This will encode a complete domain name into Punycode (see RFC 3490).

Update: Corrected small mistake, 7bit ends at \x7F not \x8F...

use IDNA::Punycode;
use Net::IDN::Nameprep;
use warnings;
use strict;
our $ACE = 'xn--';

sub punycode {
    my $utf8name = shift;
    my @nameparts = split /[\x{002E}\x{3002}\x{FF0E}\x{FF61}]/, $utf8n
+ame;
    my $asciiname = '';
    foreach my $part (@nameparts) {
        if ($part =~ /[^\x00-\x7F]/) {
            eval {
                $part = nameprep($part);
            }; if (my $e = $@) {
                die "Preparing domain part '$part' of domain '$utf8nam
+e' failed with '$e'";
            }
        }
        if ($part =~ /([\x00-\x2C\x2E-\x2F\x3A-\x40\x5B-\x60\x7B-\x7F]
+)/) {
            die "Illegal character $1 in domain part '$part' of domain
+ '$utf8name' found";
        }
        if ($part =~ /^\x2D/ or $part =~ /\x2D$/) {
            die "Domain part '$part' of domain '$utf8name' may not sta
+rt or end with a hyphen";
        }
        if ($part =~ /[^\x00-\x7F]/) {
            if (substr($part, 0, length($ACE)) eq $ACE) {
                die "International domain part '$part' of domain '$utf
+8name' may not start with ACE";
            }
            eval {
                $part = encode_punycode($part);
            }; if (my $e = $@) {
                die "Converting domain part '$part' of domain '$utf8na
+me' failed with '$e'";
            }
            $part = $ACE . $part;
        }
        if (length($part) < 1 or length($part) > 63) {
            die "Domain part '$part' of domain '$utf8name' must be bet
+ween 1 and 63 characters long";
        }
    }
    $asciiname = join "\x{002E}", @nameparts;
    return $asciiname;
}

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In reply to Punycode by Beechbone

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