#!/usr/bin/perl
use strict;
use warnings;
use CGI;
use CGI::Carp 'fatalsToBrowser';

my $template_dir = '/path/to/template_dir';

my $q=CGI->new();

if ( $q->param() ) {
    show_template();
}
else {
    show_form();
}

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

    open(TMPL,"$template_dir/$template") || die $!;
    my $content = join '',(<TMPL>);
    close(TMPL);

    $content =~ s/<TMPL[^>]*>//gs;

    print $q->header(),
          $content;

    exit(0);
}

sub show_form {
    print $q->header,
          $q->start_html,
          $q->start_form,
          'Template: ',
          $q->textfield('template'),
          $q->submit,
          $q->end_form,
          $q->end_html;

    exit(0);
}