That's interesting. As is often the case with Perl, things move (silently) on as new versions appear. I just re-ran a series of tests that I last performed shortly after IO layers were added.

Back then, on my system ':raw' was exactly equivalent to using binmode. It no longer is, nor is either the fastest option.

Using this:

#! perl -sl
use Time::HiRes qw[ time ];

our $LAYER //= ':raw';
our $B;

$s = time;
open (FILE, "<$LAYER", "junk.bin")
   or die "ERROR: Could not open $path.\n";

binmode FILE if $B;

$n=0;
while (1) {
   $eof = read (FILE, $header, 4);

   ($size, $code, $ftype) = unpack ("nCC", $header) ;
#   print join(':',$size, $code, $ftype, "\n");
   if ($size == 0) {
      print "Size is zero.  Exiting";
      last;
   }

   $size = $size - 4;
   if ($size > 0) {
      $eof = read (FILE, $data, $size);
   }
   $n += 4 + $size;
}
close FILE;
print $n;
printf "Took %.3f\n", time() - $s;
[download]

You can see (and interpret) the results for yourself:

On my system, I'll be using :perlio & binmode for fast binary access from now on. (Until it changes again:)

Perhaps even more indicative of the lag in the documentation is this:

C:\test>junk41 -LAYER=:crlf
Size is zero.  Exiting
50466132
Took 0.668

C:\test>junk41 -LAYER=:crlf -B
Size is zero.  Exiting
50466132
Took 0.283

C:\test>junk41 -LAYER=:crlf:raw
Size is zero.  Exiting
50466132
Took 0.815

C:\test>junk41 -LAYER=:crlf:raw -B
Size is zero.  Exiting
50466132
Took 0.845
[download]

If :raw popped all layers that were incompatible with binary reading, then :crlf:raw should be as fast as :crlf + binmode. But it ain't!

Thanks for the very informative benchmarks!