子外壳程序始终从父外壳程序中获取所有变量.

A subshell always gets all variables from the parent shell.

man bash 将描述使用子shell的所有情况，主要是:命令& 命令|命令和(命令)

man bash will describe all the circumstances in which a subshell is used, which are mainly: command & command | command and ( command )

所谓的环境仅包含环境变量( export变量)，并传递给每个子进程.即使调用 bash -c命令，它也不是子shell，而是全新的bash实例.

The so called environment only includes environment variables (export variable), and is passed on to every sub-process. Even when invoking bash -c command, which is not a sub-shell but a completely new bash instance.

在两种情况下，更改后的值都不会传递回父进程.

In both cases changed values are not passed back to the parent process.