Log::Any(3) User Contributed Perl Documentation Log::Any(3)NAMELog::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');
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.
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.
perl v5.14.1 2010-02-12 Log::Any(3)
