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
%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} The message to be logged, stripped off a trailing newline
%M Method or function where the logging request was issued
%n Newline (OS-independent)
%p Priority 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 compontent, 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://java.sun.com/j2se/1.3/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
Here's the symbols and their meaning, according to the SimpleDateFormat
specification:
Symbol Meaning Presentation Example
------ ------- ------------ -------
G era designator (Text) AD
y year (Number) 1996
M month in year (Text & Number) July & 07
d day in month (Number) 10
h hour in am/pm (1-12) (Number) 12
H hour in day (0-23) (Number) 0
m minute in hour (Number) 30
s second in minute (Number) 55
E day in week (Text) Tuesday
D day in year (Number) 189
a am/pm marker (Text) PM
(Text): 4 or more pattern letters--use full form, < 4--use short or
abbreviated form if one exists.
(Number): the minimum number of digits. Shorter numbers are
zero-padded to this amount. Year is handled
specially; that is, if the count of 'y' is 2, the
Year will be truncated to 2 digits.
(Text & Number): 3 or over, use text, otherwise use number.
There's also a bunch of pre-defined formats:
%d{ABSOLUTE} "HH:mm:ss,SSS"
%d{DATE} "dd MMM yyyy HH:mm:ss,SSS"
%d{ISO8601} "yyyy-MM-dd HH:mm:ss,SSS"
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).
COPYRIGHT AND LICENSE¶
Copyright 2002-2009 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.