如何创建一个读取最后一个命令退出状态的程序？

Question

在 Linux C 中，如何读取最后一个程序的退出状态。

例如：

true; echo $?

将显示 0 表示成功。但我想用 C 程序替换它：

true; ./echo_exit_status

最后一个退出代码 $ 如何/在哪里？可用于 C 程序？

Answer 1

最后一个命令的退出状态不可供后续执行的程序访问（不存在极其可怕的骇客——使用调试器或类似工具附加到父 shell）。

您可以编写一个 shell 函数或帮助程序，将这个值导出到环境中——但没有任何解决方案不需要 shell 参与。

Answer 2

您必须知道 pid，否则它是 http://linux.die.net/man/2/waitpid 来自手册页的更多信息

   WIFEXITED(status)
          returns true if the child terminated normally, that is, by
          calling exit(3) or _exit(2), or by returning from main().

   WEXITSTATUS(status)
          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.

这是一个例子

   #include <sys/wait.h>
   #include <stdlib.h>
   #include <unistd.h>
   #include <stdio.h>

   int
   main(int argc, char *argv[])
   {
       pid_t cpid, w;
       int status;

       cpid = fork();
       if (cpid == -1) {
           perror("fork");
           exit(EXIT_FAILURE);
       }

       if (cpid == 0) {            /* Code executed by child */
           printf("Child PID is %ld\n", (long) getpid());
           if (argc == 1)
               pause();                    /* Wait for signals */
           _exit(atoi(argv[1]));

       } else {                    /* Code executed by parent */
           do {
               w = waitpid(cpid, &status, WUNTRACED | WCONTINUED);
               if (w == -1) {
                   perror("waitpid");
                   exit(EXIT_FAILURE);
               }

               if (WIFEXITED(status)) {
                   printf("exited, status=%d\n", WEXITSTATUS(status)); //this line will return the exit status, whether it was 1 or 0
               } else if (WIFSIGNALED(status)) {
                   printf("killed by signal %d\n", WTERMSIG(status));
               } else if (WIFSTOPPED(status)) {
                   printf("stopped by signal %d\n", WSTOPSIG(status));
               } else if (WIFCONTINUED(status)) {
                   printf("continued\n");
               }
           } while (!WIFEXITED(status) && !WIFSIGNALED(status));
           exit(EXIT_SUCCESS);
       }
   }