my $address = "127.0.0.1";

  # from decimal to hex:
my ($a,$b,$c,$d) = $address =~ /(\d+)\.(\d+)\.(\d+)\.(\d+)/;
my $hex_addr = sprintf "%02x.%02x.%02x.%02x", $a, $b, $c, $d;

print "[$hex_addr]\n";  #prints "[7f.00.00.01]";

  # from hex to decimal:
my ($a, $b, $c, $d) = $hex_addr =~ /(\w+)\.(\w+)\.(\w+)\.(\w+)/;
my $addr = hex($a). "." . hex($b) . "." . hex($c) . "." . hex($d);

print "[$addr]\n";      #prints "[127.0.0.1]"