什么是echo $?在Linux终端? [英] What is echo $? in linux terminal?

问题描述

我已经尝试过这些命令.

I have tried those commands.

~$top
(ctrl + z)stopped the process
~$echo $?
147
~$top
(ctrl + c)killed the process
~$echo $?
0

这里发生了什么，请解释一下为什么它显示恒定值.这些值的含义是什么.

What happened here, please explain it and why it showing some constant value. What is the meaning of those values.

推荐答案

$?是上次运行过程的返回代码. 0表示没有错误发生.其他值表示某种异常情况.

$? is the return code from the last run process. 0 means no error happened. Other values represent some kind of unusual condition.

值128及以上通常表示某种信号. 147-128 = 19，表示程序接收到信号19(在Linux上为SIGSTOP).现在，通常按^ Z会发送SIGTSTP(与SIGSTOP不同的信号)，这可能意味着top捕获了该信号，进行了一些(可能与终端相关的)清理，然后重新发出SIGSTOP来实际挂起程序.

Values 128 and above usually represent some kind of signal. 147 - 128 = 19, which means the program received signal 19 (SIGSTOP on Linux). Now, normally pressing ^Z sends SIGTSTP (a different signal from SIGSTOP), which probably meant that top caught that signal, did some (probably terminal-related) cleanup, and reissued SIGSTOP to actually suspend the program.

top也捕获了SIGINT(通常按^ C后发出)，以进行清理并干净地退出(退出值为0).

top also caught SIGINT (which is normally issued after pressing ^C), to do cleanup and exit cleanly (with exit value 0).

您可以运行kill -l来查看当前平台的所有信号编号.请注意，不同平台的数字不同.例如，SIGSTOP在Darwin上为17，在Linux上为19.

You can run kill -l to see what all the signal numbers are for the current platform. Note that the numbers are different for different platforms; for example, SIGSTOP is 17 on Darwin and 19 on Linux.

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