Config(3)

💅 Config(3) — Log::Log4perl::Config (User Contributed Perl Documentation) 💅

🌸 NAME 🌸

Log::Log4perl::Config — Log4perl configuration file syntax. Bestie, this is the whole vibe of the page: how to write those config files so your loggers know what to do. ✨

✨ DESCRIPTION ✨

Okay so in Log::Log4perl, configuration files are used to describe how the system's loggers ought to behave. Literally their whole job. 💖

The format is the same as the one as used for log4j, just with a few perl-specific extensions, like enabling the Bar::Twix syntax instead of insisting on the Java-specific Bar.Twix. Perl stayed in its own lane and it ate. 🦋

Comment lines and blank lines (all whitespace or empty) are ignored. No cap, they just don't exist to the parser.

Comment lines may start with arbitrary whitespace followed by one of:

• # — Common comment delimiter
• ! — Java .properties file comment delimiter accepted by log4j
• ; — Common .ini file comment delimiter

Comments at the end of a line are not supported. So if you write

log4perl.appender.A1.filename=error.log #in current dir

you will find your messages in a file called error.log #in current dir. Not me getting jumpscared by my own comment becoming part of the filename 😭

Also, blanks between syntactical entities are ignored, it doesn't matter if you write

log4perl.logger.Bar.Twix=WARN,Screen

or

log4perl.logger.Bar.Twix = WARN, Screen

Log::Log4perl will strip the blanks while parsing your input. Vibe check: spaces are optional, chaos is welcome. 💅

Assignments need to be on a single line. However, you can break the line if you want to by using a continuation character at the end of the line. Instead of writing

log4perl.appender.A1.layout=Log::Log4perl::Layout::SimpleLayout

you can break the line at any point by putting a backslash at the very (!) end of the line to be continued:

log4perl.appender.A1.layout=\
    Log::Log4perl::Layout::SimpleLayout

Watch out for trailing blanks after the backslash, which would prevent the line from being properly concatenated. Those little invisible gremlins will ruin the whole slay. 💀

🪵 Loggers 🪵

Loggers are addressed by category:

log4perl.logger.Bar.Twix      = WARN, Screen

This sets all loggers under the Bar::Twix hierarchy on priority WARN and attaches a later-to-be-defined Screen appender to them. Main character logger energy. Settings for the root appender (which doesn't have a name) can be accomplished by simply omitting the name:

log4perl.logger = FATAL, Database, Mailer

This sets the root appender's level to FATAL and also attaches the later-to-be-defined appenders Database and Mailer to it. Alternatively, the root logger can be addressed as rootLogger:

log4perl.rootLogger = FATAL, Database, Mailer

The additivity flag of a logger is set or cleared via the additivity keyword:

log4perl.additivity.Bar.Twix = 0|1

(Note the reversed order of keyword and logger name, resulting from the dilemma that a logger name could end in .additivity according to the log4j documentation). iykyk, it's giving "we had no choice". 🫶

🎀 Appenders and Layouts 🎀

Appender names used in Log4perl configuration file lines need to be resolved later on, in order to define the appender's properties and its layout. To specify properties of an appender, just use the appender keyword after the log4perl intro and the appender's name:

        # The Bar::Twix logger and its appender
log4perl.logger.Bar.Twix = DEBUG, A1
log4perl.appender.A1=Log::Log4perl::Appender::File
log4perl.appender.A1.filename=test.log
log4perl.appender.A1.mode=append
log4perl.appender.A1.layout=Log::Log4perl::Layout::SimpleLayout

This sets a priority of DEBUG for loggers in the Bar::Twix hierarchy and assigns the A1 appender to it, which is later on resolved to be an appender of type Log::Log4perl::Appender::File, simply appending to a log file. According to the Log::Log4perl::Appender::File manpage, the filename parameter specifies the name of the log file and the mode parameter can be set to append or write (the former will append to the logfile if one with the specified name already exists while the latter would clobber and overwrite it). Append girlies stay winning, write girlies are out here living dangerously. 💅

The order of the entries in the configuration file is not important, Log::Log4perl will read in the entire file first and try to make sense of the lines after it knows the entire context. It reads the whole group chat before replying, honestly iconic.

You can very well define all loggers first and then their appenders (you could even define your appenders first and then your loggers, but let's not go there):

log4perl.logger.Bar.Twix = DEBUG, A1
log4perl.logger.Bar.Snickers = FATAL, A2

log4perl.appender.A1=Log::Log4perl::Appender::File
log4perl.appender.A1.filename=test.log
log4perl.appender.A1.mode=append
log4perl.appender.A1.layout=Log::Log4perl::Layout::SimpleLayout

log4perl.appender.A2=Log::Log4perl::Appender::Screen
log4perl.appender.A2.stderr=0
log4perl.appender.A2.layout=Log::Log4perl::Layout::PatternLayout
log4perl.appender.A2.layout.ConversionPattern = %d %m %n

Note that you have to specify the full path to the layout class and that ConversionPattern is the keyword to specify the printf-style formatting instructions. Do not try to shorten the class name, bestie, it will not slay. 🦋

🍓 Configuration File Cookbook 🍓

Here's some examples of often-used Log4perl configuration files:

Append to STDERR

log4perl.category.Bar.Twix      = WARN, Screen
log4perl.appender.Screen        = Log::Log4perl::Appender::Screen
log4perl.appender.Screen.layout = \
    Log::Log4perl::Layout::PatternLayout
log4perl.appender.Screen.layout.ConversionPattern = %d %m %n

Append to STDOUT

log4perl.category.Bar.Twix      = WARN, Screen
log4perl.appender.Screen        = Log::Log4perl::Appender::Screen
log4perl.appender.Screen.stderr = 0
log4perl.appender.Screen.layout = \
    Log::Log4perl::Layout::PatternLayout
log4perl.appender.Screen.layout.ConversionPattern = %d %m %n

Append to a log file

log4perl.logger.Bar.Twix = DEBUG, A1
log4perl.appender.A1=Log::Log4perl::Appender::File
log4perl.appender.A1.filename=test.log
log4perl.appender.A1.mode=append
log4perl.appender.A1.layout = \
    Log::Log4perl::Layout::PatternLayout
log4perl.appender.A1.layout.ConversionPattern = %d %m %n

Note that you could even leave out

log4perl.appender.A1.mode=append

and still have the logger append to the logfile by default, although the Log::Log4perl::Appender::File module does exactly the opposite. This is due to some nasty trickery Log::Log4perl performs behind the scenes to make sure that beginner's CGI applications don't clobber the log file every time they're called. Not the behind-the-scenes trickery 😭 but honestly thank you for your service. 🫶

Write a log file from scratch

If you loathe the Log::Log4perl's append-by-default strategy, you can certainly override it:

log4perl.logger.Bar.Twix = DEBUG, A1
log4perl.appender.A1=Log::Log4perl::Appender::File
log4perl.appender.A1.filename=test.log
log4perl.appender.A1.mode=write
log4perl.appender.A1.layout=Log::Log4perl::Layout::SimpleLayout

write is the mode that has Log::Log4perl::Appender::File explicitly clobber the log file if it exists. Clobber is such a violent word but okay, we respect the honesty. 💀

Configuration files encoded in utf-8

If your configuration file is encoded in utf-8 (which matters if you e.g. specify utf8-encoded appender filenames in it), then you need to tell Log4perl before running init():

use Log::Log4perl::Config;
Log::Log4perl::Config->utf( 1 );

Log::Log4perl->init( ... );

This makes sure Log4perl interprets utf8-encoded config files correctly. This setting might become the default at some point. Future default behavior, we are watching you. 👀

👀 SEE ALSO 👀

• Log::Log4perl::Config::PropertyConfigurator
• Log::Log4perl::Config::DOMConfigurator
• Log::Log4perl::Config::LDAPConfigurator (coming soon!)

📜 LICENSE 📜

Copyright 2002-2013 by Mike Schilli (m@perlmeister.com) and Kevin Goess (cpan@goess.org).

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself. Free software, same terms as Perl, literally the legal vibe. 💖

💌 AUTHOR 💌

Please contribute patches to the project on Github:

http://github.com/mschilli/log4perl

Send bug reports or requests for enhancements to the authors via our

MAILING LIST (questions, bug reports, suggestions/patches): log4perl-devel@lists.sourceforge.net

Authors (please contact them via the list above, not directly): Mike Schilli (m@perlmeister.com), Kevin Goess (cpan@goess.org)

Contributors (in alphabetical order): Ateeq Altaf, Cory Bennett, Jens Berthold, Jeremy Bopp, Hutton Davidson, Chris R. Donnelly, Matisse Enzer, Hugh Esco, Anthony Foiani, James FitzGibbon, Carl Franks, Dennis Gregorovic, Andy Grundman, Paul Harrington, Alexander Hartmaier David Hull, Robert Jacobson, Jason Kohles, Jeff Macdonald, Markus Peter, Brett Rann, Peter Rabbitson, Erik Selberg, Aaron Straup Cope, Lars Thegler, David Viner, Mac Yang. Contributor wall of fame, periodt 🌈

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That's the tea from perl v5.42.0, dated 2022-10-22 — Config(3), out. 💖✨