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Author image Jonny Schulz
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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 exists.

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 Screen.pm, File.pm and DBI.pm 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 peep.


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 not.


fatal, is_fatal

For a full list take a look into the documentation of Log::Handler::Levels.



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 program.


    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 logged.

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


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 like

    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 are:

    %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 (script.pl, 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 Log::Handler::Output::Screen.

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. Example:

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 controll 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 decription 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 yourself.

    $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!


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. Example:

    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(./trace.pl) line(15) subroutine(main::test2) hasargs(0)
       CALL(3): package(main) filename(./trace.pl) line(13) subroutine(main::test1) hasargs(0)
       CALL(2): package(main) filename(./trace.pl) line(12) subroutine(Log::Handler::__ANON__) hasargs(1)
       CALL(1): package(Log::Handler) filename(/usr/local/share/perl/5.8.8/Log/Handler.pm) line(713) subroutine(Log::Handler::_write) hasargs(1)
       CALL(0): package(Log::Handler) filename(/usr/local/share/perl/5.8.8/Log/Handler.pm) line(1022) subroutine(Devel::Backtrace::new) hasargs(1) wantarray(0)

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

       debug_mode => 2


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

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


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 with:

    $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 file.

    $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 aliases.

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


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 reload().

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.

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


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 returned.


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




The benchmark (examples/benchmark/benchmark.pl) 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)bloonix.de>.


Jonny Schulz <jschulz.cpan(at)bloonix.de>.


Do you have any questions or ideas?

MAIL: <jschulz.cpan(at)bloonix.de>

IRC: irc.perl.org#perl

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.