Good suggestion. I think it's easier not to duplicate HTML::Template's parsing if you already have it on hand though:

sub show_template {
    my $t_file = $q->param('template');

    require HTML::Template;
    my $t = HTML::Template->new_file($t_file);
    # and don't fill in any values
    print $q->header(), $t->output;

    exit(0);
}
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