Log::ger::Manual::Tutorial::200_LoggingWithLogGer - Logging with Log::ger


version 0.033.000



As shown in the previous post, logging with Log::ger is as simple as loading Log::ger with use Log::ger and then using one of the log_trace, log_debug, log_info, log_warn, log_error, log_fatal statements. These subroutines are the logger subroutines; there is one for each level. They accept a string:

 log_warn("This is a log message");

or a sprintf template and one or more arguments (so in other words, it will do sprintf if there are two or more arguments):

 log_warn("User %s does not exist", $user);
 log_warn("HTTP status code %d, message %s, result structure %s",
          $code, $message, $res);
 log_warn("Subroutine arguments(%s)", \@_);

In sprintf mode, data structure will automatically be dumped and undef will also be shown as <undef>.

In addition to the logger subroutines, there are also the level detection routines: log_is_trace, log_is_debug, log_is_info, log_is_warn, log_is_error, log_is_fatal. They are sometimes used if you want to do some complex logging:

 if (log_is_trace()) {
     require Blah;
     my $x = Blah->new(foo=>1, bar=>2);
     log_trace("Blah is %s", $x->as_string);


Some other logging frameworks use OO-style, where you first request a logger object then log (or detect level) by calling methods on the logger object. You can do this with Log::ger too, although I personally do not recommend this except when wanting to customize category (will be explained in later posts):

 use Log::ger (); # don't import log_* and log_is_* subroutines

 my $log = Log::ger->get_logger;
 if ($log->is_trace) {

The logger methods are named according to the level names (so there is no log_ prefix as in the subroutine version). The level detection methods are named is_LEVEL, e.g. is_trace, is_debug, and so on.

Why do I prefer procedural style? First, it's shorter to type and you can omit the parentheses:

 log_warn "blah";

It's more convenient to convert a print or printf statement to logging statement, or vice versa.

Second, if you use subroutine form it's possible to use Log::ger::Plugin::OptAway to remove logging statements completely during run-time.


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