why i am not able to update env variable in node js

Question

I want to update my env variable in node js, but i am not able to update its env variable, i tried with console.log(process.env.DB_HOST) but still i am getting old value, here i have added my whole code, can anyone please look in to it, and help me to resolve this issue,

function exec_api() { 
    return new Promise(async function (resolve) {
        const execSync = require('child_process').exec;
        //let child_process_obj = execSync('DB_HOST='+process.env.UNITTEST_DB_HOST+' DB_DATABASE='+process.env.UNITTEST_DB_DATABASE+'  DB_USERNAME='+process.env.UNITTEST_DB_USERNAME+' DB_PASSWORD='+process.env.UNITTEST_DB_PASSWORD+'  PORT='+process.env.UNITTEST_SERVICE_PORT+' ./node_modules/.bin/nodemon main.js'); 
        await execSync('export DB_HOST=' + process.env.UNITTEST_DB_HOST);
        await execSync('export DB_DATABASE=' + process.env.UNITTEST_DB_DATABASE);
        await execSync('export DB_USERNAME=' + process.env.UNITTEST_DB_USERNAME);
        await execSync('export DB_PASSWORD=' + process.env.UNITTEST_DB_PASSWORD);
        await execSync('export PORT=' + process.env.UNITTEST_API_BACKEND_PORT);
        let child_process_obj = await execSync('node main.js');
        unittest_api_backend_process_id = child_process_obj.pid;
        resolve(true);
    });
}

Answer 1

TLDR: Just change process.env

To change, add or delete environment variables, use process.env. The following is test code showing how this works:

In main.js:

console.log(process.env.DB_DATABASE);

In exec.js:

const execSync = require ('child_process').execSync;

process.env.DB_DATABASE = 'foo'; // this is ALL you need to do

console.log(execSync('node main.js').toString('utf8'));

With the two files above, if you run node exec.js you will see foo printed out in the console. This is printed from main.js which inherits the environment from exec.js.

So all you need to do in your code is:

function exec_api() { 
    return new Promise(function (resolve) {
        const exec = require('child_process').exec;

        // The following is node.js equivalent of bash "export":
        process.env.DB_HOST = process.env.UNITTEST_DB_HOST;
        process.env.DB_DATABASE = process.env.UNITTEST_DB_DATABASE;
        process.env.DB_USERNAME = process.env.UNITTEST_DB_USERNAME;
        process.env.DB_PASSWORD = process.env.UNITTEST_DB_PASSWORD;
        process.env.PORT = process.env.UNITTEST_SERVICE_PORT;

        let child_process_obj = exec('node main.js', {
            stdio: ['inherit', 'inherit', 'inherit']
        });
        
        unittest_api_backend_process_id = child_process_obj.pid;
        
        resolve(true);
    });
}

Note that if you want the promise to return when the main.js ends you need to do:

function exec_api() { 
    return new Promise(function (resolve) {
        const exec = require('child_process').exec;

        // The following is node.js equivalent of bash "export":
        process.env.DB_HOST = process.env.UNITTEST_DB_HOST;
        process.env.DB_DATABASE = process.env.UNITTEST_DB_DATABASE;
        process.env.DB_USERNAME = process.env.UNITTEST_DB_USERNAME;
        process.env.DB_PASSWORD = process.env.UNITTEST_DB_PASSWORD;
        process.env.PORT = process.env.UNITTEST_SERVICE_PORT;

        let child_process_obj = exec('node main.js', {
            stdio: ['inherit', 'inherit', 'inherit']
        });
        
        unittest_api_backend_process_id = child_process_obj.pid;
        
        child_process_obj.on('exit', () => resolve(true));

        // ^^^ Cannot use `await` as the API is not promise based
        //     but event based instead.
    });
}

---

Long story: The full explanation of why export doesn't work

On unixen, environment variables, and indeed, the entire environment including current working directory, root directory (which can be changed via chroot) etc. are not features of shells. They are features of processes.

We may be familiar with the export syntax of some shells to set environment variables for child processes but that is the shell's syntax. It has nothing to do with environment variables themselves. C/C++ for example don't use export instead uses the setenv() function do set environment variables (indeed, internally that's what bash/sh/ksh etc do when implementing export).

In node.js, the mechanism for reading and setting environment variables is via process.env.

Why asking a shell to do it don't work

This is not merely a node.js issue. It also won't work in bash:

In exporter.sh:

#! /bin/bash

export DB_DATABASE=$1

In exec.sh:

#! /bin/bash

./exporter.sh foo
echo $DB_DATABASE ;# does not print "foo"

This is a core security feature of unixen: other users should not be allowed to mess with your process. The way this policy is enforced in the case of the environment is that only a parent process can set the environment of the child process. A child process is not allowed to set the environment of the parent process. The assumption is that the child process belongs to the parent process so you should be allowed to do what you want to a program - but since the parent process (you) don't belong to the child process the child is not allowed to mess with the parent's environment.

That's why your attempt to use export doesn't work. It actually works (the variables are indeed created in the subshell) but is not allowed to change the environment of it's parent (the node.js process)