You can use the callbacks argument to the Log::Dispatch constructor:

my $logger = Log::Dispatch->new( ...,
                                 callbacks => \&package_filter,
                               );

sub package_filter
{
    my %message = @_;
    my ( $pkg, $file, $line ) = caller(3); # please check that 3 is th
+e correct level for your situation

    # decide if the package $pkg should be logged
    if( should_log( $pkg ) )
    {
        return $message{'message'};
    }

    # otherwise, suppress this message
    return;
}
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Note that you can also pass an arrayref of callback functions to the Log::Dispatch constructor. They will be called in the specified order.