my $q_file = "tmp.txt";
my $n = 10;

my @ques = get_questions($q_file, $n);
print for @ques;

sub get_questions {
 local $/="===\n";
 local $.; # Is this necessary?
 local @ARGV = (shift);
 # If you want 'open ... or die' behavior
 local $SIG{__WARN__} = sub { die shift };

 my $num = shift;
 my @questions;
 while (<>) {
  push(@questions, $_), next if $. <= $num;
  my $i = rand($.);
  $questions[$i] = $_ if $i < $num;
 }
 @questions;
}