Ruby Logger: how to set the log level from environment variable

# see: https://ruby-doc.org/stdlib-2.5.0/libdoc/logger/rdoc/Logger.html
  LOGLEVELS = %w[DEBUG INFO WARN ERROR FATAL UNKNOWN].freeze
  LOGGER = Logger.new(STDOUT)
  level ||= LOGLEVELS.index ENV.fetch("LOG_LEVEL","WARN") # default to WARN index: 2
  level ||= Logger::WARN  # FIX default in case of environment LOG_LEVEL value is present but not correct
  LOGGER.level = level
 
 # Usage: 
 #  before launching the program: 
 #  $ export LOG_LEVEL=DEBUG