$> for a in `seq 1 100`; do if $( perl is_prime.pl $a ); then echo $a; fi; done

is_prime.pl

#!/usr/bin/env perl
use strict;
use POSIX;
 
exit 2 unless &is_prime(pop @ARGV);
 
sub is_prime {
  my $num = shift || 0;
  return if $num<2
            || ($num%2==0 && $num>2)
            || floor($num)<$num;
  for (my $i=3; $i<=sqrt($num); $i+=2) {
    return if $num % $i == 0;
  }
  
  1;#true
}