See https://metacpan.org/pod/Log::Log4perl#Appenders and Log::Log4perl::Appender as Log::Log4perl::Appender::String docs have a mistake, you're supposed to write 
Log::Log4perl::Appender->new(
    'Log::Log4perl::Appender::String', 
    "name" => 'string_appender',
);

[download]

This isn't the first time I've tripped over that :)

In reply to Re: Log::Log4perl appender added at runtime doesn't receive messages by Anonymous Monk
in thread Log::Log4perl appender added at runtime doesn't receive messages by mcso

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