[log4perl-devel] Log::Log4perl Recipe of the Week (#21)

[<log...@pe...>]

Welcome to the Log::Log4perl recipe of the week. Today:

============================================================
Log::Log4perl Recipe of the Week (#21):

My new module uses Log4perl -- but what happens if the
calling program didn't configure it?
============================================================

If a Perl module uses Log::Log4perl, it will typically rely
on the calling program to initialize it. If it is using
Log::Log4perl in ":easy" mode, like in

    package MyMod;
    use Log::Log4perl qw(:easy);

    sub foo {
        DEBUG("In foo");
    }
    
    1;

and the calling program doesn't initialize Log::Log4perl at
all (e.g. because it has no clue that it's available),
Log::Log4perl will silently ignore all logging messages.
However, if the module is using Log::Log4perl in regular
mode like in

    package MyMod;
    use Log::Log4perl qw(get_logger);

    sub foo {
        my $logger = get_logger("");
        $logger->debug("blah");
    }

    1;

and the main program is just using the module like in

    use MyMode;
    MyMode::foo();

then Log::Log4perl will also ignore all logging messages but
issue a warning like

    Log4perl: Seems like no initialization happened. 
    Forgot to call init()?

(only once!) to remind novice users to not forget to
initialize the logging system before using it. However, if
you want to suppress this message, just add the ":nowarn"
target to the module's "use Log::Log4perl" call:

    use Log::Log4perl qw(get_logger :nowarn);

This will have Log::Log4perl silently ignore all logging
statements if no initialization has taken place.

If the module wants to figure out if some other program part
has already initialized Log::Log4perl, it can do so by
calling

    Log::Log4perl::initialized()

which will return a true value in case Log::Log4perl has
been initialized and a false value if not.


Have fun! Until next week.

-- Mike

###################################
# Mike Schilli                    #
# log...@pe...        #
# http://perlmeister.com          #
# http://log4perl.sourceforge.net #
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