multicat.cs

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

// usage: multicat.exe - logfile1.log logfile2.log
// '-' means STDOUT
class Program
{
  public static void Main(string[] args)
  {
    try
    {
      foreach(var path in args)
      {
        if (path == "-")
          writers[path] = Console.Out;
        else
          writers[path] = new StreamWriter(path);
      }

      string input;
      while ((input = Console.ReadLine()) != null)
      {
        foreach (var writer in writers.Values)
        {
          writer.WriteLine(input);
        }
      }
    }
    finally
    {
      foreach (var kvp in writers)
      {
        if (kvp.Key != "-")
          kvp.Value.Dispose();
      }
    }
  }

  static readonly IDictionary<string, TextWriter> writers = new SortedDictionary<string, TextWriter>();
}