my $text =  'this is my text with a <%VAR%> to interpolate';
  my $vars = { 'VAR' => 'value taken from a data structure' };
  $_ = $text;
  while ( /<%(.+?)%>/g)
  {
    #print "$1\n";
    if (!defined $vars->{$1} )
    {
      $vars->{$1}  = 'undefined';
      $vars->{MESSAGE} .= "$1 undefined <br />\n"; ## keep a log of missing variables
    }
  }
  $text =~ s/<%(.+?)%>/$vars->{$1}/g || warn("unable to substitute $1");
  print qq{$text\n};