001// ***************************************************************************************************************************
002// * Licensed to the Apache Software Foundation (ASF) under one or more contributor license agreements.  See the NOTICE file *
003// * distributed with this work for additional information regarding copyright ownership.  The ASF licenses this file        *
004// * to you under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance            *
005// * with the License.  You may obtain a copy of the License at                                                              *
006// *                                                                                                                         *
007// *  http://www.apache.org/licenses/LICENSE-2.0                                                                             *
008// *                                                                                                                         *
009// * Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an  *
010// * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the License for the        *
011// * specific language governing permissions and limitations under the License.                                              *
012// ***************************************************************************************************************************
013package org.apache.juneau.svl.vars;
014
015import org.apache.juneau.svl.*;
016
017/**
018 * Environment variable variable resolver.
019 *
020 * <p>
021 * The format for this var is <js>"$E{envVar[,defaultValue]}"</js>.
022 *
023 * <h5 class='section'>Example:</h5>
024 * <p class='bjava'>
025 *    <jc>// Create a variable resolver that resolves environment variables (e.g. "$E{PATH}")</jc>
026 *    VarResolver <jv>varResolver</jv> = VarResolver.<jsm>create</jsm>().vars(EnvVariablesVar.<jk>class</jk>).build();
027 *
028 *    <jc>// Use it!</jc>
029 *    System.<jsf>out</jsf>.println(<jv>varResolver</jv>.resolve(<js>"Environment variable PATH is set to $E{PATH}"</js>));
030 * </p>
031 *
032 * <p>
033 * Since this is a {@link SimpleVar}, any variables contained in the result will be recursively resolved.
034 * <br>Likewise, if the arguments contain any variables, those will be resolved before they are passed to this var.
035 *
036 * <h5 class='section'>See Also:</h5><ul>
037 *    <li class='link'><a class="doclink" href="../../../../../index.html#jm.SimpleVariableLanguage">Simple Variable Language</a>
038 * </ul>
039 */
040public class EnvVariablesVar extends DefaultingVar {
041
042   /** The name of this variable. */
043   public static final String NAME = "E";
044
045   /**
046    * Constructor.
047    */
048   public EnvVariablesVar() {
049      super(NAME);
050   }
051
052   @Override /* Var */
053   public String resolve(VarResolverSession session, String varVal) {
054      // Note that lookup is case-insensitive on windows.
055      return System.getenv(varVal);
056   }
057}