@nestjs/config/dist/utils/read-env-files.util.js

Configuration for NestJS: load .env files and custom configuration, validate it at startup, and read it through an injectable ConfigService.

import * as fs from 'fs';
import { hasOwn } from './property-path.util.js';
/**
 * Reads and parses env files. A variable defined in more than one file gets
 * its value from the first file that defines it. The variables of the first
 * file come first, so that chains of references are expanded in file order.
 */
export function readEnvFiles(envFilePaths, parser) {
    const config = {};
    for (const envFilePath of envFilePaths) {
        if (!fs.existsSync(envFilePath)) {
            continue;
        }
        const parsed = parser(fs.readFileSync(envFilePath));
        for (const [key, value] of Object.entries(parsed)) {
            // "__proto__" (e.g. returned by a JSON parser) would replace the
            // prototype of the merged object instead of defining a variable
            if (key === '__proto__' || hasOwn(config, key)) {
                continue;
            }
            // process.env cuts a value off at a NUL character, so what is
            // validated would not be what the application gets
            if (typeof value === 'string' && value.includes('\0')) {
                throw new Error(`Environment variable "${key}" in "${envFilePath}" contains a NUL character`);
            }
            config[key] = value;
        }
    }
    return config;
}