/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.commons.configuration2.interpol;



A specialized lookup implementation that allows access to environment
variables.

 This implementation relies on System.getenv() to resolve environment variables. It can be used for referencing environment variables in configuration files in an easy way, for instance: 
java.home = ${env:JAVA_HOME}

 EnvironmentLookup is one of the standard lookups that is registered per default for each configuration. 
Since:
1.7
Deprecated:
Use DefaultLookups.ENVIRONMENT./**
 * <p>
 * A specialized lookup implementation that allows access to environment
 * variables.
 * </p>
 * <p>
 * This implementation relies on {@link System#getenv()} to resolve
 * environment variables. It can be used for referencing environment variables
 * in configuration files in an easy way, for instance:
 * </p>
 *
 * <pre>
 * java.home = ${env:JAVA_HOME}
 * </pre>
 *
 * <p>
 * {@code EnvironmentLookup} is one of the standard lookups that is
 * registered per default for each configuration.
 * </p>
 *
 * @since 1.7
 * @deprecated Use {@link DefaultLookups#ENVIRONMENT}.
 */
@Deprecated
public class EnvironmentLookup implements Lookup
{
    
Performs a lookup for the specified variable. This implementation directly delegates to a System.getenv(). 
Params:
key – the key to lookup
Returns:
the value of this key or null if it cannot be resolved/**
     * Performs a lookup for the specified variable. This implementation
     * directly delegates to a {@code System.getenv()}.
     *
     * @param key the key to lookup
     * @return the value of this key or <b>null</b> if it cannot be resolved
     */
    @Override
    public String lookup(final String key)
    {
        return System.getenv(key);
    }
}