if (exists $db{$url}) {
my $value = $db{$url};

$value++;
$db{$url} = $value;

print "Location: $url\n\n";
}
else {
$db{$url} = 1;
print "Location: $url\n\n";
}
[download]

Should be replaced by:

$db{ $url } ++;
print "Location: $url\n\n";
[download]

in order to improve readability. The $hash{ 'key' } ++; idiom is quite common for incrementing the value of a hash key.

-- am