Question

I want to change “variable” in Ant file, in one target and see that change in another target.

<variable name="foo" value="hello" />
<target name="print-me">
    <echo message="${foo}" />
    <antcall target="change-me" />
    <echo message="${foo}" />
</target>

<target name="change-me">
    <variable name="foo" value="world" />
</target>

While I want it to print: ‘hello , world’ , it prints ‘hello, hello’

Answer 1

Either use :

<target name="change-me">
    <variable name="foo" unset="true"/>
    <variable name="foo" value="world"/>
</target>

as Oers already mentioned in his comment to your question or use a more
straightforward approach with the let task of Ant addon Flaka :

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

...
<!-- overwrite any existing property or userproperty
     (those properties defined on the commandline via -Dfoo=bar ..) --> 
<fl:let> foo ::= 'world'</fl:let>

...
</project>