Question

Using this in VB 2010:

Imports System.Text.RegularExpressions

Public Class Form1
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Dim lines() As String = IO.File.ReadAllLines("filename.txt")
        Dim foundIndex As Integer = Array.FindIndex(lines, Function(l) l.StartsWith(TextBox1.Text)) 'assuming TextBox1.Text = the part of the line before the =
        lines(foundIndex) = Regex.Replace(lines(foundIndex), "(?<=" & TextBox1.Text & "=)\d+", TextBox2.Text) 'TextBox2.Text is the replacement number
        Stop
        'to rewrite the file:
        'IO.File.WriteAllLines("filename.txt", lines)
    End Sub
End Class

…but it keeps adding numbers after equals sign every time i save the text file.

I want it to replace everything on that line after equals sign.

Answer 1

I executed your code and It works unchanged:

Sub Main
     Dim lines() As String = IO.File.ReadAllLines("c:\temp\filename.txt")
     lines.Dump()
        Dim foundIndex As Integer = Array.FindIndex(lines, Function(l) l.StartsWith("blah")) 'assuming TextBox1.Text = the part of the line before the =
        foundIndex.Dump()
        lines(foundIndex) = Regex.Replace(lines(foundIndex), "(?<=blah=)[\d.e+]+", "replaced") 'TextBox2.Text is the replacement number
        IO.File.WriteAllLines("c:\temp\filename.txt", lines)
End Sub

If the file is

test=456
blah=456
blah=just

it will become

test=456
blah=replaced
blah=just

This is as you want it no?

Update 1

I replaced

"(?<=blah=)\d+"

With

"(?<=blah=)[\d.]+"

Update 2

Regarding the issue with strings like “1e+007”. The part that matches the string after the “=” is currently [\d.]

Remember that there was a problem with numbers that had the decimal point like 3.25? This was solved by adding the “.” to the character class [\d] so it becomes [\d.]
Now anything that is a number “\d” and a “.” will match.

The new issue is solved in the same way. Now “e” and “+” should also be matched. Get it? So the character class now becomes [\d.e+]

Give it a go and let me know how it went.

Now it should also be clear how to modify the regex to match “BGS_LOGO.BIK” If you can solve that you understand what’s going on.