C# Recurse Directories using Directory.GetFiles and search pattern

Question

I want to find all excel files within a directory structure using recursion. The problem is, the search pattern used in Directory.GetFiles only allows a single extension at a t

Answer 1

In .NET every version there is SearchOption.TopDirectoryOnly and SearchOption.AllDirectories

In .NET 4 you could very efficiently do e.g.:

        var regex = new Regex(@"\d+", RegexOptions.Compiled);

        var files = new DirectoryInfo(topdir)

            .EnumerateFiles("*.*", SearchOption.AllDirectories)

            .Where(fi => regex.IsMatch(fi.Name));

(This example filters for files having two digits in the name)

To emulate this, write a recursive enumerator method (yield return) to return all files, and filter the result like so:

 IEnumerable Recurse(string topdir)
 { 
      // for each GetFiles() array element
      //      if is_not_dir yield return
      //      else Recurse(subdir)          
 }

 var filtered = Recurse.Where(fi => regex.IsMatch(fi.Name));

HTH