如何根据操作系统在Go中设置变量

I'm aware that I can name particular go files _windows.go, _linux.go, etc and that this will make them only compile for that particular operating system.

Within a file that doesn't have the go os specified in the filename, is there a way I can set a variable and/or constant within a file depending on the go os? Maybe in a case statement?

runtime.GOOS is your friend. However, keep in mind that you can't set constants based on it (although you can copy it to your own constant) - only variables, and only in runtime. You can use an init() function in a module to run the detection automatically when the program starts.

package main

import "fmt"
import "runtime"

func main() {

    fmt.Println("this is", runtime.GOOS)

    foo := 1
    switch runtime.GOOS {
    case "linux":
        foo = 2
    case "darwin":
        foo = 3
    case "nacl": //this is what the playground shows!
        foo = 4
    default:
        fmt.Println("What os is this?", runtime.GOOS)

    }

    fmt.Println(foo)
}

Take a look at runtime.GOOS.

GOOS is the running program's operating system target: one of darwin, freebsd, linux, and so on.

switch runtime.GOOS {
case "linux":
    fmt.Println("Linux")
default:
    fmt.Println(runtime.GOOS)
}