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

In CWLog::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 CWlog4j, just with a few perl-specific extensions, like enabling the CWBar::Twix syntax instead of insisting on the Java-specific CWBar.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

or

    log4perl.logger.Bar.Twix = WARN, Screen

CWLog::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 are addressed by category:

    log4perl.logger.Bar.Twix      = WARN, Screen

This sets all loggers under the CWBar::Twix hierarchy on priority CWWARN and attaches a later-to-be-defined CWScreen 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 CWFATAL and also attaches the later-to-be-defined appenders CWDatabase and CWMailer to it.

The additivity flag of a logger is set or cleared via the CWadditivity 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 CW.additivity according to the log4j documentation).

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 CWappender keyword after the CWlog4perl 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 CWDEBUG for loggers in the CWBar::Twix hierarchy and assigns the CWA1 appender to it, which is later on resolved to be an appender of type CWLog::Log4perl::Appender::File, simply appending to a log file. According to the CWLog::Log4perl::Appender::File manpage, the CWfilename parameter specifies the name of the log file and the CWmode parameter can be set to CWappend or CWwrite (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, CWLog::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 CWConversionPattern is the keyword to specify the printf-style formatting instructions.

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

    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

    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

    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 CWLog::Log4perl::Appender::File module does exactly the opposite. This is due to some nasty trickery CWLog::Log4perl performs behind the scenes to make sure that beginner's CGI applications don't clobber the log file every time they're called.

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

CWwrite is the CWmode that has CWLog::Log4perl::Appender::File explicitely clobber the log file if it exists.

Mike Schilli, <log4perl@perlmeister.com>

Log::Log4perl::Config::PropertyConfigurator

Log::Log4perl::Config::DOMConfigurator

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