如何让我的C外壳认识到这是命令？

Question

我在C上很新，但目前正在努力创建C程序以充当外壳接口。它应该接受命令，然后在单独的过程中执行每个命令。目前，我被困在试图让C认识到这是命令。我不确定该怎么做，似乎找不到任何有用的例子。

这是我的代码，它说的一切都不是有效的命令（“否CMD”）。有人知道为什么会发生这种情况吗？ C是否无法识别它是execvp（）函数中的命令，还是我需要为该特定目的实现某些内容？

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

#define MAX_LINE 80
/* 80 chars per line per command */

int main(void) {
  //char *args[MAX_LINE/2 + 1];
    char *args = calloc(MAX_LINE, (MAX_LINE/2 +1));
    const size_t sz = MAX_LINE;
    pid_t pid;
  /* command line (of 80) has max of 40 arguments*/
  int should_run = 1;

  while (should_run) {
    printf("osh>"); //beginning of command line
        fgets(args, sz, stdin); //gets the stdin

        char *token = strtok(args, " \n"); //supposed to break str if it has a space or line and recognize there are 2 commands
        printf("%s\n", token);
        
        token = strtok(NULL," \n");
        printf("%s\n", token);
            pid_t parent = getpid();
      pid = fork(); //forking child
            if(pid == 0){ //if forking occurred
                int status = execvp(&args[0], &args); //status of input, is it a command?
                printf("%d", status);
                printf("forked!");
                if(status == -1) { //if cmd err, print
                    printf("no cmd");
                    return 1;
                } else {
                    printf("line will be printed");
                }
                return 0;
            }
        fflush(stdout); //flush
        /*

   
    * After reading user input, the steps are :
    * 1: fork a child process
    * 2: the child process will invoke execvp()
    * 3: parent process waits for the child to exit before       
    continuing
    */
  }

  exit(0);
  /**
  return to the operating system:
    -exit this process
    -flush all
  */

  
}

Answer 1

如果您查看exec函数系列的文档，您会注意到，仅当exec失败时，功能才返回。这是因为exec成功时，用调用程序完全替换了调用过程。

您需要做的是，从父级进程（即获得从fork>的正值），通过waitpid等待子进程。

pid_t pid;

pid = fork();
if ( pid < 0 ) {
    // Handle the error.
}
else if ( pid == 0 ) {
    execvp(&args[0], &args);
    // The fact that we've reached this line means that execvp failed.
    exit(1);
}
else {
    int status;

    while ( waitpid(pid, &status, 0) != pid ) {} // We need this loop in case waitpid gets interrupted by a signal.

    // status doesn't equal the return value of the child process.  We need to extract that with macros.
    if ( WIFEXITED(status) ) {
        printf("Child process exited with code %i\n", WEXITSTATUS(status));
    }
    else {
        printf("Child process was terminated by signal number %i\n", WTERMSIG(status));
    }
}