NAME

Log::Log4perl::Tiny - mimic Log::Log4perl in one single module

VERSION

This document describes Log::Log4perl::Tiny version 1.8.0.

SYNOPSIS

use Log::Log4perl::Tiny qw( :easy );
Log::Log4perl->easy_init({
   file   => '/var/log/something.log',
   layout => '[%d] [%-5P:%-5p] %m%n',
   level  => $INFO,
});

WARN 'something weird happened';
INFO 'just doing it';
DEBUG 'this does not get printed at $INFO level';

# LOGLEVEL isn't in Log::Log4perl, but might come handy
LOGLEVEL($DEBUG);   # enable debugging for small section
# otherwise, "get_logger()->level($DEBUG)", see below

DEBUG 'now this gets printed';
LOGLEVEL($INFO);    # disable debugging again
DEBUG 'skipped, again';
DEBUG 'complex evaluation value:', sub { 
   # evaluation skipped if log level filters DEBUG out
};

# Object-oriented interface is available as well
my $logger = get_logger();
$logger->level($DEBUG);   # enable debugging for small section
$logger->debug('whatever you want');
$logger->level($INFO);    # disable debugging again

# All stealth loggers are available
LOGCONFESS 'I cannot accept this, for a whole stack of reasons!';

# Want to change layout?
$logger->layout('[%d %p] %m%n');
# or, equivalently
$logger->format('[%d %p] %m%n');

# Want to send the output somewhere else?
use IO::Handle;
open my $fh, '>>', '/path/to/new.log';
$fh->autoflush();
$logger->fh($fh);

# Want to multiplex output to different channels?
$logger->fh(
   build_channels(
      fh          => \*STDERR,
      file_create => '/var/log/lastrun.log',
      file_append => '/var/log/overall.log',
   )
);

# Want to handle the output message by yourself?
my @queue; # e.g. all log messages will be put here
$logger->fh(sub { push @queue, $_[0] });

# As of 1.4.0, you can set key-value pairs in the logger
$logger->loglocal(foo => 'bar');
LOGLOCAL(baz => 100);

# You can later retrieve the value in the format with %{key}e
$logger->format("[%{foo}e] [%{baz}e] %m%n");

# You are not limited to scalars, you can use references too
LOGLOCAL(baz => sub {
   my ($data, $op, $ekey) = @_;
   return join '.', @{$data->{tod}}; # epoch from gettimeofday
});
LOGLOCAL(foo => sub { return rand 100 });

DESCRIPTION

Yes... yet another logging module. Nothing particularly fancy nor original, too, but a single-module implementation of the features I use most from Log::Log4perl for quick things, namely:

easy mode and stealth loggers (aka log functions INFO, WARN, etc.);
debug message filtering by log level;
line formatting customisation;
quick sending of messages to a log file.

There are many, many things that are not included; probably the most notable one is the ability to provide a configuration file.

Why?

I have really nothing against Log::Log4perl, to the point that one of the import options is to check whether Log::Log4perl is installed and use it if possible. I just needed to crunch the plethora of modules down to a single-file module, so that I can embed it easily in scripts I use in machines where I want to reduce my impact as much as possible.

Log Levels

Log::Log4perl::Tiny implements all standard Log::Log4perl's log levels, without the possibility to change them. The correspondent values are available in the following variables (in order of increasing severity or importance):

$TRACE
$DEBUG
$INFO
$WARN
$ERROR
$FATAL

The default log level is $INFO. In addition to the above, the following levels are defined as well:

$OFF: also in Log::Log4perl, useful to turn off all logging except for ALWAYS
$DEAD: not in Log::Log4perl, when the threshold log level is set to this value every log is blocked (even when called from the ALWAYS stealth logger).

You can import these variables using the :levels import facility, or you can use the directly from the Log::Log4perl::Tiny namespace. They are imported automatically if the :easy import option is specified.

Default Log Level

As of version 1.1.0 the default logging level is still $INFO like any previous version, but it is possible to modify this value to $DEAD through the :dead_if_first import key.

This import key is useful to load Log::Log4perl in modules that you want to publish but where you don't want to force the end user to actually use it. In other terms, if you do this:

package My::Module;
use Log::Log4perl::Tiny qw( :easy :dead_if_first );

you will import all the functionalities associated to :easy but will silence the logger off unless somewhere else the module is loaded (and imported) without this option. In this way:

if the user of your module does not import Log::Log4perl::Tiny, all log messages will be dropped (thanks to the log level set to $DEAD)
otherwise, if the user imports Log::Log4perl::Tiny without the option, the log level will be set to the default value (unless it has already been explicitly set somewhere else).

Easy Mode Overview

I love Log::Log4perl's easy mode because it lets you set up a sophisticated logging infrastructure with just a few keystrokes:

use Log::Log4perl qw( :easy );
Log::Log4perl->easy_init({
   file   => '>>/var/log/something.log',
   layout => '[%d] [%-5P:%-5p] %m%n',
   level  => $INFO,
});
INFO 'program started, yay!';

use Data::Dumper;
DEBUG 'Some stuff in main package', sub { Dumper(\%main::) };

If you want, you can replicate it with just a change in the first line:

use Log::Log4perl::Tiny qw( :easy );
Log::Log4perl->easy_init({
   file   => '>>/var/log/something.log',
   layout => '[%d] [%-5P:%-5p] %m%n',
   level  => $INFO,
});
INFO 'program started, yay!';

use Data::Dumper;
DEBUG 'Some stuff in main package', sub { Dumper(\%main::) };

Well... yes, I'm invading the Log::Log4perl namespace in order to reduce the needed changes as mush as possible. This is useful when I begin using Log::Log4perl and then realise I want to make a single script with all modules embedded. There is also another reason why I put easy_init() in Log::Log4perl namespace:

use Log::Log4perl::Tiny qw( :full_or_fake :easy );
Log::Log4perl->easy_init({
   file   => '>>/var/log/something.log',
   layout => '[%d] [%-5P:%-5p] %m%n',
   level  => $INFO,
});
INFO 'program started, yay!';

use Data::Dumper;
DEBUG 'Some stuff in main package', sub { Dumper(\%main::) };

With import option full_or_fake, in fact, the module first tries to load Log::Log4perl in the caller's namespace with the provided options (except full_or_fake, of course), returning immediately if it is successful; otherwise, it tries to "fake" Log::Log4perl and installs its own logging functions. In this way, if Log::Log4perl is available it will be used, but you don't have to change anything if it isn't.

Easy mode tries to mimic what Log::Log4perl does, or at least the things that (from a purely subjective point of view) are most useful: easy_init() and stealth loggers.

`easy_init()`

Log::Log4perl::Tiny only supports three options from the big brother, plus its own:

level

the log level threshold. Logs sent at a higher or equal priority (i.e. at a more important level, or equal) will be printed out, the others will be ignored. The default value is $INFO;

file

a file name where to send the log lines. For compatibility with Log::Log4perl, a 2-arguments open() will be performed, which means you can easily set the opening mode, e.g. >>filename.

Note that the 2-arguments open() is intrinsically insecure and will trigger the following error when running setuid:

Insecure dependency in open while running setuid

so be sure to use either file_create or file_append instead if you're running setuid. These are extensions added by Log::Log4perl::Tiny to cope with this specific case (and also to allow you avoid the 2-args open() anyway).

Another Log::Log4perl::Tiny extension added as of version 1.3.0 is the key channels where you can pass an array reference with channels descriptions (see "build_channels" for details).

The default is to send logging messages to STDERR;

filter

(Not in Log::Log4perl) (As of 1.8.0)

a filter function to be applied onto every message before it is emitted. This can be useful for multi-line log messages, when a specific start-of-line is needed (e.g. a hash character).

By default nothing is done.

layout

the log line layout (it can also be spelled format, they are synonims). The default value is the following:

[%d] [%5p] %m%n

which means date in brackets, then log level in brackets always using five chars, left-aligned, the log message and a newline.

If you call easy_init() with a single unblessed scalar, it is considered to be the level and it will be set accordingly. Otherwise, you have to pass a hash ref with the keys above.

In addition to the above keys, the easy_init() method installed by Log::Log4perl::Tiny also accepts all keys defined for "new", e.g. format (an alias for layout) and the different alternatives to file (file_insecure, file_create and file_append).

Stealth Loggers

Stealth loggers are functions that emit a log message at a given severity; they are installed when :easy mode is turned on (see "Easy Mode Overview").

They are named after the corresponding level:

TRACE
DEBUG
INFO
WARN
ERROR
FATAL

Additionally, you get the following logger functions (again, these are in line with Log::Log4perl):

ALWAYS: emit log whatever the configured logging level, apart from $DEAD that disables all logging;
LOGWARN: emit log at WARN level and then warn() it;
LOGDIE: emit log at FATAL level, die() and then exit (if die() didn't already exit);
LOGEXIT: emit log at FATAL level and then exit;
LOGCARP: emit log at WARN level and then call Carp::carp();
LOGCLUCK: emit log at WARN level and then call Carp::cluck();
LOGCROAK: emit log at FATAL level and then call Carp::croak();
LOGCONFESS: emit log at FATAL level and then call Carp::confess();

If you want to set the exit code for LOGEXIT above (and LOGDIE as well, in case die() does not exit by itself), you can go "the Log::Log4perl way" and set $Log::Log4perl::LOGEXIT_CODE, or set a code with logexit_code() - but you have to wait to read something about the object-oriented interface before doing this!

As indicated, functions "LOGWARN", "LOGDIE", "LOGCARP", "LOGCLUCK", "LOGCROAK", and "LOGCONFESS" (as well as their lowercase counterparts called as object methods) both emit the log message on the normal output channel for Log::Log4perl::Tiny and call the respective function. This might not be what you want in the default case where the output channel is standard error, because you will end up with duplicate error messages. You can avoid the call to the canonical function setting import option :no_extra_logdie_message, in line with what Log::Log4perl provides.

There is also one additional stealth function that Log::Log4perl misses but that I think is of the outmoste importance: LOGLEVEL, to set the log level threshold for printing. If you want to be 100% compatible with Log::Log4perl, anyway, you should rather do the following:

get_logger()->level(...);  # instead of LOGLEVEL(...)

This function does not get imported when you specify :easy, anyway, so you have to import it explicitly. This will help you remembering that you are deviating from Log::Log4perl.

Emitting Logs

To emit a log, you can call any of the stealth logger functions or any of the corresponding log methods. All the parameters that you pass are sent to the output stream as they are, except code references that are first evaluated. This lets you embed costly evaluations (e.g. generate heavy dumps of variabls) inside subroutines, and avoid the cost of evaluation in case the log is filtered out:

use Data::Dumper;
LOGLEVEL($INFO); # cut DEBUG and TRACE out
TRACE 'costly evaluation: ', sub { Dumper($heavy_object) };
# Dumper() is not actually called because DEBUG level is
# filtered out

If you use the log() method, the first parameter is the log level, then the others are interpreted as described above.

Log Line Layout

The log line layout sets the contents of a log line. The layout is configured as a printf-like string, with placeholder identifiers that are modeled (with simplifications) after Log::Log4perl's ones:

%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 strftime's "%Y-%m-%d %H:%M:%S.$u%z" (localtime)
%{type}D Current date as strftime's "%Y-%m-%d %H:%M:%S.$u%z"
   (type can be utc or local)
%{key}e Evaluate or substitute (extension WRT Log::Log4perl)
%F File where the logging event occurred
%H Hostname
%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 Method or function where the logging request was issued
%n Newline (OS-independent)
%p Priority of the logging event
%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 including
   a %R to current logging event
%T A stack trace of functions called
%% A literal percent (%) sign

Notably, both %x (NDC) and %X (MDC) are missing. The functionality for the latter is partially covered by the extension %e explained below. Moreover, the extended specifier feature with additional info in braces (like %d{HH:mm}) is missing, i.e. the structure of each specifier above is fixed. (Thanks to Log::Tiny for the cool trick of how to handle the printf-like string, which is probably mutuated from Log::Log4perl itself according to the comments).

There are also two extensions with respect to Log::Log4perl, that help partially cover the missing items explained above, as of release 1.4.0:

%D

%{type}D

expanded to a timestamp according to "strftime" in POSIX specifier %Y-%m-%d %H:%M:%S.$u%z, i.e. a timestamp that includes up to the microsecond (on platform where this is available, otherwise zeros will be used for sub-second values). By default the local time is used, but you can also pass a type specifier set to the string utc, in which case the UTC time will be used (via gmtime).

%{key}e

expanded according to what set via "loglocal"/"LOGLOCAL". These two functions allow setting key-value pairs; the key is used to find the associated value, then the value is returned as-is if it's a simple defined scalar, otherwise if it is a sub reference it is invoked, otherwise the empty string is returned.

In case a subroutine reference is set, it is called with the following parameters:

$sub->($data, $op, $options);

where $data is a reference to a hash that contains at least the tod key, associated to an array with the output of gettimeofday (if Time::HiRes is available) or its equivalent (if Time::HiRes is not available), $op is the letter e and $options is the string containing the key in braces (e.g. {this-is-the-key}).

As of release 1.4.0 all time-expansions in a single log refer to the same time, i.e. if you specify the format string %D %D and you have microsecond-level resolution, the two values in output will be the same (as opposed to show two slightly different times, related to the different expansion times of the %D specifier).

Wrapping Log::Log4perl::Tiny

As of release 1.4.0, all expansion sequences that imply using caller (namely %C, %F, %l, %L, %M, and %T) will honor whatever you set for $Log::Log4perl::caller_depth or $Log::Log4perl::Tiny::caller_depth (they're aliased), defaulting to value 0. You can basically increase this value by 1 for each wrapper function that you don't want to appear from the real caller's point of view. In the following example, we have two nested wrappers, each of which takes care to increase the value by 1 to be hidden:

sub my_wrapper_logger {
   local $Log::Log4perl::Tiny::caller_depth =
      $Log::Log4perl::Tiny::caller_depth + 1; # ignore my_wrapper_logger
   INFO(@_);
}

# ... somewhere else...
sub wrap_wrapper {
   local $Log::Log4perl::Tiny::caller_depth =
      $Log::Log4perl::Tiny::caller_depth + 1; # ignore wrap_wrapper
   my_wrapper_logger(@_);
}

The control variable is either $Log::Log4perl::Tiny::caller_depth or $Log::Log4perl::caller_depth, as a matter of fact they are aliased (i.e. changing either one will also change the other). This is intentional to let you switch towards Log::Log4perl should you need to upgrade to it.

See "Using Log::Log4perl with wrapper functions and classes" in Log::Log4perl for further information.

INTERFACE

You have two interfaces at your disposal, the functional one (with all the stealth logger functions) and the object-oriented one (with explicit actions upon a logger object). Choose your preferred option.

Functional Interface

The functional interface sports the following functions (imported automatically when :easy is passed as import option except for LEVELID_FOR, LEVELNAME_FOR and LOGLEVEL):

TRACE

DEBUG

INFO

WARN

ERROR

FATAL

stealth logger functions, each emits a log at the corresponding level;

ALWAYS

emit log whatever the configured logging level (except $DEAD);

LEVELID_FOR

returns the identifier related to a certain level. The input level can be either a name or an identifier itself. Returns undef if it is neither.

It can be used e.g. if you want to use "log" but you only have the level name, not its identifier;

LEVELNAME_FOR

returns the name related to a certain level. The input level can be either a name or an identifier itself. Returns undef if it is neither.

LOGWARN

emit log at WARN level and then warn() it;

LOGDIE

emit log at FATAL level, die() and then exit (if die() didn't already exit);

LOGEXIT

emit log at FATAL level and then exit;

LOGCARP

emit log at WARN level and then call Carp::carp();

LOGCLUCK

emit log at WARN level and then call Carp::cluck();

LOGCROAK

emit log at FATAL level and then call Carp::croak();

LOGCONFESS

emit log at FATAL level and then call Carp::confess();

LOGLEVEL

(Not in Log::Log4perl) (Not imported with :easy)

set the minimum log level for sending a log message to the output;

LOGLOCAL

(Not in Log::Log4perl) (Not imported with :easy) (As of 1.4.0)

set a key-value pair useful for later expansion via code %{key}e. See "loglocal" below;

FILTER

(Not in Log::Log4perl) (Not imported with :easy) (As of 1.8.0)

set a filter function to apply to every expanded message before it is printed. See "filter" below;

build_channels

(Not in Log::Log4perl) (Not imported with :easy)

build multiple channels for emitting logs.

my $channels = build_channels(@key_value_pairs);  # OR
my $channels = build_channels(\@key_value_pairs);

The input is a sequence of key-value pairs, provided either as a list or through a reference to an array containing them. They are not forced into a hash because the same key can appear multiple times to initialize multiple channels.

The key specifies the type of the channel, while the value is specific to the key:

fh

value is a filehandle (or anything that can be passed to the print function)

sub

code

value is a reference to a subroutine. This will be called with two positional parameters: the message (already properly formatted) and a reference to the logger message

channel

whatever can be passed to keys fh or to sub/code above

file

file_insecure

file_create

file_append

value is the file where log data should be sent.

The first one is kept for compliance with Log::Log4perl::easy_init's way of accepting a file. It eventually results in a two-arguments open() call, so that you can quickly set how you want to open the file:

file => '>>/path/to/appended', # append mode
file => '>/path/to/new-file',  # create mode

You should avoid doing this, because it is intrinsically insecure and will yield an error message when running setuid:

Insecure dependency in open while running setuid

file_insecure is an alias to file, so that you can explicitly signal to the maintainer that you know what you're doing.

file_create and file_append will use the three-arguments open() call and thus they don't trigger the error above when running setuid. As the respective names suggest the former creates the file from scratch (possibly deleting any previous file with the same path) while the latter opens the file in append mode.

Object-Oriented Interface

The functional interface is actually based upon actions on a pre-defined fixed instance of a Log::Log4perl::Tiny object, so you can do the same with a logger object as well:

get_logger

this function gives you the pre-defined logger instance (i.e. the same used by the stealth logger functions described above).

new

if for obscure reasons the default logger isn't what you want, you can get a brand new object! The constructor accepts either a list of key-values or a reference to a hash, supporting the following keys:

channels

set a list (through an array reference) of channels. See "build_channels" for additional information.

fh

see method fh below

file

file_insecure

file_create

file_append

set the file where the log data will be sent.

The first one is kept for compliance with Log::Log4perl::easy_init's way of accepting a file. It eventually results in a two-arguments open(), so you might want to take care when running in taint mode.

See also "build_channels" for additional information. This option takes precedence over fh described below.

filter

format

layout

level

see easy_init() and the methods below with the same name

loglocal

pass a reference to a hash with key-value pairs to be set via "loglocal";

The methods you can call upon the object mimic the functional interface, but with lowercase method names:

trace
debug
info
warn
error
fatal: logging functions, each emits a log at the corresponding level;
is_trace
is_debug
is_info
is_warn
is_error
is_fatal
isTraceEnabled
isDebugEnabled
isInfoEnabled
isWarnEnabled
isErrorEnabled
isFatalEnabled: log level test functions, each returns the status of the corresponding level;
always: emit log whatever the configured logging level;
logwarn: emit log at WARN level (if allowed) and warn() (always);
logdie: emit log at FATAL level, die() and then exit (if die() didn't already exit);
logexit: emit log at FATAL level and then exit;
logcarp: emit log at WARN level and then call Carp::carp();
logcluck: emit log at WARN level and then call Carp::cluck();
logcroak: emit log at FATAL level and then call Carp::croak();
logconfess: emit log at FATAL level and then call Carp::confess();

The main logging function is actually the following:

log: the first parameter is the log level, the rest is the message to log apart from references to subroutines that are first evaluated
emit_log: emit the message in the first positional parameter to all logging channels

Additionally, you have the following accessors:

level

get/set the minimum level for sending messages to the output stream. By default the level is set to $INFO.

fh

get/set the output channel.

As an extention over Log::Log4perl, you can also pass a reference to a subroutine or to an array.

If you set a reference to a sub, it will be called with two parameters: the message that would be print and a reference to the logger object that is calling the sub. For example, if you simply want to collect the log messages without actually outputting them anywhere, you can do this:

my @messages;
get_logger()->fh(sub {
   my ($message, $logger) = @_;
   push @messages, $message;
   return;
});

If you set a reference to an array, each item inside will be used for log output; its elements can be either filehandles or sub references, used as described above. This is a handy way to set multiple output channels (it might be implemented externally through a proper subroutine reference of course).

By default this parameter is set to be equal to STDERR.

filter

(Not in Log::Log4perl) (As of 1.8.0)

get/set a filter CODE reference to be applied to every expanded message. The filter function is passed the message as its only argument.

This can be e.g. useful in case a specific start-of-line character sequence is needed for multi-line messages:

get_logger()->filter(sub {
   my $message = shift;
   $message =~ s{^}{# }gmxs; # pre-pend "# " to each line
   return $message;
});

Another use case might be taming some sensitive data:

get_logger()->filter(sub {
   my $message = shift;
   $message =~ s{password<.*?>}{password<***>}gmxs;
   return $message;
});

It is anyway suggested to deal with these cases explicitly at the source and not as an afterthought (only). As an example, the regular expression in the example above will leak parts of passwords that contain the > character, and there might be other ways passwords are written too.

format

layout

get/set the line formatting;

logexit_code

get/set the exit code to be used with logexit() (and logdie() as well if die() doesn't exit).

loglocal

get/set a local key-value pair for expansion with %{key}e.

Always returns the previous value associated to the provided key, removing it:

my $value = $logger->loglocal('some-key');
# now, 'some-key' does not exist any more and has no value associated

If you pass a value too, it will be set:

$logger->loglocal(foo => 'bar');
my $old = $logger->loglocal(foo => 'whatever');
# $old is 'bar'
# current value associated to foo is 'whatever'

DEPENDENCIES

Runs on perl 5.8.0 on with no additional runtime requirements.

See cpanfile for additional requirements when testing and/or developing. In particular, developing will require Log::Log4perl to perform a comparison between the expansions of a few items related to caller().

BUGS AND LIMITATIONS

Please view/report any bugs or feature requests through Github at https://github.com/polettix/Log-Log4perl-Tiny/issues.

AUTHOR

Flavio Poletti <polettix@cpan.org>

COPYRIGHT AND LICENSE

This module is free software. You can redistribute it and/or modify it under the terms of the Artistic License 2.0.

This program is distributed in the hope that it will be useful, but without any warranty; without even the implied warranty of merchantability or fitness for a particular purpose.

To install Log::Log4perl::Tiny, copy and paste the appropriate command in to your terminal.

cpanm

cpanm Log::Log4perl::Tiny

CPAN shell

perl -MCPAN -e shell
install Log::Log4perl::Tiny

For more information on module installation, please visit the detailed CPAN module installation guide.

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