1###################################################################### 2 Log::Log4perl 1.49 3###################################################################### 4 5NAME 6 Log::Log4perl - Log4j implementation for Perl 7 8SYNOPSIS 9 # Easy mode if you like it simple ... 10 11 use Log::Log4perl qw(:easy); 12 Log::Log4perl->easy_init($ERROR); 13 14 DEBUG "This doesn't go anywhere"; 15 ERROR "This gets logged"; 16 17 # ... or standard mode for more features: 18 19 Log::Log4perl::init('/etc/log4perl.conf'); 20 21 --or-- 22 23 # Check config every 10 secs 24 Log::Log4perl::init_and_watch('/etc/log4perl.conf',10); 25 26 --then-- 27 28 $logger = Log::Log4perl->get_logger('house.bedrm.desk.topdrwr'); 29 30 $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 36 #####/etc/log4perl.conf############################### 37 log4perl.logger.house = WARN, FileAppndr1 38 log4perl.logger.house.bedroom.desk = DEBUG, FileAppndr1 39 40 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 46ABSTRACT 47 Log::Log4perl provides a powerful logging API for your application 48 49DESCRIPTION 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 54 For a detailed tutorial on Log::Log4perl usage, please read 55 56 <http://www.perl.com/pub/a/2002/09/11/log4perl.html> 57 58 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 won't 61 help you. 62 63 "Log::Log4perl" is different. It allows you to control the number of 64 logging messages generated at three different levels: 65 66 * At a central location in your system (either in a configuration file 67 or in the startup code) you specify *which components* (classes, 68 functions) of your system should generate logs. 69 70 * You specify how detailed the logging of these components should be 71 by specifying logging *levels*. 72 73 * 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 file 76 name and line number, and then the log message") they should be in. 77 78 This is a very powerful and flexible mechanism. You can turn on and off 79 your logs at any time, specify the level of detail and make that 80 dependent on the subsystem that's currently executed. 81 82 Let me give you an example: You might find out that your system has a 83 problem in the "MySystem::Helpers::ScanDir" component. Turning on 84 detailed debugging logs all over the system would generate a flood of 85 useless log messages and bog your system down beyond recognition. With 86 "Log::Log4perl", however, you can tell the system: "Continue to log only 87 severe errors to the log file. Open a second log file, turn on full 88 debug logs in the "MySystem::Helpers::ScanDir" component and dump all 89 messages originating from there into the new log file". And all this is 90 possible by just changing the parameters in a configuration file, which 91 your system can re-read even while it's running! 92 93How to use it 94 The "Log::Log4perl" package can be initialized in two ways: Either via 95 Perl commands or via a "log4j"-style configuration file. 96 97 Initialize via a configuration file 98 This is the easiest way to prepare your system for using 99 "Log::Log4perl". Use a configuration file like this: 100 101 ############################################################ 102 # A simple root logger with a Log::Log4perl::Appender::File 103 # file appender in Perl. 104 ############################################################ 105 log4perl.rootLogger=ERROR, LOGFILE 106 107 log4perl.appender.LOGFILE=Log::Log4perl::Appender::File 108 log4perl.appender.LOGFILE.filename=/var/log/myerrs.log 109 log4perl.appender.LOGFILE.mode=append 110 111 log4perl.appender.LOGFILE.layout=PatternLayout 112 log4perl.appender.LOGFILE.layout.ConversionPattern=[%r] %F %L %c - %m%n 113 114 These lines define your standard logger that's appending severe errors 115 to "/var/log/myerrs.log", using the format 116 117 [millisecs] source-filename line-number class - message newline 118 119 Assuming that this configuration file is saved as "log.conf", you need 120 to read it in the startup section of your code, using the following 121 commands: 122 123 use Log::Log4perl; 124 Log::Log4perl->init("log.conf"); 125 126 After that's done *somewhere* in the code, you can retrieve logger 127 objects *anywhere* in the code. Note that there's no need to carry any 128 logger references around with your functions and methods. You can get a 129 logger anytime via a singleton mechanism: 130 131 package My::MegaPackage; 132 use Log::Log4perl; 133 134 sub some_method { 135 my($param) = @_; 136 137 my $log = Log::Log4perl->get_logger("My::MegaPackage"); 138 139 $log->debug("Debug message"); 140 $log->info("Info message"); 141 $log->error("Error message"); 142 143 ... 144 } 145 146 With the configuration file above, "Log::Log4perl" will write "Error 147 message" to the specified log file, but won't do anything for the 148 "debug()" and "info()" calls, because the log level has been set to 149 "ERROR" for all components in the first line of configuration file shown 150 above. 151 152 Why "Log::Log4perl->get_logger" and not "Log::Log4perl->new"? We don't 153 want to create a new object every time. Usually in OO-Programming, you 154 create an object once and use the reference to it to call its methods. 155 However, this requires that you pass around the object to all functions 156 and the last thing we want is pollute each and every function/method 157 we're using with a handle to the "Logger": 158 159 sub function { # Brrrr!! 160 my($logger, $some, $other, $parameters) = @_; 161 } 162 163 Instead, if a function/method wants a reference to the logger, it just 164 calls the Logger's static "get_logger($category)" method to obtain a 165 reference to the *one and only* possible logger object of a certain 166 category. That's called a *singleton* if you're a Gamma fan. 167 168 How does the logger know which messages it is supposed to log and which 169 ones to suppress? "Log::Log4perl" works with inheritance: The config 170 file above didn't specify anything about "My::MegaPackage". And yet, 171 we've defined a logger of the category "My::MegaPackage". In this case, 172 "Log::Log4perl" will walk up the namespace hierarchy ("My" and then 173 we're at the root) to figure out if a log level is defined somewhere. In 174 the case above, the log level at the root (root *always* defines a log 175 level, but not necessarily an appender) defines that the log level is 176 supposed to be "ERROR" -- meaning that *DEBUG* and *INFO* messages are 177 suppressed. Note that this 'inheritance' is unrelated to Perl's class 178 inheritance, it is merely related to the logger namespace. By the way, 179 if you're ever in doubt about what a logger's category is, use 180 "$logger->category()" to retrieve it. 181 182 Log Levels 183 There are six predefined log levels: "FATAL", "ERROR", "WARN", "INFO", 184 "DEBUG", and "TRACE" (in descending priority). Your configured logging 185 level has to at least match the priority of the logging message. 186 187 If your configured logging level is "WARN", then messages logged with 188 "info()", "debug()", and "trace()" will be suppressed. "fatal()", 189 "error()" and "warn()" will make their way through, because their 190 priority is higher or equal than the configured setting. 191 192 Instead of calling the methods 193 194 $logger->trace("..."); # Log a trace message 195 $logger->debug("..."); # Log a debug message 196 $logger->info("..."); # Log a info message 197 $logger->warn("..."); # Log a warn message 198 $logger->error("..."); # Log a error message 199 $logger->fatal("..."); # Log a fatal message 200 201 you could also call the "log()" method with the appropriate level using 202 the constants defined in "Log::Log4perl::Level": 203 204 use Log::Log4perl::Level; 205 206 $logger->log($TRACE, "..."); 207 $logger->log($DEBUG, "..."); 208 $logger->log($INFO, "..."); 209 $logger->log($WARN, "..."); 210 $logger->log($ERROR, "..."); 211 $logger->log($FATAL, "..."); 212 213 This form is rarely used, but it comes in handy if you want to log at 214 different levels depending on an exit code of a function: 215 216 $logger->log( $exit_level{ $rc }, "..."); 217 218 As for needing more logging levels than these predefined ones: It's 219 usually best to steer your logging behaviour via the category mechanism 220 instead. 221 222 If you need to find out if the currently configured logging level would 223 allow a logger's logging statement to go through, use the logger's 224 "is_*level*()" methods: 225 226 $logger->is_trace() # True if trace messages would go through 227 $logger->is_debug() # True if debug messages would go through 228 $logger->is_info() # True if info messages would go through 229 $logger->is_warn() # True if warn messages would go through 230 $logger->is_error() # True if error messages would go through 231 $logger->is_fatal() # True if fatal messages would go through 232 233 Example: "$logger->is_warn()" returns true if the logger's current 234 level, as derived from either the logger's category (or, in absence of 235 that, one of the logger's parent's level setting) is $WARN, $ERROR or 236 $FATAL. 237 238 Also available are a series of more Java-esque functions which return 239 the same values. These are of the format "is*Level*Enabled()", so 240 "$logger->isDebugEnabled()" is synonymous to "$logger->is_debug()". 241 242 These level checking functions will come in handy later, when we want to 243 block unnecessary expensive parameter construction in case the logging 244 level is too low to log the statement anyway, like in: 245 246 if($logger->is_error()) { 247 $logger->error("Erroneous array: @super_long_array"); 248 } 249 250 If we had just written 251 252 $logger->error("Erroneous array: @super_long_array"); 253 254 then Perl would have interpolated @super_long_array into the string via 255 an expensive operation only to figure out shortly after that the string 256 can be ignored entirely because the configured logging level is lower 257 than $ERROR. 258 259 The to-be-logged message passed to all of the functions described above 260 can consist of an arbitrary number of arguments, which the logging 261 functions just chain together to a single string. Therefore 262 263 $logger->debug("Hello ", "World", "!"); # and 264 $logger->debug("Hello World!"); 265 266 are identical. 267 268 Note that even if one of the methods above returns true, it doesn't 269 necessarily mean that the message will actually get logged. What 270 is_debug() checks is that the logger used is configured to let a message 271 of the given priority (DEBUG) through. But after this check, Log4perl 272 will eventually apply custom filters and forward the message to one or 273 more appenders. None of this gets checked by is_xxx(), for the simple 274 reason that it's impossible to know what a custom filter does with a 275 message without having the actual message or what an appender does to a 276 message without actually having it log it. 277 278 Log and die or warn 279 Often, when you croak / carp / warn / die, you want to log those 280 messages. Rather than doing the following: 281 282 $logger->fatal($err) && die($err); 283 284 you can use the following: 285 286 $logger->logdie($err); 287 288 And if instead of using 289 290 warn($message); 291 $logger->warn($message); 292 293 to both issue a warning via Perl's warn() mechanism and make sure you 294 have the same message in the log file as well, use: 295 296 $logger->logwarn($message); 297 298 Since there is an ERROR level between WARN and FATAL, there are two 299 additional helper functions in case you'd like to use ERROR for either 300 warn() or die(): 301 302 $logger->error_warn(); 303 $logger->error_die(); 304 305 Finally, there's the Carp functions that, in addition to logging, also 306 pass the stringified message to their companions in the Carp package: 307 308 $logger->logcarp(); # warn w/ 1-level stack trace 309 $logger->logcluck(); # warn w/ full stack trace 310 $logger->logcroak(); # die w/ 1-level stack trace 311 $logger->logconfess(); # die w/ full stack trace 312 313 Appenders 314 If you don't define any appenders, nothing will happen. Appenders will 315 be triggered whenever the configured logging level requires a message to 316 be logged and not suppressed. 317 318 "Log::Log4perl" doesn't define any appenders by default, not even the 319 root logger has one. 320 321 "Log::Log4perl" already comes with a standard set of appenders: 322 323 Log::Log4perl::Appender::Screen 324 Log::Log4perl::Appender::ScreenColoredLevels 325 Log::Log4perl::Appender::File 326 Log::Log4perl::Appender::Socket 327 Log::Log4perl::Appender::DBI 328 Log::Log4perl::Appender::Synchronized 329 Log::Log4perl::Appender::RRDs 330 331 to log to the screen, to files and to databases. 332 333 On CPAN, you can find additional appenders like 334 335 Log::Log4perl::Layout::XMLLayout 336 337 by Guido Carls <gcarls@cpan.org>. It allows for hooking up Log::Log4perl 338 with the graphical Log Analyzer Chainsaw (see "Can I use Log::Log4perl 339 with log4j's Chainsaw?" in Log::Log4perl::FAQ). 340 341 Additional Appenders via Log::Dispatch 342 "Log::Log4perl" also supports *Dave Rolskys* excellent "Log::Dispatch" 343 framework which implements a wide variety of different appenders. 344 345 Here's the list of appender modules currently available via 346 "Log::Dispatch": 347 348 Log::Dispatch::ApacheLog 349 Log::Dispatch::DBI (by Tatsuhiko Miyagawa) 350 Log::Dispatch::Email, 351 Log::Dispatch::Email::MailSend, 352 Log::Dispatch::Email::MailSendmail, 353 Log::Dispatch::Email::MIMELite 354 Log::Dispatch::File 355 Log::Dispatch::FileRotate (by Mark Pfeiffer) 356 Log::Dispatch::Handle 357 Log::Dispatch::Screen 358 Log::Dispatch::Syslog 359 Log::Dispatch::Tk (by Dominique Dumont) 360 361 Please note that in order to use any of these additional appenders, you 362 have to fetch Log::Dispatch from CPAN and install it. Also the 363 particular appender you're using might require installing the particular 364 module. 365 366 For additional information on appenders, please check the 367 Log::Log4perl::Appender manual page. 368 369 Appender Example 370 Now let's assume that we want to log "info()" or higher prioritized 371 messages in the "Foo::Bar" category to both STDOUT and to a log file, 372 say "test.log". In the initialization section of your system, just 373 define two appenders using the readily available 374 "Log::Log4perl::Appender::File" and "Log::Log4perl::Appender::Screen" 375 modules: 376 377 use Log::Log4perl; 378 379 # Configuration in a string ... 380 my $conf = q( 381 log4perl.category.Foo.Bar = INFO, Logfile, Screen 382 383 log4perl.appender.Logfile = Log::Log4perl::Appender::File 384 log4perl.appender.Logfile.filename = test.log 385 log4perl.appender.Logfile.layout = Log::Log4perl::Layout::PatternLayout 386 log4perl.appender.Logfile.layout.ConversionPattern = [%r] %F %L %m%n 387 388 log4perl.appender.Screen = Log::Log4perl::Appender::Screen 389 log4perl.appender.Screen.stderr = 0 390 log4perl.appender.Screen.layout = Log::Log4perl::Layout::SimpleLayout 391 ); 392 393 # ... passed as a reference to init() 394 Log::Log4perl::init( \$conf ); 395 396 Once the initialization shown above has happened once, typically in the 397 startup code of your system, just use the defined logger anywhere in 398 your system: 399 400 ########################## 401 # ... in some function ... 402 ########################## 403 my $log = Log::Log4perl::get_logger("Foo::Bar"); 404 405 # Logs both to STDOUT and to the file test.log 406 $log->info("Important Info!"); 407 408 The "layout" settings specified in the configuration section define the 409 format in which the message is going to be logged by the specified 410 appender. The format shown for the file appender is logging not only the 411 message but also the number of milliseconds since the program has 412 started (%r), the name of the file the call to the logger has happened 413 and the line number there (%F and %L), the message itself (%m) and a 414 OS-specific newline character (%n): 415 416 [187] ./myscript.pl 27 Important Info! 417 418 The screen appender above, on the other hand, uses a "SimpleLayout", 419 which logs the debug level, a hyphen (-) and the log message: 420 421 INFO - Important Info! 422 423 For more detailed info on layout formats, see "Log Layouts". 424 425 In the configuration sample above, we chose to define a *category* 426 logger ("Foo::Bar"). This will cause only messages originating from this 427 specific category logger to be logged in the defined format and 428 locations. 429 430 Logging newlines 431 There's some controversy between different logging systems as to when 432 and where newlines are supposed to be added to logged messages. 433 434 The Log4perl way is that a logging statement *should not* contain a 435 newline: 436 437 $logger->info("Some message"); 438 $logger->info("Another message"); 439 440 If this is supposed to end up in a log file like 441 442 Some message 443 Another message 444 445 then an appropriate appender layout like "%m%n" will take care of adding 446 a newline at the end of each message to make sure every message is 447 printed on its own line. 448 449 Other logging systems, Log::Dispatch in particular, recommend adding the 450 newline to the log statement. This doesn't work well, however, if you, 451 say, replace your file appender by a database appender, and all of a 452 sudden those newlines scattered around the code don't make sense 453 anymore. 454 455 Assigning matching layouts to different appenders and leaving newlines 456 out of the code solves this problem. If you inherited code that has 457 logging statements with newlines and want to make it work with Log4perl, 458 read the Log::Log4perl::Layout::PatternLayout documentation on how to 459 accomplish that. 460 461 Configuration files 462 As shown above, you can define "Log::Log4perl" loggers both from within 463 your Perl code or from configuration files. The latter have the 464 unbeatable advantage that you can modify your system's logging behaviour 465 without interfering with the code at all. So even if your code is being 466 run by somebody who's totally oblivious to Perl, they still can adapt 467 the module's logging behaviour to their needs. 468 469 "Log::Log4perl" has been designed to understand "Log4j" configuration 470 files -- as used by the original Java implementation. Instead of 471 reiterating the format description in [2], let me just list three 472 examples (also derived from [2]), which should also illustrate how it 473 works: 474 475 log4j.rootLogger=DEBUG, A1 476 log4j.appender.A1=org.apache.log4j.ConsoleAppender 477 log4j.appender.A1.layout=org.apache.log4j.PatternLayout 478 log4j.appender.A1.layout.ConversionPattern=%-4r %-5p %c %x - %m%n 479 480 This enables messages of priority "DEBUG" or higher in the root 481 hierarchy and has the system write them to the console. 482 "ConsoleAppender" is a Java appender, but "Log::Log4perl" jumps through 483 a significant number of hoops internally to map these to their 484 corresponding Perl classes, "Log::Log4perl::Appender::Screen" in this 485 case. 486 487 Second example: 488 489 log4perl.rootLogger=DEBUG, A1 490 log4perl.appender.A1=Log::Log4perl::Appender::Screen 491 log4perl.appender.A1.layout=PatternLayout 492 log4perl.appender.A1.layout.ConversionPattern=%d %-5p %c - %m%n 493 log4perl.logger.com.foo=WARN 494 495 This defines two loggers: The root logger and the "com.foo" logger. The 496 root logger is easily triggered by debug-messages, but the "com.foo" 497 logger makes sure that messages issued within the "Com::Foo" component 498 and below are only forwarded to the appender if they're of priority 499 *warning* or higher. 500 501 Note that the "com.foo" logger doesn't define an appender. Therefore, it 502 will just propagate the message up the hierarchy until the root logger 503 picks it up and forwards it to the one and only appender of the root 504 category, using the format defined for it. 505 506 Third example: 507 508 log4j.rootLogger=DEBUG, stdout, R 509 log4j.appender.stdout=org.apache.log4j.ConsoleAppender 510 log4j.appender.stdout.layout=org.apache.log4j.PatternLayout 511 log4j.appender.stdout.layout.ConversionPattern=%5p (%F:%L) - %m%n 512 log4j.appender.R=org.apache.log4j.RollingFileAppender 513 log4j.appender.R.File=example.log 514 log4j.appender.R.layout=org.apache.log4j.PatternLayout 515 log4j.appender.R.layout.ConversionPattern=%p %c - %m%n 516 517 The root logger defines two appenders here: "stdout", which uses 518 "org.apache.log4j.ConsoleAppender" (ultimately mapped by "Log::Log4perl" 519 to Log::Log4perl::Appender::Screen) to write to the screen. And "R", a 520 "org.apache.log4j.RollingFileAppender" (mapped by "Log::Log4perl" to 521 Log::Dispatch::FileRotate with the "File" attribute specifying the log 522 file. 523 524 See Log::Log4perl::Config for more examples and syntax explanations. 525 526 Log Layouts 527 If the logging engine passes a message to an appender, because it thinks 528 it should be logged, the appender doesn't just write it out haphazardly. 529 There's ways to tell the appender how to format the message and add all 530 sorts of interesting data to it: The date and time when the event 531 happened, the file, the line number, the debug level of the logger and 532 others. 533 534 There's currently two layouts defined in "Log::Log4perl": 535 "Log::Log4perl::Layout::SimpleLayout" and 536 "Log::Log4perl::Layout::PatternLayout": 537 538 "Log::Log4perl::SimpleLayout" 539 formats a message in a simple way and just prepends it by the debug 540 level and a hyphen: ""$level - $message", for example "FATAL - Can't 541 open password file". 542 543 "Log::Log4perl::Layout::PatternLayout" 544 on the other hand is very powerful and allows for a very flexible 545 format in "printf"-style. The format string can contain a number of 546 placeholders which will be replaced by the logging engine when it's 547 time to log the message: 548 549 %c Category of the logging event. 550 %C Fully qualified package (or class) name of the caller 551 %d Current date in yyyy/MM/dd HH:mm:ss format 552 %F File where the logging event occurred 553 %H Hostname (if Sys::Hostname is available) 554 %l Fully qualified name of the calling method followed by the 555 callers source the file name and line number between 556 parentheses. 557 %L Line number within the file where the log statement was issued 558 %m The message to be logged 559 %m{chomp} The message to be logged, stripped off a trailing newline 560 %M Method or function where the logging request was issued 561 %n Newline (OS-independent) 562 %p Priority of the logging event (AKA log level) 563 %P pid of the current process 564 %r Number of milliseconds elapsed from program start to logging 565 event 566 %R Number of milliseconds elapsed from last logging event to 567 current logging event 568 %T A stack trace of functions called 569 %x The topmost NDC (see below) 570 %X{key} The entry 'key' of the MDC (see below) 571 %% A literal percent (%) sign 572 573 NDC and MDC are explained in "Nested Diagnostic Context (NDC)" and 574 "Mapped Diagnostic Context (MDC)". 575 576 Also, %d can be fine-tuned to display only certain characteristics 577 of a date, according to the SimpleDateFormat in the Java World 578 (<https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/ 579 text/SimpleDateFormat.html>) 580 581 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, followed 583 by a spelled-out day (like "Wednesday"). 584 585 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. 588 %c{2} only logs the last two components of the current category, 589 "Foo::Bar::Baz" becomes "Bar::Baz" and saves space. 590 591 If those placeholders aren't enough, then you can define your own 592 right in the config file like this: 593 594 log4perl.PatternLayout.cspec.U = sub { return "UID $<" } 595 596 See Log::Log4perl::Layout::PatternLayout for further details on 597 customized specifiers. 598 599 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 qualify 601 functions and variables if they're located in different packages. 602 603 SECURITY NOTE: this feature means arbitrary perl code can be 604 embedded in the config file. In the rare case where the people who 605 have access to your config file are different from the people who 606 write your code and shouldn't have execute rights, you might want to 607 call 608 609 Log::Log4perl::Config->allow_code(0); 610 611 before you call init(). Alternatively you can supply a restricted 612 set of Perl opcodes that can be embedded in the config file as 613 described in "Restricting what Opcodes can be in a Perl Hook". 614 615 All placeholders are quantifiable, just like in *printf*. Following this 616 tradition, "%-20c" will reserve 20 chars for the category and 617 left-justify it. 618 619 For more details on logging and how to use the flexible and the simple 620 format, check out the original "log4j" website under 621 622 SimpleLayout 623 <http://logging.apache.org/log4j/1.2/apidocs/org/apache/log4j/SimpleLayo 624 ut.html> and PatternLayout 625 <http://logging.apache.org/log4j/1.2/apidocs/org/apache/log4j/PatternLay 626 out.html> 627 628 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. 631 632 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. 636 637 Here's a couple of tricks which help "Log::Log4perl" to avoid 638 unnecessary delays: 639 640 You can save serious time if you're logging something like 641 642 # Expensive in non-debug mode! 643 for (@super_long_array) { 644 $logger->debug("Element: $_"); 645 } 646 647 and @super_long_array is fairly big, so looping through it is pretty 648 expensive. Only you, the programmer, knows that going through that "for" 649 loop can be skipped entirely if the current logging level for the actual 650 component is higher than "debug". In this case, use this instead: 651 652 # Cheap in non-debug mode! 653 if($logger->is_debug()) { 654 for (@super_long_array) { 655 $logger->debug("Element: $_"); 656 } 657 } 658 659 If you're afraid that generating the parameters to the logging function 660 is fairly expensive, use closures: 661 662 # Passed as subroutine ref 663 use Data::Dumper; 664 $logger->debug(sub { Dumper($data) } ); 665 666 This won't unravel $data via Dumper() unless it's actually needed 667 because it's logged. 668 669 Also, Log::Log4perl lets you specify arguments to logger functions in 670 *message output filter syntax*: 671 672 $logger->debug("Structure: ", 673 { filter => \&Dumper, 674 value => $someref }); 675 676 In this way, shortly before Log::Log4perl sending the message out to any 677 appenders, it will be searching all arguments for hash references and 678 treat them in a special way: 679 680 It will invoke the function given as a reference with the "filter" key 681 ("Data::Dumper::Dumper()") and pass it the value that came with the key 682 named "value" as an argument. The anonymous hash in the call above will 683 be replaced by the return value of the filter function. 684 685Categories 686 Categories are also called "Loggers" in Log4perl, both refer to the same 687 thing and these terms are used interchangeably. "Log::Log4perl" uses 688 *categories* to determine if a log statement in a component should be 689 executed or suppressed at the current logging level. Most of the time, 690 these categories are just the classes the log statements are located in: 691 692 package Candy::Twix; 693 694 sub new { 695 my $logger = Log::Log4perl->get_logger("Candy::Twix"); 696 $logger->debug("Creating a new Twix bar"); 697 bless {}, shift; 698 } 699 700 # ... 701 702 package Candy::Snickers; 703 704 sub new { 705 my $logger = Log::Log4perl->get_logger("Candy.Snickers"); 706 $logger->debug("Creating a new Snickers bar"); 707 bless {}, shift; 708 } 709 710 # ... 711 712 package main; 713 Log::Log4perl->init("mylogdefs.conf"); 714 715 # => "LOG> Creating a new Snickers bar" 716 my $first = Candy::Snickers->new(); 717 # => "LOG> Creating a new Twix bar" 718 my $second = Candy::Twix->new(); 719 720 Note that you can separate your category hierarchy levels using either 721 dots like in Java (.) or double-colons (::) like in Perl. Both notations 722 are equivalent and are handled the same way internally. 723 724 However, categories are just there to make use of inheritance: if you 725 invoke a logger in a sub-category, it will bubble up the hierarchy and 726 call the appropriate appenders. Internally, categories are not related 727 to the class hierarchy of the program at all -- they're purely virtual. 728 You can use arbitrary categories -- for example in the following 729 program, which isn't oo-style, but procedural: 730 731 sub print_portfolio { 732 733 my $log = Log::Log4perl->get_logger("user.portfolio"); 734 $log->debug("Quotes requested: @_"); 735 736 for(@_) { 737 print "$_: ", get_quote($_), "\n"; 738 } 739 } 740 741 sub get_quote { 742 743 my $log = Log::Log4perl->get_logger("internet.quotesystem"); 744 $log->debug("Fetching quote: $_[0]"); 745 746 return yahoo_quote($_[0]); 747 } 748 749 The logger in first function, "print_portfolio", is assigned the 750 (virtual) "user.portfolio" category. Depending on the "Log4perl" 751 configuration, this will either call a "user.portfolio" appender, a 752 "user" appender, or an appender assigned to root -- without 753 "user.portfolio" having any relevance to the class system used in the 754 program. The logger in the second function adheres to the 755 "internet.quotesystem" category -- again, maybe because it's bundled 756 with other Internet functions, but not because there would be a class of 757 this name somewhere. 758 759 However, be careful, don't go overboard: if you're developing a system 760 in object-oriented style, using the class hierarchy is usually your best 761 choice. Think about the people taking over your code one day: The class 762 hierarchy is probably what they know right up front, so it's easy for 763 them to tune the logging to their needs. 764 765 Turn off a component 766 "Log4perl" doesn't only allow you to selectively switch *on* a category 767 of log messages, you can also use the mechanism to selectively *disable* 768 logging in certain components whereas logging is kept turned on in 769 higher-level categories. This mechanism comes in handy if you find that 770 while bumping up the logging level of a high-level (i. e. close to root) 771 category, that one component logs more than it should, 772 773 Here's how it works: 774 775 ############################################################ 776 # Turn off logging in a lower-level category while keeping 777 # it active in higher-level categories. 778 ############################################################ 779 log4perl.rootLogger=DEBUG, LOGFILE 780 log4perl.logger.deep.down.the.hierarchy = ERROR, LOGFILE 781 782 # ... Define appenders ... 783 784 This way, log messages issued from within "Deep::Down::The::Hierarchy" 785 and below will be logged only if they're "ERROR" or worse, while in all 786 other system components even "DEBUG" messages will be logged. 787 788 Return Values 789 All logging methods return values indicating if their message actually 790 reached one or more appenders. If the message has been suppressed 791 because of level constraints, "undef" is returned. 792 793 For example, 794 795 my $ret = $logger->info("Message"); 796 797 will return "undef" if the system debug level for the current category 798 is not "INFO" or more permissive. If Log::Log4perl forwarded the message 799 to one or more appenders, the number of appenders is returned. 800 801 If appenders decide to veto on the message with an appender threshold, 802 the log method's return value will have them excluded. This means that 803 if you've got one appender holding an appender threshold and you're 804 logging a message which passes the system's log level hurdle but not the 805 appender threshold, 0 will be returned by the log function. 806 807 The bottom line is: Logging functions will return a *true* value if the 808 message made it through to one or more appenders and a *false* value if 809 it didn't. This allows for constructs like 810 811 $logger->fatal("@_") or print STDERR "@_\n"; 812 813 which will ensure that the fatal message isn't lost if the current level 814 is lower than FATAL or printed twice if the level is acceptable but an 815 appender already points to STDERR. 816 817 Pitfalls with Categories 818 Be careful with just blindly reusing the system's packages as 819 categories. If you do, you'll get into trouble with inherited methods. 820 Imagine the following class setup: 821 822 use Log::Log4perl; 823 824 ########################################### 825 package Bar; 826 ########################################### 827 sub new { 828 my($class) = @_; 829 my $logger = Log::Log4perl::get_logger(__PACKAGE__); 830 $logger->debug("Creating instance"); 831 bless {}, $class; 832 } 833 ########################################### 834 package Bar::Twix; 835 ########################################### 836 our @ISA = qw(Bar); 837 838 ########################################### 839 package main; 840 ########################################### 841 Log::Log4perl->init(\ qq{ 842 log4perl.category.Bar.Twix = DEBUG, Screen 843 log4perl.appender.Screen = Log::Log4perl::Appender::Screen 844 log4perl.appender.Screen.layout = SimpleLayout 845 }); 846 847 my $bar = Bar::Twix->new(); 848 849 "Bar::Twix" just inherits everything from "Bar", including the 850 constructor "new()". Contrary to what you might be thinking at first, 851 this won't log anything. Reason for this is the "get_logger()" call in 852 package "Bar", which will always get a logger of the "Bar" category, 853 even if we call "new()" via the "Bar::Twix" package, which will make 854 perl go up the inheritance tree to actually execute "Bar::new()". Since 855 we've only defined logging behaviour for "Bar::Twix" in the 856 configuration file, nothing will happen. 857 858 This can be fixed by changing the "get_logger()" method in "Bar::new()" 859 to obtain a logger of the category matching the *actual* class of the 860 object, like in 861 862 # ... in Bar::new() ... 863 my $logger = Log::Log4perl::get_logger( $class ); 864 865 In a method other than the constructor, the class name of the actual 866 object can be obtained by calling "ref()" on the object reference, so 867 868 package BaseClass; 869 use Log::Log4perl qw( get_logger ); 870 871 sub new { 872 bless {}, shift; 873 } 874 875 sub method { 876 my( $self ) = @_; 877 878 get_logger( ref $self )->debug( "message" ); 879 } 880 881 package SubClass; 882 our @ISA = qw(BaseClass); 883 884 is the recommended pattern to make sure that 885 886 my $sub = SubClass->new(); 887 $sub->meth(); 888 889 starts logging if the "SubClass" category (and not the "BaseClass" 890 category has logging enabled at the DEBUG level. 891 892 Initialize once and only once 893 It's important to realize that Log::Log4perl gets initialized once and 894 only once, typically at the start of a program or system. Calling 895 "init()" more than once will cause it to clobber the existing 896 configuration and *replace* it by the new one. 897 898 If you're in a traditional CGI environment, where every request is 899 handled by a new process, calling "init()" every time is fine. In 900 persistent environments like "mod_perl", however, Log::Log4perl should 901 be initialized either at system startup time (Apache offers startup 902 handlers for that) or via 903 904 # Init or skip if already done 905 Log::Log4perl->init_once($conf_file); 906 907 "init_once()" is identical to "init()", just with the exception that it 908 will leave a potentially existing configuration alone and will only call 909 "init()" if Log::Log4perl hasn't been initialized yet. 910 911 If you're just curious if Log::Log4perl has been initialized yet, the 912 check 913 914 if(Log::Log4perl->initialized()) { 915 # Yes, Log::Log4perl has already been initialized 916 } else { 917 # No, not initialized yet ... 918 } 919 920 can be used. 921 922 If you're afraid that the components of your system are stepping on each 923 other's toes or if you are thinking that different components should 924 initialize Log::Log4perl separately, try to consolidate your system to 925 use a centralized Log4perl configuration file and use Log4perl's 926 *categories* to separate your components. 927 928 Custom Filters 929 Log4perl allows the use of customized filters in its appenders to 930 control the output of messages. These filters might grep for certain 931 text chunks in a message, verify that its priority matches or exceeds a 932 certain level or that this is the 10th time the same message has been 933 submitted -- and come to a log/no log decision based upon these 934 circumstantial facts. 935 936 Check out Log::Log4perl::Filter for detailed instructions on how to use 937 them. 938 939 Performance 940 The performance of Log::Log4perl calls obviously depends on a lot of 941 things. But to give you a general idea, here's some rough numbers: 942 943 On a Pentium 4 Linux box at 2.4 GHz, you'll get through 944 945 * 500,000 suppressed log statements per second 946 947 * 30,000 logged messages per second (using an in-memory appender) 948 949 * init_and_watch delay mode: 300,000 suppressed, 30,000 logged. 950 init_and_watch signal mode: 450,000 suppressed, 30,000 logged. 951 952 Numbers depend on the complexity of the Log::Log4perl configuration. For 953 a more detailed benchmark test, check the "docs/benchmark.results.txt" 954 document in the Log::Log4perl distribution. 955 956Cool Tricks 957 Here's a collection of useful tricks for the advanced "Log::Log4perl" 958 user. For more, check the FAQ, either in the distribution 959 (Log::Log4perl::FAQ) or on <http://log4perl.sourceforge.net>. 960 961 Shortcuts 962 When getting an instance of a logger, instead of saying 963 964 use Log::Log4perl; 965 my $logger = Log::Log4perl->get_logger(); 966 967 it's often more convenient to import the "get_logger" method from 968 "Log::Log4perl" into the current namespace: 969 970 use Log::Log4perl qw(get_logger); 971 my $logger = get_logger(); 972 973 Please note this difference: To obtain the root logger, please use 974 "get_logger("")", call it without parameters ("get_logger()"), you'll 975 get the logger of a category named after the current package. 976 "get_logger()" is equivalent to "get_logger(__PACKAGE__)". 977 978 Alternative initialization 979 Instead of having "init()" read in a configuration file by specifying a 980 file name or passing it a reference to an open filehandle 981 ("Log::Log4perl->init( \*FILE )"), you can also pass in a reference to a 982 string, containing the content of the file: 983 984 Log::Log4perl->init( \$config_text ); 985 986 Also, if you've got the "name=value" pairs of the configuration in a 987 hash, you can just as well initialize "Log::Log4perl" with a reference 988 to it: 989 990 my %key_value_pairs = ( 991 "log4perl.rootLogger" => "ERROR, LOGFILE", 992 "log4perl.appender.LOGFILE" => "Log::Log4perl::Appender::File", 993 ... 994 ); 995 996 Log::Log4perl->init( \%key_value_pairs ); 997 998 Or also you can use a URL, see below: 999 1000 Using LWP to parse URLs 1001 (This section borrowed from XML::DOM::Parser by T.J. Mather). 1002 1003 The init() function now also supports URLs, e.g. 1004 *http://www.erols.com/enno/xsa.xml*. It uses LWP to download the file 1005 and then calls parse() on the resulting string. By default it will use a 1006 LWP::UserAgent that is created as follows: 1007 1008 use LWP::UserAgent; 1009 $LWP_USER_AGENT = LWP::UserAgent->new; 1010 $LWP_USER_AGENT->env_proxy; 1011 1012 Note that env_proxy reads proxy settings from environment variables, 1013 which is what Log4perl needs to do to get through our firewall. If you 1014 want to use a different LWP::UserAgent, you can set it with 1015 1016 Log::Log4perl::Config::set_LWP_UserAgent($my_agent); 1017 1018 Currently, LWP is used when the filename (passed to parsefile) starts 1019 with one of the following URL schemes: http, https, ftp, wais, gopher, 1020 or file (followed by a colon.) 1021 1022 Don't use this feature with init_and_watch(). 1023 1024 Automatic reloading of changed configuration files 1025 Instead of just statically initializing Log::Log4perl via 1026 1027 Log::Log4perl->init($conf_file); 1028 1029 there's a way to have Log::Log4perl periodically check for changes in 1030 the configuration and reload it if necessary: 1031 1032 Log::Log4perl->init_and_watch($conf_file, $delay); 1033 1034 In this mode, Log::Log4perl will examine the configuration file 1035 $conf_file every $delay seconds for changes via the file's last 1036 modification timestamp. If the file has been updated, it will be 1037 reloaded and replace the current Log::Log4perl configuration. 1038 1039 The way this works is that with every logger function called (debug(), 1040 is_debug(), etc.), Log::Log4perl will check if the delay interval has 1041 expired. If so, it will run a -M file check on the configuration file. 1042 If its timestamp has been modified, the current configuration will be 1043 dumped and new content of the file will be loaded. 1044 1045 This convenience comes at a price, though: Calling time() with every 1046 logging function call, especially the ones that are "suppressed" (!), 1047 will slow down these Log4perl calls by about 40%. 1048 1049 To alleviate this performance hit a bit, "init_and_watch()" can be 1050 configured to listen for a Unix signal to reload the configuration 1051 instead: 1052 1053 Log::Log4perl->init_and_watch($conf_file, 'HUP'); 1054 1055 This will set up a signal handler for SIGHUP and reload the 1056 configuration if the application receives this signal, e.g. via the 1057 "kill" command: 1058 1059 kill -HUP pid 1060 1061 where "pid" is the process ID of the application. This will bring you 1062 back to about 85% of Log::Log4perl's normal execution speed for 1063 suppressed statements. For details, check out "Performance". For more 1064 info on the signal handler, look for "SIGNAL MODE" in 1065 Log::Log4perl::Config::Watch. 1066 1067 If you have a somewhat long delay set between physical config file 1068 checks or don't want to use the signal associated with the config file 1069 watcher, you can trigger a configuration reload at the next possible 1070 time by calling "Log::Log4perl::Config->watcher->force_next_check()". 1071 1072 One thing to watch out for: If the configuration file contains a syntax 1073 or other fatal error, a running application will stop with "die" if this 1074 damaged configuration will be loaded during runtime, triggered either by 1075 a signal or if the delay period expired and the change is detected. This 1076 behaviour might change in the future. 1077 1078 To allow the application to intercept and control a configuration reload 1079 in init_and_watch mode, a callback can be specified: 1080 1081 Log::Log4perl->init_and_watch($conf_file, 10, { 1082 preinit_callback => \&callback }); 1083 1084 If Log4perl determines that the configuration needs to be reloaded, it 1085 will call the "preinit_callback" function without parameters. If the 1086 callback returns a true value, Log4perl will proceed and reload the 1087 configuration. If the callback returns a false value, Log4perl will keep 1088 the old configuration and skip reloading it until the next time around. 1089 Inside the callback, an application can run all kinds of checks, 1090 including accessing the configuration file, which is available via 1091 "Log::Log4perl::Config->watcher()->file()". 1092 1093 Variable Substitution 1094 To avoid having to retype the same expressions over and over again, 1095 Log::Log4perl's configuration files support simple variable 1096 substitution. New variables are defined simply by adding 1097 1098 varname = value 1099 1100 lines to the configuration file before using 1101 1102 ${varname} 1103 1104 afterwards to recall the assigned values. Here's an example: 1105 1106 layout_class = Log::Log4perl::Layout::PatternLayout 1107 layout_pattern = %d %F{1} %L> %m %n 1108 1109 log4perl.category.Bar.Twix = WARN, Logfile, Screen 1110 1111 log4perl.appender.Logfile = Log::Log4perl::Appender::File 1112 log4perl.appender.Logfile.filename = test.log 1113 log4perl.appender.Logfile.layout = ${layout_class} 1114 log4perl.appender.Logfile.layout.ConversionPattern = ${layout_pattern} 1115 1116 log4perl.appender.Screen = Log::Log4perl::Appender::Screen 1117 log4perl.appender.Screen.layout = ${layout_class} 1118 log4perl.appender.Screen.layout.ConversionPattern = ${layout_pattern} 1119 1120 This is a convenient way to define two appenders with the same layout 1121 without having to retype the pattern definitions. 1122 1123 Variable substitution via "${varname}" will first try to find an 1124 explicitly defined variable. If that fails, it will check your shell's 1125 environment for a variable of that name. If that also fails, the program 1126 will "die()". 1127 1128 Perl Hooks in the Configuration File 1129 If some of the values used in the Log4perl configuration file need to be 1130 dynamically modified by the program, use Perl hooks: 1131 1132 log4perl.appender.File.filename = \ 1133 sub { return getLogfileName(); } 1134 1135 Each value starting with the string "sub {..." is interpreted as Perl 1136 code to be executed at the time the application parses the configuration 1137 via "Log::Log4perl::init()". The return value of the subroutine is used 1138 by Log::Log4perl as the configuration value. 1139 1140 The Perl code is executed in the "main" package, functions in other 1141 packages have to be called in fully-qualified notation. 1142 1143 Here's another example, utilizing an environment variable as a username 1144 for a DBI appender: 1145 1146 log4perl.appender.DB.username = \ 1147 sub { $ENV{DB_USER_NAME } } 1148 1149 However, please note the difference between these code snippets and 1150 those used for user-defined conversion specifiers as discussed in 1151 Log::Log4perl::Layout::PatternLayout: While the snippets above are run 1152 *once* when "Log::Log4perl::init()" is called, the conversion specifier 1153 snippets are executed *each time* a message is rendered according to the 1154 PatternLayout. 1155 1156 SECURITY NOTE: this feature means arbitrary perl code can be embedded in 1157 the config file. In the rare case where the people who have access to 1158 your config file are different from the people who write your code and 1159 shouldn't have execute rights, you might want to set 1160 1161 Log::Log4perl::Config->allow_code(0); 1162 1163 before you call init(). Alternatively you can supply a restricted set of 1164 Perl opcodes that can be embedded in the config file as described in 1165 "Restricting what Opcodes can be in a Perl Hook". 1166 1167 Restricting what Opcodes can be in a Perl Hook 1168 The value you pass to Log::Log4perl::Config->allow_code() determines 1169 whether the code that is embedded in the config file is eval'd 1170 unrestricted, or eval'd in a Safe compartment. By default, a value of 1171 '1' is assumed, which does a normal 'eval' without any restrictions. A 1172 value of '0' however prevents any embedded code from being evaluated. 1173 1174 If you would like fine-grained control over what can and cannot be 1175 included in embedded code, then please utilize the following methods: 1176 1177 Log::Log4perl::Config->allow_code( $allow ); 1178 Log::Log4perl::Config->allowed_code_ops($op1, $op2, ... ); 1179 Log::Log4perl::Config->vars_shared_with_safe_compartment( [ \%vars | $package, \@vars ] ); 1180 Log::Log4perl::Config->allowed_code_ops_convenience_map( [ \%map | $name, \@mask ] ); 1181 1182 Log::Log4perl::Config->allowed_code_ops() takes a list of opcode masks 1183 that are allowed to run in the compartment. The opcode masks must be 1184 specified as described in Opcode: 1185 1186 Log::Log4perl::Config->allowed_code_ops(':subprocess'); 1187 1188 This example would allow Perl operations like backticks, system, fork, 1189 and waitpid to be executed in the compartment. Of course, you probably 1190 don't want to use this mask -- it would allow exactly what the Safe 1191 compartment is designed to prevent. 1192 1193 Log::Log4perl::Config->vars_shared_with_safe_compartment() takes the 1194 symbols which should be exported into the Safe compartment before the 1195 code is evaluated. The keys of this hash are the package names that the 1196 symbols are in, and the values are array references to the literal 1197 symbol names. For convenience, the default settings export the '%ENV' 1198 hash from the 'main' package into the compartment: 1199 1200 Log::Log4perl::Config->vars_shared_with_safe_compartment( 1201 main => [ '%ENV' ], 1202 ); 1203 1204 Log::Log4perl::Config->allowed_code_ops_convenience_map() is an accessor 1205 method to a map of convenience names to opcode masks. At present, the 1206 following convenience names are defined: 1207 1208 safe = [ ':browse' ] 1209 restrictive = [ ':default' ] 1210 1211 For convenience, if Log::Log4perl::Config->allow_code() is called with a 1212 value which is a key of the map previously defined with 1213 Log::Log4perl::Config->allowed_code_ops_convenience_map(), then the 1214 allowed opcodes are set according to the value defined in the map. If 1215 this is confusing, consider the following: 1216 1217 use Log::Log4perl; 1218 1219 my $config = <<'END'; 1220 log4perl.logger = INFO, Main 1221 log4perl.appender.Main = Log::Log4perl::Appender::File 1222 log4perl.appender.Main.filename = \ 1223 sub { "example" . getpwuid($<) . ".log" } 1224 log4perl.appender.Main.layout = Log::Log4perl::Layout::SimpleLayout 1225 END 1226 1227 $Log::Log4perl::Config->allow_code('restrictive'); 1228 Log::Log4perl->init( \$config ); # will fail 1229 $Log::Log4perl::Config->allow_code('safe'); 1230 Log::Log4perl->init( \$config ); # will succeed 1231 1232 The reason that the first call to ->init() fails is because the 1233 'restrictive' name maps to an opcode mask of ':default'. getpwuid() is 1234 not part of ':default', so ->init() fails. The 'safe' name maps to an 1235 opcode mask of ':browse', which allows getpwuid() to run, so ->init() 1236 succeeds. 1237 1238 allowed_code_ops_convenience_map() can be invoked in several ways: 1239 1240 allowed_code_ops_convenience_map() 1241 Returns the entire convenience name map as a hash reference in 1242 scalar context or a hash in list context. 1243 1244 allowed_code_ops_convenience_map( \%map ) 1245 Replaces the entire convenience name map with the supplied hash 1246 reference. 1247 1248 allowed_code_ops_convenience_map( $name ) 1249 Returns the opcode mask for the given convenience name, or undef if 1250 no such name is defined in the map. 1251 1252 allowed_code_ops_convenience_map( $name, \@mask ) 1253 Adds the given name/mask pair to the convenience name map. If the 1254 name already exists in the map, it's value is replaced with the new 1255 mask. 1256 1257 as can vars_shared_with_safe_compartment(): 1258 1259 vars_shared_with_safe_compartment() 1260 Return the entire map of packages to variables as a hash reference 1261 in scalar context or a hash in list context. 1262 1263 vars_shared_with_safe_compartment( \%packages ) 1264 Replaces the entire map of packages to variables with the supplied 1265 hash reference. 1266 1267 vars_shared_with_safe_compartment( $package ) 1268 Returns the arrayref of variables to be shared for a specific 1269 package. 1270 1271 vars_shared_with_safe_compartment( $package, \@vars ) 1272 Adds the given package / varlist pair to the map. If the package 1273 already exists in the map, it's value is replaced with the new 1274 arrayref of variable names. 1275 1276 For more information on opcodes and Safe Compartments, see Opcode and 1277 Safe. 1278 1279 Changing the Log Level on a Logger 1280 Log4perl provides some internal functions for quickly adjusting the log 1281 level from within a running Perl program. 1282 1283 Now, some people might argue that you should adjust your levels from 1284 within an external Log4perl configuration file, but Log4perl is 1285 everybody's darling. 1286 1287 Typically run-time adjusting of levels is done at the beginning, or in 1288 response to some external input (like a "more logging" runtime command 1289 for diagnostics). 1290 1291 You get the log level from a logger object with: 1292 1293 $current_level = $logger->level(); 1294 1295 and you may set it with the same method, provided you first imported the 1296 log level constants, with: 1297 1298 use Log::Log4perl::Level; 1299 1300 Then you can set the level on a logger to one of the constants, 1301 1302 $logger->level($ERROR); # one of DEBUG, INFO, WARN, ERROR, FATAL 1303 1304 To increase the level of logging currently being done, use: 1305 1306 $logger->more_logging($delta); 1307 1308 and to decrease it, use: 1309 1310 $logger->less_logging($delta); 1311 1312 $delta must be a positive integer (for now, we may fix this later ;). 1313 1314 There are also two equivalent functions: 1315 1316 $logger->inc_level($delta); 1317 $logger->dec_level($delta); 1318 1319 They're included to allow you a choice in readability. Some folks will 1320 prefer more/less_logging, as they're fairly clear in what they do, and 1321 allow the programmer not to worry too much about what a Level is and 1322 whether a higher level means more or less logging. However, other folks 1323 who do understand and have lots of code that deals with levels will 1324 probably prefer the inc_level() and dec_level() methods as they want to 1325 work with Levels and not worry about whether that means more or less 1326 logging. :) 1327 1328 That diatribe aside, typically you'll use more_logging() or inc_level() 1329 as such: 1330 1331 my $v = 0; # default level of verbosity. 1332 1333 GetOptions("v+" => \$v, ...); 1334 1335 if( $v ) { 1336 $logger->more_logging($v); # inc logging level once for each -v in ARGV 1337 } 1338 1339 Custom Log Levels 1340 First off, let me tell you that creating custom levels is heavily 1341 deprecated by the log4j folks. Indeed, instead of creating additional 1342 levels on top of the predefined DEBUG, INFO, WARN, ERROR and FATAL, you 1343 should use categories to control the amount of logging smartly, based on 1344 the location of the log-active code in the system. 1345 1346 Nevertheless, Log4perl provides a nice way to create custom levels via 1347 the create_custom_level() routine function. However, this must be done 1348 before the first call to init() or get_logger(). Say you want to create 1349 a NOTIFY logging level that comes after WARN (and thus before INFO). 1350 You'd do such as follows: 1351 1352 use Log::Log4perl; 1353 use Log::Log4perl::Level; 1354 1355 Log::Log4perl::Logger::create_custom_level("NOTIFY", "WARN"); 1356 1357 And that's it! "create_custom_level()" creates the following functions / 1358 variables for level FOO: 1359 1360 $FOO_INT # integer to use in L4p::Level::to_level() 1361 $logger->foo() # log function to log if level = FOO 1362 $logger->is_foo() # true if current level is >= FOO 1363 1364 These levels can also be used in your config file, but note that your 1365 config file probably won't be portable to another log4perl or log4j 1366 environment unless you've made the appropriate mods there too. 1367 1368 Since Log4perl translates log levels to syslog and Log::Dispatch if 1369 their appenders are used, you may add mappings for custom levels as 1370 well: 1371 1372 Log::Log4perl::Level::add_priority("NOTIFY", "WARN", 1373 $syslog_equiv, $log_dispatch_level); 1374 1375 For example, if your new custom "NOTIFY" level is supposed to map to 1376 syslog level 2 ("LOG_NOTICE") and Log::Dispatch level 2 ("notice"), use: 1377 1378 Log::Log4perl::Logger::create_custom_level("NOTIFY", "WARN", 2, 2); 1379 1380 System-wide log levels 1381 As a fairly drastic measure to decrease (or increase) the logging level 1382 all over the system with one single configuration option, use the 1383 "threshold" keyword in the Log4perl configuration file: 1384 1385 log4perl.threshold = ERROR 1386 1387 sets the system-wide (or hierarchy-wide according to the log4j 1388 documentation) to ERROR and therefore deprives every logger in the 1389 system of the right to log lower-prio messages. 1390 1391 Easy Mode 1392 For teaching purposes (especially for [1]), I've put ":easy" mode into 1393 "Log::Log4perl", which just initializes a single root logger with a 1394 defined priority and a screen appender including some nice standard 1395 layout: 1396 1397 ### Initialization Section 1398 use Log::Log4perl qw(:easy); 1399 Log::Log4perl->easy_init($ERROR); # Set priority of root logger to ERROR 1400 1401 ### Application Section 1402 my $logger = get_logger(); 1403 $logger->fatal("This will get logged."); 1404 $logger->debug("This won't."); 1405 1406 This will dump something like 1407 1408 2002/08/04 11:43:09 ERROR> script.pl:16 main::function - This will get logged. 1409 1410 to the screen. While this has been proven to work well familiarizing 1411 people with "Log::Logperl" slowly, effectively avoiding to clobber them 1412 over the head with a plethora of different knobs to fiddle with 1413 (categories, appenders, levels, layout), the overall mission of 1414 "Log::Log4perl" is to let people use categories right from the start to 1415 get used to the concept. So, let's keep this one fairly hidden in the 1416 man page (congrats on reading this far :). 1417 1418 Stealth loggers 1419 Sometimes, people are lazy. If you're whipping up a 50-line script and 1420 want the comfort of Log::Log4perl without having the burden of carrying 1421 a separate log4perl.conf file or a 5-liner defining that you want to 1422 append your log statements to a file, you can use the following 1423 features: 1424 1425 use Log::Log4perl qw(:easy); 1426 1427 Log::Log4perl->easy_init( { level => $DEBUG, 1428 file => ">>test.log" } ); 1429 1430 # Logs to test.log via stealth logger 1431 DEBUG("Debug this!"); 1432 INFO("Info this!"); 1433 WARN("Warn this!"); 1434 ERROR("Error this!"); 1435 1436 some_function(); 1437 1438 sub some_function { 1439 # Same here 1440 FATAL("Fatal this!"); 1441 } 1442 1443 In ":easy" mode, "Log::Log4perl" will instantiate a *stealth logger* and 1444 introduce the convenience functions "TRACE", "DEBUG()", "INFO()", 1445 "WARN()", "ERROR()", "FATAL()", and "ALWAYS" into the package namespace. 1446 These functions simply take messages as arguments and forward them to 1447 the stealth loggers methods ("debug()", "info()", and so on). 1448 1449 If a message should never be blocked, regardless of the log level, use 1450 the "ALWAYS" function which corresponds to a log level of "OFF": 1451 1452 ALWAYS "This will be printed regardless of the log level"; 1453 1454 The "easy_init" method can be called with a single level value to create 1455 a STDERR appender and a root logger as in 1456 1457 Log::Log4perl->easy_init($DEBUG); 1458 1459 or, as shown below (and in the example above) with a reference to a 1460 hash, specifying values for "level" (the logger's priority), "file" (the 1461 appender's data sink), "category" (the logger's category and "layout" 1462 for the appender's pattern layout specification. All key-value pairs are 1463 optional, they default to $DEBUG for "level", "STDERR" for "file", "" 1464 (root category) for "category" and "%d %m%n" for "layout": 1465 1466 Log::Log4perl->easy_init( { level => $DEBUG, 1467 file => ">test.log", 1468 utf8 => 1, 1469 category => "Bar::Twix", 1470 layout => '%F{1}-%L-%M: %m%n' } ); 1471 1472 The "file" parameter takes file names preceded by ">" (overwrite) and 1473 ">>" (append) as arguments. This will cause 1474 "Log::Log4perl::Appender::File" appenders to be created behind the 1475 scenes. Also the keywords "STDOUT" and "STDERR" (no ">" or ">>") are 1476 recognized, which will utilize and configure 1477 "Log::Log4perl::Appender::Screen" appropriately. The "utf8" flag, if set 1478 to a true value, runs a "binmode" command on the file handle to 1479 establish a utf8 line discipline on the file, otherwise you'll get a 1480 'wide character in print' warning message and probably not what you'd 1481 expect as output. 1482 1483 The stealth loggers can be used in different packages, you just need to 1484 make sure you're calling the "use" function in every package you're 1485 using "Log::Log4perl"'s easy services: 1486 1487 package Bar::Twix; 1488 use Log::Log4perl qw(:easy); 1489 sub eat { DEBUG("Twix mjam"); } 1490 1491 package Bar::Mars; 1492 use Log::Log4perl qw(:easy); 1493 sub eat { INFO("Mars mjam"); } 1494 1495 package main; 1496 1497 use Log::Log4perl qw(:easy); 1498 1499 Log::Log4perl->easy_init( { level => $DEBUG, 1500 file => ">>test.log", 1501 category => "Bar::Twix", 1502 layout => '%F{1}-%L-%M: %m%n' }, 1503 { level => $DEBUG, 1504 file => "STDOUT", 1505 category => "Bar::Mars", 1506 layout => '%m%n' }, 1507 ); 1508 Bar::Twix::eat(); 1509 Bar::Mars::eat(); 1510 1511 As shown above, "easy_init()" will take any number of different logger 1512 definitions as hash references. 1513 1514 Also, stealth loggers feature the functions "LOGWARN()", "LOGDIE()", and 1515 "LOGEXIT()", combining a logging request with a subsequent Perl warn() 1516 or die() or exit() statement. So, for example 1517 1518 if($all_is_lost) { 1519 LOGDIE("Terrible Problem"); 1520 } 1521 1522 will log the message if the package's logger is at least "FATAL" but 1523 "die()" (including the traditional output to STDERR) in any case 1524 afterwards. 1525 1526 See "Log and die or warn" for the similar "logdie()" and "logwarn()" 1527 functions of regular (i.e non-stealth) loggers. 1528 1529 Similarily, "LOGCARP()", "LOGCLUCK()", "LOGCROAK()", and "LOGCONFESS()" 1530 are provided in ":easy" mode, facilitating the use of "logcarp()", 1531 "logcluck()", "logcroak()", and "logconfess()" with stealth loggers. 1532 1533 When using Log::Log4perl in easy mode, please make sure you understand 1534 the implications of "Pitfalls with Categories". 1535 1536 By the way, these convenience functions perform exactly as fast as the 1537 standard Log::Log4perl logger methods, there's *no* performance penalty 1538 whatsoever. 1539 1540 Nested Diagnostic Context (NDC) 1541 If you find that your application could use a global (thread-specific) 1542 data stack which your loggers throughout the system have easy access to, 1543 use Nested Diagnostic Contexts (NDCs). Also check out "Mapped Diagnostic 1544 Context (MDC)", this might turn out to be even more useful. 1545 1546 For example, when handling a request of a web client, it's probably 1547 useful to have the user's IP address available in all log statements 1548 within code dealing with this particular request. Instead of passing 1549 this piece of data around between your application functions, you can 1550 just use the global (but thread-specific) NDC mechanism. It allows you 1551 to push data pieces (scalars usually) onto its stack via 1552 1553 Log::Log4perl::NDC->push("San"); 1554 Log::Log4perl::NDC->push("Francisco"); 1555 1556 and have your loggers retrieve them again via the "%x" placeholder in 1557 the PatternLayout. With the stack values above and a PatternLayout 1558 format like "%x %m%n", the call 1559 1560 $logger->debug("rocks"); 1561 1562 will end up as 1563 1564 San Francisco rocks 1565 1566 in the log appender. 1567 1568 The stack mechanism allows for nested structures. Just make sure that at 1569 the end of the request, you either decrease the stack one by one by 1570 calling 1571 1572 Log::Log4perl::NDC->pop(); 1573 Log::Log4perl::NDC->pop(); 1574 1575 or clear out the entire NDC stack by calling 1576 1577 Log::Log4perl::NDC->remove(); 1578 1579 Even if you should forget to do that, "Log::Log4perl" won't grow the 1580 stack indefinitely, but limit it to a maximum, defined in 1581 "Log::Log4perl::NDC" (currently 5). A call to "push()" on a full stack 1582 will just replace the topmost element by the new value. 1583 1584 Again, the stack is always available via the "%x" placeholder in the 1585 Log::Log4perl::Layout::PatternLayout class whenever a logger fires. It 1586 will replace "%x" by the blank-separated list of the values on the 1587 stack. It does that by just calling 1588 1589 Log::Log4perl::NDC->get(); 1590 1591 internally. See details on how this standard log4j feature is 1592 implemented in Log::Log4perl::NDC. 1593 1594 Mapped Diagnostic Context (MDC) 1595 Just like the previously discussed NDC stores thread-specific 1596 information in a stack structure, the MDC implements a hash table to 1597 store key/value pairs in. 1598 1599 The static method 1600 1601 Log::Log4perl::MDC->put($key, $value); 1602 1603 stores $value under a key $key, with which it can be retrieved later 1604 (possibly in a totally different part of the system) by calling the 1605 "get" method: 1606 1607 my $value = Log::Log4perl::MDC->get($key); 1608 1609 If no value has been stored previously under $key, the "get" method will 1610 return "undef". 1611 1612 Typically, MDC values are retrieved later on via the "%X{...}" 1613 placeholder in "Log::Log4perl::Layout::PatternLayout". If the "get()" 1614 method returns "undef", the placeholder will expand to the string 1615 "[undef]". 1616 1617 An application taking a web request might store the remote host like 1618 1619 Log::Log4perl::MDC->put("remote_host", $r->headers("HOST")); 1620 1621 at its beginning and if the appender's layout looks something like 1622 1623 log4perl.appender.Logfile.layout.ConversionPattern = %X{remote_host}: %m%n 1624 1625 then a log statement like 1626 1627 DEBUG("Content delivered"); 1628 1629 will log something like 1630 1631 adsl-63.dsl.snf.pacbell.net: Content delivered 1632 1633 later on in the program. 1634 1635 For details, please check Log::Log4perl::MDC. 1636 1637 Resurrecting hidden Log4perl Statements 1638 Sometimes scripts need to be deployed in environments without having 1639 Log::Log4perl installed yet. On the other hand, you don't want to live 1640 without your Log4perl statements -- they're gonna come in handy later. 1641 1642 So, just deploy your script with Log4perl statements commented out with 1643 the pattern "###l4p", like in 1644 1645 ###l4p DEBUG "It works!"; 1646 # ... 1647 ###l4p INFO "Really!"; 1648 1649 If Log::Log4perl is available, use the ":resurrect" tag to have Log4perl 1650 resurrect those buried statements before the script starts running: 1651 1652 use Log::Log4perl qw(:resurrect :easy); 1653 1654 ###l4p Log::Log4perl->easy_init($DEBUG); 1655 ###l4p DEBUG "It works!"; 1656 # ... 1657 ###l4p INFO "Really!"; 1658 1659 This will have a source filter kick in and indeed print 1660 1661 2004/11/18 22:08:46 It works! 1662 2004/11/18 22:08:46 Really! 1663 1664 In environments lacking Log::Log4perl, just comment out the first line 1665 and the script will run nevertheless (but of course without logging): 1666 1667 # use Log::Log4perl qw(:resurrect :easy); 1668 1669 ###l4p Log::Log4perl->easy_init($DEBUG); 1670 ###l4p DEBUG "It works!"; 1671 # ... 1672 ###l4p INFO "Really!"; 1673 1674 because everything's a regular comment now. Alternatively, put the magic 1675 Log::Log4perl comment resurrection line into your shell's PERL5OPT 1676 environment variable, e.g. for bash: 1677 1678 set PERL5OPT=-MLog::Log4perl=:resurrect,:easy 1679 export PERL5OPT 1680 1681 This will awaken the giant within an otherwise silent script like the 1682 following: 1683 1684 #!/usr/bin/perl 1685 1686 ###l4p Log::Log4perl->easy_init($DEBUG); 1687 ###l4p DEBUG "It works!"; 1688 1689 As of "Log::Log4perl" 1.12, you can even force *all* modules loaded by a 1690 script to have their hidden Log4perl statements resurrected. For this to 1691 happen, load "Log::Log4perl::Resurrector" *before* loading any modules: 1692 1693 use Log::Log4perl qw(:easy); 1694 use Log::Log4perl::Resurrector; 1695 1696 use Foobar; # All hidden Log4perl statements in here will 1697 # be uncommented before Foobar gets loaded. 1698 1699 Log::Log4perl->easy_init($DEBUG); 1700 ... 1701 1702 Check the "Log::Log4perl::Resurrector" manpage for more details. 1703 1704 Access defined appenders 1705 All appenders defined in the configuration file or via Perl code can be 1706 retrieved by the "appender_by_name()" class method. This comes in handy 1707 if you want to manipulate or query appender properties after the 1708 Log4perl configuration has been loaded via "init()". 1709 1710 Note that internally, Log::Log4perl uses the "Log::Log4perl::Appender" 1711 wrapper class to control the real appenders (like 1712 "Log::Log4perl::Appender::File" or "Log::Dispatch::FileRotate"). The 1713 "Log::Log4perl::Appender" class has an "appender" attribute, pointing to 1714 the real appender. 1715 1716 The reason for this is that external appenders like 1717 "Log::Dispatch::FileRotate" don't support all of Log::Log4perl's 1718 appender control mechanisms (like appender thresholds). 1719 1720 The previously mentioned method "appender_by_name()" returns a reference 1721 to the *real* appender object. If you want access to the wrapper class 1722 (e.g. if you want to modify the appender's threshold), use the hash 1723 $Log::Log4perl::Logger::APPENDER_BY_NAME{...} instead, which holds 1724 references to all appender wrapper objects. 1725 1726 Modify appender thresholds 1727 To set an appender's threshold, use its "threshold()" method: 1728 1729 $app->threshold( $FATAL ); 1730 1731 To conveniently adjust *all* appender thresholds (e.g. because a script 1732 uses more_logging()), use 1733 1734 # decrease thresholds of all appenders 1735 Log::Log4perl->appender_thresholds_adjust(-1); 1736 1737 This will decrease the thresholds of all appenders in the system by one 1738 level, i.e. WARN becomes INFO, INFO becomes DEBUG, etc. To only modify 1739 selected ones, use 1740 1741 # decrease thresholds of selected appenders 1742 Log::Log4perl->appender_thresholds_adjust(-1, ['AppName1', ...]); 1743 1744 and pass the names of affected appenders in a ref to an array. 1745 1746Advanced configuration within Perl 1747 Initializing Log::Log4perl can certainly also be done from within Perl. 1748 At last, this is what "Log::Log4perl::Config" does behind the scenes. 1749 Log::Log4perl's configuration file parsers are using a publically 1750 available API to set up Log::Log4perl's categories, appenders and 1751 layouts. 1752 1753 Here's an example on how to configure two appenders with the same layout 1754 in Perl, without using a configuration file at all: 1755 1756 ######################## 1757 # Initialization section 1758 ######################## 1759 use Log::Log4perl; 1760 use Log::Log4perl::Layout; 1761 use Log::Log4perl::Level; 1762 1763 # Define a category logger 1764 my $log = Log::Log4perl->get_logger("Foo::Bar"); 1765 1766 # Define a layout 1767 my $layout = Log::Log4perl::Layout::PatternLayout->new("[%r] %F %L %m%n"); 1768 1769 # Define a file appender 1770 my $file_appender = Log::Log4perl::Appender->new( 1771 "Log::Log4perl::Appender::File", 1772 name => "filelog", 1773 filename => "/tmp/my.log"); 1774 1775 # Define a stdout appender 1776 my $stdout_appender = Log::Log4perl::Appender->new( 1777 "Log::Log4perl::Appender::Screen", 1778 name => "screenlog", 1779 stderr => 0); 1780 1781 # Have both appenders use the same layout (could be different) 1782 $stdout_appender->layout($layout); 1783 $file_appender->layout($layout); 1784 1785 $log->add_appender($stdout_appender); 1786 $log->add_appender($file_appender); 1787 $log->level($INFO); 1788 1789 Please note the class of the appender object is passed as a *string* to 1790 "Log::Log4perl::Appender" in the *first* argument. Behind the scenes, 1791 "Log::Log4perl::Appender" will create the necessary 1792 "Log::Log4perl::Appender::*" (or "Log::Dispatch::*") object and pass 1793 along the name value pairs we provided to 1794 "Log::Log4perl::Appender->new()" after the first argument. 1795 1796 The "name" value is optional and if you don't provide one, 1797 "Log::Log4perl::Appender->new()" will create a unique one for you. The 1798 names and values of additional parameters are dependent on the 1799 requirements of the particular appender class and can be looked up in 1800 their manual pages. 1801 1802 A side note: In case you're wondering if 1803 "Log::Log4perl::Appender->new()" will also take care of the "min_level" 1804 argument to the "Log::Dispatch::*" constructors called behind the scenes 1805 -- yes, it does. This is because we want the "Log::Dispatch" objects to 1806 blindly log everything we send them ("debug" is their lowest setting) 1807 because *we* in "Log::Log4perl" want to call the shots and decide on 1808 when and what to log. 1809 1810 The call to the appender's *layout()* method specifies the format (as a 1811 previously created "Log::Log4perl::Layout::PatternLayout" object) in 1812 which the message is being logged in the specified appender. If you 1813 don't specify a layout, the logger will fall back to 1814 "Log::Log4perl::SimpleLayout", which logs the debug level, a hyphen (-) 1815 and the log message. 1816 1817 Layouts are objects, here's how you create them: 1818 1819 # Create a simple layout 1820 my $simple = Log::Log4perl::SimpleLayout(); 1821 1822 # create a flexible layout: 1823 # ("yyyy/MM/dd HH:mm:ss (file:lineno)> message\n") 1824 my $pattern = Log::Log4perl::Layout::PatternLayout("%d (%F:%L)> %m%n"); 1825 1826 Every appender has exactly one layout assigned to it. You assign the 1827 layout to the appender using the appender's "layout()" object: 1828 1829 my $app = Log::Log4perl::Appender->new( 1830 "Log::Log4perl::Appender::Screen", 1831 name => "screenlog", 1832 stderr => 0); 1833 1834 # Assign the previously defined flexible layout 1835 $app->layout($pattern); 1836 1837 # Add the appender to a previously defined logger 1838 $logger->add_appender($app); 1839 1840 # ... and you're good to go! 1841 $logger->debug("Blah"); 1842 # => "2002/07/10 23:55:35 (test.pl:207)> Blah\n" 1843 1844 It's also possible to remove appenders from a logger: 1845 1846 $logger->remove_appender($appender_name); 1847 1848 will remove an appender, specified by name, from a given logger. Please 1849 note that this does *not* remove an appender from the system. 1850 1851 To eradicate an appender from the system, you need to call 1852 "Log::Log4perl->eradicate_appender($appender_name)" which will first 1853 remove the appender from every logger in the system and then will delete 1854 all references Log4perl holds to it. 1855 1856 To remove a logger from the system, use 1857 "Log::Log4perl->remove_logger($logger)". After the remaining reference 1858 $logger goes away, the logger will self-destruct. If the logger in 1859 question is a stealth logger, all of its convenience shortcuts (DEBUG, 1860 INFO, etc) will turn into no-ops. 1861 1862How about Log::Dispatch::Config? 1863 Tatsuhiko Miyagawa's "Log::Dispatch::Config" is a very clever simplified 1864 logger implementation, covering some of the *log4j* functionality. Among 1865 the things that "Log::Log4perl" can but "Log::Dispatch::Config" can't 1866 are: 1867 1868 * You can't assign categories to loggers. For small systems that's 1869 fine, but if you can't turn off and on detailed logging in only a 1870 tiny subsystem of your environment, you're missing out on a majorly 1871 useful log4j feature. 1872 1873 * Defining appender thresholds. Important if you want to solve 1874 problems like "log all messages of level FATAL to STDERR, plus log 1875 all DEBUG messages in "Foo::Bar" to a log file". If you don't have 1876 appenders thresholds, there's no way to prevent cluttering STDERR 1877 with DEBUG messages. 1878 1879 * PatternLayout specifications in accordance with the standard (e.g. 1880 "%d{HH:mm}"). 1881 1882 Bottom line: Log::Dispatch::Config is fine for small systems with simple 1883 logging requirements. However, if you're designing a system with lots of 1884 subsystems which you need to control independently, you'll love the 1885 features of "Log::Log4perl", which is equally easy to use. 1886 1887Using Log::Log4perl with wrapper functions and classes 1888 If you don't use "Log::Log4perl" as described above, but from a wrapper 1889 function, the pattern layout will generate wrong data for %F, %C, %L, 1890 and the like. Reason for this is that "Log::Log4perl"'s loggers assume a 1891 static caller depth to the application that's using them. 1892 1893 If you're using one (or more) wrapper functions, "Log::Log4perl" will 1894 indicate where your logger function called the loggers, not where your 1895 application called your wrapper: 1896 1897 use Log::Log4perl qw(:easy); 1898 Log::Log4perl->easy_init({ level => $DEBUG, 1899 layout => "%M %m%n" }); 1900 1901 sub mylog { 1902 my($message) = @_; 1903 1904 DEBUG $message; 1905 } 1906 1907 sub func { 1908 mylog "Hello"; 1909 } 1910 1911 func(); 1912 1913 prints 1914 1915 main::mylog Hello 1916 1917 but that's probably not what your application expects. Rather, you'd 1918 want 1919 1920 main::func Hello 1921 1922 because the "func" function called your logging function. 1923 1924 But don't despair, there's a solution: Just register your wrapper 1925 package with Log4perl beforehand. If Log4perl then finds that it's being 1926 called from a registered wrapper, it will automatically step up to the 1927 next call frame. 1928 1929 Log::Log4perl->wrapper_register(__PACKAGE__); 1930 1931 sub mylog { 1932 my($message) = @_; 1933 1934 DEBUG $message; 1935 } 1936 1937 Alternatively, you can increase the value of the global variable 1938 $Log::Log4perl::caller_depth (defaults to 0) by one for every wrapper 1939 that's in between your application and "Log::Log4perl", then 1940 "Log::Log4perl" will compensate for the difference: 1941 1942 sub mylog { 1943 my($message) = @_; 1944 1945 local $Log::Log4perl::caller_depth = 1946 $Log::Log4perl::caller_depth + 1; 1947 DEBUG $message; 1948 } 1949 1950 Also, note that if you're writing a subclass of Log4perl, like 1951 1952 package MyL4pWrapper; 1953 use Log::Log4perl; 1954 our @ISA = qw(Log::Log4perl); 1955 1956 and you want to call get_logger() in your code, like 1957 1958 use MyL4pWrapper; 1959 1960 sub get_logger { 1961 my $logger = Log::Log4perl->get_logger(); 1962 } 1963 1964 then the get_logger() call will get a logger for the "MyL4pWrapper" 1965 category, not for the package calling the wrapper class as in 1966 1967 package UserPackage; 1968 my $logger = MyL4pWrapper->get_logger(); 1969 1970 To have the above call to get_logger return a logger for the 1971 "UserPackage" category, you need to tell Log4perl that "MyL4pWrapper" is 1972 a Log4perl wrapper class: 1973 1974 use MyL4pWrapper; 1975 Log::Log4perl->wrapper_register(__PACKAGE__); 1976 1977 sub get_logger { 1978 # Now gets a logger for the category of the calling package 1979 my $logger = Log::Log4perl->get_logger(); 1980 } 1981 1982 This feature works both for Log4perl-relaying classes like the wrapper 1983 described above, and for wrappers that inherit from Log4perl use 1984 Log4perl's get_logger function via inheritance, alike. 1985 1986Access to Internals 1987 The following methods are only of use if you want to peek/poke in the 1988 internals of Log::Log4perl. Be careful not to disrupt its inner 1989 workings. 1990 1991 "Log::Log4perl->appenders()" 1992 To find out which appenders are currently defined (not only for a 1993 particular logger, but overall), a "appenders()" method is available 1994 to return a reference to a hash mapping appender names to their 1995 Log::Log4perl::Appender object references. 1996 1997Dirty Tricks 1998 infiltrate_lwp() 1999 The famous LWP::UserAgent module isn't Log::Log4perl-enabled. Often, 2000 though, especially when tracing Web-related problems, it would be 2001 helpful to get some insight on what's happening inside 2002 LWP::UserAgent. Ideally, LWP::UserAgent would even play along in the 2003 Log::Log4perl framework. 2004 2005 A call to "Log::Log4perl->infiltrate_lwp()" does exactly this. In a 2006 very rude way, it pulls the rug from under LWP::UserAgent and 2007 transforms its "debug/conn" messages into "debug()" calls of loggers 2008 of the category "LWP::UserAgent". Similarily, "LWP::UserAgent"'s 2009 "trace" messages are turned into "Log::Log4perl"'s "info()" method 2010 calls. Note that this only works for LWP::UserAgent versions < 2011 5.822, because this (and probably later) versions miss debugging 2012 functions entirely. 2013 2014 Suppressing 'duplicate' LOGDIE messages 2015 If a script with a simple Log4perl configuration uses logdie() to 2016 catch errors and stop processing, as in 2017 2018 use Log::Log4perl qw(:easy) ; 2019 Log::Log4perl->easy_init($DEBUG); 2020 2021 shaky_function() or LOGDIE "It failed!"; 2022 2023 there's a cosmetic problem: The message gets printed twice: 2024 2025 2005/07/10 18:37:14 It failed! 2026 It failed! at ./t line 12 2027 2028 The obvious solution is to use LOGEXIT() instead of LOGDIE(), but 2029 there's also a special tag for Log4perl that suppresses the second 2030 message: 2031 2032 use Log::Log4perl qw(:no_extra_logdie_message); 2033 2034 This causes logdie() and logcroak() to call exit() instead of die(). 2035 To modify the script exit code in these occasions, set the variable 2036 $Log::Log4perl::LOGEXIT_CODE to the desired value, the default is 1. 2037 2038 Redefine values without causing errors 2039 Log4perl's configuration file parser has a few basic safety 2040 mechanisms to make sure configurations are more or less sane. 2041 2042 One of these safety measures is catching redefined values. For 2043 example, if you first write 2044 2045 log4perl.category = WARN, Logfile 2046 2047 and then a couple of lines later 2048 2049 log4perl.category = TRACE, Logfile 2050 2051 then you might have unintentionally overwritten the first value and 2052 Log4perl will die on this with an error (suspicious configurations 2053 always throw an error). Now, there's a chance that this is 2054 intentional, for example when you're lumping together several 2055 configuration files and actually *want* the first value to overwrite 2056 the second. In this case use 2057 2058 use Log::Log4perl qw(:nostrict); 2059 2060 to put Log4perl in a more permissive mode. 2061 2062 Prevent croak/confess from stringifying 2063 The logcroak/logconfess functions stringify their arguments before 2064 they pass them to Carp's croak/confess functions. This can get in 2065 the way if you want to throw an object or a hashref as an exception, 2066 in this case use: 2067 2068 $Log::Log4perl::STRINGIFY_DIE_MESSAGE = 0; 2069 2070 eval { 2071 # throws { foo => "bar" } 2072 # without stringification 2073 $logger->logcroak( { foo => "bar" } ); 2074 }; 2075 2076EXAMPLE 2077 A simple example to cut-and-paste and get started: 2078 2079 use Log::Log4perl qw(get_logger); 2080 2081 my $conf = q( 2082 log4perl.category.Bar.Twix = WARN, Logfile 2083 log4perl.appender.Logfile = Log::Log4perl::Appender::File 2084 log4perl.appender.Logfile.filename = test.log 2085 log4perl.appender.Logfile.layout = \ 2086 Log::Log4perl::Layout::PatternLayout 2087 log4perl.appender.Logfile.layout.ConversionPattern = %d %F{1} %L> %m %n 2088 ); 2089 2090 Log::Log4perl::init(\$conf); 2091 2092 my $logger = get_logger("Bar::Twix"); 2093 $logger->error("Blah"); 2094 2095 This will log something like 2096 2097 2002/09/19 23:48:15 t1 25> Blah 2098 2099 to the log file "test.log", which Log4perl will append to or create it 2100 if it doesn't exist already. 2101 2102INSTALLATION 2103 If you want to use external appenders provided with "Log::Dispatch", you 2104 need to install "Log::Dispatch" (2.00 or better) from CPAN, which itself 2105 depends on "Attribute-Handlers" and "Params-Validate". And a lot of 2106 other modules, that's the reason why we're now shipping Log::Log4perl 2107 with its own standard appenders and only if you wish to use additional 2108 ones, you'll have to go through the "Log::Dispatch" installation 2109 process. 2110 2111 Log::Log4perl needs "Test::More", "Test::Harness" and "File::Spec", but 2112 they already come with fairly recent versions of perl. If not, 2113 everything's automatically fetched from CPAN if you're using the CPAN 2114 shell (CPAN.pm), because they're listed as dependencies. 2115 2116 "Time::HiRes" (1.20 or better) is required only if you need the 2117 fine-grained time stamps of the %r parameter in 2118 "Log::Log4perl::Layout::PatternLayout". 2119 2120 Manual installation works as usual with 2121 2122 perl Makefile.PL 2123 make 2124 make test 2125 make install 2126 2127DEVELOPMENT 2128 Log::Log4perl is still being actively developed. We will always make 2129 sure the test suite (approx. 500 cases) will pass, but there might still 2130 be bugs. please check <http://github.com/mschilli/log4perl> for the 2131 latest release. The api has reached a mature state, we will not change 2132 it unless for a good reason. 2133 2134 Bug reports and feedback are always welcome, just email them to our 2135 mailing list shown in the AUTHORS section. We're usually addressing them 2136 immediately. 2137 2138REFERENCES 2139 [1] Michael Schilli, "Retire your debugger, log smartly with 2140 Log::Log4perl!", Tutorial on perl.com, 09/2002, 2141 <http://www.perl.com/pub/a/2002/09/11/log4perl.html> 2142 2143 [2] Ceki Gülcü, "Short introduction to log4j", 2144 <http://logging.apache.org/log4j/1.2/manual.html> 2145 2146 [3] Vipan Singla, "Don't Use System.out.println! Use Log4j.", 2147 <http://www.vipan.com/htdocs/log4jhelp.html> 2148 2149 [4] The Log::Log4perl project home page: <http://log4perl.com> 2150 2151SEE ALSO 2152 Log::Log4perl::Config, Log::Log4perl::Appender, 2153 Log::Log4perl::Layout::PatternLayout, 2154 Log::Log4perl::Layout::SimpleLayout, Log::Log4perl::Level, 2155 Log::Log4perl::JavaMap Log::Log4perl::NDC, 2156 2157AUTHORS 2158 Please contribute patches to the project on Github: 2159 2160 http://github.com/mschilli/log4perl 2161 2162 Send bug reports or requests for enhancements to the authors via our 2163 2164 MAILING LIST (questions, bug reports, suggestions/patches): 2165 log4perl-devel@lists.sourceforge.net 2166 2167 Authors (please contact them via the list above, not directly): Mike 2168 Schilli <m@perlmeister.com>, Kevin Goess <cpan@goess.org> 2169 2170 Contributors (in alphabetical order): Ateeq Altaf, Cory Bennett, Jens 2171 Berthold, Jeremy Bopp, Hutton Davidson, Chris R. Donnelly, Matisse 2172 Enzer, Hugh Esco, Anthony Foiani, James FitzGibbon, Carl Franks, Dennis 2173 Gregorovic, Andy Grundman, Paul Harrington, Alexander Hartmaier, David 2174 Hull, Robert Jacobson, Jason Kohles, Jeff Macdonald, Markus Peter, Brett 2175 Rann, Peter Rabbitson, Erik Selberg, Aaron Straup Cope, Lars Thegler, 2176 David Viner, Mac Yang. 2177 2178LICENSE 2179 Copyright 2002-2013 by Mike Schilli <m@perlmeister.com> and Kevin Goess 2180 <cpan@goess.org>. 2181 2182 This library is free software; you can redistribute it and/or modify it 2183 under the same terms as Perl itself. 2184 2185