#!/usr/bin/perl

use strict;
use warnings;

my $line = <DATA>;

# First capture the row:
if ($line =~ /<tr>(BBBBB.*?)<\/tr>/) {

# Then capture the cells:
  my @data = $1 =~ /<td>([^<]+)<\/td>/g;
  print $_ for @data;
}

__DATA__
<h3>AAA 28/07/2018</h3><table><tr><td>1351</td><td>990</td><td>783</td><td>523</td></tr></table><h3><table><tr>BBBBB 01/08/2018</h3><td>236</td><td>002</td><td>121</td><td>266</td></tr></table><h3>KK K P 25/07/2018</h3><table><tr><td>200</td><td>3345</td><td>667</td><td>137</td></tr></table>