| Log::Any - Bringing loggers and listeners together |
Log::Any - Bringing loggers and listeners together
version 1.040
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 Log::Any ();
use Moo;
has log => (
is => 'ro',
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
Log::Any provides a standard log production API for modules.
the Log::Any::Adapter manpage allows applications to choose the mechanism for log
consumption, whether screen, file or another logging mechanism like
the Log::Dispatch manpage or the Log::Log4perl manpage.
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 $log->is_debug). This is generally all that CPAN modules care
about. The second, log consumption, includes a way to configure where
logging goes (a file, the screen, etc.) and the code to send it there. This
choice generally belongs to the application.
A CPAN module uses Log::Any to get a log producer object. An application,
in turn, may choose one or more logging mechanisms via the Log::Any::Adapter manpage, or
none at all.
Log::Any has a very tiny footprint and no dependencies beyond Perl 5.8.1,
which makes it appropriate for even small CPAN modules to use. It defaults to
'null' logging activity, so a module can safely log without worrying about
whether the application has chosen (or will ever choose) a logging mechanism.
See http://www.openswartz.com/2007/09/06/standard-logging-api/ for the original post proposing this module.
Log::Any supports the following log levels and aliases, which is meant to be
inclusive of the major logging packages:
trace
debug
info (inform)
notice
warning (warn)
error (err)
critical (crit, fatal)
alert
emergency
Levels are translated as appropriate to the underlying logging mechanism. For example, log4perl only has six levels, so we translate 'notice' to 'info' and the top three levels to 'fatal'. See the documentation of an adapter class for specifics.
Every logger has a category, generally the name of the class that asked for the logger. Some logging mechanisms, like log4perl, can direct logs to different places depending on category.
The most convenient way to get a logger in your module is:
use Log::Any qw($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 the Log::Any::Proxy manpage, which passes on messages to the the Log::Any::Adapter manpage handling its category.
If the proxy_class argument is passed, an alternative to
the Log::Any::Proxy manpage (such as a subclass) will be instantiated and returned
instead. The argument is automatically prepended with ``Log::Any::Proxy::''.
If instead you want to pass the full name of a proxy class, prefix it with
a ``+''. E.g.
# Log::Any::Proxy::Foo
my $log = Log::Any->get_logger(proxy_class => 'Foo');
# MyLog::Proxy
my $log = Log::Any->get_logger(proxy_class => '+MyLog::Proxy');
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
the Log::Any::Proxy manpage object.
$log->errorf("an error occurred: %s", $@);
$log->debugf("called with %d params: %s", $param_count, \@params);
By default it renders like sprintf, with the following additional features:
\@params above) are automatically converted to
single-line strings with Data::Dumper.
Any undefined values are automatically converted to the string ``<undef>''.
To detect whether a log level is on, use ``is_'' followed by any of the log levels or aliases. e.g.
if ($log->is_info()) { ... }
$log->debug("arguments are: " . Dumper(\@_))
if $log->is_debug();
This is important for efficiency, as you can avoid the work of putting together
the logging message (in the above case, stringifying @_) if the log level is
not active.
The formatting methods (infof, errorf, etc.) check the log level for you.
Some logging mechanisms don't support detection of log levels. In these cases the detection methods will always return 1.
In contrast, the default logging mechanism - Null - will return 0 for all detection methods.
To choose something other than Null as the default, pass it as a parameter when
loading Log::Any
use Log::Any '$log', default_adapter => 'Stderr';
The name of the default class follows the same rules as used by the Log::Any::Adapter manpage.
Any parameter passed on the import line or via the get_logger method
are passed on the the the Log::Any::Proxy manpage constructor.
use Log::Any '$log', filter => \&myfilter;
the Log::Any::Test manpage provides a mechanism to test code that uses Log::Any.
Log::Any provides modules with a the Log::Any::Proxy manpage object, which is the log producer. To consume its output and direct it where you want (a file, the screen, syslog, etc.), you use the Log::Any::Adapter manpage along with a destination-specific subclass.
For example, to send output to a file via the Log::Any::Adapter::File manpage, your application could do this:
use Log::Any::Adapter ('File', '/path/to/file.log');
See the the Log::Any::Adapter manpage documentation for more details.
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.
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.
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.
Log::Any, we aim to have
as few dependencies and chances of breakage as possible. Thus, no Moose or
other niceties.
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.
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
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.
| Log::Any - Bringing loggers and listeners together |