my ($lastMod) = (head($url))[2];

##</code><code>##

if (my (undef,undef,$lastMod) = head($url)) {
   # success
   if (!defined $lastMod) {
      # but alas no mod time
   }
}

##</code><code>##

my $gotHead = (my (undef,undef,$lastMod) = head($url));