davorg++

Concerning the usage of $", one could augment your solution by doing

my @file = <>;
$" = '#';
print "#@file";
#     ^^^
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but that just adds obscurity to an already obscure solution. So I agree with your assessment of the homework-giver.

On a funny sidenote, something like the following also uses $" :)

$" = '#';
print $", $_ while <>;
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