$a="<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";
print $a if $a=~s#\A.*?(<tr>.*<\/tr>).*?\Z#$1#smi;