Print or Format Logging Data

Print or Format Logging Data

Usage

# S3 method for class 'LogEvent'
print(
  x,
  fmt = "%L [%t] %m  %f",
  timestamp_fmt = "%Y-%m-%d %H:%M:%S",
  colors = getOption("lgr.colors"),
  log_levels = getOption("lgr.log_levels"),
  pad_levels = "right",
  excluded_fields = NULL,
  ...
)

# S3 method for class 'LogEvent'
format(
  x,
  fmt = "%L [%t] %m  %f",
  timestamp_fmt = "%Y-%m-%d %H:%M:%S",
  colors = NULL,
  log_levels = getOption("lgr.log_levels"),
  pad_levels = "right",
  excluded_fields = NULL,
  ...
)

Arguments

x

a LogEvent

fmt

A character scalar that may contain any of the tokens listed bellow in the section Format Tokens.

timestamp_fmt

see format.POSIXct()

colors

A list of functions that will be used to color the log levels (likely from crayon::crayon).

log_levels

named integer vector of valid log levels

pad_levels

right, left or NULL. Whether or not to pad the log level names to the same width on the left or right side, or not at all.

excluded_fields

a character vector of fields to exclude from %j and %f

...

ignored

Value

x for print() and a character scalar for format()

Format Tokens

%t

The timestamp of the message, formatted according to timestamp_fmt)

%l

the log level, lowercase character representation

%L

the log level, uppercase character representation

%k

the log level, first letter of lowercase character representation

%K

the log level, first letter of uppercase character representation

%n

the log level, integer representation

%g

the name of the logger

%p

the PID (process ID). Useful when logging code that uses multiple threads.

%c

the calling function

%m

the log message

%r

the raw log message (without string interpolation)

%f

all custom fields of x in a pseudo-JSON like format that is optimized for human readability and console output

%j

all custom fields of x in proper JSON. This requires that you have jsonlite installed and does not support colors as opposed to %f

Examples

# standard fields can be printed using special tokens
x <- LogEvent$new(
  level = 300, msg = "a test event", caller = "testfun()", logger = lgr
)
print(x)
#> WARN  [2025-07-23 06:40:37] a test event
print(x, fmt = c("%t (%p) %c: %n - %m"))
#> 2025-07-23 06:40:37 (7318) testfun(): 300 - a test event
print(x, colors = NULL)
#> WARN  [2025-07-23 06:40:37] a test event

# custom values
y <- LogEvent$new(
  level = 300, msg = "a gps track", logger = lgr,
  waypoints = 10, location = "Austria"
)

# default output with %f
print(y)
#> WARN  [2025-07-23 06:40:37] a gps track  {waypoints: `10`, location: `Austria`}

# proper JSON output with %j
if (requireNamespace("jsonlite")){
print(y, fmt = "%L [%t] %m  %j")
}
#> WARN  [2025-07-23 06:40:37] a gps track  {"waypoints":10,"location":"Austria"}