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.

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.