Imports System.IO
Module WriteDateFile
    Sub Main()
        '- Location of the Text file
        Dim fileName As String = WattChangeForm.Files.SelectedItem
        '- Set the line counter
        Dim lineNumber As Integer = 0

        '- Open the text file/stream
        Dim sr As StreamReader = New StreamReader(fileName)

        '- Initialize name variables
        Dim sequenzs As String = ""
        Dim pspeed As String = ""
        Dim speed As String = ""
        Dim temp As String = ""
        Dim textline As String = ""
        Dim strFull As String = ""
        Dim strOriginal As String = ""
        Dim strReplace As String = ""
        Dim fline

        '- Cycle thru the text file 1 line at a time pulling
        '- substrings into the variables initialized above
        Do
            textline = sr.ReadLine()
            temp = temp + textline + vbCrLf
            '- If it goes past the last line of the file,
            '- it drops out of the loop
            If textline <> Nothing Then
                Try
                    sequenzs = textline.Substring(0, 8).Trim()
                    If sequenzs = "SEQUENZs" Then
                        Do
                            textline = sr.ReadLine()
                            temp = temp + textline + vbCrLf
                            If textline = "P_SPEED" Then
                                pspeed = textline.Substring(0, 7).Trim()
                                If pspeed = "P_SPEED" Then
                                    textline = sr.ReadLine()
                                    fline = Split(textline, " ")
                                    'replace the current from the input current text box
                                    'write it to the file
                                    strFull = textline
                                    strOriginal = fline(5)
                                    strReplace = WattChangeForm.ChangeCurrentbox.Text
                                    strFull = strFull.Replace(strOriginal, strReplace)
                                    textline = strFull
                                    temp = temp + textline + vbCrLf
                                End If
                            End If
                        Loop Until textline = Nothing
                    End If
                Catch ex As Exception
                    'WattChangeForm.RichTextBox1.Text = "Error nothing to read"
                End Try
            End If
        Loop Until textline = Nothing
        '- Close the file/stream
        sr.Close()

        'after building the temp file with the new values, overwrite the 
        '.lso with the temp file data
        Dim SW As StreamWriter = New StreamWriter(fileName)
        SW.Write(temp)
        SW.Close()
        WattChangeForm.ChangeCurrentbox.Text = ""
        WattChangeForm.RichTextBox1.Text = ""
        Call ReadDataFile.Main()
    End Sub
End Module

 
    ' My own equivalent of VB.NET's inbuilt "instr" function. Because I can
    Function InString(ByRef sMas As String, ByRef sDum As String) As Integer
        For i As Integer = 1 To sMas.Length Step 1
            If Mid(sMas, i, sDum.Length) = sDum Then
                Return i
            End If
        Next
        Return 0
    End Function
 
    Function SearchAndReplace(ByRef sMas As String, ByRef sDum As String, ByRef sRep As String) As String
        Do Until InString(sMas, sDum) = 0 Or InString(sRep, sDum) > 0
            For i As Integer = 1 To sMas.Length Step 1
                If Mid(sMas.ToLower, i, sDum.ToLower.Length) = sDum.ToLower Then
                    sMas = (Mid(sMas, 1, i - 1) + sRep + Mid(sMas, i + sDum.Length, sMas.Length - i + 1 + sDum.Length))
                    Exit For
                End If
            Next
        Loop
        Return sMas
    End Function

Call System.Console.WriteLine(SearchAndReplace("redundant box is redundant", "redundant", "non-volatile redundant, hairy, and by all rights awesome"))

    ' Replaces (with sRep) only the first instance of sDum in the string sMas
    Function searchReplace(ByRef sMas As String, _
                           ByRef sDum As String, _
                           ByRef sRep As String) As String
        Try : sMas = Mid(sMas, 1, InStr(sMas, sDum) - 1) _
               + sRep _
               + Mid(sMas, InStr(sMas, sDum) + sDum.Length _
                  , sMas.Length - InStr(sMas, sDum) + 1 + sDum.Length)
        Catch ex As Exception : End Try : Return sMas
    End Function
 
    ' Replaces (with sRep) all instances of sDum in the string sMas
    Function allSearchReplace(ByRef sMas As String, _
                              ByRef sDum As String, _
                              ByRef sRep As String) As String
        Dim sTemp As String = "" : Do Until InStr(sMas, sDum) = 0
            Try : sTemp += Mid(sMas, 1, InStr(sMas, sDum) - 1) + sRep _
                : sMas = Mid(sMas, InStr(sMas, sDum) + sDum.Length _
                   , sMas.Length - InStr(sMas, sDum) + 1 + sDum.Length)
            Catch ex As Exception : End Try : Loop : Return sTemp + sMas
    End Function