http://www.perlmonks.org?node_id=326975


in reply to Case insensitive hash keys

Hash::Case::Preserve is what you want. 
use Hash::Case::Preserve;
tie my(%hash), 'Hash::Case::Preserve';
$hash{StraNGeKeY} = 3;
print keys %hash;         # StraNGeKeY
print $hash{strangekey};  # 3
print $hash{STRANGEKEY};  # 3

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See especially the note about first or last use case preservation.

In Section Seekers of Perl Wisdom