# Log::Log4perl::Filter::Boolean - phpMan

## 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::MDC],
    [Log::Log4perl::Filter::StringRange]

## LICENSE
    Copyright 2002-2013 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.

## AUTHOR
    Please contribute patches to the project on Github:

        <http://github.com/mschilli/log4perl>

    Send bug reports or requests for enhancements to the authors via our

    MAILING LIST (questions, bug reports, suggestions/patches):
    <log4perl-devel@lists.sourceforge.net>

    Authors (please contact them via the list above, not directly): Mike
    Schilli <<m@perlmeister.com>>, Kevin Goess <<cpan@goess.org>>

    Contributors (in alphabetical order): Ateeq Altaf, Cory Bennett, Jens
    Berthold, Jeremy Bopp, Hutton Davidson, Chris R. Donnelly, Matisse
    Enzer, Hugh Esco, Anthony Foiani, James FitzGibbon, Carl Franks, Dennis
    Gregorovic, Andy Grundman, Paul Harrington, Alexander Hartmaier David
    Hull, Robert Jacobson, Jason Kohles, Jeff Macdonald, Markus Peter, Brett
    Rann, Peter Rabbitson, Erik Selberg, Aaron Straup Cope, Lars Thegler,
    David Viner, Mac Yang.