Cool! I couldn't resist porting it to Java, so here is my Java version
(It is not one-liner, but maybe one statement?) :

public class PrimeTester {
  public static void main(String[] args) {
    System.out.println(String.format("%0" + args[0] + "d",
0).matches("^0$|^(00+?)\\1+$") ? "Not prime" : "Prime");
  }
}

http://davidtran.doublegifts.com/blog/?p=12


On Mar 19, 3:07 pm, "Tim Pease" <tim.pe... / gmail.com> wrote:
> This is a one-liner Ruby script that will tell you if a given number isprime.
>
> ruby -wle 'puts "Prime" unless ("1" * ARGV[0].to_i) =~
> /^1$|^(11+?)\1+$/' [number]
>
> I cannot take credit for this one -- it originally came from Perl. The
> website listed below gives the full explanation of how theregexp
> works.
>
> http://montreal.pm.org/tech/neil_kandalgaonkar.shtml
>
> I highly recommend reading this if you want to flex yourregexpmuscles today.
>
> Blessings,
> TwP
>
> ruby -wle 'puts "Prime" unless ("1" * ARGV[0].to_i) =~ /^1$|^(11+?)\1+$/' 42
>
> It may be the answer to life, the universe, and everything, but it
> certainly isn'tprime!