Log::Any(3pm) User Contributed Perl Documentation Log::Any(3pm)
NAME
Log::Any - Bringing loggers and listeners together
VERSION
version 1.713
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 some data
$log->info("program started",
{progname => $0, pid => $$, perl_version => $]});
# log a string and data using a format string
$log->debugf("arguments are: %s", \@_);
# log an error and throw an exception
die $log->fatal("a fatal error occurred");
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
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.
If the "proxy_class" argument is passed, an alternative to
Log::Any::Proxy (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');
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");
The log string will be returned so that it can be used further (e.g.
for a "die" or "warn" call).
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.
If you want to log additional structured data alongside with your
string, you can add a single hashref after your log string. e.g.
$log->info("program started",
{progname => $0, pid => $$, perl_version => $]});
If the configured Log::Any::Adapter does not support logging structured
data, the hash will be converted to a string using Data::Dumper.
There are also versions of each of the logging 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", $param_count, \@params);
By default it renders like "sprintf", with the following additional
features:
• Any complex references (like "\@params" above) are automatically
converted to single-line strings with Data::Dumper.
• Any undefined values are automatically converted to the string
"<undef>".
Log level detection
To detect whether a log level is on, use "is_" followed by any of the
log levels or aliases. e.g.
if ($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.
Log context data
"Log::Any" supports logging context data by exposing the "context"
hashref. All the key/value pairs added to this hash will be printed
with every log message. You can localize the data so that it will be
removed again automatically at the end of the block:
$log->context->{directory} = $dir;
for my $file (glob "$dir/*") {
local $log->context->{file} = basename($file);
$log->warn("Can't read file!") unless -r $file;
}
This will produce the following line:
Can't read file! {directory => '/foo',file => 'bar'}
If the configured Log::Any::Adapter does not support structured data,
the context hash will be converted to a string using Data::Dumper, and
will be appended to the log message.
Setting an alternate default logger
When no other adapters are configured for your logger, "Log::Any" uses
the "default_adapter". To choose something other than Null as the
default, either set the "LOG_ANY_DEFAULT_ADAPTER" environment variable,
or pass it as a parameter when loading "Log::Any"
use Log::Any '$log', default_adapter => 'Stderr';
The name of the default class follows the same rules as used by
Log::Any::Adapter.
To pass arguments to the default adapter's constructor, use an
arrayref:
use Log::Any '$log', default_adapter => [ 'File' => '/var/log/mylog.log' ];
When a consumer configures their own adapter, the default adapter will
be overridden. If they later remove their adapter, the default adapter
will be used again.
Configuring the proxy
Any parameters passed on the import line or via the "get_logger" method
are passed on to the Log::Any::Proxy constructor.
use Log::Any '$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.
To detect if a consumer exists, use "Log::Any->has_consumer".
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.
AUTHORS
• Jonathan Swartz <swartz@pobox.com>
• David Golden <dagolden@cpan.org>
• Doug Bell <preaction@cpan.org>
• Daniel Pittman <daniel@rimspace.net>
• Stephen Thirlwall <sdt@cpan.org>
CONTRIBUTORS
• Andrew Grechkin <andrew.grechkin@gmail.com>
• bj5004 <bartosz.jakubski@hurra.com>
• cm-perl <cm-perl@users.noreply.github.com>
• Doug Bell <preaction@users.noreply.github.com>
• Jonathan <jjrs.pam+github@gmail.com>
• Karen Etheridge <ether@cpan.org>
• Konstantin S. Uvarin <khedin@gmail.com>
• Larry Leszczynski <larryl@cpan.org>
• Lucas Kanashiro <kanashiro.duarte@gmail.com>
• Maros Kollar <maros.kollar@geizhals.at>
• Maxim Vuets <maxim.vuets@booking.com>
• mephinet <mephinet@gmx.net>
• Michael Conrad <mconrad@intellitree.com>
• Nick Tonkin <1nickt@users.noreply.github.com>
• Paul Durden <alabamapaul@gmail.com>
• Philipp Gortan <philipp.gortan@apa.at>
• Phill Legault <saladdayllc@gmail.com>
• Shlomi Fish <shlomif@shlomifish.org>
• Sven Willenbuecher <sven.willenbuecher@kuehne-nagel.com>
• XSven <XSven@users.noreply.github.com>
COPYRIGHT AND LICENSE
This software is copyright (c) 2017 by Jonathan Swartz, David Golden,
and Doug Bell.
This is free software; you can redistribute it and/or modify it under
the same terms as the Perl 5 programming language system itself.
perl v5.36.0 2023-01-07 Log::Any(3pm)
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