core/src/test/resources/com/opensymphony/xwork2/config/providers/xwork-test-envs-substitution.xml

<?xml version="1.0" encoding="UTF-8"?>
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 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
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<!DOCTYPE struts PUBLIC
        "-//Apache Software Foundation//DTD Struts Configuration 6.0//EN"
        "https://struts.apache.org/dtds/struts-6.0.dtd">
<struts>

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

    <!-- Linux/Unix (or Unix-like) Environment -->
    <constant name="user" value="${env.USER}"/>
    <constant name="home" value="Current HOME = ${env.HOME}"/>
    <!-- Linux/Unix (or Unix-like) Environment -->

    <!-- Windows (or Windows-like) Environment -->
    <constant name="username" value="${env.USERNAME}"/>
    <constant name="homedrive.homepath" value="Current HOMEDRIVE.HOMEPATH = ${env.HOMEDRIVE}${env.HOMEPATH}"/>
    <!-- Windows (or Windows-like) Environment -->

    <constant name="os" value="Current OS = ${os.name}"/>
    <constant name="unknown" value="Unknown = ${env.UNKNOWN:default}"/>

    <constant name="struts.devMode" value="${env.STRUTS_DEV_MODE:false}"/>

</struts>