I want to distribute the build.xml file with an application and therefore
not include any paths to software the application depends on. Ideally I
would want to take this from an environment variable and show an error
message if the environment variable is not set.
Currently I set a property like this:
<property name="sw.home" location="${env.THE_VARIABLE}" />
and later use sw.home wherever needed.
I cannot figure out how to best provide a default here or even better, abort
with a descriptive error message if the environment variable is not set.
