# file test.pl

use HTML::Template;
use strict;
use warnings;

my $template = HTML::Template->new(filename => 'test.tmpl');

# params
$template->param(tag1 => '<tag1_test_value>');
$template->param(tag2 => '<tag2_test_value>');

print $template->output();

# file test.tmpl

<root>
    <tag1><TMPL_VAR ESCAPE=HTML tag1></tag1>
    <tag2><TMPL_VAR ESCAPE=HTML tag2></tag2>
</root>

# output

<root>
    <tag1>&lt;tag1_test_value&gt;</tag1>
    <tag2>&lt;tag2_test_value&gt;</tag2>
</root>