Perl 5.8 with PerlIO gives a neat encapsulation of md5 digests with PerlIO::via::MD5:

use PerlIO::via::MD5;
my ($string, $digest) = 'foobarbaz';
{
    open my $fh, '<:via(MD5)', \$string;
    $digest = <$fh>;
}
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That is obviously more useful for getting digests of files.

After Compline,
Zaxo