README.md - metacpan.org

NAME

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

VERSION

version 2.49

SYNOPSIS

  use Log::Dispatch;

  # Simple API
  #
  my $log = Log::Dispatch->new(
      outputs => [
          [ 'File',   min_level => 'debug', filename => 'logfile' ],
          [ 'Screen', min_level => 'warning' ],
      ],
  );

  $log->info('Blah, blah');

  # More verbose API
  #
  my $log = Log::Dispatch->new();
  $log->add(
      Log::Dispatch::File->new(
          name      => 'file1',
          min_level => 'debug',
          filename  => 'logfile'
      )
  );
  $log->add(
      Log::Dispatch::Screen->new(
          name      => 'screen',
          min_level => 'warning',
      )
  );

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

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

DESCRIPTION

This module manages a set of Log::Dispatch::* output objects that can
be logged to via a unified interface.

The idea 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 log 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.

METHODS

This class provides the following methods:

Log::Dispatch->new(...)

This method takes the following parameters:

  * outputs( [ [ class, params, ... ], [ class, params, ... ], ... ] )

  This parameter is a reference to a list of lists. Each inner list
  consists of a class name and a set of constructor params. The class
  is automatically prefixed with 'Log::Dispatch::' unless it begins
  with '+', in which case the string following '+' is taken to be a
  full classname. e.g.

      outputs => [ [ 'File',          min_level => 'debug', filename => 'logfile' ],
                   [ '+My::Dispatch', min_level => 'info' ] ]

  For each inner list, a new output object is created and added to the
  dispatcher (via the add() method).

  See "OUTPUT CLASSES" for the parameters that can be used when
  creating an output object.

  * 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 log or log_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!

$dispatch->clone()

This returns a shallow clone of the original object. The underlying
output objects and callbacks are shared between the two objects.
However any changes made to the outputs or callbacks that the object
contains are not shared.

$dispatch->log( level => $, message => $ or \& )

Sends the message (at the appropriate level) to all the output objects
that the dispatcher contains (by calling the log_to method repeatedly).

This method also accepts a subroutine reference as the message
argument. This reference will be called only if there is an output that
will accept a message of the specified level.

$dispatch->debug (message), info (message), ...

You may call any valid log level (including valid abbreviations) as a
method with a single argument that is the message to be logged. This is
converted into a call to the log method with the appropriate level.

For example:

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

translates to:

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

If you pass an array to these methods, it will be stringified as is:

 my @array = ('Something', 'bad', 'is', 'here');
 $log->alert(@array);

 # is equivalent to

 $log->alert("@array");

You can also pass a subroutine reference, just like passing one to the
log() method.

$dispatch->log_and_die( level => $, message => $ or \& )

Has the same behavior as calling log() but calls _die_with_message() at
the end.

$dispatch->log_and_croak( level => $, message => $ or \& )

This method adjusts the $Carp::CarpLevel scalar so that the croak comes
from the context in which it is called.

You can throw exception objects by subclassing this method.

If the carp_level parameter is present its value will be added to the
current value of $Carp::CarpLevel.

$dispatch->log_to( name => $, level => $, message => $ )

Sends the message only to the named object. Note: this will not
properly handle a subroutine reference as the message.

$dispatch->add_callback( $code )

Adds a callback (like those given during construction). It is added to
the end of the list of callbacks. Note that this can also be called on
individual output objects.

$dispatch->callbacks()

Returns a list of the callbacks in a given output.

$dispatch->level_is_valid( $string )

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.

$dispatch->would_log( $string )

Given a log level, returns true or false to indicate whether or not
anything would be logged for that log level.

$dispatch->is_$level

There are methods for every log level: is_debug(), is_warning(), etc.

This returns true if the logger will log a message at the given level.

$dispatch->add( Log::Dispatch::* OBJECT )

Adds a new output object to the dispatcher. If an object of the same
name already exists, then that object is replaced, with a warning if
$^W is true.

$dispatch->remove($)

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.

$dispatch->outputs()

Returns a list of output objects.

$dispatch->output( $name )

Returns the output object of the given name. Returns undef or an empty
list, depending on context, if the given output does not exist.

$dispatch->diewith_message( message => $, carp_level => $ )

This method is used by log_and_die and will either die() or croak()
depending on the value of message: if it's a reference or it ends with
a new line then a plain die will be used, otherwise it will croak.

OUTPUT CLASSES

An output class - e.g. Log::Dispatch::File or Log::Dispatch::Screen -
implements a particular way of dispatching logs. Many output classes
come with this distribution, and others are available separately on
CPAN.

The following common parameters can be used when creating an output
class. All are optional. Most output classes will have additional
parameters beyond these, see their documentation for details.

  * name ($)

  A name for the object (not the filename!). This is useful if you want
  to refer to the object later, e.g. to log specifically to it or
  remove it.

  By default a unique name will be generated. You should not depend on
  the form of generated names, as they may change.

  * min_level ($)

  The minimum logging level this object will accept. Required.

  * max_level ($)

  The maximum logging level this object will accept. By default the
  maximum is the highest possible level (which means functionally that
  the object has no maximum).

  * 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 )

  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 log or log_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!

  * newline (0|1)

  If true, a callback will be added to the end of the callbacks list
  that adds a newline to the end of each message. Default is false, but
  some output classes may decide to make the default true.

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:

debug

info

notice

warning

error

critical

alert

emergency

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. We also allow 'warn' as a synonym for 'warning'.

SUBCLASSING

This module was designed to be easy to subclass. If you want to handle
messaging in a way not implemented in this package, you should be able
to add this with minimal effort. It is generally as simple as
subclassing Log::Dispatch::Output and overriding the new and
log_message 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
send_email method. See the Log::Dispatch::Email docs for more details.

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").

RELATED MODULES

Log::Dispatch::DBI

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

Log::Dispatch::FileRotate

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

Log::Dispatch::File::Stamped

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

Log::Dispatch::Jabber

Written by Aaron Straup Cope. Logs messages via Jabber.

Log::Dispatch::Tk

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

Log::Dispatch::Win32EventLog

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

Log::Log4perl

An implementation of Java's log4j API in Perl. Log messages can be
limited by fine-grained controls, and if they end up being logged, both
native Log4perl and Log::Dispatch appenders can be used to perform the
actual logging job. Created by Mike Schilli and Kevin Goess.

Log::Dispatch::Config

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.

Log::Agent

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

SUPPORT

Please submit bugs and patches to the CPAN RT system at
http://rt.cpan.org/NoAuth/ReportBug.html?Queue=Log%3A%3ADispatch or via
email at bug-log-dispatch@rt.cpan.org.

Support questions can be sent to me at my email address, shown below.

DONATIONS

If you'd like to thank me for the work I've done on this module, please
consider making a "donation" to me via PayPal. I spend a lot of free
time creating free software, and would appreciate any support you'd
care to offer.

Please note that I am not suggesting that you must do this in order for
me to continue working on this particular software. I will continue to
do so, inasmuch as I have in the past, for as long as it interests me.

Similarly, a donation made in this way will probably not make me work
on this software much more, unless I get so many donations that I can
consider working on free software full time, which seems unlikely at
best.

To donate, log into PayPal and send money to autarch@urth.org or use
the button on this page: http://www.urth.org/~autarch/fs-donation.html

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