using System;
using System.Collections;
using System.Text.RegularExpressions;

class test {

    static Hashtable hash = new Hashtable();

    static void Main () {

        hash.Add("a", "abc");
        hash.Add("d", "def");
        hash.Add("g", "ghi");

        string text = "%a% %d% %g%";
        
        Console.WriteLine( "Before: {0}", text ); 
        Console.WriteLine( "After : {0}", fillTemplate( text ) );

    }

    static string fillTemplate ( string text ) {
        return Regex.Replace( text, 
                              @"%(?<templ>\w)%", 
                              new MatchEvaluator( hashLookup ) );
    }

    static string hashLookup ( Match m ) {
        return (string)hash[m.Groups["templ"].Value];
    } 
}