... and then make this array unique and print the unique elements

For this part of the operation I would think that List::Util::uniqstr() is what you want.

use warnings;
use strict;
use List::Util qw(uniqstr);

my $str = 'olivia-niels-peter-lars-niels-lars-olivia-olivia';
my @s = split /\-/, $str;
print "@s\n";
my @s_new = uniqstr(@s);
print "@s_new\n";

__END__
Outputs:
olivia niels peter lars niels lars olivia olivia
olivia niels peter lars
[download]

Cheers,
Rob