How do I append a string to a property in ant?

Question

I'm using ANT 1.7.0

I'd like to create a target that on call, will append text to a string (saved in property).

for example:

<property name="str.text" value="" />

<target name="append.to.property" >
  <property name="temp.text" value="${str.text}${new.text}" />
  <property name="str.text" value="${temp.text}" />
</target>

The problem is that I can't overwrite the property value in one target and read the changed value in another target.

How do I append a string to a property in ant?

Answer 1

You can't change value of property in Ant.

You may use Ant Contrib variable task (see http://ant-contrib.sourceforge.net/tasks/tasks/variable_task.html) which provide mutable properties.

<property name="str.text" value="A" />
<property name="new.text" value="B"/>

<target name="append.to.property" >
  <var name="temp.text" value="${str.text}${new.text}" />
  <var name="str.text" value="${temp.text}" />
</target>

<target name="some.target" depends="append.to.property">
  <echo message=${str.text}/>
</target>

Answer 2

Normally properties in ant are immutable once set. With Ant addon Flaka you may change or overwrite exisiting properties - even userproperties (those properties set via commandline -Dkey=value), i.e. create a macrodef and use it like that :

<project name="demo" xmlns:fl="antlib:it.haefelinger.flaka">

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

 <macrodef name="createproperty">
    <attribute name="outproperty"/>
    <attribute name="input"/>
    <sequential>
     <fl:let> @{outproperty} ::= '@{input}'</fl:let>
    </sequential>
 </macrodef>

 <!-- create new property -->
 <createproperty input="${foo}bar" outproperty="fooo"/>

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

    <echo>1. $${foo} => ${foo}</echo> 

 <!-- overwrite existing property -->
 <createproperty input="foo${foo}" outproperty="foo"/>

    <echo>2. $${foo} => ${foo}</echo>

</project>

output

 [echo] ${fooo} => barbar
 [echo] 1. ${foo} => bar
 [echo] 2. ${foo} => foobar

alternatively you may use some scripting language (Groovy, Javascript, JRuby..) and use ant api :
project.setProperty(String name, String value) to overwrite a property.