Ruby rot13 Script

[fugibo]

I made this a while back and just converted it into an executable library, so I'd thought I'd post it here. The code is probably horribly inefficient, but it works.

#! /usr/bin/ruby
#  This is an executable Ruby library that adds rot13 functinality to the String class,
#  and can encrypt/decrypt STDIN.

class String

	def rot13!
		size.times do |i|
			if self[i].between? 65, 90
				self[i] += 13
				self[i] = 64 + self[i] - 90 if self[i] > 90
			elsif self[i].between? 97, 122
				self[i] += 13
				self[i] = 96 + self[i] - 122 if self[i] > 122
			end
		end

		return self
	end

	def rot13
		return self.dup.rot13!
	end
	
end

begin
	if $0 == __FILE__
		input = ''
		while ( b = STDIN.gets ) != nil
			input << b
		end
		
		STDOUT.print input.rot13
	end
rescue
	nil
end

Enjoy.

EDIT: rot13

[Blizzard]

Why don't you just modulate? o.o

			if self[i].between? 65, 90
				self[i] = (self[i] - 65 + 13) % 26 + 65
			elsif self[i].between? 97, 122
				self[i] = (self[i] - 97 + 13) % 26 + 97
			end