dotenv

by dotenv-rs

dotenv-rs / dotenv

Library to help supply environment variables in testing and development

181 Stars 17 Forks Last release: 9 months ago (v0.15.0) MIT License 234 Commits 4 Releases

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rust-dotenv

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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

dotenv::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:
# a comment, will be ignored
REDIS_ADDRESS=localhost:6379
MEANING_OF_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:

extern crate dotenv;

use dotenv::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:
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=$VAR_2 #value: 'one_2' 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:
#[macro_use]
extern crate dotenv_codegen;

Then, in your crate:

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

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