direnv Skill

This skill provides comprehensive guidance for working with direnv, covering installation, configuration, stdlib functions, and best practices for per-project environment management.

When to Use This Skill

Use this skill when:

• Installing and configuring direnv on macOS or Linux
• Creating or modifying .envrc files for projects
• Setting up per-project environment variables
• Configuring language-specific layouts (Python, Node.js, Ruby, Go, Perl)
• Integrating direnv with Nix or Nix Flakes
• Managing secrets and environment configuration for teams
• Troubleshooting environment loading issues
• Creating custom direnv extensions

Core Concepts

What is direnv?

direnv is a shell extension that loads and unloads environment variables based on the current directory. When you cd into a directory with a .envrc file, direnv automatically loads the environment. When you leave, it unloads the changes.

Security Model

direnv uses an allowlist-based security approach:

• New or modified .envrc files must be explicitly allowed with direnv allow
• Prevents automatic execution of untrusted scripts
• Use direnv deny to revoke access

How It Works

1. Shell hook intercepts directory changes
2. Checks for .envrc file in current or parent directories
3. If allowed, executes .envrc in a bash subshell
4. Captures exported variables and applies them to current shell

Installation

macOS (Homebrew - Recommended)

brew install direnv

Linux

# Ubuntu/Debian
sudo apt install direnv

# Fedora
sudo dnf install direnv

# Arch
sudo pacman -S direnv

# Binary installer (any system)
curl -sfL https://direnv.net/install.sh | bash

Verify Installation

direnv version

Shell Configuration

Add the hook to your shell's config file. This is required for direnv to function.

Zsh (~/.zshrc)

eval "$(direnv hook zsh)"

With Oh My Zsh:

plugins=(... direnv)

Bash (~/.bashrc)

eval "$(direnv hook bash)"

Important: Place after rvm, git-prompt, and other prompt-modifying extensions.

Fish (~/.config/fish/config.fish)

direnv hook fish | source

After Configuration

Restart your shell:

exec $SHELL

.envrc File Basics

Creating an .envrc

# In your project directory
touch .envrc

# Edit with your preferred editor
vim .envrc

Basic Syntax

# Export environment variables
export NODE_ENV=development
export API_URL=http://localhost:3000
export DATABASE_URL=postgres://localhost/myapp

# The export keyword is required for direnv to capture variables

Allowing the .envrc

# Allow current directory
direnv allow

# Allow specific path
direnv allow /path/to/project

# Deny/revoke access
direnv deny

Standard Library Functions

direnv includes a powerful stdlib. Always prefer stdlib functions over manual exports.

PATH Management

# Prepend to PATH (safer than manual export)
PATH_add bin
PATH_add node_modules/.bin
PATH_add scripts

# Add to arbitrary path-like variable
path_add PYTHONPATH lib
path_add LD_LIBRARY_PATH /opt/lib

# Remove from PATH
PATH_rm "*/.git/bin"

Environment File Loading

# Load .env file (current directory)
dotenv

# Load specific file
dotenv .env.local

# Load only if exists (no error)
dotenv_if_exists .env.local
dotenv_if_exists .env.${USER}

# Source another .envrc
source_env ../.envrc
source_env /path/to/.envrc

# Search upward and source parent .envrc
source_up

# Source if exists
source_env_if_exists .envrc.local

Language Layouts

Node.js:

# Adds node_modules/.bin to PATH
layout node

Python:

# Creates virtualenv in .direnv/python-X.X/
layout python

# Use specific Python version
layout python python3.11

# Shortcut for Python 3
layout python3

# Use Pipenv (reads from Pipfile)
layout pipenv

Ruby:

# Sets GEM_HOME to project directory
layout ruby

Go:

# Modifies GOPATH and adds bin to PATH
layout go

Perl:

# Configures local::lib environment
layout perl

Nix Integration

# Load nix-shell environment
use nix

# With specific file
use nix shell.nix

# Load from Nix flake
use flake

# Load specific flake
use flake "nixpkgs#hello"
use flake ".#devShell"

For better Nix Flakes support, install nix-direnv:

# Provides faster, cached use_flake implementation
# https://github.com/nix-community/nix-direnv

Version Managers

# rbenv
use rbenv

# Node.js (with fuzzy version matching)
use node 18
use node 18.17.0

# Reads from .nvmrc if version not specified
use node

# Julia
use julia 1.9

Validation

# Require environment variables (errors if missing)
env_vars_required API_KEY DATABASE_URL SECRET_KEY

# Enforce minimum direnv version
direnv_version 2.32.0

# Check git branch
if on_git_branch main; then
  export DEPLOY_ENV=production
fi
if on_git_branch develop; then
  export DEPLOY_ENV=staging
fi

File Watching

# Reload when files change
watch_file package.json
watch_file requirements.txt
watch_file .tool-versions
watch_file config/*.yaml

# Watch entire directory
watch_dir config
watch_dir migrations

Utility Functions

# Check if command exists
if has docker; then
  export DOCKER_HOST=unix:///var/run/docker.sock
fi

# Expand relative path to absolute
expand_path ./bin

# Find file searching upward
find_up package.json

# Enable strict mode (exit on errors)
strict_env

# Load prefix (configures CPATH, LD_LIBRARY_PATH, etc.)
load_prefix /usr/local/custom

# Load remote script with integrity verification
source_url https://example.com/script.sh "sha256-HASH..."

Best Practices

Recommended .envrc Template

#!/usr/bin/env bash
# .envrc - Project environment configuration

# Enforce direnv version for team consistency
direnv_version 2.32.0

# Load .env if exists
dotenv_if_exists

# Load local overrides (not committed to git)
source_env_if_exists .envrc.local

# Language-specific layout
layout node  # or: layout python3

# Add project bin directories
PATH_add bin
PATH_add scripts

# Development defaults
export NODE_ENV="${NODE_ENV:-development}"
export LOG_LEVEL="${LOG_LEVEL:-debug}"

# Watch for dependency changes
watch_file package.json
watch_file .nvmrc

Git Configuration

.gitignore:

# Environment files with secrets
.env
.env.local
.envrc.local

# direnv virtualenv/cache
.direnv/

Commit to repository:

• .envrc (base configuration, no secrets)
• .env.example (template for team members)

Secrets Management

Never commit secrets. Use environment variable fallbacks:

# .envrc (committed)
export DATABASE_URL="${DATABASE_URL:-postgres://localhost/dev}"
export API_KEY="${API_KEY:-}"

# Validate required secrets
env_vars_required API_KEY

# .envrc.local (gitignored)
export DATABASE_URL="postgres://user:secret@prod/app"
export API_KEY="actual-secret-key"

Layered Configuration

# ~/projects/.envrc (global dev settings)
export EDITOR=vim

# ~/projects/api/.envrc
source_up
export API_PORT=3000

# ~/projects/api/feature/.envrc
source_up
export FEATURE_FLAG=true

Project Structure

my-project/
├── .envrc           # Base environment (committed)
├── .envrc.local     # Local overrides (gitignored)
├── .env             # Environment variables (gitignored)
├── .env.example     # Template for team (committed)
└── .direnv/         # direnv cache (gitignored)

Custom Extensions

Create ~/.config/direnv/direnvrc for custom functions:

#!/usr/bin/env bash
# ~/.config/direnv/direnvrc

# Custom function: Use specific Kubernetes context
use_kubernetes() {
  local context="${1:-default}"
  export KUBECONFIG="${HOME}/.kube/config"
  kubectl config use-context "$context" >/dev/null 2>&1
  log_status "kubernetes context: $context"
}

# Custom function: Load from AWS Secrets Manager
use_aws_secrets() {
  local secret_name="$1"
  local region="${2:-us-east-1}"
  eval "$(aws secretsmanager get-secret-value \
    --secret-id "$secret_name" \
    --region "$region" \
    --query SecretString \
    --output text | jq -r 'to_entries | .[] | "export \(.key)=\"\(.value)\""')"
  log_status "loaded secrets from: $secret_name"
}

# Custom function: Use asdf versions from .tool-versions
use_asdf() {
  watch_file .tool-versions
  source_env "$(asdf direnv local)"
}

Usage in .envrc:

use kubernetes dev-cluster
use aws_secrets myapp/dev
use asdf

Commands Reference

Command	Description
direnv allow	Allow the current .envrc
direnv deny	Revoke .envrc access
direnv reload	Force reload environment
direnv status	Show current status
direnv dump	Dump current environment
direnv edit	Open .envrc in editor
direnv version	Show direnv version

Troubleshooting

Environment Not Loading

# Check status
direnv status

# Force reload
direnv reload

# Re-allow .envrc
direnv allow

# Check if hook is installed
echo $DIRENV_DIR

Shell Hook Issues

1. Verify hook is in shell config file
2. Ensure it's at the END of the file
3. Restart shell completely: exec $SHELL
4. Check for errors: direnv hook zsh

Performance Issues

# Show what's being evaluated
direnv show_dump

# For Nix, use nix-direnv for caching
# https://github.com/nix-community/nix-direnv

Debugging

# Verbose output
export DIRENV_LOG_FORMAT='%s'

# Show exported variables
direnv dump | jq

# Test .envrc syntax
bash -n .envrc

IDE Integration

VS Code

Install direnv extension for automatic environment loading in integrated terminal.

JetBrains

Install direnv integration plugin.

Neovim

Use direnv.vim or configure with lua.

Common Patterns

Development vs Production

# .envrc
export NODE_ENV="${NODE_ENV:-development}"

if [[ "$NODE_ENV" == "development" ]]; then
  export DEBUG=true
  export LOG_LEVEL=debug
else
  export DEBUG=false
  export LOG_LEVEL=info
fi

Multi-Service Projects (Monorepo)

# root/.envrc
export PROJECT_ROOT="$(pwd)"
export COMPOSE_PROJECT_NAME=myapp

# services/api/.envrc
source_up
export SERVICE_NAME=api
export SERVICE_PORT=3000

# services/web/.envrc
source_up
export SERVICE_NAME=web
export SERVICE_PORT=8080

Docker Integration

# .envrc
export COMPOSE_FILE=docker-compose.yml
export COMPOSE_PROJECT_NAME="${PWD##*/}"

if has docker-compose; then
  export DOCKER_HOST="${DOCKER_HOST:-unix:///var/run/docker.sock}"
fi

# Add Docker bin for containers that install CLI tools
PATH_add .docker/bin

References

• Official Documentation
• Installation Guide
• Shell Hook Setup
• Standard Library Reference
• nix-direnv
• Homebrew Formula