log4r (version 0.5.0)

layouts: Format logs with Layouts

Description

In log4j etymology, Layouts are how Appenders control the format of messages. Most users will use one of the general-purpose layouts provided by the package:

• default_log_layout() formats messages much like the original log4j library. simple_log_layout() does the same, but omits the timestamp.

• bare_log_layout() emits only the log message, with no level or timestamp fields.

• logfmt_log_layout() and json_log_layout() format structured logs in the two most popular machine-readable formats.

For implementing your own layouts, see Details.

Usage

default_log_layout(time_format = "%Y-%m-%d %H:%M:%S")
simple_log_layout()
bare_log_layout()
logfmt_log_layout()
json_log_layout()

Value

A layout: a function with the interface function(level, ...) that returns a single newline-terminated string.

Arguments

time_format

A valid format string for timestamps. See base::strptime().

Details

Layouts return a function with the signature function(level, ...) that itself returns a single newline-terminated string. Anything that meets this interface can be passed as a layout to one of the existing appenders.

json_log_layout requires the jsonlite package.

Examples

# The behaviour of a layout can be seen by using them directly:
simple <- simple_log_layout()
simple("INFO", "Input has length ", 0, ".")

with_timestamp <- default_log_layout()
with_timestamp("INFO", "Input has length ", 0, ".")

logfmt <- logfmt_log_layout()
logfmt("INFO", msg = "got input", length = 24)