An ``<environment_variables>`` top-level XML block can be used to define these.
```
<environment_variables>
<environment_variable name="FOO">$bar</environment_variable>
<environment_variable name="FOO2">$bar2</environment_variable
</environment_variables>
```
The expressions are contained in the text of the block.
Implementation Detials:
In order to avoid odd shell expression stuff - the evaluated expressions are written to files and environment variables are read from these files at runtime.
Testing:
A demo tool ``test/functional/tools/environment_variables.xml`` with a test case that can be executed with the following expression.
```
./run_tests.sh -framework -id environment_variables
```
John Chilton