Stripping out non-numeric characters in string

public static string RemoveNonNumeric(string value) => Regex.Replace(value, "[^0-9]", "");

Strips out all non Numeric characters

Public Function OnlyNumeric(strIn As String) As String
      Try
            Return Regex.Replace(strIn, "[^0-9]", "")
      Catch
            Return String.Empty
      End Try
End Function

If you're working in VB and ended up here, the ".Where" threw an error for me. Got this from here: https://forums.asp.net/t/1067058.aspx?Trimming+a+string+to+remove+special+non+numeric+characters

Function ParseDigits(ByVal inputString as String) As String
  Dim numberString As String = ""
  If inputString = Nothing Then Return numberString

  For Each c As Char In inputString.ToCharArray()
    If c.IsDigit Then
      numberString &= c
    End If
  Next c

  Return numberString
End Function

As of C# 3.0, you should use method groups in lieu of lambda expressions where possible. This is because using method groups results in one less redirect, and is thus more efficient.

The currently accepted answer would thus become:

private static string GetNumbers(string input)
{
    return new string(input.Where(char.IsDigit).ToArray());
}