How to filter Directory.EnumerateFiles with multiple criteria?

string path = "C:\\";
var result = new List<string>();
string[] extensions = { ".mp3", ".wma", ".mp4", ".wav" };

foreach (string file in Directory.EnumerateFiles(path, "*.*", SearchOption.AllDirectories)
    .Where(s => extensions.Any(ext => ext == Path.GetExtension(s))))
{
    result.Add(file);
    Console.WriteLine(file);
}

I created some helper methods to solve this which I blogged about earlier this year.

One version takes a regex pattern \.mp3|\.mp4, and the other a string list and runs in parallel.

public static class MyDirectory
{   // Regex version
   public static IEnumerable<string> GetFiles(string path, 
                       string searchPatternExpression = "",
                       SearchOption searchOption = SearchOption.TopDirectoryOnly)
   {
      Regex reSearchPattern = new Regex(searchPatternExpression, RegexOptions.IgnoreCase);
      return Directory.EnumerateFiles(path, "*", searchOption)
                      .Where(file =>
                               reSearchPattern.IsMatch(Path.GetExtension(file)));
   }

   // Takes same patterns, and executes in parallel
   public static IEnumerable<string> GetFiles(string path, 
                       string[] searchPatterns, 
                       SearchOption searchOption = SearchOption.TopDirectoryOnly)
   {
      return searchPatterns.AsParallel()
             .SelectMany(searchPattern => 
                    Directory.EnumerateFiles(path, searchPattern, searchOption));
   }
}

The most elegant approach is probably:

var directory = new DirectoryInfo(path);
var masks = new[] { "*.mp3", "*.wav" };
var files = masks.SelectMany(directory.EnumerateFiles);

But it might not be the most efficient.

As I noted in a comment, while Mikael Svenson's helper methods are great little solutions, if you're ever trying to do something for a one-off project in a hurry again, consider the Linq extension .Union( ). This allows you to join together two enumerable sequences. In your case, the code would look like this:

List<string> result = Directory.EnumerateFiles(path,"*.mp3", SearchOption.AllDirectories)
.Union(Directory.EnumerateFiles(path, ".wma", SearchOption.AllDirectories)).ToList();

This creates and fills your result list all in one line.