文件操作

1、写文件
static const char *boilerplate_1 =
  "#!/bin/sh\nexport DISPLAY=:1\nexport LD_LIBRARY_PATH=/usr/local/lib\n";

fd = open (filename, O_WRONLY | O_CREAT, 0700);
  if (fd < 0)
  {
    g_free (filename);
    g_free (uid_str);
    return FALSE;
  }
  if ((fp = fdopen (fd, "w")) == NULL)
  {
#ifdef DEBUG
    printf ("can't reopen atjob file\n");
#endif
    return FALSE;
  }

  fwrite (boilerplate_1, sizeof (char), strlen (boilerplate_1), fp);//真正写文件的地方
2、执行shell脚本

 sprintf (call_at,
           "/usr/bin/at -q g -f /tmp/atjob.txt %02d:%02d %02d.%02d.%02d 2>&1",
           tm->tm_hour, tm->tm_min, tm->tm_mday, tm->tm_mon + 1,
           tm->tm_year - 100);
  g_print ("%s\n", call_at);
  if ((at_return = popen (call_at, "r")) != NULL)


 范例
    #include
main()
{
FILE * fp;
char buffer[80];
fp=popen(“cat /etc/passwd”,”r”);
fgets(buffer,sizeof(buffer),fp);
printf(“%s”,buffer);
pclose(fp);
}
执行
    root :x:0 0: root: /root: /bin/bash


3、把文件改成类似管道（先进先出）的操作

        int ret;
    int fd;

    ret = mkfifo(PIPESERVER, S_IRUSR|S_IWUSR|S_IRGRP|S_IWGRP|S_IROTH|S_IWOTH);
    if (ret == -1) {
        fprintf(stderr, "make pipe error:%s\n", strerror(errno));
        return -1;
    }
    if ((s_fd = open(PIPESERVER,O_RDWR)) < 0) {
        fprintf(stderr, "Open ioctl device file %s error.\n", "pipe");
        return -1;
    }
    while (1) {
        memset( &event, 0 ,sizeof(struct ipm_event));

        FD_ZERO(&rfds);
        if( flag ) {
            FD_SET(ipmc_fd, &rfds);
        }
        FD_SET(s_fd, &rfds);

        /* tv.tv_sec = 1;      tv.tv_usec = 0; */
        tv.tv_sec = 0;
        tv.tv_usec = 100000;

        ret = select(temp + 1, &rfds, NULL, NULL, &tv);
            if( FD_ISSET(s_fd, &rfds) ) {  
                   if ((size = read(s_fd, msg, IPM_MSG_SIZE))!=IPM_MSG_SIZE) {
           fprintf(stderr, "read pipe error:%s\n", strerror(errno));
           return -1;
               }



这样，在一端用select监听，一端写入时就可以监听得到
写入端：
    fd = open(PIPESERVER, O_WRONLY|O_NONBLOCK, 0);
        if (fd == -1) {
            printf("open pipe error:%s\n", strerror(errno));
            return -1;
        }
    }        
    ret = write(fd, msg, IPM_MSG_SIZE);
    if (ret == -1) {
        printf("write to pipe error:%s\n", strerror(errno));
        return -1;
    }
    if( ret != IPM_MSG_SIZE ) {               
        printf("write to pipe failed. return %d.\n",ret);
        return -1;
    }    
            
注意：写入的时间的字节数以IPM_MSG_SIZE为准，而不是msg的字节大小