiverse
deb-src http://mirrors.sohu.com/ubuntu/ precise-backports main restricted universe multiverse
网易源：
deb http://mirrors.163.com/ubuntu/ precise-updates main restricted
deb-src http://mirrors.163.com/ubuntu/ precise-updates main restricted
deb http://mirrors.163.com/ubuntu/ precise universe
deb-src http://mirrors.163.com/ubuntu/ precise universe
deb http://mirrors.163.com/ubuntu/ precise-updates universe
deb-src http://mirrors.163.com/ubuntu/ precise-updates universe
deb http://mirrors.163.com/ubuntu/ precise multiverse
deb-src http://mirrors.163.com/ubuntu/ precise multiverse
deb http://mirrors.163.com/ubuntu/ precise-updates multiverse
deb-src http://mirrors.163.com/ubuntu/ precise-updates multiverse
deb http://mirrors.163.com/ubuntu/ precise-backports main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ precise-backports main restricted universe multiverse
保存文件，再试试下面的命令
sudo apt-get update
sudo apt-get upgrade