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Access Environment Variables in a Native Executable at Runtime

A native executable accesses environment variables in the same way as a regular Java application.

Run a Demo

For example, run a Java application that iterates over your environment variables and prints out the ones that contain the String of characters passed as a command-line argument.

Prerequisite

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.

  1. Save the following source code in a file named EnvMap.java: 
     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));
             }
         }
     }
 }
  2. Compile the file and build a native executable, as follows: 
     javac EnvMap.java

     native-image EnvMap
  3. Run the native application 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>

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  1. 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).

  2. 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).

    5d2ccd84b74 (Review Native Image Guides to be consistent)

     export HELLOWORLD='Hello World!'

     ./envmap HELLO

    You should receive the expected output:

     HELLOWORLD=Hello World!

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