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Add line number to text file

Posted on 2013-06-17
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Last Modified: 2013-06-17
I have a text file without line numbers and i need to insert a line number for each file.

Text File

aaaaaa
bbbbb
cccccc
.....

With line numbers

1 aaaaaa
2 bbbbb
3 cccccc
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Question by:rflorencio
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2 Comments
 
LVL 42

Assisted Solution

by:sedgwick
sedgwick earned 600 total points
ID: 39253353
        Dim lines = File.ReadAllLines("c:\temp\1.txt")
        Dim list As List(Of String) = New List(Of String)
        For Each l In lines
            list.Add((list.Count + 1).ToString & " " & l)
        Next

        File.WriteAllLines("c:\temp\1.txt", list.ToArray)

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LVL 75

Accepted Solution

by:
käµfm³d   👽 earned 1400 total points
ID: 39253398
Depending on how large your files are, it may be more prudent to use StreamReaders and StreamWriters.

e.g.

Imports System.IO

...

Using reader As New StreamReader("C:\path\to\your\file.txt")
    Using writer As New StreamWriter("C:\path\to\temp\file.txt")
        Dim i As Integer = 1

        While Not reader.AtEndOfStream
            writer.WriteLine("{0} {1}", i.ToString(), reader.ReadLine())
            i += 1
        End While
    End Using
End Using

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You can move (i.e. rename) the temp file to the original file to effectively overwrite the old file.
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