Module env_logger::fmt

Formatting for log records.

This module contains a Formatter that can be used to format log records into without needing temporary allocations. Usually you won’t need to worry about the contents of this module and can use the Formatter like an ordinary Write.

Formatting log records

The format used to print log records can be customised using the Builder::format method.

Terminal styling is done through ANSI escape codes and will be adapted to the capabilities of the target stream. For example, you could use one of:

• anstyle is a minimal, runtime string styling API and is re-exported as style
• owo-colors is a feature rich runtime string styling API
• color-print for feature-rich compile-time styling API See also Formatter::default_level_style

use std::io::Write;

let mut builder = env_logger::Builder::new();

builder.format(|buf, record| {
    writeln!(buf, "{}: {}",
        record.level(),
        record.args())
});

Key Value arguments

If the unstable-kv feature is enabled, then the default format will include key values from the log by default, but this can be disabled by calling Builder::format_key_values with [hidden_kv_format] as the format function.

The way these keys and values are formatted can also be customized with a separate format function that is called by the default format with Builder::format_key_values.

use log::info;
env_logger::init();
info!(x="45"; "Some message");
info!(x="12"; "Another message {x}", x="12");

See https://docs.rs/log/latest/log/#structured-logging.

Re-exports

• pub use anstyle as style;

Structs

• Formatter
  A formatter to write logs into.
• Timestamp
  An RFC3339 formatted timestamp.

Enums

• Target
  Log target, either stdout, stderr or a custom pipe.
• TimestampPrecision
  Formatting precision of timestamps.
• WriteStyle
  Whether or not to print styles to the target.