add deprecation message

cmd/grpcurl/grpcurl.go

@@ -45,6 +45,8 @@ var version = noVersion
 var (
 	exit = os.Exit
 
+	isUnixSocket func() bool // nil when run on non-unix platform
+
 	flags = flag.NewFlagSet(os.Args[0], flag.ExitOnError)
 
 	help = flags.Bool("help", false, prettify(`
@@ -361,6 +363,9 @@ func main() {
 	if *format != "json" && *format != "text" {
 		fail(nil, "The -format option must be 'json' or 'text'.")
 	}
+	if isUnixSocket != nil && isUnixSocket() {
+		fail(nil, "The -unix option is deprecated, please use unix://{path} as the address instead.")
+	}
 	if *emitDefaults && *format != "json" {
 		warn("The -emit-defaults is only used when using json format.")
 	}

cmd/grpcurl/unix.go

@@ -0,0 +1,15 @@
+//go:build darwin || dragonfly || freebsd || linux || netbsd || openbsd || solaris || windows
+// +build darwin dragonfly freebsd linux netbsd openbsd solaris windows
+
+package main
+
+var (
+	unix = flags.Bool("unix", false, prettify(`
+		Indicates that the server address is the path to a Unix domain socket.`))
+)
+
+func init() {
+	isUnixSocket = func() bool {
+		return *unix
+	}
+}