A common practice in software projects is to keep certain information separated but accessible from the codebase which uses it. Developers usually do this with secrets such as passwords or private keys, or with user or context-specific info pieces.
But managing environment variables can be a pain. There are a number of solutions to ease that pain, and there are even built-in ones such as bash_profile.
One solution I've discovered recently and found particularly convenient is direnv. It's a shell extension which lets you define environment variables scoped by directory.
After installing and hooking the extension to your shell,
direnv will execute every time you change directories, looking for an
.envrc file in the same or in a superior directory tree level. It will then load the defined variables to the current environment, and unload them if it ceases to detect the same
direnv will load the first detected
.envrc file, which means that the environment will not inherit values from a
.envrc in a parent directory.
It is also important to keep in mind that the environment variables will only be loaded to your shell session once you move to a directory affected by a
.envrc file. So if you try something like running a script which loads an environment defined in a directory below your current level, the variables won't be accessible.
How to Install
Here's a list of supported systems. It is very likely that your UNIX-based system's main open source package manager has it available.
Suppose we are on Debian, we can install
direnv by running the standard external package install command in the terminal:
sudo apt-get install direnv
How to Setup
After you install it, you need to hook
direnv to your shell. If you're using bash, you can do this by appending this line to the end of your shell startup config file:
echo 'eval "$(direnv hook bash)"' >> ~/.bashrc
It's almost the same for ZShell:
echo 'eval "$(direnv hook zsh)"' >> ~/.zshrc
Direnv also supports FISH, TCSH, and Elvish. Here are the hooking instructions for each supported shell.
How to Use
Now we must create an
.envrc file for the directory we would like to scope the environment variables to.
Say we create it for the directory
echo export FOO='I love Linux!' >> ~/project/.envrc
You will then receive a warning that the current
.envrc wasn't read.
direnv will block loading
.envrc every time it detects changes which were not explicitly allowed. So now run:
direnv allow ~/project
and voilà!, you now have a directory-scoped environment.
Remember when I told you that '
direnv will block loading
.envrc every time it detects changes which were not explicitly allowed'? This isn't limited to newly introduced changes – the whole file will be unauthorized. So when you do this:
echo export BAR='It is actually called GNU/Linux!' >> ~/project/.envrc
you will have to run
direnv allow ~/project again, even to access
$FOO. Kinda boring, but biased towards safety.
Every time an
.envrc is loaded, direnv will output a message with the file path and also the names of the variables loaded, so you don't need to worry about forgetting your setup. It will also tell you whenever an environment was unloaded.
Thanks for reading!
That's it! It's pretty straightforward, and I hope you find it as convenient as I did.