实现linux命令ls -l， ls -l显示指定目录下的文件和子目录。可以显示文件的权限，大小，所有者，创建时间等。目录通过运行时参数传入。

代码：
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <pwd.h>
#include <grp.h>
#include <time.h>

int main(int argc ,char *argv[])
{
 struct stat buf;
 char out[100];
 if(argc == 1 )
 {
  fprintf(stderr,"Using %s filename\n",argv[0]);
  return 0;
 }
 if(lstat(argv[1],&buf)<0)
 {
  fprintf(stderr,"stat error:%s\n",strerror(errno));
  return -1;
 }
 switch(buf.st_mode & S_IFMT)
 {
 case S_IFREG:
  printf("-");
  break;
 case S_IFDIR:
  printf("d");
  break;
 case S_IFCHR:
  printf("c");
  break;
 case S_IFBLK:
  printf("b");
  break;
 case S_IFIFO:
  printf("p");
  break;
 case S_IFLNK:
  printf("l");
  break;
 case S_IFSOCK:
  printf("s");
  break;
 }

 if(S_IRUSR & buf.st_mode)
  printf("r");
 else
  printf("-");
 if(S_IWUSR & buf.st_mode)
  printf("w");
 else
  printf("-");
 if(S_IXUSR & buf.st_mode)
  printf("x");
 else
  printf("-");

 if(S_IRGRP & buf.st_mode)
  printf("r");
 else
  printf("-");
 if(S_IWGRP & buf.st_mode)
  printf("w");
 else
  printf("-");
 if(S_IXGRP & buf.st_mode)
  printf("x");
 else
  printf("-");

 if(S_IROTH & buf.st_mode)
  printf("r");
 else
  printf("-");
 if(S_IWOTH & buf.st_mode)
  printf("w");
 else
  printf("-");
 if(S_IXOTH & buf.st_mode)
  printf("x");
 else
  printf("-");

 printf(" %d",buf.st_nlink);

 struct passwd *pw;
 pw = getpwuid(buf.st_uid);
 printf(" %s",pw->pw_name);

 struct group *gr;
 gr = getgrgid(buf.st_gid);
 printf(" %s",gr->gr_name);

 printf(" %ld",buf.st_size);

 struct tm *t;
 t = localtime(&buf.st_atime);
 printf(" %d-%d-%d %d:%d",t->tm_year+1900,
       t->tm_mon+1,
       t->tm_mday,
       t->tm_hour,
       t->tm_min);
    printf(" %s ",argv[1]);

 if(S_ISLNK(buf.st_mode))
 {
  printf(" -> ");
  if(readlink(argv[1],out,100)==-1)
  {

  }
  printf("%s",out);

 }
 printf("\n");
 return 0;
}