Write Logs To A File And STDOUT At The Same Time In Rust

````cargo
[dependencies]
tracing = "0.1.40"
tracing-appender = "0.2"
tracing-subscriber = { version = "0.3", features = ["json"] }
```

use tracing::{Level, event, instrument};
use tracing_subscriber::prelude::*;
use tracing_subscriber::{fmt, filter};

fn main() {
  let log_dir = "./";
  let log_basename = "example-log.log";

  let file_appender = tracing_appender::rolling::never(log_dir, log_basename);
  let (file_writer, _guard) = tracing_appender::non_blocking(file_appender);
  let file_layer_format = tracing_subscriber::fmt::format()
    .json();
  let file_layer = fmt::Layer::default()
    .event_format(file_layer_format)
    .with_writer(file_writer)
    .json();

  let stdout_layer = fmt::Layer::default()
    .with_writer(std::io::stdout)
    .with_ansi(false)
    .with_filter(filter::LevelFilter::INFO);

  let subscriber = tracing_subscriber::Registry::default()
    .with(file_layer)
    .with(stdout_layer);

  tracing::subscriber::set_global_default(subscriber).expect("unable to set global subscriber");

  do_something();
}

#[instrument]
fn do_something() {
  event!(Level::ERROR, "Error message");
  event!(Level::WARN, "Warn message");
  event!(Level::INFO, "Info message");
  event!(Level::DEBUG, "Debug message");
  event!(Level::TRACE, "Trace message");
}

For most projects I send log messages to the command line or to a files. Sometimes, I want both. This is how I'm doing that in Rust with the tracing crate.

• I didn't realize at first that the [TODO: Code shorthand span ] create is mainly a foundation that other things are built off of. In this case, the file and STDOUT comes from a combination of [TODO: Code shorthand span ] and [TODO: Code shorthand span ]

• I'm using [TODO: Code shorthand span ] in this example. It always writes to the same file ("example - log.log" in this case). There are also [TODO: Code shorthand span ] , [TODO: Code shorthand span ] , and [TODO: Code shorthand span ] versions that append strings with intervals to the filenames to create a rotation mechanism

• The [TODO: Code shorthand span ] calls turn off extra characters in the output that enable colors on the terminal. I find it useful to skip that for the STDOUT output in prod, but it shows up weird in this web output so I've got it set to false

• There are five levels available. In order, they are : ERROR, WARN, INFO, DEBUG, TRACE

• All five layres are output by default

• The [TODO: Code shorthand span ] call on the STDOUT layer limits that output to just INFO and above. That is, ERROR, WARN, and INFO messages all appear, but DEBUG and TRACE messages do not

• Being able to set different log levels a big reason why I set this up instead of just running a [TODO: Code shorthand span ] on the log file itself

• In some of my reading it sounds like you can set up the subscriber in a function outside of main, but if you do you need to make sure to keep the [TODO: Code shorthand span ] in scope. If it goes out of scope, nothing else will be written to the file

• I'm also using ` .json() [TODO: Code shorthand span ] to make JSON formatted logs. That's not strictly necessary, but I find them way more useful