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.IX Title "Filter::Boolean 3"
.TH Filter::Boolean 3 2026-08-14 "perl v5.42.2" "User Contributed Perl Documentation"
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.SH NAME
Log::Log4perl::Filter::Boolean \- Special filter to combine the results of others
.SH SYNOPSIS
.IX Header "SYNOPSIS"
.Vb 1
\&    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
.Ve
.SH DESCRIPTION
.IX Header "DESCRIPTION"
Sometimes, it\*(Aqs useful to combine the output of various filters to
arrive at a log/no log decision. While Log4j, Log4perl\*(Aqs mother ship,
chose to implement this feature as a filter chain, similar to Linux\*(Aq IP chains,
Log4perl tries a different approach.
.PP
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 \*(Aqyes\*(Aq and that filter says \*(Aqno\*(Aq" 
is a fairly common requirement but hard to implement as a chain.
.PP
\&\f(CW\*(C`Log::Log4perl::Filter::Boolean\*(C'\fR is a special predefined custom filter
for Log4perl which combines the results of other custom filters 
in arbitrary ways, using boolean expressions:
.PP
.Vb 1
\&    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
.Ve
.PP
\&\f(CW\*(C`Log::Log4perl::Filter::Boolean\*(C'\fR\*(Aqs 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\*(Aqs a bunch of examples:
.PP
.Vb 3
\&    Match1 && !Match2            # Match1 and not Match2
\&    !(Match1 || Match2)          # Neither Match1 nor Match2
\&    (Match1 && Match2) || Match3 # Both Match1 and Match2 or Match3
.Ve
.SH "SEE ALSO"
.IX Header "SEE ALSO"
Log::Log4perl::Filter,
Log::Log4perl::Filter::LevelMatch,
Log::Log4perl::Filter::LevelRange,
Log::Log4perl::Filter::MDC,
Log::Log4perl::Filter::StringRange
.SH LICENSE
.IX Header "LICENSE"
Copyright 2002\-2026 by Mike Schilli <m@perlmeister.com>
and Kevin Goess <cpan@goess.org>.
.PP
This library is free software; you can redistribute it and/or modify
it under the same terms as Perl itself.