Access Environment Variables in a Native Executable at Run Time

A native executable accesses your environment variables in the same way as a regular Java application. For example, assume you have the following source code:

import java.util.Map;

public class EnvMap {
    public static void main (String[] args) {
        var filter = args.length > 0 ? args[0] : "";
        Map<String, String> env = System.getenv();
        for (String envName : env.keySet()) {
            if(envName.contains(filter)) {
                System.out.format("%s=%s%n",
                                envName,
                                env.get(envName));
            }
        }
    }
}

This code iterates over your environment variables and prints out the ones that contain the String of characters passed as the command-line argument.

  1. Make sure you have installed a GraalVM JDK. The easiest way to get started is with SDKMAN!. For other installation options, visit the Downloads section.

  2. Compile the file and build a native executable, as follows: 
     javac EnvMap.java

     native-image EnvMap
  3. Run the resulting native executable and pass a command-line argument, such as “HELLO”. There should be no output, because there is no environment variable with a matching name. 
     ./envmap HELLO
 <no output>
  4. Create a new environment variable named “HELLOWORLD” and give it the value “Hello World!”. (If you are using a bash shell, follow the example below.) Now, run the native executable again–it will correctly print out the name and value of the matching environment variable(s). 
     export HELLOWORLD='Hello World!'

     ./envmap HELLO

    You should receive the expected output:

     HELLOWORLD=Hello World!