Skip to content

HTTPS clone URL

Subversion checkout URL

You can clone with
or
.
Download ZIP
Log4j Implementation For Perl
Perl Shell

Fetching latest commit…

Cannot retrieve the latest commit at this time

Failed to load latest commit information.
docs
eg
lib/Log
t
.cvsignore
Changes
MANIFEST
MANIFEST.SKIP
Makefile.PL
README

README

######################################################################
    Log::Log4perl 0.15
######################################################################

NAME
    Log::Log4perl - Log4j implementation for Perl

DESCRIPTION
    "Log::Log4perl" implements the widely popular "Log4j" logging package
    ([1]) in pure Perl.

    A WORD OF CAUTION: THIS LIBRARY IS 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 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 [1] for more details on how to define loggers with "Log4j", the
    equivalent Java implementation of this package.

    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::File;
      use Log::Log4perl::Layout;

      my $disp   = Log::Dispatch::File->new(
                       name      => "screenlog",
                       filename  => "/tmp/my.log",
                       min_level => "debug",
                   );

      my $log = Log::Log4perl->get_logger(""); # root logger
      $log->layout("[%r] %F %L %m%n");
      $log->add_appender($disp);

    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, though, 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.

    The constants defined in "Log::Log4perl::Level" will come in handy
    later, however, when we want to block unnecessary expensive parameter
    construction in case the logging level is too low to log anyway like in:

        if($logger->level() >= $ERROR) {
            $logger->error("Erroneous array: @super_long_array");
        }

    If we just had 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.

  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 so.

    Here's the list of appender modules currently available via
    "Log::Dispatch":

           Log::Dispatch::ApacheLog
           Log::Dispatch::DBI
           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

    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:

      ########################
      # Initialisation section
      ########################
      use Log::Log4perl;
      use Log::Dispatch::File;
      use Log::Log4perl::Layout;
      use Log::Log4perl::Level;

      my $log = Log::Log4perl->get_logger("My::Category");

      my $file_appender = Log::Dispatch::File->new(
          name      => "filelog",
          filename  => "/tmp/my.log",
          min_level => "debug",
      );

      my $stdout_appender = Log::Dispatch::Screen->new(
          name      => "screenlog",
          stderr    => 0,
          min_level => "debug",
      );

      $log->level($INFO);
      $log->layout("screenlog", "[%r] %F %L %m%n");
      $log->layout("filelog", "[%r] %F %L %m%n");
      $log->add_appender("screenlog", $stdout_appender);
      $log->add_appender("filelog", $file_appender);

    Please note that the constructor calls to the "Log::Dispatch" objects
    are all setting the mandatory "min_level" parameter to "debug". 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 *layout()* method specifies the format in which the
    message is logged in the appender specified by name. The formats shown
    above are 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 the Layouts manpage. If
    you don't specify a layout, the logger will just log the plain 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 [1], let me just list three
    examples (also derived from [1]), 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.

  Layout patterns

    Instead of copying the original documentation from which this format has
    been derived for "Log::Log4perl", please refer to it directly:

        http://jakarta.apache.org/log4j/docs/api/org/apache/log4j/PatternLayout.html

    Only exceptions so far are "%t", "%x" and "%X" which aren't implemented
    yet and "%d" which stubburnly uses "yyyy/mm/dd hh:mm:ss" as the time
    stamp format (no support yet for "%d{yada}".

  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");
            }
        }

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 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.

How about Log::Dispatch::Config?
    Yeah, I've seen it. I like it, but I think it is too dependent on
    defining everything in a configuration file. I've designed
    "Log::Log4perl" to be more flexible.

AUTHORS
        Mike Schilli, <m@perlmeister.com>
        Kevin Goess, <cpan@goess.org>

INSTALLATION
    "Log::Log4perl" needs "Log::Dispatch" (2.00 or better) and "Time::HiRes"
    (1.20 or better) from CPAN. They're automatically fetched if you're
    using the CPAN shell (CPAN.pm), because they're listed as requirements
    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 sourcforge, check "http://log4perl.sorceforge.net" for
    details. Bug reports and feedback are always welcome, just email to the
    authors.

REFERENCES
    [1] Ceki Gülcü, "Short introduction to log4j",
        http://jakarta.apache.org/log4j/docs/manual.html

    [2] Vipan Singla, "Don't Use System.out.println! Use Log4j.",
        http://www.vipan.com/htdocs/log4jhelp.html

COPYRIGHT AND LICENSE
    Copyright 2002 by Mike Schilli <m@perlmeister.com> and Kevin Goess
    <cpan@goess.org>.

    This library is free software; you can redistribute it and/or modify it
    under the same terms as Perl itself.

Something went wrong with that request. Please try again.