A small file utility class for Unity. Transform an absolute path into an Assets folder relative path, and get a list of all Resources directories in the project.

FileUtility.cs

using UnityEngine;
using System.Collections;
using System.Collections.Generic;
using System.IO;

public class FileUtility {
  
	/// <summary>
	/// Determine whether a given path is a directory.
	/// </summary>
	public static bool PathIsDirectory (string absolutePath)
	{
		FileAttributes attr = File.GetAttributes(absolutePath);
		if ((attr & FileAttributes.Directory) == FileAttributes.Directory)
			return true;
		else
			return false;
	}


	/// <summary>
	/// Given an absolute path, return a path rooted at the Assets folder.
	/// </summary>
	/// <remarks>
	/// Asset relative paths can only be used in the editor. They will break in builds.
	/// </remarks>
	/// <example>
	/// /Folder/UnityProject/Assets/resources/music returns Assets/resources/music
	/// </example>
	public static string AssetsRelativePath (string absolutePath)
	{
		if (absolutePath.StartsWith(Application.dataPath)) {
			return "Assets" + absolutePath.Substring(Application.dataPath.Length);
		}
		else {
			throw new System.ArgumentException("Full path does not contain the current project's Assets folder", "absolutePath");
		}
	}

	
	/// <summary>
	/// Get all available Resources directory paths within the current project.
	/// </summary>
	public static string[] GetResourcesDirectories ()
	{
		List<string> result = new List<string>();
		Stack<string> stack = new Stack<string>();
		// Add the root directory to the stack
		stack.Push(Application.dataPath);
		// While we have directories to process...
		while (stack.Count > 0) {
			// Grab a directory off the stack
			string currentDir = stack.Pop();
			try {
				foreach (string dir in Directory.GetDirectories(currentDir)) {
					if (Path.GetFileName(dir).Equals("Resources")) {
						// If one of the found directories is a Resources dir, add it to the result
						result.Add(dir);
					}
					// Add directories at the current level into the stack
					stack.Push(dir);
				}
			}
			catch {
				Debug.LogError("Directory " + currentDir + " couldn't be read from.");
			}
		}
		return result.ToArray();
	}
}