NAME¶
Log::Agent::Logger - a logging interface
SYNOPSIS¶
require Log::Agent::Logger;
my $log = Log::Agent::Logger->make(
-channel => $chan,
-max_prio => 'info',
-min_prio => 'emerg',
);
$log->error("can't open file %s: $!", $file);
$log->warning("can't 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>
SEE ALSO¶
Log::Agent::Channel(3).