Extract the nth to nth characters of an string object

Question

I have a filename and I wish to extract two portions of this and add into variables so I can compare if they are the same.

$name = FILE_20161012_054146_Import_5785_1234.xml 

So I want...

$a = 5785
$b = 1234

if ($a = $b) {
  # do stuff
}

I have tried to extract the 36th up to the 39th character

Select-Object {$_.Name[35,36,37,38]}

but I get

{5, 7, 8, 5}

Have considered splitting but looks messy.

Solution

There are several ways to do this. One of the most straightforward, as PetSerAl suggested is with .Substring():

$_.name.Substring(35,4)

Another way is with square braces, as you tried to do, but it gives you an array of [char] objects, not a string. You can use -join and you can use a range to make that easier:

$_.name[35..38] -join ''

For what you're doing, matching a pattern, you could also use a regular expression with capturing groups:

if ($_.name -match '_(\d{4})_(\d{4})\.xml$') {
    if ($Matches[1] -eq $Matches[2]) {
        # ...
    }
}

This way can be very powerful, but you need to learn more about regex if you're not familiar. In this case it's looking for an underscore _ followed by 4 digits (0-9), followed by an underscore, and four more digits, followed by .xml at the end of the string. The digits are wrapped in parentheses so they are captured separately to be referenced later (in $Matches).