Can Ant expand environment variables from a properties file? - ant

Question

I have a question regarding Ant and its treatment of environment variables.
To illustrate I have a small sample.
Given the Ant build file test.xml:
<project name="myproj" default="testProps">
<property environment="env"/>
<target name="testProps">
<echo message="${env.MyEnvVar}"/>
<echo message="${MY_PROPERTY}"/>
</target>
</project>
And the properties file test.props:
MY_PROPERTY=${env.MyEnvVar}
Now set the environment variable MyEnvVar to some value (foo in my case) and run Ant using this command line:
ant -f test.xml -propertyfile test.props testProps
The output I get is:
[echo] foo
[echo] ${env.MyEnvVar}
What I would like to know is whether there is any way to structure the input properties file such that I get
[echo] foo
[echo] foo
That is, I would like to name an environment variable in the properties file which is replaced within the Ant script. Note - I know how to access environment variables directly (as is done here). What I need to do is make use of a set of Ant scripts that expect one collection of properties in an environment that defines the same properties using different names. Thus the thought of "bridging" them in a properties file.
I am using Ant version 1.6.5.

Answer 1

You need to read the test.props property file after the environment - you could do so using another property task, i.e. add
<property file="test.props" />
after your existing property environment task.
In full:
<property environment="env" />
<property file="test.props" />
<target name="testProps">
<echo message="${env.MyEnvVar}"/>
<echo message="${MY_PROPERTY}"/>
</target>
When you supply the properties file on the command line this gets processed before the content of the build, but at that time ${env.MyEnvVar} is not yet set.