use strict;
use warnings;

my %hash = ( 
             "a" => "abc",
             "d" => "def",
             "g" => "ghi"
           );

my $text = "%a% %d% %g%";

print "Before: $text\n";
print "After : ", fillTemplate($text, \%hash), "\n";

sub fillTemplate {
  my ($text, $hash) = @_;
  $text =~ s/%(\w)%/$hash->{$1}/g;
  return $text;
}

##</code><code>##

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];
    } 
}