Provided by: liblog-log4perl-perl_1.57-1_all bug

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@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.

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@lists.sourceforge.net

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