Bare-bones Grok implementation in C#, translated from http://stackoverflow.com/a/23078970/28381

Grok.cs

            var Types = new Dictionary<string, string>
            {
                {"WORD", @"\w+"},
                {"NUMBER", @"\d+"},
            };

            var grok = new Regex(@"%{(\w+):(\w+)}");
            MatchEvaluator e = match => string.Format("(?<{0}>{1})", match.Groups[2].Value, Types[match.Groups[1].Value]);
            var regex = new Regex(grok.Replace("%{WORD:method} %{NUMBER:bytes} %{NUMBER:duration}", e));

            var matchCollection = regex.Match("hello 123 456");

            Console.WriteLine("Method: {0} Bytes: {1}, Duration: {2}",
                matchCollection.Groups["method"].Value,
                matchCollection.Groups["bytes"].Value,
                matchCollection.Groups["duration"].Value);