The problem is that you're trying to use the 'fat comma' (=>) to assign to the hash, where in actual fact you just want the plain assignment operator e.g

$hash_codes{$2} = $5;
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The 'fat comma' behaves just like the normal comma operator but stringifies its left-hand argument and if its left-hand argument is a bareword it is exempt from strict. See. the perlop manpage for more information on the assignment and 'fat comma' operators.
HTH

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broquaint