#!/usr/bin/perl -w
use strict;

my $string = <<"EOT";
<title>stuff</title>
<br>Header</br>
<tr>
  <td>1</td>
  <td>2</td>
</tr>
<tr>
  <td>3</td>
  <td>4</td>
</tr>
<br>Trailing Info
EOT

my ($wanted) = $string =~ /(<tr>.*<\/tr>)/s;

print "$wanted\n";