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
or
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).
AppendersandLayouts
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.
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