NAME
   Log::Any -- Bringing loggers and listeners together

VERSION
   version 0.13

SYNOPSIS
   In a CPAN or other module:

       package Foo;
       use Log::Any qw($log);

       $log->error("an error occurred");
       $log->debugf("arguments are: %s", \@_)
           if $log->is_debug();

       my $log2 = Log::Any->get_logger(category => 'My::Class');

   In your application:

       use Log::Any::Adapter;

       # Send all logs to Log::Log4perl
       Log::Any::Adapter->set('Log4perl');

       # Send all logs to Log::Dispatch
       my $log = Log::Dispatch->new(outputs => [[ ... ]]);
       Log::Any::Adapter->set( 'Dispatch', dispatcher => $log );

       # See Log::Any::Adapter documentation for more options

DESCRIPTION
   `Log::Any' allows CPAN modules to safely and efficiently log messages,
   while letting the application choose (or decline to choose) a logging
   mechanism such as `Log::Dispatch' or `Log::Log4perl'.

   `Log::Any' has a very tiny footprint and no dependencies beyond Perl
   5.6, which makes it appropriate for even small CPAN modules to use. It
   defaults to 'null' logging activity, so a module can safely log without
   worrying about whether the application has chosen (or will ever choose)
   a logging mechanism.

   The application, in turn, may choose one or more logging mechanisms via
   Log::Any::Adapter.

LOG LEVELS
   `Log::Any' supports the following log levels and aliases, which is meant
   to be inclusive of the major logging packages:

        trace
        debug
        info (inform)
        notice
        warning (warn)
        error (err)
        critical (crit, fatal)
        alert
        emergency

   Levels are translated as appropriate to the underlying logging
   mechanism. For example, log4perl only has six levels, so we translate
   'notice' to 'info' and the top three levels to 'fatal'.

CATEGORIES
   Every logger has a category, generally the name of the class that asked
   for the logger. Some logging mechanisms, like log4perl, can direct logs
   to different places depending on category.

PRODUCING LOGS (FOR MODULES)
 Getting a logger
   The most convenient way to get a logger in your module is:

       use Log::Any qw($log);

   This creates a package variable *$log* and assigns it to the logger for
   the current package. It is equivalent to

       our $log = Log::Any->get_logger(category => __PACKAGE__);

   In general, to get a logger for a specified category:

       my $log = Log::Any->get_logger(category => $category)

   If no category is specified, the caller package is used.

 Logging
   To log a message, use any of the log levels or aliases. e.g.

       $log->error("this is an error");
       $log->warn("this is a warning");
       $log->warning("this is also a warning");

   You should not include a newline in your message; that is the
   responsibility of the logging mechanism, which may or may not want the
   newline.

   There are also printf-style versions of each of these methods:

       $log->errorf("an error occurred: %s", $@);
       $log->debugf("called with %d params: %s", $param_count, \@params);

   The printf-style methods have a few advantages, besides being arguably
   more readable:

   *   Any complex references (like `\@params' above) are automatically
       converted to single-line strings with `Data::Dumper'.

   *   Any undefined values are automatically converted to the string
       "<undef>".

   *   A logging mechanism could potentially use the unchanging format
       string (or a digest thereof) to group related log messages together.

 Log level detection
   To detect whether a log level is on, use "is_" followed by any of the
   log levels or aliases. e.g.

       if ($log->is_info()) { ... }
       $log->debug("arguments are: " . Dumper(\@_))
           if $log->is_debug();

   This is important for efficiency, as you can avoid the work of putting
   together the logging message (in the above case, stringifying `@_') if
   the log level is not active.

   Some logging mechanisms don't support detection of log levels. In these
   cases the detection methods will always return 1.

   In contrast, the default logging mechanism - Null - will return 0 for
   all detection methods.

 Testing
   Log::Any::Test provides a mechanism to test code that uses `Log::Any'.

CONSUMING LOGS (FOR APPLICATIONS)
   To direct logs somewhere - a file, the screen, etc. - you must use
   Log::Any::Adapter. This is intentionally kept in a separate
   distributions to keep `Log::Any' as simple and unchanging as possible.

MOTIVATION
   Many modules have something interesting to say. Unfortunately there is
   no standard way for them to say it - some output to STDERR, others to
   `warn', others to custom file logs. And there is no standard way to get
   a module to start talking - sometimes you must call a uniquely named
   method, other times set a package variable.

   This being Perl, there are many logging mechanisms available on CPAN.
   Each has their pros and cons. Unfortunately, the existence of so many
   mechanisms makes it difficult for a CPAN author to commit his/her users
   to one of them. This may be why many CPAN modules invent their own
   logging or choose not to log at all.

   To untangle this situation, we must separate the two parts of a logging
   API. The first, *log production*, includes methods to output logs (like
   `$log->debug') and methods to inspect whether a log level is activated
   (like `$log->is_debug'). This is generally all that CPAN modules care
   about. The second, *log consumption*, includes a way to configure where
   logging goes (a file, the screen, etc.) and the code to send it there.
   This choice generally belongs to the application.

   `Log::Any' provides a standard log production API for modules.
   `Log::Any::Adapter' allows applications to choose the mechanism for log
   consumption.

   See http://www.openswartz.com/2007/09/06/standard-logging-api/ for the
   original post proposing this module.

Q & A
   Isn't Log::Any just yet another logging mechanism?
       No. `Log::Any' does not, and never will, include code that knows how
       to log to a particular place (file, screen, etc.) It can only
       forward logging requests to another logging mechanism.

   Why don't you just pick the best logging mechanism, and use and promote
   it?
       Each of the logging mechanisms have their pros and cons,
       particularly in terms of how they are configured. For example,
       log4perl offers a great deal of power and flexibility but uses a
       global and potentially heavy configuration, whereas `Log::Dispatch'
       is extremely configuration-light but doesn't handle categories.
       There is also the unnamed future logger that may have advantages
       over either of these two, and all the custom in-house loggers people
       have created and cannot (for whatever reason) stop using.

   Is it safe for my critical module to depend on Log::Any?
       Our intent is to keep `Log::Any' minimal, and change it only when
       absolutely necessary. Most of the "innovation", if any, is expected
       to occur in `Log::Any::Adapter', which your module should not have
       to depend on (unless it wants to direct logs somewhere specific).
       `Log::Any' has no module dependencies other than Test::Simple for
       testing.

   Why doesn't Log::Any use *insert modern Perl technique*?
       To encourage CPAN module authors to adopt and use `Log::Any', we aim
       to have as few dependencies and chances of breakage as possible.
       Thus, no `Moose' or other niceties.

SEE ALSO
   Log::Any::Adapter, the many Log:: modules on CPAN

COPYRIGHT AND LICENSE
   This software is copyright (c) 2011 by Jonathan Swartz.

   This is free software; you can redistribute it and/or modify it under
   the same terms as the Perl 5 programming language system itself.

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