Seriously, this is better achieved using one of the HTML::Parser modules. For example take a look at HTML::TokeParser

use strict;
use warnings;
use HTML::TokeParser;
my $p = HTML::TokeParser->new("file.html") # your source file
     ||die "Cant open: $!";
my $depth=0;
while (my $token = $p->get_token) { 
   if (lc(${$token}[1]) eq "table"){
      $depth++ if (${$token}[0] eq "S");
      $depth-- if (${$token}[0] eq "E");
   print "$depth\n";
   }
}
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Try out the code above and see where it takes you