Richard North's Blog

More practical direnv

Some considerable time ago I wrote my praise for direnv along with some usage tips. That blog post continues to receive plenty of traffic from people seeking direnv configuration guidance.

Since then, I have continued to use direnv and (quietly) advocate for it among anyone who will listen. However, what I have not done is share how my usage of the tool has evolved and improved.

For anyone needing a brief introduction, direnv is a tool that runs hook scripts (.envrc) as you cd around a file system. For example, you can cd into a directory holding a Python codebase and have its virtualenv automatically activated. If you leave the directory, the virtualenv is automatically deactivated. direnv's power is its flexibility: it can run any script, update the PATH or any other environment variables, without coupling to a specific shell.

With a custom ~/.direnvrc script direnv gives me automatic setup of language tooling for:

Examples #

All examples assume that my custom ~/.direnvrc script is being used. My script is only set up for use with Mac OS and requires Homebrew.

You'll also need to have direnv installed and hooked in to your shell, of course!

Java #

If you want to use Java 11 in a specific directory, you just create an .envrc file containing:

use java adopt@1.11.0-6

After modifying an .envrc file you must allow direnv to run it, for security reasons. This is simply done by entering direnv allow at the shell. For example:

$ echo "use java [email protected]" >> .envrc
direnv: error /Users/rnorth/somedir/.envrc is blocked. Run `direnv allow` to approve its content

$ direnv allow
direnv: loading ~/somedir/.envrc
direnv: using java [email protected]
JAVA_HOME=/Users/rnorth/.jabba/jdk/[email protected]/Contents/Home
direnv: export +CPATH +JAVA_HOME +LD_LIBRARY_PATH +LIBRARY_PATH +MANPATH +NODE_VERSIONS +PKG_CONFIG_PATH +PYENV_ROOT ~PATH

$ java -version
openjdk version "11.0.6" 2020-01-14
OpenJDK Runtime Environment AdoptOpenJDK (build 11.0.6+10)
OpenJDK 64-Bit Server VM AdoptOpenJDK (build 11.0.6+10, mixed mode)

From now on, any time you cd into this directory, direnv will:

.jabbarc files are also respected, and will be automatically applied from the current or parent directory. All that's needed is a blank .envrc file to trigger direnv into action.

Python #

Similarly, create an .envrc file containing:

use python 3.7.6

direnv will:

NodeJS and Ruby #

Unsurprisingly, the pattern continues for NodeJS and Ruby! For example:

use node 12.16.3

and

use ruby 2.3.3

install and set up NodeJS and Ruby automatically, as above.

Summary #

direnv is a powerful tool, and one that I'm still very happy to use more than five years after first discovering it.

With a small amount of setting up, with a custom ~/.direnvrc file, it's extremely powerful, and I hope you find my example a useful starting point!

I'd strongly recommend direnv for:

Enjoy a more productive, less hassle, shell experience!

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