Macro env_var 

macro_rules! env_var {
    {required $key:expr} => { ... };
    {required $key:expr, default: $default:expr} => { ... };
    {required $key:expr, msg: $msg:expr} => { ... };
    {required $key:expr, default: $default:expr, msg: $msg:expr} => { ... };
    {optional $key:expr} => { ... };
    {optional $key:expr, default: $default:expr} => { ... };
    {optional $key:expr, msg: $msg:expr} => { ... };
    {optional $key:expr, default: $default:expr, msg: $msg:expr} => { ... };
    {optional $key:expr, msg: $msg:expr, default: $default:expr} => { ... };
}

env_var macro

Examples

#[macro_use]
extern crate env_var;

fn main() {
  // retrieving a optional value
  // var1 either contains the value or an empty string
  let var1 = env_var!(optional "TEST_OPT_1");

  // retrieving a optional value with default
  // var1 either contains the value or "default1"
  let var1 = env_var!(optional "TEST_OPT_1", default: "default1");

  // retrieving a optional value with default
  // if not found, the message will be logged as info message
  // var1 either contains the value or "default1"
  let var1 = env_var!(optional "TEST_OPT_1", default: "default1", msg: "using default");

  // retrieving a required value
  // var1 either contains the value or the programm panics
  let var1 = env_var!(required "TEST_OPT_1");

  // retrieving a required value with default
  // var1 either contains the value or "default1"
  let var1 = env_var!(required "TEST_OPT_1", default: "default1");

  // retrieving a required value with default
  // if not found, the message will be logged as warn message
  // var1 either contains the value or "default1"
  let var1 = env_var!(required "TEST_OPT_1", default: "default1", msg: "using default");
}