Imports System.IO
Public Class Form1

    Dim WithEvents _PORT As New System.IO.Ports.SerialPort
    Dim Batch_file_exists As Boolean

    Private Sub Form1_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
        _PORT.BaudRate = 9600         'desired baud rate
        _PORT.PortName = "COM3"       'desired com port
        _PORT.Open()
        _PORT.ReadExisting()
    End Sub

    Private Sub _PORT_DataReceived(ByVal sender As Object, ByVal e As System.IO.Ports.SerialDataReceivedEventArgs) Handles _PORT.DataReceived
        Dim sData As String            'expects path and name of batch file

        If _PORT.IsOpen Then
            sData = _PORT.ReadLine
            Batch_file_exists = File.Exists(sData)
            If Batch_file_exists = True Then
                Process.Start(sData)
            End If
        End If

    End Sub

End Class 