“set -e"是怎么来的?使用子外壳? [英] How does "set -e" work with subshells?

问题描述

我想知道 set -e 是否通过子 shell 传播(即子 shell 是否继承了其父级的 -e 设置)，所以我做了一些实验.我发现了一些我无法解释的奇怪结果.

I was wondering whether set -e propagates through subshells (i.e. does a subshell inherit the -e setting of its parent), so I made some experiments. I found some strange results that I can't explain.

首先，这里有一些基本的测试.他们返回了我所期望的.

First, here are some basic tests. They return what I expect.

( true; false )         # 1
( false; true )         # 0
( set -e; false; true ) # 1

现在我尝试在我的子shell中放置一个子shell会发生什么.此表达式返回 1，这表明它会传播.

Now I tried what happens if I put a subshell within my subshell. This expression returns 1, which suggests that it propagates.

( set -e; ( false; true ) )

然后我尝试了这些表达方式.我期望他们返回 1，但我发现他们返回 0.

Then I tried these expressions. I expected them to return 1, but I found that they return 0.

( set -e; ( true; false ); true )
( set -e; ( set -e; false; true ); true )

为什么?在这两种情况下，无论 set -e 是否传播，内部子 shell 都返回 1(正如我在开始时检查的那样).外层子shell有set -e，这意味着它应该在内子shell退出后失败，但它没有.有人能解释一下吗?

Why? In both cases, the inner subshell returns 1, whether set -e propagates or not (as I checked in the beginning). The outer subshell has set -e, which means that it should fail after the inner subshell exits, but it does not. Can someone explain this?

推荐答案

在 bash 4 之前，set -e 似乎只会导致 shell 退出，如果一个简单的命令有一个非零退出(强调我的):

Prior to bash 4, set -e appears to only cause the shell to exit if a simple command has a non-zero exit (emphasis mine):

-e 如果简单命令(参见上面的 SHELL GRAMMAR)以非零状态退出，则立即退出.

-e Exit immediately if a simple command (see SHELL GRAMMAR above) exits with a non-zero status.

在 bash 4(可能是 4.1，我没有 4.0 可以检查)中，-e 的效果扩展到更复杂的命令:

In bash 4 (possibly 4.1, I don't have a 4.0 to check), the effect of -e was extended to more complicated commands:

-e 如果管道(可能由单个简单命令组成)、子shell com-括在括号中的命令，或作为括起的命令列表的一部分执行的命令之一by 大括号(参见上面的 SHELL GRAMMAR)以非零状态退出.

-e Exit immediately if a pipeline (which may consist of a single simple command), a subshell com- mand enclosed in parentheses, or one of the commands executed as part of a command list enclosed by braces (see SHELL GRAMMAR above) exits with a non-zero status.

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