sw.WriteLine(content & Environment.NewLine)

 Dim content As String = sr.ReadToEnd.Replace(Environment.NewLine, "")
 If Not String.IsNullOrEmpty(content) Then
     sw.WriteLine(content & Environment.NewLine)
 End If
 

While Not sr.EndOfStream
   Dim content As String = sr.ReadLine
   If content.Length > 0 Then
      sw.WriteLine(content)
End While
 

archivotxt = Regex.Replace(archivotxt, "^\r|\n\r|\n$", "")

...Replace(txtfind, txtreplace, comparisonType)

    Private Function Replace(ByVal sender As String,
                             ByVal findWhat As String,
                             ByVal replaceWith As String,
                             ByVal comparisonType As StringComparison,
                             ByVal stringBuilderCapacity As Integer) As String
 
        If String.IsNullOrEmpty(sender) Then
            Return sender
 
        ElseIf String.IsNullOrEmpty(findWhat) Then
            Throw New ArgumentNullException(paramName:="findWhat")
 
        Else
            Return StringExtensions.Replace(findWhat, replaceWith, comparisonType)
 
        End If
 

    Public Function Replace(ByVal sender As String,
                            ByVal findWhat As String,
                            ByVal replaceWith As String,
                            ByVal comparisonType As StringComparison) As String
        If String.IsNullOrEmpty(sender) Then
            Return sender
        ElseIf String.IsNullOrEmpty(findWhat) Then
            Throw New ArgumentNullException(paramName:="findWhat")
        Else
            Return StringExtensions.Replace(sender, findWhat, replaceWith, comparisonType, stringBuilderCapacity:=0)
        End If
    End Function
 

Private Function Replace(ByVal sender As String,
                             ByVal findWhat As String,
                             ByVal replaceWith As String,
                             ByVal comparisonType As StringComparison,
                             ByVal stringBuilderCapacity As Integer) As String
        If String.IsNullOrEmpty(sender) Then
            Return sender
        ElseIf String.IsNullOrEmpty(findWhat) Then
            Throw New ArgumentNullException(paramName:="findWhat")
        Else
            Dim posCurrent As Integer = 0
            Dim lenPattern As Integer = findWhat.Length
            Dim idxNext As Integer = sender.IndexOf(findWhat, comparisonType)
            Dim result As New StringBuilder(capacity:=If(stringBuilderCapacity <= 0, Math.Min(4096, sender.Length), stringBuilderCapacity))
            While (idxNext >= 0)
                result.Append(sender, posCurrent, (idxNext - posCurrent))
                result.Append(replaceWith)
                posCurrent = (idxNext + lenPattern)
                idxNext = sender.IndexOf(findWhat, posCurrent, comparisonType)
            End While
            result.Append(sender, posCurrent, (sender.Length - posCurrent))
            Return result.ToString
        End If
    End Function
 

FindFileAndReplaceTextIn

Public Sub FindFileAndReplaceTextIn(ByVal sourceDir As String, ByVal filenameFind As String,
                                    ByVal txtfind As String, ByVal txtreplace As String,
                                    ByVal comparisonType As StringComparison)
        For Each topDir As DirectoryInfo In New DirectoryInfo(sourceDir).GetDirectories("*", SearchOption.TopDirectoryOnly)
            For Each txtfile As FileInfo In topDir.GetFiles("*.txt", SearchOption.TopDirectoryOnly)
                If txtfile.Name.Equals(filenameFind, StringComparison.OrdinalIgnoreCase) Then
                    Dim txt As String = File.ReadAllText(txtfile.FullName, Encoding.Default).
                                             Replace(txtfile.FullName, txtfind, txtreplace, comparisonType)
                    File.WriteAllText(txtfile.FullName, txt, Encoding.Default)
                End If
            Next txtfile
        Next topDir
    End Sub
 

String

StringComparison

FindFileAndReplaceTextIn(sourceDir, "GL.txt", "AGENO-02", "AGEN-03", comparisonType)

FindFileAndReplaceTextIn(sourceDir, "GL.txt", "textbuscar", "textoreemplaza", comparisonType)
 

FindFileAndReplaceTextIn(sourceDir, "GL.txt", "textbuscar", CType("textoreemplaza", StringComparison), comparisonType)