CODEWITHSUNDEEP
antbuild
amitsalyan
amitsalyan

Reputation: 678

Ant build.xml $$

I have a Ant build.xml that does a check as below, i was just wondering what the $$ signifies?

Thanks in advance for your help.

 <equals casesensitive="false" arg1="${subPlan}" arg2="$${subPlan}"/>

Upvotes: 0

Views: 196

Answers (1)

Rebse
Rebse

Reputation: 10377

From ant manual Properties and PropertyHelpers :

..Ant will expand the text $$ to a single $ and suppress the normal property expansion mechanism..

It's often used for output like that :

<property name="foo" value="bar"/>

<echo>$${foo} => ${foo}</echo>

output :

[echo] ${foo} => bar

In your case it checks whether a property with the name subPlan is set within your project, as ${subPlan} won't be expanded if it doesn't exist, f.e. :

<project>
 <property name="subPlan" value="whatever"/>
 <echo>${subPlan}</echo>
</project>

output :

[echo] whatever

whereas :

<project>
 <echo>${subPlan}</echo>
</project>

output :

[echo] ${subPlan}

It's actually possible to set the propertyvalue for Property subPlan to ${subPlan} :

<property name="subPlan" value="$${subPlan}"/>

but that doesn't make sense, so your snippet does a combined check => is Property subPlan set and has a useful value ? could be used like that :

<fail message="Property not set or invalid value !">
 <condition>
  <equals casesensitive="false" arg1="${subPlan}" arg2="$${subPlan}"/>
 </condition>
</fail>

Finally the standard way to check whether a property is set is using the isset condition, f.e. :

<fail message="Property not set !">
 <condition>
  <not>
   <isset property="subPlan"/>
  </not>
 </condition>
</fail>

Upvotes: 3

Related Questions