How to replace a string in a string except first occurrence

The key insight here is the existence of an indexOf that starts searching the string at a certain point into the string, rather than from the start. Here: http://msdn.microsoft.com/en-us/library/7cct0x33.aspx

First off, you want to use .indexOf("-Processed") to find the first index of -Processed in the string. Remember this index.

Now, use .indexOf("-Processed", index+1) to find the next index of -Processed that is not the first.

Repeated that and Substring(nextindex, "-Processed".Length) to remove these extra instances until you find no more.

string ReplaceExceptFirst(string text, string search, string replace)
{
    int pos = text.IndexOf(search);
    if (pos < 0)
    {
        return text;
    }

    int strlen = pos + search.Length;
    return text.Substring(0, strlen) +  (text.Substring(strlen)).Replace(search,replace);
}

Something like so:

String str = @"C:\\Test-Processed\1-Processed\2-Processed";
System.Console.WriteLine(new Regex("(\\d+)-Processed").Replace(str, "$1"));

will yield C:\\Test-Processed\1\2. The regular expression assumes that the elements you want to remove are always preceded by one or more digits. It will put those digits in a capture group and replace the sub string (example 1-Processed) with only the digit (1).

EDIT: If the assumption fails, you might want to take the approach @Patashu suggested.

This is one of the solutions given above. (Solution by Habib and parameter naming by Pintu Paul). I used it but then defined the function as a String Extension.

public static class StringExtensions
{
    public static string ReplaceAllButFirst(this string originalStr, string search, string replace)
    {
        string str = originalStr.Substring(0, originalStr.IndexOf(search, System.StringComparison.InvariantCultureIgnoreCase) + search.Length);
        return str + originalStr.Substring(str.Length).Replace(search, replace);  
    }
}