How can I print to Stderr in Go without using log

The Go builtin functions print and println print to stderr. So if you simply want to output some text to stderr you can do

package main

func main() {
    println("Hello stderr!")
}

Documentation: https://golang.org/pkg/builtin/#print

Using the fmt package, you can choose to write to stderr this way:

import "fmt"
import "os"

func main() {
    fmt.Fprintln(os.Stderr, "hello world")
}

os.Stderr is an io.Writer, so you can use it in any function which accepts an io.Writer. Here are a few examples:

str := "Message"
fmt.Fprintln(os.Stderr, str)
io.WriteString(os.Stderr, str)
io.Copy(os.Stderr, bytes.NewBufferString(str))
os.Stderr.Write([]byte(str))

It all depends on how exactly you have the string you want to print (i.e. if you want to format it first, if you have it as an io.Reader, if you have it as a byte slice...). And there can be a lot more ways.

If you don't want timestamps, just create a new log.Logger with flag set to 0:

l := log.New(os.Stderr, "", 0)
l.Println("log msg")

EDIT:

Is the following good Go?

os.Stderr.WriteString("Message")

This is acceptable, and you can also use fmt.Fprintf and friends to get formatted output:

fmt.Fprintf(os.Stderr, "number of foo: %d", nFoo)