Send logs to their final destination with Appenders

In log4j etymology, Appenders are destinations where logs are written. Appenders have no control over formatting; this is controlled by the Layout.

The most basic appenders write logs to the console or to a file; these are described below.

For implementing your own appenders, see Details.

Usage

console_appender(layout = default_log_layout())

file_appender(file, append = TRUE, layout = default_log_layout())

Arguments

layout: A layout function taking a level parameter and additional arguments corresponding to the message. See layouts().
file: The file to write messages to.
append: When TRUE, the file is not truncated when opening for the first time.

Value

An appender: a function with the interface function(level, ...) that writes its arguments to a destination and returns invisible(NULL).

Details

Appenders are implemented as functions with the interface function(level, ...). These functions are expected to write their arguments to a destination and return invisible(NULL).

Examples

# The behaviour of an appender can be seen by using them directly; the
# following snippet will write the message to the console.
appender <- console_appender()
appender("INFO", "Input has length ", 0, ".")
#> INFO  [2026-08-14 17:00:30] Input has length 0.