Gray Soft / The Standard Library / The Books are Wrong About Logger

The 7th Comment on "The Books are Wrong About Logger"

2014-04-03T19:31:38Z

That works too, but I prefer to stick to the public interface the library defines for adjusting the format. My hope that it will stay supported even if the call() method is no longer used internally.

The 6th Comment on "The Books are Wrong About Logger"

2014-04-03T19:31:56Z

You can even simplify this a bit more by redefining Logger::Formatter's call method via module_eval:

Logger::Formatter.module_eval(
  %q{ def call(severity, time, progname, msg)} +
  %q{ "#{severity} -- #{format_datetime(time)}  #{progname}:: #{msg2str(msg)}" end}
)

Adding this to your script will overwrite the call method in Formatter. I much prefer to manually editing the core Ruby library files, and is more efficient than creating a new subclass.

The 5th Comment on "The Books are Wrong About Logger"

2014-04-03T19:28:48Z

Thanks for showing that Neville. I was unaware of that feature.

The 4th Comment on "The Books are Wrong About Logger"

2014-04-03T19:28:48Z

AFAIK, the following example can be simplified using Logger's block parameter, whereby the block is not "yielded" to unless the level is active… ie:

if log.error?
  log.error(expensive_error_report)
end

becomes:

log.error { expensive_error_report }

(Note the curly braces)

The 3rd Comment on "The Books are Wrong About Logger"

2014-03-27T01:38:24Z

James, thanks for that! Too bad they didn't allow for custom logging levels. I just <a href="http://www.justinlanghorst.com/2006/06/23/adding-to-the-ruby-logger/">hacked it</a>, but my solution is just that, a quick hack.

The 2nd Comment on "The Books are Wrong About Logger"

2014-04-03T19:26:06Z

I just checked the Ruby Cookbook and it mentions call(), though your technique of using a subclass is better than my technique of just overriding call().

The 1st Comment on "The Books are Wrong About Logger"

2014-04-03T19:25:47Z

Thanks for this post. I've just started learning about the Ruby Logger, so this was good timing for me.

The Books are Wrong About Logger

2014-04-03T19:31:56Z

I've read several books that introduced the standard Logger library and they all agree on one thing: you can't customize the output. That's so last version in thinking! Behold…

Here's a trivial Logger script, showing basic functionality:

#!/usr/bin/env ruby -w

require "logger"

def expensive_error_report
  sleep 3  # Heavy Computation Simulation (patent pending)
  "YOU BROKE IT!"
end

log       = Logger.new(STDOUT)
log.level = Logger::INFO  # set out output level above the DEBUG default

log.debug("We're not in the verbose debug mode.")
log.info("We do see informative logs though.")
if log.error?  # check that this will be printed, before waste time
  log.error(expensive_error_report)
end

If you run that you will see:

I, [2006-07-08T11:17:19.531943 #340]  INFO -- : We do see informative logs though.
E, [2006-07-08T11:17:22.532424 #340] ERROR -- : YOU BROKE IT!

Now everyone has always known you can format the date and time display using a strftime() compatible pattern:

#!/usr/bin/env ruby -w

require "logger"

def expensive_error_report
  sleep 3
  "YOU BROKE IT!"
end

log                 = Logger.new(STDOUT)
log.level           = Logger::INFO
log.datetime_format = "%Y-%m-%d %H:%M "  # simplify time output

log.debug("We're not in the verbose debug mode.")
log.info("We do see informative logs though.")
if log.error?
  log.error(expensive_error_report)
end

Which gives us the slightly easier to read:

I, [2006-07-08 11:23 #384]  INFO -- : We do see informative logs though.
E, [2006-07-08 11:23 #384] ERROR -- : YOU BROKE IT!

All books I've read to date though tell you that's the end of the customization line. But, if you are using Ruby 1.8.4 or higher, it's no longer true:

#!/usr/bin/env ruby -w

require "logger"

# Build a Logger::Formatter subclass.
class PrettyErrors < Logger::Formatter
  # Provide a call() method that returns the formatted message.
  def call(severity, time, program_name, message)
    if severity == "ERROR"
      datetime      = time.strftime("%Y-%m-%d %H:%M")
      print_message = "!!! #{String(message)} (#{datetime}) !!!"
      border        = "!" * print_message.length
      [border, print_message, border].join("\n") + "\n"
    else
      super
    end
  end
end

def expensive_error_report
  sleep 3
  "YOU BROKE IT!"
end

log           = Logger.new(STDOUT)
log.level     = Logger::INFO
log.formatter = PrettyErrors.new  # Install custom formatter!

log.debug("We're not in the verbose debug mode.")
log.info("We do see informative logs though.")
if log.error?
  log.error(expensive_error_report)
end

Here's what that code produces:

I, [2006-07-08T12:20:31.325112 #521]  INFO -- : We do see informative logs though.
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!! YOU BROKE IT! (2006-07-08 12:20) !!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Don't believe everything you read.