How to set and retrieve JVM system variables when running java/groovy from CLI

setSystemPropertyFromCLI.groovy

// http://stackoverflow.com/questions/8098564/is-it-possible-to-specify-java-system-properties-when-running-groovy-from-comman
/*
System properties are set on the java command line using the 
  java -Dpropertyname=value 
syntax. 
They can also be added at runtime using 
  System.setProperty(name, value) 
or via the various 
  System.getProperties().load() 
methods.

  System.getProperties() 
lists all java system properties, and those set from command line will be there, 
but there's no way to distinguish those from the other properties added by the system.

Note that you can also set system properties with the environment variable JAVA_TOOL_OPTIONS



Environment variables are set in the OS, eg in linux 
  export HOME=/Users/myusername 
or on windows 
  SET WINDIR=C:\Windows 
etc., and, unlike system properties, may not be set at runtime.

Java chose to expose OS environment variables as Properties with 
  System.getEnv() or System.getEnv(variable)
(just as Java exposes current directory and "other stuff" as Properties).
*/

/* SET A JAVA/GROOVY SYSTEM VARIABLE FROM CLI
 * Exactly as in java: 
 * java -Dproperty_name="property_value appName.java
 */
groovy -Dproperty_name="property_value" myGroovy.groovy