I have a large text file that I have so far written code that reads the file.
The next thing I want to do is to export the file to excel.
I want to split the file into different sheets in the same excel based on the first 5 digit string of each line.

example of text file:

12345 test line 1

12345 test line 2

67890 test line 3

12345 test line 4

12345 test line 5

67890 test line 6

67890 test line 7

eg. Sheet one:

12345 test line 1

12345 test line 2

12345 test line 4

12345 test line 5

sheet two:

67890 test line 3

67890 test line 6

67890 test line 7

If anyone knows the best way to export to excel using asp.net vb please let me know

    Dim fu As FileUpload = FileUpload1

    If fu.HasFile Then
        Using reader As New StreamReader(fu.FileContent)
            Const blockSize As Integer = 4 * 1024
            Dim buffer(blockSize - 1) As Char
            Dim charCount As Integer
            Dim builder As New StringBuilder
            Do Until reader.EndOfStream
                'Read the next 4KB of the file.
                charCount = reader.ReadBlock(buffer, 0, blockSize)
                builder.Clear()
                builder.Append(buffer, 0, charCount)

                If charCount = blockSize Then
                    'Read up to the next line break and append to the block just read.
                    builder.Append(reader.ReadLine())
                End If

                Dim textBlock = builder.ToString()

                'Rpt1.DataSource = textBlock
                'Rpt1.DataBind()

            Loop
            reader.Close()
        End Using