Hi, This cannot be your code; it does not compile. After removing the comma from the opening brace of the subroutine, I get "Can't use an undefined value as a HASH reference".

Maybe you want something more like this?

use strict; use warnings;
use feature qw/ say /;

my @captains = qw/ kirk picard popeye /;
my $commanded_by = trivia( @captains );

for my $captain ( sort keys %{ $commanded_by } ) {
    say sprintf '%s was on Enterprise #: %s',
                ucfirst $captain,
                join ', ', @{ $commanded_by->{ $captain } };
}

sub trivia {
    my @captains = @_;

    my %commands = (
        kirk   => [ 'EntTOS', 'EntA' ],
        picard => [ 'EntD',   'EntE' ],
    );

    my %output;
    $output{ $_ } = $commands{ $_ } || [] for @captains;

    return \%output;
}

__END__
[download]

Output:

$ perl 1202155.pl

Kirk was on Enterprise #: EntTOS, EntA
Picard was on Enterprise #: EntD, EntE
Popeye was on Enterprise #:
[download]

Hope this helps!