use utf8;
use open ':std', ':utf8';
use feature 'unicode_strings';

...

for my $file ( @files ) {

    open my $FH, '<', $file or die "Cannot open '$file' because: $!";
    my $size = read $FH, my $data, -s $FH or die "Cannot read from '$file' because: $!";
    $size == length( $data ) or die "Error reading from '$file'\n";
    close $FH;

...

##</code><code>##

perl check-size.pl ./data.mixed
$VAR1 = {
          '-s' => 282,
          'length' => 226,
          'read' => 226,
          'tr' => 226
        };

##</code><code>##


# Usage: perl5.36.3 check-size.pl ./data-mixed

use v5.32;
use warnings;
use warnings qw[ FATAL utf8 ];
use open qw[ :encoding(UTF-8) :std ];

use Data::Dumper;
local $Data::Dumper::Sortkeys = 1;

my $data = $ARGV[0]
   or die qq[Give a file to count sizes of different kinds.\n];

my %stat = ( q/-s/ => -s $data );

open( my $fh, q/</, $data )
   or die qq/Cannot open $data to read: $!/;

my $string;
$stat{q/read/} = read( $fh, $string, $stat{q/-s/} )
                  or die qq/read from \$fh failed: $!/;

close( $fh )
   or die qq/Could not close $data: $!/;

$stat{q/length/} = length( $string );
$stat{q/tr/} = $string =~ tr///c;

print( Dumper( \%stat ) );

##</code><code>##

Tj9EOzg3aHosYU9NbDtrLmZQcUt4M3l3dl8hR1IyLEpvNHJCMVdRVTVUaVpkQ2pMSVM2XzlFY1hl
dUhuIXRtLlkwRlZzZ3A/QS0tYk4/RDs4N2h6LGFPTWw7ay5mUHFLeDN5dwpGNVRuRUtsOGrwn5it
MGhQTzHvuI/ig6Mxc0lvQUx24KWsUyAgcHo2M0NiWuClr/CfpK9XVjJrR23wn5iSUnU3VWNI4KWv
YXFneDR34KWnWPCfmI85ZDHvuI/ig6Pwn6SjZk5Z8J+YrXlNSuClpmXgpajgpaZp4KWqdFFyREJG
NVRuRUtsOGrwn5itMGhQTzHvuI/ig6Mxc0lvQUx24KWsUyAgcHo2M0NiWuClr/CfpK9XVjIK