[powershell] Find character position and update file name

I know this thread is a bit old but, I was looking for something similar and could not find it. Here's what I came up with. I create a string object using the .Net String class to expose all the methods normally found if using C#

[System.String]$myString
 $myString = "237801_201011221155.xml"
 $startPos = $myString.LastIndexOf("_") + 1 # Do not include the "_" character
 $subString = $myString.Substring($startPos,$myString.Length - $startPos)

Result: 201011221155.xml