配置不同版本软件包优先级

1. 为不同版本建立配置

$sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-8 60
$sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-9 70

2. 使用时动态选择

$sudo update-alternatives --config gcc
There are 2 choices for the alternative gcc (providing /usr/bin/gcc).

  Selection    Path            Priority   Status
------------------------------------------------------------
* 0            /usr/bin/gcc-9   70        auto mode
  1            /usr/bin/gcc-8   30        manual mode
  2            /usr/bin/gcc-9   70        manual mode