#!/usr/bin/perl --
use strict;
use warnings;

use Net::CIDR qw/ cidr2octets /;

while(<STDIN>){
    s{\s+$}{}; ## trim
    print "$_\n" for cidr2octets( $_ );
}
__END__
$ echo dead::beef::/46 | perl cidr2octets.pl
dead:beef:0000
dead:beef:0001
dead:beef:0002
dead:beef:0003