Ruby rot13

rot13.rb

# or simply:
'foobar'.tr 'A-Za-z','N-ZA-Mn-za-m'


# rot(x)
class String
  def rot(num = 13)
    return self.split("").collect { |ch|
      if /^[a-z]$/ === ch
	((ch[0] + num - 'a'[0]) % 26 + 'a'[0]).chr
      elsif /^[A-Z]$/ === ch
	((ch[0] + num - 'A'[0]) % 26 + 'A'[0]).chr
      else
	ch
      end
    }.join("")
  end

  alias rot13 rot
end


p "foobar".rot(2)

Rot by anything:

class String
  def rot(shift=13)
    tr "A-Za-z", "#{(65 + shift).chr}-ZA-#{(64 + shift).chr}#{(97 + shift).chr}-za-#{(96 + shift).chr}"
  end
end

"abc".rot(1) #=> "Abc"

@xfaider approach is simple and elegant. I think this should work for a flexible approach:

def rot(string, amount)
  pivot = ('a'.ord + amount)
  string.tr('a-z', "#{(pivot - 1).chr}-za-#{pivot.chr}")
end

# not working
# rot("b", 25) == rot("b", 24)

if you want amount to be higher than 26:

amount = (amount % 26 + 1) if amount >= 26