什么是美元?(美元问号)shell 脚本中的变量? [英] What is the $? (dollar question mark) variable in shell scripting?

问题描述

我正在尝试学习 shell 脚本，我需要了解其他人的代码.$? 变量是什么?我无法在 Google 上搜索答案，因为它们会屏蔽标点符号.

I'm trying to learn shell scripting, and I need to understand someone else's code. What is the $? variable hold? I can't Google search the answer because they block punctuation characters.

推荐答案

$? 用于查找上次执行命令的返回值.在 shell 中尝试以下操作:

$? is used to find the return value of the last executed command. Try the following in the shell:

ls somefile
echo $?

如果somefile存在(不管是文件还是目录)，都会得到ls命令抛出的返回值，应该是0(默认成功"返回值).如果它不存在，您应该得到一个非 0 的数字.确切的数字取决于程序.

If somefile exists (regardless whether it is a file or directory), you will get the return value thrown by the ls command, which should be 0 (default "success" return value). If it doesn't exist, you should get a number other then 0. The exact number depends on the program.

对于许多程序，您可以在相应的手册页中找到编号及其含义.这些通常会被描述为退出状态"，并且可能有自己的部分.

For many programs you can find the numbers and their meaning in the corresponding man page. These will usually be described as "exit status" and may have their own section.

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