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";
   }
}