# How to format log message in Ruby

In Ruby, you can format log messages using the built-in Logger class. The Logger class provides various options for customizing the log message format. You can include timestamps, log levels, and other relevant information in the log message format. Here's how you can format log messages:

```ruby
require 'logger'

# Create a logger instance and specify the log file
logger = Logger.new('application.log')

# Customize the log message format
logger.formatter = proc do |severity, datetime, progname, msg|
  "#{datetime.strftime('%Y-%m-%d %H:%M:%S')} [#{severity}] #{msg}\n"
end

# Set the log level (e.g., INFO)
logger.level = Logger::INFO

# Log some messages
logger.debug("This is a debug message")   # This won't be printed because the log level is set to INFO
logger.info("This is an info message")    # This will be printed with the custom format
logger.warn("This is a warning message")  # This will be printed with the custom format
logger.error("This is an error message")  # This will be printed with the custom format
logger.fatal("This is a fatal message")   # This will be printed with the custom format
```

In this example, we create a logger instance and set it to log messages to a file called *application.log*. The `logger.formatter` attribute is assigned a `proc` (a block of code) that customizes the log message format. The `proc` takes four arguments:

1. `severity`: The log level of the message (e.g., "DEBUG," "INFO," "WARN," "ERROR," "FATAL").
2. `datetime`: The timestamp of when the log message is created.
3. `progname`: The program name, which can be set when logging the message (not used in this example).
4. `msg`: The actual log message.

In the `proc`, we use `datetime.strftime` to format the timestamp in the desired way. `%Y-%m-%d %H:%M:%S` represents the format "year-month-day hour:minute:second." You can customize the format according to your preferences.

The `logger.level` is set to `Logger::INFO`, which means only messages with severity INFO and above will be printed. If you want to include DEBUG level messages in the log, you can change the log level to `Logger::DEBUG`.

The resulting log messages will be formatted as follows:

```ruby
2023-07-28 12:34:56 [INFO] This is an info message
2023-07-28 12:34:57 [WARN] This is a warning message
2023-07-28 12:34:58 [ERROR] This is an error message
2023-07-28 12:34:59 [FATAL] This is a fatal message
```

You can modify the `logger.formatter` block to customize the log message format further as per your requirements.

To learn more about logging in Ruby, visit [Better Stack Community](https://betterstack.com/community/guides/logging/#ruby).