c - 为什么 "system"的返回与被调用脚本的返回不匹配？

Question

我有一个简单的脚本

#!/usr/bin/bash
# exit5.bash
exit 5

我在c程序中用system调用它

#include <stdlib.h>
#include <stdio.h>

int main()
{
    int ret = system("./exit5.bash");
    printf("%d\n", ret);
    return 0;
}

我看到屏幕上打印了 1280，这与 5 << 8 相同

为什么我看不到常规 5？

Answer 1

system 的返回值是终止状态，而不是退出代码。

参见 return value section of man system :

In the last two cases, the return value is a "wait status" that can be examined using the macros described in waitpid(2). (i.e., WIFEXITED(), WEXITSTATUS(), and so on).

WEXITSTATUS 宏返回您要查找的内容:

WEXITSTATUS(wstatus)

returns the exit status of the child. This consists of the least significant 8 bits of the status argument that the child specified in a call to exit(3) or _exit(2) or as the argument for a return statement in main(). This macro should be employed only if WIFEXITED returned true.