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.

echo %time:~0,5%
@set yymmdd=%date:~12,2%%date:~7,2%%date:~4,2%
echo %date% >> logs\pinger-%yymmdd%.txt
::using "time /t | tee -a [...]" take 4 time the processing of doing the command twice
echo %time:~0,5% >> logs\pinger-%yymmdd%.txt
ping google.ca >> logs\pinger-%yymmdd%.txt
pinger-win10.bat

and since a good ping should end with something like

Ping statistics for 172.217.13.99:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 12ms, Maximum = 12ms, Average = 12ms

but when the ping goes bad it's like

Request timed out.

Ping statistics for 172.217.13.99:
Packets: Sent = 4, Received = 0, Lost = 4 (100% loss),

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

SEARCH logs\pinger-%yymmdd%.txt -line m -match false "(0% loss)" then pinger-win10.bat REM else it stops

; 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

The OP was long so I understand you might have missed it, but I already have a minute logger, which will contain many thousand lines per day. Now I'd like something to be run continuously until the connection is back either manually when I notice it's disconnected, or preferably but not necessarily, automatically when there's a disconnection. The most important thing is it stops by itself; so I can go do something else offline and not worry about the log being huge for no reason (since that can be > 1 hr and a continuous ping log for that time would definitively be huge).

I assume the continuous ping log will be a few hundred lines per day. But even if it never went beyond 200 lines, I think beyond 50 lines that the delay for a script as you suggested would add, say > 5 seconds, for something that's meant to be quick as I want to ping often, say every 10-15 seconds, when disconnected.

Was repeating

Try3 said:

What is your objective?

a mistake? If not my previous post 1st paragraph is my answer.

I'd rather use the program tail through Cygwin than do it on separate files. I'd prefer to keep it Windows-native only but I install Cygwin on almost all the systems I spent a good amount of time on which I have sufficient privilege, so it's not a big problem if I have to.

Instead of continiously writing time and ping to the log why not make it like this:

12:50 - 15:16 Internet OK
15:16 - 17:04 Internet Interrupted
17:04 - 20:05 Internet Ok
20:05 - 21:30 Internet Interrupted

You only log when the internet disconnects and only log when the internet is back...

You can accomplish this by monitoring the errorlevel of the ping command...

ricardobohner said:

monitoring the errorlevel of the ping command

1 ping / min is plenty for the overall goal. I'd just like to be more precise only when there's a disconnection which is almost always < 5 mins, but currently happen often.

Try3 said:

It was not a mistake. I do not know what your objective is.
- All I know is how you intend to approach the task.
- If I knew what the objective was I might be able to suggest an alternative approach.

Where in the post #3 1st paragraph is there anything about approaching the task? I want something that ping like every 10 seconds but only until it reconnects; it can start manually or automatically but it need to stop automatically. I don't think I can be any cleared than that.