my @list = 'a'..'z';                                # use your data instead of this
my $n = 5;                                          # how many do you need?

foreach my $i (0..$n-1) {
  my $j = rand @list;
  ($list[$i], $list[$j]) = ($list[$j], $list[$i]);  # swap ith and jth elements
};

print join(', ', @list[0..$n-1]), "\n";