1FAQ(3)                User Contributed Perl Documentation               FAQ(3)
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NAME

6       Log::Log4perl::FAQ - Frequently Asked Questions on Log::Log4perl
7

DESCRIPTION

9       This FAQ shows a wide variety of commonly encountered logging tasks and
10       how to solve them in the most elegant way with Log::Log4perl. Most of
11       the time, this will be just a matter of smartly configuring your
12       Log::Log4perl configuration files.
13
14   Why use Log::Log4perl instead of any other logging module on CPAN?
15       That's a good question. There's dozens of logging modules on CPAN.
16       When it comes to logging, people typically think: "Aha. Writing out
17       debug and error messages. Debug is lower than error. Easy. I'm gonna
18       write my own." Writing a logging module is like a rite of passage for
19       every Perl programmer, just like writing your own templating system.
20
21       Of course, after getting the basics right, features need to be added.
22       You'd like to write a timestamp with every message. Then timestamps
23       with microseconds. Then messages need to be written to both the screen
24       and a log file.
25
26       And, as your application grows in size you might wonder: Why doesn't my
27       logging system scale along with it? You would like to switch on logging
28       in selected parts of the application, and not all across the board,
29       because this kills performance. This is when people turn to
30       Log::Log4perl, because it handles all of that.
31
32       Avoid this costly switch.
33
34       Use "Log::Log4perl" right from the start. "Log::Log4perl"'s ":easy"
35       mode supports easy logging in simple scripts:
36
37           use Log::Log4perl qw(:easy);
38           Log::Log4perl->easy_init($DEBUG);
39
40           DEBUG "A low-level message";
41           ERROR "Won't make it until level gets increased to ERROR";
42
43       And when your application inevitably grows, your logging system grows
44       with it without you having to change any code.
45
46       Please, don't re-invent logging. "Log::Log4perl" is here, it's easy to
47       use, it scales, and covers many areas you haven't thought of yet, but
48       will enter soon.
49
50   What's the easiest way to use Log4perl?
51       If you just want to get all the comfort of logging, without much
52       overhead, use Stealth Loggers. If you use Log::Log4perl in ":easy" mode
53       like
54
55           use Log::Log4perl qw(:easy);
56
57       you'll have the following functions available in the current package:
58
59           DEBUG("message");
60           INFO("message");
61           WARN("message");
62           ERROR("message");
63           FATAL("message");
64
65       Just make sure that every package of your code where you're using them
66       in pulls in "use Log::Log4perl qw(:easy)" first, then you're set.
67       Every stealth logger's category will be equivalent to the name of the
68       package it's located in.
69
70       These stealth loggers will be absolutely silent until you initialize
71       Log::Log4perl in your main program with either
72
73               # Define any Log4perl behavior
74           Log::Log4perl->init("foo.conf");
75
76       (using a full-blown Log4perl config file) or the super-easy method
77
78               # Just log to STDERR
79           Log::Log4perl->easy_init($DEBUG);
80
81       or the parameter-style method with a complexity somewhat in between:
82
83               # Append to a log file
84           Log::Log4perl->easy_init( { level   => $DEBUG,
85                                       file    => ">>test.log" } );
86
87       For more info, please check out "Stealth Loggers" in Log::Log4perl.
88
89   How can I simply log all my ERROR messages to a file?
90       After pulling in the "Log::Log4perl" module, just initialize its
91       behavior by passing in a configuration to its "init" method as a string
92       reference. Then, obtain a logger instance and write out a message with
93       its "error()" method:
94
95           use Log::Log4perl qw(get_logger);
96
97               # Define configuration
98           my $conf = q(
99               log4perl.logger                    = ERROR, FileApp
100               log4perl.appender.FileApp          = Log::Log4perl::Appender::File
101               log4perl.appender.FileApp.filename = test.log
102               log4perl.appender.FileApp.layout   = PatternLayout
103               log4perl.appender.FileApp.layout.ConversionPattern = %d> %m%n
104           );
105
106               # Initialize logging behavior
107           Log::Log4perl->init( \$conf );
108
109               # Obtain a logger instance
110           my $logger = get_logger("Bar::Twix");
111           $logger->error("Oh my, a dreadful error!");
112           $logger->warn("Oh my, a dreadful warning!");
113
114       This will append something like
115
116           2002/10/29 20:11:55> Oh my, a dreadful error!
117
118       to the log file "test.log". How does this all work?
119
120       While the Log::Log4perl "init()" method typically takes the name of a
121       configuration file as its input parameter like in
122
123           Log::Log4perl->init( "/path/mylog.conf" );
124
125       the example above shows how to pass in a configuration as text in a
126       scalar reference.
127
128       The configuration as shown defines a logger of the root category, which
129       has an appender of type "Log::Log4perl::Appender::File" attached. The
130       line
131
132           log4perl.logger = ERROR, FileApp
133
134       doesn't list a category, defining a root logger. Compare that with
135
136           log4perl.logger.Bar.Twix = ERROR, FileApp
137
138       which would define a logger for the category "Bar::Twix", showing
139       probably different behavior. "FileApp" on the right side of the
140       assignment is an arbitrarily defined variable name, which is only used
141       to somehow reference an appender defined later on.
142
143       Appender settings in the configuration are defined as follows:
144
145           log4perl.appender.FileApp          = Log::Log4perl::Appender::File
146           log4perl.appender.FileApp.filename = test.log
147
148       It selects the file appender of the "Log::Log4perl::Appender"
149       hierarchy, which will append to the file "test.log" if it already
150       exists. If we wanted to overwrite a potentially existing file, we would
151       have to explicitly set the appropriate "Log::Log4perl::Appender::File"
152       parameter "mode":
153
154           log4perl.appender.FileApp          = Log::Log4perl::Appender::File
155           log4perl.appender.FileApp.filename = test.log
156           log4perl.appender.FileApp.mode     = write
157
158       Also, the configuration defines a PatternLayout format, adding the
159       nicely formatted current date and time, an arrow (>) and a space before
160       the messages, which is then followed by a newline:
161
162           log4perl.appender.FileApp.layout   = PatternLayout
163           log4perl.appender.FileApp.layout.ConversionPattern = %d> %m%n
164
165       Obtaining a logger instance and actually logging something is typically
166       done in a different system part as the Log::Log4perl initialisation
167       section, but in this example, it's just done right after init for the
168       sake of compactness:
169
170               # Obtain a logger instance
171           my $logger = get_logger("Bar::Twix");
172           $logger->error("Oh my, a dreadful error!");
173
174       This retrieves an instance of the logger of the category "Bar::Twix",
175       which, as all other categories, inherits behavior from the root logger
176       if no other loggers are defined in the initialization section.
177
178       The "error()" method fires up a message, which the root logger catches.
179       Its priority is equal to or higher than the root logger's priority
180       (ERROR), which causes the root logger to forward it to its attached
181       appender. By contrast, the following
182
183           $logger->warn("Oh my, a dreadful warning!");
184
185       doesn't make it through, because the root logger sports a higher
186       setting (ERROR and up) than the WARN priority of the message.
187
188   How can I install Log::Log4perl on Microsoft Windows?
189       You can install Log::Log4perl using the CPAN client.
190
191       Alternatively you can install it using
192
193           ppm install Log-Log4perl
194
195       if you're using ActiveState perl.
196
197       That's it! Afterwards, just create a Perl script like
198
199           use Log::Log4perl qw(:easy);
200           Log::Log4perl->easy_init($DEBUG);
201
202           my $logger = get_logger("Twix::Bar");
203           $logger->debug("Watch me!");
204
205       and run it. It should print something like
206
207           2002/11/06 01:22:05 Watch me!
208
209       If you find that something doesn't work, please let us know at
210       log4perl-devel@lists.sourceforge.net -- we'll appreciate it. Have fun!
211
212   How can I include global (thread-specific) data in my log messages?
213       Say, you're writing a web application and want all your log messages to
214       include the current client's IP address. Most certainly, you don't want
215       to include it in each and every log message like in
216
217           $logger->debug( $r->connection->remote_ip,
218                           " Retrieving user data from DB" );
219
220       do you? Instead, you want to set it in a global data structure and have
221       Log::Log4perl include it automatically via a PatternLayout setting in
222       the configuration file:
223
224           log4perl.appender.FileApp.layout.ConversionPattern = %X{ip} %m%n
225
226       The conversion specifier %X{ip} references an entry under the key "ip"
227       in the global "MDC" (mapped diagnostic context) table, which you've set
228       once via
229
230           Log::Log4perl::MDC->put("ip", $r->connection->remote_ip);
231
232       at the start of the request handler. Note that this is a static (class)
233       method, there's no logger object involved.  You can use this method
234       with as many key/value pairs as you like as long as you reference them
235       under different names.
236
237       The mappings are stored in a global hash table within Log::Log4perl.
238       Luckily, because the thread model in 5.8.0 doesn't share global
239       variables between threads unless they're explicitly marked as such,
240       there's no problem with multi-threaded environments.
241
242       For more details on the MDC, please refer to "Mapped Diagnostic Context
243       (MDC)" in Log::Log4perl and Log::Log4perl::MDC.
244
245   My application is already logging to a file. How can I duplicate all
246       messages to also go to the screen?
247       Assuming that you already have a Log4perl configuration file like
248
249           log4perl.logger                    = DEBUG, FileApp
250
251           log4perl.appender.FileApp          = Log::Log4perl::Appender::File
252           log4perl.appender.FileApp.filename = test.log
253           log4perl.appender.FileApp.layout   = PatternLayout
254           log4perl.appender.FileApp.layout.ConversionPattern = %d> %m%n
255
256       and log statements all over your code, it's very easy with Log4perl to
257       have the same messages both printed to the logfile and the screen. No
258       reason to change your code, of course, just add another appender to the
259       configuration file and you're done:
260
261           log4perl.logger                    = DEBUG, FileApp, ScreenApp
262
263           log4perl.appender.FileApp          = Log::Log4perl::Appender::File
264           log4perl.appender.FileApp.filename = test.log
265           log4perl.appender.FileApp.layout   = PatternLayout
266           log4perl.appender.FileApp.layout.ConversionPattern = %d> %m%n
267
268           log4perl.appender.ScreenApp          = Log::Log4perl::Appender::Screen
269           log4perl.appender.ScreenApp.stderr   = 0
270           log4perl.appender.ScreenApp.layout   = PatternLayout
271           log4perl.appender.ScreenApp.layout.ConversionPattern = %d> %m%n
272
273       The configuration file above is assuming that both appenders are active
274       in the same logger hierarchy, in this case the "root" category.  But
275       even if you've got file loggers defined in several parts of your
276       system, belonging to different logger categories, each logging to
277       different files, you can gobble up all logged messages by defining a
278       root logger with a screen appender, which would duplicate messages from
279       all your file loggers to the screen due to Log4perl's appender
280       inheritance. Check
281
282           http://www.perl.com/pub/a/2002/09/11/log4perl.html
283
284       for details. Have fun!
285
286   How can I make sure my application logs a message when it dies
287       unexpectedly?
288       Whenever you encounter a fatal error in your application, instead of
289       saying something like
290
291           open FILE, "<blah" or die "Can't open blah -- bailing out!";
292
293       just use Log::Log4perl's fatal functions instead:
294
295           my $log = get_logger("Some::Package");
296           open FILE, "<blah" or $log->logdie("Can't open blah -- bailing out!");
297
298       This will both log the message with priority FATAL according to your
299       current Log::Log4perl configuration and then call Perl's "die()"
300       afterwards to terminate the program. It works the same with stealth
301       loggers (see "Stealth Loggers" in Log::Log4perl), all you need to do is
302       call
303
304           use Log::Log4perl qw(:easy);
305           open FILE, "<blah" or LOGDIE "Can't open blah -- bailing out!";
306
307       What can you do if you're using some library which doesn't use
308       Log::Log4perl and calls "die()" internally if something goes wrong? Use
309       a $SIG{__DIE__} pseudo signal handler
310
311           use Log::Log4perl qw(get_logger);
312
313           $SIG{__DIE__} = sub {
314               if($^S) {
315                   # We're in an eval {} and don't want log
316                   # this message but catch it later
317                   return;
318               }
319               local $Log::Log4perl::caller_depth =
320                     $Log::Log4perl::caller_depth + 1;
321               my $logger = get_logger("");
322               $logger->fatal(@_);
323               die @_; # Now terminate really
324           };
325
326       This will catch every "die()"-Exception of your application or the
327       modules it uses. In case you want to It will fetch a root logger and
328       pass on the "die()"-Message to it.  If you make sure you've configured
329       with a root logger like this:
330
331           Log::Log4perl->init(\q{
332               log4perl.category         = FATAL, Logfile
333               log4perl.appender.Logfile = Log::Log4perl::Appender::File
334               log4perl.appender.Logfile.filename = fatal_errors.log
335               log4perl.appender.Logfile.layout = \
336                          Log::Log4perl::Layout::PatternLayout
337               log4perl.appender.Logfile.layout.ConversionPattern = %F{1}-%L (%M)> %m%n
338           });
339
340       then all "die()" messages will be routed to a file properly. The line
341
342            local $Log::Log4perl::caller_depth =
343                  $Log::Log4perl::caller_depth + 1;
344
345       in the pseudo signal handler above merits a more detailed explanation.
346       With the setup above, if a module calls "die()" in one of its
347       functions, the fatal message will be logged in the signal handler and
348       not in the original function -- which will cause the %F, %L and %M
349       placeholders in the pattern layout to be replaced by the filename, the
350       line number and the function/method name of the signal handler, not the
351       error-throwing module. To adjust this, Log::Log4perl has the
352       $caller_depth variable, which defaults to 0, but can be set to positive
353       integer values to offset the caller level. Increasing it by one will
354       cause it to log the calling function's parameters, not the ones of the
355       signal handler.  See "Using Log::Log4perl from wrapper classes" in
356       Log::Log4perl for more details.
357
358   How can I hook up the LWP library with Log::Log4perl?
359       Or, to put it more generally: How can you utilize a third-party
360       library's embedded logging and debug statements in Log::Log4perl?  How
361       can you make them print to configurable appenders, turn them on and
362       off, just as if they were regular Log::Log4perl logging statements?
363
364       The easiest solution is to map the third-party library logging
365       statements to Log::Log4perl's stealth loggers via a typeglob
366       assignment.
367
368       As an example, let's take LWP, one of the most popular Perl modules,
369       which makes handling WWW requests and responses a breeze.  Internally,
370       LWP uses its own logging and debugging system, utilizing the following
371       calls inside the LWP code (from the LWP::Debug man page):
372
373               # Function tracing
374           LWP::Debug::trace('send()');
375
376               # High-granular state in functions
377           LWP::Debug::debug('url ok');
378
379               # Data going over the wire
380           LWP::Debug::conns("read $n bytes: $data");
381
382       First, let's assign Log::Log4perl priorities to these functions: I'd
383       suggest that "debug()" messages have priority "INFO", "trace()" uses
384       "DEBUG" and "conns()" also logs with "DEBUG" -- although your mileage
385       may certainly vary.
386
387       Now, in order to transparently hook up LWP::Debug with Log::Log4perl,
388       all we have to do is say
389
390           package LWP::Debug;
391           use Log::Log4perl qw(:easy);
392
393           *trace = *INFO;
394           *conns = *DEBUG;
395           *debug = *DEBUG;
396
397           package main;
398           # ... go on with your regular program ...
399
400       at the beginning of our program. In this way, every time the, say,
401       "LWP::UserAgent" module calls "LWP::Debug::trace()", it will implicitly
402       call INFO(), which is the "info()" method of a stealth logger defined
403       for the Log::Log4perl category "LWP::Debug". Is this cool or what?
404
405       Here's a complete program:
406
407           use LWP::UserAgent;
408           use HTTP::Request::Common;
409           use Log::Log4perl qw(:easy);
410
411           Log::Log4perl->easy_init(
412               { category => "LWP::Debug",
413                 level    => $DEBUG,
414                 layout   => "%r %p %M-%L %m%n",
415               });
416
417           package LWP::Debug;
418           use Log::Log4perl qw(:easy);
419           *trace = *INFO;
420           *conns = *DEBUG;
421           *debug = *DEBUG;
422
423           package main;
424           my $ua = LWP::UserAgent->new();
425           my $resp = $ua->request(GET "http://amazon.com");
426
427           if($resp->is_success()) {
428               print "Success: Received ",
429                     length($resp->content()), "\n";
430           } else {
431               print "Error: ", $resp->code(), "\n";
432           }
433
434       This will generate the following output on STDERR:
435
436           174 INFO LWP::UserAgent::new-164 ()
437           208 INFO LWP::UserAgent::request-436 ()
438           211 INFO LWP::UserAgent::send_request-294 GET http://amazon.com
439           212 DEBUG LWP::UserAgent::_need_proxy-1123 Not proxied
440           405 INFO LWP::Protocol::http::request-122 ()
441           859 DEBUG LWP::Protocol::collect-206 read 233 bytes
442           863 DEBUG LWP::UserAgent::request-443 Simple response: Found
443           869 INFO LWP::UserAgent::request-436 ()
444           871 INFO LWP::UserAgent::send_request-294
445            GET http://www.amazon.com:80/exec/obidos/gateway_redirect
446           872 DEBUG LWP::UserAgent::_need_proxy-1123 Not proxied
447           873 INFO LWP::Protocol::http::request-122 ()
448           1016 DEBUG LWP::UserAgent::request-443 Simple response: Found
449           1020 INFO LWP::UserAgent::request-436 ()
450           1022 INFO LWP::UserAgent::send_request-294
451            GET http://www.amazon.com/exec/obidos/subst/home/home.html/
452           1023 DEBUG LWP::UserAgent::_need_proxy-1123 Not proxied
453           1024 INFO LWP::Protocol::http::request-122 ()
454           1382 DEBUG LWP::Protocol::collect-206 read 632 bytes
455           ...
456           2605 DEBUG LWP::Protocol::collect-206 read 77 bytes
457           2607 DEBUG LWP::UserAgent::request-443 Simple response: OK
458           Success: Received 42584
459
460       Of course, in this way, the embedded logging and debug statements
461       within LWP can be utilized in any Log::Log4perl way you can think of.
462       You can have them sent to different appenders, block them based on the
463       category and everything else Log::Log4perl has to offer.
464
465       Only drawback of this method: Steering logging behavior via category is
466       always based on the "LWP::Debug" package. Although the logging
467       statements reflect the package name of the issuing module properly, the
468       stealth loggers in "LWP::Debug" are all of the category "LWP::Debug".
469       This implies that you can't control the logging behavior based on the
470       package that's initiating a log request (e.g. LWP::UserAgent) but only
471       based on the package that's actually executing the logging statement,
472       "LWP::Debug" in this case.
473
474       To work around this conundrum, we need to write a wrapper function and
475       plant it into the "LWP::Debug" package. It will determine the caller
476       and create a logger bound to a category with the same name as the
477       caller's package:
478
479           package LWP::Debug;
480
481           use Log::Log4perl qw(:levels get_logger);
482
483           sub l4p_wrapper {
484               my($prio, @message) = @_;
485               $Log::Log4perl::caller_depth += 2;
486               get_logger(scalar caller(1))->log($prio, @message);
487               $Log::Log4perl::caller_depth -= 2;
488           }
489
490           no warnings 'redefine';
491           *trace = sub { l4p_wrapper($INFO, @_); };
492           *debug = *conns = sub { l4p_wrapper($DEBUG, @_); };
493
494           package main;
495           # ... go on with your main program ...
496
497       This is less performant than the previous approach, because every log
498       request will request a reference to a logger first, then call the
499       wrapper, which will in turn call the appropriate log function.
500
501       This hierarchy shift has to be compensated for by increasing
502       $Log::Log4perl::caller_depth by 2 before calling the log function and
503       decreasing it by 2 right afterwards. Also, the "l4p_wrapper" function
504       shown above calls caller(1) which determines the name of the package
505       two levels down the calling hierarchy (and therefore compensates for
506       both the wrapper function and the anonymous subroutine calling it).
507
508       "no warnings 'redefine'" suppresses a warning Perl would generate
509       otherwise upon redefining "LWP::Debug"'s "trace()", "debug()" and
510       "conns()" functions. In case you use a perl prior to 5.6.x, you need to
511       manipulate $^W instead.
512
513       To make things easy for you when dealing with LWP, Log::Log4perl 0.47
514       introduces "Log::Log4perl->infiltrate_lwp()" which does exactly the
515       above.
516
517   What if I need dynamic values in a static Log4perl configuration file?
518       Say, your application uses Log::Log4perl for logging and therefore
519       comes with a Log4perl configuration file, specifying the logging
520       behavior.  But, you also want it to take command line parameters to set
521       values like the name of the log file.  How can you have both a static
522       Log4perl configuration file and a dynamic command line interface?
523
524       As of Log::Log4perl 0.28, every value in the configuration file can be
525       specified as a Perl hook. So, instead of saying
526
527           log4perl.appender.Logfile.filename = test.log
528
529       you could just as well have a Perl subroutine deliver the value
530       dynamically:
531
532           log4perl.appender.Logfile.filename = sub { logfile(); };
533
534       given that "logfile()" is a valid function in your "main" package
535       returning a string containing the path to the log file.
536
537       Or, think about using the value of an environment variable:
538
539           log4perl.appender.DBI.user = sub { $ENV{USERNAME} };
540
541       When "Log::Log4perl->init()" parses the configuration file, it will
542       notice the assignment above because of its "sub {...}" pattern and
543       treat it in a special way: It will evaluate the subroutine (which can
544       contain arbitrary Perl code) and take its return value as the right
545       side of the assignment.
546
547       A typical application would be called like this on the command line:
548
549           app                # log file is "test.log"
550           app -l mylog.txt   # log file is "mylog.txt"
551
552       Here's some sample code implementing the command line interface above:
553
554           use Log::Log4perl qw(get_logger);
555           use Getopt::Std;
556
557           getopt('l:', \our %OPTS);
558
559           my $conf = q(
560           log4perl.category.Bar.Twix         = WARN, Logfile
561           log4perl.appender.Logfile          = Log::Log4perl::Appender::File
562           log4perl.appender.Logfile.filename = sub { logfile(); };
563           log4perl.appender.Logfile.layout   = SimpleLayout
564           );
565
566           Log::Log4perl::init(\$conf);
567
568           my $logger = get_logger("Bar::Twix");
569           $logger->error("Blah");
570
571           ###########################################
572           sub logfile {
573           ###########################################
574               if(exists $OPTS{l}) {
575                   return $OPTS{l};
576               } else {
577                   return "test.log";
578               }
579           }
580
581       Every Perl hook may contain arbitrary perl code, just make sure to
582       fully qualify eventual variable names (e.g. %main::OPTS instead of
583       %OPTS).
584
585       SECURITY NOTE: this feature means arbitrary perl code can be embedded
586       in the config file.  In the rare case where the people who have access
587       to your config file are different from the people who write your code
588       and shouldn't have execute rights, you might want to call
589
590           $Log::Log4perl::Config->allow_code(0);
591
592       before you call init(). This will prevent Log::Log4perl from executing
593       any Perl code in the config file (including code for custom conversion
594       specifiers (see "Custom cspecs" in
595       Log::Log4perl::Layout::PatternLayout).
596
597   How can I roll over my logfiles automatically at midnight?
598       Long-running applications tend to produce ever-increasing logfiles.
599       For backup and cleanup purposes, however, it is often desirable to move
600       the current logfile to a different location from time to time and start
601       writing a new one.
602
603       This is a non-trivial task, because it has to happen in sync with the
604       logging system in order not to lose any messages in the process.
605
606       Luckily, Mark Pfeiffer's "Log::Dispatch::FileRotate" appender works
607       well with Log::Log4perl to rotate your logfiles in a variety of ways.
608
609       Note, however, that having the application deal with rotating a log
610       file is not cheap. Among other things, it requires locking the log file
611       with every write to avoid race conditions.  There are good reasons to
612       use external rotators like "newsyslog" instead.  See the entry "How can
613       I rotate a logfile with newsyslog?" in the FAQ for more information on
614       how to configure it.
615
616       When using "Log::Dispatch::FileRotate", all you have to do is specify
617       it in your Log::Log4perl configuration file and your logfiles will be
618       rotated automatically.
619
620       You can choose between rolling based on a maximum size ("roll if
621       greater than 10 MB") or based on a date pattern ("roll everyday at
622       midnight").  In both cases, "Log::Dispatch::FileRotate" allows you to
623       define a number "max" of saved files to keep around until it starts
624       overwriting the oldest ones. If you set the "max" parameter to 2 and
625       the name of your logfile is "test.log", "Log::Dispatch::FileRotate"
626       will move "test.log" to "test.log.1" on the first rollover. On the
627       second rollover, it will move "test.log.1" to "test.log.2" and then
628       "test.log" to "test.log.1". On the third rollover, it will move
629       "test.log.1" to "test.log.2" (therefore discarding the old
630       "test.log.2") and "test.log" to "test.log.1". And so forth. This way,
631       there's always going to be a maximum of 2 saved log files around.
632
633       Here's an example of a Log::Log4perl configuration file, defining a
634       daily rollover at midnight (date pattern "yyyy-MM-dd"), keeping a
635       maximum of 5 saved logfiles around:
636
637           log4perl.category         = WARN, Logfile
638           log4perl.appender.Logfile = Log::Dispatch::FileRotate
639           log4perl.appender.Logfile.filename    = test.log
640           log4perl.appender.Logfile.max         = 5
641           log4perl.appender.Logfile.DatePattern = yyyy-MM-dd
642           log4perl.appender.Logfile.TZ          = PST
643           log4perl.appender.Logfile.layout = \
644               Log::Log4perl::Layout::PatternLayout
645           log4perl.appender.Logfile.layout.ConversionPattern = %d %m %n
646
647       Please see the "Log::Dispatch::FileRotate" documentation for details.
648       "Log::Dispatch::FileRotate" is available on CPAN.
649
650   What's the easiest way to turn off all logging, even with a lengthy
651       Log4perl configuration file?
652       In addition to category-based levels and appender thresholds,
653       Log::Log4perl supports system-wide logging thresholds. This is the
654       minimum level the system will require of any logging events in order
655       for them to make it through to any configured appenders.
656
657       For example, putting the line
658
659           log4perl.threshold = ERROR
660
661       anywhere in your configuration file will limit any output to any
662       appender to events with priority of ERROR or higher (ERROR or FATAL
663       that is).
664
665       However, in order to suppress all logging entirely, you need to use a
666       priority that's higher than FATAL: It is simply called "OFF", and it is
667       never used by any logger. By definition, it is higher than the highest
668       defined logger level.
669
670       Therefore, if you keep the line
671
672           log4perl.threshold = OFF
673
674       somewhere in your Log::Log4perl configuration, the system will be quiet
675       as a graveyard. If you deactivate the line (e.g. by commenting it out),
676       the system will, upon config reload, snap back to normal operation,
677       providing logging messages according to the rest of the configuration
678       file again.
679
680   How can I log DEBUG and above to the screen and INFO and above to a file?
681       You need one logger with two appenders attached to it:
682
683           log4perl.logger = DEBUG, Screen, File
684
685           log4perl.appender.Screen   = Log::Log4perl::Appender::Screen
686           log4perl.appender.Screen.layout = SimpleLayout
687
688           log4perl.appender.File   = Log::Log4perl::Appender::File
689           log4perl.appender.File.filename = test.log
690           log4perl.appender.File.layout = SimpleLayout
691           log4perl.appender.Screen.Threshold = INFO
692
693       Since the file logger isn't supposed to get any messages with a
694       priority less than INFO, the appender's "Threshold" setting blocks
695       those out, although the logger forwards them.
696
697       It's a common mistake to think you can define two loggers for this, but
698       it won't work unless those two loggers have different categories. If
699       you wanted to log all DEBUG and above messages from the Foo::Bar module
700       to a file and all INFO and above messages from the Quack::Schmack
701       module to the screen, then you could have defined two loggers with
702       different levels "log4perl.logger.Foo.Bar" (level INFO) and
703       "log4perl.logger.Quack.Schmack" (level DEBUG) and assigned the file
704       appender to the former and the screen appender to the latter. But what
705       we wanted to accomplish was to route all messages, regardless of which
706       module (or category) they came from, to both appenders. The only way to
707       accomplish this is to define the root logger with the lower level
708       (DEBUG), assign both appenders to it, and block unwanted messages at
709       the file appender ("Threshold" set to INFO).
710
711   I keep getting duplicate log messages! What's wrong?
712       Having several settings for related categories in the Log4perl
713       configuration file sometimes leads to a phenomenon called "message
714       duplication". It can be very confusing at first, but if thought through
715       properly, it turns out that Log4perl behaves as advertised. But, don't
716       despair, of course there's a number of ways to avoid message
717       duplication in your logs.
718
719       Here's a sample Log4perl configuration file that produces the
720       phenomenon:
721
722           log4perl.logger.Cat        = ERROR, Screen
723           log4perl.logger.Cat.Subcat = WARN, Screen
724
725           log4perl.appender.Screen   = Log::Log4perl::Appender::Screen
726           log4perl.appender.Screen.layout = SimpleLayout
727
728       It defines two loggers, one for category "Cat" and one for
729       "Cat::Subcat", which is obviously a subcategory of "Cat".  The parent
730       logger has a priority setting of ERROR, the child is set to the lower
731       "WARN" level.
732
733       Now imagine the following code in your program:
734
735           my $logger = get_logger("Cat.Subcat");
736           $logger->warn("Warning!");
737
738       What do you think will happen? An unexperienced Log4perl user might
739       think: "Well, the message is being sent with level WARN, so the
740       "Cat::Subcat" logger will accept it and forward it to the attached
741       "Screen" appender. Then, the message will percolate up the logger
742       hierarchy, find the "Cat" logger, which will suppress the message
743       because of its ERROR setting."  But, perhaps surprisingly, what you'll
744       get with the code snippet above is not one but two log messages written
745       to the screen:
746
747           WARN - Warning!
748           WARN - Warning!
749
750       What happened? The culprit is that once the logger "Cat::Subcat"
751       decides to fire, it will forward the message unconditionally to all
752       directly or indirectly attached appenders. The "Cat" logger will never
753       be asked if it wants the message or not -- the message will just be
754       pushed through to the appender attached to "Cat".
755
756       One way to prevent the message from bubbling up the logger hierarchy is
757       to set the "additivity" flag of the subordinate logger to 0:
758
759           log4perl.logger.Cat            = ERROR, Screen
760           log4perl.logger.Cat.Subcat     = WARN, Screen
761           log4perl.additivity.Cat.Subcat = 0
762
763           log4perl.appender.Screen   = Log::Log4perl::Appender::Screen
764           log4perl.appender.Screen.layout = SimpleLayout
765
766       The message will now be accepted by the "Cat::Subcat" logger, forwarded
767       to its appender, but then "Cat::Subcat" will suppress any further
768       action. While this setting avoids duplicate messages as seen before, it
769       is often not the desired behavior. Messages percolating up the
770       hierarchy are a useful Log4perl feature.
771
772       If you're defining different appenders for the two loggers, one other
773       option is to define an appender threshold for the higher-level
774       appender. Typically it is set to be equal to the logger's level
775       setting:
776
777           log4perl.logger.Cat           = ERROR, Screen1
778           log4perl.logger.Cat.Subcat    = WARN, Screen2
779
780           log4perl.appender.Screen1   = Log::Log4perl::Appender::Screen
781           log4perl.appender.Screen1.layout = SimpleLayout
782           log4perl.appender.Screen1.Threshold = ERROR
783
784           log4perl.appender.Screen2   = Log::Log4perl::Appender::Screen
785           log4perl.appender.Screen2.layout = SimpleLayout
786
787       Since the "Screen1" appender now blocks every message with a priority
788       less than ERROR, even if the logger in charge lets it through, the
789       message percolating up the hierarchy is being blocked at the last
790       minute and not appended to "Screen1".
791
792       So far, we've been operating well within the boundaries of the Log4j
793       standard, which Log4perl adheres to. However, if you would really,
794       really like to use a single appender and keep the message percolation
795       intact without having to deal with message duplication, there's a non-
796       standard solution for you:
797
798           log4perl.logger.Cat        = ERROR, Screen
799           log4perl.logger.Cat.Subcat = WARN, Screen
800
801           log4perl.appender.Screen   = Log::Log4perl::Appender::Screen
802           log4perl.appender.Screen.layout = SimpleLayout
803
804           log4perl.oneMessagePerAppender = 1
805
806       The "oneMessagePerAppender" flag will suppress duplicate messages to
807       the same appender. Again, that's non-standard. But way cool :).
808
809   How can I configure Log::Log4perl to send me email if something happens?
810       Some incidents require immediate action. You can't wait until someone
811       checks the log files, you need to get notified on your pager right
812       away.
813
814       The easiest way to do that is by using the
815       "Log::Dispatch::Email::MailSend" module as an appender. It comes with
816       the "Log::Dispatch" bundle and allows you to specify recipient and
817       subject of outgoing emails in the Log4perl configuration file:
818
819           log4perl.category = FATAL, Mailer
820           log4perl.appender.Mailer         = Log::Dispatch::Email::MailSend
821           log4perl.appender.Mailer.to      = drone@pageme.net
822           log4perl.appender.Mailer.subject = Something's broken!
823           log4perl.appender.Mailer.layout  = SimpleLayout
824
825       The message of every log incident this appender gets will then be
826       forwarded to the given email address. Check the
827       "Log::Dispatch::Email::MailSend" documentation for details. And please
828       make sure there's not a flood of email messages sent out by your
829       application, filling up the recipient's inbox.
830
831       There's one caveat you need to know about: The "Log::Dispatch::Email"
832       hierarchy of appenders turns on buffering by default. This means that
833       the appender will not send out messages right away but wait until a
834       certain threshold has been reached. If you'd rather have your alerts
835       sent out immediately, use
836
837           log4perl.appender.Mailer.buffered = 0
838
839       to turn buffering off.
840
841   How can I write my own appender?
842       First off, Log::Log4perl comes with a set of standard appenders. Then,
843       there's a lot of Log4perl-compatible appenders already available on
844       CPAN: Just run a search for "Log::Dispatch" on http://search.cpan.org
845       and chances are that what you're looking for has already been
846       developed, debugged and been used successfully in production -- no need
847       for you to reinvent the wheel.
848
849       Also, Log::Log4perl ships with a nifty database appender named
850       Log::Log4perl::Appender::DBI -- check it out if talking to databases is
851       your desire.
852
853       But if you're up for a truly exotic task, you might have to write an
854       appender yourself. That's very easy -- it takes no longer than a couple
855       of minutes.
856
857       Say, we wanted to create an appender of the class
858       "ColorScreenAppender", which logs messages to the screen in a
859       configurable color. Just create a new class in
860       "ColorScreenAppender.pm":
861
862           package ColorScreenAppender;
863
864       Now let's assume that your Log::Log4perl configuration file "test.conf"
865       looks like this:
866
867           log4perl.logger = INFO, ColorApp
868
869           log4perl.appender.ColorApp=ColorScreenAppender
870           log4perl.appender.ColorApp.color=blue
871
872           log4perl.appender.ColorApp.layout = PatternLayout
873           log4perl.appender.ColorApp.layout.ConversionPattern=%d %m %n
874
875       This will cause Log::Log4perl on "init()" to look for a class
876       ColorScreenAppender and call its constructor new(). Let's add new() to
877       ColorScreenAppender.pm:
878
879           sub new {
880               my($class, %options) = @_;
881
882               my $self = { %options };
883               bless $self, $class;
884
885               return $self;
886           }
887
888       To initialize this appender, Log::Log4perl will call and pass all
889       attributes of the appender as defined in the configuration file to the
890       constructor as name/value pairs (in this case just one):
891
892           ColorScreenAppender->new(color => "blue");
893
894       The new() method listed above stores the contents of the %options hash
895       in the object's instance data hash (referred to by $self).  That's all
896       for initializing a new appender with Log::Log4perl.
897
898       Second, ColorScreenAppender needs to expose a "log()" method, which
899       will be called by Log::Log4perl every time it thinks the appender
900       should fire. Along with the object reference (as usual in Perl's object
901       world), log() will receive a list of name/value pairs, of which only
902       the one under the key "message" shall be of interest for now since it
903       is the message string to be logged. At this point, Log::Log4perl has
904       already taken care of joining the message to be a single string.
905
906       For our special appender ColorScreenAppender, we're using the
907       Term::ANSIColor module to colorize the output:
908
909           use Term::ANSIColor;
910
911           sub log {
912               my($self, %params) = @_;
913
914               print colored($params{message},
915                             $self->{color});
916           }
917
918       The color (as configured in the Log::Log4perl configuration file) is
919       available as $self->{color} in the appender object. Don't forget to
920       return
921
922           1;
923
924       at the end of ColorScreenAppender.pm and you're done. Install the new
925       appender somewhere where perl can find it and try it with a test script
926       like
927
928           use Log::Log4perl qw(:easy);
929           Log::Log4perl->init("test.conf");
930           ERROR("blah");
931
932       to see the new colored output. Is this cool or what?
933
934       And it gets even better: You can write dynamically generated appender
935       classes using the "Class::Prototyped" module. Here's an example of an
936       appender prepending every outgoing message with a configurable number
937       of bullets:
938
939           use Class::Prototyped;
940
941           my $class = Class::Prototyped->newPackage(
942             "MyAppenders::Bulletizer",
943             bullets => 1,
944             log     => sub {
945               my($self, %params) = @_;
946               print "*" x $self->bullets(),
947                     $params{message};
948             },
949           );
950
951           use Log::Log4perl qw(:easy);
952
953           Log::Log4perl->init(\ q{
954             log4perl.logger = INFO, Bully
955
956             log4perl.appender.Bully=MyAppenders::Bulletizer
957             log4perl.appender.Bully.bullets=3
958
959             log4perl.appender.Bully.layout = PatternLayout
960             log4perl.appender.Bully.layout.ConversionPattern=%m %n
961           });
962
963               # ... prints: "***Boo!\n";
964           INFO "Boo!";
965
966   How can I drill down on references before logging them?
967       If you've got a reference to a nested structure or object, then you
968       probably don't want to log it as "HASH(0x81141d4)" but rather dump it
969       as something like
970
971           $VAR1 = {
972                     'a' => 'b',
973                     'd' => 'e'
974                   };
975
976       via a module like Data::Dumper. While it's syntactically correct to say
977
978           $logger->debug(Data::Dumper::Dumper($ref));
979
980       this call imposes a huge performance penalty on your application if the
981       message is suppressed by Log::Log4perl, because Data::Dumper will
982       perform its expensive operations in any case, because it doesn't know
983       that its output will be thrown away immediately.
984
985       As of Log::Log4perl 0.28, there's a better way: Use the message output
986       filter format as in
987
988           $logger->debug( {filter => \&Data::Dumper::Dumper,
989                            value  => $ref} );
990
991       and Log::Log4perl won't call the filter function unless the message
992       really gets written out to an appender. Just make sure to pass the
993       whole slew as a reference to a hash specifying a filter function (as a
994       sub reference) under the key "filter" and the value to be passed to the
995       filter function in "value").  When it comes to logging, Log::Log4perl
996       will call the filter function, pass the "value" as an argument and log
997       the return value.  Saves you serious cycles.
998
999   How can I collect all FATAL messages in an extra log file?
1000       Suppose you have employed Log4perl all over your system and you've
1001       already activated logging in various subsystems. On top of that,
1002       without disrupting any other settings, how can you collect all FATAL
1003       messages all over the system and send them to a separate log file?
1004
1005       If you define a root logger like this:
1006
1007           log4perl.logger                  = FATAL, File
1008           log4perl.appender.File           = Log::Log4perl::Appender::File
1009           log4perl.appender.File.filename  = /tmp/fatal.txt
1010           log4perl.appender.File.layout    = PatternLayout
1011           log4perl.appender.File.layout.ConversionPattern= %d %m %n
1012               # !!! Something's missing ...
1013
1014       you'll be surprised to not only receive all FATAL messages issued
1015       anywhere in the system, but also everything else -- gazillions of
1016       ERROR, WARN, INFO and even DEBUG messages will end up in your fatal.txt
1017       logfile!  Reason for this is Log4perl's (or better: Log4j's) appender
1018       additivity.  Once a lower-level logger decides to fire, the message is
1019       going to be forwarded to all appenders upstream -- without further
1020       priority checks with their attached loggers.
1021
1022       There's a way to prevent this, however: If your appender defines a
1023       minimum threshold, only messages of this priority or higher are going
1024       to be logged. So, just add
1025
1026           log4perl.appender.File.Threshold = FATAL
1027
1028       to the configuration above, and you'll get what you wanted in the first
1029       place: An overall system FATAL message collector.
1030
1031   How can I bundle several log messages into one?
1032       Would you like to tally the messages arriving at your appender and dump
1033       out a summary once they're exceeding a certain threshold?  So that
1034       something like
1035
1036           $logger->error("Blah");
1037           $logger->error("Blah");
1038           $logger->error("Blah");
1039
1040       won't be logged as
1041
1042           Blah
1043           Blah
1044           Blah
1045
1046       but as
1047
1048           [3] Blah
1049
1050       instead? If you'd like to hold off on logging a message until it has
1051       been sent a couple of times, you can roll that out by creating a
1052       buffered appender.
1053
1054       Let's define a new appender like
1055
1056           package TallyAppender;
1057
1058           sub new {
1059               my($class, %options) = @_;
1060
1061               my $self = { maxcount => 5,
1062                            %options
1063                          };
1064
1065               bless $self, $class;
1066
1067               $self->{last_message}        = "";
1068               $self->{last_message_count}  = 0;
1069
1070               return $self;
1071           }
1072
1073       with two additional instance variables "last_message" and
1074       "last_message_count", storing the content of the last message sent and
1075       a counter of how many times this has happened. Also, it features a
1076       configuration parameter "maxcount" which defaults to 5 in the snippet
1077       above but can be set in the Log4perl configuration file like this:
1078
1079           log4perl.logger = INFO, A
1080           log4perl.appender.A=TallyAppender
1081           log4perl.appender.A.maxcount = 3
1082
1083       The main tallying logic lies in the appender's "log" method, which is
1084       called every time Log4perl thinks a message needs to get logged by our
1085       appender:
1086
1087           sub log {
1088               my($self, %params) = @_;
1089
1090                   # Message changed? Print buffer.
1091               if($self->{last_message} and
1092                  $params{message} ne $self->{last_message}) {
1093                   print "[$self->{last_message_count}]: " .
1094                         "$self->{last_message}";
1095                   $self->{last_message_count} = 1;
1096                   $self->{last_message} = $params{message};
1097                   return;
1098               }
1099
1100               $self->{last_message_count}++;
1101               $self->{last_message} = $params{message};
1102
1103                   # Threshold exceeded? Print, reset counter
1104               if($self->{last_message_count} >=
1105                  $self->{maxcount}) {
1106                   print "[$self->{last_message_count}]: " .
1107                         "$params{message}";
1108                   $self->{last_message_count} = 0;
1109                   $self->{last_message}       = "";
1110                   return;
1111               }
1112           }
1113
1114       We basically just check if the oncoming message in $param{message} is
1115       equal to what we've saved before in the "last_message" instance
1116       variable. If so, we're increasing "last_message_count".  We print the
1117       message in two cases: If the new message is different than the buffered
1118       one, because then we need to dump the old stuff and store the new. Or,
1119       if the counter exceeds the threshold, as defined by the "maxcount"
1120       configuration parameter.
1121
1122       Please note that the appender always gets the fully rendered message
1123       and just compares it as a whole -- so if there's a date/timestamp in
1124       there, that might confuse your logic. You can work around this by
1125       specifying %m %n as a layout and add the date later on in the appender.
1126       Or, make the comparison smart enough to omit the date.
1127
1128       At last, don't forget what happens if the program is being shut down.
1129       If there's still messages in the buffer, they should be printed out at
1130       that point. That's easy to do in the appender's DESTROY method, which
1131       gets called at object destruction time:
1132
1133           sub DESTROY {
1134               my($self) = @_;
1135
1136               if($self->{last_message_count}) {
1137                   print "[$self->{last_message_count}]: " .
1138                         "$self->{last_message}";
1139                   return;
1140               }
1141           }
1142
1143       This will ensure that none of the buffered messages are lost.  Happy
1144       buffering!
1145
1146   I want to log ERROR and WARN messages to different files! How can I do
1147       that?
1148       Let's assume you wanted to have each logging statement written to a
1149       different file, based on the statement's priority. Messages with
1150       priority "WARN" are supposed to go to "/tmp/app.warn", events
1151       prioritized as "ERROR" should end up in "/tmp/app.error".
1152
1153       Now, if you define two appenders "AppWarn" and "AppError" and assign
1154       them both to the root logger, messages bubbling up from any loggers
1155       below will be logged by both appenders because of Log4perl's message
1156       propagation feature. If you limit their exposure via the appender
1157       threshold mechanism and set "AppWarn"'s threshold to "WARN" and
1158       "AppError"'s to "ERROR", you'll still get "ERROR" messages in
1159       "AppWarn", because "AppWarn"'s "WARN" setting will just filter out
1160       messages with a lower priority than "WARN" -- "ERROR" is higher and
1161       will be allowed to pass through.
1162
1163       What we need for this is a Log4perl Custom Filter, available with
1164       Log::Log4perl 0.30.
1165
1166       Both appenders need to verify that the priority of the oncoming
1167       messages exactly matches the priority the appender is supposed to log
1168       messages of. To accomplish this task, let's define two custom filters,
1169       "MatchError" and "MatchWarn", which, when attached to their appenders,
1170       will limit messages passed on to them to those matching a given
1171       priority:
1172
1173           log4perl.logger = WARN, AppWarn, AppError
1174
1175               # Filter to match level ERROR
1176           log4perl.filter.MatchError = Log::Log4perl::Filter::LevelMatch
1177           log4perl.filter.MatchError.LevelToMatch  = ERROR
1178           log4perl.filter.MatchError.AcceptOnMatch = true
1179
1180               # Filter to match level WARN
1181           log4perl.filter.MatchWarn  = Log::Log4perl::Filter::LevelMatch
1182           log4perl.filter.MatchWarn.LevelToMatch  = WARN
1183           log4perl.filter.MatchWarn.AcceptOnMatch = true
1184
1185               # Error appender
1186           log4perl.appender.AppError = Log::Log4perl::Appender::File
1187           log4perl.appender.AppError.filename = /tmp/app.err
1188           log4perl.appender.AppError.layout   = SimpleLayout
1189           log4perl.appender.AppError.Filter   = MatchError
1190
1191               # Warning appender
1192           log4perl.appender.AppWarn = Log::Log4perl::Appender::File
1193           log4perl.appender.AppWarn.filename = /tmp/app.warn
1194           log4perl.appender.AppWarn.layout   = SimpleLayout
1195           log4perl.appender.AppWarn.Filter   = MatchWarn
1196
1197       The appenders "AppWarn" and "AppError" defined above are logging to
1198       "/tmp/app.warn" and "/tmp/app.err" respectively and have the custom
1199       filters "MatchWarn" and "MatchError" attached.  This setup will direct
1200       all WARN messages, issued anywhere in the system, to /tmp/app.warn (and
1201       ERROR messages to /tmp/app.error) -- without any overlaps.
1202
1203   On our server farm, Log::Log4perl configuration files differ slightly from
1204       host to host. Can I roll them all into one?
1205       You sure can, because Log::Log4perl allows you to specify attribute
1206       values dynamically. Let's say that one of your appenders expects the
1207       host's IP address as one of its attributes. Now, you could certainly
1208       roll out different configuration files for every host and specify the
1209       value like
1210
1211           log4perl.appender.MyAppender    = Log::Log4perl::Appender::SomeAppender
1212           log4perl.appender.MyAppender.ip = 10.0.0.127
1213
1214       but that's a maintenance nightmare. Instead, you can have Log::Log4perl
1215       figure out the IP address at configuration time and set the appender's
1216       value correctly:
1217
1218               # Set the IP address dynamically
1219           log4perl.appender.MyAppender    = Log::Log4perl::Appender::SomeAppender
1220           log4perl.appender.MyAppender.ip = sub { \
1221              use Sys::Hostname; \
1222              use Socket; \
1223              return inet_ntoa(scalar gethostbyname hostname); \
1224           }
1225
1226       If Log::Log4perl detects that an attribute value starts with something
1227       like "sub {...", it will interpret it as a perl subroutine which is to
1228       be executed once at configuration time (not runtime!) and its return
1229       value is to be used as the attribute value. This comes in handy for
1230       rolling out applications where Log::Log4perl configuration files show
1231       small host-specific differences, because you can deploy the unmodified
1232       application distribution on all instances of the server farm.
1233
1234   Log4perl doesn't interpret my backslashes correctly!
1235       If you're using Log4perl's feature to specify the configuration as a
1236       string in your program (as opposed to a separate configuration file),
1237       chances are that you've written it like this:
1238
1239           # *** WRONG! ***
1240
1241           Log::Log4perl->init( \ <<END_HERE);
1242               log4perl.logger = WARN, A1
1243               log4perl.appender.A1 = Log::Log4perl::Appender::Screen
1244               log4perl.appender.A1.layout = \
1245                   Log::Log4perl::Layout::PatternLayout
1246               log4perl.appender.A1.layout.ConversionPattern = %m%n
1247           END_HERE
1248
1249           # *** WRONG! ***
1250
1251       and you're getting the following error message:
1252
1253           Layout not specified for appender A1 at .../Config.pm line 342.
1254
1255       What's wrong? The problem is that you're using a here-document with
1256       substitution enabled ("<<END_HERE") and that Perl won't interpret
1257       backslashes at line-ends as continuation characters but will
1258       essentially throw them out. So, in the code above, the layout line will
1259       look like
1260
1261           log4perl.appender.A1.layout =
1262
1263       to Log::Log4perl which causes it to report an error. To interpret the
1264       backslash at the end of the line correctly as a line-continuation
1265       character, use the non-interpreting mode of the here-document like in
1266
1267           # *** RIGHT! ***
1268
1269           Log::Log4perl->init( \ <<'END_HERE');
1270               log4perl.logger = WARN, A1
1271               log4perl.appender.A1 = Log::Log4perl::Appender::Screen
1272               log4perl.appender.A1.layout = \
1273                   Log::Log4perl::Layout::PatternLayout
1274               log4perl.appender.A1.layout.ConversionPattern = %m%n
1275           END_HERE
1276
1277           # *** RIGHT! ***
1278
1279       (note the single quotes around 'END_HERE') or use "q{...}" instead of a
1280       here-document and Perl will treat the backslashes at line-end as
1281       intended.
1282
1283   I want to suppress certain messages based on their content!
1284       Let's assume you've plastered all your functions with Log4perl
1285       statements like
1286
1287           sub some_func {
1288
1289               INFO("Begin of function");
1290
1291               # ... Stuff happens here ...
1292
1293               INFO("End of function");
1294           }
1295
1296       to issue two log messages, one at the beginning and one at the end of
1297       each function. Now you want to suppress the message at the beginning
1298       and only keep the one at the end, what can you do? You can't use the
1299       category mechanism, because both messages are issued from the same
1300       package.
1301
1302       Log::Log4perl's custom filters (0.30 or better) provide an interface
1303       for the Log4perl user to step in right before a message gets logged and
1304       decide if it should be written out or suppressed, based on the message
1305       content or other parameters:
1306
1307           use Log::Log4perl qw(:easy);
1308
1309           Log::Log4perl::init( \ <<'EOT' );
1310               log4perl.logger             = INFO, A1
1311               log4perl.appender.A1        = Log::Log4perl::Appender::Screen
1312               log4perl.appender.A1.layout = \
1313                   Log::Log4perl::Layout::PatternLayout
1314               log4perl.appender.A1.layout.ConversionPattern = %m%n
1315
1316               log4perl.filter.M1 = Log::Log4perl::Filter::StringMatch
1317               log4perl.filter.M1.StringToMatch = Begin
1318               log4perl.filter.M1.AcceptOnMatch = false
1319
1320               log4perl.appender.A1.Filter = M1
1321       EOT
1322
1323       The last four statements in the configuration above are defining a
1324       custom filter "M1" of type "Log::Log4perl::Filter::StringMatch", which
1325       comes with Log4perl right out of the box and allows you to define a
1326       text pattern to match (as a perl regular expression) and a flag
1327       "AcceptOnMatch" indicating if a match is supposed to suppress the
1328       message or let it pass through.
1329
1330       The last line then assigns this filter to the "A1" appender, which will
1331       call it every time it receives a message to be logged and throw all
1332       messages out not matching the regular expression "Begin".
1333
1334       Instead of using the standard "Log::Log4perl::Filter::StringMatch"
1335       filter, you can define your own, simply using a perl subroutine:
1336
1337           log4perl.filter.ExcludeBegin  = sub { !/Begin/ }
1338           log4perl.appender.A1.Filter   = ExcludeBegin
1339
1340       For details on custom filters, check Log::Log4perl::Filter.
1341
1342   My new module uses Log4perl -- but what happens if the calling program
1343       didn't configure it?
1344       If a Perl module uses Log::Log4perl, it will typically rely on the
1345       calling program to initialize it. If it is using Log::Log4perl in
1346       ":easy" mode, like in
1347
1348           package MyMod;
1349           use Log::Log4perl qw(:easy);
1350
1351           sub foo {
1352               DEBUG("In foo");
1353           }
1354
1355           1;
1356
1357       and the calling program doesn't initialize Log::Log4perl at all (e.g.
1358       because it has no clue that it's available), Log::Log4perl will
1359       silently ignore all logging messages. However, if the module is using
1360       Log::Log4perl in regular mode like in
1361
1362           package MyMod;
1363           use Log::Log4perl qw(get_logger);
1364
1365           sub foo {
1366               my $logger = get_logger("");
1367               $logger->debug("blah");
1368           }
1369
1370           1;
1371
1372       and the main program is just using the module like in
1373
1374           use MyMode;
1375           MyMode::foo();
1376
1377       then Log::Log4perl will also ignore all logging messages but issue a
1378       warning like
1379
1380           Log4perl: Seems like no initialization happened.
1381           Forgot to call init()?
1382
1383       (only once!) to remind novice users to not forget to initialize the
1384       logging system before using it.  However, if you want to suppress this
1385       message, just add the ":nowarn" target to the module's "use
1386       Log::Log4perl" call:
1387
1388           use Log::Log4perl qw(get_logger :nowarn);
1389
1390       This will have Log::Log4perl silently ignore all logging statements if
1391       no initialization has taken place. If, instead of using init(), you're
1392       using Log4perl's API to define loggers and appenders, the same
1393       notification happens if no call to add_appenders() is made, i.e. no
1394       appenders are defined.
1395
1396       If the module wants to figure out if some other program part has
1397       already initialized Log::Log4perl, it can do so by calling
1398
1399           Log::Log4perl::initialized()
1400
1401       which will return a true value in case Log::Log4perl has been
1402       initialized and a false value if not.
1403
1404   How can I synchronize access to an appender?
1405       If you're using the same instance of an appender in multiple processes,
1406       and each process is passing on messages to the appender in parallel,
1407       you might end up with overlapping log entries.
1408
1409       Typical scenarios include a file appender that you create in the main
1410       program, and which will then be shared between the parent and a forked
1411       child process. Or two separate processes, each initializing a Log4perl
1412       file appender on the same logfile.
1413
1414       Log::Log4perl won't synchronize access to the shared logfile by
1415       default. Depending on your operating system's flush mechanism, buffer
1416       size and the size of your messages, there's a small chance of an
1417       overlap.
1418
1419       The easiest way to prevent overlapping messages in logfiles written to
1420       by multiple processes is setting the file appender's "syswrite" flag
1421       along with a file write mode of "append".  This makes sure that
1422       "Log::Log4perl::Appender::File" uses "syswrite()" (which is guaranteed
1423       to run uninterrupted) instead of "print()" which might buffer the
1424       message or get interrupted by the OS while it is writing. And in
1425       "append" mode, the OS kernel ensures that multiple processes share one
1426       end-of-file marker, ensuring that each process writes to the real end
1427       of the file. (The value of "append" for the "mode" parameter is the
1428       default setting in Log4perl's file appender so you don't have to set it
1429       explicitly.)
1430
1431             # Guarantees atomic writes
1432
1433           log4perl.category.Bar.Twix          = WARN, Logfile
1434
1435           log4perl.appender.Logfile           = Log::Log4perl::Appender::File
1436           log4perl.appender.Logfile.mode      = append
1437           log4perl.appender.Logfile.syswrite  = 1
1438           log4perl.appender.Logfile.filename  = test.log
1439           log4perl.appender.Logfile.layout    = SimpleLayout
1440
1441       Another guaranteed way of having messages separated with any kind of
1442       appender is putting a Log::Log4perl::Appender::Synchronized composite
1443       appender in between Log::Log4perl and the real appender. It will make
1444       sure to let messages pass through this virtual gate one by one only.
1445
1446       Here's a sample configuration to synchronize access to a file appender:
1447
1448           log4perl.category.Bar.Twix          = WARN, Syncer
1449
1450           log4perl.appender.Logfile           = Log::Log4perl::Appender::File
1451           log4perl.appender.Logfile.autoflush = 1
1452           log4perl.appender.Logfile.filename  = test.log
1453           log4perl.appender.Logfile.layout    = SimpleLayout
1454
1455           log4perl.appender.Syncer            = Log::Log4perl::Appender::Synchronized
1456           log4perl.appender.Syncer.appender   = Logfile
1457
1458       "Log::Log4perl::Appender::Synchronized" uses the "IPC::Shareable"
1459       module and its semaphores, which will slow down writing the log
1460       messages, but ensures sequential access featuring atomic checks.  Check
1461       Log::Log4perl::Appender::Synchronized for details.
1462
1463   Can I use Log::Log4perl with log4j's Chainsaw?
1464       Yes, Log::Log4perl can be configured to send its events to log4j's
1465       graphical log UI Chainsaw.
1466
1467       Here's how it works:
1468
1469       •   Get Guido Carls' <gcarls@cpan.org> Log::Log4perl extension
1470           "Log::Log4perl::Layout::XMLLayout" from CPAN and install it:
1471
1472               perl -MCPAN -eshell
1473               cpan> install Log::Log4perl::Layout::XMLLayout
1474
1475       •   Install and start Chainsaw, which is part of the "log4j"
1476           distribution now (see http://jakarta.apache.org/log4j ). Create a
1477           configuration file like
1478
1479             <log4j:configuration debug="true">
1480               <plugin name="XMLSocketReceiver"
1481                       class="org.apache.log4j.net.XMLSocketReceiver">
1482                 <param name="decoder" value="org.apache.log4j.xml.XMLDecoder"/>
1483                 <param name="Port" value="4445"/>
1484               </plugin>
1485               <root> <level value="debug"/> </root>
1486             </log4j:configuration>
1487
1488           and name it e.g. "config.xml". Then start Chainsaw like
1489
1490             java -Dlog4j.debug=true -Dlog4j.configuration=config.xml \
1491               -classpath ".:log4j-1.3alpha.jar:log4j-chainsaw-1.3alpha.jar" \
1492               org.apache.log4j.chainsaw.LogUI
1493
1494           and watch the GUI coming up.
1495
1496       •   Configure Log::Log4perl to use a socket appender with an XMLLayout,
1497           pointing to the host/port where Chainsaw (as configured above) is
1498           waiting with its XMLSocketReceiver:
1499
1500             use Log::Log4perl qw(get_logger);
1501             use Log::Log4perl::Layout::XMLLayout;
1502
1503             my $conf = q(
1504               log4perl.category.Bar.Twix          = WARN, Appender
1505               log4perl.appender.Appender          = Log::Log4perl::Appender::Socket
1506               log4perl.appender.Appender.PeerAddr = localhost
1507               log4perl.appender.Appender.PeerPort = 4445
1508               log4perl.appender.Appender.layout   = Log::Log4perl::Layout::XMLLayout
1509             );
1510
1511             Log::Log4perl::init(\$conf);
1512
1513               # Nasty hack to suppress encoding header
1514             my $app = Log::Log4perl::appenders->{"Appender"};
1515             $app->layout()->{enc_set} = 1;
1516
1517             my $logger = get_logger("Bar.Twix");
1518             $logger->error("One");
1519
1520           The nasty hack shown in the code snippet above is currently
1521           (October 2003) necessary, because Chainsaw expects XML messages to
1522           arrive in a format like
1523
1524             <log4j:event logger="Bar.Twix"
1525                          timestamp="1066794904310"
1526                          level="ERROR"
1527                          thread="10567">
1528               <log4j:message><![CDATA[Two]]></log4j:message>
1529               <log4j:NDC><![CDATA[undef]]></log4j:NDC>
1530               <log4j:locationInfo class="main"
1531                 method="main"
1532                 file="./t"
1533                 line="32">
1534               </log4j:locationInfo>
1535             </log4j:event>
1536
1537           without a preceding
1538
1539             <?xml version = "1.0" encoding = "iso8859-1"?>
1540
1541           which Log::Log4perl::Layout::XMLLayout applies to the first event
1542           sent over the socket.
1543
1544       See figure 1 for a screenshot of Chainsaw in action, receiving events
1545       from the Perl script shown above.
1546
1547       Many thanks to Chainsaw's Scott Deboy <sdeboy@comotivsystems.com> for
1548       his support!
1549
1550   How can I run Log::Log4perl under mod_perl?
1551       In persistent environments it's important to play by the rules outlined
1552       in section "Initialize once and only once" in Log::Log4perl.  If you
1553       haven't read this yet, please go ahead and read it right now. It's very
1554       important.
1555
1556       And no matter if you use a startup handler to init() Log::Log4perl or
1557       use the init_once() strategy (added in 0.42), either way you're very
1558       likely to have unsynchronized writes to logfiles.
1559
1560       If Log::Log4perl is configured with a log file appender, and it is
1561       initialized via the Apache startup handler, the file handle created
1562       initially will be shared among all Apache processes. Similarly, with
1563       the init_once() approach: although every process has a separate L4p
1564       configuration, processes are gonna share the appender file names
1565       instead, effectively opening several different file handles on the same
1566       file.
1567
1568       Now, having several appenders using the same file handle or having
1569       several appenders logging to the same file unsynchronized, this might
1570       result in overlapping messages. Sometimes, this is acceptable. If it's
1571       not, here's two strategies:
1572
1573       •   Use the Log::Log4perl::Appender::Synchronized appender to connect
1574           to your file appenders. Here's the writeup:
1575           http://log4perl.sourceforge.net/releases/Log-Log4perl/docs/html/Log/Log4perl/FAQ.html#23804
1576
1577       •   Use a different logfile for every process like in
1578
1579                #log4perl.conf
1580                ...
1581                log4perl.appender.A1.filename = sub { "mylog.$$.log" }
1582
1583   My program already uses warn() and die(). How can I switch to Log4perl?
1584       If your program already uses Perl's "warn()" function to spew out error
1585       messages and you'd like to channel those into the Log4perl world, just
1586       define a "__WARN__" handler where your program or module resides:
1587
1588           use Log::Log4perl qw(:easy);
1589
1590           $SIG{__WARN__} = sub {
1591               local $Log::Log4perl::caller_depth =
1592                   $Log::Log4perl::caller_depth + 1;
1593               WARN @_;
1594           };
1595
1596       Why the "local" setting of $Log::Log4perl::caller_depth?  If you leave
1597       that out, "PatternLayout" conversion specifiers like %M or %F (printing
1598       the current function/method and source filename) will refer to where
1599       the __WARN__ handler resides, not the environment Perl's "warn()"
1600       function was issued from. Increasing "caller_depth" adjusts for this
1601       offset. Having it "local", makes sure the level gets set back after the
1602       handler exits.
1603
1604       Once done, if your program does something like
1605
1606           sub some_func {
1607               warn "Here's a warning";
1608           }
1609
1610       you'll get (depending on your Log::Log4perl configuration) something
1611       like
1612
1613           2004/02/19 20:41:02-main::some_func: Here's a warning at ./t line 25.
1614
1615       in the appropriate appender instead of having a screen full of STDERR
1616       messages. It also works with the "Carp" module and its "carp()" and
1617       "cluck()" functions.
1618
1619       If, on the other hand, catching "die()" and friends is required, a
1620       "__DIE__" handler is appropriate:
1621
1622           $SIG{__DIE__} = sub {
1623               if($^S) {
1624                   # We're in an eval {} and don't want log
1625                   # this message but catch it later
1626                   return;
1627               }
1628               local $Log::Log4perl::caller_depth =
1629                   $Log::Log4perl::caller_depth + 1;
1630               LOGDIE @_;
1631           };
1632
1633       This will call Log4perl's "LOGDIE()" function, which will log a fatal
1634       error and then call die() internally, causing the program to exit.
1635       Works equally well with "Carp"'s "croak()" and "confess()" functions.
1636
1637   Some module prints messages to STDERR. How can I funnel them to
1638       Log::Log4perl?
1639       If a module you're using doesn't use Log::Log4perl but prints logging
1640       messages to STDERR instead, like
1641
1642           ########################################
1643           package IgnorantModule;
1644           ########################################
1645
1646           sub some_method {
1647               print STDERR "Parbleu! An error!\n";
1648           }
1649
1650           1;
1651
1652       there's still a way to capture these messages and funnel them into
1653       Log::Log4perl, even without touching the module. What you need is a
1654       trapper module like
1655
1656           ########################################
1657           package Trapper;
1658           ########################################
1659
1660           use Log::Log4perl qw(:easy);
1661
1662           sub TIEHANDLE {
1663               my $class = shift;
1664               bless [], $class;
1665           }
1666
1667           sub PRINT {
1668               my $self = shift;
1669               $Log::Log4perl::caller_depth++;
1670               DEBUG @_;
1671               $Log::Log4perl::caller_depth--;
1672           }
1673
1674           1;
1675
1676       and a "tie" command in the main program to tie STDERR to the trapper
1677       module along with regular Log::Log4perl initialization:
1678
1679           ########################################
1680           package main;
1681           ########################################
1682
1683           use Log::Log4perl qw(:easy);
1684
1685           Log::Log4perl->easy_init(
1686               {level  => $DEBUG,
1687                file   => 'stdout',   # make sure not to use stderr here!
1688                layout => "%d %M: %m%n",
1689               });
1690
1691           tie *STDERR, "Trapper";
1692
1693       Make sure not to use STDERR as Log::Log4perl's file appender here
1694       (which would be the default in ":easy" mode), because it would end up
1695       in an endless recursion.
1696
1697       Now, calling
1698
1699           IgnorantModule::some_method();
1700
1701       will result in the desired output
1702
1703           2004/05/06 11:13:04 IgnorantModule::some_method: Parbleu! An error!
1704
1705   How come PAR (Perl Archive Toolkit) creates executables which then can't
1706       find their Log::Log4perl appenders?
1707       If not instructed otherwise, "Log::Log4perl" dynamically pulls in
1708       appender classes found in its configuration. If you specify
1709
1710           #!/usr/bin/perl
1711           # mytest.pl
1712
1713           use Log::Log4perl qw(get_logger);
1714
1715           my $conf = q(
1716             log4perl.category.Bar.Twix = WARN, Logfile
1717             log4perl.appender.Logfile  = Log::Log4perl::Appender::Screen
1718             log4perl.appender.Logfile.layout = SimpleLayout
1719           );
1720
1721           Log::Log4perl::init(\$conf);
1722           my $logger = get_logger("Bar::Twix");
1723           $logger->error("Blah");
1724
1725       then "Log::Log4perl::Appender::Screen" will be pulled in while the
1726       program runs, not at compile time. If you have PAR compile the script
1727       above to an executable binary via
1728
1729           pp -o mytest mytest.pl
1730
1731       and then run "mytest" on a machine without having Log::Log4perl
1732       installed, you'll get an error message like
1733
1734           ERROR: can't load appenderclass 'Log::Log4perl::Appender::Screen'
1735           Can't locate Log/Log4perl/Appender/Screen.pm in @INC ...
1736
1737       Why? At compile time, "pp" didn't realize that
1738       "Log::Log4perl::Appender::Screen" would be needed later on and didn't
1739       wrap it into the executable created. To avoid this, either say "use
1740       Log::Log4perl::Appender::Screen" in the script explicitly or compile it
1741       with
1742
1743           pp -o mytest -M Log::Log4perl::Appender::Screen mytest.pl
1744
1745       to make sure the appender class gets included.
1746
1747   How can I access a custom appender defined in the configuration?
1748       Any appender defined in the configuration file or somewhere in the code
1749       can be accessed later via
1750       "Log::Log4perl->appender_by_name("appender_name")", which returns a
1751       reference of the appender object.
1752
1753       Once you've got a hold of the object, it can be queried or modified to
1754       your liking. For example, see the custom "IndentAppender" defined
1755       below: After calling "init()" to define the Log4perl settings, the
1756       appender object is retrieved to call its "indent_more()" and
1757       "indent_less()" methods to control indentation of messages:
1758
1759           package IndentAppender;
1760
1761           sub new {
1762               bless { indent => 0 }, $_[0];
1763           }
1764
1765           sub indent_more  { $_[0]->{indent}++ }
1766           sub indent_less  { $_[0]->{indent}-- }
1767
1768           sub log {
1769               my($self, %params) = @_;
1770               print " " x $self->{indent}, $params{message};
1771           }
1772
1773           package main;
1774
1775           use Log::Log4perl qw(:easy);
1776
1777           my $conf = q(
1778           log4perl.category          = DEBUG, Indented
1779           log4perl.appender.Indented = IndentAppender
1780           log4perl.appender.Indented.layout = Log::Log4perl::Layout::SimpleLayout
1781           );
1782
1783           Log::Log4perl::init(\$conf);
1784
1785           my $appender = Log::Log4perl->appender_by_name("Indented");
1786
1787           DEBUG "No identation";
1788           $appender->indent_more();
1789           DEBUG "One more";
1790           $appender->indent_more();
1791           DEBUG "Two more";
1792           $appender->indent_less();
1793           DEBUG "One less";
1794
1795       As you would expect, this will print
1796
1797           DEBUG - No identation
1798            DEBUG - One more
1799             DEBUG - Two more
1800            DEBUG - One less
1801
1802       because the very appender used by Log4perl is modified dynamically at
1803       runtime.
1804
1805   I don't know if Log::Log4perl is installed. How can I prepare my script?
1806       In case your script needs to be prepared for environments that may or
1807       may not have Log::Log4perl installed, there's a trick.
1808
1809       If you put the following BEGIN blocks at the top of the program, you'll
1810       be able to use the DEBUG(), INFO(), etc. macros in Log::Log4perl's
1811       ":easy" mode.  If Log::Log4perl is installed in the target environment,
1812       the regular Log::Log4perl rules apply. If not, all of DEBUG(), INFO(),
1813       etc. are "stubbed" out, i.e. they turn into no-ops:
1814
1815           use warnings;
1816           use strict;
1817
1818           BEGIN {
1819               eval { require Log::Log4perl; };
1820
1821               if($@) {
1822                   print "Log::Log4perl not installed - stubbing.\n";
1823                   no strict qw(refs);
1824                   *{"main::$_"} = sub { } for qw(DEBUG INFO WARN ERROR FATAL);
1825               } else {
1826                   no warnings;
1827                   print "Log::Log4perl installed - life is good.\n";
1828                   require Log::Log4perl::Level;
1829                   Log::Log4perl::Level->import(__PACKAGE__);
1830                   Log::Log4perl->import(qw(:easy));
1831                   Log::Log4perl->easy_init($main::DEBUG);
1832               }
1833           }
1834
1835               # The regular script begins ...
1836           DEBUG "Hey now!";
1837
1838       This snippet will first probe for Log::Log4perl, and if it can't be
1839       found, it will alias DEBUG(), INFO(), with empty subroutines via
1840       typeglobs.  If Log::Log4perl is available, its level constants are
1841       first imported ($DEBUG, $INFO, etc.) and then "easy_init()" gets called
1842       to initialize the logging system.
1843
1844   Can file appenders create files with different permissions?
1845       Typically, when "Log::Log4perl::Appender::File" creates a new file, its
1846       permissions are set to "rw-r--r--". Why? Because your environment's
1847       umask most likely defaults to 0022, that's the standard setting.
1848
1849       What's a umask, you're asking? It's a template that's applied to the
1850       permissions of all newly created files. While calls like "open(FILE,
1851       ">foo")" will always try to create files in "rw-rw-rw- " mode, the
1852       system will apply the current umask template to determine the final
1853       permission setting. umask is a bit mask that's inverted and then
1854       applied to the requested permission setting, using a bitwise AND:
1855
1856           $request_permission &~ $umask
1857
1858       So, a umask setting of 0000 (the leading 0 simply indicates an octal
1859       value) will create files in "rw-rw-rw-" mode, a setting of 0277 will
1860       use "r--------", and the standard 0022 will use "rw-r--r--".
1861
1862       As an example, if you want your log files to be created with
1863       "rw-r--rw-" permissions, use a umask of 0020 before calling
1864       Log::Log4perl->init():
1865
1866           use Log::Log4perl;
1867
1868           umask 0020;
1869               # Creates log.out in rw-r--rw mode
1870           Log::Log4perl->init(\ q{
1871               log4perl.logger = WARN, File
1872               log4perl.appender.File = Log::Log4perl::Appender::File
1873               log4perl.appender.File.filename = log.out
1874               log4perl.appender.File.layout = SimpleLayout
1875           });
1876
1877   Using Log4perl in an END block causes a problem!
1878       It's not easy to get to this error, but if you write something like
1879
1880           END { Log::Log4perl::get_logger()->debug("Hey there."); }
1881
1882           use Log::Log4perl qw(:easy);
1883           Log::Log4perl->easy_init($DEBUG);
1884
1885       it won't work. The reason is that "Log::Log4perl" defines an END block
1886       that cleans up all loggers. And perl will run END blocks in the reverse
1887       order as they're encountered in the compile phase, so in the scenario
1888       above, the END block will run after Log4perl has cleaned up its
1889       loggers.
1890
1891       Placing END blocks using Log4perl after a "use Log::Log4perl" statement
1892       fixes the problem:
1893
1894           use Log::Log4perl qw(:easy);
1895           Log::Log4perl->easy_init($DEBUG);
1896
1897           END { Log::Log4perl::get_logger()->debug("Hey there."); }
1898
1899       In this scenario, the shown END block is executed before Log4perl
1900       cleans up and the debug message will be processed properly.
1901
1902   Help! My appender is throwing a "Wide character in print" warning!
1903       This warning shows up when Unicode strings are printed without
1904       precautions. The warning goes away if the complaining appender is set
1905       to utf-8 mode:
1906
1907             # Either in the log4perl configuration file:
1908         log4perl.appender.Logfile.filename = test.log
1909         log4perl.appender.Logfile.utf8     = 1
1910
1911             # Or, in easy mode:
1912         Log::Log4perl->easy_init( {
1913           level => $DEBUG,
1914           file  => ":utf8> test.log"
1915         } );
1916
1917       If the complaining appender is a screen appender, set its "utf8"
1918       option:
1919
1920             log4perl.appender.Screen.stderr = 1
1921             log4perl.appender.Screen.utf8   = 1
1922
1923       Alternatively, "binmode" does the trick:
1924
1925             # Either STDOUT ...
1926           binmode(STDOUT, ":utf8);
1927
1928             # ... or STDERR.
1929           binmode(STDERR, ":utf8);
1930
1931       Some background on this: Perl's strings are either byte strings or
1932       Unicode strings. "Mike" is a byte string.  "\x{30DE}\x{30A4}\x{30AF}"
1933       is a Unicode string. Unicode strings are marked specially and are UTF-8
1934       encoded internally.
1935
1936       If you print a byte string to STDOUT, all is well, because STDOUT is by
1937       default set to byte mode. However, if you print a Unicode string to
1938       STDOUT without precautions, "perl" will try to transform the Unicode
1939       string back to a byte string before printing it out. This is
1940       troublesome if the Unicode string contains 'wide' characters which
1941       can't be represented in Latin-1.
1942
1943       For example, if you create a Unicode string with three japanese
1944       Katakana characters as in
1945
1946           perl -le 'print "\x{30DE}\x{30A4}\x{30AF}"'
1947
1948       (coincidentally pronounced Ma-i-ku, the japanese pronunciation of
1949       "Mike"), STDOUT is in byte mode and the warning
1950
1951           Wide character in print at ./script.pl line 14.
1952
1953       appears. Setting STDOUT to UTF-8 mode as in
1954
1955           perl -le 'binmode(STDOUT, ":utf8"); print "\x{30DE}\x{30A4}\x{30AF}"'
1956
1957       will silently print the Unicode string to STDOUT in UTF-8. To see the
1958       characters printed, you'll need a UTF-8 terminal with a font including
1959       japanese Katakana characters.
1960
1961   How can I send errors to the screen, and debug messages to a file?
1962       Let's assume you want to maintain a detailed DEBUG output in a file and
1963       only messages of level ERROR and higher should be printed on the
1964       screen. Often times, developers come up with something like this:
1965
1966            # Wrong!!!
1967           log4perl.logger = DEBUG, FileApp
1968           log4perl.logger = ERROR, ScreenApp
1969            # Wrong!!!
1970
1971       This won't work, however. Logger definitions aren't additive, and the
1972       second statement will overwrite the first one. Log4perl versions below
1973       1.04 were silently accepting this, leaving people confused why it
1974       wouldn't work as expected.  As of 1.04, this will throw a fatal error
1975       to notify the user of the problem.
1976
1977       What you want to do instead, is this:
1978
1979           log4perl.logger                    = DEBUG, FileApp, ScreenApp
1980
1981           log4perl.appender.FileApp          = Log::Log4perl::Appender::File
1982           log4perl.appender.FileApp.filename = test.log
1983           log4perl.appender.FileApp.layout   = SimpleLayout
1984
1985           log4perl.appender.ScreenApp          = Log::Log4perl::Appender::Screen
1986           log4perl.appender.ScreenApp.stderr   = 0
1987           log4perl.appender.ScreenApp.layout   = SimpleLayout
1988              ### limiting output to ERROR messages
1989           log4perl.appender.ScreenApp.Threshold = ERROR
1990              ###
1991
1992       Note that without the second appender's "Threshold" setting, both
1993       appenders would receive all messages prioritized DEBUG and higher. With
1994       the threshold set to ERROR, the second appender will filter the
1995       messages as required.
1996
1997   Where should I put my logfiles?
1998       Your log files may go anywhere you want them, but the effective user id
1999       of the calling process must have write access.
2000
2001       If the log file doesn't exist at program start, Log4perl's file
2002       appender will create it. For this, it needs write access to the
2003       directory where the new file will be located in. If the log file
2004       already exists at startup, the process simply needs write access to the
2005       file. Note that it will need write access to the file's directory if
2006       you're encountering situations where the logfile gets recreated, e.g.
2007       during log rotation.
2008
2009       If Log::Log4perl is used by a web server application (e.g. in a CGI
2010       script or mod_perl), then the webserver's user (usually "nobody" or
2011       "www") must have the permissions mentioned above.
2012
2013       To prepare your web server to use log4perl, we'd recommend:
2014
2015           webserver:~$ su -
2016           webserver:~# mkdir /var/log/cgiapps
2017           webserver:~# chown nobody:root /var/log/cgiapps/
2018           webserver:~# chown nobody:root -R /var/log/cgiapps/
2019           webserver:~# chmod 02755 -R /var/log/cgiapps/
2020
2021       Then set your /etc/log4perl.conf file to include:
2022
2023           log4perl.appender.FileAppndr1.filename =
2024               /var/log/cgiapps/<app-name>.log
2025
2026   How can my file appender deal with disappearing log files?
2027       The file appender that comes with Log4perl,
2028       Log::Log4perl::Appender::File, will open a specified log file at
2029       initialization time and will keep writing to it via a file handle.
2030
2031       In case the associated file goes way, messages written by a long-
2032       running process will still be written to the file handle. In case the
2033       file has been moved to a different location on the same file system,
2034       the writer will keep writing to it under the new filename. In case the
2035       file has been removed from the file system, the log messages will end
2036       up in nowhere land. This is not a bug in Log4perl, this is how Unix
2037       works. There is no error message in this case, because the writer has
2038       no idea that the file handle is not associated with a visible file.
2039
2040       To prevent the loss of log messages when log files disappear, the file
2041       appender's "recreate" option needs to be set to a true value:
2042
2043           log4perl.appender.Logfile.recreate = 1
2044
2045       This will instruct the file appender to check in regular intervals
2046       (default: 30 seconds) if the log file is still there. If it finds out
2047       that the file is missing, it will recreate it.
2048
2049       Continuously checking if the log file still exists is fairly expensive.
2050       For this reason it is only performed every 30 seconds. To change this
2051       interval, the option "recreate_check_interval" can be set to the number
2052       of seconds between checks. In the extreme case where the check should
2053       be performed before every write, it can even be set to 0:
2054
2055           log4perl.appender.Logfile.recreate = 1
2056           log4perl.appender.Logfile.recreate_check_interval = 0
2057
2058       To avoid having to check the file system so frequently, a signal
2059       handler can be set up:
2060
2061           log4perl.appender.Logfile.recreate = 1
2062           log4perl.appender.Logfile.recreate_check_signal = USR1
2063
2064       This will install a signal handler which will recreate a missing log
2065       file immediately when it receives the defined signal.
2066
2067       Note that the init_and_watch() method for Log4perl's initialization can
2068       also be instructed to install a signal handler, usually using the HUP
2069       signal. Make sure to use a different signal if you're using both of
2070       them at the same time.
2071
2072   How can I rotate a logfile with newsyslog?
2073       Here's a few things that need to be taken care of when using the
2074       popular log file rotating utility "newsyslog"
2075       (http://www.courtesan.com/newsyslog) with Log4perl's file appender in
2076       long-running processes.
2077
2078       For example, with a newsyslog configuration like
2079
2080           # newsyslog.conf
2081           /tmp/test.log 666  12  5  *  B
2082
2083       and a call to
2084
2085           # newsyslog -f /path/to/newsyslog.conf
2086
2087       "newsyslog" will take action if "/tmp/test.log" is larger than the
2088       specified 5K in size. It will move the current log file "/tmp/test.log"
2089       to "/tmp/test.log.0" and create a new and empty "/tmp/test.log" with
2090       the specified permissions (this is why "newsyslog" needs to run as
2091       root).  An already existing "/tmp/test.log.0" would be moved to
2092       "/tmp/test.log.1", "/tmp/test.log.1" to "/tmp/test.log.2", and so
2093       forth, for every one of a max number of 12 archived logfiles that have
2094       been configured in "newsyslog.conf".
2095
2096       Although a new file has been created, from Log4perl's appender's point
2097       of view, this situation is identical to the one described in the
2098       previous FAQ entry, labeled "How can my file appender deal with
2099       disappearing log files".
2100
2101       To make sure that log messages are written to the new log file and not
2102       to an archived one or end up in nowhere land, the appender's "recreate"
2103       and "recreate_check_interval" have to be configured to deal with the
2104       'disappearing' log file.
2105
2106       The situation gets interesting when "newsyslog"'s option to compress
2107       archived log files is enabled. This causes the original log file not to
2108       be moved, but to disappear. If the file appender isn't configured to
2109       recreate the logfile in this situation, log messages will actually be
2110       lost without warning. This also applies for the short time frame of
2111       "recreate_check_interval" seconds in between the recreator's file
2112       checks.
2113
2114       To make sure that no messages get lost, one option is to set the
2115       interval to
2116
2117           log4perl.appender.Logfile.recreate_check_interval = 0
2118
2119       However, this is fairly expensive. A better approach is to define a
2120       signal handler:
2121
2122           log4perl.appender.Logfile.recreate = 1
2123           log4perl.appender.Logfile.recreate_check_signal  = USR1
2124           log4perl.appender.Logfile.recreate_pid_write = /tmp/myappid
2125
2126       As a service for "newsyslog" users, Log4perl's file appender writes the
2127       current process ID to a PID file specified by the "recreate_pid_write"
2128       option.  "newsyslog" then needs to be configured as in
2129
2130           # newsyslog.conf configuration for compressing archive files and
2131           # sending a signal to the Log4perl-enabled application
2132           /tmp/test.log 666  12  5  *  B /tmp/myappid 30
2133
2134       to send the defined signal (30, which is USR1 on FreeBSD) to the
2135       application process at rotation time. Note that the signal number is
2136       different on Linux, where USR1 denotes as 10. Check "man signal" for
2137       details.
2138
2139   How can a process under user id A log to a file under user id B?
2140       This scenario often occurs in configurations where processes run under
2141       various user IDs but need to write to a log file under a fixed, but
2142       different user id.
2143
2144       With a traditional file appender, the log file will probably be created
2145       under one user's id and appended to under a different user's id. With a
2146       typical umask of 0002, the file will be created with -rw-rw-r--
2147       permissions. If a user who's not in the first user's group subsequently
2148       appends to the log file, it will fail because of a permission problem.
2149
2150       Two potential solutions come to mind:
2151
2152       •   Creating the file with a umask of 0000 will allow all users to
2153           append to the log file. Log4perl's file appender
2154           "Log::Log4perl::Appender::File" has an "umask" option that can be
2155           set to support this:
2156
2157               log4perl.appender.File = Log::Log4perl::Appender::File
2158               log4perl.appender.File.umask = sub { 0000 };
2159
2160           This way, the log file will be created with -rw-rw-rw- permissions
2161           and therefore has world write permissions. This might open up the
2162           logfile for unwanted manipulations by arbitrary users, though.
2163
2164       •   Running the process under an effective user id of "root" will allow
2165           it to write to the log file, no matter who started the process.
2166           However, this is not a good idea, because of security concerns.
2167
2168       Luckily, under Unix, there's the syslog daemon which runs as root and
2169       takes log requests from user processes over a socket and writes them to
2170       log files as configured in "/etc/syslog.conf".
2171
2172       By modifying "/etc/syslog.conf" and HUPing the syslog daemon, you can
2173       configure new log files:
2174
2175           # /etc/syslog.conf
2176           ...
2177           user.* /some/path/file.log
2178
2179       Using the "Log::Dispatch::Syslog" appender, which comes with the
2180       "Log::Log4perl" distribution, you can then send messages via syslog:
2181
2182           use Log::Log4perl qw(:easy);
2183
2184           Log::Log4perl->init(\<<EOT);
2185               log4perl.logger = DEBUG, app
2186               log4perl.appender.app=Log::Dispatch::Syslog
2187               log4perl.appender.app.Facility=user
2188               log4perl.appender.app.layout=SimpleLayout
2189           EOT
2190
2191               # Writes to /some/path/file.log
2192           ERROR "Message!";
2193
2194       This way, the syslog daemon will solve the permission problem.
2195
2196       Note that while it is possible to use syslog() without Log4perl (syslog
2197       supports log levels, too), traditional syslog setups have a significant
2198       drawback.
2199
2200       Without Log4perl's ability to activate logging in only specific parts
2201       of a system, complex systems will trigger log events all over the place
2202       and slow down execution to a crawl at high debug levels.
2203
2204       Remote-controlling logging in the hierarchical parts of an application
2205       via Log4perl's categories is one of its most distinguished features.
2206       It allows for enabling high debug levels in specified areas without
2207       noticeable performance impact.
2208
2209   I want to use UTC instead of the local time!
2210       If a layout defines a date, Log::Log4perl uses local time to populate
2211       it.  If you want UTC instead, set
2212
2213           log4perl.utcDateTimes = 1
2214
2215       in your configuration. Alternatively, you can set
2216
2217           $Log::Log4perl::DateFormat::GMTIME = 1;
2218
2219       in your program before the first log statement.
2220
2221   Can Log4perl intercept messages written to a filehandle?
2222       You have a function that prints to a filehandle. You want to tie into
2223       that filehandle and forward all arriving messages to a Log4perl logger.
2224
2225       First, let's write a package that ties a file handle and forwards it to
2226       a Log4perl logger:
2227
2228           package FileHandleLogger;
2229           use Log::Log4perl qw(:levels get_logger);
2230
2231           sub TIEHANDLE {
2232              my($class, %options) = @_;
2233
2234              my $self = {
2235                  level    => $DEBUG,
2236                  category => '',
2237                  %options
2238              };
2239
2240              $self->{logger} = get_logger($self->{category}),
2241              bless $self, $class;
2242           }
2243
2244           sub PRINT {
2245               my($self, @rest) = @_;
2246               $Log::Log4perl::caller_depth++;
2247               $self->{logger}->log($self->{level}, @rest);
2248               $Log::Log4perl::caller_depth--;
2249           }
2250
2251           sub PRINTF {
2252               my($self, $fmt, @rest) = @_;
2253               $Log::Log4perl::caller_depth++;
2254               $self->PRINT(sprintf($fmt, @rest));
2255               $Log::Log4perl::caller_depth--;
2256           }
2257
2258           1;
2259
2260       Now, if you have a function like
2261
2262           sub function_printing_to_fh {
2263               my($fh) = @_;
2264               printf $fh "Hi there!\n";
2265           }
2266
2267       which takes a filehandle and prints something to it, it can be used
2268       with Log4perl:
2269
2270           use Log::Log4perl qw(:easy);
2271           usa FileHandleLogger;
2272
2273           Log::Log4perl->easy_init($DEBUG);
2274
2275           tie *SOMEHANDLE, 'FileHandleLogger' or
2276               die "tie failed ($!)";
2277
2278           function_printing_to_fh(*SOMEHANDLE);
2279               # prints "2007/03/22 21:43:30 Hi there!"
2280
2281       If you want, you can even specify a different log level or category:
2282
2283           tie *SOMEHANDLE, 'FileHandleLogger',
2284               level => $INFO, category => "Foo::Bar" or die "tie failed ($!)";
2285
2286   I want multiline messages rendered line-by-line!
2287       With the standard "PatternLayout", if you send a multiline message to
2288       an appender as in
2289
2290           use Log::Log4perl qw(:easy);
2291           Log
2292
2293       it gets rendered this way:
2294
2295           2007/04/04 23:23:39 multi
2296           line
2297           message
2298
2299       If you want each line to be rendered separately according to the layout
2300       use "Log::Log4perl::Layout::PatternLayout::Multiline":
2301
2302           use Log::Log4perl qw(:easy);
2303
2304           Log::Log4perl->init(\<<EOT);
2305             log4perl.category         = DEBUG, Screen
2306             log4perl.appender.Screen = Log::Log4perl::Appender::Screen
2307             log4perl.appender.Screen.layout = \\
2308               Log::Log4perl::Layout::PatternLayout::Multiline
2309             log4perl.appender.Screen.layout.ConversionPattern = %d %m %n
2310           EOT
2311
2312           DEBUG "some\nmultiline\nmessage";
2313
2314       and you'll get
2315
2316           2007/04/04 23:23:39 some
2317           2007/04/04 23:23:39 multiline
2318           2007/04/04 23:23:39 message
2319
2320       instead.
2321
2322   I'm on Windows and I'm getting all these 'redefined' messages!
2323       If you're on Windows and are getting warning messages like
2324
2325         Constant subroutine Log::Log4perl::_INTERNAL_DEBUG redefined at
2326           C:/Programme/Perl/lib/constant.pm line 103.
2327         Subroutine import redefined at
2328           C:/Programme/Perl/site/lib/Log/Log4Perl.pm line 69.
2329         Subroutine initialized redefined at
2330           C:/Programme/Perl/site/lib/Log/Log4Perl.pm line 207.
2331
2332       then chances are that you're using 'Log::Log4Perl' (wrong uppercase P)
2333       instead of the correct 'Log::Log4perl'. Perl on Windows doesn't handle
2334       this error well and spits out a slew of confusing warning messages. But
2335       now you know, just use the correct module name and you'll be fine.
2336
2337   Log4perl complains that no initialization happened during shutdown!
2338       If you're using Log4perl log commands in DESTROY methods of your
2339       objects, you might see confusing messages like
2340
2341           Log4perl: Seems like no initialization happened. Forgot to call init()?
2342           Use of uninitialized value in subroutine entry at
2343           /home/y/lib/perl5/site_perl/5.6.1/Log/Log4perl.pm line 134 during global
2344           destruction. (in cleanup) Undefined subroutine &main:: called at
2345           /home/y/lib/perl5/site_perl/5.6.1/Log/Log4perl.pm line 134 during global
2346           destruction.
2347
2348       when the program shuts down. What's going on?
2349
2350       This phenomenon happens if you have circular references in your
2351       objects, which perl can't clean up when an object goes out of scope but
2352       waits until global destruction instead. At this time, however, Log4perl
2353       has already shut down, so you can't use it anymore.
2354
2355       For example, here's a simple class which uses a logger in its DESTROY
2356       method:
2357
2358           package A;
2359           use Log::Log4perl qw(:easy);
2360           sub new { bless {}, shift }
2361           sub DESTROY { DEBUG "Waaah!"; }
2362
2363       Now, if the main program creates a self-referencing object, like in
2364
2365           package main;
2366           use Log::Log4perl qw(:easy);
2367           Log::Log4perl->easy_init($DEBUG);
2368
2369           my $a = A->new();
2370           $a->{selfref} = $a;
2371
2372       then you'll see the error message shown above during global
2373       destruction.  How to tackle this problem?
2374
2375       First, you should clean up your circular references before global
2376       destruction. They will not only cause objects to be destroyed in an
2377       order that's hard to predict, but also eat up memory until the program
2378       shuts down.
2379
2380       So, the program above could easily be fixed by putting
2381
2382           $a->{selfref} = undef;
2383
2384       at the end or in an END handler. If that's hard to do, use weak
2385       references:
2386
2387           package main;
2388           use Scalar::Util qw(weaken);
2389           use Log::Log4perl qw(:easy);
2390           Log::Log4perl->easy_init($DEBUG);
2391
2392           my $a = A->new();
2393           $a->{selfref} = weaken $a;
2394
2395       This allows perl to clean up the circular reference when the object
2396       goes out of scope, and doesn't wait until global destruction.
2397
2398   How can I access POE heap values from Log4perl's layout?
2399       POE is a framework for creating multitasked applications running in a
2400       single process and a single thread. POE's threads equivalents are
2401       'sessions' and since they run quasi-simultaneously, you can't use
2402       Log4perl's global NDC/MDC to hold session-specific data.
2403
2404       However, POE already maintains a data store for every session. It is
2405       called 'heap' and is just a hash storing session-specific data in key-
2406       value pairs.  To access this per-session heap data from a Log4perl
2407       layout, define a custom cspec and reference it with the newly defined
2408       pattern in the layout:
2409
2410           use strict;
2411           use POE;
2412           use Log::Log4perl qw(:easy);
2413
2414           Log::Log4perl->init( \ q{
2415               log4perl.logger = DEBUG, Screen
2416               log4perl.appender.Screen = Log::Log4perl::Appender::Screen
2417               log4perl.appender.Screen.layout = PatternLayout
2418               log4perl.appender.Screen.layout.ConversionPattern = %U %m%n
2419               log4perl.PatternLayout.cspec.U = \
2420                   sub { POE::Kernel->get_active_session->get_heap()->{ user } }
2421           } );
2422
2423           for (qw( Huey Lewey Dewey )) {
2424               POE::Session->create(
2425                   inline_states => {
2426                       _start    => sub {
2427                           $_[HEAP]->{user} = $_;
2428                           POE::Kernel->yield('hello');
2429                       },
2430                       hello     => sub {
2431                           DEBUG "I'm here now";
2432                       }
2433                   }
2434               );
2435           }
2436
2437           POE::Kernel->run();
2438           exit;
2439
2440       The code snippet above defines a new layout placeholder (called 'cspec'
2441       in Log4perl) %U which calls a subroutine, retrieves the active session,
2442       gets its heap and looks up the entry specified ('user').
2443
2444       Starting with Log::Log4perl 1.20, cspecs also support parameters in
2445       curly braces, so you can say
2446
2447           log4perl.appender.Screen.layout.ConversionPattern = %U{user} %U{id} %m%n
2448           log4perl.PatternLayout.cspec.U = \
2449                   sub { POE::Kernel->get_active_session-> \
2450                         get_heap()->{ $_[0]->{curlies} } }
2451
2452       and print the POE session heap entries 'user' and 'id' with every
2453       logged message. For more details on cpecs, read the PatternLayout
2454       manual.
2455
2456   I want to print something unconditionally!
2457       Sometimes it's a script that's supposed to log messages regardless if
2458       Log4perl has been initialized or not. Or there's a logging statement
2459       that's not going to be suppressed under any circumstances -- many
2460       people want to have the final word, make the executive decision,
2461       because it seems like the only logical choice.
2462
2463       But think about it: First off, if a messages is supposed to be printed,
2464       where is it supposed to end up at? STDOUT? STDERR? And are you sure you
2465       want to set in stone that this message needs to be printed, while
2466       someone else might find it annoying and wants to get rid of it?
2467
2468       The truth is, there's always going to be someone who wants to log a
2469       messages at all cost, but also another person who wants to suppress it
2470       with equal vigilance. There's no good way to serve these two
2471       conflicting desires, someone will always want to win at the cost of
2472       leaving the other party disappointed.
2473
2474       So, the best Log4perl offers is the ALWAYS level for a message that
2475       even fires if the system log level is set to $OFF:
2476
2477           use Log::Log4perl qw(:easy);
2478
2479           Log::Log4perl->easy_init( $OFF );
2480           ALWAYS "This gets logged always. Well, almost always";
2481
2482       The logger won't fire, though, if Log4perl hasn't been initialized or
2483       if someone defines a custom log hurdle that's higher than $OFF.
2484
2485       Bottom line: Leave the setting of the logging level to the initial Perl
2486       script -- let their owners decided what they want, no matter how
2487       tempting it may be to decide it for them.
2488
2489   Why doesn't my END handler remove my log file on Win32?
2490       If you have code like
2491
2492           use Log::Log4perl qw( :easy );
2493           Log::Log4perl->easy_init( { level => $DEBUG, file => "my.log" } );
2494           END { unlink "my.log" or die };
2495
2496       then you might be in for a surprise when you're running it on Windows,
2497       because the "unlink()" call in the END handler will complain that the
2498       file is still in use.
2499
2500       What happens in Perl if you have something like
2501
2502           END { print "first end in main\n"; }
2503           use Module;
2504           END { print "second end in main\n"; }
2505
2506       and
2507
2508           package Module;
2509           END { print "end in module\n"; }
2510           1;
2511
2512       is that you get
2513
2514           second end in main
2515           end in module
2516           first end in main
2517
2518       because perl stacks the END handlers in reverse order in which it
2519       encounters them in the compile phase.
2520
2521       Log4perl defines an END handler that cleans up left-over appenders
2522       (e.g.  file appenders which still hold files open), because those
2523       appenders have circular references and therefore aren't cleaned up
2524       otherwise.
2525
2526       Now if you define an END handler after "use Log::Log4perl", it'll
2527       trigger before Log4perl gets a chance to clean up, which isn't a
2528       problem on Unix where you can delete a file even if some process has a
2529       handle to it open, but it's a problem on Win32, where the OS won't let
2530       you do that.
2531
2532       The solution is easy, just place the END handler before Log4perl gets
2533       loaded, like in
2534
2535           END { unlink "my.log" or die };
2536           use Log::Log4perl qw( :easy );
2537           Log::Log4perl->easy_init( { level => $DEBUG, file => "my.log" } );
2538
2539       which will call the END handlers in the intended order.
2540

SEE ALSO

2542       Log::Log4perl
2543

LICENSE

2545       Copyright 2002-2013 by Mike Schilli <m@perlmeister.com> and Kevin Goess
2546       <cpan@goess.org>.
2547
2548       This library is free software; you can redistribute it and/or modify it
2549       under the same terms as Perl itself.
2550

AUTHOR

2552       Please contribute patches to the project on Github:
2553
2554           http://github.com/mschilli/log4perl
2555
2556       Send bug reports or requests for enhancements to the authors via our
2557
2558       MAILING LIST (questions, bug reports, suggestions/patches):
2559       log4perl-devel@lists.sourceforge.net
2560
2561       Authors (please contact them via the list above, not directly): Mike
2562       Schilli <m@perlmeister.com>, Kevin Goess <cpan@goess.org>
2563
2564       Contributors (in alphabetical order): Ateeq Altaf, Cory Bennett, Jens
2565       Berthold, Jeremy Bopp, Hutton Davidson, Chris R. Donnelly, Matisse
2566       Enzer, Hugh Esco, Anthony Foiani, James FitzGibbon, Carl Franks, Dennis
2567       Gregorovic, Andy Grundman, Paul Harrington, Alexander Hartmaier  David
2568       Hull, Robert Jacobson, Jason Kohles, Jeff Macdonald, Markus Peter,
2569       Brett Rann, Peter Rabbitson, Erik Selberg, Aaron Straup Cope, Lars
2570       Thegler, David Viner, Mac Yang.
2571
2572
2573
2574perl v5.34.0                      2021-07-22                            FAQ(3)
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