C# extension method for walking the file system.

FileSystemExtensions.cs

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text.RegularExpressions;

namespace FileSystemHelper
{
	public static class FileSystemExtensions
	{
		/// <summary>
		/// Walks the file system, similar to Python's os.walk function.
		/// </summary>
		/// <param name="root">The root directory where the walking starts.</param>
		/// <param name="handler">A function that will be invoked for each directory.</param>
		/// <param name="searchRegex">A regular expression used to filter the list of files.  If a value is provided, <paramref name="searchPattern"/> will be ignored.</param>
		/// <param name="searchPattern">The search pattern used to limit the files and directories.</param>
		/// <param name="searchOption">Option to use when searching files and directories.</param>
		/// <param name="searchPatternAppliesToDirectories">Determines if the <paramref name="searchPattern"/> and <paramref name="searchOption"/> are used on only the files or both the files and directories.</param>
		/// <param name="ignoredFileRegex">Any file with a file name matching this <see cref="Regex"/> will be skipped.  Only the file name (and not the full path) is checked against this <see cref="Regex"/>.</param>
		/// <example><code>static void AddToFileList(DirectoryInfo root, DirectoryInfo[] directories, FileInfo[] files)
		/// {
		///     foreach (var file in files)
		///     {
		///         Console.WriteLine(file.FullName);
		///     }
		/// }
		/// 
		/// static void Main(string[] args)
		/// {
		///     var root = new DirectoryInfo(@"C:\temp");
		///     root.Walk(AddToFileList);
		/// }</code></example>
		public static void Walk(this DirectoryInfo root, Action<DirectoryInfo, IEnumerable<DirectoryInfo>, IEnumerable<FileInfo>> handler, Regex searchRegex = null,
			string searchPattern = null, SearchOption searchOption = SearchOption.AllDirectories, bool searchPatternAppliesToDirectories = false, Regex ignoredFileRegex = null)
		{
			if (root == null)
			{
				throw new ArgumentNullException("directory");
			}
			IEnumerable<DirectoryInfo> directories = !searchPatternAppliesToDirectories || (searchRegex != null && searchPattern == null) ? root.GetDirectories() 
				: searchRegex != null ? root.GetDirectories().Where(d => searchRegex.IsMatch(d.Name))
				: root.GetDirectories(searchPattern, searchOption);
			IEnumerable<FileInfo> files = 
				searchRegex == null && searchPattern == null 
				? root.GetFiles() : searchRegex != null ? root.GetFiles().Where(f => searchRegex.IsMatch(f.Name)) 
				: root.GetFiles(searchPattern, searchOption);

			// Remove the ignored files from the list.
			if (ignoredFileRegex != null)
			{
				files = files.Where(f => !ignoredFileRegex.IsMatch(f.Name));
			}

			handler.Invoke(root, directories, files);

			foreach (var d in directories)
			{
				d.Walk(handler, searchRegex, searchPattern, searchOption, searchPatternAppliesToDirectories, ignoredFileRegex);
			}
		}
	}
}