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 (starting with arbitrary whitespace and a #) and blank lines (all whitespace or empty) are ignored.

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.

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.layout = \
    log4perl.appender.Screen.stderr = 0
        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 explicitely clobber the log file if it exists.

AUTHOR

Mike Schilli, <log4perl@perlmeister.com>