Understanding .env files: what they are and how to use them safely

What are .env files?

Env files store environment-specific configuration as KEY=VALUE pairs used by many apps during development. They’re typically loaded at startup and become environment variables available to your app.

A simple format

Key-value pairs in plain text, one per line. Example:

DBHOST=localhost DBPORT=5432 DBUSER=youruser DBPASSWORD=secret

Notes: avoid spaces around =, and quote values if they contain special characters. If you need to include a value with spaces, wrap in quotes: APP_NAME="My App".

Common use cases

• Storing database credentials, API keys, feature flags, and other secrets.
• Configuring behavior per environment (development, staging, production).

Security and best practices

Never commit .env files

Store them locally and add .env to your .gitignore. If you share code, include a .env.example with the required KEY names.

Use a .env.example

Provide a template showing the required variables without values.

Consider secrets management for production

For production, rely on dedicated secret management (e.g., AWS Secrets Manager, Vault) or runtime environment variables provided by your hosting platform.

Using .env files in your project

Loading environment variables

Most languages have a dotenv library. Examples:

• Node.js: require('dotenv').config(); variables via process.env.VAR
• Python: from dotenv import loaddotenv; loaddotenv(); env vars via os.environ['VAR']
• Ruby, PHP, and others have similar libraries.

Cross-language usage and best practices

Keep .env files out of version control, and load them at startup before your app logic runs.

Alternatives and tips

Separate per-environment files

Use .env.development, .env.production and load the appropriate one via your app or hosting platform.

Production deployment considerations

In production, prefer real environment variables or secrets managers and limit who can read them.