What is direnv

direnv is a tool that allows you to set up different environments for different directories. direnv allows you to automatically set up the specified environment variables, aliases, commands, and shell functions for a directory each time you navigate to it. This makes it easy to switch between environments as needed for different projects.

direnv uses a file .envrc to set the environment for a directory. The .envrc file is read by direnv when it is moved with the cd command, and sets the environment for that directory.

The following is an example of .envrc file.

# environment variable
export MY_VAR=example_value
export PATH=$PWD/bin:$PATH

# alias
alias ll='ls -l'

# shell function
function my_function() {
  echo "Hello, World!"
}

This example defines an environment variable called MY_VAR and adds $PWD/bin to $PATH. It also defines an alias ll and a shell function my_function. In this way, you can easily set up different environments for different projects.

How to use direnv

Here is how to use direnv.

Install

On Mac, you can easily install direnv with the brew command.

$ brew install direnv

After installing direnv, add hooks to your shell; for bash, run the following command.

$ echo 'eval "$(direnv hook bash)"' >> ~/.bashrc
$ source ~/.bashrc

allow

Read the .envrc file with the direnv allow command.

For example, in the /my-project directory, create a .envrc file like this.

export TEST=test

Execute the following command.

$ direnv allow

direnv: loading ~/my-project/.envrc
direnv: export +TEST

Under the /my-project directory, the environment variable TEST will be set.

$ echo $TEST

test

Moving from the /my-project directory will unload direnv.

$ cd ..

direnv: unloading

You can see that the environment variable TEST is unset.

$ echo $TEST

Other commands

direnv has several commands in addition to the allow command. See the direnv --help command for details.

$ direnv --help

direnv v2.32.2
Usage: direnv COMMAND [...ARGS]

Available commands
------------------
allow [PATH_TO_RC]:
permit [PATH_TO_RC]:
grant [PATH_TO_RC]:
  Grants direnv permission to load the given .envrc or .env file.
block [PATH_TO_RC]:
deny [PATH_TO_RC]:
revoke [PATH_TO_RC]:
  Revokes the authorization of a given .envrc or .env file.
edit [PATH_TO_RC]:
  Opens PATH_TO_RC or the current .envrc or .env into an $EDITOR and allow
  the file to be loaded afterwards.
exec DIR COMMAND [...ARGS]:
  Executes a command after loading the first .envrc or .env found in DIR
fetchurl <url> [<integrity-hash>]:
  Fetches a given URL into direnv's CAS
help [SHOW_PRIVATE]:
  shows this help
hook SHELL:
  Used to setup the shell hook
prune:
  removes old allowed files
reload:
  triggers an env reload
status:
  prints some debug status information
stdlib:
  Displays the stdlib available in the .envrc execution context
version [VERSION_AT_LEAST]:
  prints the version or checks that direnv is older than VERSION_AT_LEAST.

Use .env and .envrc together

docker-compose and dotenv use a file .env to set environment variables.

If you want to use .env and .envrc together, you can avoid double management of environment variables in the following way.

Environment variable definitions are written in .env.

API_KEY=xxxxxxxxxxxxxxxxxxxx

You can refer to environment variables defined in .env in .envrc by writing dotenv in .envrc.

dotenv

If the file name is not .env, the path can be specified as follows.

dotenv ./.env.development

Use venv and .envrc together

By using direnv with Python's venv, you can activate a virtual environment when you move to a project directory and automatically deactivate it when you exit that directory.

First, create a Python virtual environment.

$ cd my-project
$ python -m venv venv

Create a .envrc under the project directory as follows.

source venv/bin/activate

export PYTHONPATH=${APP_HOME}
export HOGE='HOGE'
export FUGA='FUGA'

Navigate to the target directory to activate the virtual environment.

$ cd my-project

direnv: loading ~/Projects/my-project/.envrc
direnv: export +BAR +FOO ~PYTHONPATH

(venv)$

After exiting the directory, the virtual environment is deactivated.

(venv)$ cd ..

direnv: unloading

$

References

https://github.com/direnv/direnv