use strict;
use warnings;
use feature 'say';
use Encode qw/ _utf8_off _utf8_on is_utf8 /;
use utf8;
use Devel::Peek;

my $s1 = ' ';       # a space (anything)
_utf8_on( $s1 );    # or assign not-ascii above, instead
my $s2 = $s1;

open my $fh, '<', 'data.bin';
binmode $fh;
sysread $fh, $s1, 1;
Dump $s1;
seek $fh, 0, 0;
$s2 = do { local $/; <$fh> };
Dump $s2;