Config

Section: User Contributed Perl Documentation (3)
Updated: 2021-02-08
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NAME

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

DESCRIPTION

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

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".

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

    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 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.

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. 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).

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).

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.

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.

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.

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.

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.

LICENSE

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

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.