Using tryCatchLog with futile.logger: write to file instead of console - r

Question

I am using tryCatchLog and want to send all warnings and error messages to a log file. I do not want any output to the console.
In the documentation for tryCatchLog I came across this code snippet:
library(futile.logger)
# log to a file (not the console which is the default target of futile.logger).
# You could also redirect console output into a file if start your R > script with a shell script using Rscript!
flog.appender(appender.file("my_app.log"))
The vignette for tryCatchLog includes the following code snippet to change the logging behavior and send errors to a file instead of the console:
library(futile.logger)
flog.appender(appender.file("app.log"))
flog.threshold(ERROR) # TRACE, DEBUG, INFO, WARN, ERROR, FATAL
try(log(-1)) # the warning will not be logged!
This suggests to me that I can simply re-direct the messages to a log file using flog.apppender(appender.file()). However, instead of writing to a file I get the following output on the console:
NULL
NULL
Warning in log(-1) : NaNs produced
[1] NaN
The vignette for tryCatchLog provides this code example in the Best Practice section:
library(futile.logger)
library(tryCatchLog)
options(keep.source = TRUE) # source code file name and line number tracking
options("tryCatchLog.write.error.dump.file" = TRUE) # dump for post-mortem analysis
flog.appender(appender.file("my_app.log")) # to log into a file instead of console
flog.threshold(INFO) # TRACE, DEBUG, INFO, WARN, ERROR, FATAL
tryCatchLog(source("your_main_script.R"))
Adapting the last line of code to tryCatchLog(log("this will produce an error")) to make the example easier, I am still not writing to a log file but to the console:
NULL
NULL
Error in log("this will produce an error") : non-numeric argument to mathematical function
Looking at the documentation of futile.logger and examples on stackoverflow also did not help me. Based on them, I thought the following should write the error message to a file. I am using try() as a stand-in for more involved versions of tryCatchLog() to make sure that it is not an issue with tryCatchLog.
library(futile.logger)
flog.appender(appender.file(file.path(getwd(),'logs.txt')))
flog.threshold(WARN) # TRACE, DEBUG, INFO, WARN, ERROR, FATAL
try(log(-1)) # this will create a warning
try(log("this will create an error")) # this will create an error
The command neither creates a log file nor appends an existing one.
Instead, flog.appender() and flog.threshold() return NULL (to the console). And the warning and error message are also printed to the console. Presumably, I am missing something when linking the logger to the file (hence the NULL return value?).
How can I redirect all warnings and errors caught by tryCatchLog to a file (with futile.logger) without ANY output to the console?

Answer 1

The output of try() has nothing to do with futile.logger().
If you configure a file appender in futile.logger you still have to write your log output using the flog.* functions (that's how logging works):
library(futile.logger)
flog.info("this is an info log output")
# INFO [2021-12-08 19:51:13] this is an info log output
flog.warn("this is an warning log output")
# WARN [2021-12-08 19:51:14] this is an warning log output
flog.error("this is an error log output")
# ERROR [2021-12-08 19:51:14] this is an error log output
I guess what you want is kinda output redirection of the standard or error output (eg. via capture.output) but this function does not add logging information like a timestamp and does not support severity level management ("info", "warn", "error"...).
If you want to use try*() in combination with logging you can use the CRAN package tryCatchLog which does exactly what you want (and supports futile.logger too):
library(tryCatchLog)
tryLog(log(-1)) # this will create a warning
tryLog(log("this will create an error")) # this will create an error