Using direnv to help with local development

One of the tools I find most useful for local development is direnv. It’s one of a number of similar utilities that hooks into your shell, and alters the environment when you enter or leave a directory.

To give an example, if you have a folder ~/example with the file ~/example/.envrc

export EXAMPLE_NAME="Danie"

Then when in your shell session you cd into ~/example it will export the EXAMPLE_NAME variable:

❯ cd ~/example
direnv: loading ~/example/.envrc
direnv: export +EXAMPLE_NAME
❯ echo Hello $EXAMPLE_NAME
Hello Danie

Just as importantly, when you navigate away, the variable will be unset:

❯ cd ~
direnv: unloading
❯ echo Hello $EXAMPLE_NAME
Hello

Simple use cases

More command line tools than you might think make use of environment variables, as of course does your shell. There are some obvious and less obvious uses for direnv. Here are a few that I use:

QUICKLY LAUNCH THE CORRECT DEVELOPMENT DATABASE

Setting Postgres Environment Variables PGDATABASE, PGUSER, and PGPASSWORD1 to match my development database credentials means that when in a project folder, psql will open the correct database.

SECURELY USE AWS SECRETS (via 1Password)

Unlike a development database password, I’m more careful with AWS credentials. While AWS_PROFILE, AWS_REGION, and AWS_ACCESS_KEY_ID are safe to share, I prefer to keep AWS_SECRET_ACCESS_KEY values out of my .envrc files. But that doesn’t mean I can’t use them. I store these secrets in 1Password and use the CLI to retrieve them. So my .envrc looks like this:

export AWS_REGION=eu-west-2
export AWS_ACCESS_KEY_ID=AKABCDEFGHIJKLMNO
export AWS_SECRET_ACCESS_KEY="$(op read op://dev/aws/SECRET_ACCESS_KEY)"

The environment variable is still set to the secret, but the secret itself is stored more securely than in an unencrypted .envrc.

Add arbitrary commands to the path

In one of the clojure projects I work on, the command I use start the REPL is:

clojure -A:dev:test:backend:backend-test:system-test:repl

To save having to type this (or more accurately — search the shell history), I put it in a very short script, saved (and .gitignored) in .local/bin/repl. Then my .envrc I’ve put:

PATH_add ./.local/bin

When I’m in the project folder, typing repl launches the repl.

Footnotes

  1. If I’d set one. YOLO. ↩