Cargo.toml

[package]
name = "foo"
version = "0.1.0"
authors = ["drbluefall"]
edition = "2018"

# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html

[dependencies]
slog = "2.5"
slog-async = "*"
slog-term = "*"
slog-scope = "*"
slog-envlogger = "*"
slog-unwrap = { version = "0.9", features = [ "scope" ] }

src_main.rs

extern crate slog;
extern crate slog_async;
extern crate slog_term;
#[macro_use]
extern crate slog_scope;
extern crate slog_envlogger;
extern crate slog_unwrap;

mod log {
use slog::Drain;

pub fn setup() -> slog_scope::GlobalLoggerGuard {

    let file_log = {
        let log_file = std::fs::OpenOptions::new()
            .create(true)
            .write(true)
            .truncate(true)
            .open("bot.log")
            .unwrap();

        let decorator = slog_term::PlainDecorator::new(log_file);
        let drain = slog_term::FullFormat::new(decorator)
            .build()
            .fuse();
        slog_async::Async::new(drain).build().fuse()
    };

    let term_log = {
        let decorator = slog_term::TermDecorator::new().build();
        let drain = slog_async::Async::new(
            slog_envlogger::new(
            slog_term::FullFormat::new(decorator).build().fuse())
        ).build().fuse();
        
        drain
    };

    let logger = slog::Logger::root(
        slog::Duplicate::new(file_log, term_log).fuse(),
        slog::o!());

    slog_scope::set_global_logger(logger)

}
}

fn main() {
    println!("Hello, world!");
    let _l = log::setup();
    trace!("foo");
    debug!("bar");
}