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I'm using the following command

tail -f /mydir/myfile |  grep "searchterm" >> outfile

Without the -f it works fine, but with the -f, which I need, nothing is written to the file. The following outputs to the console just fine

tail -f /mydir/myfile |  grep "searchterm"

What do I need to do in order to get my command to correctly write out to a file?

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2 Answers

up vote 4 down vote accepted

If you have GNU grep:

tail -f /mydir/myfile |  grep --line-buffered "searchterm" >> outfile

Which will write every line, for a performance penalty.

Alternatively, wait for more output. If you're killing the processes, just kill the tail process and the buffer should flush before grep exits.

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I will try this out first thing Monday and report back. Thanks for the quick reply. –  pyInTheSky Feb 23 '13 at 17:57
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Is grep buffering the output perhaps, making it appear like there is none? Try:

tail -f /mydir/myfile | grep --line-buffered "searchterm" >> outfile
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