man Log::Dispatch () - Dispatches messages to one or more outputs


Log::Dispatch - Dispatches messages to one or more outputs


  use Log::Dispatch;

  my $dispatcher = Log::Dispatch->new;

  $dispatcher->add( Log::Dispatch::File->new( name => 'file1',
                                              min_level => 'debug',
                                              filename => 'logfile' ) );

  $dispatcher->log( level => 'info',
                    message => 'Blah, blah' );

  my $sub = sub { my %p = @_;  return reverse $p{message}; };
  my $reversing_dispatcher = Log::Dispatch->new( callbacks => $sub );


This module manages a set of Log::Dispatch::* objects, allowing you to add and remove output objects as desired.


* new
Returns a new Log::Dispatch object. This method takes one optional parameter:
* callbacks( \& or [ \&, \&, ... ] )
This parameter may be a single subroutine reference or an array reference of subroutine references. These callbacks will be called in the order they are given and passed a hash containing the following keys:
 ( message => $log_message, level => $log_level )
In addition, any key/value pairs passed to a logging method will be passed onto your callback. The callbacks are expected to modify the message and then return a single scalar containing that modified message. These callbacks will be called when either the CWlog or CWlog_to methods are called and will only be applied to a given message once. If they do not return the message then you will get no output. Make sure to return the message!
* add( Log::Dispatch::* OBJECT )
Adds a new a Log::Dispatch::* object to the dispatcher. If an object of the same name already exists, then that object is replaced. A warning will be issued if the CW$^W is true. NOTE: This method can really take any object that has methods called 'name' and 'log'.
* remove($)
Removes the object that matches the name given to the remove method. The return value is the object being removed or undef if no object matched this.
* log( level => $, message => $ )
Sends the message (at the appropriate level) to all the Log::Dispatch::* objects that the dispatcher contains (by calling the CWlog_to method repeatedly).
* log_to( name => $, level => $, message => $ )
Sends the message only to the named object. Returns true or false to indicate whether or not the given string is a valid log level. Can be called as either a class or object method. Given a log level, returns true or false to indicate whether or not anything would be logged for that log level. Returns an output of the given name. Returns undef or an empty list, depending on context, if the given output does not exist.


Version 1.6 of Log::Dispatch adds a number of convenience methods for logging. You may now call any valid log level (including valid abbreviations) as a method on the Log::Dispatch object with a single argument that is the message to be logged. This is converted into a call to the CWlog method with the appropriate level.

For example:

 $dispatcher->alert('Strange data in incoming request');

translates to:

 $dispatcher->log( level => 'alert', message => 'Strange data in incoming request' );

These methods act like Perl's CWprint built-in when given a list of arguments. Thus, the following calls are equivalent:

 my @array = ('Something', 'bad', 'is', here');

 my $scalar = "@array";

One important caveat about these methods is that its not that forwards compatible. If I were to add more parameters to the CWlog call, it is unlikely that these could be integrated into these methods without breaking existing uses. This probably means that any future parameters to the CWlog method will never be integrated into these convenience methods. OTOH, I don't see any immediate need to expand the parameters given to the CWlog method.

Log Levels

The log levels that Log::Dispatch uses are taken directly from the syslog man pages (except that I expanded them to full words). Valid levels are:


Alternately, the numbers 0 through 7 may be used (debug is 0 and emergency is 7). The syslog standard of 'err', 'crit', and 'emerg' is also acceptable.


This module is designed to be used as a one-stop logging system. In particular, it was designed to be easy to subclass so that if you want to handle messaging in a way not implemented in this package, you should be able to add this with minimal effort.

The basic idea behind Log::Dispatch is that you create a Log::Dispatch object and then add various logging objects to it (such as a file logger or screen logger). Then you call the CWlog method of the dispatch object, which passes the message to each of the objects, which in turn decide whether or not to accept the message and what to do with it.

This makes it possible to call single method and send a message to a log file, via email, to the screen, and anywhere else, all with very little code needed on your part, once the dispatching object has been created.

The logging levels that Log::Dispatch uses are borrowed from the standard UNIX syslog levels, except that where syslog uses partial words (err) Log::Dispatch also allows the use of the full word as well (error).

Making your own logging objects

Making your own logging object is generally as simple as subclassing Log::Dispatch::Output and overriding the CWnew and CWlog methods. See the Log::Dispatch::Output docs for more details.

If you would like to create your own subclass for sending email then it is even simpler. Simply subclass Log::Dispatch::Email and override the CWsend_email method. See the Log::Dispatch::Email docs for more details.

Why doesn't Log::Dispatch add a newline to the message?

A few people have written email to me asking me to add something that would tack a newline onto the end of all messages that don't have one. This will never happen. There are several reasons for this. First of all, Log::Dispatch was designed as a simple system to broadcast a message to multiple outputs. It does not attempt to understand the message in any way at all. Adding a newline implies an attempt to understand something about the message and I don't want to go there. Secondly, this is not very cross-platform and I don't want to go down the road of testing Config values to figure out what to tack onto messages based on OS.

I think people's desire to do this is because they are too focused on just the logging to files aspect of this module. In this case newlines make sense. However, imagine someone is using this module to log to a remote server and the interactions between the client and server use newlines as part of the control flow. Casually adding a newline could cause serious problems.

However, the 1.2 release adds the callbacks parameter for the Log::Dispatch object which you can easily use to add newlines to messages if you so desire.



Written by Tatsuhiko Miyagawa. Log output to a database table.


Written by Mark Pfeiffer. Rotates log files periodically as part of its usage.


Written by Eric Cholet. Stamps log files with date and time information.


Written by Aaron Straup Cope. Logs messages via Jabber.


Written by Dominique Dumont. Logs messages to a Tk window.


Written by Arthur Bergman. Logs messages to the Windows event log.


An implementation of Java's log4j API in Perl, using Log::Dispatch to do the actual logging. Created by Mike Schilli and Kevin Goess.


Written by Tatsuhiko Miyagawa. Allows configuration of logging via a text file similar (or so I'm told) to how it is done with log4j. Simpler than Log::Log4perl.


A very different API for doing many of the same things that Log::Dispatch does. Originally written by Raphael Manfredi.


Copyright (c) 1999-2003 David Rolsky. All rights reserved. This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

The full text of the license can be found in the LICENSE file included with this module.


Dave Rolsky, <>


Log::Dispatch::ApacheLog, Log::Dispatch::Email, Log::Dispatch::Email::MailSend, Log::Dispatch::Email::MailSender, Log::Dispatch::Email::MailSendmail, Log::Dispatch::Email::MIMELite, Log::Dispatch::File, Log::Dispatch::File::Locked, Log::Dispatch::Handle, Log::Dispatch::Output, Log::Dispatch::Screen, Log::Dispatch::Syslog