From: Tim Pease <tim.pease@...>
Date: 2007-03-20T04:07:03+09:00
Subject: Regexp and Prime numbers

This is a one-liner Ruby script that will tell you if a given number is prime.

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 the regexp
works.

http://montreal.pm.org/tech/neil_kandalgaonkar.shtml

I highly recommend reading this if you want to flex your regexp muscles 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't prime!