在使用&&时如何执行退出命令和||? [英] How to execute exit command while using && and ||?
问题描述
我有两种情况.
-
回显&/dev/null&&回声b ||(回声c；出口1)；echo d; echo e; echo f
输出:
b
d
e
f
-
回显&/dev/null&&回声b ||(回声c；出口1)；echo d; echo e; echo f
输出:
c
d
e
f
我需要我的脚本在退出命令后退出，并且不执行其他命令.我该怎么办?
I need my script to exit after the exit command and not execute further commands. How I can do it?
推荐答案
()中的命令在子shell中执行，因此parens中的 exit 仅退出子shell，不是主要的外壳.您可以使用 {} 而不是parens来对命令不进行分组，而不强制使用子外壳.注意:与括号不同，您需要在 {之后加上一个空格，并在} 之前使用一个分号(或&"号).
Commands in ( ) are executed in a subshell, so exit inside parens only exits the subshell, not the main shell. You can group commands without forcing a subshell using { } instead of parens. Note: unlike with parens, you need a space after the {, and a semicolon (or ampersand) before }.
$ eco a &>/dev/null && echo b || { echo c ; exit 1; } ; echo d ;echo e;echo f output
c
logout
此外，您还应该注意使用&&... || 与结构相同，否则为fi 结构；特别是如果& 和 || 之间的命令(与 if 语句)应该碰巧失败，它也会执行 || 之后的内容.仅使用 echo b ，它不太可能(但从技术上来说)失败.如果比较复杂，您会得到意想不到的结果.
Also, you should be aware that using && ... || is not the same as an if then else fi structure; in particular, if the command between && and || (which corresponds to the then clause in an if statement) should happen to fail, it'll execute what's after the || as well. With just echo b in there, it's unlikely (but technically possible) for it to fail; if it's more complicated, you can get unexpected results.
因此，我建议使用 if然后else fi 代替&&||| -可以正确处理分组，而不会带来额外的麻烦，并且没有明显的执行路径.与&&|| ，它就可以工作.
As a result, I recommend using if then else fi instead of && || -- it handles the grouping properly without additional hassle, and doesn't have non-obvious execution paths. Unlike && ||, it just works.
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