Windows 10: Do command when file 3rd-to-last line does NOT contains a string

I'm having connection issues which I'm documenting. I have a close variant of the following that has 60 seconds in between each call, but I'd like one to be continuous until the connection is reestablished. The way I see it, at the end of the following there would be some way of checking the log content and if what's at the end of the log reflect a disconnection and if so immediately make another call.

and since a good ping should end with something like

but when the ping goes bad it's like

, I think the batch last line would be something like if

; that's just an example and I'm not good at these kind of things.

TLDR How to do a command if a file 3rd-to-last line does NOT contains a specific string?

Thank you kindly for your assistance

:)

 

GPU-Z what command line parameter ?

Suggestion: /? (-?) and /help (-help) command-line arguments to show a list of all possible arguments in a small window. *Smile

 

GPU-Z what command line parameter ?

Current /? (-?) or / help (-help) parameter is invalid

 

Deleting Lines in a Text File Given Strings From Another File Using Set-String (Powershell)

Basically what's happening is that I have two files, one with a list of allowed users and another list of users that are actually on the desktop. What I'm trying to do is use a for loop to grab each name in the AllowedUsers.txt file, and use Select-String
to find any names that match and delete them from the original Users.txt (with the list of users actually on the desktop). The end goal is to have a list of users that aren't allowed on the desktop left in the Users.txt file, where I can then for loop through
once again and simply delete those users through command line.

Unfortunately, I have been unable to get this to work as I don't fully grasp how Select-String or for loops work, but any help writing the script would be greatly appreciated.