从子shell设置父shell的变量 [英] Set a parent shell's variable from a subshell

问题描述

如何在子外壳的父外壳中设置变量?

How do I set a variable in the parent shell, from a subshell?

a=3
(a=4)
echo $a

推荐答案

子shell的全部要点是不会影响调用会话.在bash中，子外壳程序是子进程，其他外壳程序有所不同，但是即使这样，子外壳程序中的变量设置也不会影响调用方.根据定义.

The whole point of a subshell is that it doesn't affect the calling session. In bash a subshell is a child process, other shells differ but even then a variable setting in a subshell does not affect the caller. By definition.

您需要一个子壳吗?如果您只需要一组，请使用花括号:

Do you need a subshell? If you just need a group then use braces:

a=3
{ a=4;}
echo $a

给出4(注意其中的空格).或者，将变量值写入stdout并在调用方中捕获它:

gives 4 (be careful of the spaces in that one). Alternatively, write the variable value to stdout and capture it in the caller:

a=3
a=$(a=4;echo $a)
echo $a

避免使用反引号``，它们已被弃用并且可能难以阅读.

avoid using back-ticks ``, they are deprecated and can be difficult to read.

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