Yeah, I thought about a loop, but I was afraid it would obscure what the code is doing - I'd certainly switch to a loop if doing more than 3 or four repetitions, and if I were doing more than two statements per offset, but at less than that the loop syntax just clutters things up. (I realize that this is a matter of personal taste, and I might change my answer depending on my mood).

Good point about using length - again, I think my way is clearer, but I'm not sure whether that's the use of length or the ->. (which you could drop)

By the way, I would have written the first line of your loop as:

    $triplets{$_} = [unpack("x$_ (a3)*", $line)];
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But that's only because I don't like using @{$unusedvarref} to auto-vivify.