Dim F As Integer
Dim N As Integer
Dim sLine As String
Dim sNr As String
 
F = FreeFile
Open "Quelldatei.txt" For Input As #F
While Not Eof(F)
  Line Input #F, sLine
  If Left$(sLine, 3)<> sNr Or Len(sNr) = 0 Then
    If N > 0 Then Close #N
    sNr = Left$(sLine, 3)
    N = FreeFile
    Open sNr & ".txt" For Output As #N
    sNr = Left$(sLine, 3)
  End If
  Print #N, sLine
Wend
If N > 0Then Close #N
Close #F