こんな感じかなぁ
my @new_array = get_rand_array(\@old_array,3);
sub get_rand_array{
my ($arrayref, $num) = @_;
my @old_array = @{$arrayref};
my @new_array;
while($num){
push( @new_array, splice(@old_array, rand @old_array , 1) );
$num--;
}
return @new_array;
}

