Walk a directory up or down, looking for a file or folder.

walk_directories.c

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <dirent.h>
#include <string.h>

/*
 *  A NON-CONSTANT VARIABLE
 *  THAT CAN BE SET BY THE FIND_UP() FUNCTION
 */
char found_path[1024];

/*
 *  Function PROTOTYPES.
 */
int find_up(char *path, char *target);
int find_down(char *path, char *target);

/*
 *  The MAIN entry point into the program.
 *  That is to say, this function runs first.
 *
 *  @return int Status code
 */
int main(void) {

  // What is the path?
  char path[100];
  path[0] = '\0';
  strcat(path, "./test");

  // What are we looking for?
  char target[100];
  target[0] = '\0';
  strcat(target, "foo.txt");

  // Can we find it?
  int success = find_up(path, target);

  if (success) {
    puts("We found it: ");
    puts(found_path);
  } else {
    puts("Not found");
  }

  // Exit cleanly.
  return 0;

}

/*
 *  Walk a directory tree up, looking for 
 *  a file/directory that matches the specified path.
 *
 *  @return int
 */
int find_up(char *path, char *target) {

  DIR *stream;
  struct dirent *item;

  // Open the directory.
  stream = opendir(path);
  if (stream != NULL) {

    // Check each item in the directory.
    while ((item = readdir(stream))) {

      // Ignore "." and ".." items.
      if (strcmp(item->d_name, ".") == 0 || strcmp(item->d_name, "..") == 0) {
        continue;
      }

      // Is this the item we're looking for?
      if (strcmp(item->d_name, target) == 0) {

        // Store the path as "found_path".
        found_path[0] = '\0';
        strcat(found_path, path);
        strcat(found_path, "/");
        strcat(found_path, target);
        return 1;

      }

    }

    // What's the path to the parent directory?
    char parent_directory[strlen(path) + 4];
    char full_path[1024];
    parent_directory[0] = '\0';
    strcat(parent_directory, path);
    strcat(parent_directory, "/../");

    // If there is a parent directory, check it.
    int success;
    realpath(parent_directory, full_path);
    if (strcmp(full_path, "/") == 0) {
      success = 0;
    } else {
      success = find_up(full_path, target);
    }

    // Close the stream and return the results.
    (void) closedir(stream);
    return success;

  } 

  // If we couldn't open the directory, let's print an error.
  else {
    return 0;
  }

}

/*
 *  Walk a directory tree down, looking for 
 *  a file/directory that matches the specified path.
 *
 *  @return int
 */
int find_down(char *path, char *target) {

  // We need to store our directory stream in a DIR object.
  DIR *stream;

  // We need to store items in the directory in a "dirent" struct.
  struct dirent *item;

  // We need to store info about files in a "stat" struct.
  struct stat info;

  // Open the current directory.
  stream = opendir(path);

  // Did we get a valid stream? Let's make sure the stream isn't NULL.
  if (stream != NULL) {

    // Read the stream, one item at a time.
    while ((item = readdir(stream))) {

      // Ignore "." and ".." items.
      if (strcmp(item->d_name, ".") == 0 || strcmp(item->d_name, "..") == 0) {
        continue;
      }

      // Is it the item we're looking for?
      if (strcmp(item->d_name, target) == 0) {
        return 1;
      }

      // If not, keep searching.
      else {

        // Generate a path for this file.
        char full_path[1024];
        full_path[0] = '\0';
        strcat(full_path, path);
        strcat(full_path, "/");
        strcat(full_path, item->d_name);

        // Can we get some info about the item?
        if (stat(full_path, &info) == 0) {

          // Is it a directory? If so, look in it.
          if (info.st_mode & S_IFDIR) {
            int success = find_down(full_path, target);

            // Did we find what we're looking for?
            if (success) {
              return 1;
            }

          }

        }

        // if we got no info, report the error.
        else {
          printf("Could not stat the file: %s", full_path);
        }

      }

    }

    // Be sure to close our stream.
    (void) closedir(stream);
    return 0;

  } 

  // If we couldn't open the directory, let's print an error.
  else {
    printf("Could not open the directory: %s", path);
    return 0;
  }

}