Prerequisites

All your Grails versions must be installed under the same base directory. Ex:
```
  /opt/grails-1.0.3
  /opt/grails-1.1.1
  /opt/grails-2.1.0.RC1
```
GRAILS_HOME environment variable must be set and point to your "default" Grails installation
cURL and unzip (If you want it to automatically pull missing versions)
This script was tested on Mac OS X (Lion), but should work fine on Linux and Windows (with cygwin)

Installation

Using the script is as transparent as possible:

If you invoke it from a project folder, it will detect the version used by the project and call the correct grails
- If the required version does not exist locally, the script will attempt to download the version specified from grails amazon mirror
If you invoke it from any other folder that does not contain a Grails project, it will call the "default" Grails installation
If you want to call a specific Grails version (i.e. when doing an upgrade) you can specify the version you want in the first parameter.
- If the version you specified does not exist locally, it will also attempt to download the version specified. Ex:
  
  $ grails 2.2.3 upgrade
It tries to determine the command to run based on its name, so you can create symlinks for it to use the grails-debug command, or use it with Griffon. It should also work with any other tool that uses the same installation structure than Grails (like Groovy, Gradle)