how to send the output to a logfile and richtextbox - vb.net

Question

I have the follow code that works for sending the output to a richtextbox. I cant figure out how to also have the output sent to a log file if I choose as well. this is the beginnings of my code for choosing to log the output. I cant figure out how to get it to log the output to the file location.
Private Sub Button2_Click(sender As Object, e As EventArgs) Handles Button2.Click
If (OpenFileDialog1.ShowDialog() = DialogResult.OK) Then
TextBox31.Text = Chr(34) & OpenFileDialog1.FileName & Chr(34)
End If
End Sub
here is my working code for displaying the output in the richtextbox.
Private Sub ExecuteButton_Click(sender As Object, e As EventArgs) Handles ExecuteButton.Click
System.Windows.Forms.Application.DoEvents()
Dim myprocess As New Process
Dim startinfo As New ProcessStartInfo(TextBox3.Text, TextBox1.Text) With {
.UseShellExecute = False,
.RedirectStandardOutput = True,
.CreateNoWindow = True
}
myprocess.StartInfo = startinfo
myprocess.Start()
Dim str1 As String = ""
Using MyStreamReader As IO.StreamReader = myprocess.StandardOutput
str1 &= MyStreamReader.ReadToEnd
End Using
RichTextBox1.Text = str1
End Sub
Note: This is what I used to be able to log the output
If CheckBox34.Checked = True Then
Dim objWriter As New System.IO.StreamWriter(TextBox31.Text & "\" & Format(Now, "dd-MMM-yyyy") & ".log", True)
objWriter.WriteLine(Format(Now, "dd-MMM-yyyy HH:mm:ss ") & TextBox4.Text & vbCrLf & str1)
objWriter.Close()
End If

Answer 1

Try With this sample:
Dim MyPath = "C:\MyLog.Log"
FileOpen(1, MyPath, OpenMode.Append)
Dim lNumberofRecs = LOF(1)
Print(1, Format(Now, "dd-MMM-yyyy HH:mm:ss") & "#Import Begin" & vbCrLf)
FileClose(1)
or with this:
Dim objWriter As New System.IO.StreamWriter("C:\MyData\mylog.log", True)
objWriter.WriteLine("each log data you have")
objWriter.Close()