David Golden > Log-Any > Log::Any

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Module Version: 1.03   Source  

NAME ^

Log::Any - Bringing loggers and listeners together

VERSION ^

version 1.03

SYNOPSIS ^

In a CPAN or other module:

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

    # log a string
    $log->error("an error occurred");

    # log a string and data using a formatting filter
    $log->debugf("arguments are: %s", \@_);

In a Moo/Moose-based module:

    package Foo;
    use Moo;

    has log => (
        is => 'ro',
        isa => 'Log::Any::Proxy',
        default => sub { Log::Any->get_logger },
    );

In your application:

    use Foo;
    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 provides a standard log production API for modules. Log::Any::Adapter allows applications to choose the mechanism for log consumption, whether screen, file or another logging mechanism like Log::Dispatch or Log::Log4perl.

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.

A CPAN module uses Log::Any to get a log producer object. An application, in turn, may choose one or more logging mechanisms via Log::Any::Adapter, or none at all.

Log::Any has a very tiny footprint and no dependencies beyond Perl 5.8.1, 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.

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

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'. See the documentation of an adapter class for specifics.

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;

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

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

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

A logger object is an instance of Log::Any::Proxy, which passes on messages to the Log::Any::Adapter handling its category.

Logging

To log a message, pass a single string to 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 versions of each of these methods with an additional "f" suffix (infof, errorf, debugf, etc.) that format a list of arguments. The specific formatting mechanism and meaning of the arguments is controlled by the Log::Any::Proxy object.

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

By default it renders like sprintf, with the following additional features:

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.

The formatting methods (infof, errorf, etc.) check the log level for you.

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.

Setting an alternate default logger

To choose something other than Null as the default, pass it as a parameter when loading Log::Any

    use Log::Any '$log', default_adapter => 'Stderr';

The name of the default class follows the same rules as used by Log::Any::Adapter.

Configuring the proxy

Any parameter passed on the import line or via the get_logger method are passed on the the Log::Any::Proxy constructor.

    use Log::Any '$log', filter => \&myfilter;

Testing

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

CONSUMING LOGS (FOR APPLICATIONS) ^

Log::Any provides modules with a Log::Any::Proxy object, which is the log producer. To consume its output and direct it where you want (a file, the screen, syslog, etc.), you use Log::Any::Adapter along with a destination-specific subclass.

For example, to send output to a file via Log::Any::Adapter::File, your application could do this:

    use Log::Any::Adapter ('File', '/path/to/file.log');

See the Log::Any::Adapter documentation for more details.

Q & A ^

Isn't Log::Any just yet another logging mechanism?

No. Log::Any does not 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 non-core dependencies.

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.

SUPPORT ^

Bugs / Feature Requests

Please report any bugs or feature requests through the issue tracker at https://github.com/dagolden/Log-Any/issues. You will be notified automatically of any progress on your issue.

Source Code

This is open source software. The code repository is available for public review and contribution under the terms of the license.

https://github.com/dagolden/Log-Any

  git clone https://github.com/dagolden/Log-Any.git

AUTHORS ^

CONTRIBUTORS ^

COPYRIGHT AND LICENSE ^

This software is copyright (c) 2014 by Jonathan Swartz and David Golden.

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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