I am trying to change the logging format to include the line number of the file for a Dancer2 app. The default does not seem to do this. If I add the line
log_format: "[%f--%l] %m"
log_format isn't a global configuration directive. It's specific to the particular logging engine you're using, so you have to put it in the configuration section for that engine.
For example, if you're using the Dancer2::Logger::File engine:
logger: "File" engines: logger: File: log_format: "[%f--%l] %m"