// Licensed under the Apache License, Version 2.0 or the MIT license // , at your // option. This file may not be copied, modified, or distributed // except according to those terms. //! A simple logger that can be configured via environment variables, for use //! with the logging facade exposed by the [`log` crate][log-crate-url]. //! //! Despite having "env" in its name, **`env_logger`** can also be configured by //! other means besides environment variables. See [the examples][gh-repo-examples] //! in the source repository for more approaches. //! //! By default, `env_logger` writes logs to `stderr`, but can be configured to //! instead write them to `stdout`. //! //! ## Example //! //! ``` //! use log::{debug, error, log_enabled, info, Level}; //! //! env_logger::init(); //! //! debug!("this is a debug {}", "message"); //! error!("this is printed by default"); //! //! if log_enabled!(Level::Info) { //! let x = 3 * 4; // expensive computation //! info!("the answer was: {}", x); //! } //! ``` //! //! Assumes the binary is `main`: //! //! ```{.bash} //! $ RUST_LOG=error ./main //! [2017-11-09T02:12:24Z ERROR main] this is printed by default //! ``` //! //! ```{.bash} //! $ RUST_LOG=info ./main //! [2017-11-09T02:12:24Z ERROR main] this is printed by default //! [2017-11-09T02:12:24Z INFO main] the answer was: 12 //! ``` //! //! ```{.bash} //! $ RUST_LOG=debug ./main //! [2017-11-09T02:12:24Z DEBUG main] this is a debug message //! [2017-11-09T02:12:24Z ERROR main] this is printed by default //! [2017-11-09T02:12:24Z INFO main] the answer was: 12 //! ``` //! //! You can also set the log level on a per module basis: //! //! ```{.bash} //! $ RUST_LOG=main=info ./main //! [2017-11-09T02:12:24Z ERROR main] this is printed by default //! [2017-11-09T02:12:24Z INFO main] the answer was: 12 //! ``` //! //! And enable all logging: //! //! ```{.bash} //! $ RUST_LOG=main ./main //! [2017-11-09T02:12:24Z DEBUG main] this is a debug message //! [2017-11-09T02:12:24Z ERROR main] this is printed by default //! [2017-11-09T02:12:24Z INFO main] the answer was: 12 //! ``` //! //! If the binary name contains hyphens, you will need to replace //! them with underscores: //! //! ```{.bash} //! $ RUST_LOG=my_app ./my-app //! [2017-11-09T02:12:24Z DEBUG my_app] this is a debug message //! [2017-11-09T02:12:24Z ERROR my_app] this is printed by default //! [2017-11-09T02:12:24Z INFO my_app] the answer was: 12 //! ``` //! //! This is because Rust modules and crates cannot contain hyphens //! in their name, although `cargo` continues to accept them. //! //! See the documentation for the [`log` crate][log-crate-url] for more //! information about its API. //! //! ## Enabling logging //! //! **By default all logging is disabled except for the `error` level** //! //! The **`RUST_LOG`** environment variable controls logging with the syntax: //! ```text //! RUST_LOG=[target][=][level][,...] //! ``` //! Or in other words, its a comma-separated list of directives. //! Directives can filter by **target**, by **level**, or both (using `=`). //! //! For example, //! ```text //! RUST_LOG=data=debug,hardware=debug //! ``` //! //! **target** is typically the path of the module the message //! in question originated from, though it can be overridden. //! The path is rooted in the name of the crate it was compiled for, so if //! your program is in a file called, for example, `hello.rs`, the path would //! simply be `hello`. //! //! Furthermore, the log can be filtered using prefix-search based on the //! specified log target. //! //! For example, `RUST_LOG=example` would match the following targets: //! - `example` //! - `example::test` //! - `example::test::module::submodule` //! - `examples::and_more_examples` //! //! When providing the crate name or a module path, explicitly specifying the //! log level is optional. If omitted, all logging for the item will be //! enabled. //! //! **level** is the maximum [`log::Level`][level-enum] to be shown and includes: //! - `error` //! - `warn` //! - `info` //! - `debug` //! - `trace` //! - `off` (pseudo level to disable all logging for the target) //! //! Logging level names are case-insensitive; e.g., //! `debug`, `DEBUG`, and `dEbuG` all represent the same logging level. For //! consistency, our convention is to use the lower case names. Where our docs //! do use other forms, they do so in the context of specific examples, so you //! won't be surprised if you see similar usage in the wild. //! //! Some examples of valid values of `RUST_LOG` are: //! //! - `RUST_LOG=hello` turns on all logging for the `hello` module //! - `RUST_LOG=trace` turns on all logging for the application, regardless of its name //! - `RUST_LOG=TRACE` turns on all logging for the application, regardless of its name (same as previous) //! - `RUST_LOG=info` turns on all info logging //! - `RUST_LOG=INFO` turns on all info logging (same as previous) //! - `RUST_LOG=hello=debug` turns on debug logging for `hello` //! - `RUST_LOG=hello=DEBUG` turns on debug logging for `hello` (same as previous) //! - `RUST_LOG=hello,std::option` turns on `hello`, and std's option logging //! - `RUST_LOG=error,hello=warn` turn on global error logging and also warn for `hello` //! - `RUST_LOG=error,hello=off` turn on global error logging, but turn off logging for `hello` //! - `RUST_LOG=off` turns off all logging for the application //! - `RUST_LOG=OFF` turns off all logging for the application (same as previous) //! //! ## Filtering results //! //! A `RUST_LOG` directive may include a regex filter. The syntax is to append `/` //! followed by a regex. Each message is checked against the regex, and is only //! logged if it matches. Note that the matching is done after formatting the //! log string but before adding any logging meta-data. There is a single filter //! for all modules. //! //! Some examples: //! //! * `hello/foo` turns on all logging for the 'hello' module where the log //! message includes 'foo'. //! * `info/f.o` turns on all info logging where the log message includes 'foo', //! 'f1o', 'fao', etc. //! * `hello=debug/foo*foo` turns on debug logging for 'hello' where the log //! message includes 'foofoo' or 'fofoo' or 'fooooooofoo', etc. //! * `error,hello=warn/[0-9]scopes` turn on global error logging and also //! warn for hello. In both cases the log message must include a single digit //! number followed by 'scopes'. //! //! ## Capturing logs in tests //! //! Records logged during `cargo test` will not be captured by the test harness by default. //! The [`Builder::is_test`] method can be used in unit tests to ensure logs will be captured: //! //! ``` //! #[cfg(test)] //! mod tests { //! use log::info; //! //! fn init() { //! let _ = env_logger::builder().is_test(true).try_init(); //! } //! //! #[test] //! fn it_works() { //! init(); //! //! info!("This record will be captured by `cargo test`"); //! //! assert_eq!(2, 1 + 1); //! } //! } //! ``` //! //! Enabling test capturing comes at the expense of color and other style support //! and may have performance implications. //! //! ## Disabling colors //! //! Colors and other styles can be configured with the `RUST_LOG_STYLE` //! environment variable. It accepts the following values: //! //! * `auto` (default) will attempt to print style characters, but don't force the issue. //! If the console isn't available on Windows, or if TERM=dumb, for example, then don't print colors. //! * `always` will always print style characters even if they aren't supported by the terminal. //! This includes emitting ANSI colors on Windows if the console API is unavailable. //! * `never` will never print style characters. //! //! ## Tweaking the default format //! //! Parts of the default format can be excluded from the log output using the [`Builder`]. //! The following example excludes the timestamp from the log output: //! //! ``` //! env_logger::builder() //! .format_timestamp(None) //! .init(); //! ``` //! //! ### Stability of the default format //! //! The default format won't optimise for long-term stability, and explicitly makes no //! guarantees about the stability of its output across major, minor or patch version //! bumps during `0.x`. //! //! If you want to capture or interpret the output of `env_logger` programmatically //! then you should use a custom format. //! //! ### Using a custom format //! //! Custom formats can be provided as closures to the [`Builder`]. //! These closures take a [`Formatter`][crate::fmt::Formatter] and `log::Record` as arguments: //! //! ``` //! use std::io::Write; //! //! env_logger::builder() //! .format(|buf, record| { //! writeln!(buf, "{}: {}", record.level(), record.args()) //! }) //! .init(); //! ``` //! //! See the [`fmt`] module for more details about custom formats. //! //! ## Specifying defaults for environment variables //! //! `env_logger` can read configuration from environment variables. //! If these variables aren't present, the default value to use can be tweaked with the [`Env`] type. //! The following example defaults to log `warn` and above if the `RUST_LOG` environment variable //! isn't set: //! //! ``` //! use env_logger::Env; //! //! env_logger::Builder::from_env(Env::default().default_filter_or("warn")).init(); //! ``` //! //! [gh-repo-examples]: https://github.com/rust-cli/env_logger/tree/main/examples //! [level-enum]: https://docs.rs/log/latest/log/enum.Level.html //! [log-crate-url]: https://docs.rs/log //! [`Builder`]: struct.Builder.html //! [`Builder::is_test`]: struct.Builder.html#method.is_test //! [`Env`]: struct.Env.html //! [`fmt`]: fmt/index.html #![doc( html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png", html_favicon_url = "https://www.rust-lang.org/static/images/favicon.ico" )] #![cfg_attr(docsrs, feature(doc_auto_cfg))] // When compiled for the rustc compiler itself we want to make sure that this is // an unstable crate #![cfg_attr(rustbuild, feature(staged_api, rustc_private))] #![cfg_attr(rustbuild, unstable(feature = "rustc_private", issue = "27812"))] #![deny(missing_debug_implementations, missing_docs)] mod logger; pub mod filter; pub mod fmt; pub use self::fmt::glob::*; pub use self::logger::*;