Regex VB.Net Regex.Replace - regex

Question

I'm trying to perform a simple regex find and replace, adding a tab into the string after some digits as outlined below.
From
a/users/12345/badges
To
a/users/12345 /badges
I'm using the following:
s = regex.replace(s, "(a\/users\/\d*)("a\/users\/\d*\t)", $1 $2")
But im clearly doing something wrong.
Where am I going wrong, I know its a stupid mistake but help would be gratefully received.
VBVirg

Answer 1

You can achieve that with a mere look-ahead that will find the position right before the last /:
Dim s As String = Regex.Replace("a/users/12345/badges", "(?=/[^/]*$)", vbTab)
Output:
a/users/12345 /badges
See IDEONE demo
Or, you can just use LastIndexOf owith Insert:
Dim str2 As String
Dim str As String = "a/users/12345/badges"
Dim idx = str.LastIndexOf("/")
If idx > 0 Then
str2 = str.Insert(idx, vbTab)
End If

Answer 2

When I read, "adding a tab into the string after some digits" I think there could be more than one set of digits that can appear between forward slashes. This pattern:
"/(\d+)/"
Will capture only digits that are between forward slashes and will allow you to insert a tab like so:
Imports System.Text.RegularExpressions
Module Module1
Sub Main()
Dim str As String = "a/54321/us123ers/12345/badges"
str = Regex.Replace(str, "/(\d+)/", String.Format("/$1{0}/", vbTab))
Console.WriteLine(str)
Console.ReadLine()
End Sub
End Module
Results (NOTE: The tab spaces can vary in length):
a/54321 /us123ers/12345 /badges
When String is "a/54321/users/12345/badges" results are:
a/54321 /users/12345 /badges