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Environment variables

There are a few ways to use environment variables in Deno:

Built-in Deno.env Jump to heading

The Deno runtime offers built-in support for environment variables with Deno.env.

Deno.env has getter and setter methods. Here is example usage:

Deno.env.set("FIREBASE_API_KEY", "examplekey123");
Deno.env.set("FIREBASE_AUTH_DOMAIN", "firebasedomain.com");

console.log(Deno.env.get("FIREBASE_API_KEY")); // examplekey123
console.log(Deno.env.get("FIREBASE_AUTH_DOMAIN")); // firebasedomain.com
console.log(Deno.env.has("FIREBASE_AUTH_DOMAIN")); // true

.env file Jump to heading

Deno supports .env files. You can cause Deno to read environment variables from .env using the --env flag: deno run --env <script>. This will read .env by default; if you want need to load environment variables from a different file, you can specify that file as a parameter to the flag.

Alternately, the dotenv package in the standard library will load environment variables from .env as well.

Let's say you have an .env file that looks like this:

GREETING="Hello, world."

Import the load module to auto-import from the .env file and into the process environment.

import "jsr:@std/dotenv/load";

console.log(Deno.env.get("GREETING")); // "Hello, world."

Further documentation for .env handling can be found in the @std/dotenv documentation.

std/cli Jump to heading

The Deno Standard Library has a std/cli module for parsing command line arguments. Please refer to the module for documentation and examples.

Special environment variables Jump to heading

The Deno runtime has these special environment variables.

name description
DENO_AUTH_TOKENS A semi-colon separated list of bearer tokens and hostnames to use when fetching remote modules from private repositories
(e.g. abcde12345@deno.land;54321edcba@github.com)
DENO_TLS_CA_STORE Comma-separated list of order dependent certificate stores.
Possible values: system, mozilla. Defaults to mozilla.
DENO_CERT Load certificate authority from PEM encoded file
DENO_DIR Set the cache directory
DENO_INSTALL_ROOT Set deno install's output directory (defaults to $HOME/.deno/bin)
DENO_REPL_HISTORY Set REPL history file path History file is disabled when the value is empty
(defaults to $DENO_DIR/deno_history.txt)
DENO_NO_PACKAGE_JSON Disables auto-resolution of package.json
DENO_NO_PROMPT Set to disable permission prompts on access
(alternative to passing --no-prompt on invocation)
DENO_NO_UPDATE_CHECK Set to disable checking if a newer Deno version is available
DENO_V8_FLAGS Set V8 command line options
DENO_JOBS Number of parallel workers used for the --parallel flag with the test subcommand.
Defaults to number of available CPUs.
DENO_WEBGPU_TRACE Path to a directory to output a WGPU trace to when using the WebGPU API
DENO_WEBGPU_BACKEND Select the backend WebGPU will use, or a comma separated list of backends in order of preference. Possible values are vulkan, dx12, metal, or opengl
HTTP_PROXY Proxy address for HTTP requests (module downloads, fetch)
HTTPS_PROXY Proxy address for HTTPS requests (module downloads, fetch)
NPM_CONFIG_REGISTRY URL to use for the npm registry.
NO_COLOR Set to disable color
NO_PROXY Comma-separated list of hosts which do not use a proxy (module downloads, fetch)