#!/localperl/bin/perl

use warnings;
use strict;
use feature 'fc';

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

my %hash = map { $_, 1 } @castaways;
for my $person (@list_1) {
    if ( $hash{ fc($person) }) { # Tried with exists as well. Same result.
        print "$person is a castaway\n";
    }
}