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 => $log );
# See Log::Any::Adapter documentation for more options
DESCRIPTION¶
"Log::Any" allows CPAN modules to safely and efficiently log messages,
while letting the application choose (or decline to choose) a logging
mechanism such as "Log::Dispatch" or "Log::Log4perl".
"Log::Any" has a very tiny footprint and no dependencies beyond Perl
5.6, which makes it appropriate for even small CPAN modules to use. It
defaults to 'null' logging activity, so a module can safely log without
worrying about whether the application has chosen (or will ever choose) a
logging mechanism.
The application, in turn, may choose one or more logging mechanisms via
Log::Any::Adapter.
LOG LEVELS¶
"Log::Any" supports the following log levels and aliases, which is
meant to be inclusive of the major logging packages:
trace
debug
info (inform)
notice
warning (warn)
error (err)
critical (crit, fatal)
alert
emergency
Levels are translated as appropriate to the underlying logging mechanism. For
example, log4perl only has six levels, so we translate 'notice' to 'info' and
the top three levels to 'fatal'.
CATEGORIES¶
Every logger has a category, generally the name of the class that asked for the
logger. Some logging mechanisms, like log4perl, can direct logs to different
places depending on category.
PRODUCING LOGS (FOR MODULES)¶
Getting a logger¶
The most convenient way to get a logger in your module is:
use Log::Any qw($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.
SEE ALSO¶
Log::Any::Adapter, the many Log:: modules on CPAN
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.