Any idea concerning the use of 'eq' operator?

ikegami has already given you the answer to that. Your line

my @temp = $info{$humangi};
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assigns a single scalar value to element zero only of the @temp array and no other element is initialised, but your line

my ($source, $position, $sink) = split(/(\d+)(\w)/, $Variant);
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assigns the value of 82 to $position using your example of "P82L" in $Variant. Your comparison

if ( $temp[$position] eq $source) {
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attempts to access element 82 of @temp which does not exist, hence the warning.

I hope this clarifies things for you.