Small correction: 
my $file = "/file/to/hash";
my $md5 = Digest::MD5->new();

open(MD5, $file) || die "Unable to open file: $!\n";
binmode(MD5);

$md5->addfile(*MD5);
$md5->add("seekrit passwerd"); # tee hee

my $digest = $md5->digest;

[download]
Your original code will not work with the latest Digest::MD5, producing the error "Not a valid filehandle." I know this because I'm currently writing a utility script that uses MD5 to verify downloaded files (for the Slackware distrib, actually) and I tried it your way to no avail. =)

'kaboo

In reply to (correction) Re (5): Using MD5 and the theory behind it by mwp
in thread Using MD5 and the theory behind it by r.joseph

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