在C中创建一个shell。如何实现输入和输出重定向？

Question

我在C中创建一个shell，我需要帮助实现输入和输出重定向。

当我尝试使用＆＃34;＆gt;＆＃34;创建文件时我收到一条错误消息，指出该文件不存在。当我尝试做类似ls＆gt;的事情时test.txt的;它不会创建新文件。

我使用提供给我的建议更新了代码，但现在我遇到了不同的错误。但是，仍未为输出重定向创建新文件。

这是我的完整代码：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <unistd.h>
#include <errno.h>
#include <fcntl.h>

#define MAX_BUF 160
#define MAX_TOKS 100

int main(int argc, char **argv) 
{
    char *pos;
    char *tok;
    char *path;
    char s[MAX_BUF];
    char *toks[MAX_TOKS];
    time_t rawtime;
    struct tm *timeinfo;
    static const char prompt[] = "msh> ";
    FILE *infile;
    int in;
    int out;
    int fd0;
    int fd1;
    in = 0;
    out = 0;

 /* 
 * process command line options
*/

  if (argc > 2) {
    fprintf(stderr, "msh: usage: msh [file]\n");
    exit(EXIT_FAILURE);
  }
  if (argc == 2) {
    /* read from script supplied on the command line */
    infile = fopen(argv[1], "r");
    if (infile == NULL) 
    {
       fprintf(stderr, "msh: cannot open script '%s'.\n", argv[1]);
       exit(EXIT_FAILURE);
    }
  } else {
      infile = stdin;
  }

  while (1) 
  {
    // prompt for input, if interactive input
     if (infile == stdin) {
     printf(prompt);
  }

/*
 * read a line of input and break it into tokens 
 */

  // read input 
  char *status = fgets(s, MAX_BUF-1, infile);

  // exit if ^d or "exit" entered
  if (status == NULL || strcmp(s, "exit\n") == 0) {
       if (status == NULL && infile == stdin) {
              printf("\n");
        }
        exit(EXIT_SUCCESS);
  }

  // remove any trailing newline
  if ((pos = strchr(s, '\n')) != NULL) {
    *pos = '\0';
   }

   // break input line into tokens 
    char *rest = s;
    int i = 0;

  while((tok = strtok_r(rest, " ", &rest)) != NULL && i < MAX_TOKS) 
  {
      toks[i] = tok;
      if(strcmp(tok, "<") == 0)
      {
          in = i + 1;
           i--;
       }
       else if(strcmp(tok, ">")==0)
       {
          out = i + 1;
          i--;
       }
       i++;
  }

  if (i == MAX_TOKS) {
      fprintf(stderr, "msh: too many tokens");
      exit(EXIT_FAILURE);
  }
  toks[i] = NULL;

/*
 * process a command
 */

  // do nothing if no tokens found in input
  if (i == 0) {
     continue;
  }


  // if a shell built-in command, then run it 
  if (strcmp(toks[0], "help") == 0) {
      // help 
       printf("enter a Linux command, or 'exit' to quit\n");
       continue;
   } 
  if (strcmp(toks[0], "today") == 0) {
       // today
       time(&rawtime);
       timeinfo = localtime(&rawtime);
       printf("Current local time: %s", asctime(timeinfo));
      continue;
  }
  if (strcmp(toks[0], "cd") == 0) 
  {
     // cd 
     if (i == 1) {
         path = getenv("HOME");
     } else {
         path = toks[1];
     }
     int cd_status = chdir(path);
     if (cd_status != 0) 
     {
         switch(cd_status) 
         {
            case ENOENT:
                printf("msh: cd: '%s' does not exist\n", path);
                break;
            case ENOTDIR:
                printf("msh: cd: '%s' not a directory\n", path);
                break;
            default:
                printf("msh: cd: bad path\n");
          }
      }
     continue;
  }

  // not a built-in, so fork a process that will run the command
  int rc = fork();
  if (rc < 0) 
  {
     fprintf(stderr, "msh: fork failed\n");
      exit(1);
   }
   if (rc == 0) 
   {
        if(in)
        {
            int fd0;
            if((fd0 = open(toks[in], O_RDONLY, 0)) == -1)
            {
                perror(toks[in]);
                exit(EXIT_FAILURE);
            }
            dup2(fd0, 0);
            close(fd0);
         }

        if(out)
        {
           int fd1;
           if((fd1 = open(toks[out], O_WRONLY | O_CREAT | O_TRUNC | O_CREAT, 
            S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH)) == -1)
            { 
               perror (toks[out]);
               exit( EXIT_FAILURE);
             }
            dup2(fd1, 1);
            close(fd1);
        }
        // child process: run the command indicated by toks[0]
        execvp(toks[0], toks);
        /* if execvp returns than an error occurred */
        printf("msh: %s: %s\n", toks[0], strerror(errno));
        exit(1);
     } 
    else 
    {
        // parent process: wait for child to terminate
       wait(NULL);
    }
  }
}