MAN page from RedHat EL 8 perl-Log-Log4perl-1.50-1.el8.noarch.rpm


Section: User Contributed Perl Documentation (3)
Updated: 2020-07-22


Log::Log4perl::Config - Log4perl configuration file syntax 


In "Log::Log4perl", configuration files are used to describe how thesystem's loggers ought to behave.

The format is the same as the one as used for "log4j", just witha few perl-specific extensions, like enabling the "Bar::Twix"syntax instead of insisting on the Java-specific "Bar.Twix".

Comment lines and blank lines (all whitespace or empty) are ignored.

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".

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



    log4perl.logger.Bar.Twix = WARN, Screen

"Log::Log4perl" will strip the blanks while parsing your input.

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


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 preventthe line from being properly concatenated. 


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.Settings for the root appender (which doesn't have a name) can beaccomplished 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, resultingfrom the dilemma that a logger name could end in ".additivity"according to the log4j documentation). 

Appenders and Layouts

Appender names used in Log4perl configuration filelines need to be resolved later on, in order todefine the appender's properties and its layout. To specify propertiesof 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 onresolved to be an appender of type "Log::Log4perl::Appender::File", simplyappending to a log file. According to the "Log::Log4perl::Appender::File"manpage, the "filename" parameter specifies the name of the log fileand the "mode" parameter can be set to "append" or "write" (theformer will append to the logfile if one with the specified namealready exists while the latter would clobber and overwrite it).

The order of the entries in the configuration file is not important,"Log::Log4perl" will read in the entire file first and try to makesense of the lines after it knows the entire context.

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 classand that "ConversionPattern" is the keyword to specify the printf-styleformatting instructions. 

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


and still have the logger append to the logfile by default, althoughthe "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. 

Write a log file from scratch

If you loathe the Log::Log4perl's append-by-default strategy, you cancertainly 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. 

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. 




Log::Log4perl::Config::LDAPConfigurator (coming soon!) 


Copyright 2002-2013 by Mike Schilli <> and Kevin Goess <>.

This library is free software; you can redistribute it and/or modifyit under the same terms as Perl itself. 


Please contribute patches to the project on Github:

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

MAILING LIST (questions, bug reports, suggestions/patches):

Authors (please contact them via the list above, not directly):Mike Schilli <>,Kevin Goess <>

Contributors (in alphabetical order):Ateeq Altaf, Cory Bennett, Jens Berthold, Jeremy Bopp, HuttonDavidson, Chris R. Donnelly, Matisse Enzer, Hugh Esco, AnthonyFoiani, James FitzGibbon, Carl Franks, Dennis Gregorovic, AndyGrundman, 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.



Appenders and Layouts
Configuration File Cookbook
Append to STDERR
Append to STDOUT
Append to a log file
Write a log file from scratch
Configuration files encoded in utf-8

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