Crate cli_log[][src]

The boilerplate to have some file logging with a level given by an environment variable, and a facility to log execution durations according to the relevant log level.

It’s especially convenient for terminal applications because you don’t want to mix log with stdout or stderr.

The use of an env variable makes it possible to distribute the application and have users generate some logs without recompilation or configuration.

The names of the log file and the env variable are computed from the name of the application.

So log initialization is just

#[macro_use] extern crate log;
#[macro_use] extern crate cli_log;

With the "mem" feature (enabled by default), when the OS is compatible (unix like), you may dump the current and peak memory usage with the log_mem function.

Here’s a complete application using cli-log (it can be found in examples):

#[macro_use] extern crate log;
#[macro_use] extern crate cli_log;

struct AppData {
    count: usize,
impl AppData {
    fn compute(&mut self) {
        self.count += 7;

fn main() {
    let mut app_data = AppData { count: 35 };
    time!(Debug, app_data.compute());
    info!("count is {}", app_data.count);
    debug!("data: {:#?}", &app_data);
    warn!("this application does nothing");

If you don’t set any SMALL_APP_LOG env variable, there won’t be any log.

A convenient way to set the env variable is to launch the app as

SMALL_APP_LOG=debug small_app

or, during development,

SMALL_APP_LOG=debug cargo run

This creates a small_app.log file containing information like the level, app version, and of course the log operations you did with time precise to the ms and the logging module (target):

21:03:24.081 [INFO] cli_log::init: Starting small-app v1.0.1 with log level DEBUG
21:03:24.081 [DEBUG] small_app: app_data.compute() took 312ns
21:03:24.081 [INFO] small_app: count is 42
21:03:24.081 [DEBUG] small_app: data: AppData {
    count: 42,
21:03:24.081 [WARN] small_app: this application does nothing
21:03:24.081 [INFO] cli_log::mem: Physical mem usage: current=938K, peak=3.3M
21:03:24.082 [INFO] small_app: bye



configure the application log according to env variable


print the time that executing some expression took but only when relevant according to log level.



configure the application log according to env variable.


log the current and peak physical memory used by the current process, if the given log level is reached