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


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

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


AUTHOR

Mike Schilli, <log4perl@perlmeister.com>, 2003

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