Log::Message(3) Perl Programmers Reference Guide Log::Message(3)NAMELog::Message - A generic message storing mechanism;
SYNOPSIS
use Log::Message private => 0, config => '/our/cf_file';
my $log = Log::Message->new( private => 1,
level => 'log',
config => '/my/cf_file',
);
$log->store('this is my first message');
$log->store( message => 'message #2',
tag => 'MY_TAG',
level => 'carp',
extra => ['this is an argument to the handler'],
);
my @last_five_items = $log->retrieve(5);
my @items = $log->retrieve( tag => qr/my_tag/i,
message => qr/\d/,
remove => 1,
);
my @items = $log->final( level => qr/carp/, amount => 2 );
my $first_error = $log->first()
# croak with the last error on the stack
$log->final->croak;
# empty the stack
$log->flush();
DESCRIPTIONLog::Message is a generic message storage mechanism. It allows you to
store messages on a stack -- either shared or private -- and assign
meta-data to it. Some meta-data will automatically be added for you,
like a timestamp and a stack trace, but some can be filled in by the
user, like a tag by which to identify it or group it, and a level at
which to handle the message (for example, log it, or die with it)
Log::Message also provides a powerful way of searching through items by
regexes on messages, tags and level.
Hierarchy
There are 4 modules of interest when dealing with the Log::Message::*
modules:
Log::Message
Log::Message provides a few methods to manipulate the stack it
keeps. It has the option of keeping either a private or a public
stack. More on this below.
Log::Message::Item
These are individual message items, which are objects that contain
the user message as well as the meta-data described above. See the
Log::Message::Item manpage to see how to extract this meta-data and
how to work with the Item objects. You should never need to create
your own Item objects, but knowing about their methods and
accessors is important if you want to write your own handlers. (See
below)
Log::Message::Handlers
These are a collection of handlers that will be called for a level
that is used on a Log::Message::Item object. For example, if a
message is logged with the 'carp' level, the 'carp' handler from
Log::Message::Handlers will be called. See the
Log::Message::Handlers manpage for more explanation about how
handlers work, which one are available and how to create your own.
Log::Message::Config
Per Log::Message object, there is a configuration required that
will fill in defaults if the user did not specify arguments to
override them (like for example what tag will be set if none was
provided), Log::Message::Config handles the creation of these
configurations.
Configuration can be specified in 4 ways:
· As a configuration file when you "use Log::Message"
· As arguments when you "use Log::Message"
· As a configuration file when you create a new Log::Message
object. (The config will then only apply to that object if you
marked it as private)
· As arguments when you create a new Log::Message object.
You should never need to use the Log::Message::Config module
yourself, as this is transparently done by Log::Message, but
its manpage does provide an explanation of how you can create a
config file.
Options
When using Log::Message, or creating a new Log::Message object, you can
supply various options to alter its behaviour. Of course, there are
sensible defaults should you choose to omit these options.
Below an explanation of all the options and how they work.
config
The path to a configuration file to be read. See the manpage of
Log::Message::Config for the required format
These options will be overridden by any explicit arguments passed.
private
Whether to create, by default, private or shared objects. If you
choose to create shared objects, all Log::Message objects will use
the same stack.
This means that even though every module may make its own $log
object they will still be sharing the same error stack on which
they are putting errors and from which they are retrieving.
This can be useful in big projects.
If you choose to create a private object, then the stack will of
course be private to this object, but it will still fall back to
the shared config should no private config or overriding arguments
be provided.
verbose
Log::Message makes use of another module to validate its arguments,
which is called Params::Check, which is a lightweight, yet powerful
input checker and parser. (See the Params::Check manpage for
details).
The verbose setting will control whether this module will generate
warnings if something improper is passed as input, or merely
silently returns undef, at which point Log::Message will generate a
warning.
It's best to just leave this at its default value, which is '1'
tag The tag to add to messages if none was provided. If neither your
config, nor any specific arguments supply a tag, then Log::Message
will set it to 'NONE'
Tags are useful for searching on or grouping by. For example, you
could tag all the messages you want to go to the user as 'USER
ERROR' and all those that are only debug information with 'DEBUG'.
At the end of your program, you could then print all the ones
tagged 'USER ERROR' to STDOUT, and those marked 'DEBUG' to a log
file.
level
"level" describes what action to take when a message is logged.
Just like "tag", Log::Message will provide a default (which is
'log') if neither your config file, nor any explicit arguments are
given to override it.
See the Log::Message::Handlers manpage to see what handlers are
available by default and what they do, as well as to how to add
your own handlers.
remove
This indicates whether or not to automatically remove the messages
from the stack when you've retrieved them. The default setting
provided by Log::Message is '0': do not remove.
chrono
This indicates whether messages should always be fetched in
chronological order or not. This simply means that you can choose
whether, when retrieving items, the item most recently added should
be returned first, or the one that had been added most long ago.
The default is to return the newest ones first
Methods
new
This creates a new Log::Message object; The parameters it takes are
described in the "Options" section below and let it just be repeated
that you can use these options like this:
my $log = Log::Message->new( %options );
as well as during "use" time, like this:
use Log::Message option1 => value, option2 => value
There are but 3 rules to keep in mind:
· Provided arguments take precedence over a configuration file.
· Arguments to new take precedence over options provided at "use"
time
· An object marked private will always have an empty stack to begin
with
store
This will create a new Item object and store it on the stack.
Possible arguments you can give to it are:
message
This is the only argument that is required. If no other arguments
are given, you may even leave off the "message" key. The argument
will then automatically be assumed to be the message.
tag The tag to add to this message. If not provided, Log::Message will
look in your configuration for one.
level
The level at which this message should be handled. If not provided,
Log::Message will look in your configuration for one.
extra
This is an array ref with arguments passed to the handler for this
message, when it is called from store();
The handler will receive them as a normal list
store() will return true upon success and undef upon failure, as well
as issue a warning as to why it failed.
retrieve
This will retrieve all message items matching the criteria specified
from the stack.
Here are the criteria you can discriminate on:
tag A regex to which the tag must adhere. For example "qr/\w/".
level
A regex to which the level must adhere.
message
A regex to which the message must adhere.
amount
Maximum amount of errors to return
chrono
Return in chronological order, or not?
remove
Remove items from the stack upon retrieval?
In scalar context it will return the first item matching your criteria
and in list context, it will return all of them.
If an error occurs while retrieving, a warning will be issued and undef
will be returned.
first
This is a shortcut for retrieving the first item(s) stored on the
stack. It will default to only retrieving one if called with no
arguments, and will always return results in chronological order.
If you only supply one argument, it is assumed to be the amount you
wish returned.
Furthermore, it can take the same arguments as "retrieve" can.
last
This is a shortcut for retrieving the last item(s) stored on the stack.
It will default to only retrieving one if called with no arguments, and
will always return results in reverse chronological order.
If you only supply one argument, it is assumed to be the amount you
wish returned.
Furthermore, it can take the same arguments as "retrieve" can.
flush
This removes all items from the stack and returns them to the caller
SEE ALSO
Log::Message::Item, Log::Message::Handlers, Log::Message::Config
AUTHOR
This module by Jos Boumans <kane@cpan.org>.
Acknowledgements
Thanks to Ann Barcomb for her suggestions.
COPYRIGHT
This module is copyright (c) 2002 Jos Boumans <kane@cpan.org>. All
rights reserved.
This library is free software; you may redistribute and/or modify it
under the same terms as Perl itself.
perl v5.10.1 2009-02-25 Log::Message(3)
