#!/usr/bin/perl --
package TieTest;
sub TIEHANDLE { return bless {}, shift }
sub OPEN      { open my $fh, $_[1], $_[2]; $_[0]->{fh} = $fh; }
sub READ      { warn "...tied read\n"; read $_[0]->{fh}, $_[1], $_[2], $_[3]; }
sub SEEK      { seek $_[0]->{fh}, $_[1], $_[2]; }

package main;

use strict;
use warnings;
use Digest::MD5;
use Digest::Perl::MD5;

my $filename = $ARGV[0] || __FILE__;

open FH_PLAIN, '<', $filename or die $!;

#open FH_TIED,  '<', $ARGV[1]; # try uncommenting this
tie(*FH_TIED, 'TieTest');
open FH_TIED, '<',  $filename or die $!;


open FH_EEP, '<',  $filename or die $!;
tie(*FH_EEP, 'TieTest');
open FH_EEP, '<',  $filename or die $!;



my %handles = (
    PLAIN => \*FH_PLAIN, 
    TIED => \*FH_TIED, 
    EEP => \*FH_EEP, 
    PEE => eval {
        my $pee; 
        tie $pee, 'TieTest'; 
        open $pee, '<', $filename or die $!;
        $pee;
    },
);
for my $title ( keys %handles ){

    my $fh = $handles{$title};
    for my $class (qw/Digest::Perl::MD5 Digest::MD5/) {

        my $sum = eval { $class->new->addfile($fh)->hexdigest } || $@;
        printf "%-7s%-19s%-32s\n", $title, $class, $sum;
        seek $fh, 0, 0;
    
    }

}

#~ use Devel::Peek qw/ Dump /; Dump( $_) for values %handles ; ## uninformative

__END__

$ perl perliotiehandle.pl
Odd number of elements in hash assignment at perliotiehandle.pl line 44.
...tied read
...tied read
EEP    Digest::Perl::MD5  623cf1cdac049dc6527cb0f28fc5aa76
EEP    Digest::MD5        623cf1cdac049dc6527cb0f28fc5aa76
PLAIN  Digest::Perl::MD5  623cf1cdac049dc6527cb0f28fc5aa76
PLAIN  Digest::MD5        623cf1cdac049dc6527cb0f28fc5aa76
...tied read
...tied read
TIED   Digest::Perl::MD5  623cf1cdac049dc6527cb0f28fc5aa76
TIED   Digest::MD5        No filehandle passed at perliotiehandle.pl line 56.

PEE    Digest::Perl::MD5  Digest::Perl::MD5 read failed: Bad file descriptor at C:/citrusperl/site/lib/Digest/Perl/MD5.pm line 164.

Can't use an undefined value as a symbol reference at perliotiehandle.pl line 58.