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A collection of functions for checking/getting/setting **environment variables** in **`Elixir`**.

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## Why?

We needed a way of checking that environment variables were defined
and improving the developer experience when they are not.

## What?

**`envar`** is our solution to a very specific problem:
the developer experience when a required environment variable is undefined.

<br />

## How?

### Installation

Install the package
by adding `envar` to your list of dependencies in your `mix.exs` file:

```elixir
def deps do
  [
    {:envar, "~> 1.1.0"}
  ]
end
```

## Usage

Load an `.env` file
containing a line-separated list of environment variables
on your `localhost`:

```elixir
Envar.load(".env")
```

That will locate the `.env` file in your project
and set each environment variable in it.

If the `.env` _must_ exist e.g. in a `:test` context,
invoke:

```elixir
Envar.require_env_file(".env")
```

That will log an `Error` if the file does not exist (or can't be found):

```sh
09:10:54.103 [error] Required .env file does not exist at path: /Alex/awesome/project/.env
```


<br />

When you need to retrieve a specific environment variable,
use the following:

```elixir
DATABASE_URL = Envar.get("DATABASE_URL")
```

<br />

If you want to define a default/fallback value
for the environment variable when it's not set,
simply add it as the second argument:

```elixir
DATABASE_URL = Envar.get("DATABASE_URL", "postgres://uname:pass@host:5432/dbname"")
```

<br />

If you need to check that a variable is set,
use `is_set?/1`

```elixir
if Envar.is_set?("Heroku") do
  # do stuff on Heroku
end
```

To check if _any_ of the variables in a `List` are set,
invoke `Envar.is_set_any?/1`:

```elixir
if Envar.is_set_any?(~w/HEROKU FLYIO/) do
  # Do something on non-prod environment
end
```

Conversely, to confirm that _all_ the environment variables
in a list are set, invoke `Envar.is_set_all?/1`:

```elixir
if Envar.is_set_all?(~w/ADMIN_EMAIL AUTH_API_KEY/) do
  # Do something with the required environment variables
end
```

We needed a couple more convenience functions,
so we wrote them!

If you need to read an `.env` file and get the
keys & values as a `Map`, invoke `Envar.read/1`:

```elixir
iex> Envar.read(".env")
%{
  "ADMIN_EMAIL" => "alex@gmail.com",
  "EVERYTHING" => "awesome!",
  "SECRET" => "master plan"
}
```

If you need just the `keys`
of the list of environment variables in an `.env` file,
invoke: `Envar.keys/1`:

```elixir
iex> Envar.keys(".env")
["ADMIN_EMAIL", "EVERYTHING", "SECRET"]
```

And if you need just the `values`
of the environment variables in an `.env` file,
invoke: `Envar.values/1`:

```elixir
iex> Envar.values(".env")
["alex@gmail.com", "awesome!", "master plan"]
```

For more detail, please see docs:
https://hexdocs.pm/envar/Envar.html#functions

<br /><br />

Happy `Elixir` Coding! 🚀

<br /><br />

## Context

We created this module after doing
a search of the `Elixir` (Hex.pm)
ecosystem, <br />
see:
[dwyl/learn-environment-variables/issues/18](https://github.com/dwyl/learn-environment-variables/issues/18)

There are several modules available,
we wanted something very basic/specific to our needs. <br />
We don't expect anyone else to use this;
it's Open Source
because that's just what we do: <br />
[/manifesto.md#open-source-always](https://github.com/dwyl/start-here/blob/master/manifesto.md#open-source-always)