env-file-reader

Library for reading environment variables from an environment file in rust.

Usage

Imagine this to be the content of your environment file located at examples/.env:

CLIENT_ID=YOUR_CLIENT_ID
CLIENT_SECRET=YOUR_CLIENT_SECRET

Now you want to read this file and expose the environment variables to your rust application. You can easily do this using the env-file-reader crate:

use env_file_reader::read_file;

fn main() -> std::io::Result<()> {
  let env_variables = read_file("examples/.env")?;
  
  assert_eq!(&env_variables["CLIENT_ID"], "YOUR_CLIENT_ID");
  assert_eq!(&env_variables["CLIENT_SECRET"], "YOUR_CLIENT_SECRET");

  Ok(())
}

The env-file-reader crate exposes the read_file function to which you can pass the path to your environment file. The read_file function then parses the environment file and extracts the contained variables, returning them as a HashMap<String, String>, from which they can be accessed easily by your rust application.

Variable names and unicode support

Variables and values support UTF-8. It is perfectly okay to have an environment file that looks like this:

🦄=💖
💖=🦄

use env_file_reader::read_file;

fn main() -> std::io::Result<()> {
  let env_variables = read_file("examples/.env.utf8")?;
  
  assert_eq!(&env_variables["🦄"], "💖");
  assert_eq!(&env_variables["💖"], "🦄");

  Ok(())
}

Variables (and non-quoted values) support every character except whitespace characters, quotes (`, ', or "), # and =, so go nuts:

use env_file_reader::read_str;

fn main() -> std::io::Result<()> {
  let env_variables = read_str(
    r"123-_variable\$*-@🦄=sprinkely-sprinkely-💖s-and_🐱s@the🏟️",
  )?;
  
  assert_eq!(
    &env_variables[r"123-_variable\$*-@🦄"],
    "sprinkely-sprinkely-💖s-and_🐱s@the🏟️",
  );

  Ok(())
}

Optional export keyword

env-file-reader supports bash-like environment files where the variables are exported to the environment via the export command:

export CLIENT_ID=YOUR_EXPORTED_CLIENT_ID
export CLIENT_SECRET=YOUR_EXPORTED_CLIENT_SECRET

use env_file_reader::read_file;

fn main() -> std::io::Result<()> {
  let env_variables = read_file("examples/.env.exported")?;
  
  assert_eq!(&env_variables["CLIENT_ID"], "YOUR_EXPORTED_CLIENT_ID");
  assert_eq!(
    &env_variables["CLIENT_SECRET"], "YOUR_EXPORTED_CLIENT_SECRET",
  );

  Ok(())
}

Reading multiple environment files

Sometimes your environment is split into multiple files (e.g. one environment file with your secrets you want to store in a kubernetes secret and one environment file with non-secrets you want to store in a kubernetes config map). env-file-reader supports reading multiple environment files into one HashMap with all variables with the read_files function:

use env_file_reader::read_files;

fn main() -> std::io::Result<()> {
  let env_variables = read_files(&[
    "examples/.env",
    "examples/.env.utf8",
  ])?;
  
  assert_eq!(&env_variables["CLIENT_ID"], "YOUR_CLIENT_ID");
  assert_eq!(&env_variables["CLIENT_SECRET"], "YOUR_CLIENT_SECRET");
  assert_eq!(&env_variables["🦄"], "💖");
  assert_eq!(&env_variables["💖"], "🦄");

  Ok(())
}

The environment files are read consecutively in the order they are supplied to read_files. Therefore, variables are overridden by the ones that are defined later:

use env_file_reader::read_files;

fn main() -> std::io::Result<()> {
  let env_variables = read_files(&[
    "examples/.env",
    "examples/.env.exported",
  ])?;
  
  assert_eq!(&env_variables["CLIENT_ID"], "YOUR_EXPORTED_CLIENT_ID");
  assert_eq!(
    &env_variables["CLIENT_SECRET"], "YOUR_EXPORTED_CLIENT_SECRET",
  );

  Ok(())
}

Reading environment variables from string

Besides read_file and read_files env-file-reader offers the option to read environment variables directly from a string:

use env_file_reader::read_str;

const ENV_FILE: &str = "
  CLIENT_ID=YOUR_CLIENT_ID
  CLIENT_SECRET=YOUR_CLIENT_SECRET
";

fn main() -> std::io::Result<()> {
  let env_variables = read_str(ENV_FILE)?;
  
  assert_eq!(&env_variables["CLIENT_ID"], "YOUR_CLIENT_ID");
  assert_eq!(&env_variables["CLIENT_SECRET"], "YOUR_CLIENT_SECRET");

  Ok(())
}

Comments and empty lines

Environment files can contain single line comments beginning with a # and empty lines. Imagine this to be your environment file located at examples/.env.comments:

# A comment
CLIENT_ID=YOUR_CLIENT_ID # A comment at the end of the line

# Empty lines are fine, too

# Another comment
CLIENT_SECRET=YOUR_CLIENT_SECRET # Another comment behind a value

env-file-reader can parse this file, ignoring empty lines and comments:

use env_file_reader::read_file;

fn main() -> std::io::Result<()> {
  let env_variables = read_file("examples/.env.comments")?;
  
  assert_eq!(&env_variables["CLIENT_ID"], "YOUR_CLIENT_ID");
  assert_eq!(&env_variables["CLIENT_SECRET"], "YOUR_CLIENT_SECRET");

  Ok(())
}

Quoted and multiline values

If you need a value to be more powerful, e.g. contain whitespaces, quotes, equal sign, etc. (see the section about unicode support), you can wrap them in quotes. The supported quotes are double quotes ("), single quotes (') and backticks (`). A string wrapped in double quotes can contain single quotes and backticks and so on. They also support escaped quotes, so "a string with \"double quotes\"" will work.

1="I support whitespaces and = and # and even this: \""
2='single quotes work, too and they can contain "double quotes"'
3=`backticks are "also" valid 'quotes'`

use env_file_reader::read_file;

fn main() -> std::io::Result<()> {
  let env_variables = read_file("examples/.env.quotes")?;
  
  assert_eq!(
    &env_variables["1"], 
    "I support whitespaces and = and # and even this: \"",
  );
  assert_eq!(
    &env_variables["2"], 
    "single quotes work, too and they can contain \"double quotes\"",
  );
  assert_eq!(
    &env_variables["3"], 
    "backticks are \"also\" valid 'quotes'",
  );

  Ok(())
}

Multiline strings are supported as well and look like this, either with a literal line break or with an explicitly typed \n:

PRIVATE_KEY1="-----BEGIN PRIVATE KEY-----
...
-----END PRIVATE KEY-----"

# PRIVATE_KEY2 is identical to PRIVATE_KEY1
PRIVATE_KEY2="-----BEGIN PRIVATE KEY-----\n...\n-----END PRIVATE KEY-----"

use env_file_reader::read_file;

fn main() -> std::io::Result<()> {
  let env_variables = read_file("examples/.env.multiline")?;
  
  assert_eq!(
    &env_variables["PRIVATE_KEY1"], 
    "-----BEGIN PRIVATE KEY-----\n...\n-----END PRIVATE KEY-----",
  );
  assert_eq!(
    &env_variables["PRIVATE_KEY2"], 
    "-----BEGIN PRIVATE KEY-----\n...\n-----END PRIVATE KEY-----",
  );

  Ok(())
}

Note on escaped characters: A quoted string only supports explicitly typed newlines and the escaped quote itself. Other explicitly typed special characters like \t or \r are not supported. So a value equal to "hello\n\t\"world\"" will have the following value when being processed by env-file-reader

hello
\t"world"

not

hello
    "world"

If you need support for other explicitly typed special characters, please open an issue.

Whitespaces

Whitespaces around the equal sign are allowed. As are whitespaces before the variable name and after the value. They are trimmed during parsing.

use env_file_reader::read_str;

const ENV_FILE: &str = "
      CLIENT_ID =     YOUR_CLIENT_ID
  CLIENT_SECRET =YOUR_CLIENT_SECRET
";

fn main() -> std::io::Result<()> {
  let env_variables = read_str(ENV_FILE)?;
  
  assert_eq!(&env_variables["CLIENT_ID"], "YOUR_CLIENT_ID");
  assert_eq!(&env_variables["CLIENT_SECRET"], "YOUR_CLIENT_SECRET");

  Ok(())
}

If you need leading or trailing whitespaces in your value, consider wrapping it in quotes:

use env_file_reader::read_str;

const ENV_FILE: &str = "
      CLIENT_ID = '    YOUR_CLIENT_ID    '
  CLIENT_SECRET =YOUR_CLIENT_SECRET
";

fn main() -> std::io::Result<()> {
  let env_variables = read_str(ENV_FILE)?;
  
  assert_eq!(&env_variables["CLIENT_ID"], "    YOUR_CLIENT_ID    ");
  assert_eq!(&env_variables["CLIENT_SECRET"], "YOUR_CLIENT_SECRET");

  Ok(())
}

Empty values

Your variables can be empty:

CLIENT_ID=
CLIENT_SECRET=

use env_file_reader::read_file;

fn main() -> std::io::Result<()> {
  let env_variables = read_file("examples/.env.empty")?;
  
  assert_eq!(&env_variables["CLIENT_ID"], "");
  assert_eq!(&env_variables["CLIENT_SECRET"], "");

  Ok(())
}

Errors

Should parsing the environment file fail a std::io::Error is returned. The error includes all normal io mishaps, like a missing file:

use env_file_reader::read_file;

let err = read_file(".env.which.does.not.exist")
  .err()
  .unwrap();
    
assert_eq!(err.kind(), std::io::ErrorKind::NotFound);

Additionally, parsing can fail due to an ill-formatted environment file. If that is the case, a custom error, ParseError, is returned:

use env_file_reader::read_str;

let err = read_str("badly formatted env file")
  .err()
  .unwrap();

assert_eq!(err.kind(), std::io::ErrorKind::InvalidInput);
assert_eq!(err.to_string(), "ParseError");