Go: Building Web Applications

Formatting your output

When instantiating a new Logger, you can pass a few useful parameters and/or helper strings to help define and clarify the output. Each log entry can be prepended with a string, which can be helpful while reviewing multiple types of log entries. You can also define the type of date and time formatting that you would like on each entry.

To create a custom formatted log, just invoke the New() function with an io.Writer as shown:

package main import ( "log" "os" ) var ( Warn *log.Logger Error *log.Logger Notice *log.Logger ) func main() { warnFile, err := os.OpenFile("warnings.log", os.O_RDWR|os.O_APPEND, 0660) defer warnFile.Close() if err != nil { log.Fatal(err) } Warn = log.New(warnFile, "WARNING: ", log.Ldate|log.Ltime) Warn.Println("Messages ...