go-selfupdate binary uses os env to detect arch/platform so you can crosscompile

main.go

@@ -1,23 +1,21 @@
 package main
 
 import (
-    "fmt"
-    "os"
-    "encoding/json"
-    "io/ioutil"
-    "io"
-    "path/filepath"
-    "compress/gzip"
 	"bytes"
+	"compress/gzip"
 	"crypto/sha256"
+	"encoding/json"
+	"fmt"
 	"github.com/kr/binarydist"
-    "runtime"
+	"io"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	//"runtime"
 	//"encoding/base64"
 )
 
-const (
-    plat = runtime.GOOS + "-" + runtime.GOARCH
-)
+var plat string
 
 type current struct {
 	Version string
@@ -61,6 +59,8 @@ func newGzReader(r io.ReadCloser) io.ReadCloser {
 }
 
 func main() {
+	plat = os.Getenv("GOOS") + "-" + os.Getenv("GOARCH")
+
 	appPath := os.Args[1]
 	version := os.Args[2]
 	genDir := "public"