open(FILE, "<$template") or die "Template : Couldn't open $template : $!\n";
  while (<FILE>) { $HTML .= $_ }
close(FILE);

while ($HTML =~ /<!-- fillin\((.+?)\) -->/) {
  my $command_output = &{$templateCall->{$1}}; # a subroutine call
  $HTML =~ s/<!-- fillin\(.+?\) -->/$command_output/;
}