$k = 輸出數量;
@lines;
$n = 0;
srand;
while(《》) {
    $n++;
    if ($n 《= $k) {
        push(@lines, $_);
    } else {
        $r = int(rand($n));
        if ($r 《 $k) {
            $lines[$r] = $_;
        }
    }
}

#!/usr/bin/perl
 
die "Usage: $0 , where N is the number of lines to pickn"
if @ARGV < 1;
$N = shift @ARGV;
 
@pick = ();
while (《》) {
    if (@pick 《 $N) {
        push @pick, $_;
        ($r1, $r2) = (rand(@pick), rand(@pick));
        ($pick[$r1], $pick[$r2]) = ($pick[$r2], $pick[$r1]);
    } else {
        rand($.) 《= $N and $pick[rand(@pick)] = $_;
    }
}
 
print @pick;