I want to use the same ant script to do a build in either my local windows environment or on our redhat build server. 

I have a variable 'buildDirectory' in two files (build\_unix.properties & build\_windows). I want to set variables depending on the environment. 

```
<osfamily property="os.family"/>
<property file="./build_${os.family}.properties" />
<property name="tmp-base.folder" value="${buildDirectory}/tmp/"/>

```

I also tried

```
<if>
    <os family="unix"/>
    <then>
        <property file="./build_unix.properties" />
    </then>
    <else>
        <property file="./build_windows.properties" />
    </else>
</if>

```

Any ideas?