Template String Formatting Guide

Overview

Logly supports custom format strings with placeholders for complete control over log output.

Built-in Placeholders

• {time} - Timestamp (RFC3339 format)
• {time:PATTERN} - Custom time format
• {level} - Log level name
• {message} - Log message
• {module} - Module name
• {function} - Function name
• {filename} - Source filename
• {lineno} - Line number
• {FIELD} - Any custom field

Time Format Patterns

Supported Patterns

Examples

Date Only

#![allow(unused)]
fn main() {
SinkConfig {
    format: Some("{time:YYYY-MM-DD} | {level} | {message}".to_string()),
    ..Default::default()
}
// Output: 2025-10-11 | INFO | Message
}

Full DateTime

#![allow(unused)]
fn main() {
SinkConfig {
    format: Some("{time:YYYY-MM-DD HH:mm:ss} [{level}] {message}".to_string()),
    ..Default::default()
}
// Output: 2025-10-11 13:45:32 [INFO] Message
}

With Milliseconds

#![allow(unused)]
fn main() {
SinkConfig {
    format: Some("{time:HH:mm:ss.SSS} | {message}".to_string()),
    ..Default::default()
}
// Output: 13:45:32.123 | Message
}

ISO 8601 Style

#![allow(unused)]
fn main() {
SinkConfig {
    format: Some("{time:YYYY-MM-DDTHH:mm:ss} {level} {message}".to_string()),
    ..Default::default()
}
// Output: 2025-10-11T13:45:32 INFO Message
}

Readable Format

#![allow(unused)]
fn main() {
SinkConfig {
    format: Some("{time:dddd, DD MMMM YYYY at HH:mm:ss} - {level} - {message}".to_string()),
    ..Default::default()
}
// Output: Saturday, 11 October 2025 at 13:45:32 - INFO - Message
}

European Format

#![allow(unused)]
fn main() {
SinkConfig {
    format: Some("{time:DD/MM/YYYY HH:mm} {message}".to_string()),
    ..Default::default()
}
// Output: 11/10/2025 13:45 Message
}

Common Patterns

Simple Console

#![allow(unused)]
fn main() {
format: Some("{time:HH:mm:ss} [{level}] {message}".to_string())
}

Detailed File

#![allow(unused)]
fn main() {
format: Some("{time:YYYY-MM-DD HH:mm:ss.SSS} | {level:8} | {module}:{function} | {message}".to_string())
}

Request Logging

#![allow(unused)]
fn main() {
format: Some("{time:YYYY-MM-DD HH:mm:ss} | {method} {path} | status={status_code} | duration={duration_ms}ms".to_string())
}

Best Practices

1. Console vs File: Use simpler formats for console, detailed for files
2. Time Formats:
   • HH:mm:ss for console (quick reference)
   • YYYY-MM-DD HH:mm:ss.SSS for logs (precise timestamps)
   • YYYY-MM-DDTHH:mm:ss for ISO 8601 compatibility
3. Performance: Simpler formats are faster to process
4. Consistency: Use consistent formats across your application