who命令简单实现

1100阅读　0评论2014-04-18　do_my_heart
分类：C/C++


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  1. /*
  2.  *【带缓冲who命令简单实现】
  3.  *who:用来查看当前有哪些用户登录到了本台机器上。
  4.  *添加 whats_my_line支持who am i命令
  5.  */
  6. #include<stdio.h>
  7. #include<stdlib.h>
  8. #include<fcntl.h>
  9. #include<utmp.h>
  10. #include<time.h>

  12. #define    UTMP_SIZE    (sizeof(struct utmp))
  13. #define    UTMP_NRECS    16

  15. char utmp_buf[UTMP_NRECS*UTMP_SIZE];

  17. int cur_rec = 0;    //当前记录
  18. int num_recs = 0;    //记录个数

  20. struct utmp * utmp_next(int fd_utmp);
  21. int utmp_reload(int fd_utmp);

  23. char * whats_my_line(int fd);
  24. void show_info(struct utmp * utbuf_fp);


  27. int main(int argc,char *argv[])
  28. {
  29.     int fd_utmp;
  30.     char *my_line = NULL;
  31.     
  32.     if(argc == 3)                    //who am i情况
  33.         my_line = whats_my_line(0);
  34.         
  35.     if( (fd_utmp = open(UTMP_FILE,O_RDONLY)) == -1)
  36.     {
  37.         perror("open UTMP_FILE failed");
  38.         exit(1);
  39.     }
  40.     
  41.     struct utmp * utmp_p;
  42.     while( (utmp_p = utmp_next(fd_utmp)) != NULL)
  43.     {
  44.         if(my_line == NULL || strcmp(utmp_p->ut_line,my_line) == 0)
  45.             show_info(utmp_p);
  46.     }
  47.     
  48.     if(close(fd_utmp) == -1 )
  49.     {
  50.         perror("close file failed");
  51.         exit(1);
  52.     }
  53.     return 0;
  54. }

  56. struct utmp * utmp_next(int fd_utmp)
  57. {
  58.     if( (cur_rec == num_recs) && (utmp_reload(fd_utmp)==0) )    //缓冲区数据取完
  59.         return (struct utmp *)NULL;
  60.         
  61.     return (struct utmp *)&utmp_buf[cur_rec++ * UTMP_SIZE];        //下一个记录
  62. }

  64. int utmp_reload(int fd_utmp)
  65. {    //缓冲区数据读取完,重新放数据到缓冲区utmp_buf
  66.     cur_rec = num_recs = 0;
  67.     int bytes_r = read(fd_utmp,utmp_buf,UTMP_SIZE*UTMP_NRECS);
  68.     if(bytes_r == -1)
  69.     {
  70.         perror("read failed");
  71.         return 0;
  72.     }
  73.     num_recs = bytes_r / UTMP_SIZE;
  74.     
  75.     return num_recs;
  76. }

  78. char * whats_my_line(int fd)
  79. {    //获取当前终端名称
  80.     char * tty_name;
  81.     if( tty_name = ttyname(fd) )
  82.     {
  83.         printf("%s\n",tty_name);
  84.         if( strncmp("/dev/",tty_name,5) == 0 )
  85.             tty_name += 5;
  86.     }
  87.     return tty_name;
  88. }

  90. void show_info(struct utmp * utbuf_fp)
  91. {
  92.     if(utbuf_fp->ut_type != USER_PROCESS)//没有登录的用户
  93.         return;
  94.     printf("%-8.8s ",utbuf_fp->ut_name);
  95.     printf("%-8.8s ",utbuf_fp->ut_line);
  96.     printf("%s",ctime(&utbuf_fp->ut_time));//ctime转换后带\n
  97.     
  98. }
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