rust-dotenv

A fork of dotenv, designed to work better with modern Rust, and design patterns.

Achtung! This is a v0.* version! Expect bugs and issues all around. Submitting pull requests and issues is highly encouraged!

Quoting bkeepers/dotenv:

Storing configuration in the environment is one of the tenets of a twelve-factor app. Anything that is likely to change between deployment environments–such as resource handles for databases or credentials for external services–should be extracted from the code into environment variables.

This library is meant to be used on development or testing environments in which setting environment variables is not practical. It loads environment variables from a .env file, if available, and mashes those with the actual environment variables provided by the operative system.

Usage

The easiest and most common usage consists on calling rotenv::dotenv when the application starts, which will load environment variables from a file named .env in the current directory or any of its parents; after that, you can just call the environment-related method you need as provided by std::os.

If you need finer control about the name of the file or its location, you can use the from_filename and from_path methods provided by the crate.

dotenv_codegen provides the dotenv! macro, which behaves identically to env!, but first tries to load a .env file at compile time.

Examples

A .env file looks like this:

```sh

a comment, will be ignored

REDISADDRESS=localhost:6379 MEANINGOF_LIFE=42 ```

You can optionally prefix each line with the word export, which will conveniently allow you to source the whole file on your shell.

A sample project using Dotenv would look like this:

```rust extern crate dotenv;

use rotenv::dotenv; use std::env;

fn main() { dotenv().ok();

for (key, value) in env::vars() {
    println!("{}: {}", key, value);
}

} ```

Variable substitution

It's possible to reuse variables in the .env file using $VARIABLE syntax. The syntax and rules are similar to bash ones, here's the example:

```sh

VAR=one VAR_2=two

Non-existing values are replaced with an empty string

RESULT=$NOPE #value: '' (empty string)

All the letters after $ symbol are treated as the variable name to replace

RESULT=$VAR #value: 'one'

Double quotes do not affect the substitution

RESULT="$VAR" #value: 'one'

Different syntax, same result

RESULT=${VAR} #value: 'one'

Curly braces are useful in cases when we need to use a variable with non-alphanumeric name

RESULT=$VAR2 #value: 'one2' since $ with no curly braces stops after first non-alphanumeric symbol RESULT=${VAR_2} #value: 'two'

The replacement can be escaped with either single quotes or a backslash:

RESULT='$VAR' #value: '$VAR' RESULT=\$VAR #value: '$VAR'

Environment variables are used in the substutution and always override the local variables

RESULT=$PATH #value: the contents of the $PATH environment variable PATH="My local variable value" RESULT=$PATH #value: the contents of the $PATH environment variable, even though the local variable is defined ```

Dotenv will parse the file, substituting the variables the way it's described in the comments.

Using the dotenv! macro

Add dotenv_codegen to your dependencies, and add the following to the top of your crate:

```rust

[macro_use]

extern crate dotenv_codegen; ```

Then, in your crate:

rust fn main() { println!("{}", dotenv!("MEANING_OF_LIFE")); }