xxx.rs

//! ```cargo
//! [dependencies]
//! failure = "*"
//! ```
extern crate failure;

use failure::Error;
use failure::Fail;
use failure::ResultExt;

use std::env::{self, VarError};

fn logging() -> Result<(), Error> {
    let log_level = match env::var("LOG_LEVEL") {
        Ok(s) => s,
        Err(VarError::NotPresent) => "".to_owned(),
        e @ Err(VarError::NotUnicode(_)) => e.context("'LOG_LEVEL' not UTF-8 compatible!")?
    };

    println!("lvl: {}", log_level);

    Ok(())
}

fn main() {
    logging().unwrap();
    }