A no-nonsense guide to environment variables in Go

#go #configuration #tutorial

Environment variables are the best way to set configuration values for your software application as they can be defined at system-level, independently of the software. This is one of the principles of the Twelve-Factor App methodology and enables applications to be built with portability.

Using environment variables

All you need to interact with environment variables is the standard os package. Here is
an example of how you can access the system PATH environment variable.

It’s equally easy to set environment variables:

Loading environment variables from a .env file

It is not always practical to set environment variables on development machines
where multiple projects are running.

godotenv is a Go port of the Ruby
dotenv library. This allows you to define
your application’s environment variables in a .env file.

To install the package run:

$ go get github.com/joho/godotenv

Add your configuration values to a .env file at the root of your project:

GITHUB_USERNAME=craicoverflow
GITHUB_API_KEY=TCtQrZizM1xeo1v92lsVfLOHDsF7TfT5lMvwSno

Then you can use these values in your application:

It’s important to note that if an environment variable is already defined in the
system, then Go will prefer use that instead of the value in .env.

Wrapping environment variables in a configuration package

It's all well and good accessing environment variables directly like this, but having to maintain that doesn't seem fun, does it? Every value is a string - and imagine having to update every reference when an environment key is modified!

To deal with this, let’s create a configuration package to access environment variables in a much
more centralized and maintainable way.

Here is a simple config package which will return configuration values in a
Config struct. We have the option to define a default value, so when an
environment variable does not exist this will be used instead.

Next, we should add different types to the Config struct. The current implementation can only handle string types, which isn’t very practical for larger applications.

Let's add functions to handle bool, slice and integer types.

Update your .env file with these environment variables.

GITHUB_USERNAME=craicoverflow
GITHUB_API_KEY=TCtQrZizM1xeo1v92lsVfLOHDsF7TfT5lMvwSno
MAX_USERS=10
USER_ROLES=admin,super_admin,guest
DEBUG_MODE=false

And now you can access these values from the rest of your application:

And there you have it

There are several libraries out there that claim to offer a configuration
“solution” for your Go application. But is it really a solution when it’s just
as easy to make one yourself?

How do you manage configuration in your Go applications?

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