How do I print message to stderr in Go?

Question

I want to print some logs for debugging and testing, but existing logs are massive, so I want to print my own logs to stderr:

go run main.go 1>/dev/null

So that I can just see my own logs.

How can I do that?

Answer 1

There are multiple methods to send a message to stderr:

1. Creating a new log.Logger:

   l := log.New(os.Stderr, "", 1)
   l.Println("log message")
   

2. Using fmt.Fprintf:

   fmt.Fprintf(os.Stderr, "log message: %s", str)
   

3. Directly writing to os.Stderr using os.Stderr.WriteString:

   os.Stderr.WriteString("log message")
   

Answer 2

The log package by default prints to os.Stderr.

You can also use os.Stderr directly (it's an os.File).