In Rust, the debug! macro from the log crate is used for logging debug messages. By default, it logs to stderr, not stdout. However, you can configure the logging backend to redirect logs to stdout instead.

How to Redirect debug! to stdout on Linux

1. Use the env_logger Crate

The simplest way is to use the env_logger crate, which allows you to configure logging via environment variables.

Steps:

1. Add env_logger and log to your Cargo.toml:

   toml
   Copy
   [dependencies]
   log = "0.4"
   env_logger = "0.10"

2. In your code, initialize the logger and set the default target to stdout:

   rust
   Copy
   use log::debug;
   
   fn main() {
       // Initialize the logger
       env_logger::Builder::new()
           .target(env_logger::Target::Stdout)
           .init();
   
       debug!("This debug message will go to stdout");
   }

3. Run your program with the RUST_LOG environment variable to enable debug logs:

   sh
   Copy
   RUST_LOG=debug cargo run

2. Custom Logger with stdout

If you want more control, you can implement a custom logger using the log crate and redirect logs to stdout:

rust
Copy
use log::{debug, Level, LevelFilter, Metadata, Record};
use std::io::Write;

struct StdoutLogger;

impl log::Log for StdoutLogger {
    fn enabled(&self, metadata: &Metadata) -> bool {
        metadata.level() <= Level::Debug
    }

    fn log(&self, record: &Record) {
        if self.enabled(record.metadata()) {
            println!("[{}] {}", record.level(), record.args());
        }
    }

    fn flush(&self) {}
}

static LOGGER: StdoutLogger = StdoutLogger;

fn main() {
    log::set_boxed_logger(Box::new(LOGGER)).unwrap();
    log::set_max_level(LevelFilter::Debug);

    debug!("This debug message will go to stdout");
}

3. Using simple_logger

The simple_logger crate also allows you to log to stdout:

rust
Copy
use log::debug;
use simple_logger::SimpleLogger;

fn main() {
    SimpleLogger::new()
        .with_level(log::LevelFilter::Debug)
        .with_target(simple_logger::Target::Stdout)
        .init()
        .unwrap();

    debug!("This debug message will go to stdout");
}

Summary

• Use env_logger for easy configuration via environment variables.
• Use a custom logger or simple_logger for more control.
• Ensure the log level is set to debug or lower.