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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>
  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!

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