Question

您好我正在编写一个用于输入输出重定向的shell脚本。代码如下

int parse(void)
{
char *p;            /* pointer to current word */
char *msg;          /* error message */

nwds = 0;
p = strtok(line," \t");
while (p != NULL) {
if (nwds == NWORDS) {
    msg = "Error: too many words.\n";
    write(2 ,msg, strlen(msg));
    return 0;
}
if (strlen(p) >= MAXWORDLEN) {
    msg = "Error: Word too long.\n";
    write(2, msg ,strlen(msg));
    return 0;
}

if(*p == '<')   /* check if input symbol is present*/
    isInput = true;

if(*p == '>')   /* check if Output symbol is present*/
    isOutput = true;

if(isInput) {
    p = strtok(NULL," \t"); /* get pointer to next word, if any */
    input = p;
}
if(isOutput) {
    p = strtok(NULL," \t");         /* get pointer to next word, if any */
    output = p;
}

words[nwds] = p;    /* save pointer to the word */
nwds++;         /* increase the word count */
p = strtok(NULL," \t"); /* get pointer to next word, if any */
}
return 1;
}

以上代码从输入获取命令并验证命令数和字长。它还验证输入和输出重定向字符，并将文件名存储在输入和输出字符指针

中

int execute(void)
{
int i, j;
int status;
char *msg;
pid_t child_pid;
int in;
int out;

if (execok() == 0) {            /* is it executable? */
status = fork();            /* yes; create a new process */

if (status == -1) {         /* verify fork succeeded */
    perror("fork");
    exit(1);
}

if (status == 0) {          /* in the child process... */
    words[nwds] = NULL;         /* mark end of argument array */

    if(input != NULL && output != NULL)
    {
        in = open (input, O_RDONLY);
        out = open (output, O_TRUNC | O_CREAT | O_WRONLY, 0666);

        if ((in <= 0) || (out <= 0))
          {
            fprintf (stderr, "Couldn't open a file\n");
            exit (errno);
          }


      dup2(in, 0);
      dup2(out, 1);

      close(in);
      close out);
   }
  status = execve(path,words,environ); /* try to execute it */

  perror("execve");         /* we only get here if */
  _exit(0);             /* execve failed... */
}

/*------------------------------------------------*/
/* The parent process (the shell) continues here. */
/*------------------------------------------------*/
child_pid = wait(&status);      /* wait for process to end */
if (v_opt) {                /* display status? */
    char emsg[100];

    if (WIFEXITED(status))
    sprintf(emsg,"Child process %u exited with status %d.\n",
        child_pid, WEXITSTATUS(status));
    else
    sprintf(emsg,"Child process %u did not exit normally.\n",
        child_pid);
    write(1,emsg,strlen(emsg));
}
} else {
/*----------------------------------------------------------*/
/* Command cannot be executed. Display appropriate message. */
/*----------------------------------------------------------*/
msg = "Error: '";
write(2,msg,strlen(msg));
write(2,words[0],strlen(words[0]));
msg = "' cannot be executed.\n";
write(2,msg,strlen(msg));
}
}

这是执行重定向的执行功能。

我是shell脚本的新手，我通过网络获得了一些知识，并编写了这个程序。该程序不重定向输入和输出。你能帮帮我吗

用于输入输出重定向的Shell脚本

0 个答案: