Github user cestella commented on a diff in the pull request:

    https://github.com/apache/incubator-metron/pull/312#discussion_r83652687
  
    --- Diff: 
metron-platform/metron-common/src/main/java/org/apache/metron/common/dsl/functions/SystemFunctions.java
 ---
    @@ -0,0 +1,75 @@
    +/**
    + * 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.metron.common.dsl.functions;
    +
    +import org.apache.metron.common.dsl.BaseStellarFunction;
    +import org.apache.metron.common.dsl.Stellar;
    +import org.apache.metron.common.system.Environment;
    +
    +import java.util.List;
    +
    +public class SystemFunctions {
    +
    +  @Stellar(namespace = "SYSTEM",
    +          name = "ENV_GET",
    +          description = "Returns the value associated with an environment 
variable",
    +          params = {
    +                  "env_var - Environment variable name to get the value 
for"
    +          },
    +          returns = "String"
    +  )
    +  public static class EnvGet extends BaseStellarFunction {
    +    private Environment env;
    +
    +    public EnvGet() {
    +      this(new Environment());
    +    }
    +
    +    public EnvGet(Environment env) {
    +      this.env = env;
    +    }
    +
    +    @Override
    +    public Object apply(List<Object> args) {
    +      if (args.size() == 0) {
    +        return null;
    +      } else {
    +        return env.get((String) args.get(0));
    --- End diff --
    
    That being said, we could probably do better across the board.  Maybe some 
functions that consistently coerce types (or not, in the case of strings) that 
people can use.


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