#! /usr/bin/perl

use strict;
use warnings;
use Text::Template;
use List::MoreUtils qw( natatime );

my %cmd_data = ( ... );

our $max_sf_cols = 5;
my $template = Text::Template->new( TYPE => 'FILEHANDLE', SOURCE => \*DATA )
  or die "Couldn't construct template: $Text::Template::ERROR";

for my $cmd ( sort keys %cmd_data ) {

  local our $opcode = $cmd_data{$cmd}{opcode};

  my @sf_names;
  push @sf_names, $_->{subfield_name}
    for @{ $cmd_data{$cmd}{subfields} };
  @sf_names = qw( none )
    if not @sf_names;

  my $it = natatime $max_sf_cols, @sf_names;
  print $template->fill_in()
    while local our @sf_cols = $it->();

}

__DATA__
<p>
  <table border="1">
    <thead>
      <tr>
        <th>opcode</th>
        <th colspan="{ $max_sf_cols }" align="center">subfield(s)</th>
      </tr>
    </thead>
    <tbody>
      <tr>
        <td>{ $opcode }</td>
        { $OUT .= "<td>$_</td>" for @sf_cols }
      </tr>
    </tbody>
  </table>
</p>