my %seen;
my @urls; 
my $root_url = 'http://url.example.com/'; 

$seen{$root_url}++;
push @urls, $root_url; 

while ($root_url = shift @urls) {  
    for my $url ( fetch_urls($root_url) ) { 
        $url =~ s/#.*$//;

        push @urls, $url unless $seen{$url};
        $seen{$url}++;
    }
}