###################################################################### Log::Log4perl 0.23 ###################################################################### NAME Log::Log4perl - Log4j implementation for Perl SYNOPSIS Log::Log4perl::init('/etc/log4perl.conf'); --or-- Log::Log4perl::init_and_watch('/etc/log4perl.conf',10); --then-- $logger = Log::Log4perl->get_logger('house.bedrm.desk.topdrwr'); $logger->debug('this is a debug message'); $logger->info('this is an info message'); $logger->warn('etc'); $logger->error('..'); $logger->fatal('..'); #####/etc/log4perl.conf################### log4j.category.house = WARN, FileAppndr1 log4j.category.house.bedroom.desk = DEBUG, FileAppndr1 log4j.appender.FileAppndr1 = Log::Dispatch::File log4j.appender.FileAppndr1.filename = desk.log log4j.appender.FileAppndr1.layout = \ Log::Log4perl::Layout::SimpleLayout ########################################### ABSTRACT Log::Log4perl provides a powerful logging API to your application, DESCRIPTION Log::Log4perl lets you remote-control and fine-tune the logging behaviour of your system from the outside. It implements the widely popular (Java-based) Log4j logging package in pure Perl. For a detailed tutorial on Log::Log4perl usage, please read [1]. A WORD OF CAUTION: THIS LIBRARY IS ALPHA SOFTWARE AND STILL UNDER CONSTRUCTION -- ON http://log4perl.sourceforge.net YOU'LL GET THE LATEST SCOOP. THE API HAS REACHED A MATURE STATE, WE WILL NOT CHANGE IT UNLESS FOR A GOOD REASON. Logging beats a debugger when you want to know what's going on in your code during runtime. However, traditional logging packages are too static and generate a flood of log messages in your log files that won't help you. "Log::Log4perl" is different. It allows you to control the amount of logging messages generated at three different levels: * At a central location in your system (either in a configuration file or in the startup code) you specify *which components* (classes, functions) of your system should generate logs. * You specify how detailed the logging of these components should be by specifying logging *levels*. * You also specify which so-called *appenders* you want to feed your log messages to ("Print it to the screen and also append it to /tmp/my.log") and which format ("Write the date first, then the file name and line number, and then the log message") they should be in. This is a very powerful and flexible mechanism. You can turn on and off your logs at any time, specify the level of detail and make that dependent on the subsystem that's currently executed. Let me give you an example: You might find out that your system has a problem in the "MySystem::Helpers::ScanDir" component. Turning on detailed debugging logs all over the system would generate a flood of useless log messages and bog your system down beyond recognition. With "Log::Log4perl", however, you can tell the system: "Continue to log only severe errors in the log file. Open a second log file, turn on full debug logs in the "MySystem::Helpers::ScanDir" component and dump all messages originating from there into the new log file". And all this is possible by just changing the parameters in a configuration file, which your system can re-read even while it's running! How to use it The "Log::Log4perl" package can be initialized in two ways: Either via Perl commands or via a "lib4j"-style configuration file. Initialize via a configuration file This is the easiest way to prepare your system for using "Log::Log4perl". Use a configuration file like this: ############################################################ # A simple root logger with a Log::Dispatch file appender # in Perl. # Mike Schilli 2002 m@perlmeister.com ############################################################ log4j.rootLogger=error, LOGFILE log4j.appender.LOGFILE=Log::Dispatch::File log4j.appender.LOGFILE.filename=/var/log/myerrs.log log4j.appender.LOGFILE.mode=append log4j.appender.LOGFILE.layout=org.apache.log4j.PatternLayout log4j.appender.LOGFILE.layout.ConversionPattern=[%r] %F %L %c - %m%n These lines define your standard logger that's appending severe errors to "/var/log/myerrs.log", using the format [millisecs] source-filename line-number class - message newline Check "Configuration files" for more details on how to control your loggers using a configuration file. Assuming that this file is saved as "log.conf", you need to read it in in the startup section of your code, using the following commands: use Log::Log4perl; Log::Log4perl->init("log.conf"); After that's done *somewhere* in the code, you can retrieve logger objects *anywhere* in the code. Note that there's no need to carry any logger references around with your functions and methods. You can get a logger anytime via a singleton mechanism: package My::MegaPackage; sub some_method { my($param) = @_; use Log::Log4perl; my $log = Log::Log4perl->get_logger("My::MegaPackage"); $log->debug("Debug message"); $log->info("Info message"); $log->error("Error message"); ... } With the configuration file above, "Log::Log4perl" will write "Error message" to the specified log file, but won't do anything for the "debug()" and "info()" calls, because the log level has been set to "ERROR" for all components in the first line of configuration file shown above. Why "Log::Log4perl->get_logger" and not "Log::Log4perl->new"? We don't want to create a new object every time. Usually in OO-Programming, you create an object once and use the reference to it to call its methods. However, this requires that you pass around the object to all functions and the last thing we want is pollute each and every function/method we're using with a handle to the "Logger": sub function { # Brrrr!! my($logger, $some, $other, $parameters) = @_; } Instead, if a function/method wants a reference to the logger, it just calls the Logger's static "get_logger()" method to obtain a reference to the *one and only* possible logger object of a certain category. That's called a *singleton* if you're a Gamma fan. How does the logger know which messages it is supposed to log and which ones to suppress? "Log::Log4perl" works with inheritence: The config file above didn't specify anything about "My::MegaPackage". And yet, we've defined a logger of the category "My::MegaPackage". In this case, "Log::Log4perl" will walk up the class hierarchy ("My" and then the we're at the root) to figure out if a log level is defined somewhere. In the case above, the log level at the root (root *always* defines a log level, but not necessary an appender) defines that the log level is supposed to be "ERROR" -- meaning that *debug* and *info* messages are suppressed. Configuration within Perl Initializing the logger can certainly also be done from within Perl. At last, this is what "Log::Log4perl::Config" does behind the scenes. At the Perl level, we can specify exactly, which loggers work with which appenders and which layouts. Here's the code for a root logger which sends error and higher prioritized messages to the "/tmp/my.log" logfile: # Initialize the logger use Log::Log4perl; use Log::Dispatch::Screen; use Log::Log4perl::Appender; my $app = Log::Log4perl::Appender->new("Log::Dispatch::Screen"); my $layout = Log::Log4perl::Layout::PatternLayout ->new("%d> %F %L %m %n"); $app->layout($layout); my $logger = Log::Log4perl->get_logger("My.Component"); $logger->add_appender($app); And after this, we can, again, start logging *anywhere* in the system like this (remember, we don't want to pass around references, so we just get the logger via the singleton-mechanism): # Use the logger use Log::Log4perl; my $log = Log::Log4perl->get_logger("My::Component"); $log->debug("Debug Message"); $log->info("Info Message"); $log->error("Error Message"); Log Levels There's five predefined log levels: "FATAL", "ERROR", "WARN", "INFO" and "DEBUG" (in descending priority). Your configured logging level has to at least match the priority of the logging message. If your configured logging level is "WARN", then messages logged with "info()" and "debug()" message will be suppressed. "fatal()", "error()" and "warn()" will make their way through, because their priority is higher or equal than the configured setting. Instead of calling the methods $logger->debug("..."); # Log a debug message $logger->info("..."); # Log a info message $logger->warn("..."); # Log a warn message $logger->error("..."); # Log a error message $logger->fatal("..."); # Log a fatal message you could also call the "log()" method with the appropriate level using the constants defined in "Log::Log4perl::Level": use Log::Log4perl::Level; $logger->log($DEBUG, "..."); $logger->log($INFO, "..."); $logger->log($WARN, "..."); $logger->log($ERROR, "..."); $logger->log($FATAL, "..."); But nobody does that, really. Neither does anyone need more logging levels than these predefined ones. If you think you do, I would suggest you look into steering your logging behaviour via the category mechanism. If you need to find out if the currently configured logging level would allow a logger's logging statement to go through, use the logger's "is_*level*()" methods: $logger->is_debug() # True if debug messages would go through $logger->is_info() # True if info messages would go through $logger->is_warn() # True if warn messages would go through $logger->is_error() # True if error messages would go through $logger->is_fatal() # True if fatal messages would go through Example: "$logger->is_warn()" returns true if the logger's current level, as derived from either the logger's category (or, in absence of that, one of the logger's parent's level setting) is $WARN, $ERROR or $FATAL. These level checking functions will come in handy later, when we want to block unnecessary expensive parameter construction in case the logging level is too low to log the statement anyway, like in: if($logger->is_error()) { $logger->error("Erroneous array: @super_long_array"); } If we had just written $logger->error("Erroneous array: @super_long_array"); then Perl would have interpolated @super_long_array into the string via an expensive operation only to figure out shortly after that the string can be ignored entirely because the configured logging level is lower than $ERROR. The to-be-logged message passed to all of the functions described above can consist of an arbitrary number of arguments, which the logging functions just chain together to a single string. Therefore $logger->debug("Hello ", "World", "!"); # and $logger->debug("Hello World!"); are identical. Log and die or warn Often, when you croak / carp / warn / die, you want to log those messages. Rather than doing the following: $logger->fatal($err) && die($err); you can use the following: $logger->logwarn(); $logger->logdie(); These print out log messages in the WARN and FATAL level, respectively, and then call the built-in warn() and die() functions. Since there is an ERROR level between WARN and FATAL, there are two additional helper functions in case you'd like to use ERROR for either warn() or die(): $logger->error_warn(); $logger->error_die(); Finally, there's the Carp functions that do just what the Carp functions do, but with logging: $logger->logcarp(); # warn w/ 1-level stack trace $logger->logcluck(); # warn w/ full stack trace $logger->logcroak(); # die w/ 1-level stack trace $logger->logconfess(); # die w/ full stack trace Appenders If you don't define any appenders, nothing will happen. Appenders will be triggered whenever the configured logging level requires a message to be logged and not suppressed. "Log::Log4perl" doesn't define any appenders by default, not even the root logger has one. "Log::Log4perl" utilizes *Dave Rolskys* excellent "Log::Dispatch" module to implement a wide variety of different appenders. You can have your messages written to STDOUT, to a file or to a database -- or to all of them at once if you desire to do so. Here's the list of appender modules currently available via "Log::Dispatch": Log::Dispatch::ApacheLog Log::Dispatch::DBI (by Tatsuhiko Miyagawa) Log::Dispatch::Email, Log::Dispatch::Email::MailSend, Log::Dispatch::Email::MailSendmail, Log::Dispatch::Email::MIMELite Log::Dispatch::File Log::Dispatch::Handle Log::Dispatch::Screen Log::Dispatch::Syslog Log::Dispatch::Tk (by Dominique Dumont) For additional information on appenders, please check the Log::Log4perl::Appender manual page. Now let's assume that we want to go overboard and log "info()" or higher prioritized messages in the "My::Category" class to both STDOUT and to a log file, say "/tmp/my.log". In the initialisation section of your system, just define two appenders using the readily available "Log::Dispatch::File" and "Log::Dispatch::Screen" modules via the "Log::Log4perl::Appender" wrapper: ######################## # Initialisation section ######################## use Log::Log4perl; use Log::Log4perl::Layout; use Log::Log4perl::Level; # Define a category logger my $log = Log::Log4perl->get_logger("My::Category"); # Define a layout my $layout = Log::Log4perl->new("[%r] %F %L %m%n"); # Define a file appender my $file_appender = Log::Log4perl::Appender->new( "Log::Dispatch::File", name => "filelog", filename => "/tmp/my.log"); # Define a stdout appender my $stdout_appender = Log::Log4perl::Appender->new( "Log::Dispatch::Screen", name => "screenlog", stderr => 0); # Have both appenders use the same layout (could be different) $stdout_appender->layout($layout); $file_appender->layout($layout); $log->add_appender($stdout_appender); $log->add_appender($file_appender); $log->level($INFO); Please note the class of the "Log::Dispatch" object is passed as a *string* to "Log::Log4perl::Appender" in the *first* argument. Behind the scenes, "Log::Log4perl::Appender" will create the necessary "Log::Dispatch::*" object and pass along the name value pairs we provided to "Log::Log4perl::Appender->new()" after the first argument. The "name" value is optional and if you don't provide one, "Log::Log4perl::Appender->new()" will create a unique one for you. The names and values of additional parameters are dependent on the requirements of the particular "Log::Dispatch::*" class and can be looked up in their manual pages. On a side note: In case you're wondering if "Log::Log4perl::Appender->new()" will also take care of the "min_level" argument to the "Log::Dispatch::*" constructors called behind the scenes -- yes, it does. This is because we want the "Log::Dispatch" objects to blindly log everything we send them ("debug" is their lowest setting) because *we* in "Log::Log4perl" want to call the shots and decide on when and what to log. The call to the appender's *layout()* method specifies the format (as a previously created "Log::Log4perl::PatternLayout" object) in which the message is being logged in the specified appender. The format shown above is logging not only the message but also the number of milliseconds since the program has started (%r), the name of the file the call to the logger has happened and the line number there (%F and %L), the message itself (%m) and a OS-specific newline character (%n). For more detailed info on layout formats, see "Log Layouts". If you don't specify a layout, the logger will fall back to "Log::Log4perl::SimpleLayout", which logs the debug level, a hyphen (-) and the log message. Once the initialisation shown above has happened once, typically in the startup code of your system, just use this logger anywhere in your system (or better yet, only in "My::Category", since we defined it this way) as often as you like: ########################## # ... in some function ... ########################## my $log = Log::Log4perl->get_logger("My::Category"); $log->info("This is an informational message"); Above, we chose to define a *category* logger ("My::Category") in a specific way. This will cause only messages originating from this specific category logger to be logged in the defined format and locations. Instead, we could have configured the *root* logger with the appenders and layout shown above. Now ########################## # ... in some function ... ########################## my $log = Log::Log4perl->get_logger("My::Category"); $log->info("This is an informational message"); will trigger a logger with no layout or appenders or even a level defined. This logger, however, will inherit the level from categories up the hierarchy -- ultimately the root logger, since there's no "My" logger. Once it detects that it needs to log a message, it will first try to find its own appenders (which it doesn't have any of) and then walk up the hierarchy (first "My", then "root") to call any appenders defined there. This will result in exactly the same behaviour as shown above -- with the exception that other category loggers could also use the root logger's appenders and layouts, but could certainly define their own categories and levels. Turn off a component "Log4perl" doesn't only allow you to selectively switch *on* a category of log messages, you can also use the mechanism to selectively *disable* logging in certain components whereas logging is kept turned on in higher-level categories. This mechanism comes in handy if you find that while bumping up the logging level of a high-level (i. e. close to root) category, that one component logs more than it should, Here's how it works: ############################################################ # Turn off logging in a lower-level category while keeping # it active in higher-level categories. ############################################################ log4j.rootLogger=debug, LOGFILE log4j.logger.deep.down.the.hierarchy = error, LOGFILE # ... Define appenders ... This way, log messages issued from within "Deep::Down::The::Hierarchy" and below will be logged only if they're "error" or worse, while in all other system components even "debug" messages will be logged. Configuration files As shown above, you can define "Log::Log4perl" loggers both from within your Perl code or from configuration files. The latter have the unbeatible advantage that you can modify your system's logging behaviour without interfering with the code at all. So even if your code is being run by somebody who's totally oblivious to Perl, they still can adapt the module's logging behaviour to their needs. "Log::Log4perl" has been designed to understand "Log4j" configuration files -- as used by the original Java implementation. Instead of reiterating the format description in [2], let me just list three examples (also derived from [2]), which should also illustrate how it works: log4j.rootLogger=DEBUG, A1 log4j.appender.A1=ConsoleAppender log4j.appender.A1.layout=org.apache.log4j.PatternLayout log4j.appender.A1.layout.ConversionPattern=%-4r [%t] %-5p %c %x - %m%n This enables messages of priority "debug" or higher in the root hierarchy and has the system write them to the console. "ConsoleAppender" is a Java appender, but "Log::Log4perl" jumps through a significant number of hoops internally to map these to their corresponding Perl classes, "Log::Dispatch::Screen" in this case. Second example: log4j.rootLogger=DEBUG, A1 log4j.appender.A1=Log::Dispatch::Screen log4j.appender.A1.layout=org.apache.log4j.PatternLayout log4j.appender.A1.layout.ConversionPattern=%d [%t] %-5p %c - %m%n log4j.logger.com.foo=WARN This defines two loggers: The root logger and the "com.foo" logger. The root logger is easily triggered by debug-messages, but the "com.foo" logger makes sure that messages issued within the "Com::Foo" component and below are only forwarded to the appender if they're of priority *warning* or higher. Note that the "com.foo" logger doesn't define an appender. Therefore, it will just propagate the message up the hierarchy until the root logger picks it up and forwards it to the one and only appender of the root category, using the format defined for it. Third example: log4j.rootLogger=debug, stdout, R log4j.appender.stdout=org.apache.log4j.ConsoleAppender log4j.appender.stdout.layout=org.apache.log4j.PatternLayout log4j.appender.stdout.layout.ConversionPattern=%5p [%t] (%F:%L) - %m%n log4j.appender.R=org.apache.log4j.FileAppender log4j.appender.R.File=example.log log4j.appender.R.layout=org.apache.log4j.PatternLayout log4j.appender.R.layout.ConversionPattern=%p %t %c - %m%n The root logger defines two appenders here: "stdout", which uses "org.apache.log4j.ConsoleAppender" (ultimately mapped by "Log::Log4perl" to "Log::Dispatch::Screen") to write to the screen. And "R", a "org.apache.log4j.RollingFileAppender" (ultimately mapped by "Log::Log4perl" to "Log::Dispatch::File" with the "File" attribute specifying the log file. Log Layouts If the logging engine passes a message to an appender, because it thinks it should be logged, the appender doesn't just write it out haphazardly. There's ways to tell the appender how to format the message and add all sorts of interesting data to it: The date and time when the event happened, the file, the line number, the debug level of the logger and others. There's currently two layouts defined in "Log::Log4perl": "Log::Log4perl::Layout::SimpleLayout" and "Log::Log4perl::Layout::Patternlayout": "Log::Log4perl::SimpleLayout" formats a message in a simple way and just prepends it by the debug level and a hyphen: ""$level - $message", for example "FATAL - Can't open password file". "Log::Log4perl::PatternLayout" on the other hand is very powerful and allows for a very flexible format in "printf"-style. The format string can contain a number of placeholders which will be replaced by the logging engine when it's time to log the message: %c Category of the logging event. %C Fully qualified package (or class) name of the caller %d Current date in yyyy/mm/dd hh:mm:ss format %F File where the logging event occurred %l Fully qualified name of the calling method followed by the callers source the file name and line number between parentheses. %L Line number within the file where the log statement was issued %m The message to be logged %M Method or function where the logging request was issued %n Newline (OS-independent) %p Priority of the logging event %r Number of milliseconds elapsed from program start to logging event %% A literal percent (%) sign Also, %d can be fine-tuned to display only certain characteristics of a date, according to the SimpleDateFormat in the Java World (http://java.sun.com/j2se/1.3/docs/api/java/text/SimpleDateFormat.ht ml) In this way, %d{HH:mm} displays only hours and minutes of the current date, while %d{yy, EEEE} displays a two-digit year, followed by a spelled-out (like "Wednesday"). Similar options are available for shrinking the displayed category or limit file/path components, %f{1} only displays the source file *name* without any path components while %f logs the full path. %c{2} only logs the last two components of the current category, "Foo::Bar::Baz" becomes "Bar::Baz" and saves space. See Log::Log4perl::Layout::PatternLayout for details. All placeholders are quantifiable, just like in *printf*. Following this tradition, "%-20c" will reserve 20 chars for the category and left-justify it. Layouts are objects, here's how you create them: # Create a simple layout my $simple = Log::Log4perl::SimpleLayout(); # create a flexible layout: # ("yyyy/mm/dd hh:mm:ss (file:lineno)> message\n") my $pattern = Log::Log4perl::PatternLayout("%d (%F:%L)> %m%n"); Every appender has exactly one layout assigned to it. You assign the layout to the appender using the appender's "layout()" object: my $app = Log::Log4perl::Appender->new( "Log::Dispatch::Screen", name => "screenlog", stderr => 0); # Assign the previously defined flexible layout $app->layout($pattern); # Add the appender to a previously defined logger $logger->add_appender($app); # ... and you're good to go! $logger->debug("Blah"); # => "2002/07/10 23:55:35 (test.pl:207)> Blah\n" If you don't specify a layout for an appender, the logger will fall back to "SimpleLayout". For more details on logging and how to use the flexible and the simple format, check out the original "log4j" website under http://jakarta.apache.org/log4j/docs/api/org/apache/log4j/SimpleLayout.html http://jakarta.apache.org/log4j/docs/api/org/apache/log4j/PatternLayout.html Penalties Logging comes with a price tag. "Log::Log4perl" is currently being optimized to allow for maximum performance, both with logging enabled and disabled. But you need to be aware that there's a small hit every time your code encounters a log statement -- no matter if logging is enabled or not. "Log::Log4perl" has been designed to keep this so low that it will be unnoticable to most applications. Here's a couple of tricks which help "Log::Log4perl" to avoid unnecessary delays: You can save serious time if you're logging something like # Expensive in non-debug mode! for (@super_long_array) { $Logger->debug("Element: $_\n"); } and @super_long_array is fairly big, so looping through it is pretty expensive. Only you, the programmer, knows that going through that "for" loop can be skipped entirely if the current logging level for the actual component is higher than "debug". In this case, use this instead: # Cheap in non-debug mode! if($Logger->is_debug()) { for (@super_long_array) { $Logger->debug("Element: $_\n"); } } If you're afraid that the way you're generating the parameters to the of the logging function is fairly expensive, use closures: # Passed as subroutine ref use Data::Dumper; $Logger->debug(sub { Dumper($data) } ); This won't unravel $data via Dumper() unless it's actually needed because it's logged. Categories "Log::Log4perl" uses *categories* to determine if a log statement in a component should be executed or suppressed at the current logging level. Most of the time, these categories are just the classes the log statements are located in: package Candy::Twix; sub new { my $logger = Log::Log4perl->new("Candy::Twix"); $logger->debug("Creating a new Twix bar"); bless {}, shift; } # ... package Candy::Snickers; sub new { my $logger = Log::Log4perl->new("Candy.Snickers"); $logger->debug("Creating a new Snickers bar"); bless {}, shift; } # ... package main; Log::Log4perl->init("mylogdefs.conf") or die "Whoa, cannot read mylogdefs.conf!"; # => "LOG> Creating a new Snickers bar" my $first = Candy::Snickers->new(); # => "LOG> Creating a new Twix bar" my $second = Candy::Twix->new(); Note that you can separate your category hierarchy levels using either dots like in Java (.) or double-colons (::) like in Perl. Both notations are equivalent and are handled the same way internally. However, categories are just there to make use of inheritance: if you invoke a logger in a sub-category, it will bubble up the hierarchy and call the appropriate appenders. Internally, categories are not related to the class hierarchy of the program at all -- they're purely virtual. You can use arbitrary categories -- for example in the following program, which isn't oo-style, but procedural: sub print_portfolio { my $log = Log::Log4perl->new("user.portfolio"); $log->debug("Quotes requested: @_"); for(@_) { print "$_: ", get_quote($_), "\n"; } } sub get_quote { my $log = Log::Log4perl->new("internet.quotesystem"); $log->debug("Fetching quote: $_[0]"); return yahoo_quote($_[0]); } The logger in first function, "print_portfolio", is assigned the (virtual) "user.portfolio" category. Depending on the "Log4perl" configuration, this will either call a "user.portfolio" appender, a "user" appender, or an appender assigned to root -- without "user.portfolio" having any relevance to the class system used in the program. The logger in the second function adheres to the "internet.quotesystem" category -- again, maybe because it's bundled with other Internet functions, but not because there would be a class of this name somewhere. However, be careful, don't go overboard: if you're developing a system in object-oriented style, using the class hierarchy is usually your best choice. Think about the people taking over your code one day: The class hierarchy is probably what they know right up front, so it's easy for them to tune the logging to their needs. Cool Tricks Shortcuts When getting an instance of a logger, instead of saying use Log::Log4perl; my $logger = Log::Log4perl->get_logger(); it's often more convenient to import the "get_logger" method from "Log::Log4perl" into the current namespace: use Log::Log4perl qw(get_logger); my $logger = get_logger(); Alternative initialization Instead of having "init()" read in a configuration file, you can also pass in a reference to a string, containing the content of the file: Log::Log4perl->init( \$config_text ); Also, if you've got the "name=value" pairs of the configuration in a hash, you can just as well initialized "Log::Log4perl" with a reference to it: my %key_value_pairs = ( "log4j.rootLogger" => "error, LOGFILE", "log4j.appender.LOGFILE" => "Log::Dispatch::File", ... ); Log::Log4perl->init( \%key_value_pairs ); Incrementing and Decrementing the Log Levels Log4perl provides some internal functions for quickly adjusting the log level from within a running Perl program. Now, some people might argue that you should adjust your levels from within an external Log4perl configuration file, but Log4perl is everybody's darling. Typically run-time adjusting of levels is done at the beginning, or in response to some external input (like a "more logging" runtime command for diagnostics). To increase the level of logging currently being done, use: $logger->more_logging($delta); and to decrease it, use: $logger->less_logging($delta); $delta must be a positive integer (for now, we may fix this later ;). There are also two equivalent functions: $logger->inc_level($delta); $logger->dec_level($delta); They're included to allow you a choice in readability. Some folks will prefer more/less_logging, as they're fairly clear in what they do, and allow the programmer not to worry too much about what a Level is and whether a higher Level means more or less logging. However, other folks who do understand and have lots of code that deals with levels will probably prefer the inc_level() and dec_level() methods as they want to work with Levels and not worry about whether that means more or less logging. :) That diatribe aside, typically you'll use more_logging() or inc_level() as such: my $v = 0; # default level of verbosity. GetOptions("v+" => \$v, ...); $logger->more_logging($v); # inc logging level once for each -v in ARGV Custom Log Levels First off, let me tell you that creating custom levels is heavily deprechiated by the log4j folks. Indeed, instead of creating additional levels on top of the predefined DEBUG, INFO, WARN, ERROR and FATAL, you should use categories to control the amount of logging smartly, based on the location of the log-active code in the system. Nevertheless, Log4perl provides a nice way to create custom levels via the create_custom_level() routine function. However, this must be done before the first call to init() or get_logger(). Say you want to create a NOTIFY logging level that comes after WARN (and thus before INFO). You'd do such as follows: use Log::Log4perl; use Log::Log4perl::Level; Log::Log4perl::Logger::create_custom_level("NOTIFY", "WARN"); And that's it! create_custom_level() creates the following functions / variables for level FOO: $FOO_INT # integer to use in toLevel() $logger->foo() # log function to log if level = FOO $logger->is_foo() # true if current level is >= FOO These levels can also be used in your config file, but note that your config file probably won't be portable to another log4perl or log4j environment unless you've made the appropriate mods there too. How about Log::Dispatch::Config? Tatsuhiko Miyagawa's "Log::Dispatch::Config" is a very clever simplified logger implementation, covering some of the *log4j* functionality. Among the things that "Log::Log4perl" can but "Log::Dispatch::Config" can't are: * You can't assing categories to loggers. For small systems that's fine, but if you can't turn off and on detailed logging in only a tiny subsystem of your environment, you're missing out on a majorly useful log4j feature. * Defining appender thresholds. Important if you want to solve problems like "log all messages of level FATAL to STDERR, plus log all DEBUG messages in "Foo::Bar" to a log file". If you don't have appenders thresholds, there's no way to prevent cluttering STDERR with DEBUG messages. * PatternLayout specifications in accordance with the standard (e.g. "%d{HH:mm}"). Bottom line: Log::Dispatch::Config is fine for small systems with simple logging requirements. However, if you're designing a system with lots of subsystems which you need to control independantly, you'll love the features of "Log::Log4perl", which is equally easy to use. Using Log::Log4perl from wrapper classes If you don't use "Log::Log4perl" as described above, but from a wrapper class (like your own Logging class which in turn uses "Log::Log4perl"), the pattern layout will generate wrong data for %F, %C, %L and the like. Reason for this is that "Log::Log4perl"'s loggers assume a static caller depth to the application that's using them. If you're using one (or more) wrapper classes, "Log::Log4perl" will indicate where your logger classes called the loggers, not where your application called your wrapper, which is probably what you want in this case. But don't dispair, there's a solution: Just increase the value of $Log::Log4perl::caller_depth (defaults to 0) by one for every wrapper that's in between your application and "Log::Log4perl", then "Log::Log4perl" will compensate for the difference. EXAMPLE A simple example to cut-and-paste and get started: use Log::Log4perl qw(get_logger); my $conf = q( log4perl.category.Bar.Twix = WARN, Screen log4perl.appender.Screen = Log::Dispatch::Screen log4perl.appender.Screen.layout = \ Log::Log4perl::Layout::PatternLayout log4perl.appender.Screen.layout.ConversionPattern = %d %m %n ); Log::Log4perl::init(\$conf); my $logger = get_logger("Bar::Twix"); $logger->error("Blah"); INSTALLATION "Log::Log4perl" needs "Log::Dispatch" (2.00 or better) from CPAN. "Time::HiRes" (1.20 or better) is required only if you need the fine-grained time stamps of the %r parameter in "Log::Log4perl::Layout::PatternLayout". "Log::Dispatch" is automatically fetched from CPAN if you're using the CPAN shell (CPAN.pm), because it's listed as requirement in Makefile.PL. Manual installation works as usual with perl Makefile.PL make make test make install DEVELOPMENT "Log::Log4perl" is under heavy development. The latest CVS tarball can be obtained from SourceForge, check "http://log4perl.sourceforge.net" for details. Bug reports and feedback are always welcome, just email to our mailing list shown in CONTACT. REFERENCES [1] Michael Schilli, "Retire your debugger, log smartly with Log::Log4perl!", Tutorial on perl.com, 09/2002, http://www.perl.com/pub/a/2002/09/11/log4perl.html [2] Ceki Gülcü, "Short introduction to log4j", http://jakarta.apache.org/log4j/docs/manual.html [3] Vipan Singla, "Don't Use System.out.println! Use Log4j.", http://www.vipan.com/htdocs/log4jhelp.html [4] The Log::Log4perl project home page: http://log4perl.sourceforge.net CONTACT Please send bug reports or requests for enhancements to the authors via our log4perl development mailing list: log4perl-devel@lists.sourceforge.net AUTHORS Mike Schilli Kevin Goess Contributors: Chris R. Donnelly Erik Selberg COPYRIGHT AND LICENSE Copyright 2002 by Mike Schilli and Kevin Goess . This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.