Ubuntu Manpage: Log::Any -- Bringing loggers and listeners together

NAME

       Log::Any -- Bringing loggers and listeners together

VERSION

       version 0.15

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'.

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.

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.