root/ruby/rot13.rb

#!/usr/bin/env ruby

# Author:: Andrew Pennebaker (andrew.pennebaker@gmail.com)
# License:: GPLv3
# Copyright:: Copyright 2007-2008 Andrew Pennebaker
#
# == Usage
#
# rot13 [OPTIONS]
#
# Data is read from STDIN and written to STDOUT.
#
# --help, -h:
#    Help with usage
#
# --shift, -s:
#    Set Caesar shift (default 13).

require "getoptlong"
require "rdoc/usage"

def create_rule(n=13)
        rule={}

        # "A"[0].upto("Z"[0])
        65.upto(90) { |b|
                rule[b]=(b+n-65)%26+65
        }

        # "a"[0].upto("z"[0])
        97.upto(122) { |b|
                rule[b]=(b+n-97)%26+97
        }

        return rule
end

def crypt(rule, b)
        if rule.include?(b)
                return rule[b]
        else
                return b
        end
end

def main
        shift=13

        begin
                opts=GetoptLong.new(
                        ["--help", "-h", GetoptLong::NO_ARGUMENT],
                        ["--shift", "-s", GetoptLong::REQUIRED_ARGUMENT]
                )

                opts.each { |option, value|
                        case option
                                when "--help"
                                        raise
                                when "--shift"
                                        shift=value.to_i
                        end
                }
        rescue
                RDoc::usage("Usage")
        end

        rule=create_rule(shift)

        STDIN.each_byte { |b|
                putc crypt(rule, b)
        }
end

if __FILE__==$0
        begin
                main
        rescue Interrupt=>e
                nil
        end
end