Log to a file

A simple Appender that outputs to a file in the file system. If you plan to log to text files, consider logging to JSON files and take a look at AppenderJson, which is a shortcut for AppenderFile preconfigured with LayoutJson.

See also

LayoutFormat, LayoutJson

LayoutFormat, LayoutJson

Other Appenders: AppenderBuffer, AppenderConsole, AppenderFileRotatingDate, AppenderFileRotatingTime, AppenderFileRotating, AppenderTable, Appender

Other Appenders: AppenderBuffer, AppenderConsole, AppenderFileRotatingDate, AppenderFileRotatingTime, AppenderFileRotating, AppenderTable, Appender

Super classes

lgr::Filterable -> lgr::Appender -> AppenderFile

Active bindings

file

character scalar. path to the log file

data

data.frame. Contents of file parsed to a data.frame if used with a Layout that supports parsing of log file data (notably LayoutJson). Will throw an error if Layout does not support parsing.

data

character scalar. Like $data, but returns a data.table instead (requires the data.table package).

Methods

Public methods

• AppenderFile$new()

• AppenderFile$append()

• AppenderFile$set_file()

• AppenderFile$show()

Inherited methods

• lgr::Filterable$add_filter()
• lgr::Filterable$filter()
• lgr::Filterable$remove_filter()
• lgr::Filterable$set_filters()
• lgr::Appender$format()
• lgr::Appender$set_layout()
• lgr::Appender$set_threshold()

---

Method new()

Usage

AppenderFile$new(
  file,
  threshold = NA_integer_,
  layout = LayoutFormat$new(),
  filters = NULL
)

---

Method append()

Usage

AppenderFile$append(event)

---

Method set_file()

Set a log file

Usage

AppenderFile$set_file(file)

Arguments

file

character scalar. Path to the log file. If file does not exist it will be created.

---

Method show()

Display the contents of the log file.

Usage

AppenderFile$show(threshold = NA_integer_, n = 20L)

Arguments

threshold

character or integer scalar. The minimum log level that should be displayed.

n

integer scalar. Show only the last n log entries that match threshold.

Super classes

lgr::Filterable -> lgr::Appender -> lgr::AppenderFile -> AppenderJson

Methods

Public methods

• AppenderJson$new()

Inherited methods

• lgr::Filterable$add_filter()
• lgr::Filterable$filter()
• lgr::Filterable$remove_filter()
• lgr::Filterable$set_filters()
• lgr::Appender$format()
• lgr::Appender$set_layout()
• lgr::Appender$set_threshold()
• lgr::AppenderFile$append()
• lgr::AppenderFile$set_file()
• lgr::AppenderFile$show()

---

Method new()

Usage

AppenderJson$new(
  file,
  threshold = NA_integer_,
  layout = LayoutJson$new(),
  filters = NULL
)

Examples

lg <- get_logger("test")
default <- tempfile()
fancy <- tempfile()
json <- tempfile()

lg$add_appender(AppenderFile$new(default), "default")
lg$add_appender(
  AppenderFile$new(fancy, layout = LayoutFormat$new("[%t] %c(): %L %m")), "fancy"
)
lg$add_appender(
  AppenderFile$new(json, layout = LayoutJson$new()), "json"
)

lg$info("A test message")
#> INFO  [20:04:22.082] A test message

readLines(default)
#> [1] "INFO  [2023-03-04 20:04:22.082] A test message"
readLines(fancy)
#> [1] "[2023-03-04 20:04:22.082] eval(): INFO  A test message"
readLines(json)
#> [1] "{\"level\":400,\"timestamp\":\"2023-03-04 20:04:22\",\"logger\":\"test\",\"caller\":\"eval\",\"msg\":\"A test message\"}"

# cleanup
lg$config(NULL)
#> <Logger> [info] test
#> 
#> inherited appenders:
#>   console: <AppenderConsole> [all] -> console
unlink(default)
unlink(fancy)
unlink(json)
tf <- tempfile()
lg <- get_logger("test")$
  set_appenders(AppenderJson$new(tf))$
  set_propagate(FALSE)

lg$info("A test message")
lg$info("A test message %s strings", "with format strings", and = "custom_fields")

lg$appenders[[1]]$show()
#> {"level":400,"timestamp":"2023-03-04 20:04:22","logger":"test","caller":"eval","msg":"A test message"}
#> {"level":400,"timestamp":"2023-03-04 20:04:22","logger":"test","caller":"eval","msg":"A test message with format strings strings","and":"custom_fields"}
lg$appenders[[1]]$data
#>   level           timestamp logger caller
#> 1   400 2023-03-04 20:04:22   test   eval
#> 2   400 2023-03-04 20:04:22   test   eval
#>                                          msg           and
#> 1                             A test message          <NA>
#> 2 A test message with format strings strings custom_fields

# cleanup
lg$config(NULL)
#> <Logger> [info] test
#> 
#> inherited appenders:
#>   console: <AppenderConsole> [all] -> console
unlink(tf)