# take IP4 address string
my $IP_str = '192.0.2.4';

# convert the numbers to hex
my @IP4_a = map { sprintf("%02x", $_) } split(/\./,$IP_str);

# embed these hex numbers in the IPv6 template
my $R = sprintf("2002:%s%s:%s%s::/48", @IP4_a);

# output the result
die  "($R)";