在bash中进行命令分组的正确方法是什么 [英] What is the right way to do command grouping in bash

问题描述

我想在条件之后对一些bash指令进行分组:

I would like to group few bash instructions after a condition:

第一次尝试:

$ [[ 0 == 1 ]] && echo 1; echo 2
2

第二次尝试:

$ [[ 0 == 1 ]] && (echo 1; echo 2)
$ [[ 0 == 0 ]] && (echo 1; echo 2)
1
2

所以后者就是我想要的.

So the latter is what I want.

问题:这是我第一次在bash中使用( ... )语法. ( ... )是正确的方法吗，还是有一些我可能会缺少的副作用?

Question: This is the 1st time I'm using (...) syntax in bash. Is (...) the right way to go, or does it have some side effects I might be missing?

推荐答案

放置()中的命令创建一个子外壳，在该子外壳中执行分组的命令.这意味着，例如，在subshel​​l中对变量所做的任何更改都将保留在subshel​​l中

Placing commands in () creates a subshell in which the grouped commands are executed. That means that any changes to variables made in subshell, stay in subshell, for example

$ n=5; [[ "$n" == "5" ]] && ( ((n++)); echo $n); echo $n
6
5

相反，您希望与不调用子外壳程序的{}分组.那么输出将是

Instead you want to group with {} which doesn't invoke a subshell. Then the output would be

$ n=5; [[ "$n" == "5" ]] && { ((n++)); echo $n; }; echo $n
6
6

还请注意{}和分号内部的空格:{ ((n++)); echo $n; };.

Also mind the spaces on the inside of {} and semicolons: { ((n++)); echo $n; };.

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