sub check_tags_balance {
    my @tagstack;
    while(/<(\/)?([^>]+)>/g) {
        unless($1) { # opening tag
            push @tagstack, $2;
        } else {  # closing tag
            unless(@tagstack and $2 eq pop @tagstack) {
                print "Found an unbalanced closing tag $2\n";
                return;
            }
        }
    }
    if(@tagstack) {
        print "Missing closing tags for @tagstack\n";
    } else {
        print "Tags balanced.\n";
    }
}

$_ = "I assume <b>everything</b> is <i><b>ok</b></i>";
check_tags_balance();