Versions 6 and 7

With spaces (version6.rb):

candidate_prime = 5
while candidate_prime < 1000
  divisor = 2
  found = false
  while divisor < candidate_prime
    if candidate_prime.modulo(divisor) == 0
      found = true
      break
    end
    divisor = divisor + 1
    if divisor * divisor > candidate_prime
      break
    end
  end
  if !found
    puts candidate_prime
  end
  candidate_prime = candidate_prime + 1
end

Redesigned (version7.rb):

candidate_prime = 5
while candidate_prime < 1000
  divisor = 2
  while divisor * divisor <= candidate_prime &&
        candidate_prime.modulo(divisor) != 0
    divisor += 1
  end
  puts candidate_prime if divisor * divisor > candidate_prime
  candidate_prime += 1
end