You can lowercase the keys of the hash, but you can store the original string as the value if you need it later:

#!/usr/bin/perl
use warnings;
use strict;

my @castaways = qw( john Jane LUKE );
my @list_1 = qw( not John JANE luke );

my %hash = map { lc, $_ } @castaways;
for my $person (@list_1) {
    if (exists $hash{ lc $person }) {
        print "$person is a castaway (as $hash{ lc $person }).\n";
    }
}
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I used exists so even 0 can be a castaway.

($q=q:Sq=~/;[c](.)(.)/;chr(-||-|5+lengthSq)`"S|oS2"`map{chr |+ord
}map{substrSq`S_+|`|}3E|-|`7**2-3:)=~y+S|`+$1,++print+eval$q,q,a,
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