1Log::Any(3)           User Contributed Perl Documentation          Log::Any(3)
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NAME

6       Log::Any - Bringing loggers and listeners together
7

VERSION

9       version 1.710
10

SYNOPSIS

12       In a CPAN or other module:
13
14           package Foo;
15           use Log::Any qw($log);
16
17           # log a string
18           $log->error("an error occurred");
19
20           # log a string and some data
21           $log->info("program started",
22               {progname => $0, pid => $$, perl_version => $]});
23
24           # log a string and data using a format string
25           $log->debugf("arguments are: %s", \@_);
26
27           # log an error and throw an exception
28           die $log->fatal("a fatal error occurred");
29
30       In a Moo/Moose-based module:
31
32           package Foo;
33           use Log::Any ();
34           use Moo;
35
36           has log => (
37               is => 'ro',
38               default => sub { Log::Any->get_logger },
39           );
40
41       In your application:
42
43           use Foo;
44           use Log::Any::Adapter;
45
46           # Send all logs to Log::Log4perl
47           Log::Any::Adapter->set('Log4perl');
48
49           # Send all logs to Log::Dispatch
50           my $log = Log::Dispatch->new(outputs => [[ ... ]]);
51           Log::Any::Adapter->set( 'Dispatch', dispatcher => $log );
52
53           # See Log::Any::Adapter documentation for more options
54

DESCRIPTION

56       "Log::Any" provides a standard log production API for modules.
57       Log::Any::Adapter allows applications to choose the mechanism for log
58       consumption, whether screen, file or another logging mechanism like
59       Log::Dispatch or Log::Log4perl.
60
61       Many modules have something interesting to say. Unfortunately there is
62       no standard way for them to say it - some output to STDERR, others to
63       "warn", others to custom file logs. And there is no standard way to get
64       a module to start talking - sometimes you must call a uniquely named
65       method, other times set a package variable.
66
67       This being Perl, there are many logging mechanisms available on CPAN.
68       Each has their pros and cons. Unfortunately, the existence of so many
69       mechanisms makes it difficult for a CPAN author to commit his/her users
70       to one of them. This may be why many CPAN modules invent their own
71       logging or choose not to log at all.
72
73       To untangle this situation, we must separate the two parts of a logging
74       API.  The first, log production, includes methods to output logs (like
75       "$log->debug") and methods to inspect whether a log level is activated
76       (like "$log->is_debug"). This is generally all that CPAN modules care
77       about. The second, log consumption, includes a way to configure where
78       logging goes (a file, the screen, etc.) and the code to send it there.
79       This choice generally belongs to the application.
80
81       A CPAN module uses "Log::Any" to get a log producer object.  An
82       application, in turn, may choose one or more logging mechanisms via
83       Log::Any::Adapter, or none at all.
84
85       "Log::Any" has a very tiny footprint and no dependencies beyond Perl
86       5.8.1, which makes it appropriate for even small CPAN modules to use.
87       It defaults to 'null' logging activity, so a module can safely log
88       without worrying about whether the application has chosen (or will ever
89       choose) a logging mechanism.
90
91       See <http://www.openswartz.com/2007/09/06/standard-logging-api/> for
92       the original post proposing this module.
93

LOG LEVELS

95       "Log::Any" supports the following log levels and aliases, which is
96       meant to be inclusive of the major logging packages:
97
98            trace
99            debug
100            info (inform)
101            notice
102            warning (warn)
103            error (err)
104            critical (crit, fatal)
105            alert
106            emergency
107
108       Levels are translated as appropriate to the underlying logging
109       mechanism. For example, log4perl only has six levels, so we translate
110       'notice' to 'info' and the top three levels to 'fatal'.  See the
111       documentation of an adapter class for specifics.
112

CATEGORIES

114       Every logger has a category, generally the name of the class that asked
115       for the logger. Some logging mechanisms, like log4perl, can direct logs
116       to different places depending on category.
117

PRODUCING LOGS (FOR MODULES)

119   Getting a logger
120       The most convenient way to get a logger in your module is:
121
122           use Log::Any qw($log);
123
124       This creates a package variable $log and assigns it to the logger for
125       the current package. It is equivalent to
126
127           our $log = Log::Any->get_logger;
128
129       In general, to get a logger for a specified category:
130
131           my $log = Log::Any->get_logger(category => $category)
132
133       If no category is specified, the calling package is used.
134
135       A logger object is an instance of Log::Any::Proxy, which passes on
136       messages to the Log::Any::Adapter handling its category.
137
138       If the "proxy_class" argument is passed, an alternative to
139       Log::Any::Proxy (such as a subclass) will be instantiated and returned
140       instead.  The argument is automatically prepended with
141       "Log::Any::Proxy::".  If instead you want to pass the full name of a
142       proxy class, prefix it with a "+". E.g.
143
144           # Log::Any::Proxy::Foo
145           my $log = Log::Any->get_logger(proxy_class => 'Foo');
146
147           # MyLog::Proxy
148           my $log = Log::Any->get_logger(proxy_class => '+MyLog::Proxy');
149
150   Logging
151       To log a message, pass a single string to any of the log levels or
152       aliases. e.g.
153
154           $log->error("this is an error");
155           $log->warn("this is a warning");
156           $log->warning("this is also a warning");
157
158       The log string will be returned so that it can be used further (e.g.
159       for a "die" or "warn" call).
160
161       You should not include a newline in your message; that is the
162       responsibility of the logging mechanism, which may or may not want the
163       newline.
164
165       If you want to log additional structured data alongside with your
166       string, you can add a single hashref after your log string. e.g.
167
168           $log->info("program started",
169               {progname => $0, pid => $$, perl_version => $]});
170
171       If the configured Log::Any::Adapter does not support logging structured
172       data, the hash will be converted to a string using Data::Dumper.
173
174       There are also versions of each of the logging methods with an
175       additional "f" suffix ("infof", "errorf", "debugf", etc.) that format a
176       list of arguments.  The specific formatting mechanism and meaning of
177       the arguments is controlled by the Log::Any::Proxy object.
178
179           $log->errorf("an error occurred: %s", $@);
180           $log->debugf("called with %d params: %s", $param_count, \@params);
181
182       By default it renders like "sprintf", with the following additional
183       features:
184
185       •   Any complex references (like "\@params" above) are automatically
186           converted to single-line strings with Data::Dumper.
187
188       •   Any undefined values are automatically converted to the string
189           "<undef>".
190
191   Log level detection
192       To detect whether a log level is on, use "is_" followed by any of the
193       log levels or aliases. e.g.
194
195           if ($log->is_info()) { ... }
196           $log->debug("arguments are: " . Dumper(\@_))
197               if $log->is_debug();
198
199       This is important for efficiency, as you can avoid the work of putting
200       together the logging message (in the above case, stringifying @_) if
201       the log level is not active.
202
203       The formatting methods ("infof", "errorf", etc.) check the log level
204       for you.
205
206       Some logging mechanisms don't support detection of log levels. In these
207       cases the detection methods will always return 1.
208
209       In contrast, the default logging mechanism - Null - will return 0 for
210       all detection methods.
211
212   Log context data
213       "Log::Any" supports logging context data by exposing the "context"
214       hashref. All the key/value pairs added to this hash will be printed
215       with every log message. You can localize the data so that it will be
216       removed again automatically at the end of the block:
217
218           $log->context->{directory} = $dir;
219           for my $file (glob "$dir/*") {
220               local $log->context->{file} = basename($file);
221               $log->warn("Can't read file!") unless -r $file;
222           }
223
224       This will produce the following line:
225
226           Can't read file! {directory => '/foo',file => 'bar'}
227
228       If the configured Log::Any::Adapter does not support structured data,
229       the context hash will be converted to a string using Data::Dumper, and
230       will be appended to the log message.
231
232   Setting an alternate default logger
233       When no other adapters are configured for your logger, "Log::Any" uses
234       the "default_adapter". To choose something other than Null as the
235       default, either set the "LOG_ANY_DEFAULT_ADAPTER" environment variable,
236       or pass it as a parameter when loading "Log::Any"
237
238           use Log::Any '$log', default_adapter => 'Stderr';
239
240       The name of the default class follows the same rules as used by
241       Log::Any::Adapter.
242
243       To pass arguments to the default adapter's constructor, use an
244       arrayref:
245
246           use Log::Any '$log', default_adapter => [ 'File' => '/var/log/mylog.log' ];
247
248       When a consumer configures their own adapter, the default adapter will
249       be overridden. If they later remove their adapter, the default adapter
250       will be used again.
251
252   Configuring the proxy
253       Any parameters passed on the import line or via the "get_logger" method
254       are passed on to the Log::Any::Proxy constructor.
255
256           use Log::Any '$log', filter => \&myfilter;
257
258   Testing
259       Log::Any::Test provides a mechanism to test code that uses "Log::Any".
260

CONSUMING LOGS (FOR APPLICATIONS)

262       Log::Any provides modules with a Log::Any::Proxy object, which is the
263       log producer.  To consume its output and direct it where you want (a
264       file, the screen, syslog, etc.), you use Log::Any::Adapter along with a
265       destination-specific subclass.
266
267       For example, to send output to a file via Log::Any::Adapter::File, your
268       application could do this:
269
270           use Log::Any::Adapter ('File', '/path/to/file.log');
271
272       See the Log::Any::Adapter documentation for more details.
273
274       To detect if a consumer exists, use "Log::Any->has_consumer".
275

Q & A

277       Isn't Log::Any just yet another logging mechanism?
278           No. "Log::Any" does not include code that knows how to log to a
279           particular place (file, screen, etc.) It can only forward logging
280           requests to another logging mechanism.
281
282       Why don't you just pick the best logging mechanism, and use and promote
283       it?
284           Each of the logging mechanisms have their pros and cons,
285           particularly in terms of how they are configured. For example,
286           log4perl offers a great deal of power and flexibility but uses a
287           global and potentially heavy configuration, whereas Log::Dispatch
288           is extremely configuration-light but doesn't handle categories.
289           There is also the unnamed future logger that may have advantages
290           over either of these two, and all the custom in-house loggers
291           people have created and cannot (for whatever reason) stop using.
292
293       Is it safe for my critical module to depend on Log::Any?
294           Our intent is to keep "Log::Any" minimal, and change it only when
295           absolutely necessary. Most of the "innovation", if any, is expected
296           to occur in "Log::Any::Adapter", which your module should not have
297           to depend on (unless it wants to direct logs somewhere specific).
298           "Log::Any" has no non-core dependencies.
299
300       Why doesn't Log::Any use insert modern Perl technique?
301           To encourage CPAN module authors to adopt and use "Log::Any", we
302           aim to have as few dependencies and chances of breakage as
303           possible. Thus, no "Moose" or other niceties.
304

AUTHORS

306       •   Jonathan Swartz <swartz@pobox.com>
307
308       •   David Golden <dagolden@cpan.org>
309
310       •   Doug Bell <preaction@cpan.org>
311
312       •   Daniel Pittman <daniel@rimspace.net>
313
314       •   Stephen Thirlwall <sdt@cpan.org>
315

CONTRIBUTORS

317       •   bj5004 <bartosz.jakubski@hurra.com>
318
319       •   cm-perl <cm-perl@users.noreply.github.com>
320
321       •   Jonathan <jjrs.pam+github@gmail.com>
322
323       •   Karen Etheridge <ether@cpan.org>
324
325       •   Konstantin S. Uvarin <khedin@gmail.com>
326
327       •   Lucas Kanashiro <kanashiro.duarte@gmail.com>
328
329       •   Maros Kollar <maros.kollar@geizhals.at>
330
331       •   Maxim Vuets <maxim.vuets@booking.com>
332
333       •   mephinet <mephinet@gmx.net>
334
335       •   Michael Conrad <mconrad@intellitree.com>
336
337       •   Nick Tonkin <1nickt@users.noreply.github.com>
338
339       •   Paul Durden <alabamapaul@gmail.com>
340
341       •   Philipp Gortan <philipp.gortan@apa.at>
342
343       •   Phill Legault <saladdayllc@gmail.com>
344
345       •   Shlomi Fish <shlomif@shlomifish.org>
346
348       This software is copyright (c) 2017 by Jonathan Swartz, David Golden,
349       and Doug Bell.
350
351       This is free software; you can redistribute it and/or modify it under
352       the same terms as the Perl 5 programming language system itself.
353
354
355
356perl v5.34.0                      2022-01-21                       Log::Any(3)
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