Here is a simple solution with arrayref and one that can cope with array sizes not having multiples of threes

my $array= [1,2,3,4,5];

while (@$array) {
    push my @r, shift @$array if (@$array);
    push @r, shift @$array if (@$array);
    push @r, shift @$array if (@$array);
    print join(',',@r),"\n";
}
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