Was your test string "100" by chance? :) 31 = hex 1, 30 = hex 0. You're getting the right output, it just doesn't look like what you expected.

Here's an example you can try:

my $text = 'WHY HELLO THERE!';

# split into array of individual characters
my @characters = split(//,$text);

# transform each one individually into uppercase hex
foreach my $char (@characters) {
    $char = uc(unpack "H*", $char);
}

# print in quotes to demonstrate separation between array elements
print "@characters";
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You can cross-check the results with http://www.lookuptables.com.