linux下ls命令（支持-R參数）的c语言实现：

#include <stdio.h>
#include <sys/types.h>
#include <dirent.h>
#include <sys/stat.h>
#include <pwd.h>
#include <grp.h>
#include <string.h>

void do_ls(char *);
void do_stat(char *,char *);
void show_file_info(char *,struct stat *,char *);
void mode_to_letters(int ,char []);
char * uid_to_name(uid_t);
char * gid_to_name(gid_t);
int recursive = 0;

int main(int argc,char * argv[])
{
  int i;
  for(i = 1;i < argc;i++)
  {
    if(strcmp(argv[i],"-R") == 0)
    {
      recursive = 1;
      break;
    }
  }
  if(argc == 1 && recursive == 0)
    do_ls(".");
  else if(argc == 2 && recursive == 1)
    do_ls(".");
  else
  {
    int index = 1;
    while(argc > 1)
    {
      if(strcmp(argv[index],"-R") != 0)
        do_ls(argv[index]);
      index++;
      argc--;
    }
  }
  return 0;
}

void do_ls(char * path)
{
  DIR * dir;
  struct dirent * direntp;
  if((dir = opendir(path)) != NULL)
  {
    while((direntp = readdir(dir)) != NULL)
    {
      char absolute_pathname[255];
      strcpy(absolute_pathname,path);
      strcat(absolute_pathname,"/");
      strcat(absolute_pathname,direntp->d_name);
      printf("%s\n",absolute_pathname);
      do_stat(absolute_pathname,direntp->d_name);
    }
    closedir(dir);
  }
  else
    fprintf(stderr,"can't open %s",path);
}

void do_stat(char * absolute_filename,char * filename)
{
  struct stat  s;
  if(lstat(absolute_filename,&s) == -1)
    perror(absolute_filename);
  else
    show_file_info(absolute_filename,&s,filename);
}

void show_file_info(char * absolute_filename,struct stat * info,char * filename)
{
  char mode[11];
  mode_to_letters(info->st_mode,mode);
  printf("%s ",mode);
  printf("%d ",info->st_nlink);
  printf("%s ",uid_to_name(info->st_uid));
  printf("%s ",gid_to_name(info->st_gid));
  printf("%d ",info->st_size);
  printf("%.12s ",4+ctime(&info->st_mtime));
  printf("\n");
  if(recursive == 1)
  {
    if(S_ISDIR(info->st_mode) && strcmp(filename,".") != 0 && strcmp(filename,"..") != 0)
      do_ls(absolute_filename);
  }
}

void mode_to_letters(int mode,char * c_mode)
{
  strcpy(c_mode,"----------");

  if(S_ISDIR(mode))
    c_mode[0] = 'd';
  if(S_ISCHR(mode))
    c_mode[0] = 'c';
  if(S_ISBLK(mode))
    c_mode[0] = 'b';

  if(mode & S_IRUSR)
    c_mode[1] = 'r';
  if(mode & S_IWUSR)
    c_mode[2] = 'w';
  if(mode & S_IXUSR)
    c_mode[3] = 'x';

  if(mode & S_IRGRP)
                c_mode[4] = 'r';
        if(mode & S_IWGRP)
                c_mode[5] = 'w';
        if(mode & S_IXGRP)
                c_mode[6] = 'x';

  if(mode & S_IROTH)
                c_mode[7] = 'r';
        if(mode & S_IWOTH)
                c_mode[8] = 'w';
        if(mode & S_IXOTH)
                c_mode[9] = 'x';

  if(mode & S_ISUID)
    c_mode[3] = 's';
  if(mode & S_ISGID)
    c_mode[6] = 's';
  if(mode & S_ISVTX)
    c_mode[9] = 's';
}

char * uid_to_name(uid_t uid)
{
  struct passwd * passwd_pointer;
  passwd_pointer = getpwuid(uid);
  return passwd_pointer->pw_name;
}

char * gid_to_name(gid_t gid)
{

  struct group * group_pointer;
  static char numstr[10];
  if((group_pointer = getgrgid(gid)) == NULL)
  {
    sprintf(numstr,"%d",gid);
    return numstr;
  }
  return group_pointer->gr_name;
}