Shell Programming and Scripting

-I've realized that the script only stops and 5:05 and 17:05 so I thought that maybe was a cron job in the server but I could not fin anything. I tried the same in my local area network and the same happens so maybe the data streams is doing something weird and that times.

-I use vim to take a look to the files when this happens, to see if theres any special mark. I found that at the end of the file there are several trailing characters:


·Maybe this is causing any problem to the awk sentence?
·Any clues of waht is happening or how to solve it?

All the best

I know what is happening hopefully you can help me now:

-Two times a day the receiver from where I'm getting the data stops sending for a couple of seconds due to an internal cron job.

-Because of this my entire all the process of getting AIS sentences stops:

Code:

nc -ul -p 56045 -q -1 | awk -F: 'NF > 1 {print strftime("%d-%m-%Y %H:%M:%S"),$0;fflush();  }' > awk.txt 2>&1 &

but I'm listening forever in my nc sentences, so what is happening¿?

All the best

Instead of why? how about using tail -f which is meant to solve this problem.

Code:

nc -ul -p 56045 -q -1 | tail -f | awk -F: 'NF > 1 {print strftime("%d-%m-%Y %H:%M:%S"),$0;fflush();  }' > awk.txt 2>&1 &

What you need to consider, if you do not like tail, is to develop some kind of daemon - usually written in C. You have an attached child process that leaves the parent there forever. If I understand what you have there.

PS: fflush() on every line forces disk I/O instead of buffered I/O. Since nc can produce an endless stream of data this change might help.

Thanks a lot Jim!

I will try with tail then and see what happens

About fflush(), I'm already using it inside my awk sentence do you mean that It better to avoid using it¿?

All the best

Can you please try the bsd version
It should take little time and effort.
This was a well intent suggestion before, since i had issues with gnu nc while experimenting with go and stuff.

Similar issues as you describe here.

I did not debug further.
Only switched version which resulted in expected behavior..

Regards
Peasant.

Dear Jim,

your adding of tail -f is not working, the file its not created and nothing else happens..

Dear Peasant,

I can't try that in the server because I dont have that privilegies but I did that on my laptop with no changes...

All the best

a closer look at what the cron cron job is doing could shed some light here.
I suspect it could be doing something to disrupt the sending process.

What is the purpose of the cron job that runs at these times?

If it's doing something like a backup for example, it could quiesce or stop services like databases, etc that the sender relies on. Log rotation jobs could stop and re-start the sender causing a loss of the open socket.