@echo off
:: filename: rot13.btm
:: notes by: Eric Pement
::  updated: 2014-12-06 17:26
:: requires: tr

if "%1" eq "/?" .or. "%1" eq "/h" .or. "%1" eq "-?" .or. "%1" eq "--help" goto syntax
if "%1" eq "" goto filter
if not exist %1 (echo Input file [%1] not found. %+ quit)
:: else, we must have one argument here....

:: GNU 'tr' does not support the System V syntax that uses square brackets
:: to enclose ranges. (see additional notes in GNU info page)
tr "a-zA-Z" "n-za-mN-ZA-M" < %1
goto end

:filter
tr "a-zA-Z" "n-za-mN-ZA-M"
goto end

:syntax
TEXT
ROT13 - simple Caesar cipher for reversible obfuscation. ROT13
affects alphabetic characters only (A-Z and a-z), nothing else.

Usage: rot13 [file]

Samples:
  {cat|type|echo|etc.} filename | rot13   # use as a filter
  rot13 filename                          # use with one argument
  rot13 /?, /h, -?, --help                # brings up this help message
ENDTEXT
:end