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Help On tail script

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# 1  
Old 02-16-2012
Help On tail script
Hi Guys,

I would like to create a script which tails the content of a log file in real time, looks for a specific string , like "ERROR" and captures in a text file the previous 10.000 lines that were existing before this string.


Any help is appreciated.
# 2  
Old 02-16-2012
This is not possible by tail command to predict when ERROR is coming and capture the 10 lines before that, instead of this, script can read the file in a loop every time where it left and parse the file up to next error and get the previous 10 line. let me get the some raw script for you.
# 3  
Old 02-16-2012
This could be the foundation of such a script
Code:
while true ; do 
  tail  $logfile | grep ERROR ||  tail -10000 $logfile > prev &&echo "Dumped log records to prev"&& break ; done

# 4  
Old 02-16-2012
Let me make it more clear for you.
I am using some application that puts all the logging under /var/adm/messages. Once i capture the string "Error" I need to find out what actually caused it, 1000 lines before and after, to have the full picture.Then put all these lines in a text file.
It's going to be something like this :

Code:
$logfile= /var/adm/messages
while true ; do    tail  $logfile | grep ERROR ||  tail -1000 $logfile  > prev file.txt &&echo "Dumped log records to prev"&& break ; done

---------- Post updated at 04:24 PM ---------- Previous update was at 03:03 PM ----------

Hi,

Is my above expression correct ?

Thanks!
Last edited by methyl; 02-16-2012 at 06:04 PM.. Reason: please use code tags
# 5  
Old 02-16-2012
The script posted contains too many syntax errors to make the intention clear.

What Operating System and version do you have and what Shell are you using?
# 6  
Old 02-17-2012
try this.
Code:
#!/bin/bash
previousSearch=0
while true;
do
        Lines=$(cat  /var/adm/messages | grep -n ERROR | cut -d ":" -f1)  #to get the all lines numbers which has word ERROR
        for i in $Lines
        do
                if [ $i -gt previousSearch ]; then
                line=$(expr $i + 1000)                             #get the maximun number of line which is needed
                head -$line | tail -2000 >> newfile.txt                   # get exact 2000 line, 1000 before ERROR and 1000 after ERROR
                previousSearch=$i                                         # setting counter to last search result.
                fi
        done
done

I was not able to run this but if there is any syntax error please fix thos, but logic seems to be good.

you run this script as background process and tail the newfile.txt to get the result.

---------- Post updated at 10:44 AM ---------- Previous update was at 10:34 AM ----------

in fact you can use this line also instead of original

Lines=$(grep -n ERROR /var/adm/messages | cut -d ":" -f1) #to get the all lines numbers which has word ERROR

This would be must efficient then original "cat".
Last edited by vishal_vsh1; 02-17-2012 at 04:38 AM.. Reason: updating the syntax
# 7  
Old 02-17-2012
I'm still getting an error when running the script :

[: previousSearch: bad number
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