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How do I set environment variables from Java?

I'm working on Java. I have to add an environment variable in java code programmatic such that it will be available when i get list using process builder as follows:

import java.util.Map; import java.util.Set; class helloworld { public static void main(String[] args) { ProcessBuilder pb = new ProcessBuilder("export MY_ENV_VAR=1"); Map<String, String> envMap = pb.environment(); Set<String> keys = envMap.keySet(); for(String key:keys){ System.out.println(key+" ==> "+envMap.get(key)); } } }

But with above trial i cant get environment variable properly. so How to set the environment variable ?

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  • Have you tried pb.environment().put("key", "value"); ? Commented Jan 18, 2013 at 12:43
  • @berry120 ya its kide of, but i did not get exact answer. Commented Jan 18, 2013 at 12:49
  • java java.lang.UnsupportedOperationException at java.util.Collections$UnmodifiableMap.put(Collections.java:1457) at br.com.stilingue.services.remove_occupation.RemoveOccupationTest.setUpTestEnv(RemoveOccupationTest.java:29) Commented Apr 1, 2019 at 14:45

3 Answers 3

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9 
 Map<String, String> env = pb.environment(); env.put("MV_ENV_VAR", "1");

would set MY_ENV_VAR=1. Before you invoke the Process by 

Process p = pb.start();

export would only be interpreted by a shell.

See also ProcessBuilder

A full example:

public static void main(String[] args) throws IOException { ProcessBuilder pb = new ProcessBuilder("CMD", "/C", "SET"); Map<String, String> env = pb.environment(); env.put("MYVAR", "myValue"); Process p = pb.start(); InputStreamReader isr = new InputStreamReader(p.getInputStream()); char[] buf = new char[1024]; while (!isr.ready()) { ; } while (isr.read(buf) != -1) { System.out.println(buf); } }

prints among other environment values:

MYVAR=myValue

This should prove that the created process uses the manipulated environment.

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2 Comments

thanks, but env.put("MV_ENV_VAR", "1"); will set the env variable only in local variable, but if u again take processbuilder instance and get the content of map, it will not show the variable that we have set as mentioned by you.
@BSalunke updated my answer and added an example.
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You can add the desired variables directly into ProcessBuilder.environment() map. The code below should work:

import java.util.Map; import java.util.Set; class helloworld { public static void main(String[] args) { ProcessBuilder pb = new ProcessBuilder("/bin/sh"); // or any other program you want to run Map<String, String> envMap = pb.environment(); envMap.put("MY_ENV_VAR", "1"); Set<String> keys = envMap.keySet(); for(String key:keys){ System.out.println(key+" ==> "+envMap.get(key)); } }

}

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@masksim_khokhlov what if we again took the processBuilder instance and get the contained of map? it will not contain our variable
@BSalunke Why it won't? It will! ProcessBuilder.environment() will always return the same Map instance. Check out the javadoc.
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You can get the environment variable with the process Builder object :

 ProcessBuilder pb = new ProcessBuilder("myCommand", "myArg1", "myArg2"); Map<String, String> env = pb.environment(); env.put("VAR1", "myValue"); env.remove("OTHERVAR"); env.put("VAR2", env.get("VAR1") + "suffix");
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It looks like pb.start() is missing.

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