为什么apt-get在安装东西时会消耗stdin而不是其他东西呢？

Question

我通过macOS终端连接到远程Debian系统。

Command after apt-get never runs if apt-get installs something

首先，我从macOS上的文本文件中复制这三个命令，然后使用单个命令将其粘贴到终端中+ v press：

sudo apt-get -y remove tree
sudo apt-get -y install tree
echo hi

这是我在终端看到的。

lone@lone:~$ sudo apt-get -y remove tree
Reading package lists... Done
Building dependency tree       
Reading state information... Done
Package 'tree' is not installed, so not removed
0 upgraded, 0 newly installed, 0 to remove and 17 not upgraded.
lone@lone:~$ sudo apt-get -y install tree
Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following NEW packages will be installed:
  tree
0 upgraded, 1 newly installed, 0 to remove and 17 not upgraded.
Need to get 0 B/46.1 kB of archives.
After this operation, 106 kB of additional disk space will be used.
Selecting previously unselected package tree.
(Reading database ... 31853 files and directories currently installed.)
Preparing to unpack .../tree_1.7.0-5_amd64.deb ...
Unpacking tree (1.7.0-5) ...
Setting up tree (1.7.0-5) ...
Processing triggers for man-db (2.7.6.1-2) ...
lone@lone:~$ 

第三个命令echo hi从未执行过。为什么？

Command after apt-get does run if apt-get does not install anything

下次，我只需使用一个命令+ v press粘贴这两个命令：

sudo apt-get -y install tree
echo hi

这一次，由于tree已经安装，apt-get不需要再次安装它。这是我看到的输出：

lone@lone:~$ sudo apt-get -y install tree
Reading package lists... Done
Building dependency tree       
Reading state information... Done
tree is already the newest version (1.7.0-5).
0 upgraded, 0 newly installed, 0 to remove and 17 not upgraded.
lone@lone:~$ echo hi
hi

这次echo hi被执行了。为什么？

每次执行这两组操作时，这两个结果都是可重现的。为什么echo hi命令不在第一个例子中运行，而在第二个例子中运行？

Answer 1

apt-get或apt-get调用的程序正在清空它的stdin（它恰好与shell的命令列表相同）。

既然您不需要从用户那里读取任何内容，那么从/ dev / null重定向stdin：

sudo apt-get -y remove tree </dev/null
sudo apt-get -y install tree </dev/null
echo hi