...
my $flat_data =  
   [{data=>'A'} , {data=>'B'}, {data=>'C'}, {data=>'D'},{data=>'E'}];
my $columnized_data = columnize($flat_data, 3, "across");
my $tmpl_file = ...;
my $tmpl =  HTML::Template->new(
        filename          => $tmpl_file,
        loop_context_vars => 1
    ) or die "Creation of template object from $tmpl_file failed.";
$tmpl->param( {DATA_LOOP => $columnized_data});
print "Content-type: text/html\n\n", $tmpl->output();