ReadEnv

Simple program that reads .env file and use it to run given command.

Never load environment variables manually or pollute your interpreter profile again.

How it works

1. Read current environment variables
2. Read .env file in current or parent directory
3. Extend current environment variables with ones read from .env file
4. Spawn <COMMAND> with generated environment variables
5. Replace current process with spawned one

Installation

cargo install readenv

Usage

1. Create .env file in with <KEY>=<VALUE> structure in current or parent directory

2. Run the app:

   renv <COMMAND>
   

During the run, the <COMMAND> acts exactly as executed directly, including environment variables, stdin, stdout, stderr, pipelines support and signals handling.

.env format

Support of .env file is provided by dotenv library. See its documentation for the format.

Recipes

Django

To run a Django project, a settings file is needed. One approach is to have different settings file per enviroment (e.g. for development and production).

The easiest way to do that is to define environment variable DJANGO_SETTINGS_MODULE with name of the settings module.

Let's create .env file (given settings module is local_settings):

echo 'DJANGO_SETTINGS_MODULE=local_settings' >> .env

Now run Django server with one command:

renv django-admin.py runserver

Virtualenv

Virtualenv is a nice tool to isolate Python dependencies for a project.

To switch to given virtualenv one has to use command . <VENV>/bin/activate.

Let's create .env file (given virtualenv directory is .venv):

echo "VIRTUAL_ENV=$PWD/.venv" >> .env
echo "PATH=$PWD/.venv/bin:\${PATH}" >> .env

Now check Python interpreter:

renv which python

Result should be:

$PWD/.venv/bin/python

Try pip:

renv pip freeze

Result should be the list of dependencies installed in your virtualenv.

Design considerations

12-factor App methodology is great but could be boring. A simple tool that automates work with environment variables would be helpful.

That tool should be a drop-in replacement for any app, so it:

• Must support stdin, stdout and stderr
• Could be used in pipelines
• Must handle signals (e.g. SIGTERM or SIGKILL) identically

Also, it would be nice to:

• Have small application size
• Have low RAM footprint
• Do not depend on shell used
• Be safe

Solution:

• Produce binary program
• Use Rust
• Replace its process with executed command (like exec in BASH)

Kudos

Thanks team of dotenv and dotenv library for the most of work ;-)