[redhead]

First of all, I didn't wanted to get into this, since it is OS specific..
I started out by telling you which functions to look up and read on, since they are implemented differently on every OS.

Anyway I've found a solution which is quite ANSI C complient..

#include <stdio.h>
#include <dirent.h>
#include <string.h>


int found_state(char* name, char* state, int offset);

int main(int argc, char* argv[])
{
  DIR* dir_pointer;
  struct dirent* directory;
  int len, found = 0;
  if(argc < 2)
    {
      printf("Usage: %s <state> [dir]\n\n", argv[0]);
      printf("\tIn order to search for every instace of .doc files\n");
      printf("\tin the current directory use:\n");
      printf("\t\t%s .doc\n", argv[0]);
      printf("\tIf it should be searched for in your /usr/lib dir use:\n");
      printf("\t\t%s .doc /usr/lib\n", argv[0]);
      return -1;
    }
   len = strlen(argv[1]);
   if(argc == 2)
     dir_pointer = opendir(".");
   else
     dir_pointer = opendir(argv[2]);
   if(!dir_pointer)
     {
       printf("Error reading from directory\n");
       return -1;
     }
   printf("Found files:\n");
   for (directory = readdir(dir_pointer);
        directory != NULL;
        directory = readdir(dir_pointer))
     {
       if(found_state(directory->d_name,
                       argv[1],
                       strlen(directory->d_name) - len))
         {
           found = 1;
           printf("%s\n", directory->d_name);
         }
     }
   if(!found)
     printf("No files found to match %s\n", argv[1]);
   closedir(dir_pointer);
  return 0;
}


int found_state(char* name, char* state, int offset)
{
  int count;
  if(offset < 1)
    return 0;
  for(count = 0;
      name[offset + count] != '\0'
        && state[count] != '\0'
        && name[offset + count] == state[count]; count++)
    /* just compare */;
  if(name[offset + count] == '\0' && state[count] == '\0')
    return 1;
  return 0;
}

Now the found_state() function can be altered, infact the entire program can be altered..
But this is the basic directory/algorithem for achieving such things.