The solution is

just to count the bytes, if that's really what you want.

my $bytecount = (stat $file)[7];
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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 $FH or die "Cannot read from '$f
+ile' because: $!";
    $size == length( $data ) or die "Error reading from '$file'\n";
    close $FH;

...
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This will always result (if $data contains Unicode characters) in dieing with the message "Error reading from '$file'\n".

Unlike in OP, here with perl v5.36.3/FreeBSD 14 (with the code below) the numbers from length & read functions match (226); do not obviously match the size in byte (282). Is it matter of the perl version; and/or, is it how one is holding the encoding layer?

perl check-size.pl ./data.mixed
$VAR1 = {
          '-s' => 282,
          'length' => 226,
          'read' => 226,
          'tr' => 226
        };
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Base64-encoded generated data -- if anyone would rather have it than run above "make-data.pl" -- with SHA256 sum of a1e81919b72403bd3c9d95979dae8d928354cf64de8d999bcad00aec4298cf76 (decoded value has the sum of 02bec20353169b58ea51558fa7d6c4316bd13f5e4a3d976484e8ed7700935962) ...

Update: *ugh*...

• The Base64-encoded sample has different checksum after downloaded from here (than on the machine where it was posted from). The checksum for the decoded value is still the same as posted.
• Removed the program that produced the sample Unicode output as I had apparently changed it (during the (re)editing of this post) such that it produced different output than the above mentioned Bas64-encoded text (for which the size result is shown).

Update

That's kind of a "creative" way to slurp a whole file...

Anyway to answer the title's question

• Counting bytes in a Unicode document

While I doubt that's what you want, others might stumble over this thread asking exactly this.

Remove temporarily the utf8 flag and use length then.

You can just use bytes::length (after use bytes ();).


--
A math joke: r = | |csc(θ)|+|sec(θ)| |-| |csc(θ)|-|sec(θ)| |

Indeed,

The bytes pragma is in core and

require bytes; 
bytes::length($data);
 

does the job.

Cheers Rolf
_{(addicted to the Perl Programming Language :)
see Wikisyntax for the Monastery}

Replacing

open my $FH, '<', $file
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open my $FH, '<:raw', $file
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will do the trick, but the aforementioned stat solution is much more efficient.

> the aforementioned stat solution is much more efficient

I suppose the -s in the OP's code does exactly the same.

Cheers Rolf
_{(addicted to the Perl Programming Language :)
see Wikisyntax for the Monastery}

Yes, -s is just another way to stat.

For example, one could write the following:

defined( my $s = -s $qfn )
   or die( "Can't stat `$qfn`: $!\n" );

... $s ...
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But it could also be written as follows:

stat( $qfn )
   or die( "Can't stat `$qfn`: $!\n" );

... -s _ ...
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or

defined( my $s = ( stat( $qfn ) )[ 7 ] )
   or die( "Can't stat `$qfn`: $!\n" );

... $s ...
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Every time I see people using UTF-8 I think they massively over complicate it. All you usually need to do is use decode() and encode() on your scalars.

Example: read the bytes raw, then get the number of Unicode characters by decoding the utf-8 into a scalar of unicode characters:

use Encode;
open my $FH, '<:raw', $utf8file;
read $FH, my $data, -s $FH;
print length decode("utf8",$data);
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What are you trying to accomplish with your $size == length( $data ) check?

read is supposed to be returning a count of characters returned, which should always match the length. From your description you are getting a byte count instead?

What perl version are you using?

Are you using CORE::read or are you doing something to override it?