1Log::Any(3) User Contributed Perl Documentation Log::Any(3)
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6 Log::Any -- Bringing loggers and listeners together
7
9 In a CPAN or other module:
10 package Foo;
12 use Log::Any qw($log);
13 $log->error("an error occurred");
15 $log->debugf("arguments are: %s", \@_)
16 if $log->is_debug();
17 my $log2 = Log::Any->get_logger(category => 'My::Class');
19 In your application:
21 use Log::Any::Adapter;
23 # Send all logs to Log::Log4perl
25 Log::Any::Adapter->set('Log4perl');
26 # Send all logs to Log::Dispatch
28 my $log = Log::Dispatch->new(outputs => [[ ... ]]);
29 Log::Any::Adapter->set( 'Dispatch', dispatcher => $log );
30 # See Log::Any::Adapter documentation for more options
32
34 "Log::Any" allows CPAN modules to safely and efficiently log messages,
35 while letting the application choose (or decline to choose) a logging
36 mechanism such as "Log::Dispatch" or "Log::Log4perl".
37 "Log::Any" has a very tiny footprint and no dependencies beyond Perl
39 5.6, which makes it appropriate for even small CPAN modules to use. It
40 defaults to 'null' logging activity, so a module can safely log without
41 worrying about whether the application has chosen (or will ever choose)
42 a logging mechanism.
43 The application, in turn, may choose one or more logging mechanisms via
45 Log::Any::Adapter.
46
48 "Log::Any" supports the following log levels and aliases, which is
49 meant to be inclusive of the major logging packages:
50 trace
52 debug
53 info (inform)
54 notice
55 warning (warn)
56 error (err)
57 critical (crit, fatal)
58 alert
59 emergency
60 Levels are translated as appropriate to the underlying logging
62 mechanism. For example, log4perl only has six levels, so we translate
63 'notice' to 'info' and the top three levels to 'fatal'.
64
66 Every logger has a category, generally the name of the class that asked
67 for the logger. Some logging mechanisms, like log4perl, can direct logs
68 to different places depending on category.
69
71 Getting a logger
72 The most convenient way to get a logger in your module is:
73 use Log::Any qw($log);
75 This creates a package variable $log and assigns it to the logger for
77 the current package. It is equivalent to
78 our $log = Log::Any->get_logger(category => __PACKAGE__);
80 In general, to get a logger for a specified category:
82 my $log = Log::Any->get_logger(category => $category)
84 If no category is specified, the caller package is used.
86 Logging
88 To log a message, use any of the log levels or aliases. e.g.
89 $log->error("this is an error");
91 $log->warn("this is a warning");
92 $log->warning("this is also a warning");
93 You should not include a newline in your message; that is the
95 responsibility of the logging mechanism, which may or may not want the
96 newline.
97 There are also printf-style versions of each of these methods:
99 $log->errorf("an error occurred: %s", $@);
101 $log->debugf("called with %d params: %s", $param_count, \@params);
102 The printf-style methods have a few advantages, besides being arguably
104 more readable:
105 · Any complex references (like "\@params" above) are automatically
107 converted to single-line strings with "Data::Dumper".
108 · Any undefined values are automatically converted to the string
110 "<undef>".
111 · A logging mechanism could potentially use the unchanging format
113 string (or a digest thereof) to group related log messages
114 together.
115 Log level detection
117 To detect whether a log level is on, use "is_" followed by any of the
118 log levels or aliases. e.g.
119 if ($log->is_info()) { ... }
121 $log->debug("arguments are: " . Dumper(\@_))
122 if $log->is_debug();
123 This is important for efficiency, as you can avoid the work of putting
125 together the logging message (in the above case, stringifying @_) if
126 the log level is not active.
127 Some logging mechanisms don't support detection of log levels. In these
129 cases the detection methods will always return 1.
130 In contrast, the default logging mechanism - Null - will return 0 for
132 all detection methods.
133 Testing
135 Log::Any::Test provides a mechanism to test code that uses "Log::Any".
136
138 To direct logs somewhere - a file, the screen, etc. - you must use
139 Log::Any::Adapter. This is intentionally kept in a separate
140 distributions to keep "Log::Any" as simple and unchanging as possible.
141
143 Many modules have something interesting to say. Unfortunately there is
144 no standard way for them to say it - some output to STDERR, others to
145 "warn", others to custom file logs. And there is no standard way to get
146 a module to start talking - sometimes you must call a uniquely named
147 method, other times set a package variable.
148 This being Perl, there are many logging mechanisms available on CPAN.
150 Each has their pros and cons. Unfortunately, the existence of so many
151 mechanisms makes it difficult for a CPAN author to commit his/her users
152 to one of them. This may be why many CPAN modules invent their own
153 logging or choose not to log at all.
154 To untangle this situation, we must separate the two parts of a logging
156 API. The first, log production, includes methods to output logs (like
157 "$log->debug") and methods to inspect whether a log level is activated
158 (like "$log->is_debug"). This is generally all that CPAN modules care
159 about. The second, log consumption, includes a way to configure where
160 logging goes (a file, the screen, etc.) and the code to send it there.
161 This choice generally belongs to the application.
162 "Log::Any" provides a standard log production API for modules.
164 "Log::Any::Adapter" allows applications to choose the mechanism for log
165 consumption.
166 See http://www.openswartz.com/2007/09/06/standard-logging-api/ for the
168 original post proposing this module.
169
171 Isn't Log::Any just yet another logging mechanism?
172 No. "Log::Any" does not, and never will, include code that knows
173 how to log to a particular place (file, screen, etc.) It can only
174 forward logging requests to another logging mechanism.
175 Why don't you just pick the best logging mechanism, and use and promote
177 it?
178 Each of the logging mechanisms have their pros and cons,
179 particularly in terms of how they are configured. For example,
180 log4perl offers a great deal of power and flexibility but uses a
181 global and potentially heavy configuration, whereas "Log::Dispatch"
182 is extremely configuration-light but doesn't handle categories.
183 There is also the unnamed future logger that may have advantages
184 over either of these two, and all the custom in-house loggers
185 people have created and cannot (for whatever reason) stop using.
186 Is it safe for my critical module to depend on Log::Any?
188 Our intent is to keep "Log::Any" minimal, and change it only when
189 absolutely necessary. Most of the "innovation", if any, is expected
190 to occur in "Log::Any::Adapter", which your module should not have
191 to depend on (unless it wants to direct logs somewhere specific).
192 "Log::Any" has no module dependencies other than Test::Simple for
193 testing.
194 Why doesn't Log::Any use insert modern Perl technique?
196 To encourage CPAN module authors to adopt and use "Log::Any", we
197 aim to have as few dependencies and chances of breakage as
198 possible. Thus, no "Moose" or other niceties.
199
201 Jonathan Swartz
202
204 Log::Any::Adapter; the many Log:: modules on CPAN
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207 Copyright (C) 2009 Jonathan Swartz.
208 Log::Any is provided "as is" and without any express or implied
210 warranties, including, without limitation, the implied warranties of
211 merchantibility and fitness for a particular purpose.
212 This program is free software; you canredistribute it and/or modify it
214 under the same terms as Perl itself.
215perl v5.12.2 2010-02-12 Log::Any(3)