use warnings;
use strict;

my @arr = qw (J K L M N O);

print join (' - ', splice @arr, 0, 2), "\n" while @arr;

##</code><code>##

J - K
L - M
N - O

##</code><code>##

use warnings;
use strict;

my @arr = qw (J K L M N O J K);
my %done;

while (@arr) {
    my $str = join ' - ', splice @arr, 0, 2;
    next if exists $done{$str};
    
    $done{$str}++;
    print "$str\n";
}