I didn't quite understood what you're trying to do, as this didn't help. The error is the way you empty the arrays/hashes (undef), so instead of

undef %hash,@index,@a2;
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maybe you should try:

undef %hash;
undef @index;
undef @a2;
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which will make perl forget about those variables, or

%hash=();
@index=();
@a2=();
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which will make perl empty the contents of those variables