🔒 Remap environment variables ending in `_FILE` with the contents of the file

deno.ts

import { existsSync } from "@std/fs/exists";

interface LoadOptions {
  /**
   * Whether to overwrite existing env vars.
   *
   * @default false
   */
  overwrite?: boolean;
  /**
   * Whether to remove the _FILE env var after loading the value.
   *
   * @default false
   */
  prune?: boolean;
}

/**
 * Load environment variables from files.
 *
 * @description This function will check all environment variables that end with `_FILE`
 * and load the value from the file path specified in the variable.
 *
 * @param [options.overwrite=false] - Whether to overwrite existing env vars.
 * @param [options.prune=false] - Whether to remove the _FILE env var after loading the value.
 */
export function load(options: LoadOptions = {}): void {
  const { overwrite = false, prune = false } = options;

  const env = Deno.env.toObject();
  const entries = Object.entries(env).filter(([key]) => key.endsWith("_FILE"));

  for (const [key, path] of entries) {
    const keyWithoutSuffix = key.replace(/_FILE$/, "");

    if (Deno.env.has(keyWithoutSuffix) && !overwrite) continue;

    if (!existsSync(path)) continue;

    if (!Deno.lstatSync(path).isFile) continue;

    const value = Deno.readTextFileSync(path);
    Deno.env.set(keyWithoutSuffix, value);

    if (prune) Deno.env.delete(key);
  }
}

node.ts

import { existsSync, readFileSync, statSync } from "node:fs";

interface LoadOptions {
  /**
   * Whether to overwrite existing env vars.
   *
   * @default false
   */
  overwrite?: boolean;
  /**
   * Whether to remove the _FILE env var after loading the value.
   *
   * @default false
   */
  prune?: boolean;
}

/**
 * Load environment variables from files.
 *
 * @description This function will check all environment variables that end with `_FILE`
 * and load the value from the file path specified in the variable.
 *
 * @param [options.overwrite=false] - Whether to overwrite existing env vars.
 * @param [options.prune=false] - Whether to remove the _FILE env var after loading the value.
 */
export function load(options: LoadOptions = {}): void {
  const { overwrite = false, prune = false } = options;

  const entries = Object.entries(process.env).filter(([key]) =>
    key.endsWith("_FILE")
  );

  for (const [key, path] of entries) {
    const keyWithoutSuffix = key.replace(/_FILE$/, "");

    if (!!process.env[keyWithoutSuffix] && !overwrite) continue;

    if (!existsSync(path)) continue;

    if (!statSync(path).isFile()) continue;

    const value = readFileSync(path, "utf8").trim();
    process.env[keyWithoutSuffix] = value;

    if (prune) delete process.env[key];
  }
}

The primary use case for this helper function is for Docker Secrets.

Currently when using Docker Secrets it will expose the added secrets as files in the /run/secrets directory & the most widely used / accepted pattern is to take your existing environment variable name and add a _FILE suffix at the end to make it clear it is pointing to a file.
However, Node.js or any other JavaScript currently does not account for this (of course). As such this small helper function is designed to fix that by simply finding all environment variables ending with _FILE, attempting to load the value from the value or path & then setting a new environment variable to the contents of the loaded file. With additional options to remove any _FILE environment variables & also whether to overwrite any existing or duplicate environment variables.