The `log` package in Go

The log package in Go

The log package in Go provides basic logging functionality. Below are some of the most commonly used functions in the log package:

1. log.Print(v ...interface{})

   • Logs a message with the default log format (typically followed by a newline).
   • Example:

     log.Print("This is a log message")

2. log.Println(v ...interface{})

   • Logs a message with the default log format, followed by a newline.
   • It’s similar to Print but automatically adds a newline.
   • Example:

     log.Println("This is a log message")

3. log.Printf(format string, v ...interface{})

   • Logs a formatted message, similar to fmt.Printf, with a default log format.
   • Example:

     log.Printf("User %s has logged in", username)

4. log.Fatal(v ...interface{})

   • Logs a message and then calls os.Exit(1) to terminate the program. It’s used for fatal errors.
   • Example:

     if err != nil {
         log.Fatal("Error:", err)
     }

5. log.Fatalln(v ...interface{})

   • Similar to log.Fatal, but adds a newline at the end of the log message before calling os.Exit(1).
   • Example:

     if err != nil {
         log.Fatalln("Fatal error:", err)
     }

6. log.Fatalf(format string, v ...interface{})

   • Logs a formatted message and then calls os.Exit(1). It’s useful when you need to format the error message before exiting.
   • Example:

     log.Fatalf("Error: %v\n", err)

7. log.Panic(v ...interface{})

   • Logs a message and then calls panic(). It’s used for non-recoverable errors that need to be logged before panicking.
   • Example:

     if err != nil {
         log.Panic("Error:", err)
     }

8. log.Panicln(v ...interface{})

   • Similar to log.Panic, but adds a newline after the log message before calling panic().
   • Example:

     log.Panicln("This is a panic message")

9. log.Panicf(format string, v ...interface{})

   • Similar to log.Panic, but with formatted output.
   • Example:

     log.Panicf("Something went wrong: %v", err)

10. log.SetFlags(flag int)

    • Sets the flags for the default logger. Common flags include log.Ldate, log.Ltime, log.Lshortfile, etc., which control the output format of log messages.
    • Example:

      log.SetFlags(log.Ldate | log.Ltime | log.Lshortfile)

11. log.SetPrefix(prefix string)

    • Sets a prefix to be included at the start of every log message.
    • Example:

      log.SetPrefix("[INFO] ")

These functions provide a simple interface for logging messages in Go applications.