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

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');

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
    Every logging mechanism on CPAN uses a slightly different set of levels.
    For `Log::Any' we've standardized on the log levels from syslog, and
    also added a number of common aliases:

         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 five 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. First, they can be more
    readable than concatenated strings (subjective of course); second, any
    complex references (like `\@params' above) are automatically converted
    to single-line strings with `Data::Dumper'; third, a logging mechanism
    could potentially hash the format string to a unique id, e.g. 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.

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).

    Why doesn't Log::Any use Moose or *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.

AUTHOR
    Jonathan Swartz

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

COPYRIGHT & LICENSE
    Copyright (C) 2009 Jonathan Swartz.

    Log::Any is provided "as is" and without any express or implied
    warranties, including, without limitation, the implied warranties of
    merchantibility and fitness for a particular purpose.

    This program is free software; you canredistribute it and/or modify it
    under the same terms as Perl itself.

