How to modify file line by line - vba

Question

I have a txt file in this syntax:
'foo','bar'
'foo','foo bar'
'foo','foo
bar bar'
'bar', 'foo'
I want to find each line that doens't start with ' and correct them. I want to end with:
'foo','bar'
'foo','foo bar'
'foo','foo bar bar'
'bar', 'foo'
The new line must be removed and added to the end of the previous line with a leading space.
My code cicles through a file line by line and checks, if the first character is unequal to 'already.
I thought about adding every line to an array and do the correction within that array.
I'd use
Open myFile For Output As #1
Write #1, lineOfArray
Close #1
to update the file.
My current code:
Sub Update_File(fileToUpdate As String, fileSys As Variant)
Set File = fileSys.OpenTextFile(fileToUpdate)
Do Until File.AtEndOfStream
currentLine = File.ReadLine
If Left(currentFile, 1) <> "'" Then
'Magic here
End If
Loop
File.Close
End Sub
I am struggeling with what is best practice and what is lean and quick code because the script should run over many 1000 files at the end.
I don't know if it is possible to store the current and the next line and if next line doesn't start with ' then currentLine = currentLine & " " & nextLine and somehow update the the file, decrease the loop value by one and go ahead.

Answer 1

Based on TinMan's wonderful code, try this vserion
Sub Test_UpdateFile()
UpdateFile ThisWorkbook.Path & "\Sample.txt", CreateObject("Scripting.FileSystemObject")
End Sub
Sub UpdateFile(ByVal filePath As String, ByRef fso As Object)
Const forReading = 1
Dim lines() As String
Dim dirty As Boolean
Dim r As Long
Dim x As Long
Dim k As Long
With fso.OpenTextFile(filePath, forReading)
lines = Split(.ReadAll, vbNewLine)
.Close
End With
For r = 1 To UBound(lines)
If Left(lines(r), 1) <> "'" Then
lines(r - 1) = lines(r - 1) & " " & lines(r)
lines(r) = Empty
dirty = True
x = x + 1
End If
Next r
If dirty Then
ReDim nLines(0 To UBound(lines) - x + 1)
For r = 0 To UBound(lines)
If lines(r) <> Empty Then
nLines(k) = lines(r)
k = k + 1
End If
Next r
With fso.CreateTextFile(filePath, True)
.Write Join(nLines, vbNewLine)
.Close
End With
End If
End Sub

Answer 2

Here is how I would do it.
Sub Update_File(ByVal FilePath As String, ByRef fso As Object)
Const ForReading = 1
Dim lines() As String
Dim r As Long
Dim Dirty As Boolean
With fso.OpenTextFile(FilePath, ForReading)
lines = Split(.ReadAll, vbNewLine)
.Close
End With
For r = 0 To UBound(lines)
If Left(lines(r), 1) <> "'" Then
lines(r) = "'" & lines(r)
Dirty = True
End If
Next
If Dirty Then
With fso.CreateTextFile(FilePath, True)
.Write Join(lines, vbNewLine)
.Close
End With
End If
End Sub

Answer 3

What about this:
currentline = File.ReadLine
NextLine = vbNullString
Do
If Not File.AtEndOfStream Then
NextLine = File.ReadLine
Do While Left$(NextLine, 1) <> "'"
If Len(currentline) > 0 Then currentline = Trim(currentline) & " "
currentline = currentline & Trim(NextLine)
NextLine = File.ReadLine
Loop
End If
Write #1, currentline
currentline = NextLine
Loop Until File.AtEndOfStream