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The following does not work...

tail -f /var/log/mysql/general.log | grep Connect > /home/myfile.txt

If I remove the "-f" switch then I am able to save the output to a text file, but it does not work wile tail is running.

Nor does tee works

tail -f /var/log/mysql/general.log | grep Connect -tee "/home/myfile.txt"

update

Command provided by quanta does work.

tail -f /var/log/mysql/general.log | tee >(grep Connect > /home/myfile.txt)

But I have to keep the window open. nohup tail -f ... does not seem to work. How do I keep this command running continuously?

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3 Answers

up vote 1 down vote accepted 
tail -f /var/log/mysql/general.log | tee >(grep Connect > /home/myfile.txt)
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Updated my question. will nohup work with this command? – shantanuo Aug 8 '11 at 5:18
No need to use nohup. tail -f will run continuously until you stop it by pressing Ctrl+C. – quanta Aug 8 '11 at 5:47
When I close the putty window, it seems to be killing the process – shantanuo Aug 8 '11 at 5:57
OK. I misunderstand you mean. Read the SvenW's answer. – quanta Aug 8 '11 at 6:17
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Actually, it works just fine.

The problem is probably that the output is buffered along each step so you'll need to have a lot of output before it actually gets flushed to the file.

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You can use grep --line-buffered Connect > /home/myfile.txt. – quanta Aug 8 '11 at 4:44
Right, should have mentioned that. No option for tail though. – MikeyB Aug 8 '11 at 4:49
grep without --line-buffered didn't work on my system. Does it works for you? – quanta Aug 8 '11 at 4:52
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up vote 1 down vote

About your nohup problem: If you don't want to see the output continuously for some reason, I wouldn't create a separate file with part of the logs (which is essentially what you are doing), but create the extraction on demand with just a grep command.

If you insist on your method, you could use screen or tmux to run your command.

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