Tail -f piped through grep not outputing to file, but outputs to console

Question

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?

score 13 · Accepted Answer · edited Feb 23 '13 at 02:50

13

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.

edited Feb 23 '13 at 02:50

Aaron D. Marasco

answered Feb 22 '13 at 23:05

Matt

I will try this out first thing Monday and report back. Thanks for the quick reply. – pyInTheSky Feb 23 '13 at 17:57

score 1 · Answer 2 · answered Feb 22 '13 at 22:58

1

Is grep buffering the output perhaps, making it appear like there is none? Try:

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

answered Feb 22 '13 at 22:58

foo

2 Answers2