Log::Handler - Log messages to several outputs.


        use Log::Handler;
        my $log = Log::Handler->new();
            file => {
                filename => "file.log",
                maxlevel => "debug",
                minlevel => "warning",


        use Log::Handler;
        my $log = Log::Handler->new(
            screen => {
                log_to   => "STDOUT",
                maxlevel => "debug",
                minlevel => "debug",
                message_layout => "%T [%L] %m (%C)",
            screen => {
                log_to   => "STDOUT",
                maxlevel => "info",
                minlevel => "notice",
            screen => {
                log_to   => "STDERR",
                maxlevel => "warning",
                minlevel => "emergency",


        use Log::Handler;
        my $log = Log::Handler->new();
        $log->config( config => "logger.conf" );
        # and maybe later
        $log->reload( config => "logger.conf" );


        # create a application wide logger
        package MyApp;
        use Log::Handler;
        my $log = Log::Handler->create_logger("myapp");
        $log->add(screen => { maxlevel => "info" });
        $log->info("info message");
        # get logger with get_logger()
        package MyApp::Admin;
        use Log::Handler;
        my $log = Log::Handler->get_logger("myapp");
        $log->info("info message from MyApp::Admin");


    The Log::Handler is a object oriented handler for logging, tracing and
    debugging. It is very easy to use and provides a simple interface for
    multiple output objects with lots of configuration parameters. You can
    easily filter the amount of logged information on a per-output base,
    define priorities, create patterns to format the messages and reload
    the complete logging machine.

    See the documentation for details.


    Note that the default for option newline is now set to TRUE and
    newlines will be appended automatically to each message if no newline

    A long time I thought about this serious change and have come to the
    decision to change it.

    The default for option mode from Log::Handler::Output::File is now
    append and not excl anymore.

    The methods reload() and validate() are new since version 0.62. I
    tested it with, and and it runs fine. If you
    find bugs then open a bug report please :-)


    There are eigth levels available:

        7   debug
        6   info
        5   notice
        4   warning, warn
        3   error, err
        2   critical, crit
        1   alert
        0   emergency, emerg

    debug is the highest and emergency is the lowest level.

    Level debug is the highest level because it basically says to log every


 Level methods




    warning(), warn()

    error(), err()

    critical(), crit()


    emergency(), emerg()

    The call of a log level method is very simple:

        $log->info("Hello World! How are you?");

    Or maybe:

        $log->info("Hello World!", "How are you?");

    Both calls would log - if level INFO is active:

        Feb 01 12:56:31 [INFO] Hello World! How are you?

 is_* methods




    is_warning(), is_warn()

    is_error(), is_err()

    is_critical(), is_crit()


    is_emergency(), is_emerg()

    These twelve methods could be very useful if you want to kwow if the
    current level would log the message. All methods returns TRUE if the
    current set of minlevel and maxlevel would log the message and FALSE if


    fatal, is_fatal





    For a full list take a look into the documentation of



    Call new() to create a new log handler object.

        my $log = Log::Handler->new();


    Call add() to add a new output object.

    The method expects 2 parts of options; the options for the handler and
    the options for the output module you want to use. The output modules
    got it's own documentation for all options.


        use Log::Handler;
        my $log = Log::Handler->new();
            # Add "file output"
            file => {
                # handler options (see Log::Handler)
                timeformat      => "%Y/%m/%d %H:%M:%S",
                message_layout  => "%T [%L] %S: %m",
                maxlevel        => "debug",
                minlevel        => "emergency",
                die_on_errors   => 1,
                debug_trace     => 0,
                debug_mode      => 2,
                debug_skip      => 0,
                # file options (see Log::Handler::Output::File)
                filename        => "file.log",
                filelock        => 1,
                fileopen        => 1,
                reopen          => 1,
                autoflush       => 1,
                permissions     => "0660",
                utf8            => 1,

    Take a look to Log::Handler::Examples for more examples.

    The following options are possible for the handler:

    maxlevel and minlevel

      With these options it's possible to set the log levels for your


          maxlevel => "error"
          minlevel => "emergency"
          # or
          maxlevel => "err"
          minlevel => "emerg"
          # or
          maxlevel => 3
          minlevel => 0

      It's possible to set the log level as string or as number. The
      default setting for maxlevel is warning and the default setting for
      minlevel is emergency.

      Example: If maxlevel is set to warning and minlevel to emergency then
      the levels warning, error, critical, alert and emergency would be

      You can set both to 8 or nothing if you want to disable the logging


      The option timeformat is used to set the format for the placeholder
      %T. The string is converted with POSIX::strftime. The default format
      is set to "%b %d %H:%M:%S" and looks like

          Feb 01 12:56:31

      If you would set the format to "%Y/%m/%d %H:%M:%S" it would looks

          2007/02/01 12:56:31


      This options works like timeformat. You can set a format that is used
      for the placeholder %D. It's just useful if you want to split the
      date and time:

          $log->add(file => {
              filename       => "file.log",
              dateformat     => "%Y-%m-%d",
              timeformat     => "%H:%M:%S",
              message_layout => "%D %T %L %m",
          $log->error("an error here");

      This looks like

          2007-02-01 12:56:31 ERROR an error here

      This option is not used by default.


      newline is a very helpful option. It let the logger appends a newline
      to the message if a newline doesn't exist.

          0 - do nothing
          1 - append a newline if not exist (default)


              screen => {
                  newline  => 1,
                  maxlevel => "info",

      In both cases the message would be logged with a newline at the end.


      With this option it's possible to create your own message layout with
      different placeholders in printf() style. The available placeholders

          %L   Log level
          %T   Time or full timestamp (option timeformat)
          %D   Date (option dateformat)
          %P   PID
          %H   Hostname
          %U   User name
          %G   Group name
          %N   Newline
          %S   Program name
          %C   Caller - filename and line number
          %p   Caller - package name
          %f   Caller - file name
          %l   Caller - line number
          %s   Caller - subroutine name
          %r   Runtime in seconds since program start
          %t   Time measurement - replaced with the time since the last call of $log->$level
          %m   Message
          %%   Percent

      The default message layout is set to "%T [%L] %m".

      As example the following code

          $log->alert("foo bar");

      would log

          Feb 01 12:56:31 [ALERT] foo bar

      If you set message_layout to

          message_layout => "%T foo %L bar %m (%C)"

      and call


      then it would log

          Feb 01 12:56:31 foo INFO bar baz (, line 40)

      Traces will be appended after the complete message.

      You can create your own placeholders with the method set_pattern().


      This option is just useful if you want to forward messages to output
      modules that needs the parts of a message as a hash reference - as
      example Log::Handler::Output::Forward, Log::Handler::Output::DBI or

      The option expects a list of placeholders:

          # as a array reference
          message_pattern => [ qw/%T %L %H %m/ ]
          # or as a string
          message_pattern => "%T %L %H %m"

      The patterns will be replaced with real names as hash keys.

          %L   level
          %T   time
          %D   date
          %P   pid
          %H   hostname
          %U   user
          %G   group
          %N   newline
          %r   runtime
          %C   caller
          %p   package
          %f   filename
          %l   line
          %s   subroutine
          %S   progname
          %t   mtime
          %m   message

      Here a full code example:

          use Log::Handler;
          my $log = Log::Handler->new();
          $log->add(forward => {
              forward_to      => \&my_func,
              message_pattern => [ qw/%T %L %H %m/ ],
              message_layout  => "%m",
              maxlevel        => "info",
          $log->info("a forwarded message");
          # now you can access it
          sub my_func {
              my $msg = shift;
              print "Timestamp: $msg->{time}\n";
              print "Level:     $msg->{level}\n";
              print "Hostname:  $msg->{hostname}\n";
              print "Message:   $msg->{message}\n";


      prepare_message is useful if you want to do something with the
      message before it will be logged... maybe you want to create your own
      layout because message_layout doesn't meet your claim.

              screen => {
                  newline => 1,
                  message_layout  => "%m (%t)",
                  message_pattern => [ qw/%T %L %H %m/ ],
                  prepare_message => \&format,
          sub format {
              my $m = shift;
              $m->{message} = sprintf("%-20s %-20s %-20s %s",
                  $m->{time}, $m->{level}, $m->{hostname}, $m->{message});

      The output looks like

          Mar 08 15:14:20      ERROR                h1434036             foo (0.039694)
          Mar 08 15:14:20      ERROR                h1434036             bar (0.000510)
          Mar 08 15:14:20      ERROR                h1434036             baz (0.000274)


      With this option you can set the priority of your output objects.
      This means that messages will be logged at first to the outputs with
      a higher priority. If this option is not set then the default
      priority begins with 10 and will be increased +1 with each output.

      We add a output with no priority

          $log->add(file => { filename => "file1.log" });

      This output gets the priority of 10. Now we add another output

          $log->add(file => { filename => "file2.log" });

      This output gets the priority of 11... and so on.

      Messages would be logged at first to the output with the priority of
      10 and then to the output with the priority of 11. Now you can add
      another output and set the priority to 1.

          $log->add(screen => { dump => 1, priority => 1 });

      Messages would be logged now at first to the screen.


      Set die_on_errors to 0 if you don't want that the handler dies on
      failed write operations.

          0 - to disable it
          1 - to enable it

      If you set die_on_errors to 0 then you have to control it yourself.

          $log->info("info message") or die $log->errstr();
          # or Log::Handler->errstr()
          # or Log::Handler::errstr()
          # or $Log::Handler::ERRSTR


      This option is set to 1 by default.

      Take a look to the description of the method reload for more
      information about this option.


      With this option it's possible to set a filter. If the filter is set
      then only messages will be logged that match the filter. You can pass
      a regexp, a code reference or a simple string. Example:

          $log->add(file => {
              filename => "file.log",
              maxlevel => 6,
              filter_message => qr/log this/,
              # or
              # filter_message => "log this",
              # filter_message => '^log only this$',
          $log->info("log this");
          $log->info("but not that");

      If you pass your own code then you have to check the message

          $log->add(file => {
              filename => "file.log",
              maxlevel => 6,
              filter_message => \&my_filter
          # return TRUE if you want to log the message, FALSE if not
          sub my_filter {
              my $msg = shift;
              $msg->{message} =~ /your filter/;

      It's also possible to define a simple condition with matches. Just
      pass a hash reference with the options matchN and condition. Example:

          $log->add(file => {
              filename => "file.log",
              maxlevel => 6,
              filter_message => {
                  match1    => "log this",
                  match2    => qr/with that/,
                  match3    => "(?:or this|or that)",
                  condition => "(match1 && match2) || match3",

      NOTE that re-eval in regexes is not valid! Something like

          match1 => '(?{unlink("file.txt")})'

      would cause an error!


      This is the opposite of option filter_message, but it's only possible
      to set a simple string or regular expression.

          $log->add(file => {
              filename => "file.log",
              maxlevel => 6,
              skip => '^do not log this.+$'


      The parameter category works like filter_caller but is much easier to
      configure. You can set a comma separated list of modules. As example
      if you would set the category to

          category => "MyApp::User"

      then all messages of MyApp::User and the submodules would be logged.


          my $log = Log::Handler->new();
              screen => {
                  maxlevel => "info",
                  category => "MyApp::User, MyApp::Session"
          package MyApp;
          package MyApp::Products;
          package MyApp::User;
          package MyApp::Users;
          package MyApp::User::Settings;
          package MyApp::Session;
          package MyApp::Session::Settings;

      The messages of MyApp and MyApp::Products would not be logged.

      The usage of categories is much faster than to filter by caller.


      You can use this option to set a package name. Only messages from
      this packages will be logged.


          my $log = Log::Handler->new();
          $log->add(screen => {
              maxlevel => "info",
              filter_caller  => qr/^Foo::Bar\z/,
              # or
              # filter_caller => "^Foo::Bar\z",
          package Foo::Bar;
          $log->info("log this");
          package Foo::Baz;
          $log->info("but not that");

      This would only log the message from the package Foo::Bar.


      This option is just the opposite of filter_caller.

      If you want to log messages from all callers but Foo::Bar:

          except_caller => qr/^Foo::Bar\z/


      You can set an alias if you want to get the output object later.

          my $log = Log::Handler->new();
          $log->add(screen => {
              maxlevel => 7,
              alias    => "screen-out",
          my $screen = $log->output("screen-out");
          $screen->log(message => "foo");
          # or in one step
          $log->output("screen-out")->log(message => "foo");


      You can activate a debugger that writes caller() information about
      each active log level. The debugger is logging all defined values
      except hints and bitmask. Set debug_trace to 1 to activate the
      debugger. The debugger is set to 0 by default.


      There are two debug modes: line(1) and block(2) mode. The default
      mode is 1.

      The line mode looks like this:

          use strict;
          use warnings;
          use Log::Handler;
          my $log = Log::Handler->new()
          $log->add(file => {
              filename    => "*STDOUT",
              maxlevel    => "debug",
              debug_trace => 1,
              debug_mode  => 1
          sub test1 { $log->warning() }
          sub test2 { &test1; }


          Apr 26 12:54:11 [WARNING]
             CALL(4): package(main) filename(./ line(15) subroutine(main::test2) hasargs(0)
             CALL(3): package(main) filename(./ line(13) subroutine(main::test1) hasargs(0)
             CALL(2): package(main) filename(./ line(12) subroutine(Log::Handler::__ANON__) hasargs(1)
             CALL(1): package(Log::Handler) filename(/usr/local/share/perl/5.8.8/Log/ line(713) subroutine(Log::Handler::_write) hasargs(1)
             CALL(0): package(Log::Handler) filename(/usr/local/share/perl/5.8.8/Log/ line(1022) subroutine(Devel::Backtrace::new) hasargs(1) wantarray(0)

      The same code example but the debugger in block mode would looks like

             debug_mode => 2


         Apr 26 12:52:17 [DEBUG]
               package     main
               filename    ./
               line        15
               subroutine  main::test2
               hasargs     0
               package     main
               filename    ./
               line        13
               subroutine  main::test1
               hasargs     0
               package     main
               filename    ./
               line        12
               subroutine  Log::Handler::__ANON__
               hasargs     1
               package     Log::Handler
               filename    /usr/local/share/perl/5.8.8/Log/
               line        681
               subroutine  Log::Handler::_write
               hasargs     1
               package     Log::Handler
               filename    /usr/local/share/perl/5.8.8/Log/
               line        990
               subroutine  Devel::Backtrace::new
               hasargs     1
               wantarray   0


      This option let skip the caller() information the count of


    Call output($alias) to get the output object that you added with the
    option alias.

    It's possible to access a output directly:

        $log->output($alias)->log(message => "booo");

    For more information take a look to the option alias.


    Call flush() if you want to send flush to all outputs that can flush.

    Flush means to flush buffers and/or close and re-open outputs.

    If you want to send it only to some outputs you can pass the aliases.

        $log->flush(); # flush all
        $log->flush("foo", "bar"); # flush only foo and bar

    If option "die_on_errors" is set to 0 then you can intercept errors

        $log->flush or die $log->errstr;


    Call errstr() if you want to get the last error message. This is useful
    if you set die_on_errors to 0 and the handler wouldn't die on failed
    write operations.

        use Log::Handler;
        my $log = Log::Handler->new();
        $log->add(file => {
            filename      => "file.log",
            maxlevel      => "info",
            die_on_errors => 0,
        $log->info("Hello World!") or die $log->errstr;


        unless ( $log->info("Hello World!") ) {
            $error_string = $log->errstr;
            # do something with $error_string

    The exception is that the handler dies in any case if the call of new()
    or add() fails because on missing or wrong settings!


    With this method it's possible to load your output configuration from a

        $log->config(config => "file.conf");


        $log->config(config => {
            file => [
                    alias    => "error_log",
                    filename => "error.log",
                    maxlevel => "warning",
                    minlevel => "emerg",
                    priority => 1
                    alias    => "common_log",
                    filename => "common.log",
                    maxlevel => "info",
                    minlevel => "emerg",
                    priority => 2
            screen => {
                alias    => "screen",
                maxlevel => "debug",
                minlevel => "emerg",
                log_to   => "STDERR",

    The key "default" is used here to define default parameters for all
    file outputs. All other keys (error_log, common_log) are used as

    Take a look into the documentation of Log::Handler::Config for more


    With the method reload() it's possible to reload the logging machine.
    Just pass the complete new configuration for all outputs, it works
    exaclty like config().

    At first you should know that it's highly recommended to set a alias
    for each output. If you don't set a alias then the logger doesn't know
    which output-objects to reload. If a output-objects doesn't have a
    alias then the objects will be removed and the new configuration will
    be added.



            alias    = debug
            filename = debug.log
            maxlevel = debug
            minlevel = emerg
            alias    = common
            filename = common.log
            maxlevel = info
            minlevel = emerg

    Load the configuration

        $log->config(config => "logger.conf");

    Now change the configuration in logger.conf

            alias    = common
            filename = common.log
            maxlevel = notice
            minlevel = emerg
            alias   = sendmail
            from    = bar@foo.example
            to      = foo@bar.example
            subject = your subject

    What happends now...

    The file-output with the alias debug will be removed, the file-output
    with the alias common will be reloaded and the output with the alias
    sendmail will be added.

    If you don't want that output-objects will be removed because they were
    added internal, then you can set the option remove_on_reload to 0.


        $log->config(config => "logger.conf");
            forward => {
                forward_to => \&my_func,
                remove_on_reload => 0,

    The forward-output is not removed after a reload.


    The method validate() expects the same arguments like config() and

    Maybe you want to validate your options before you pass them to
    config() or reload().


        my $log = Log::Handler->new();
        $log->config( config => \%config );
        # and maybe later
        if ( $log->validate( config => \%new_config ) ) {
            $log->reload( config => \%new_config );
        } else {
            warn "unable to reload configuration";
            warn $log->errstr;


    With this option you can set your own placeholders. Example:

        $log->set_pattern("%X", "key_name", sub { "value" });
        # or
        $log->set_pattern("%X", "key_name", "value");

    Then you can use this pattern in your message layout:

        $log->add(file => {
            filename        => "file.log",
            message_layout  => "%X %m%N",

    Or use it with message_pattern:

        sub func {
            my $m = shift;
            print "$m->{key_name} $m->{message}\n";
        $log->add(forward => {
            forward_to      => \&func,
            message_pattern => "%X %m",

    Note: valid character for the key name are: [%\w\-\.]+


    With this method it's possible to change the log level at runtime.

    To change the log level it's necessary to use a alias - see option

            $alias => { # option alias
                minlevel => $new_minlevel,
                maxlevel => $new_maxlevel,


    With this methods it's possible to overwrite the default settings for
    new outputs.

    Normally you would do something like

            file => {
                filename => "debug.log",
                maxlevel => "info",
                timeformat => "%b %d %Y %H:%M:%S",
                message_layout => "[%T] %L %P %t %m (%C)"
            file => {
                filename => "error.log",
                maxlevel => "error",
                timeformat => "%b %d %Y %H:%M:%S",
                message_layout => "[%T] %L %P %t %m (%C)"

    Now you can simplify it with

            timeformat => "%b %d %Y %H:%M:%S",
            message_layout => "[%T] %L %P %t %m (%C)"
            file => {
                filename => "debug.log",
                maxlevel => "info"
            file => {
                filename => "error.log",
                maxlevel => "error"


    create_logger() is the same like new() but it creates a global logger.

        my $log = Log::Handler->create_logger("myapp");


    With get_logger() it's possible to get a logger that was created with
    create_logger() or with

        use Log::Handler "myapp";

    Just call

        my $log = Log::Handler->get_logger("myapp");

    If the logger does not exists then a new logger will be created and


    With exists_logger() it's possible to check if a logger exists and it
    returns TRUE or FALSE.




    The benchmark (examples/benchmark/ runs on a Intel Core
    i7-920 with the following result:

        simple pattern output took     :  1 wallclock secs ( 1.26 usr +  0.01 sys =  1.27 CPU) @ 78740.16/s (n=100000)
        default pattern output took    :  2 wallclock secs ( 2.08 usr +  0.15 sys =  2.23 CPU) @ 44843.05/s (n=100000)
        complex pattern output took    :  4 wallclock secs ( 3.22 usr +  0.23 sys =  3.45 CPU) @ 28985.51/s (n=100000)
        message pattern output took    :  3 wallclock secs ( 2.72 usr +  0.16 sys =  2.88 CPU) @ 34722.22/s (n=100000)
        suppressed output took         :  0 wallclock secs ( 0.08 usr +  0.00 sys =  0.08 CPU) @ 1250000.00/s (n=100000)
        filtered caller output took    :  2 wallclock secs ( 2.10 usr +  0.68 sys =  2.78 CPU) @ 35971.22/s (n=100000)
        suppressed caller output took  :  1 wallclock secs ( 0.54 usr +  0.00 sys =  0.54 CPU) @ 185185.19/s (n=100000)
        filtered messages output took  :  3 wallclock secs ( 2.62 usr +  0.08 sys =  2.70 CPU) @ 37037.04/s (n=100000)


    Send me a mail if you have questions.


    Prerequisites for all modules:


    Recommended modules:


    Just for the test suite:



    No exports.


    Please report all bugs to <jschulz.cpan(at)>.


    Jonny Schulz <jschulz.cpan(at)>.


    Do you have any questions or ideas?

    MAIL: <jschulz.cpan(at)>


    If you send me a mail then add Log::Handler into the subject.


    Copyright (C) 2007-2009 by Jonny Schulz. All rights reserved.

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