Filter::Boolean(3pm)					User Contributed Perl Documentation				      Filter::Boolean(3pm)

NAME

       Log::Log4perl::Filter::Boolean - Special filter to combine the results of others

SYNOPSIS

	   log4perl.logger = WARN, AppWarn, AppError

	   log4perl.filter.Match1	= sub { /let this through/ }
	   log4perl.filter.Match2	= sub { /and that, too/ }
	   log4perl.filter.MyBoolean	   = Log::Log4perl::Filter::Boolean
	   log4perl.filter.MyBoolean.logic = Match1 || Match2

	   log4perl.appender.Screen	   = Log::Dispatch::Screen
	   log4perl.appender.Screen.Filter = MyBoolean
	   log4perl.appender.Screen.layout = Log::Log4perl::Layout::SimpleLayout

DESCRIPTION

       Sometimes, it's useful to combine the output of various filters to arrive at a log/no log decision. While Log4j, Log4perl's mother ship,
       chose to implement this feature as a filter chain, similar to Linux' IP chains, Log4perl tries a different approach.

       Typically, filter results will not need to be passed along in chains but combined in a programmatic manner using boolean logic. "Log if
       this filter says 'yes' and that filter says 'no'" is a fairly common requirement but hard to implement as a chain.

       "Log::Log4perl::Filter::Boolean" is a special predefined custom filter for Log4perl which combines the results of other custom filters in
       arbitrary ways, using boolean expressions:

	   log4perl.logger = WARN, AppWarn, AppError

	   log4perl.filter.Match1	= sub { /let this through/ }
	   log4perl.filter.Match2	= sub { /and that, too/ }
	   log4perl.filter.MyBoolean	   = Log::Log4perl::Filter::Boolean
	   log4perl.filter.MyBoolean.logic = Match1 || Match2

	   log4perl.appender.Screen	   = Log::Dispatch::Screen
	   log4perl.appender.Screen.Filter = MyBoolean
	   log4perl.appender.Screen.layout = Log::Log4perl::Layout::SimpleLayout

       "Log::Log4perl::Filter::Boolean"'s boolean expressions allow for combining different appenders by name using AND (&& or &), OR (|| or |)
       and NOT (!) as logical expressions. Parentheses are used for grouping. Precedence follows standard Perl. Here's a bunch of examples:

	   Match1 && !Match2		# Match1 and not Match2
	   !(Match1 || Match2)		# Neither Match1 nor Match2
	   (Match1 && Match2) || Match3 # Both Match1 and Match2 or Match3

SEE ALSO

       Log::Log4perl::Filter, Log::Log4perl::Filter::LevelMatch, Log::Log4perl::Filter::LevelRange, Log::Log4perl::Filter::StringRange

COPYRIGHT AND LICENSE

       Copyright 2002-2009 by Mike Schilli <m@perlmeister.com> and Kevin Goess <cpan@goess.org>.

       This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

perl v5.10.1							    2010-07-21						      Filter::Boolean(3pm)