Mimetype - a simple, command line utility that uses go's http.DetectContentType to get the mimetype of a file.

Mimetype.go

package main

import (
	"net/http"
	"os"
)

const (
	usage = `usage: mimetype [filename]`
)

func main() {
	if len(os.Args) < 2 {
		println(usage)
		os.Exit(1)
	}

	f, err := os.Open(os.Args[1])
	if err != nil {
		println("could not open file:", err.Error())
		os.Exit(1)
	}
	defer f.Close()
	b := make([]byte, 512)
	_, err = f.Read(b)
	if err != nil {
		println("could not read file:", err.Error())
		os.Exit(1)
	}
	println(http.DetectContentType(b))
}