for ( 0 .. 2**$n-1 ) {
   my @combo = map { $_ + 1 } split //, sprintf("%0*b", $n, $_);
   say "@combo";
}

##</code><code>##

use Algorithm::Loops qw( NestedLoops );

my $iter = NestedLoops([
   map [ 1, 2 ], 1..$n
]);

while ( my @combo = $iter->() ) {
   say "@combo";
}