Shell Programming and Scripting

Hi,

I want to monitor a log file using tail -f command and search for a specific string on the most recent entry from the file. If the search string matches with the most recent or last line from the file, I want send an email to the people with the message.

Code:

tail -f service.log|tail -n 1

But the above code does not seem to work.

Thanks,
S

Your tail | tail pipeline will never end. The 2nd tail reads one line from the end of the pipeline; but, since the tail -f will never terminate, the pipeline won't deliver an EOF to the 2nd tail until you manually kill the 1st tail.

If you want to read the last line of a file, just use tail -n 1 service.log. If you want to search for the first occurrence of a line containing a fixed string on the last line of a file, and, if the string is not found on that line, continue reading lines newly written to that file until that string is found, try something like:

Code:

tail -f -n 1 service.log | grep  -F "fixed string" | while IFS= read -r line
do	echo "found: $line"	# Do whatever you want to do with that line...
	break			# Terminate the pipeline and continue processing
				# with whatever follows the end of this loop.
done

You haven't told us what operating system or shell you're using (which you should always do on the first post in a new thread).

With many shells, the value assigned to the line variable will disappear when you exit the loop. With a few shells, the value assigned to line will remain in force after the loop ends.

Thank you. I am working on bourne shell.

Sorry I am a rookie here. As soon as the value (from the last line of the file) matches the search string, I want to send an email and continue to monitor the log for the next message.

Example:

Search String = AWX_38900
file name=service.log

I want to search for the string 'AWX_38900' in the last line of the file service.log and if it finds a match, it has to send an email to the group of people and continue monitoring the service.log for the next message.

Someone with over 100 posts who has been in the forums for more than seven years doesn't really count as a rookie...

Great. So, take the code I suggested for doing what you're trying to do, replace the echo command with a command to invoke your mail sending utility (with an appropriate subject line, destination address, and a message body including the line you captured.

You still haven't told us what operating system you're using so there's no way we can guess at what mail sending utilities might be available to you. But with over 100 posts to your credit, you should be able to come close to solving any remaining issues on your own. See what you can do and show us where you get stuck if you can't get it to work.

Thanks for being judgmental about my seniority on this forum just by looking at the years and number of posts I have posted on this forum. Unix programming is not my mainstream work and I get to work on scripting only once in a while. My most recent post was back in july '17 which clearly indicates that I am not a regular visitor or poster on this forum.

The dictionary on my desk says that a newbie is an inexperienced newcomer to a particular activity. You may be inexperienced, but with the length of time you have been a member of this forum, you are not a newcomer.

I'm sorry you think I'm being judgmental. But, our goal in this forum is to help you learn how to use the utilities available on your operating system to do whatever you're trying to do. We are not here to act as your unpaid programming staff.

If you're unwilling to tell us what operating system you're using and you're unwilling to even attempt to use the unspecified mail sending utility of your choice to send a message to one or more e-mail addresses you have not specified with a subject line you have not specified with a message body you have not specified other than that it is to contain the text in the line variable included in the code template I provided you, there isn't much more that I can do for you. I wish you luck in your endeavor and I'm truly sorry that the suggestions and examples I have provided are of no use to you.