gistfile1.txt

<!-- Set's the FLEX_HOME property based on a command line parameter or environment variable. -->
<target name="init">
    <if>
        <equals arg1="${FLEX_HOME}" arg2="$${FLEX_HOME}" />
        <then>
            <if>
                <equals arg1="${env.FLEX_HOME}" arg2="$${env.FLEX_HOME}" /> 
                <then>
                    <fail message="Variable FLEX_HOME does not exist. Set an environment variable or pass Ant a parameter like so: ant -DFLEX_HOME='/sdk/flex/4.1' compile-swf" />
                </then>
                <else>
                    <property name="FLEX_HOME" value="${env.FLEX_HOME}" />
                </else>
            </if>
        </then>
    </if>
    <echo>FLEX_HOME: ${FLEX_HOME}</echo>
</target>