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Manual Reference Pages  -  LOG::AGENT::LOGGER (3)

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NAME

Log::Agent::Logger - a logging interface

CONTENTS

SYNOPSIS



 require Log::Agent::Logger;

 my $log = Log::Agent::Logger->make(
     -channel    => $chan,
     -max_prio   => info,
     -min_prio   => emerg,
 );

 $log->error("cant open file %s: $!", $file);
 $log->warning("cant open file: $!");



DESCRIPTION

The Log::Agent::Logger class defines a generic interface for application logging. It must not be confused with the interface provided by Log::Agent, which is meant to be used by re-usable modules that do not wish to commit on a particular logging method, so that they remain true building blocks.

By contrast, Log::Agent::Logger explicitely requests an object to be used, and that object must commit upon the logging channel to be used, at creation time.

Optionally, minimum and maximum priority levels may be defined (and changed dynamically) to limit the messages to effectively log, depending on the advertised priority. The standard syslog(3) priorities are used.

CHANNEL LIST

The following channels are available:

    Standard Log::Agent Channels

Those channels are documented in Log::Agent::Channel.

    Other Channels

Future Log::Agent::Logger extension will extend the set of available channels.

INTERFACE

    Creation Routine

The creation routine is called make and takes the following switches:
-caller => [ parameters ] Request that caller information (relative to the ->log() call) be part of the log message. The given parameters are handed off to the creation routine of Log::Agent::Tag::Caller and are documented there.

I usually say something like:



 -caller => [ -display => ($sub/$line), -postfix => 1 ]



which I find informative enough. On occasion, I found myself using more complex sequences. See Log::Agent::Tag::Caller.

-channel This defines the Log::Agent::Channel to be used for logging. Please refer to Log::Agent::Channel for details, and in particular to get a list of pre-defined logging channels.
-min_prio Defines the minimum priority to be logged (included). Defaults to emerg.
-max_prio Defines the maximum priority to be logged (included). Defaults to debug.
-priority => [ parameters ] Request that message priority information be part of the log message. The given parameters are handed off to the creation routine of Log::Agent::Tag::Priority and are documented there.

I usually say something like:



        -priority => [ -display => [$priority] ]



which will display the whole priority name at the beginning of the messages, e.g. [warning] for a warn() or [error] for error(). See Log::Agent::Tag::Priority and Log::Agent::Priorities.

-tags => [ list of Log::Agent::Tag objects ] Specifies user-defined tags to be added to each message. The objects given here must inherit from Log::Agent::Tag and conform to its interface. See Log::Agent::Tag for details.

At runtime, well after the creation of the logging object, it may be desirable to add (or remove) a user tag. Use the tags attribute to retrieve the tag list object and interact with it, as explained in Log::Agent::Tag_List.

    Logging Interface

Each routine is documented to take a single string, but you may also supply a code reference as the first argument, followed by extra arguments. That routine will be called, along with the extra arguments, to generate the message to be logged. If that sounds crazy, think about the CPU time we save by NOT calling the routine. If nothing is returned by the routine, nothing is logged.

If more than one argument is given, and the first argument is not a code reference, then it is taken as a printf() format, and the remaining arguments are used to fill the various % placeholders in the format. The special %m placeholder does not make use of any extra argument and is replaced by a stringification of the error message contained in $!, aka errno.

There is a logging routine defined for each syslog(3) priority, along with aliases for some of them. Here is an exhaustive table, sorted by decreasing priority.



    Syslog     Alias
    --------   ---------
    emerg      emergency
    alert
    crit       critical
    err        error
    warning    warn
    notice
    info
    debug



We shall document only one routine for a given level: for instance, we document warn but you could also use the standard warning to achieve exactly the same funciton.
emergency($str) Log at the emerg level, usually just before panicing. Something terribly bad has been detected, and the program might crash soon after logging this.
alert($str) Log at the alert level, to signal a problem requiring immediate attention. Usually, some functionality will be missing until the condition is fixed.
critical($str) Log at the crit level, to signal a severe error that prevents fulfilling some activity.
error($str) Log at the err level, to signal a regular error.
warn($str) Log at the warning level, which is an indication that something unusual occurred.
notice($str) Log at the notice level, indicating something that is fully handled by the applicaiton, but which is not the norm. A significant condition, as they say.
info($str) Log at the info level, for their amusement.
debug($str) Log at the debug level, to further confuse them.

    Closing Channel

close This routine closes the channel. Further logging to the logger is permitted, but will be simply discarded without notice.

    Attribute Access

The following access routines are defined:
channel The defined logging channel. Cannot be changed.
max_prio and max_prio_str Returns the maximum priority recorded, either as a numeric value or as a string. For the correspondance between the two, see Log::Agent::Priorities.
min_prio and min_prio_str Returns the minimum priority recorded, either as a numeric value or as a string. For the correspondance between the two, see Log::Agent::Priorities.
set_caller_info list Dynamically change the caller information formatting in the logs. The list given supersedes the initial settings done via the -caller argument, if any, and is passed to the creation routine of the Log::Agent::Tag::Caller class. Note that a plain list must be given, not a list ref. An empty list removes caller information from subsequent logs.

Please see Log::Agent::Tag::Caller to get the allowed parameters for list.

set_max_prio($prio) and set_min_prio($prio) Used to modify the maximum/minimum priorities. You can use either the string value or the numerical equivalent, as documented in Log::Agent::Priorities.
set_priority_info list Dynamically change the priority information formatting in the logs. The list given supersedes the initial settings done via the -priority argument, if any, and is passed to the creation routine of the Log::Agent::Tag::Priority class. Note that a plain list must be given, not a list ref. An empty list removes priority information from subsequent logs.

Please see Log::Agent::Tag::Priority to get the allowed parameters for list.

tags Returns a Log::Agent::Tag_List object, which holds all user-defined tags that are to be added to each log message.

The initial list of tags is normally supplied by the application at creation time, via the -tags argument. See Log::Agent::Tag_List for the operations that can be performed on that object.

AUTHOR

Raphael Manfredi <Raphael_Manfredi@pobox.com>

Test suite updated for Cygwin by Terrence Brannon, <tbone@cpan.org<gt>

SEE ALSO

Log::Agent::Channel(3).
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