Shell Programming and Scripting

Just my second week working on awk I need a hint for the following tasks.
I want to limit my logfile from the very outset to 200 lines. All I do until now is

head -c 10K >> /home/uplog.txt | awk 'END{print NR " swap " NF$5; exit}' /home/uplog.txt;

After being read it shall print the very last record " some text " of the fifth field and right after that exit, due to the size of the file.

How can I set the limit to a certain number of lines?

My wiry selfmade logfile should be read only the last n lines, e.g. 10. I've been typing something like NR-1 but that gives just the line before the very last one. So how can I set a range like NR>=1&&NR<=5 or even more sophisticated /~^start !/,/~^stop !/ ?
If someone can give me a hint that would be great, thanks in advance.

Is this a homework assignment? If so, please repost as directed here: Rules for Homework & Coursework Questions Forum

Not sure I understand the logics of your code snippet. After appending stdout of the head command to /home/uplog.txt, you pipe stdout (which will be empty) to awk's stdin but make awk read the recently appended to file /home/uplog.txt at the same time? That can't work.
Does it have to be awk? Then you need e.g. a circular buffer that you print in the END section. Did you try the tail command?

It is not a homework, I am not a student of IT, surely just for my machine here. Yes, there are people out there who do scripts for themselves, just like me. And I've been searching on various sites to find a solution.

---------- Post updated at 07:10 PM ---------- Previous update was at 07:07 PM ----------

It is not a homework, I am not a student of IT, surely just for my machine here. Yes, there are people out there who do scripts for themselves, just like me. And I've been searching on various sites to find a solution. I tried that tail-command as well. But I'd need that one as doing a step ahead in awk.

OK, so what about the circular buffer?

I agree with RudiC. Your code:

Code:

head -c 10K >> /home/uplog.txt | awk 'END{print NR " swap " NF$5; exit}' /home/uplog.txt;

doesn't seem to be related to what you said you're trying to do. This code (depending on what OS you're using) will give you a diagnostic for an invalid head -c option-argument, a diagnostic saying that head doesn't have a -c option, or append the 1st 10000 or 10240 characters from standard input for this script to the end of /home/uplog.txt while simultaneously having awk read whatever it finds in /home/uplog.txt and then print the number of lines it found in the file (before head started adding data to it, at some point in time while head is writing to it, or after head has finished writing to it) followed by the string swap followed by (depending on what OS you're using) the number of fields in the last record in the file and the contents of the 5th field from the last line of the file, nothing, or one but not both of those values.

Your requirements are ambiguous.

Limiting a file to 200 lines from the outset is not the same thing as reading it at some later time and discarding all but the 1st 10k characters (without checking for line boundaries).

Please give us a clear English description of what you are trying to do.

@Don Cragun
Much ambition means many errors, no errors means no trouble at all, I agree that this is a task for me.
From the very outset I want to set this file to just 200 entries, nothing more. And catch the last seven and in a furhter step the last thirty lines of the fifth field for a calculation. The text-string " swap " could be any other. BTW I am not a pro so: I do not know anything about circular buffers, excuse me.
My OS here is debian wheezy 7.5, no server.
So I cut out the first statement do direct it after the awk-statement to the stdout. As you may see, this could be a beginner, but I assure you I am right in the middle, because this is my third week around with awk.