Fellow monks

I have a scalar which contains a stream of ASCII representation of binary data (one nibble = one ASCII char). If there are any bytes that are not defined, the ASCII representation of those bytes within the stream is '??'. There can be gaps within this stream and in general, I do not know the size of this stream up front. I need to get the byte address of the last defined byte within this stream. In the following example, that would be 4. While I can do something C-like, it just seems to me that there should be a much more Perl-ish way to do the same. Any ideas?

use warnings;
use strict;

# remember that a byte consists of 2 nibbles and each nibble can be re
+presented as an ASCII character within the stream.
my $stream = '0123??6789??????';
my $lastValidByteIndex;
for my $byteIndex (0 .. length($stream)/2-1) {
    my $byte = substr($stream, $byteIndex*2, 2);
    $lastValidByteIndex = $byteIndex unless $byte eq '??';
}
if (defined($lastValidByteIndex)) {
    print "last valid byte is at index $lastValidByteIndex\n";
} else {
    print "There is no valid data in the stream\n";
}

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In reply to finding the last occurence of substring in string by gri6507

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