use Encode qw( decode );

$s = "高";
print(length($s), "\n");  # 3

$s = decode('utf8', "高");
print(length($s), "\n");  # 1

$s = do { use utf8; "高" };
print(length($s), "\n");  # 1

##</code><code>##

use Encode qw( encode );

my $s = do { use utf8; "&#39640;" };
print(length($s), "\n");   # 1

open my $fh, '>:utf8', \$s2;
print $fh $s;
print(length($s2), "\n");  # 3

$s2 = encode('utf8', $s);
print(length($s2), "\n");  # 3

##</code><code>##

use strict;
use warnings;
use utf8;

use Encode qw( decode );

my $chars_src = "&#37319;&#26679;&#36895;&#29575;&#22826;&#39640;";
my $bytes_dst;

{
   open my $fh, '>:utf8', \$bytes_dst;
   print $fh $chars_src;
}

my $chars_dst = decode('utf8', $bytes_dst);

binmode(STDOUT, ':utf8');
print("$chars_src\n");
print("$chars_dst\n");

##</code><code>##

...

my $bytes_src = encode('utf8', $chars_src);

print("$bytes_src\n");
print("$bytes_dst\n");

##</code><code>##

...

binmode(STDOUT, ':utf8');
print("$chars_src\n");
binmode(STDOUT, ':bytes');
print("$bytes_dst\n");