log4r

Introduction

The log4r package is meant to provide a clean, lightweight object-oriented approach to logging in R based roughly on the widely-emulated log4j API.

Installation

• Stable CRAN version:

install.packages("log4r")

• Development version on GitHub:

devtools::install_github("johnmyleswhite/log4r")

Usage

Logging is configured by passing around logger objects created by logger(). By default, this will log to the console and suppress messages below the "INFO" level:

logger <- logger()

info(logger, "Located nearest gas station.")
#> INFO  [2019-03-26 18:35:08] Located nearest gas station.
warn(logger, "Ez-Gas sensor network is not available.")
#> WARN  [2019-03-26 18:35:08] Ez-Gas sensor network is not available.
debug(logger, "Debug messages are suppressed by default.")

Logging destinations are controlled by Appenders, a few of which are provided by the package. For instance, if we want to debug-level messages to a file:

log_file <- tempfile()
logger <- logger("DEBUG", appenders = file_appender(log_file))

info(logger, "Messages are now written to the file instead.")
debug(logger, "Debug messages are now visible.")

readLines(log_file)
#> [1] "INFO  [2019-03-26 18:35:08] Messages are now written to the file instead."
#> [2] "DEBUG [2019-03-26 18:35:08] Debug messages are now visible."

The appenders parameter takes a list, so you can log to multiple destinations transparently.

To control the format of the messages you can change the Layout used by each appender. Layouts are functions; you can write your own quite easily:

my_layout <- function(level, ...) {
  paste0(format(Sys.time()), " [", level, "] ", ..., collapse = "")
}

logger <- logger(appenders = console_appender(my_layout))
info(logger, "Messages should now look a little different.")
#> 2019-03-26 18:35:08 [INFO] Messages should now look a little different.

Older APIs

The 0.2 API is still supported:

logger <- create.logger()

logfile(logger) <- log_file
level(logger) <- "INFO"

debug(logger, 'A Debugging Message')
info(logger, 'An Info Message')
warn(logger, 'A Warning Message')
error(logger, 'An Error Message')
fatal(logger, 'A Fatal Error Message')

readLines(log_file)
#> [1] "INFO  [2019-03-26 18:35:08] An Info Message"      
#> [2] "WARN  [2019-03-26 18:35:08] A Warning Message"    
#> [3] "ERROR [2019-03-26 18:35:08] An Error Message"     
#> [4] "FATAL [2019-03-26 18:35:08] A Fatal Error Message"

The log4r Priority Levels

log4r supports five priority levels. In order from lowest to highest priority, they are:

• "DEBUG"
• "INFO"
• "WARN"
• "ERROR"
• "FATAL"

Keep in Mind

• Use a log file in a non-existent directory will fail. In general, no effort is made to create directories.

• Only messages at or above the current threshold are logged. Messages below this level are simply ignored.

• Using the internal priority level constants using the ::: notation is deprecated, but no warning is given. It is safer to simply use strings or numeric constants.