This simplest solution is LWP::Simple

use LWP::Simple;
my $url="http://cpan.org";
if (! head($url)) {
  die "The Server is DOWN!!!!" 
}
[download]

an alternative is using a get:

if (! get($url)) {
[download]

but that would fetch the content of the page. A head call uses the least resources, just telling you weather the machine is responding to that url.