Extract Part of a string in powershell

Question

I am trying to extract 2 pieces of information from a string value. The first in from the 4th last to the 2nd last character; the second is from the 2nd last to the last character. This is the code I'm using:

foreach ($item in $List)
{
    $len = $item.Length
    $folder1 = $item.Substring(($len - 2), $len)
    $folder2 = $item.Substring(($len - 4), ($len - 2))

    ..
} 

This code keeps throwing an error on the Substring function. The error description is as below:

*Exception calling "Substring" with "2" argument(s): "Index and length must refer to a
      location within the string.
Parameter name: length"
At line:7 char:1
+ $str.Substring($flen - 2, $slen)
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : NotSpecified: (:) [], MethodInvocationException
    + FullyQualifiedErrorId : ArgumentOutOfRangeException*

How do I use Substring? What should I pass as the correct parameters?

Answer 1

Substring takes an index and a length parameter. You're passing in an index and an index parameter. If you want two characters from 4th-last character, the code is

$item.Substring($len - 5, 2)

Note that the index is 0-based, not 1-based.