To change directory in ANT

[query]

  
Hi,

I want to use change directory in ANT scripts. But it is not changing 
directory.It will revert back to its original setting as soon as it comes out 
of shell prompt.I tried using

<exec executable="cmd">
                        <arg value="/c"/>
                        <arg value="cd"/>
                        <arg value="sample"/>
                </exec>

Is there any method to use cd command or any ANT task is present?