phpman > man > Log::Log4perl::Layout::PatternLayout(3pm)

NAME
    Log::Log4perl::Layout::PatternLayout - Pattern Layout

SYNOPSIS
      use Log::Log4perl::Layout::PatternLayout;

      my $layout = Log::Log4perl::Layout::PatternLayout->new(
                                                       "%d (%F:%L)> %m");

DESCRIPTION
    Creates a pattern layout according to
    http://jakarta.apache.org/log4j/docs/api/org/apache/log4j/PatternLayout.html and a couple of
    Log::Log4perl-specific extensions.

    The "new()" method creates a new PatternLayout, specifying its log format. 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
        %d{...} Current date in customized format (see below)
        %F File where the logging event occurred
        %H Hostname (if Sys::Hostname is available)
        %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{chomp} Log message, stripped off a trailing newline
        %m{indent} Log message, multi-lines indented so they line up with first
        %m{indent=n} Log message, multi-lines indented by n spaces
        %M Method or function where the logging request was issued
        %n Newline (OS-independent)
        %p Priority/level of the logging event (%p{1} shows the first letter)
        %P pid of the current process
        %r Number of milliseconds elapsed from program start to logging
           event
        %R Number of milliseconds elapsed from last logging event to
           current logging event
        %T A stack trace of functions called
        %x The topmost NDC (see below)
        %X{key} The entry 'key' of the MDC (see below)
        %% A literal percent (%) sign

    NDC and MDC are explained in "Nested Diagnostic Context (NDC)" in Log::Log4perl and "Mapped
    Diagnostic Context (MDC)" in Log::Log4perl.

    The granularity of time values is milliseconds if Time::HiRes is available. If not, only full
    seconds are used.

    Every once in a while, someone uses the "%m%n" pattern and additionally provides an extra
    newline in the log message (e.g. "->log("message\n")". To avoid printing an extra newline in
    this case, the PatternLayout will chomp the message, printing only one newline. This option can
    be controlled by PatternLayout's "message_chomp_before_newline" option. See "Advanced options"
    for details.

  Quantify placeholders
    All placeholders can be extended with formatting instructions, just like in *printf*:

        %20c   Reserve 20 chars for the category, right-justify and fill
               with blanks if it is shorter
        %-20c  Same as %20c, but left-justify and fill the right side
               with blanks
        %09r   Zero-pad the number of milliseconds to 9 digits
        %.8c   Specify the maximum field with and have the formatter
               cut off the rest of the value

  Fine-tuning with curlies
    Some placeholders have special functions defined if you add curlies with content after them:

        %c{1}  Just show the right-most category component, useful in large
               class hierarchies (Foo::Baz::Bar -> Bar)
        %c{2}  Just show the two right most category components
               (Foo::Baz::Bar -> Baz::Bar)

        %F     Display source file including full path
        %F{1}  Just display filename
        %F{2}  Display filename and last path component (dir/test.log)
        %F{3}  Display filename and last two path components (d1/d2/test.log)

        %M     Display fully qualified method/function name
        %M{1}  Just display method name (foo)
        %M{2}  Display method name and last path component (main::foo)

    In this way, you're able to shrink the displayed category or limit file/path components to save
    space in your logs.

  Fine-tune the date
    If you're not happy with the default %d format for the date which looks like

        yyyy/MM/DD HH:mm:ss

    (which is slightly different from Log4j which uses "yyyy-MM-dd HH:mm:ss,SSS") you're free to
    fine-tune it in order to display only certain characteristics of a date, according to the
    SimpleDateFormat in the Java World
    (http://docs.oracle.com/javase/8/docs/api/java/text/SimpleDateFormat.html):

        %d{HH:mm}     "23:45" -- Just display hours and minutes
        %d{yy, EEEE}  "02, Monday" -- Just display two-digit year
                                      and spelled-out weekday
        %d{e}         "1473741760" -- Epoch seconds
        %d{h a}       "12 PM"      -- Hour and am/pm marker
        ... and many more

    For an exhaustive list of all supported date features, look at Log::Log4perl::DateFormat.

  Custom cspecs
    First of all, "cspecs" is short for "conversion specifiers", which is the log4j and the
    printf(3) term for what Mike is calling "placeholders." I suggested "cspecs" for this part of
    the api before I saw that Mike was using "placeholders" consistently in the log4perl
    documentation. Ah, the joys of collaboration ;=) --kg

    If the existing corpus of placeholders/cspecs isn't good enough for you, you can easily roll
    your own:

        #'U' a global user-defined cspec
        log4j.PatternLayout.cspec.U = sub { return "UID: $< "}

        #'K' cspec local to appndr1                 (pid in hex)
        log4j.appender.appndr1.layout.cspec.K = sub { return sprintf "%1x", $$}

        #and now you can use them
        log4j.appender.appndr1.layout.ConversionPattern = %K %U %m%n

    The benefit of this approach is that you can define and use the cspecs right next to each other
    in the config file.

    If you're an API kind of person, there's also this call:

        Log::Log4perl::Layout::PatternLayout::
                        add_global_cspec('Z', sub {'zzzzzzzz'}); #snooze?

    When the log message is being put together, your anonymous sub will be called with these
    arguments:

        ($layout, $message, $category, $priority, $caller_level);

        layout: the PatternLayout object that called it
        message: the logging message (%m)
        category: e.g. groceries.beverages.adult.beer.schlitz
        priority: e.g. DEBUG|WARN|INFO|ERROR|FATAL
        caller_level: how many levels back up the call stack you have
            to go to find the caller

    Please note that the subroutines you're defining in this way are going to be run in the "main"
    namespace, so be sure to fully qualify functions and variables if they're located in different
    packages. *Also make sure these subroutines aren't using Log4perl, otherwise Log4perl will enter
    an infinite recursion.*

    With Log4perl 1.20 and better, cspecs can be written with parameters in curly braces. Writing
    something like

        log4perl.appender.Screen.layout.ConversionPattern = %U{user} %U{id} %m%n

    will cause the cspec function defined for %U to be called twice, once with the parameter 'user'
    and then again with the parameter 'id', and the placeholders in the cspec string will be
    replaced with the respective return values.

    The parameter value is available in the 'curlies' entry of the first parameter passed to the
    subroutine (the layout object reference). So, if you wanted to map %U{xxx} to entries in the POE
    session hash, you'd write something like:

       log4perl.PatternLayout.cspec.U = sub { \
         POE::Kernel->get_active_session->get_heap()->{ $_[0]->{curlies} } }

    SECURITY NOTE

    This feature means arbitrary perl code can be embedded in the config file. In the rare case
    where the people who have access to your config file are different from the people who write
    your code and shouldn't have execute rights, you might want to set

        $Log::Log4perl::Config->allow_code(0);

    before you call init(). Alternatively you can supply a restricted set of Perl opcodes that can
    be embedded in the config file as described in "Restricting what Opcodes can be in a Perl Hook"
    in Log::Log4perl.

  Advanced Options
    The constructor of the "Log::Log4perl::Layout::PatternLayout" class takes an optional hash
    reference as a first argument to specify additional options in order to (ab)use it in creative
    ways:

      my $layout = Log::Log4perl::Layout::PatternLayout->new(
        { time_function       => \&my_time_func,
        },
        "%d (%F:%L)> %m");

    Here's a list of parameters:

    time_function
        Takes a reference to a function returning the time for the time/date fields, either in
        seconds since the epoch or as an array, carrying seconds and microseconds, just like
        "Time::HiRes::gettimeofday" does.

    message_chomp_before_newline
        If a layout contains the pattern "%m%n" and the message ends with a newline, PatternLayout
        will chomp the message, to prevent printing two newlines. If this is not desired, and you
        want two newlines in this case, the feature can be turned off by setting the
        "message_chomp_before_newline" option to a false value:

          my $layout = Log::Log4perl::Layout::PatternLayout->new(
              { message_chomp_before_newline => 0
              },
              "%d (%F:%L)> %m%n");

        In a Log4perl configuration file, the feature can be turned off like this:

            log4perl.appender.App.layout   = PatternLayout
            log4perl.appender.App.layout.ConversionPattern = %d %m%n
              # Yes, I want two newlines
            log4perl.appender.App.layout.message_chomp_before_newline = 0

  Getting rid of newlines
    If your code contains logging statements like

          # WRONG, don't do that!
        $logger->debug("Some message\n");

    then it's usually best to strip the newlines from these calls. As explained in "Logging
    newlines" in Log::Log4perl, logging statements should never contain newlines, but rely on
    appender layouts to add necessary newlines instead.

    If changing the code is not an option, use the special PatternLayout placeholder %m{chomp} to
    refer to the message excluding a trailing newline:

        log4perl.appender.App.layout.ConversionPattern = %d %m{chomp}%n

    This will add a single newline to every message, regardless if it complies with the Log4perl
    newline guidelines or not (thanks to Tim Bunce for this idea).

  Multi Lines
    If a log message consists of several lines, like

        $logger->debug("line1\nline2\nline3");

    then by default, they get logged like this (assuming the the layout is set to "%d>%m%n"):

          # layout %d>%m%n
        2014/07/27 12:46:16>line1
        line2
        line3

    If you'd rather have the messages aligned like

          # layout %d>%m{indent}%n
        2014/07/27 12:46:16>line1
                            line2
                            line3

    then use the %m{indent} option for the %m specifier. This option can also take a fixed value, as
    in %m{indent=2}, which indents subsequent lines by two spaces:

          # layout %d>%m{indent=2}%n
        2014/07/27 12:46:16>line1
          line2
          line3

    Note that you can still add the "chomp" option for the %m specifier in this case (see above what
    it does), simply add it after a separating comma, like in %m{indent=2,chomp}.

LICENSE
    Copyright 2002-2013 by Mike Schilli <m AT perlmeister.com> and Kevin Goess <cpan AT goess.org>.

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

AUTHOR
    Please contribute patches to the project on Github:

        http://github.com/mschilli/log4perl

    Send bug reports or requests for enhancements to the authors via our

    MAILING LIST (questions, bug reports, suggestions/patches): log4perl-devel AT lists.net

    Authors (please contact them via the list above, not directly): Mike Schilli
    <m AT perlmeister.com>, Kevin Goess <cpan AT goess.org>

    Contributors (in alphabetical order): Ateeq Altaf, Cory Bennett, Jens Berthold, Jeremy Bopp,
    Hutton Davidson, Chris R. Donnelly, Matisse Enzer, Hugh Esco, Anthony Foiani, James FitzGibbon,
    Carl Franks, Dennis Gregorovic, Andy Grundman, Paul Harrington, Alexander Hartmaier David Hull,
    Robert Jacobson, Jason Kohles, Jeff Macdonald, Markus Peter, Brett Rann, Peter Rabbitson, Erik
    Selberg, Aaron Straup Cope, Lars Thegler, David Viner, Mac Yang.