UNIX for Dummies Questions & Answers

Hi.

I am trying to extract the output of the first few lines of a continuos sh script.

The when i run it, i wont to grep the the first 20 lines of it for an entry and basically do a crtl z out of it or to that effect, and output the results to a text file.

I basically want to script the above. so when i run the script it will call the script which, grep the first 20 lines outputted and exit this continuos script.

Would anyone have an idea what would be the easiest way in doing this.

At the moment i am able to grep the first 20 lines look for the entry, However the script is continusaally running need to exit it

Grep is a search utility. Obviously, you can use it to return results from a file to text, and I use it for this from time to time. However, I believe you can go at this in a different way, that will be a solution to your issue. I would do the following:

Code:

tail -n 20 >> output.txt

This will output the last 20 lines that are currently written to the continuously written log file, and outputs the data to a text file. The example above appends to the file (does not overwrite). If you want it to overwrite:

Code:

tail -n 20 > output.txt

Let me know if you have any questions.

Hi drewrockshard.

What i am trying to do is.

I have to run a script x ( Which loops for ever)

I need to grep a particular line from the output of the script x, Which i expect to be outputted within the first 20 lines, However this scripts stays running forever till i do a ctrl z.

So i am trying to create a script y which will execute script x grep for the expected output and ctrl d from script x. and output the findings from executing script x.

Script y
==============================

Calls script x looks for a pattern and ctrl z from script x.

i need to be able to force exit the script x when i find the pattern

as script x runs continuous


==================================

First of all, I apologize for the lack of "attention to detail". You stated the first 20 lines, not the last 20 lines. In this case, just to correct myself, it would be:

Code:

head -n 20 >> output.txt

or

Code:

head -n 20 > output.txt

Now, on with what you are actually wanting. I find your logic a bit confusing. What I would do, in this case it to take script x and code it to log everything that you need to a log file. I would then have script y run, and run script x, just like you were wanting. After it starts script x, make sure you get the PID of the process and load it into a variable. Then have script y grep the log file of script x and when if finds a match for what you are looking for, have script y kill the pid of script x.

Hi drewrockshard.

Your logic describes exactly what i should do to get the desired output.

It looks like when i find the pattern i am looking for in the log file. i should kill the process id of script x as you say,it seems to be the correct way to do this.

The way i was trying to do it was not to log the output of script x to a log, but run the script, wait till i get the pattern i was looking for and kill off the script someway. But you logic seems better

Thanks for the help

No problem man. Let me know if you need any help with the scripting part!