`echo $?` 在 bash 中是什么意思？
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What does `echo $?` mean in bash?
提问by Ivan Prodanov
I came upon the following command:
我遇到了以下命令：
echo $?
what does that command do?
该命令有什么作用？
回答by Chris Pfohl
Echoes (prints) the exit value for the previous command.
回显（打印）上一个命令的退出值。
If it failed it will be different than zero (0).
如果失败，它将不同于零 ( 0)。
$ cd ~
$ echo $?
> 0
$ cd //whatever/
> bash: cd: //whatever/: No such file or directory
$ echo $?
> 1
Programs exit with a status code. Every program is unique and has a different set of failure codes, but it's universally acknowledged that 0is the 'success' code.
程序以状态码退出。每个程序都是独一无二的，并且有一组不同的失败代码，但人们普遍认为这0就是“成功”代码。
