When working with Node.js, you might need to spawn child processes to execute external commands or run sub-processes. In some cases, you may need to pass environment variables to these child processes. In this article, we will explore how to set environment variables for a child process in Node.js.

Table of Contents

• Using the spawn method with environment variables
• Using the exec method with environment variables
• Conclusion

Using the spawn method with environment variables

Node.js provides the child_process module, which allows us to spawn child processes. The spawn method of this module enables us to execute commands in a new process.

To set environment variables for a child process using spawn, we can pass an env object as one of the options to the spawn method. The env object should contain the necessary environment variable key-value pairs.

Here’s an example:

const { spawn } = require('child_process');

const child = spawn('echo', ['Hello, World!'], { env: { MESSAGE: 'Custom message' } });

child.stdout.on('data', (data) => {
  console.log(`Child process output: ${data}`);
});

In the above code, we are spawning a child process to execute the echo command with the argument "Hello, World!". We are also passing an env object to the spawn method with a custom environment variable MESSAGE.

Using the exec method with environment variables

Another way to execute a command in a child process is by using the exec method from the child_process module. This method allows us to run a command in a shell and provides more flexibility compared to spawn.

To set environment variables for a child process using exec, we can use the env parameter. The env parameter expects an object containing the environment variable key-value pairs.

Here’s an example:

const { exec } = require('child_process');

const command = 'echo $MESSAGE';
const env = { MESSAGE: 'Custom message' };

exec(command, { env }, (error, stdout, stderr) => {
  if (error) {
    console.error(`Error occurred: ${error.message}`);
    return;
  }

  console.log(`Child process output: ${stdout}`);
});

In the above code, we use the exec method to run the command echo $MESSAGE in a shell. We pass the env object containing our custom environment variable MESSAGE.

Conclusion

Setting environment variables for child processes in Node.js can be achieved using either the spawn or exec method from the child_process module. By passing an env object with the required environment variable key-value pairs, you can control and customize the environment variables for the child processes.