Java properties handles most things but there are a couple things where we need to set/change the environment before a build is running. The classic case is to execute a build with java 1.4 and java 5. We need to be able to specify a set of environment variables that will be created before the build process starts.

The environment variable in "name=value" format.

Environment variables values may contain references to existing values in the following format: "name=${env.<NAME>};value". If the value of the <NAME> variable is "value2" in the current environment, then the above example will be expanded to: "name=value2;value". Using this technique, it is possible add an entry to PATH in the following manner: "PATH=my/path/entry;${env.PATH}. Case is significant even on Windows systems.

The above description was copied from our current tool which supports this.