Log4r configuration: "/dev/null" outputter question


#1

Well, my code does seem to work, but I have the feeling that I could
have
done it much simpler… So here is my problem:

I would like to control log4r via an environment variable, which can
contain one of 4 types of values:

stdout : logging goes to stdout
stderr : logging goes to stderr
file:FILENAME : logging goes to FILENAME
none : logging not needed

The problem is what outputter to use to implement ‘none’. My first idea
to simply use FileOutputter(‘none’,:filename => ‘/dev/null’) does not
work
because my code is also supposed to run onder Windows where we don’t
have
/dev/null. So I came up with the solution to invent a “NullOutputter”:

class NullOutputter <Outputter
def initialize(name)
super(name)
end
end

$log = Logger.new(‘TestLog’)
outputterspec=ENV[‘TFW_LOG’] || ‘stdout’
$log.outputters = case outputterspec
when ‘stdout’
Outputter.stdout
when ‘stderr’
Outputter.stderr
when /^file:(.+)$/
FileOutputter.new ‘tfw’, :filename => $1, :trunc => true
when ‘none’
NullOutputter.new ‘tfwnull’
end

Note that I did NOT use

when ‘none’
Outputter.new ‘tfwnull’

because Outputter is documented as abstract class.

My solution works, but I wonder whether I could make it simpler
(i.e. without creating the NullOutputter class).

Ronald


#2

On 7/17/07, Ronald F. removed_email_address@domain.invalid wrote:

The problem is what outputter to use to implement ‘none’. My first idea
to simply use FileOutputter(‘none’,:filename => ‘/dev/null’) does not
work
because my code is also supposed to run onder Windows where we don’t
have
/dev/null.

There is a /dev/null equivalent on Windows, NUL: You can use it in
this fashion …

fn = test(?e, ‘/dev/null’) ? ‘/dev/null’ : ‘NUL:’
fd = File.open(fn, ‘w’)

You can now write to that file descriptor and everything will go to
the bit bucket.

My solution works, but I wonder whether I could make it simpler
(i.e. without creating the NullOutputter class).

Certainly. Just create an instance of Outputter and then define the
methods you need.

out = Outputter.new ‘tfwnull’
class << out
def canonical_log(logevent) nil end
end

The canonical_log method is used by the outputters to format the log
event and then write the formatted output to a file. By setting this
to have a nil body, you will save a few cycles each time a log
messages needs to be generated.

Another options is just to set the global log level to ‘off’. That is
left as an exercise for the reader :wink:

Blessings,
TwP


#3

end
Now I wonder, since Outputter is documented as abstract class, why
I can instantiate it at all? Or is “abstract class” in Ruby not dealt
with the same strength as in, say, Java or C++?

But anyway, I tried your approach, but I don’t see how I get the
instance
of the anonymous class into my outputters. When I do it like this:

#!/usr/bin/ruby
require ‘log4r’
include Log4r
$log=Logger.new(‘testing’)
out = Outputter.new ‘tfwnull’
$log.outputters=class << out
def canonical_log(logevent) nil end
end

I get the error message

“Expected kind of Outputter, got NilClass (TypeError)”

Ronald