How to read environment variables from Node.js
The process core module of Node.js provides the env property which hosts all the environment variables that were set at the moment the process was started.
The below code runs app.js and set USER_ID and USER_KEY.
USER_ID=239482 USER_KEY=foobar node app.js
That will pass the user USER_ID as 239482 and the USER_KEY as foobar. This is suitable for testing, however for production, you will probably be configuring some bash scripts to export variables.
Note:
processdoes not need to be imported, it is a global object in Node.js.
Here is an example that accesses the USER_ID and USER_KEY environment variables, which we set in above code.
var console: ConsoleThe `console` module provides a simple debugging console that is similar to the
JavaScript console mechanism provided by web browsers.
The module exports two specific components:
* A `Console` class with methods such as `console.log()`, `console.error()` and `console.warn()` that can be used to write to any Node.js stream.
* A global `console` instance configured to write to [`process.stdout`](https://nodejs.org/docs/latest-v22.x/api/process.html#processstdout) and
[`process.stderr`](https://nodejs.org/docs/latest-v22.x/api/process.html#processstderr). The global `console` can be used without importing the `node:console` module.
_**Warning**_: The global console object's methods are neither consistently
synchronous like the browser APIs they resemble, nor are they consistently
asynchronous like all other Node.js streams. See the [`note on process I/O`](https://nodejs.org/docs/latest-v22.x/api/process.html#a-note-on-process-io) for
more information.
Example using the global `console`:
```js
console.log('hello world');
// Prints: hello world, to stdout
console.log('hello %s', 'world');
// Prints: hello world, to stdout
console.error(new Error('Whoops, something bad happened'));
// Prints error message and stack trace to stderr:
// Error: Whoops, something bad happened
// at [eval]:5:15
// at Script.runInThisContext (node:vm:132:18)
// at Object.runInThisContext (node:vm:309:38)
// at node:internal/process/execution:77:19
// at [eval]-wrapper:6:22
// at evalScript (node:internal/process/execution:76:60)
// at node:internal/main/eval_string:23:3
const name = 'Will Robinson';
console.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to stderr
```
Example using the `Console` class:
```js
const out = getStreamSomehow();
const err = getStreamSomehow();
const myConsole = new console.Console(out, err);
myConsole.log('hello world');
// Prints: hello world, to out
myConsole.log('hello %s', 'world');
// Prints: hello world, to out
myConsole.error(new Error('Whoops, something bad happened'));
// Prints: [Error: Whoops, something bad happened], to err
const name = 'Will Robinson';
myConsole.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to err
```console.Console.log(message?: any, ...optionalParams: any[]): void (+1 overload)Prints to `stdout` with newline. Multiple arguments can be passed, with the
first used as the primary message and all additional used as substitution
values similar to [`printf(3)`](http://man7.org/linux/man-pages/man3/printf.3.html)
(the arguments are all passed to [`util.format()`](https://nodejs.org/docs/latest-v22.x/api/util.html#utilformatformat-args)).
```js
const count = 5;
console.log('count: %d', count);
// Prints: count: 5, to stdout
console.log('count:', count);
// Prints: count: 5, to stdout
```
See [`util.format()`](https://nodejs.org/docs/latest-v22.x/api/util.html#utilformatformat-args) for more information.log(var process: NodeJS.Processprocess.NodeJS.Process.env: NodeJS.ProcessEnvThe `process.env` property returns an object containing the user environment.
See [`environ(7)`](http://man7.org/linux/man-pages/man7/environ.7.html).
An example of this object looks like:
```js
{
TERM: 'xterm-256color',
SHELL: '/usr/local/bin/bash',
USER: 'maciej',
PATH: '~/.bin/:/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin',
PWD: '/Users/maciej',
EDITOR: 'vim',
SHLVL: '1',
HOME: '/Users/maciej',
LOGNAME: 'maciej',
_: '/usr/local/bin/node'
}
```
It is possible to modify this object, but such modifications will not be
reflected outside the Node.js process, or (unless explicitly requested)
to other `Worker` threads.
In other words, the following example would not work:
```bash
node -e 'process.env.foo = "bar"' && echo $foo
```
While the following will:
```js
import { env } from 'node:process';
env.foo = 'bar';
console.log(env.foo);
```
Assigning a property on `process.env` will implicitly convert the value
to a string. **This behavior is deprecated.** Future versions of Node.js may
throw an error when the value is not a string, number, or boolean.
```js
import { env } from 'node:process';
env.test = null;
console.log(env.test);
// => 'null'
env.test = undefined;
console.log(env.test);
// => 'undefined'
```
Use `delete` to delete a property from `process.env`.
```js
import { env } from 'node:process';
env.TEST = 1;
delete env.TEST;
console.log(env.TEST);
// => undefined
```
On Windows operating systems, environment variables are case-insensitive.
```js
import { env } from 'node:process';
env.TEST = 1;
console.log(env.test);
// => 1
```
Unless explicitly specified when creating a `Worker` instance,
each `Worker` thread has its own copy of `process.env`, based on its
parent thread's `process.env`, or whatever was specified as the `env` option
to the `Worker` constructor. Changes to `process.env` will not be visible
across `Worker` threads, and only the main thread can make changes that
are visible to the operating system or to native add-ons. On Windows, a copy of `process.env` on a `Worker` instance operates in a case-sensitive manner
unlike the main thread.env.string | undefinedUSER_ID); // "239482"
var console: ConsoleThe `console` module provides a simple debugging console that is similar to the
JavaScript console mechanism provided by web browsers.
The module exports two specific components:
* A `Console` class with methods such as `console.log()`, `console.error()` and `console.warn()` that can be used to write to any Node.js stream.
* A global `console` instance configured to write to [`process.stdout`](https://nodejs.org/docs/latest-v22.x/api/process.html#processstdout) and
[`process.stderr`](https://nodejs.org/docs/latest-v22.x/api/process.html#processstderr). The global `console` can be used without importing the `node:console` module.
_**Warning**_: The global console object's methods are neither consistently
synchronous like the browser APIs they resemble, nor are they consistently
asynchronous like all other Node.js streams. See the [`note on process I/O`](https://nodejs.org/docs/latest-v22.x/api/process.html#a-note-on-process-io) for
more information.
Example using the global `console`:
```js
console.log('hello world');
// Prints: hello world, to stdout
console.log('hello %s', 'world');
// Prints: hello world, to stdout
console.error(new Error('Whoops, something bad happened'));
// Prints error message and stack trace to stderr:
// Error: Whoops, something bad happened
// at [eval]:5:15
// at Script.runInThisContext (node:vm:132:18)
// at Object.runInThisContext (node:vm:309:38)
// at node:internal/process/execution:77:19
// at [eval]-wrapper:6:22
// at evalScript (node:internal/process/execution:76:60)
// at node:internal/main/eval_string:23:3
const name = 'Will Robinson';
console.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to stderr
```
Example using the `Console` class:
```js
const out = getStreamSomehow();
const err = getStreamSomehow();
const myConsole = new console.Console(out, err);
myConsole.log('hello world');
// Prints: hello world, to out
myConsole.log('hello %s', 'world');
// Prints: hello world, to out
myConsole.error(new Error('Whoops, something bad happened'));
// Prints: [Error: Whoops, something bad happened], to err
const name = 'Will Robinson';
myConsole.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to err
```console.Console.log(message?: any, ...optionalParams: any[]): void (+1 overload)Prints to `stdout` with newline. Multiple arguments can be passed, with the
first used as the primary message and all additional used as substitution
values similar to [`printf(3)`](http://man7.org/linux/man-pages/man3/printf.3.html)
(the arguments are all passed to [`util.format()`](https://nodejs.org/docs/latest-v22.x/api/util.html#utilformatformat-args)).
```js
const count = 5;
console.log('count: %d', count);
// Prints: count: 5, to stdout
console.log('count:', count);
// Prints: count: 5, to stdout
```
See [`util.format()`](https://nodejs.org/docs/latest-v22.x/api/util.html#utilformatformat-args) for more information.log(var process: NodeJS.Processprocess.NodeJS.Process.env: NodeJS.ProcessEnvThe `process.env` property returns an object containing the user environment.
See [`environ(7)`](http://man7.org/linux/man-pages/man7/environ.7.html).
An example of this object looks like:
```js
{
TERM: 'xterm-256color',
SHELL: '/usr/local/bin/bash',
USER: 'maciej',
PATH: '~/.bin/:/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin',
PWD: '/Users/maciej',
EDITOR: 'vim',
SHLVL: '1',
HOME: '/Users/maciej',
LOGNAME: 'maciej',
_: '/usr/local/bin/node'
}
```
It is possible to modify this object, but such modifications will not be
reflected outside the Node.js process, or (unless explicitly requested)
to other `Worker` threads.
In other words, the following example would not work:
```bash
node -e 'process.env.foo = "bar"' && echo $foo
```
While the following will:
```js
import { env } from 'node:process';
env.foo = 'bar';
console.log(env.foo);
```
Assigning a property on `process.env` will implicitly convert the value
to a string. **This behavior is deprecated.** Future versions of Node.js may
throw an error when the value is not a string, number, or boolean.
```js
import { env } from 'node:process';
env.test = null;
console.log(env.test);
// => 'null'
env.test = undefined;
console.log(env.test);
// => 'undefined'
```
Use `delete` to delete a property from `process.env`.
```js
import { env } from 'node:process';
env.TEST = 1;
delete env.TEST;
console.log(env.TEST);
// => undefined
```
On Windows operating systems, environment variables are case-insensitive.
```js
import { env } from 'node:process';
env.TEST = 1;
console.log(env.test);
// => 1
```
Unless explicitly specified when creating a `Worker` instance,
each `Worker` thread has its own copy of `process.env`, based on its
parent thread's `process.env`, or whatever was specified as the `env` option
to the `Worker` constructor. Changes to `process.env` will not be visible
across `Worker` threads, and only the main thread can make changes that
are visible to the operating system or to native add-ons. On Windows, a copy of `process.env` on a `Worker` instance operates in a case-sensitive manner
unlike the main thread.env.string | undefinedUSER_KEY); // "foobar"
In the same way you can access any custom environment variable you set.
Node.js 20 introduced experimental support for .env files.
Now, you can use the --env-file flag to specify an environment file when running your Node.js application. Here's an example .env file and how to access its variables using process.env.
# .env file
PORT=3000
In your js file
var console: ConsoleThe `console` module provides a simple debugging console that is similar to the
JavaScript console mechanism provided by web browsers.
The module exports two specific components:
* A `Console` class with methods such as `console.log()`, `console.error()` and `console.warn()` that can be used to write to any Node.js stream.
* A global `console` instance configured to write to [`process.stdout`](https://nodejs.org/docs/latest-v22.x/api/process.html#processstdout) and
[`process.stderr`](https://nodejs.org/docs/latest-v22.x/api/process.html#processstderr). The global `console` can be used without importing the `node:console` module.
_**Warning**_: The global console object's methods are neither consistently
synchronous like the browser APIs they resemble, nor are they consistently
asynchronous like all other Node.js streams. See the [`note on process I/O`](https://nodejs.org/docs/latest-v22.x/api/process.html#a-note-on-process-io) for
more information.
Example using the global `console`:
```js
console.log('hello world');
// Prints: hello world, to stdout
console.log('hello %s', 'world');
// Prints: hello world, to stdout
console.error(new Error('Whoops, something bad happened'));
// Prints error message and stack trace to stderr:
// Error: Whoops, something bad happened
// at [eval]:5:15
// at Script.runInThisContext (node:vm:132:18)
// at Object.runInThisContext (node:vm:309:38)
// at node:internal/process/execution:77:19
// at [eval]-wrapper:6:22
// at evalScript (node:internal/process/execution:76:60)
// at node:internal/main/eval_string:23:3
const name = 'Will Robinson';
console.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to stderr
```
Example using the `Console` class:
```js
const out = getStreamSomehow();
const err = getStreamSomehow();
const myConsole = new console.Console(out, err);
myConsole.log('hello world');
// Prints: hello world, to out
myConsole.log('hello %s', 'world');
// Prints: hello world, to out
myConsole.error(new Error('Whoops, something bad happened'));
// Prints: [Error: Whoops, something bad happened], to err
const name = 'Will Robinson';
myConsole.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to err
```console.Console.log(message?: any, ...optionalParams: any[]): void (+1 overload)Prints to `stdout` with newline. Multiple arguments can be passed, with the
first used as the primary message and all additional used as substitution
values similar to [`printf(3)`](http://man7.org/linux/man-pages/man3/printf.3.html)
(the arguments are all passed to [`util.format()`](https://nodejs.org/docs/latest-v22.x/api/util.html#utilformatformat-args)).
```js
const count = 5;
console.log('count: %d', count);
// Prints: count: 5, to stdout
console.log('count:', count);
// Prints: count: 5, to stdout
```
See [`util.format()`](https://nodejs.org/docs/latest-v22.x/api/util.html#utilformatformat-args) for more information.log(var process: NodeJS.Processprocess.NodeJS.Process.env: NodeJS.ProcessEnvThe `process.env` property returns an object containing the user environment.
See [`environ(7)`](http://man7.org/linux/man-pages/man7/environ.7.html).
An example of this object looks like:
```js
{
TERM: 'xterm-256color',
SHELL: '/usr/local/bin/bash',
USER: 'maciej',
PATH: '~/.bin/:/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin',
PWD: '/Users/maciej',
EDITOR: 'vim',
SHLVL: '1',
HOME: '/Users/maciej',
LOGNAME: 'maciej',
_: '/usr/local/bin/node'
}
```
It is possible to modify this object, but such modifications will not be
reflected outside the Node.js process, or (unless explicitly requested)
to other `Worker` threads.
In other words, the following example would not work:
```bash
node -e 'process.env.foo = "bar"' && echo $foo
```
While the following will:
```js
import { env } from 'node:process';
env.foo = 'bar';
console.log(env.foo);
```
Assigning a property on `process.env` will implicitly convert the value
to a string. **This behavior is deprecated.** Future versions of Node.js may
throw an error when the value is not a string, number, or boolean.
```js
import { env } from 'node:process';
env.test = null;
console.log(env.test);
// => 'null'
env.test = undefined;
console.log(env.test);
// => 'undefined'
```
Use `delete` to delete a property from `process.env`.
```js
import { env } from 'node:process';
env.TEST = 1;
delete env.TEST;
console.log(env.TEST);
// => undefined
```
On Windows operating systems, environment variables are case-insensitive.
```js
import { env } from 'node:process';
env.TEST = 1;
console.log(env.test);
// => 1
```
Unless explicitly specified when creating a `Worker` instance,
each `Worker` thread has its own copy of `process.env`, based on its
parent thread's `process.env`, or whatever was specified as the `env` option
to the `Worker` constructor. Changes to `process.env` will not be visible
across `Worker` threads, and only the main thread can make changes that
are visible to the operating system or to native add-ons. On Windows, a copy of `process.env` on a `Worker` instance operates in a case-sensitive manner
unlike the main thread.env.string | undefinedPORT); // "3000"
Run app.js file with environment variables set in .env file.
node --env-file=.env app.js
This command loads all the environment variables from the .env file, making them available to the application on process.env
Also, you can pass multiple --env-file arguments. Subsequent files override pre-existing variables defined in previous files.
node --env-file=.env --env-file=.development.env app.js
Note: if the same variable is defined in the environment and in the file, the value from the environment takes precedence.
In case you want to optionally read from a .env file, it's possible to avoid
throwing an error if the file is missing using the --env-file-if-exists flag.
node --env-file-if-exists=.env app.js