How can I use a Perl variable in my Log::Log4perl config file?

Question

I would like to use a Perl variable from my script in a Log::Log4perl config file. I read the documentation and found that I can use a subroutine, but I would like to do it a little bit simpler, if possible.

I want to set the filename for my appender:

log4perl.appender.av_std_LOGFILE.filename="whateverfilename.log"

But doing this this way, it is a fixed value.

I have the filename in a variable within my script and would like to use this at runtime:

log4perl.appender.av_std_LOGFILE.filename=\
 sub { return &av_getLogfileName(); }

Where this is the subroutine:

sub av_getLogfileName
{
    return $av_std_LOGFILE;
}

This works, but I would like to avoid the sub inside my script since the return value is very simple.

The documentation says:

Each value starting with the string sub {... is interpreted as Perl code to be executed at the time the application parses the configuration...

So I tried something like this, but it did not work:

log4perl.appender.av_std_LOGFILE.filename=\
    sub { print "$av_std_LOGFILE"; }

Is there a way to get result of the variable without the sub inside my script?

Answer 1

print returns 1 on success, so

sub { print "$av_std_LOGFILE"; }

returns 1, not the value of $av_std_LOGFILE. You also have to fully qualify variable names in hooks, which means you'll have to make $av_std_LOGFILE a package global.

Change your hook to:

sub { return $main::av_std_LOGFILE; } # double quotes are unnecessary

and set $av_std_LOGFILE in your script like this (before calling Log::Log4perl::init):

our $av_std_LOGFILE = '/path/to/logfile';

Generally, you should avoid global variables, so I would prefer using a subroutine.