Go言語でOS種類を判定する

runtime.GOOS で "darwin", "windows", "linux", "freebsd" などが取得出来ます。

runtime - The Go Programming Language

package main

import (
    "fmt"
    "runtime"
)

func main() {
    command := "milk"

    if runtime.GOOS == "windows" {
        command = "milk.bat"
    }