use Algorithm::Loops qw< NestedLoops >;
my $getList = NestedLoops( [ map [$_,''], 1..3 ] );
my $getStr = sub { join '', $getList->() };
my $subset;
while(  $subset = $getStr->()  ) {
    print ' ', $subset;
}
print $/;

# or, if you also want the empty subset:

$getList = NestedLoops( [ map ['',$_], 1..3 ] );
$subset = $getStr->();
do {
    print " ($subset)";
} while(  $subset = $getStr->()  );
print $/;
__END__
 123 12 13 1 23 2 3
 () (3) (2) (23) (1) (13) (12) (123)