Check if line matches regex - regex

Question

I have a file that has been generated by a server - I have no control over how this file is generated or formatted. I need to check each line begins with a string of set length (in this case 21 numerical chars). If a line doesn't match that condition, I need to join it to the previous line and, after reading and correcting the whole file, save it. I am doing this for a lot of files in a directory.
So far I have:
Dim rgx As New Regex("^[0-9]{21}$")
Dim linesList As New List(Of String)(File.ReadAllLines(finfo.FullName))
If linesList(0).Contains("BlackBerry Messenger") Then
linesList.RemoveAt(0)
For i As Integer = 0 To linesList.Count
If Not rgx.IsMatch(i.ToString) Then
linesList.Concat(linesList(i-1))
End If
Next
End If
File.WriteAllLines(finfo.FullName, linesList.ToArray())[code]
There's a for statement before and after that code block to loop over all files in the source directory, which works fine.
Hope this isn't too bad to read :/

Answer 1

I didn't think your solution was any good, you were failing on concatenating the lines. Here's a different approach:
Dim rgx As New Regex("^[0-9]{21}")
Dim linesList As New List(Of String)(File.ReadAllLines(finfo.FullName))
' We will create a new list to store the new lines data
Dim newLinesList As New List(Of String)()
If linesList(0).Contains("BlackBerry Messenger") Then
Dim i As Integer = 1
Dim newLine As String
While i < linesList.Count
newLine = linesList(i)
i += 1
' Keep going until the "real" line is over
While i < linesList.Count AndAlso Not rgx.IsMatch(linesList(i))
newLine += linesList(i)
i += 1
End While
newLinesList.Add(newLine)
End While
End If
File.WriteAllLines(finfo.FullName, newLinesList.ToArray())