Fast file compare using .NET HashAlgorithm.ComputeHash

I recently had a huge set of files in dozens of directories that I knew were somehow different from a backup. I needed to know which files were different (I just needed the file names). Normally I would use software like Beyond Compare, but this was not an option since the two sets of files were in two different remote locations without an option of copying 5G worth of data from one location to the other.

The solution I came up with, which worked out great, was to modify a set of code from my C# Recipe book that computed a hash of two files and compared the hash values. The new code accepts a file pattern, recursively finds all matching files (from the current directory), then writes out each files hash value and file name.

I executed the program on both systems, redirecting the output to a text file, then just had to compare the two text files. Note: Be careful that the FileHash program itself and any redirected output files are not included in the file pattern that you are searching on.

Example:

..\FileHash.exe *.* > ..\hashvalues.systemA.txt

using System;
using System.IO;
using System.Security.Cryptography;

namespace FileHash
{
   class Program
   {
      static void Main(string[] args)
      {
         new Program().Run(args);
      }

      private void Run(string[] args)
      {
         // Create the hashing object.
         string[] files = Directory.GetFiles(@".\", args[0], SearchOption.AllDirectories);

         foreach (string file in files)
         {
            using (HashAlgorithm hashAlg = HashAlgorithm.Create())
            {
               using (FileStream fs = new FileStream(file, FileMode.Open))
               {
                  // Calculate the hash for the files.
                  byte[] hashBytes = hashAlg.ComputeHash(fs);

                  // Compare the hashes.
                  Console.WriteLine(string.Format(
                     "{0} {1}",
                     BitConverter.ToString(hashBytes),
                     file));
               }
            }
         }
      }
   }
}