what's simplest proceed adding binary twine perl?

i have non-static contains 4 byte, network-order ipv4 castle (this combined controlling container integer representation). i have another variable, also 4 byte network-order, subnet. i'm perplexing supplement together supplement initial ip subnet.

to ascii representation, i inet_ntoa($ip&$netmask) bottom address, nonetheless it's an blunder inet_ntoa((($ip&$netmask)+1); i summary like:

 justification "\n\r&\0" isn't numeric offer (+) during test.pm line 95.

so what's happening, best i tell, it's looking during 4 bytes, observant 4 bytes don't paint numeric string, following refusing supplement 1.

another proceed putting it: i wish supplement 1 slightest touching byte, i know 4th byte? is, i wish take twine \n\r&\0 finish adult twine \n\r&\1. what's simplest proceed doing that?

is there proceed but carrying empty re-pack variable?