Log::Log4perl - Introduction to logging in Perl

This article will take you to logging in Perl using Log4perl in windows.

First check whether perl is installed on your machine. You can do this by running the following command on command prompt.

C:\perl>perl -v

This is perl 5, version 12, subversion 3 (v5.12.3) built for MSWin32-x86-multi-thread
Copyright 1987-2010, Larry Wall
Perl may be copied only under the terms of either the Artistic License or theGNU General Public License, which may be found in the Perl 5 source kit.
Complete documentation for Perl, including FAQ lists, should be found onthis system using "man perl" or "perldoc perl".  If you have access to theInternet, point your browser at http://www.perl.org/, the Perl Home Page.C:\perl>

If perl is not installed then you can install perl on windows using the below link:

http://learn.perl.org/installing/windows.html

Next we need to install log4Perl. Open a command prompt and run any one of the below command.

C:\perl>ppm install Log-Log4perl

or

C:\perl>cpan Log::Log4perl

Once the installation is successful then we are ready to start a test program using log4Perl logging.

testperl.pl

 use Log::Log4perl;  
 Log::Log4perl::init("log4perl.conf");  
  method();  
  sub method {  
  my $logger = Log::Log4perl->get_logger("");  
  $logger->info("Received a request");  
  $logger->debug("Received a request");  
  }  

log4Perl which is similar to log4J in Java uses two different approaches for configuration. One is using a configuration file and another is using Perl code. I personally prefer configuration approach because it is much cleaner and configuration changes would not need a code change.

Create log4perl.conf and place it in the same folder as the code. You can ofcourse mention the full path to the configuration file if the path of the file is somewhere else.

log4perl.conf

 log4perl.rootLogger=TRACE, errorlog  
 log4perl.appender.errorlog=Log::Log4perl::Appender::File  
 log4perl.appender.errorlog.filename=c:/perl/log-dir/error.log  
 log4perl.appender.errorlog.mode=append  
 log4perl.appender.errorlog.Threshold = INFO  
 log4perl.appender.errorlog.layout=Log::Log4perl::Layout::PatternLayout  
 log4perl.appender.errorlog.layout.ConversionPattern=%d{ISO8601}|%C|%m%n  

Run the program using following command.

C:\perl>perl testperl.pl

Which will print INFO log to the log file mentioned.

Below is the explanation of configuration parameters.

log4perl.rootLogger=TRACE, errorlog  

This indicates that the rootLogger which is the main or upper level logger accepts all log messages which are equal to TRACE or more specific than TRACE. In other words it accepts 

all log messages. 

errorlog  - indicates it is an appender

log4perl.appender.errorlog=Log::Log4perl::Appender::File 

This indicates that this appender is going to write the logs to a File.

log4perl.appender.errorlog.filename=c:/perl/log-dir/error.log 
log file name

 log4perl.appender.errorlog.mode=append
 Indicates that the log messages will be written to the end of the file if file is present

log4perl.appender.errorlog.Threshold = INFO
This appender will log all messages which are equal to INFO or more specific than INFO. In other words TRACE or DEBUG messages are not written to the file. This is a way to direct log messages to different files based on their levels.

log4perl.appender.errorlog.layout=Log::Log4perl::Layout::PatternLayout 
Indicates that log messages are following a specific pattern which is specified using ConversionPattern.

log4perl.appender.errorlog.layout.ConversionPattern=%d{ISO8601}|%C|%m%n
Specifies the pattern of the log messages.

Details can be found in : http://search.cpan.org/~mschilli/Log-Log4perl-1.46/lib/Log/Log4perl.pm

Above is a basic log4Perl configuration. Each project may require different configurations and below I am trying to provide some more advanced configurations.

How to redirect different levels to different log files using log4Perl: Here
How to create a custom log level using log4Perl:Here
How to customize log message using application data in log4Perl using MDC:Here