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<dynamicvariables>

    <variable name="previous.java.version" checkonce="true"
              dir="${INSTALL_PATH}"
              executable="jre/bin/java" stderr="true"
              type="process" ignorefailure="true"
              condition="haveInstallPath+isUpgrade">
      <arg>-version</arg>
      <filters>
        <regex regexp="java version[^\d]+([\d\._]+)" select="\1"/>
      </filters>
    </variable>

</dynamicvariables>