Write log to file (or /dev/null)

This code appends a log message to the file text.log. It creates the file if it doesn’t already exist.

f, err := os.OpenFile("text.log",
	os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0644)
if err != nil {
	log.Println(err)
}
defer f.Close()

logger := log.New(f, "prefix", log.LstdFlags)
logger.Println("text to append")
logger.Println("more text to append")

Contents of text.log:

prefix: 2017/10/20 07:52:58 text to append
prefix: 2017/10/20 07:52:58 more text to append

• log.New creates a new log.Logger that writes to f.
• The prefix appears at the beginning of each generated log line.
• The flag argument defines which text to prefix to each log entry.

Disable logging

To turn off all output from a log.Logger, set the output destination to ioutil.Discard, a writer on which all calls succeed without doing anything.

log.SetOutput(ioutil.Discard)

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