Or you could do something like this:

use strict;
use Net::IP;
my $net = new Net::IP("10.4.5.0/24");
my $host = new Net::IP("10.4.5.1");
print "yes\n" if ($net->overlaps($host) == $Net::IP::IP_B_IN_A_OVERLAP
+);
[download]

(The manual implies that qualifying IP_B_IN_A_OVERLAP is not necessary, but it seems to be).

HTH, --traveler