prelの内部文字列がわかってなくて死んだ

encode.pl

use 5.016;
use utf8;
use Encode;
use Encode::Guess qw/utf8 euc-jp shiftjis/;

my $str = 'あああ';

say guess_encoding($str)->name;
# => utf8

say $str eq encode_utf8($str);
# => ''

say $str eq encode_utf8(encode_utf8($str));
# => ''

say encode_utf8($str) eq encode_utf8(encode_utf8($str));
# => ''

encode.rb

# coding: utf-8
# ↑ (ruby2.0以降であればdefault encodingはutf8なので不要)

str = "あああ"

p str.encoding
# => #<Encoding:UTF-8>

p str == str.encode("UTF-8")
# => true

p str == str.encode("UTF-8").encode("UTF-8")
# => true