note anazawa Thanks for your suggestion. [mod://Tie::Hash::Regex] interests me. I confirmed your regex passed the following test: <c> # tie_hash_regex.t use strict; use Tie::Hash::Regex; use Test::Simple tests => 8; my @keys = qw( content-length content_length -content-length -content_length Content-Length Content_Length -Content-Length -Content_Length ); for my $key ( @keys ) { my %hash; tie %hash, 'Tie::Hash::Regex'; $hash{ $key } = 1234; ok $hash{'^(?i:-?content[_-]length)$'} == 1234; } </c> 954718 954730