not the shortest one... :-)

EDIT: but it does hold the loop to sqrt of $last...

#!/usr/bin/perl
use warnings;
use strict;
use feature qw(say);

my $last = 1000;
my @num = (2..$last);

for my $i (@num) {
 $num[$i] = 1;
}

for (my $i=2; $i*$i <= $last; $i++) {
 if ($num[$i]) {
   for (my $j=$i; $j*$i < $last; $j++) {
     $num[$i * $j] = 0;
   }
 }
}
my @prime = ();
for (my $i=2; $i<=$last; $i++) {
 if ($num[$i]) {
   push @prime, $i;
 }
}
say "@prime";
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