.env file
A .env file is a plain-text configuration file containing environment-variable assignments that applications or tools can load at runtime.
Learn Docker in a Month of Lunches, Second Edition
An environment file is a file containing environment-specific variable assignments for application configuration.
- How it is used
- Supplies default variables for Docker Compose commands and substitutions when running an environment-specific application setup.
- How deep it goes
- Shows a complete `.env` example and a startup command, but does not detail environment-variable precedence.
- Examples
- Uses a to-do application whose `.env` selects a test override, sets ports, and starts web and database containers.
- What you can do after
- Operate/configure it by placing `.env` beside Compose files and running `docker compose up -d` with fewer command arguments.
Read how Learn Docker in a Month of Lunches, Second Edition explains .env file →
Road to Kubernetes
A dotenv file is a text file containing environment-variable assignments that applications or tooling can load into an execution environment.
- How it is used
- Keeps runtime settings outside application code and supplies them to Docker containers during local or production deployment.
- How deep it goes
- Shows assignment syntax, Docker and Compose wiring, and a deployment workflow; defers dedicated secret-manager configuration and transfer encryption.
- Examples
- Uses a Redis hostname in a Python project and a GitHub Actions workflow that copies .env to a production virtual machine.
- What you can do after
- Operate/configure it with Docker --env-file or Compose env_file, then use the supplied Redis-host and deployment patterns.
Build Financial Software with Generative AI (From Scratch)
An .env file is a conventionally named environment file containing application configuration values as environment-variable assignments.
- How it is used
- Centralizes usernames, passwords, ports, and server settings for Dockerized applications instead of scattering hardcoded values through code.
- How deep it goes
- Defines assignments, Docker wiring, naming conventions, and documentation needs, but does not detail a complete file-format specification.
- Examples
- Uses PostgreSQL assignments, Docker env_file wiring, and Python os.getenv calls to build a database connection string.
- What you can do after
- Operate/configure a Dockerized application by externalizing settings and supplying them through an environment file.
Read how Build Financial Software with Generative AI (From Scratch) explains .env file →
Build AI-Enhanced Web Apps
A .env file is a configuration file containing environment-variable assignments, commonly used to provide local application settings and credentials.
- How it is used
- Stores local API credentials and configuration so backend applications can select providers without hardcoding secrets.
- How deep it goes
- Explains file placement, loading, client exposure, and version-control protection, withholds broader deployment configuration.
- Examples
- Uses OpenAI and Gemini API-key assignments plus a NEXT_PUBLIC_GOOGLE_ANALYTICS_ID example.
- What you can do after
- Configure and validate provider credentials for Express.js or Next.js applications while keeping secrets out of client bundles and repositories.
Related concepts
- environment variableconfigures · An environment variable is a named value supplied through an operating-system or process environment and made available to programs for runtime configuration or information.
- Docker Composeconfigures · Docker Compose is a tool for defining and running applications composed of multiple containers through declarative configuration.
- .gitignoreconfigured by · .gitignore is a Git configuration file containing patterns that specify files and directories Git should exclude from version-control tracking.
- runnerproduced by · A workflow runner is an execution agent or environment that runs the jobs and steps of an automated workflow or pipeline.
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