#!/usr/bin/perl 
 
use strict; 
use warnings; 
use Digest::MD5; 
 
my $file = $ARGV[0]; 
open (my $IN, "<$file") or die "can't open $file"; 
binmode $IN; 
 
# get a reference digest string. 
my $refhex = `md5sum $file`; 
chomp($refhex); 
print "md5sum:  $refhex\n"; 
 
my $md5obj = Digest::MD5->new; 
$md5obj->addfile($IN); 
 
# Get the digest hex string from Digest::MD5. 
my $hexdigest1 = $md5obj->hexdigest; 
print "hexdig1: $hexdigest1\n"; 
 
# Get the binary digest from Digest::MD5 
print "[calling Digest::MD5::digest]\n"; 
my $digest1 = $md5obj->digest; 
print "digest1: $digest1\n"; 
 
 
seek $IN, 0,0; 
$md5obj->reset; 
$md5obj->addfile($IN); 
 
my $hexdigest2 = $md5obj->hexdigest; 
print "hexdig2: $hexdigest2\n"; 
 
# but the digest method seems to return the same value each time. 
my $digest2 = $md5obj->digest; 
print "digest2: $digest2\n"; 
print "[internal digest is stable call to call]\n" if $digest1 eq $digest2;