1Log::Log4perl(3) User Contributed Perl Documentation Log::Log4perl(3)
2
6 Log::Log4perl - Log4j implementation for Perl
7
9 # Easy mode if you like it simple ...
10 use Log::Log4perl qw(:easy);
12 Log::Log4perl->easy_init($ERROR);
13 DEBUG "This doesn't go anywhere";
15 ERROR "This gets logged";
16 # ... or standard mode for more features:
18 Log::Log4perl::init('/etc/log4perl.conf');
20 --or--
22 # Check config every 10 secs
24 Log::Log4perl::init_and_watch('/etc/log4perl.conf',10);
25 --then--
27 $logger = Log::Log4perl->get_logger('house.bedrm.desk.topdrwr');
29 $logger->debug('this is a debug message');
31 $logger->info('this is an info message');
32 $logger->warn('etc');
33 $logger->error('..');
34 $logger->fatal('..');
35 #####/etc/log4perl.conf###############################
37 log4perl.logger.house = WARN, FileAppndr1
38 log4perl.logger.house.bedroom.desk = DEBUG, FileAppndr1
39 log4perl.appender.FileAppndr1 = Log::Log4perl::Appender::File
41 log4perl.appender.FileAppndr1.filename = desk.log
42 log4perl.appender.FileAppndr1.layout = \
43 Log::Log4perl::Layout::SimpleLayout
44 ######################################################
45
47 Log::Log4perl provides a powerful logging API for your application
48
50 Log::Log4perl lets you remote-control and fine-tune the logging
51 behaviour of your system from the outside. It implements the widely
52 popular (Java-based) Log4j logging package in pure Perl.
53 For a detailed tutorial on Log::Log4perl usage, please read
55 <http://www.perl.com/pub/a/2002/09/11/log4perl.html>
57 Logging beats a debugger if you want to know what's going on in your
59 code during runtime. However, traditional logging packages are too
60 static and generate a flood of log messages in your log files that
61 won't help you.
62 "Log::Log4perl" is different. It allows you to control the number of
64 logging messages generated at three different levels:
65 • At a central location in your system (either in a configuration
67 file or in the startup code) you specify which components (classes,
68 functions) of your system should generate logs.
69 • You specify how detailed the logging of these components should be
71 by specifying logging levels.
72 • You also specify which so-called appenders you want to feed your
74 log messages to ("Print it to the screen and also append it to
75 /tmp/my.log") and which format ("Write the date first, then the
76 file name and line number, and then the log message") they should
77 be in.
78 This is a very powerful and flexible mechanism. You can turn on and off
80 your logs at any time, specify the level of detail and make that
81 dependent on the subsystem that's currently executed.
82 Let me give you an example: You might find out that your system has a
84 problem in the "MySystem::Helpers::ScanDir" component. Turning on
85 detailed debugging logs all over the system would generate a flood of
86 useless log messages and bog your system down beyond recognition. With
87 "Log::Log4perl", however, you can tell the system: "Continue to log
88 only severe errors to the log file. Open a second log file, turn on
89 full debug logs in the "MySystem::Helpers::ScanDir" component and dump
90 all messages originating from there into the new log file". And all
91 this is possible by just changing the parameters in a configuration
92 file, which your system can re-read even while it's running!
93
95 The "Log::Log4perl" package can be initialized in two ways: Either via
96 Perl commands or via a "log4j"-style configuration file.
97 Initialize via a configuration file
99 This is the easiest way to prepare your system for using
100 "Log::Log4perl". Use a configuration file like this:
101 ############################################################
103 # A simple root logger with a Log::Log4perl::Appender::File
104 # file appender in Perl.
105 ############################################################
106 log4perl.rootLogger=ERROR, LOGFILE
107 log4perl.appender.LOGFILE=Log::Log4perl::Appender::File
109 log4perl.appender.LOGFILE.filename=/var/log/myerrs.log
110 log4perl.appender.LOGFILE.mode=append
111 log4perl.appender.LOGFILE.layout=PatternLayout
113 log4perl.appender.LOGFILE.layout.ConversionPattern=[%r] %F %L %c - %m%n
114 These lines define your standard logger that's appending severe errors
116 to "/var/log/myerrs.log", using the format
117 [millisecs] source-filename line-number class - message newline
119 Assuming that this configuration file is saved as "log.conf", you need
121 to read it in the startup section of your code, using the following
122 commands:
123 use Log::Log4perl;
125 Log::Log4perl->init("log.conf");
126 After that's done somewhere in the code, you can retrieve logger
128 objects anywhere in the code. Note that there's no need to carry any
129 logger references around with your functions and methods. You can get a
130 logger anytime via a singleton mechanism:
131 package My::MegaPackage;
133 use Log::Log4perl;
134 sub some_method {
136 my($param) = @_;
137 my $log = Log::Log4perl->get_logger("My::MegaPackage");
139 $log->debug("Debug message");
141 $log->info("Info message");
142 $log->error("Error message");
143 ...
145 }
146 With the configuration file above, "Log::Log4perl" will write "Error
148 message" to the specified log file, but won't do anything for the
149 "debug()" and "info()" calls, because the log level has been set to
150 "ERROR" for all components in the first line of configuration file
151 shown above.
152 Why "Log::Log4perl->get_logger" and not "Log::Log4perl->new"? We don't
154 want to create a new object every time. Usually in OO-Programming, you
155 create an object once and use the reference to it to call its methods.
156 However, this requires that you pass around the object to all functions
157 and the last thing we want is pollute each and every function/method
158 we're using with a handle to the "Logger":
159 sub function { # Brrrr!!
161 my($logger, $some, $other, $parameters) = @_;
162 }
163 Instead, if a function/method wants a reference to the logger, it just
165 calls the Logger's static "get_logger($category)" method to obtain a
166 reference to the one and only possible logger object of a certain
167 category. That's called a singleton if you're a Gamma fan.
168 How does the logger know which messages it is supposed to log and which
170 ones to suppress? "Log::Log4perl" works with inheritance: The config
171 file above didn't specify anything about "My::MegaPackage". And yet,
172 we've defined a logger of the category "My::MegaPackage". In this
173 case, "Log::Log4perl" will walk up the namespace hierarchy ("My" and
174 then we're at the root) to figure out if a log level is defined
175 somewhere. In the case above, the log level at the root (root always
176 defines a log level, but not necessarily an appender) defines that the
177 log level is supposed to be "ERROR" -- meaning that DEBUG and INFO
178 messages are suppressed. Note that this 'inheritance' is unrelated to
179 Perl's class inheritance, it is merely related to the logger namespace.
180 By the way, if you're ever in doubt about what a logger's category is,
181 use "$logger->category()" to retrieve it.
182 Log Levels
184 There are six predefined log levels: "FATAL", "ERROR", "WARN", "INFO",
185 "DEBUG", and "TRACE" (in descending priority). Your configured logging
186 level has to at least match the priority of the logging message.
187 If your configured logging level is "WARN", then messages logged with
189 "info()", "debug()", and "trace()" will be suppressed. "fatal()",
190 "error()" and "warn()" will make their way through, because their
191 priority is higher or equal than the configured setting.
192 Instead of calling the methods
194 $logger->trace("..."); # Log a trace message
196 $logger->debug("..."); # Log a debug message
197 $logger->info("..."); # Log a info message
198 $logger->warn("..."); # Log a warn message
199 $logger->error("..."); # Log a error message
200 $logger->fatal("..."); # Log a fatal message
201 you could also call the "log()" method with the appropriate level using
203 the constants defined in "Log::Log4perl::Level":
204 use Log::Log4perl::Level;
206 $logger->log($TRACE, "...");
208 $logger->log($DEBUG, "...");
209 $logger->log($INFO, "...");
210 $logger->log($WARN, "...");
211 $logger->log($ERROR, "...");
212 $logger->log($FATAL, "...");
213 This form is rarely used, but it comes in handy if you want to log at
215 different levels depending on an exit code of a function:
216 $logger->log( $exit_level{ $rc }, "...");
218 As for needing more logging levels than these predefined ones: It's
220 usually best to steer your logging behaviour via the category mechanism
221 instead.
222 If you need to find out if the currently configured logging level would
224 allow a logger's logging statement to go through, use the logger's
225 "is_level()" methods:
226 $logger->is_trace() # True if trace messages would go through
228 $logger->is_debug() # True if debug messages would go through
229 $logger->is_info() # True if info messages would go through
230 $logger->is_warn() # True if warn messages would go through
231 $logger->is_error() # True if error messages would go through
232 $logger->is_fatal() # True if fatal messages would go through
233 Example: "$logger->is_warn()" returns true if the logger's current
235 level, as derived from either the logger's category (or, in absence of
236 that, one of the logger's parent's level setting) is $WARN, $ERROR or
237 $FATAL.
238 Also available are a series of more Java-esque functions which return
240 the same values. These are of the format "isLevelEnabled()", so
241 "$logger->isDebugEnabled()" is synonymous to "$logger->is_debug()".
242 These level checking functions will come in handy later, when we want
244 to block unnecessary expensive parameter construction in case the
245 logging level is too low to log the statement anyway, like in:
246 if($logger->is_error()) {
248 $logger->error("Erroneous array: @super_long_array");
249 }
250 If we had just written
252 $logger->error("Erroneous array: @super_long_array");
254 then Perl would have interpolated @super_long_array into the string via
256 an expensive operation only to figure out shortly after that the string
257 can be ignored entirely because the configured logging level is lower
258 than $ERROR.
259 The to-be-logged message passed to all of the functions described above
261 can consist of an arbitrary number of arguments, which the logging
262 functions just chain together to a single string. Therefore
263 $logger->debug("Hello ", "World", "!"); # and
265 $logger->debug("Hello World!");
266 are identical.
268 Note that even if one of the methods above returns true, it doesn't
270 necessarily mean that the message will actually get logged. What
271 is_debug() checks is that the logger used is configured to let a
272 message of the given priority (DEBUG) through. But after this check,
273 Log4perl will eventually apply custom filters and forward the message
274 to one or more appenders. None of this gets checked by is_xxx(), for
275 the simple reason that it's impossible to know what a custom filter
276 does with a message without having the actual message or what an
277 appender does to a message without actually having it log it.
278 Log and die or warn
280 Often, when you croak / carp / warn / die, you want to log those
281 messages. Rather than doing the following:
282 $logger->fatal($err) && die($err);
284 you can use the following:
286 $logger->logdie($err);
288 And if instead of using
290 warn($message);
292 $logger->warn($message);
293 to both issue a warning via Perl's warn() mechanism and make sure you
295 have the same message in the log file as well, use:
296 $logger->logwarn($message);
298 Since there is an ERROR level between WARN and FATAL, there are two
300 additional helper functions in case you'd like to use ERROR for either
301 warn() or die():
302 $logger->error_warn();
304 $logger->error_die();
305 Finally, there's the Carp functions that, in addition to logging, also
307 pass the stringified message to their companions in the Carp package:
308 $logger->logcarp(); # warn w/ 1-level stack trace
310 $logger->logcluck(); # warn w/ full stack trace
311 $logger->logcroak(); # die w/ 1-level stack trace
312 $logger->logconfess(); # die w/ full stack trace
313 Appenders
315 If you don't define any appenders, nothing will happen. Appenders will
316 be triggered whenever the configured logging level requires a message
317 to be logged and not suppressed.
318 "Log::Log4perl" doesn't define any appenders by default, not even the
320 root logger has one.
321 "Log::Log4perl" already comes with a standard set of appenders:
323 Log::Log4perl::Appender::Screen
325 Log::Log4perl::Appender::ScreenColoredLevels
326 Log::Log4perl::Appender::File
327 Log::Log4perl::Appender::Socket
328 Log::Log4perl::Appender::DBI
329 Log::Log4perl::Appender::Synchronized
330 Log::Log4perl::Appender::RRDs
331 to log to the screen, to files and to databases.
333 On CPAN, you can find additional appenders like
335 Log::Log4perl::Layout::XMLLayout
337 by Guido Carls <gcarls@cpan.org>. It allows for hooking up
339 Log::Log4perl with the graphical Log Analyzer Chainsaw (see "Can I use
340 Log::Log4perl with log4j's Chainsaw?" in Log::Log4perl::FAQ).
341 Additional Appenders via Log::Dispatch
343 "Log::Log4perl" also supports Dave Rolskys excellent "Log::Dispatch"
344 framework which implements a wide variety of different appenders.
345 Here's the list of appender modules currently available via
347 "Log::Dispatch":
348 Log::Dispatch::ApacheLog
350 Log::Dispatch::DBI (by Tatsuhiko Miyagawa)
351 Log::Dispatch::Email,
352 Log::Dispatch::Email::MailSend,
353 Log::Dispatch::Email::MailSendmail,
354 Log::Dispatch::Email::MIMELite
355 Log::Dispatch::File
356 Log::Dispatch::FileRotate (by Mark Pfeiffer)
357 Log::Dispatch::Handle
358 Log::Dispatch::Screen
359 Log::Dispatch::Syslog
360 Log::Dispatch::Tk (by Dominique Dumont)
361 Please note that in order to use any of these additional appenders, you
363 have to fetch Log::Dispatch from CPAN and install it. Also the
364 particular appender you're using might require installing the
365 particular module.
366 For additional information on appenders, please check the
368 Log::Log4perl::Appender manual page.
369 Appender Example
371 Now let's assume that we want to log "info()" or higher prioritized
372 messages in the "Foo::Bar" category to both STDOUT and to a log file,
373 say "test.log". In the initialization section of your system, just
374 define two appenders using the readily available
375 "Log::Log4perl::Appender::File" and "Log::Log4perl::Appender::Screen"
376 modules:
377 use Log::Log4perl;
379 # Configuration in a string ...
381 my $conf = q(
382 log4perl.category.Foo.Bar = INFO, Logfile, Screen
383 log4perl.appender.Logfile = Log::Log4perl::Appender::File
385 log4perl.appender.Logfile.filename = test.log
386 log4perl.appender.Logfile.layout = Log::Log4perl::Layout::PatternLayout
387 log4perl.appender.Logfile.layout.ConversionPattern = [%r] %F %L %m%n
388 log4perl.appender.Screen = Log::Log4perl::Appender::Screen
390 log4perl.appender.Screen.stderr = 0
391 log4perl.appender.Screen.layout = Log::Log4perl::Layout::SimpleLayout
392 );
393 # ... passed as a reference to init()
395 Log::Log4perl::init( \$conf );
396 Once the initialization shown above has happened once, typically in the
398 startup code of your system, just use the defined logger anywhere in
399 your system:
400 ##########################
402 # ... in some function ...
403 ##########################
404 my $log = Log::Log4perl::get_logger("Foo::Bar");
405 # Logs both to STDOUT and to the file test.log
407 $log->info("Important Info!");
408 The "layout" settings specified in the configuration section define the
410 format in which the message is going to be logged by the specified
411 appender. The format shown for the file appender is logging not only
412 the message but also the number of milliseconds since the program has
413 started (%r), the name of the file the call to the logger has happened
414 and the line number there (%F and %L), the message itself (%m) and a
415 OS-specific newline character (%n):
416 [187] ./myscript.pl 27 Important Info!
418 The screen appender above, on the other hand, uses a "SimpleLayout",
420 which logs the debug level, a hyphen (-) and the log message:
421 INFO - Important Info!
423 For more detailed info on layout formats, see "Log Layouts".
425 In the configuration sample above, we chose to define a category logger
427 ("Foo::Bar"). This will cause only messages originating from this
428 specific category logger to be logged in the defined format and
429 locations.
430 Logging newlines
432 There's some controversy between different logging systems as to when
433 and where newlines are supposed to be added to logged messages.
434 The Log4perl way is that a logging statement should not contain a
436 newline:
437 $logger->info("Some message");
439 $logger->info("Another message");
440 If this is supposed to end up in a log file like
442 Some message
444 Another message
445 then an appropriate appender layout like "%m%n" will take care of
447 adding a newline at the end of each message to make sure every message
448 is printed on its own line.
449 Other logging systems, Log::Dispatch in particular, recommend adding
451 the newline to the log statement. This doesn't work well, however, if
452 you, say, replace your file appender by a database appender, and all of
453 a sudden those newlines scattered around the code don't make sense
454 anymore.
455 Assigning matching layouts to different appenders and leaving newlines
457 out of the code solves this problem. If you inherited code that has
458 logging statements with newlines and want to make it work with
459 Log4perl, read the Log::Log4perl::Layout::PatternLayout documentation
460 on how to accomplish that.
461 Configuration files
463 As shown above, you can define "Log::Log4perl" loggers both from within
464 your Perl code or from configuration files. The latter have the
465 unbeatable advantage that you can modify your system's logging
466 behaviour without interfering with the code at all. So even if your
467 code is being run by somebody who's totally oblivious to Perl, they
468 still can adapt the module's logging behaviour to their needs.
469 "Log::Log4perl" has been designed to understand "Log4j" configuration
471 files -- as used by the original Java implementation. Instead of
472 reiterating the format description in [2], let me just list three
473 examples (also derived from [2]), which should also illustrate how it
474 works:
475 log4j.rootLogger=DEBUG, A1
477 log4j.appender.A1=org.apache.log4j.ConsoleAppender
478 log4j.appender.A1.layout=org.apache.log4j.PatternLayout
479 log4j.appender.A1.layout.ConversionPattern=%-4r %-5p %c %x - %m%n
480 This enables messages of priority "DEBUG" or higher in the root
482 hierarchy and has the system write them to the console.
483 "ConsoleAppender" is a Java appender, but "Log::Log4perl" jumps through
484 a significant number of hoops internally to map these to their
485 corresponding Perl classes, "Log::Log4perl::Appender::Screen" in this
486 case.
487 Second example:
489 log4perl.rootLogger=DEBUG, A1
491 log4perl.appender.A1=Log::Log4perl::Appender::Screen
492 log4perl.appender.A1.layout=PatternLayout
493 log4perl.appender.A1.layout.ConversionPattern=%d %-5p %c - %m%n
494 log4perl.logger.com.foo=WARN
495 This defines two loggers: The root logger and the "com.foo" logger.
497 The root logger is easily triggered by debug-messages, but the
498 "com.foo" logger makes sure that messages issued within the "Com::Foo"
499 component and below are only forwarded to the appender if they're of
500 priority warning or higher.
501 Note that the "com.foo" logger doesn't define an appender. Therefore,
503 it will just propagate the message up the hierarchy until the root
504 logger picks it up and forwards it to the one and only appender of the
505 root category, using the format defined for it.
506 Third example:
508 log4j.rootLogger=DEBUG, stdout, R
510 log4j.appender.stdout=org.apache.log4j.ConsoleAppender
511 log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
512 log4j.appender.stdout.layout.ConversionPattern=%5p (%F:%L) - %m%n
513 log4j.appender.R=org.apache.log4j.RollingFileAppender
514 log4j.appender.R.File=example.log
515 log4j.appender.R.layout=org.apache.log4j.PatternLayout
516 log4j.appender.R.layout.ConversionPattern=%p %c - %m%n
517 The root logger defines two appenders here: "stdout", which uses
519 "org.apache.log4j.ConsoleAppender" (ultimately mapped by
520 "Log::Log4perl" to Log::Log4perl::Appender::Screen) to write to the
521 screen. And "R", a "org.apache.log4j.RollingFileAppender" (mapped by
522 "Log::Log4perl" to Log::Dispatch::FileRotate with the "File" attribute
523 specifying the log file.
524 See Log::Log4perl::Config for more examples and syntax explanations.
526 Log Layouts
528 If the logging engine passes a message to an appender, because it
529 thinks it should be logged, the appender doesn't just write it out
530 haphazardly. There's ways to tell the appender how to format the
531 message and add all sorts of interesting data to it: The date and time
532 when the event happened, the file, the line number, the debug level of
533 the logger and others.
534 There's currently two layouts defined in "Log::Log4perl":
536 "Log::Log4perl::Layout::SimpleLayout" and
537 "Log::Log4perl::Layout::PatternLayout":
538 "Log::Log4perl::SimpleLayout"
540 formats a message in a simple way and just prepends it by the debug
541 level and a hyphen: ""$level - $message", for example "FATAL -
542 Can't open password file".
543 "Log::Log4perl::Layout::PatternLayout"
545 on the other hand is very powerful and allows for a very flexible
546 format in "printf"-style. The format string can contain a number of
547 placeholders which will be replaced by the logging engine when it's
548 time to log the message:
549 %c Category of the logging event.
551 %C Fully qualified package (or class) name of the caller
552 %d Current date in yyyy/MM/dd hh:mm:ss format
553 %F File where the logging event occurred
554 %H Hostname (if Sys::Hostname is available)
555 %l Fully qualified name of the calling method followed by the
556 callers source the file name and line number between
557 parentheses.
558 %L Line number within the file where the log statement was issued
559 %m The message to be logged
560 %m{chomp} The message to be logged, stripped off a trailing newline
561 %M Method or function where the logging request was issued
562 %n Newline (OS-independent)
563 %p Priority of the logging event
564 %P pid of the current process
565 %r Number of milliseconds elapsed from program start to logging
566 event
567 %R Number of milliseconds elapsed from last logging event to
568 current logging event
569 %T A stack trace of functions called
570 %x The topmost NDC (see below)
571 %X{key} The entry 'key' of the MDC (see below)
572 %% A literal percent (%) sign
573 NDC and MDC are explained in "Nested Diagnostic Context (NDC)" and
575 "Mapped Diagnostic Context (MDC)".
576 Also, %d can be fine-tuned to display only certain characteristics
578 of a date, according to the SimpleDateFormat in the Java World
579 (<http://java.sun.com/j2se/1.3/docs/api/java/text/SimpleDateFormat.html>)
580 In this way, %d{HH:mm} displays only hours and minutes of the
582 current date, while %d{yy, EEEE} displays a two-digit year,
583 followed by a spelled-out day (like "Wednesday").
584 Similar options are available for shrinking the displayed category
586 or limit file/path components, %F{1} only displays the source file
587 name without any path components while %F logs the full path. %c{2}
588 only logs the last two components of the current category,
589 "Foo::Bar::Baz" becomes "Bar::Baz" and saves space.
590 If those placeholders aren't enough, then you can define your own
592 right in the config file like this:
593 log4perl.PatternLayout.cspec.U = sub { return "UID $<" }
595 See Log::Log4perl::Layout::PatternLayout for further details on
597 customized specifiers.
598 Please note that the subroutines you're defining in this way are
600 going to be run in the "main" namespace, so be sure to fully
601 qualify functions and variables if they're located in different
602 packages.
603 SECURITY NOTE: this feature means arbitrary perl code can be
605 embedded in the config file. In the rare case where the people who
606 have access to your config file are different from the people who
607 write your code and shouldn't have execute rights, you might want
608 to call
609 Log::Log4perl::Config->allow_code(0);
611 before you call init(). Alternatively you can supply a restricted
613 set of Perl opcodes that can be embedded in the config file as
614 described in "Restricting what Opcodes can be in a Perl Hook".
615 All placeholders are quantifiable, just like in printf. Following this
617 tradition, "%-20c" will reserve 20 chars for the category and left-
618 justify it.
619 For more details on logging and how to use the flexible and the simple
621 format, check out the original "log4j" website under
622 SimpleLayout
624 <http://logging.apache.org/log4j/1.2/apidocs/org/apache/log4j/SimpleLayout.html>
625 and PatternLayout
626 <http://logging.apache.org/log4j/1.2/apidocs/org/apache/log4j/PatternLayout.html>
627 Penalties
629 Logging comes with a price tag. "Log::Log4perl" has been optimized to
630 allow for maximum performance, both with logging enabled and disabled.
631 But you need to be aware that there's a small hit every time your code
633 encounters a log statement -- no matter if logging is enabled or not.
634 "Log::Log4perl" has been designed to keep this so low that it will be
635 unnoticeable to most applications.
636 Here's a couple of tricks which help "Log::Log4perl" to avoid
638 unnecessary delays:
639 You can save serious time if you're logging something like
641 # Expensive in non-debug mode!
643 for (@super_long_array) {
644 $logger->debug("Element: $_");
645 }
646 and @super_long_array is fairly big, so looping through it is pretty
648 expensive. Only you, the programmer, knows that going through that
649 "for" loop can be skipped entirely if the current logging level for the
650 actual component is higher than "debug". In this case, use this
651 instead:
652 # Cheap in non-debug mode!
654 if($logger->is_debug()) {
655 for (@super_long_array) {
656 $logger->debug("Element: $_");
657 }
658 }
659 If you're afraid that generating the parameters to the logging function
661 is fairly expensive, use closures:
662 # Passed as subroutine ref
664 use Data::Dumper;
665 $logger->debug(sub { Dumper($data) } );
666 This won't unravel $data via Dumper() unless it's actually needed
668 because it's logged.
669 Also, Log::Log4perl lets you specify arguments to logger functions in
671 message output filter syntax:
672 $logger->debug("Structure: ",
674 { filter => \&Dumper,
675 value => $someref });
676 In this way, shortly before Log::Log4perl sending the message out to
678 any appenders, it will be searching all arguments for hash references
679 and treat them in a special way:
680 It will invoke the function given as a reference with the "filter" key
682 ("Data::Dumper::Dumper()") and pass it the value that came with the key
683 named "value" as an argument. The anonymous hash in the call above
684 will be replaced by the return value of the filter function.
685
687 Categories are also called "Loggers" in Log4perl, both refer to the
688 same thing and these terms are used interchangeably. "Log::Log4perl"
689 uses categories to determine if a log statement in a component should
690 be executed or suppressed at the current logging level. Most of the
691 time, these categories are just the classes the log statements are
692 located in:
693 package Candy::Twix;
695 sub new {
697 my $logger = Log::Log4perl->get_logger("Candy::Twix");
698 $logger->debug("Creating a new Twix bar");
699 bless {}, shift;
700 }
701 # ...
703 package Candy::Snickers;
705 sub new {
707 my $logger = Log::Log4perl->get_logger("Candy.Snickers");
708 $logger->debug("Creating a new Snickers bar");
709 bless {}, shift;
710 }
711 # ...
713 package main;
715 Log::Log4perl->init("mylogdefs.conf");
716 # => "LOG> Creating a new Snickers bar"
718 my $first = Candy::Snickers->new();
719 # => "LOG> Creating a new Twix bar"
720 my $second = Candy::Twix->new();
721 Note that you can separate your category hierarchy levels using either
723 dots like in Java (.) or double-colons (::) like in Perl. Both
724 notations are equivalent and are handled the same way internally.
725 However, categories are just there to make use of inheritance: if you
727 invoke a logger in a sub-category, it will bubble up the hierarchy and
728 call the appropriate appenders. Internally, categories are not related
729 to the class hierarchy of the program at all -- they're purely virtual.
730 You can use arbitrary categories -- for example in the following
731 program, which isn't oo-style, but procedural:
732 sub print_portfolio {
734 my $log = Log::Log4perl->get_logger("user.portfolio");
736 $log->debug("Quotes requested: @_");
737 for(@_) {
739 print "$_: ", get_quote($_), "\n";
740 }
741 }
742 sub get_quote {
744 my $log = Log::Log4perl->get_logger("internet.quotesystem");
746 $log->debug("Fetching quote: $_[0]");
747 return yahoo_quote($_[0]);
749 }
750 The logger in first function, "print_portfolio", is assigned the
752 (virtual) "user.portfolio" category. Depending on the "Log4perl"
753 configuration, this will either call a "user.portfolio" appender, a
754 "user" appender, or an appender assigned to root -- without
755 "user.portfolio" having any relevance to the class system used in the
756 program. The logger in the second function adheres to the
757 "internet.quotesystem" category -- again, maybe because it's bundled
758 with other Internet functions, but not because there would be a class
759 of this name somewhere.
760 However, be careful, don't go overboard: if you're developing a system
762 in object-oriented style, using the class hierarchy is usually your
763 best choice. Think about the people taking over your code one day: The
764 class hierarchy is probably what they know right up front, so it's easy
765 for them to tune the logging to their needs.
766 Turn off a component
768 "Log4perl" doesn't only allow you to selectively switch on a category
769 of log messages, you can also use the mechanism to selectively disable
770 logging in certain components whereas logging is kept turned on in
771 higher-level categories. This mechanism comes in handy if you find that
772 while bumping up the logging level of a high-level (i. e. close to
773 root) category, that one component logs more than it should,
774 Here's how it works:
776 ############################################################
778 # Turn off logging in a lower-level category while keeping
779 # it active in higher-level categories.
780 ############################################################
781 log4perl.rootLogger=DEBUG, LOGFILE
782 log4perl.logger.deep.down.the.hierarchy = ERROR, LOGFILE
783 # ... Define appenders ...
785 This way, log messages issued from within "Deep::Down::The::Hierarchy"
787 and below will be logged only if they're "ERROR" or worse, while in all
788 other system components even "DEBUG" messages will be logged.
789 Return Values
791 All logging methods return values indicating if their message actually
792 reached one or more appenders. If the message has been suppressed
793 because of level constraints, "undef" is returned.
794 For example,
796 my $ret = $logger->info("Message");
798 will return "undef" if the system debug level for the current category
800 is not "INFO" or more permissive. If Log::Log4perl forwarded the
801 message to one or more appenders, the number of appenders is returned.
802 If appenders decide to veto on the message with an appender threshold,
804 the log method's return value will have them excluded. This means that
805 if you've got one appender holding an appender threshold and you're
806 logging a message which passes the system's log level hurdle but not
807 the appender threshold, 0 will be returned by the log function.
808 The bottom line is: Logging functions will return a true value if the
810 message made it through to one or more appenders and a false value if
811 it didn't. This allows for constructs like
812 $logger->fatal("@_") or print STDERR "@_\n";
814 which will ensure that the fatal message isn't lost if the current
816 level is lower than FATAL or printed twice if the level is acceptable
817 but an appender already points to STDERR.
818 Pitfalls with Categories
820 Be careful with just blindly reusing the system's packages as
821 categories. If you do, you'll get into trouble with inherited methods.
822 Imagine the following class setup:
823 use Log::Log4perl;
825 ###########################################
827 package Bar;
828 ###########################################
829 sub new {
830 my($class) = @_;
831 my $logger = Log::Log4perl::get_logger(__PACKAGE__);
832 $logger->debug("Creating instance");
833 bless {}, $class;
834 }
835 ###########################################
836 package Bar::Twix;
837 ###########################################
838 our @ISA = qw(Bar);
839 ###########################################
841 package main;
842 ###########################################
843 Log::Log4perl->init(\ qq{
844 log4perl.category.Bar.Twix = DEBUG, Screen
845 log4perl.appender.Screen = Log::Log4perl::Appender::Screen
846 log4perl.appender.Screen.layout = SimpleLayout
847 });
848 my $bar = Bar::Twix->new();
850 "Bar::Twix" just inherits everything from "Bar", including the
852 constructor "new()". Contrary to what you might be thinking at first,
853 this won't log anything. Reason for this is the "get_logger()" call in
854 package "Bar", which will always get a logger of the "Bar" category,
855 even if we call "new()" via the "Bar::Twix" package, which will make
856 perl go up the inheritance tree to actually execute "Bar::new()". Since
857 we've only defined logging behaviour for "Bar::Twix" in the
858 configuration file, nothing will happen.
859 This can be fixed by changing the "get_logger()" method in "Bar::new()"
861 to obtain a logger of the category matching the actual class of the
862 object, like in
863 # ... in Bar::new() ...
865 my $logger = Log::Log4perl::get_logger( $class );
866 In a method other than the constructor, the class name of the actual
868 object can be obtained by calling "ref()" on the object reference, so
869 package BaseClass;
871 use Log::Log4perl qw( get_logger );
872 sub new {
874 bless {}, shift;
875 }
876 sub method {
878 my( $self ) = @_;
879 get_logger( ref $self )->debug( "message" );
881 }
882 package SubClass;
884 our @ISA = qw(BaseClass);
885 is the recommended pattern to make sure that
887 my $sub = SubClass->new();
889 $sub->meth();
890 starts logging if the "SubClass" category (and not the "BaseClass"
892 category has logging enabled at the DEBUG level.
893 Initialize once and only once
895 It's important to realize that Log::Log4perl gets initialized once and
896 only once, typically at the start of a program or system. Calling
897 "init()" more than once will cause it to clobber the existing
898 configuration and replace it by the new one.
899 If you're in a traditional CGI environment, where every request is
901 handled by a new process, calling "init()" every time is fine. In
902 persistent environments like "mod_perl", however, Log::Log4perl should
903 be initialized either at system startup time (Apache offers startup
904 handlers for that) or via
905 # Init or skip if already done
907 Log::Log4perl->init_once($conf_file);
908 "init_once()" is identical to "init()", just with the exception that it
910 will leave a potentially existing configuration alone and will only
911 call "init()" if Log::Log4perl hasn't been initialized yet.
912 If you're just curious if Log::Log4perl has been initialized yet, the
914 check
915 if(Log::Log4perl->initialized()) {
917 # Yes, Log::Log4perl has already been initialized
918 } else {
919 # No, not initialized yet ...
920 }
921 can be used.
923 If you're afraid that the components of your system are stepping on
925 each other's toes or if you are thinking that different components
926 should initialize Log::Log4perl separately, try to consolidate your
927 system to use a centralized Log4perl configuration file and use
928 Log4perl's categories to separate your components.
929 Custom Filters
931 Log4perl allows the use of customized filters in its appenders to
932 control the output of messages. These filters might grep for certain
933 text chunks in a message, verify that its priority matches or exceeds a
934 certain level or that this is the 10th time the same message has been
935 submitted -- and come to a log/no log decision based upon these
936 circumstantial facts.
937 Check out Log::Log4perl::Filter for detailed instructions on how to use
939 them.
940 Performance
942 The performance of Log::Log4perl calls obviously depends on a lot of
943 things. But to give you a general idea, here's some rough numbers:
944 On a Pentium 4 Linux box at 2.4 GHz, you'll get through
946 • 500,000 suppressed log statements per second
948 • 30,000 logged messages per second (using an in-memory appender)
950 • init_and_watch delay mode: 300,000 suppressed, 30,000 logged.
952 init_and_watch signal mode: 450,000 suppressed, 30,000 logged.
953 Numbers depend on the complexity of the Log::Log4perl configuration.
955 For a more detailed benchmark test, check the
956 "docs/benchmark.results.txt" document in the Log::Log4perl
957 distribution.
958
960 Here's a collection of useful tricks for the advanced "Log::Log4perl"
961 user. For more, check the FAQ, either in the distribution
962 (Log::Log4perl::FAQ) or on <http://log4perl.sourceforge.net>.
963 Shortcuts
965 When getting an instance of a logger, instead of saying
966 use Log::Log4perl;
968 my $logger = Log::Log4perl->get_logger();
969 it's often more convenient to import the "get_logger" method from
971 "Log::Log4perl" into the current namespace:
972 use Log::Log4perl qw(get_logger);
974 my $logger = get_logger();
975 Please note this difference: To obtain the root logger, please use
977 "get_logger("")", call it without parameters ("get_logger()"), you'll
978 get the logger of a category named after the current package.
979 "get_logger()" is equivalent to "get_logger(__PACKAGE__)".
980 Alternative initialization
982 Instead of having "init()" read in a configuration file by specifying a
983 file name or passing it a reference to an open filehandle
984 ("Log::Log4perl->init( \*FILE )"), you can also pass in a reference to
985 a string, containing the content of the file:
986 Log::Log4perl->init( \$config_text );
988 Also, if you've got the "name=value" pairs of the configuration in a
990 hash, you can just as well initialize "Log::Log4perl" with a reference
991 to it:
992 my %key_value_pairs = (
994 "log4perl.rootLogger" => "ERROR, LOGFILE",
995 "log4perl.appender.LOGFILE" => "Log::Log4perl::Appender::File",
996 ...
997 );
998 Log::Log4perl->init( \%key_value_pairs );
1000 Or also you can use a URL, see below:
1002 Using LWP to parse URLs
1004 (This section borrowed from XML::DOM::Parser by T.J. Mather).
1005 The init() function now also supports URLs, e.g.
1007 http://www.erols.com/enno/xsa.xml. It uses LWP to download the file
1008 and then calls parse() on the resulting string. By default it will use
1009 a LWP::UserAgent that is created as follows:
1010 use LWP::UserAgent;
1012 $LWP_USER_AGENT = LWP::UserAgent->new;
1013 $LWP_USER_AGENT->env_proxy;
1014 Note that env_proxy reads proxy settings from environment variables,
1016 which is what Log4perl needs to do to get through our firewall. If you
1017 want to use a different LWP::UserAgent, you can set it with
1018 Log::Log4perl::Config::set_LWP_UserAgent($my_agent);
1020 Currently, LWP is used when the filename (passed to parsefile) starts
1022 with one of the following URL schemes: http, https, ftp, wais, gopher,
1023 or file (followed by a colon.)
1024 Don't use this feature with init_and_watch().
1026 Automatic reloading of changed configuration files
1028 Instead of just statically initializing Log::Log4perl via
1029 Log::Log4perl->init($conf_file);
1031 there's a way to have Log::Log4perl periodically check for changes in
1033 the configuration and reload it if necessary:
1034 Log::Log4perl->init_and_watch($conf_file, $delay);
1036 In this mode, Log::Log4perl will examine the configuration file
1038 $conf_file every $delay seconds for changes via the file's last
1039 modification timestamp. If the file has been updated, it will be
1040 reloaded and replace the current Log::Log4perl configuration.
1041 The way this works is that with every logger function called (debug(),
1043 is_debug(), etc.), Log::Log4perl will check if the delay interval has
1044 expired. If so, it will run a -M file check on the configuration file.
1045 If its timestamp has been modified, the current configuration will be
1046 dumped and new content of the file will be loaded.
1047 This convenience comes at a price, though: Calling time() with every
1049 logging function call, especially the ones that are "suppressed" (!),
1050 will slow down these Log4perl calls by about 40%.
1051 To alleviate this performance hit a bit, "init_and_watch()" can be
1053 configured to listen for a Unix signal to reload the configuration
1054 instead:
1055 Log::Log4perl->init_and_watch($conf_file, 'HUP');
1057 This will set up a signal handler for SIGHUP and reload the
1059 configuration if the application receives this signal, e.g. via the
1060 "kill" command:
1061 kill -HUP pid
1063 where "pid" is the process ID of the application. This will bring you
1065 back to about 85% of Log::Log4perl's normal execution speed for
1066 suppressed statements. For details, check out "Performance". For more
1067 info on the signal handler, look for "SIGNAL MODE" in
1068 Log::Log4perl::Config::Watch.
1069 If you have a somewhat long delay set between physical config file
1071 checks or don't want to use the signal associated with the config file
1072 watcher, you can trigger a configuration reload at the next possible
1073 time by calling "Log::Log4perl::Config->watcher->force_next_check()".
1074 One thing to watch out for: If the configuration file contains a syntax
1076 or other fatal error, a running application will stop with "die" if
1077 this damaged configuration will be loaded during runtime, triggered
1078 either by a signal or if the delay period expired and the change is
1079 detected. This behaviour might change in the future.
1080 To allow the application to intercept and control a configuration
1082 reload in init_and_watch mode, a callback can be specified:
1083 Log::Log4perl->init_and_watch($conf_file, 10, {
1085 preinit_callback => \&callback });
1086 If Log4perl determines that the configuration needs to be reloaded, it
1088 will call the "preinit_callback" function without parameters. If the
1089 callback returns a true value, Log4perl will proceed and reload the
1090 configuration. If the callback returns a false value, Log4perl will
1091 keep the old configuration and skip reloading it until the next time
1092 around. Inside the callback, an application can run all kinds of
1093 checks, including accessing the configuration file, which is available
1094 via "Log::Log4perl::Config->watcher()->file()".
1095 Variable Substitution
1097 To avoid having to retype the same expressions over and over again,
1098 Log::Log4perl's configuration files support simple variable
1099 substitution. New variables are defined simply by adding
1100 varname = value
1102 lines to the configuration file before using
1104 ${varname}
1106 afterwards to recall the assigned values. Here's an example:
1108 layout_class = Log::Log4perl::Layout::PatternLayout
1110 layout_pattern = %d %F{1} %L> %m %n
1111 log4perl.category.Bar.Twix = WARN, Logfile, Screen
1113 log4perl.appender.Logfile = Log::Log4perl::Appender::File
1115 log4perl.appender.Logfile.filename = test.log
1116 log4perl.appender.Logfile.layout = ${layout_class}
1117 log4perl.appender.Logfile.layout.ConversionPattern = ${layout_pattern}
1118 log4perl.appender.Screen = Log::Log4perl::Appender::Screen
1120 log4perl.appender.Screen.layout = ${layout_class}
1121 log4perl.appender.Screen.layout.ConversionPattern = ${layout_pattern}
1122 This is a convenient way to define two appenders with the same layout
1124 without having to retype the pattern definitions.
1125 Variable substitution via "${varname}" will first try to find an
1127 explicitly defined variable. If that fails, it will check your shell's
1128 environment for a variable of that name. If that also fails, the
1129 program will "die()".
1130 Perl Hooks in the Configuration File
1132 If some of the values used in the Log4perl configuration file need to
1133 be dynamically modified by the program, use Perl hooks:
1134 log4perl.appender.File.filename = \
1136 sub { return getLogfileName(); }
1137 Each value starting with the string "sub {..." is interpreted as Perl
1139 code to be executed at the time the application parses the
1140 configuration via "Log::Log4perl::init()". The return value of the
1141 subroutine is used by Log::Log4perl as the configuration value.
1142 The Perl code is executed in the "main" package, functions in other
1144 packages have to be called in fully-qualified notation.
1145 Here's another example, utilizing an environment variable as a username
1147 for a DBI appender:
1148 log4perl.appender.DB.username = \
1150 sub { $ENV{DB_USER_NAME } }
1151 However, please note the difference between these code snippets and
1153 those used for user-defined conversion specifiers as discussed in
1154 Log::Log4perl::Layout::PatternLayout: While the snippets above are run
1155 once when "Log::Log4perl::init()" is called, the conversion specifier
1156 snippets are executed each time a message is rendered according to the
1157 PatternLayout.
1158 SECURITY NOTE: this feature means arbitrary perl code can be embedded
1160 in the config file. In the rare case where the people who have access
1161 to your config file are different from the people who write your code
1162 and shouldn't have execute rights, you might want to set
1163 Log::Log4perl::Config->allow_code(0);
1165 before you call init(). Alternatively you can supply a restricted set
1167 of Perl opcodes that can be embedded in the config file as described in
1168 "Restricting what Opcodes can be in a Perl Hook".
1169 Restricting what Opcodes can be in a Perl Hook
1171 The value you pass to Log::Log4perl::Config->allow_code() determines
1172 whether the code that is embedded in the config file is eval'd
1173 unrestricted, or eval'd in a Safe compartment. By default, a value of
1174 '1' is assumed, which does a normal 'eval' without any restrictions. A
1175 value of '0' however prevents any embedded code from being evaluated.
1176 If you would like fine-grained control over what can and cannot be
1178 included in embedded code, then please utilize the following methods:
1179 Log::Log4perl::Config->allow_code( $allow );
1181 Log::Log4perl::Config->allowed_code_ops($op1, $op2, ... );
1182 Log::Log4perl::Config->vars_shared_with_safe_compartment( [ \%vars | $package, \@vars ] );
1183 Log::Log4perl::Config->allowed_code_ops_convenience_map( [ \%map | $name, \@mask ] );
1184 Log::Log4perl::Config->allowed_code_ops() takes a list of opcode masks
1186 that are allowed to run in the compartment. The opcode masks must be
1187 specified as described in Opcode:
1188 Log::Log4perl::Config->allowed_code_ops(':subprocess');
1190 This example would allow Perl operations like backticks, system, fork,
1192 and waitpid to be executed in the compartment. Of course, you probably
1193 don't want to use this mask -- it would allow exactly what the Safe
1194 compartment is designed to prevent.
1195 Log::Log4perl::Config->vars_shared_with_safe_compartment() takes the
1197 symbols which should be exported into the Safe compartment before the
1198 code is evaluated. The keys of this hash are the package names that
1199 the symbols are in, and the values are array references to the literal
1200 symbol names. For convenience, the default settings export the '%ENV'
1201 hash from the 'main' package into the compartment:
1202 Log::Log4perl::Config->vars_shared_with_safe_compartment(
1204 main => [ '%ENV' ],
1205 );
1206 Log::Log4perl::Config->allowed_code_ops_convenience_map() is an
1208 accessor method to a map of convenience names to opcode masks. At
1209 present, the following convenience names are defined:
1210 safe = [ ':browse' ]
1212 restrictive = [ ':default' ]
1213 For convenience, if Log::Log4perl::Config->allow_code() is called with
1215 a value which is a key of the map previously defined with
1216 Log::Log4perl::Config->allowed_code_ops_convenience_map(), then the
1217 allowed opcodes are set according to the value defined in the map. If
1218 this is confusing, consider the following:
1219 use Log::Log4perl;
1221 my $config = <<'END';
1223 log4perl.logger = INFO, Main
1224 log4perl.appender.Main = Log::Log4perl::Appender::File
1225 log4perl.appender.Main.filename = \
1226 sub { "example" . getpwuid($<) . ".log" }
1227 log4perl.appender.Main.layout = Log::Log4perl::Layout::SimpleLayout
1228 END
1229 $Log::Log4perl::Config->allow_code('restrictive');
1231 Log::Log4perl->init( \$config ); # will fail
1232 $Log::Log4perl::Config->allow_code('safe');
1233 Log::Log4perl->init( \$config ); # will succeed
1234 The reason that the first call to ->init() fails is because the
1236 'restrictive' name maps to an opcode mask of ':default'. getpwuid() is
1237 not part of ':default', so ->init() fails. The 'safe' name maps to an
1238 opcode mask of ':browse', which allows getpwuid() to run, so ->init()
1239 succeeds.
1240 allowed_code_ops_convenience_map() can be invoked in several ways:
1242 allowed_code_ops_convenience_map()
1244 Returns the entire convenience name map as a hash reference in
1245 scalar context or a hash in list context.
1246 allowed_code_ops_convenience_map( \%map )
1248 Replaces the entire convenience name map with the supplied hash
1249 reference.
1250 allowed_code_ops_convenience_map( $name )
1252 Returns the opcode mask for the given convenience name, or undef if
1253 no such name is defined in the map.
1254 allowed_code_ops_convenience_map( $name, \@mask )
1256 Adds the given name/mask pair to the convenience name map. If the
1257 name already exists in the map, it's value is replaced with the new
1258 mask.
1259 as can vars_shared_with_safe_compartment():
1261 vars_shared_with_safe_compartment()
1263 Return the entire map of packages to variables as a hash reference
1264 in scalar context or a hash in list context.
1265 vars_shared_with_safe_compartment( \%packages )
1267 Replaces the entire map of packages to variables with the supplied
1268 hash reference.
1269 vars_shared_with_safe_compartment( $package )
1271 Returns the arrayref of variables to be shared for a specific
1272 package.
1273 vars_shared_with_safe_compartment( $package, \@vars )
1275 Adds the given package / varlist pair to the map. If the package
1276 already exists in the map, it's value is replaced with the new
1277 arrayref of variable names.
1278 For more information on opcodes and Safe Compartments, see Opcode and
1280 Safe.
1281 Changing the Log Level on a Logger
1283 Log4perl provides some internal functions for quickly adjusting the log
1284 level from within a running Perl program.
1285 Now, some people might argue that you should adjust your levels from
1287 within an external Log4perl configuration file, but Log4perl is
1288 everybody's darling.
1289 Typically run-time adjusting of levels is done at the beginning, or in
1291 response to some external input (like a "more logging" runtime command
1292 for diagnostics).
1293 You get the log level from a logger object with:
1295 $current_level = $logger->level();
1297 and you may set it with the same method, provided you first imported
1299 the log level constants, with:
1300 use Log::Log4perl::Level;
1302 Then you can set the level on a logger to one of the constants,
1304 $logger->level($ERROR); # one of DEBUG, INFO, WARN, ERROR, FATAL
1306 To increase the level of logging currently being done, use:
1308 $logger->more_logging($delta);
1310 and to decrease it, use:
1312 $logger->less_logging($delta);
1314 $delta must be a positive integer (for now, we may fix this later ;).
1316 There are also two equivalent functions:
1318 $logger->inc_level($delta);
1320 $logger->dec_level($delta);
1321 They're included to allow you a choice in readability. Some folks will
1323 prefer more/less_logging, as they're fairly clear in what they do, and
1324 allow the programmer not to worry too much about what a Level is and
1325 whether a higher level means more or less logging. However, other folks
1326 who do understand and have lots of code that deals with levels will
1327 probably prefer the inc_level() and dec_level() methods as they want to
1328 work with Levels and not worry about whether that means more or less
1329 logging. :)
1330 That diatribe aside, typically you'll use more_logging() or inc_level()
1332 as such:
1333 my $v = 0; # default level of verbosity.
1335 GetOptions("v+" => \$v, ...);
1337 if( $v ) {
1339 $logger->more_logging($v); # inc logging level once for each -v in ARGV
1340 }
1341 Custom Log Levels
1343 First off, let me tell you that creating custom levels is heavily
1344 deprecated by the log4j folks. Indeed, instead of creating additional
1345 levels on top of the predefined DEBUG, INFO, WARN, ERROR and FATAL, you
1346 should use categories to control the amount of logging smartly, based
1347 on the location of the log-active code in the system.
1348 Nevertheless, Log4perl provides a nice way to create custom levels via
1350 the create_custom_level() routine function. However, this must be done
1351 before the first call to init() or get_logger(). Say you want to create
1352 a NOTIFY logging level that comes after WARN (and thus before INFO).
1353 You'd do such as follows:
1354 use Log::Log4perl;
1356 use Log::Log4perl::Level;
1357 Log::Log4perl::Logger::create_custom_level("NOTIFY", "WARN");
1359 And that's it! "create_custom_level()" creates the following functions
1361 / variables for level FOO:
1362 $FOO_INT # integer to use in L4p::Level::to_level()
1364 $logger->foo() # log function to log if level = FOO
1365 $logger->is_foo() # true if current level is >= FOO
1366 These levels can also be used in your config file, but note that your
1368 config file probably won't be portable to another log4perl or log4j
1369 environment unless you've made the appropriate mods there too.
1370 Since Log4perl translates log levels to syslog and Log::Dispatch if
1372 their appenders are used, you may add mappings for custom levels as
1373 well:
1374 Log::Log4perl::Level::add_priority("NOTIFY", "WARN",
1376 $syslog_equiv, $log_dispatch_level);
1377 For example, if your new custom "NOTIFY" level is supposed to map to
1379 syslog level 2 ("LOG_NOTICE") and Log::Dispatch level 2 ("notice"),
1380 use:
1381 Log::Log4perl::Logger::create_custom_level("NOTIFY", "WARN", 2, 2);
1383 System-wide log levels
1385 As a fairly drastic measure to decrease (or increase) the logging level
1386 all over the system with one single configuration option, use the
1387 "threshold" keyword in the Log4perl configuration file:
1388 log4perl.threshold = ERROR
1390 sets the system-wide (or hierarchy-wide according to the log4j
1392 documentation) to ERROR and therefore deprives every logger in the
1393 system of the right to log lower-prio messages.
1394 Easy Mode
1396 For teaching purposes (especially for [1]), I've put ":easy" mode into
1397 "Log::Log4perl", which just initializes a single root logger with a
1398 defined priority and a screen appender including some nice standard
1399 layout:
1400 ### Initialization Section
1402 use Log::Log4perl qw(:easy);
1403 Log::Log4perl->easy_init($ERROR); # Set priority of root logger to ERROR
1404 ### Application Section
1406 my $logger = get_logger();
1407 $logger->fatal("This will get logged.");
1408 $logger->debug("This won't.");
1409 This will dump something like
1411 2002/08/04 11:43:09 ERROR> script.pl:16 main::function - This will get logged.
1413 to the screen. While this has been proven to work well familiarizing
1415 people with "Log::Logperl" slowly, effectively avoiding to clobber them
1416 over the head with a plethora of different knobs to fiddle with
1417 (categories, appenders, levels, layout), the overall mission of
1418 "Log::Log4perl" is to let people use categories right from the start to
1419 get used to the concept. So, let's keep this one fairly hidden in the
1420 man page (congrats on reading this far :).
1421 Stealth loggers
1423 Sometimes, people are lazy. If you're whipping up a 50-line script and
1424 want the comfort of Log::Log4perl without having the burden of carrying
1425 a separate log4perl.conf file or a 5-liner defining that you want to
1426 append your log statements to a file, you can use the following
1427 features:
1428 use Log::Log4perl qw(:easy);
1430 Log::Log4perl->easy_init( { level => $DEBUG,
1432 file => ">>test.log" } );
1433 # Logs to test.log via stealth logger
1435 DEBUG("Debug this!");
1436 INFO("Info this!");
1437 WARN("Warn this!");
1438 ERROR("Error this!");
1439 some_function();
1441 sub some_function {
1443 # Same here
1444 FATAL("Fatal this!");
1445 }
1446 In ":easy" mode, "Log::Log4perl" will instantiate a stealth logger and
1448 introduce the convenience functions "TRACE", "DEBUG()", "INFO()",
1449 "WARN()", "ERROR()", "FATAL()", and "ALWAYS" into the package
1450 namespace. These functions simply take messages as arguments and
1451 forward them to the stealth loggers methods ("debug()", "info()", and
1452 so on).
1453 If a message should never be blocked, regardless of the log level, use
1455 the "ALWAYS" function which corresponds to a log level of "OFF":
1456 ALWAYS "This will be printed regardless of the log level";
1458 The "easy_init" method can be called with a single level value to
1460 create a STDERR appender and a root logger as in
1461 Log::Log4perl->easy_init($DEBUG);
1463 or, as shown below (and in the example above) with a reference to a
1465 hash, specifying values for "level" (the logger's priority), "file"
1466 (the appender's data sink), "category" (the logger's category and
1467 "layout" for the appender's pattern layout specification. All key-
1468 value pairs are optional, they default to $DEBUG for "level", "STDERR"
1469 for "file", "" (root category) for "category" and "%d %m%n" for
1470 "layout":
1471 Log::Log4perl->easy_init( { level => $DEBUG,
1473 file => ">test.log",
1474 utf8 => 1,
1475 category => "Bar::Twix",
1476 layout => '%F{1}-%L-%M: %m%n' } );
1477 The "file" parameter takes file names preceded by ">" (overwrite) and
1479 ">>" (append) as arguments. This will cause
1480 "Log::Log4perl::Appender::File" appenders to be created behind the
1481 scenes. Also the keywords "STDOUT" and "STDERR" (no ">" or ">>") are
1482 recognized, which will utilize and configure
1483 "Log::Log4perl::Appender::Screen" appropriately. The "utf8" flag, if
1484 set to a true value, runs a "binmode" command on the file handle to
1485 establish a utf8 line discipline on the file, otherwise you'll get a
1486 'wide character in print' warning message and probably not what you'd
1487 expect as output.
1488 The stealth loggers can be used in different packages, you just need to
1490 make sure you're calling the "use" function in every package you're
1491 using "Log::Log4perl"'s easy services:
1492 package Bar::Twix;
1494 use Log::Log4perl qw(:easy);
1495 sub eat { DEBUG("Twix mjam"); }
1496 package Bar::Mars;
1498 use Log::Log4perl qw(:easy);
1499 sub eat { INFO("Mars mjam"); }
1500 package main;
1502 use Log::Log4perl qw(:easy);
1504 Log::Log4perl->easy_init( { level => $DEBUG,
1506 file => ">>test.log",
1507 category => "Bar::Twix",
1508 layout => '%F{1}-%L-%M: %m%n' },
1509 { level => $DEBUG,
1510 file => "STDOUT",
1511 category => "Bar::Mars",
1512 layout => '%m%n' },
1513 );
1514 Bar::Twix::eat();
1515 Bar::Mars::eat();
1516 As shown above, "easy_init()" will take any number of different logger
1518 definitions as hash references.
1519 Also, stealth loggers feature the functions "LOGWARN()", "LOGDIE()",
1521 and "LOGEXIT()", combining a logging request with a subsequent Perl
1522 warn() or die() or exit() statement. So, for example
1523 if($all_is_lost) {
1525 LOGDIE("Terrible Problem");
1526 }
1527 will log the message if the package's logger is at least "FATAL" but
1529 "die()" (including the traditional output to STDERR) in any case
1530 afterwards.
1531 See "Log and die or warn" for the similar "logdie()" and "logwarn()"
1533 functions of regular (i.e non-stealth) loggers.
1534 Similarily, "LOGCARP()", "LOGCLUCK()", "LOGCROAK()", and "LOGCONFESS()"
1536 are provided in ":easy" mode, facilitating the use of "logcarp()",
1537 "logcluck()", "logcroak()", and "logconfess()" with stealth loggers.
1538 When using Log::Log4perl in easy mode, please make sure you understand
1540 the implications of "Pitfalls with Categories".
1541 By the way, these convenience functions perform exactly as fast as the
1543 standard Log::Log4perl logger methods, there's no performance penalty
1544 whatsoever.
1545 Nested Diagnostic Context (NDC)
1547 If you find that your application could use a global (thread-specific)
1548 data stack which your loggers throughout the system have easy access
1549 to, use Nested Diagnostic Contexts (NDCs). Also check out "Mapped
1550 Diagnostic Context (MDC)", this might turn out to be even more useful.
1551 For example, when handling a request of a web client, it's probably
1553 useful to have the user's IP address available in all log statements
1554 within code dealing with this particular request. Instead of passing
1555 this piece of data around between your application functions, you can
1556 just use the global (but thread-specific) NDC mechanism. It allows you
1557 to push data pieces (scalars usually) onto its stack via
1558 Log::Log4perl::NDC->push("San");
1560 Log::Log4perl::NDC->push("Francisco");
1561 and have your loggers retrieve them again via the "%x" placeholder in
1563 the PatternLayout. With the stack values above and a PatternLayout
1564 format like "%x %m%n", the call
1565 $logger->debug("rocks");
1567 will end up as
1569 San Francisco rocks
1571 in the log appender.
1573 The stack mechanism allows for nested structures. Just make sure that
1575 at the end of the request, you either decrease the stack one by one by
1576 calling
1577 Log::Log4perl::NDC->pop();
1579 Log::Log4perl::NDC->pop();
1580 or clear out the entire NDC stack by calling
1582 Log::Log4perl::NDC->remove();
1584 Even if you should forget to do that, "Log::Log4perl" won't grow the
1586 stack indefinitely, but limit it to a maximum, defined in
1587 "Log::Log4perl::NDC" (currently 5). A call to "push()" on a full stack
1588 will just replace the topmost element by the new value.
1589 Again, the stack is always available via the "%x" placeholder in the
1591 Log::Log4perl::Layout::PatternLayout class whenever a logger fires. It
1592 will replace "%x" by the blank-separated list of the values on the
1593 stack. It does that by just calling
1594 Log::Log4perl::NDC->get();
1596 internally. See details on how this standard log4j feature is
1598 implemented in Log::Log4perl::NDC.
1599 Mapped Diagnostic Context (MDC)
1601 Just like the previously discussed NDC stores thread-specific
1602 information in a stack structure, the MDC implements a hash table to
1603 store key/value pairs in.
1604 The static method
1606 Log::Log4perl::MDC->put($key, $value);
1608 stores $value under a key $key, with which it can be retrieved later
1610 (possibly in a totally different part of the system) by calling the
1611 "get" method:
1612 my $value = Log::Log4perl::MDC->get($key);
1614 If no value has been stored previously under $key, the "get" method
1616 will return "undef".
1617 Typically, MDC values are retrieved later on via the "%X{...}"
1619 placeholder in "Log::Log4perl::Layout::PatternLayout". If the "get()"
1620 method returns "undef", the placeholder will expand to the string
1621 "[undef]".
1622 An application taking a web request might store the remote host like
1624 Log::Log4perl::MDC->put("remote_host", $r->headers("HOST"));
1626 at its beginning and if the appender's layout looks something like
1628 log4perl.appender.Logfile.layout.ConversionPattern = %X{remote_host}: %m%n
1630 then a log statement like
1632 DEBUG("Content delivered");
1634 will log something like
1636 adsl-63.dsl.snf.pacbell.net: Content delivered
1638 later on in the program.
1640 For details, please check Log::Log4perl::MDC.
1642 Resurrecting hidden Log4perl Statements
1644 Sometimes scripts need to be deployed in environments without having
1645 Log::Log4perl installed yet. On the other hand, you don't want to live
1646 without your Log4perl statements -- they're gonna come in handy later.
1647 So, just deploy your script with Log4perl statements commented out with
1649 the pattern "###l4p", like in
1650 ###l4p DEBUG "It works!";
1652 # ...
1653 ###l4p INFO "Really!";
1654 If Log::Log4perl is available, use the ":resurrect" tag to have
1656 Log4perl resurrect those buried statements before the script starts
1657 running:
1658 use Log::Log4perl qw(:resurrect :easy);
1660 ###l4p Log::Log4perl->easy_init($DEBUG);
1662 ###l4p DEBUG "It works!";
1663 # ...
1664 ###l4p INFO "Really!";
1665 This will have a source filter kick in and indeed print
1667 2004/11/18 22:08:46 It works!
1669 2004/11/18 22:08:46 Really!
1670 In environments lacking Log::Log4perl, just comment out the first line
1672 and the script will run nevertheless (but of course without logging):
1673 # use Log::Log4perl qw(:resurrect :easy);
1675 ###l4p Log::Log4perl->easy_init($DEBUG);
1677 ###l4p DEBUG "It works!";
1678 # ...
1679 ###l4p INFO "Really!";
1680 because everything's a regular comment now. Alternatively, put the
1682 magic Log::Log4perl comment resurrection line into your shell's
1683 PERL5OPT environment variable, e.g. for bash:
1684 set PERL5OPT=-MLog::Log4perl=:resurrect,:easy
1686 export PERL5OPT
1687 This will awaken the giant within an otherwise silent script like the
1689 following:
1690 #!/usr/bin/perl
1692 ###l4p Log::Log4perl->easy_init($DEBUG);
1694 ###l4p DEBUG "It works!";
1695 As of "Log::Log4perl" 1.12, you can even force all modules loaded by a
1697 script to have their hidden Log4perl statements resurrected. For this
1698 to happen, load "Log::Log4perl::Resurrector" before loading any
1699 modules:
1700 use Log::Log4perl qw(:easy);
1702 use Log::Log4perl::Resurrector;
1703 use Foobar; # All hidden Log4perl statements in here will
1705 # be uncommented before Foobar gets loaded.
1706 Log::Log4perl->easy_init($DEBUG);
1708 ...
1709 Check the "Log::Log4perl::Resurrector" manpage for more details.
1711 Access defined appenders
1713 All appenders defined in the configuration file or via Perl code can be
1714 retrieved by the "appender_by_name()" class method. This comes in handy
1715 if you want to manipulate or query appender properties after the
1716 Log4perl configuration has been loaded via "init()".
1717 Note that internally, Log::Log4perl uses the "Log::Log4perl::Appender"
1719 wrapper class to control the real appenders (like
1720 "Log::Log4perl::Appender::File" or "Log::Dispatch::FileRotate"). The
1721 "Log::Log4perl::Appender" class has an "appender" attribute, pointing
1722 to the real appender.
1723 The reason for this is that external appenders like
1725 "Log::Dispatch::FileRotate" don't support all of Log::Log4perl's
1726 appender control mechanisms (like appender thresholds).
1727 The previously mentioned method "appender_by_name()" returns a
1729 reference to the real appender object. If you want access to the
1730 wrapper class (e.g. if you want to modify the appender's threshold),
1731 use the hash $Log::Log4perl::Logger::APPENDER_BY_NAME{...} instead,
1732 which holds references to all appender wrapper objects.
1733 Modify appender thresholds
1735 To set an appender's threshold, use its "threshold()" method:
1736 $app->threshold( $FATAL );
1738 To conveniently adjust all appender thresholds (e.g. because a script
1740 uses more_logging()), use
1741 # decrease thresholds of all appenders
1743 Log::Log4perl->appender_thresholds_adjust(-1);
1744 This will decrease the thresholds of all appenders in the system by one
1746 level, i.e. WARN becomes INFO, INFO becomes DEBUG, etc. To only modify
1747 selected ones, use
1748 # decrease thresholds of selected appenders
1750 Log::Log4perl->appender_thresholds_adjust(-1, ['AppName1', ...]);
1751 and pass the names of affected appenders in a ref to an array.
1753
1755 Initializing Log::Log4perl can certainly also be done from within Perl.
1756 At last, this is what "Log::Log4perl::Config" does behind the scenes.
1757 Log::Log4perl's configuration file parsers are using a publically
1758 available API to set up Log::Log4perl's categories, appenders and
1759 layouts.
1760 Here's an example on how to configure two appenders with the same
1762 layout in Perl, without using a configuration file at all:
1763 ########################
1765 # Initialization section
1766 ########################
1767 use Log::Log4perl;
1768 use Log::Log4perl::Layout;
1769 use Log::Log4perl::Level;
1770 # Define a category logger
1772 my $log = Log::Log4perl->get_logger("Foo::Bar");
1773 # Define a layout
1775 my $layout = Log::Log4perl::Layout::PatternLayout->new("[%r] %F %L %m%n");
1776 # Define a file appender
1778 my $file_appender = Log::Log4perl::Appender->new(
1779 "Log::Log4perl::Appender::File",
1780 name => "filelog",
1781 filename => "/tmp/my.log");
1782 # Define a stdout appender
1784 my $stdout_appender = Log::Log4perl::Appender->new(
1785 "Log::Log4perl::Appender::Screen",
1786 name => "screenlog",
1787 stderr => 0);
1788 # Have both appenders use the same layout (could be different)
1790 $stdout_appender->layout($layout);
1791 $file_appender->layout($layout);
1792 $log->add_appender($stdout_appender);
1794 $log->add_appender($file_appender);
1795 $log->level($INFO);
1796 Please note the class of the appender object is passed as a string to
1798 "Log::Log4perl::Appender" in the first argument. Behind the scenes,
1799 "Log::Log4perl::Appender" will create the necessary
1800 "Log::Log4perl::Appender::*" (or "Log::Dispatch::*") object and pass
1801 along the name value pairs we provided to
1802 "Log::Log4perl::Appender->new()" after the first argument.
1803 The "name" value is optional and if you don't provide one,
1805 "Log::Log4perl::Appender->new()" will create a unique one for you. The
1806 names and values of additional parameters are dependent on the
1807 requirements of the particular appender class and can be looked up in
1808 their manual pages.
1809 A side note: In case you're wondering if
1811 "Log::Log4perl::Appender->new()" will also take care of the "min_level"
1812 argument to the "Log::Dispatch::*" constructors called behind the
1813 scenes -- yes, it does. This is because we want the "Log::Dispatch"
1814 objects to blindly log everything we send them ("debug" is their lowest
1815 setting) because we in "Log::Log4perl" want to call the shots and
1816 decide on when and what to log.
1817 The call to the appender's layout() method specifies the format (as a
1819 previously created "Log::Log4perl::Layout::PatternLayout" object) in
1820 which the message is being logged in the specified appender. If you
1821 don't specify a layout, the logger will fall back to
1822 "Log::Log4perl::SimpleLayout", which logs the debug level, a hyphen (-)
1823 and the log message.
1824 Layouts are objects, here's how you create them:
1826 # Create a simple layout
1828 my $simple = Log::Log4perl::SimpleLayout();
1829 # create a flexible layout:
1831 # ("yyyy/MM/dd hh:mm:ss (file:lineno)> message\n")
1832 my $pattern = Log::Log4perl::Layout::PatternLayout("%d (%F:%L)> %m%n");
1833 Every appender has exactly one layout assigned to it. You assign the
1835 layout to the appender using the appender's "layout()" object:
1836 my $app = Log::Log4perl::Appender->new(
1838 "Log::Log4perl::Appender::Screen",
1839 name => "screenlog",
1840 stderr => 0);
1841 # Assign the previously defined flexible layout
1843 $app->layout($pattern);
1844 # Add the appender to a previously defined logger
1846 $logger->add_appender($app);
1847 # ... and you're good to go!
1849 $logger->debug("Blah");
1850 # => "2002/07/10 23:55:35 (test.pl:207)> Blah\n"
1851 It's also possible to remove appenders from a logger:
1853 $logger->remove_appender($appender_name);
1855 will remove an appender, specified by name, from a given logger.
1857 Please note that this does not remove an appender from the system.
1858 To eradicate an appender from the system, you need to call
1860 "Log::Log4perl->eradicate_appender($appender_name)" which will first
1861 remove the appender from every logger in the system and then will
1862 delete all references Log4perl holds to it.
1863 To remove a logger from the system, use
1865 "Log::Log4perl->remove_logger($logger)". After the remaining reference
1866 $logger goes away, the logger will self-destruct. If the logger in
1867 question is a stealth logger, all of its convenience shortcuts (DEBUG,
1868 INFO, etc) will turn into no-ops.
1869
1871 Tatsuhiko Miyagawa's "Log::Dispatch::Config" is a very clever
1872 simplified logger implementation, covering some of the log4j
1873 functionality. Among the things that "Log::Log4perl" can but
1874 "Log::Dispatch::Config" can't are:
1875 • You can't assign categories to loggers. For small systems that's
1877 fine, but if you can't turn off and on detailed logging in only a
1878 tiny subsystem of your environment, you're missing out on a majorly
1879 useful log4j feature.
1880 • Defining appender thresholds. Important if you want to solve
1882 problems like "log all messages of level FATAL to STDERR, plus log
1883 all DEBUG messages in "Foo::Bar" to a log file". If you don't have
1884 appenders thresholds, there's no way to prevent cluttering STDERR
1885 with DEBUG messages.
1886 • PatternLayout specifications in accordance with the standard (e.g.
1888 "%d{HH:mm}").
1889 Bottom line: Log::Dispatch::Config is fine for small systems with
1891 simple logging requirements. However, if you're designing a system with
1892 lots of subsystems which you need to control independently, you'll love
1893 the features of "Log::Log4perl", which is equally easy to use.
1894
1896 If you don't use "Log::Log4perl" as described above, but from a wrapper
1897 function, the pattern layout will generate wrong data for %F, %C, %L,
1898 and the like. Reason for this is that "Log::Log4perl"'s loggers assume
1899 a static caller depth to the application that's using them.
1900 If you're using one (or more) wrapper functions, "Log::Log4perl" will
1902 indicate where your logger function called the loggers, not where your
1903 application called your wrapper:
1904 use Log::Log4perl qw(:easy);
1906 Log::Log4perl->easy_init({ level => $DEBUG,
1907 layout => "%M %m%n" });
1908 sub mylog {
1910 my($message) = @_;
1911 DEBUG $message;
1913 }
1914 sub func {
1916 mylog "Hello";
1917 }
1918 func();
1920 prints
1922 main::mylog Hello
1924 but that's probably not what your application expects. Rather, you'd
1926 want
1927 main::func Hello
1929 because the "func" function called your logging function.
1931 But don't despair, there's a solution: Just register your wrapper
1933 package with Log4perl beforehand. If Log4perl then finds that it's
1934 being called from a registered wrapper, it will automatically step up
1935 to the next call frame.
1936 Log::Log4perl->wrapper_register(__PACKAGE__);
1938 sub mylog {
1940 my($message) = @_;
1941 DEBUG $message;
1943 }
1944 Alternatively, you can increase the value of the global variable
1946 $Log::Log4perl::caller_depth (defaults to 0) by one for every wrapper
1947 that's in between your application and "Log::Log4perl", then
1948 "Log::Log4perl" will compensate for the difference:
1949 sub mylog {
1951 my($message) = @_;
1952 local $Log::Log4perl::caller_depth =
1954 $Log::Log4perl::caller_depth + 1;
1955 DEBUG $message;
1956 }
1957 Also, note that if you're writing a subclass of Log4perl, like
1959 package MyL4pWrapper;
1961 use Log::Log4perl;
1962 our @ISA = qw(Log::Log4perl);
1963 and you want to call get_logger() in your code, like
1965 use MyL4pWrapper;
1967 sub get_logger {
1969 my $logger = Log::Log4perl->get_logger();
1970 }
1971 then the get_logger() call will get a logger for the "MyL4pWrapper"
1973 category, not for the package calling the wrapper class as in
1974 package UserPackage;
1976 my $logger = MyL4pWrapper->get_logger();
1977 To have the above call to get_logger return a logger for the
1979 "UserPackage" category, you need to tell Log4perl that "MyL4pWrapper"
1980 is a Log4perl wrapper class:
1981 use MyL4pWrapper;
1983 Log::Log4perl->wrapper_register(__PACKAGE__);
1984 sub get_logger {
1986 # Now gets a logger for the category of the calling package
1987 my $logger = Log::Log4perl->get_logger();
1988 }
1989 This feature works both for Log4perl-relaying classes like the wrapper
1991 described above, and for wrappers that inherit from Log4perl use
1992 Log4perl's get_logger function via inheritance, alike.
1993
1995 The following methods are only of use if you want to peek/poke in the
1996 internals of Log::Log4perl. Be careful not to disrupt its inner
1997 workings.
1998 "Log::Log4perl->appenders()"
2000 To find out which appenders are currently defined (not only for a
2001 particular logger, but overall), a "appenders()" method is
2002 available to return a reference to a hash mapping appender names to
2003 their Log::Log4perl::Appender object references.
2004
2006 infiltrate_lwp()
2007 The famous LWP::UserAgent module isn't Log::Log4perl-enabled.
2008 Often, though, especially when tracing Web-related problems, it
2009 would be helpful to get some insight on what's happening inside
2010 LWP::UserAgent. Ideally, LWP::UserAgent would even play along in
2011 the Log::Log4perl framework.
2012 A call to "Log::Log4perl->infiltrate_lwp()" does exactly this. In
2014 a very rude way, it pulls the rug from under LWP::UserAgent and
2015 transforms its "debug/conn" messages into "debug()" calls of
2016 loggers of the category "LWP::UserAgent". Similarily,
2017 "LWP::UserAgent"'s "trace" messages are turned into
2018 "Log::Log4perl"'s "info()" method calls. Note that this only works
2019 for LWP::UserAgent versions < 5.822, because this (and probably
2020 later) versions miss debugging functions entirely.
2021 Suppressing 'duplicate' LOGDIE messages
2023 If a script with a simple Log4perl configuration uses logdie() to
2024 catch errors and stop processing, as in
2025 use Log::Log4perl qw(:easy) ;
2027 Log::Log4perl->easy_init($DEBUG);
2028 shaky_function() or LOGDIE "It failed!";
2030 there's a cosmetic problem: The message gets printed twice:
2032 2005/07/10 18:37:14 It failed!
2034 It failed! at ./t line 12
2035 The obvious solution is to use LOGEXIT() instead of LOGDIE(), but
2037 there's also a special tag for Log4perl that suppresses the second
2038 message:
2039 use Log::Log4perl qw(:no_extra_logdie_message);
2041 This causes logdie() and logcroak() to call exit() instead of
2043 die(). To modify the script exit code in these occasions, set the
2044 variable $Log::Log4perl::LOGEXIT_CODE to the desired value, the
2045 default is 1.
2046 Redefine values without causing errors
2048 Log4perl's configuration file parser has a few basic safety
2049 mechanisms to make sure configurations are more or less sane.
2050 One of these safety measures is catching redefined values. For
2052 example, if you first write
2053 log4perl.category = WARN, Logfile
2055 and then a couple of lines later
2057 log4perl.category = TRACE, Logfile
2059 then you might have unintentionally overwritten the first value and
2061 Log4perl will die on this with an error (suspicious configurations
2062 always throw an error). Now, there's a chance that this is
2063 intentional, for example when you're lumping together several
2064 configuration files and actually want the first value to overwrite
2065 the second. In this case use
2066 use Log::Log4perl qw(:nostrict);
2068 to put Log4perl in a more permissive mode.
2070 Prevent croak/confess from stringifying
2072 The logcroak/logconfess functions stringify their arguments before
2073 they pass them to Carp's croak/confess functions. This can get in
2074 the way if you want to throw an object or a hashref as an
2075 exception, in this case use:
2076 $Log::Log4perl::STRINGIFY_DIE_MESSAGE = 0;
2078 eval {
2080 # throws { foo => "bar" }
2081 # without stringification
2082 $logger->logcroak( { foo => "bar" } );
2083 };
2084
2086 A simple example to cut-and-paste and get started:
2087 use Log::Log4perl qw(get_logger);
2089 my $conf = q(
2091 log4perl.category.Bar.Twix = WARN, Logfile
2092 log4perl.appender.Logfile = Log::Log4perl::Appender::File
2093 log4perl.appender.Logfile.filename = test.log
2094 log4perl.appender.Logfile.layout = \
2095 Log::Log4perl::Layout::PatternLayout
2096 log4perl.appender.Logfile.layout.ConversionPattern = %d %F{1} %L> %m %n
2097 );
2098 Log::Log4perl::init(\$conf);
2100 my $logger = get_logger("Bar::Twix");
2102 $logger->error("Blah");
2103 This will log something like
2105 2002/09/19 23:48:15 t1 25> Blah
2107 to the log file "test.log", which Log4perl will append to or create it
2109 if it doesn't exist already.
2110
2112 If you want to use external appenders provided with "Log::Dispatch",
2113 you need to install "Log::Dispatch" (2.00 or better) from CPAN, which
2114 itself depends on "Attribute-Handlers" and "Params-Validate". And a lot
2115 of other modules, that's the reason why we're now shipping
2116 Log::Log4perl with its own standard appenders and only if you wish to
2117 use additional ones, you'll have to go through the "Log::Dispatch"
2118 installation process.
2119 Log::Log4perl needs "Test::More", "Test::Harness" and "File::Spec", but
2121 they already come with fairly recent versions of perl. If not,
2122 everything's automatically fetched from CPAN if you're using the CPAN
2123 shell (CPAN.pm), because they're listed as dependencies.
2124 "Time::HiRes" (1.20 or better) is required only if you need the fine-
2126 grained time stamps of the %r parameter in
2127 "Log::Log4perl::Layout::PatternLayout".
2128 Manual installation works as usual with
2130 perl Makefile.PL
2132 make
2133 make test
2134 make install
2135
2137 Log::Log4perl is still being actively developed. We will always make
2138 sure the test suite (approx. 500 cases) will pass, but there might
2139 still be bugs. please check <http://github.com/mschilli/log4perl> for
2140 the latest release. The api has reached a mature state, we will not
2141 change it unless for a good reason.
2142 Bug reports and feedback are always welcome, just email them to our
2144 mailing list shown in the AUTHORS section. We're usually addressing
2145 them immediately.
2146
2148 [1] Michael Schilli, "Retire your debugger, log smartly with
2149 Log::Log4perl!", Tutorial on perl.com, 09/2002,
2150 <http://www.perl.com/pub/a/2002/09/11/log4perl.html>
2151 [2] Ceki Gülcü, "Short introduction to log4j",
2153 <http://logging.apache.org/log4j/1.2/manual.html>
2154 [3] Vipan Singla, "Don't Use System.out.println! Use Log4j.",
2156 <http://www.vipan.com/htdocs/log4jhelp.html>
2157 [4] The Log::Log4perl project home page: <http://log4perl.com>
2159
2161 Log::Log4perl::Config, Log::Log4perl::Appender,
2162 Log::Log4perl::Layout::PatternLayout,
2163 Log::Log4perl::Layout::SimpleLayout, Log::Log4perl::Level,
2164 Log::Log4perl::JavaMap Log::Log4perl::NDC,
2165
2167 Please contribute patches to the project on Github:
2168 http://github.com/mschilli/log4perl
2170 Send bug reports or requests for enhancements to the authors via our
2172 MAILING LIST (questions, bug reports, suggestions/patches):
2174 log4perl-devel@lists.sourceforge.net
2175 Authors (please contact them via the list above, not directly): Mike
2177 Schilli <m@perlmeister.com>, Kevin Goess <cpan@goess.org>
2178 Contributors (in alphabetical order): Ateeq Altaf, Cory Bennett, Jens
2180 Berthold, Jeremy Bopp, Hutton Davidson, Chris R. Donnelly, Matisse
2181 Enzer, Hugh Esco, Anthony Foiani, James FitzGibbon, Carl Franks, Dennis
2182 Gregorovic, Andy Grundman, Paul Harrington, Alexander Hartmaier, David
2183 Hull, Robert Jacobson, Jason Kohles, Jeff Macdonald, Markus Peter,
2184 Brett Rann, Peter Rabbitson, Erik Selberg, Aaron Straup Cope, Lars
2185 Thegler, David Viner, Mac Yang.
2186
2188 Copyright 2002-2013 by Mike Schilli <m@perlmeister.com> and Kevin Goess
2189 <cpan@goess.org>.
2190 This library is free software; you can redistribute it and/or modify it
2192 under the same terms as Perl itself.
2193perl v5.34.0 2022-01-21 Log::Log4perl(3)